Lab Report Learning Proccesses

Social Interaction with an

Intoxicated Sibling Can Result

in Increased Intake of Ethanol

by Periadolescent Rats

Pamela S. Hunt

Jennifer L. Holloway

Elka M. Scordalakes Department of Psychology

College of William & Mary Williamsburg, VA 23187-8795

Received 13 December 1999; accepted 10 October 2000

ABSTRACT: A novel procedure for enhancing voluntary intake of ethanol in periadolescent rats is described. The procedure is a modi®cation of Galef et al.'s (e.g., Galet, Kennett, & Stein, 1985; Anim Learn Behave 13:25 ± 30) demonstrator± observer procedure. Subjects were Sprague-Dawley rats, 28 ± 35 days of age. The experimental subject (observer) interacted with a same-sex conspeci®c (demonstrator) previously administered (a) 1.5 g/kg ethanol, (b) an equal volume of water, or (c) 2.1% Sanka coffee intragastrically. Observers were tested with 24-hour access to ethanol and coffee solutions. Observers that had interacted with demonstrators administered ethanol ingested signi®cantly more ethanol during the test than observers in the other two groups. In Experiment 2 demonstrators were administered one of several doses of ethanol (0.0, 1.0, 1.5, or 3.0 g/kg) and observers' ethanol intakes were assessed. Only those observers that interacted with 1.5 g/kg demonstrators increased their ingestion of ethanol, relative to water controls. The lower (1.0 g/kg) and higher (3.0 g/kg) dose groups did not show altered ethanol ingestion. These results are discussed with respect to threshold levels of respired ethanol cues and the ability of observers to detect these cues from demonstrators. The demonstrator± observer procedure appears to be effective for the social transmission of preferences for ethanol in periadolescent rats. ß 2001 John Wiley & Sons, Inc. Dev Psychobiol 38: 101 ± 109, 2001

Keywords: ethanol; periadolescent rats; alcohol ingestion; social learning

Alcohol abuse continues to be one of the most health-

costly issues in today's society, and the incidence of

alcohol abuse is ever-increasing. Particularly disturb-

ing statistics have recently been reported that the age

at which adolescents and young adults begin to

consume alcohol in rather large quantities is dropping

appreciably. A recent University of Michigan health

survey noted that 51% of 12th graders reported

drinking within the previous month and 26% of 8th

graders reported doing so. Binge drinking, de®ned as

having ®ve or more drinks on occasion, is also on the

rise, with 30% of all 12th graders and 16% of all 8th

graders reporting binge drinking at least once in the 2

weeks prior to the survey (National Institute on

Alcohol Abuse and Alcoholism, 1997).

Given the abuse potential for alcohol, and the

decreasing age at which alcohol is being consumed, it

is imperative that information be gained about the

causative factors involved in the initiation of drinking,

from both basic and applied research domains. To

Correspondence to: P. S. Hunt ([email protected]) Contract grant sponsor: National Institutes of Alcohol Abuse

and Alcoholism Contract grant numbers: AA12135, AA12466

ß 2001 John Wiley & Sons, Inc.

adequately achieve these goals, there is also a need for

adequate animal models to examine relevant social,

environmental and genetic contributions to alcohol

consumption, especially early in development. Cur-

rent research using selectively bred rodent strains

continues to afford valuable insights into the role of

genetic predispositions toward alcohol consumption

and physical dependence (e.g., Brown, Tate, Vik, Haas,

& Aarons, 1999; Grahame, Li, & Lumeng, 1999;

Lumeng, Waller, McBride, & Li, 1982). However, it is

also recognized that genetic factors alone cannot

account for the widespread incidence of alcohol

abuse, either during adolescence or later in life (e.g.,

McKinzie et al., 1998). Experience also contributes

enormously.

As a means of examining experiential factors,

several paradigms have been developed to induce

ethanol intake in rats, a species valuable to addiction

and teratological research, but one that typically

avoids ethanol solutions. Many of the procedures that

result in increased intake of ethanol add confounding

stressor variables (e.g., Adams, 1995; Hansen, Fahlke,

Soederpalm, & Hard, 1995; Le et al., 1998; Roske,

Baeger, Frenzel, & Oehme, 1994), making the study

of mechanistic issues underlying the initiation of

voluntary ethanol intake dif®cult, if not impossible.

Moreover, these and other methods can involve rather

long training histories or complex motor require-

ments, making them unsuitable for use with young

rats because of their rapid rate of development and

relatively immature sensorimotor capabilities. A few

procedures have been speci®cally designed to exam-

ine the consequences of direct exposure to ethanol

cues during the preweanling period on subsequent

alcohol intake patterns (e.g., Bannoura, Kraebel,

Spear, & Spear, 1998; Hunt, Kraebel, Rabin, Spear,

& Spear, 1993; Hunt, Lant, & Carroll, 2000). To date,

however, the effects of direct social contact with an

intoxicated sibling on periadolescent animal's sub-

sequent willingness to ingest ethanol has not been

systematically examined.

It is known that rats detect and learn about foods

through olfactory cues present on the breath or peri-

oral region of a conspeci®c that has recently ingested

a particular food (e.g., Galef, Kennett, & Stein, 1985;

Galef & Stein, 1985; Posadas-Andrews & Roper,

1983; Strupp & Levitsky, 1984). In the experimental

preparation used to examine this social transmission

of dietary information, Galef and colleagues term the

animal that is fed a diet initially the `̀ demonstrator.''

The experimental subject, the one that is tested for

intake of that diet, is termed the `̀ observer.'' The

demonstrator is ®rst fed a diet with a particularly

salient olfactory component, such as chocolate, coffee,

or cinnamon. After the demonstrator has eaten the

food, it is introduced into a cage housing the observer

animal and the two are allowed to interact for a brief

period of time (e.g., 5 ± 30 min). The observer is then

given access to two diets simultaneouslyÐthe one

previously eaten by the demonstrator and another,

novel diet. In several reports, the observer animal was

found to preferentially ingest the diet eaten by its

demonstrator, even if the alternative is normally the

more preferred of the two. The effect is not one of

mere familiarity or simple exposure to the diet (Galef

et al., 1985), but requires a speci®c type of social

context to be established; that is, exposure to food

cues surrounding the peri-oral region of the demon-

strator (Galef & Stein, 1985; Galef & Wigmore, 1983).

Given the pervasive role of social behaviors in the

transmission of dietary information in rats (e.g., Galef,

Kennett, & Wigmore, 1984), it was hypothesized

that the same or similar processes might also act

when the food of interest is a drug of abuse, that is,

alcohol. Because ethanol is eliminated in unmeta-

bolized form through routes such as respiration and

salivation (Hollstedt & Rydberg, 1985) these cues

would be present on the breath of an organism follow-

ing ingestion of alcohol.

We have recently shown that this type of socially

mediated learning can be applied to alcohol intake in

preweanling animals (Hunt et al., 2000). In that study,

the observers were pups ranging in age from 8 to 16

days. After a brief period of social deprivation these

subjects were allowed to interact with a sibling that

had been intragastrically administered a 1.5 g/kg dose

of ethanol or water. Following this interaction, pups

were tested for voluntary intake of ethanol by infusing

ethanol into the mouth via an intra-oral cannula (Hall

& Rosenblatt, 1977). Observers that had interacted

with demonstrators administered ethanol ingested

signi®cantly more ethanol during the test than those

observers that had interacted with demonstrators

administered water.

The purpose of the present experiments was to test

the role of this type of social context in modifying

voluntary ethanol intake in periadolescent Sprague-

Dawley rats. The subjects ranged in age from 28 to 35

days at the beginning of the experiment, considered to

encompass the periadolescent period (Spear & Brake,

1983). In the experimental preparation, the subject of

interest (the observer) interacted with an animal (the

demonstrator) that had previously been force-fed

ethanol. Following this interaction, the observer was

tested for intake of ethanol versus coffee in a two-

bottle test. In two experiments the effectiveness of

this preparation for increasing observers' voluntary

ethanol intake was shown.

102 Hunt, Holloway, and Scordalakes

EXPERIMENT 1

The purpose of Experiment 1 was to determine whether

the demonstrator± observer preparation (Galef et al.,

1985) would be an effective means by which to

promote voluntary intake of ethanol in periadolescent

rats (cf., Hunt et al., 2000). Our choice of periadoles-

cent rats for subjects was in¯uenced by our interest in

adolescent alcohol intake and the social factors that

may contribute to the initiation of drinking. Addi-

tionally, this age allowed for the use of a two-bottle

test, potentially providing more information than that

available when testing preweanlings about alcohol

choice behavior.

Methods

Subjects. The subjects were 30 pairs of same-sex sibling Sprague-Dawley-derived rats (16 female, 14

male), representing seven different litters. No more

than one male and one female from each litter served

as observers in each treatment group. The subjects

ranged from 30 to 35 days of age at the beginning of

the procedure. All animals were born and reared in the

psychology department vivarium at the College of

William & Mary. Breeders were housed together in

50.8�40.6�21.6 cm3 clear polycarbonate cages with pine chip bedding and free access to food

(ProLab, St. Louis, MO) and water. Cages were

checked daily for births. Two days after birth (day of

birth�Postnatal Day [PD] 0) litters were culled to 8 ± 10 pups. Animals were maintained on a 12:12 hr

light:dark cycle with light onset at 0700 hr in the

temperature-controlled vivarium. On PD21 pups were

weaned and group-housed with same-sex littermates

in 50.8�40.6�21.6 cm3 clear polycarbonate cages with ad lib access to food and water until the ®rst day

of the experiment. All procedures were approved by

the College of William & Mary Research on Animal

Subjects Committee and followed guidelines estab-

lished by the International Society for Developmental

Psychobiology.

Apparatus. All training and testing occurred in indi- vidually sized stainless steel hanging cages located in

a room adjacent to the main vivarium, and maintained

on the same temperature and light control systems.

Demonstrators were intragastrically administered

ethanol, water, or coffee solutions using 12-cm lengths

of polyethylene tubing (PE-50; Clay Adams) attached

to 5-cc disposable syringes. Observers were tested for

intake of ethanol and coffee using 50-ml graduated

borosilicate drinking tubes with curved sipper spouts

that were attached to the outside of the hanging cages.

Procedure. The experiment was conducted over 5 days and is outlined in Table 1. On days 1 and 2 of

the procedure, same-sex siblings were pair-housed in

metal hanging cages and handled for approximately

2 min each day. At this time animals within each pair

were assigned to be the demonstrator or the observer.

On Day 3, the demonstrator was removed from the

home cage and placed alone in an adjacent hanging

cage. The demonstrator was given free access to both

food and water, while at this time the observer was

water-deprived but continued to have free access to

food.

On Day 4, 23 hr following separation and the

initiation of water deprivation, demonstrators were

weighed to the nearest 0.1 g. Next, the demonstrator

was intragastrically administered a 1.5 g/kg dose of

12.0% v/v ethanol solution (EtOH, n�10), an equal volume of 2.1% w/v Sanka decaffeinated coffee (COF,

n�9), or an equal volume of the tap water vehicle (WATER, n�10). One pair of male COF subjects was eliminated from the experiment because of improper

intubation. Following intubation, demonstrators were

returned to their cages for 30 min. The 30-minute

period was selected because it has been shown to be

suf®cient for attaining approximately peak blood ±

alcohol levels and respiratory/salivary elimination

of alcohol cues (Molina & Chotro, 1989a; Molina,

Chotro, & Spear, 1989; Pohorecky & Brick, 1982).

The demonstrator was then placed into the observer's

cage and the two animals were left undisturbed for 30

min. After the interaction phase the demonstrator was

once again removed from the observer's cage.

Observers (34 ± 39 days at test) were then offered

two graduated drinking tubes; one containing a 5.6%

v/v ethanol solution and the second containing a 2.1%

Table 1. Procedure Used for Experiments 1 and 2

Day/time Procedure

1/10:00 am Pair-house demonstrators and

observers

Handle subjects 2 min

2/10:00 am Handle subjects 2 min

3/10:00 am Remove demonstrator and individually

house animals

Water deprive observers

4/9:00 am Weigh demonstrator

i.g. administration of EtOH, WATER,

or COF

4/9:30 am Demonstrators placed into observers'

cages

4/10:00 am Demonstrators removed

Two-bottle test begins (observer)

5/10:00 am End of two-bottle test

Periadolescent Ethanol Intake 103

w/v Sanka decaffeinated coffee solution. Both test

solutions were prepared with tap water and the

concentrations of each were chosen on the basis of

preliminary data (Scordalakes & Hunt, unpublished

data) indicating an equal preference for these solu-

tions in naõÈve animals. Observers were allowed free

access to both solutions for 24 hr. The left ± right

placement of the drinking bottles containing the two

solutions was counterbalanced across subjects in all

conditions to avoid a side-preference bias in the data.

At the end of the testing interval, the volume of each

solution ingested (ml) was recorded. The data were

also expressed in terms of the dose of ethanol ingested

during the 24-hour test period (g/kg/day).

Results

The data from this experiment are shown in Figure 1

and Table 2. It was predicted that EtOH observers,

those that had interacted with demonstrators adminis-

tered ethanol, would ingest more ethanol during the

test than WATER controls. Furthermore, observers

interacting with demonstrators administered coffee

(COF) were expected to ingest more coffee than

WATER controls (cf. Galef & Stein, 1985). The ®rst

prediction was realized. Observers that had interacted

with EtOH demonstrators exhibited increased intake

of the ethanol solution relative to coffee. Second, and

in contrast to what was predicted, observers that had

interacted with COF demonstrators did not exhibit

altered intake of coffee relative to that observed in the

WATER controls. When the data were expressed as a

daily dose of ethanol ingested (g/kg/day), again the

observers that had interacted with demonstrators

administered ethanol ingested a higher dose of ethanol

than controls.

The ethanol and coffee intake data were analyzed

using a 3 (demonstrator solution)�2 (test solution: ethanol or coffee)�2 (gender) mixed-design analysis of variance (ANOVA). This analysis yielded a signi-

®cant main effect of test solution [F (1,23)�6.23, p < :05]. The demonstrator solution � test solution [F (2,23)�4.85, p < :05] and test solution�gender [F (2,23)�5.93, p < :05] interactions were also sig- ni®cant. Post hoc comparisons conducted with Neu-

man ± Keuls tests revealed that the EtOH observers

ingested more ethanol and less coffee than either

the WATER or COF observers. Additionally, male

observers ingested more of the ethanol solution than

females, regardless of prior experience. Finally, total

¯uid intake during the test did not differ as a function

of group assignment. A 3 (demonstrator solution)�2 (gender) ANOVA conducted on the dose (g/kg/day)

data revealed signi®cant main effects of demon-

strator solution [F (2,23)�5.37, p < :05] and gender [F (1,23)�7.87, p < :01]. Observers interacting with ethanol-administered demonstrators ingested a higher

dose of ethanol during the test, and males ingested a

higher dose of ethanol than females, regardless of group.

Discussion

Results of the ®rst experiment indicate that an ob-

server animal will increase its intake of a 5.6% v/v

FIGURE 1 Mean (�SEM) intakes of ethanol and coffee (ml) by observers in Experiment 1 during a 24-hour two-

bottle choice test. Observers had previously interacted for

30 min with demonstrators that had been intragastrically

administered a 1.5 g/kg dose of ethanol (EtOH), an equal

volume of tap water (WATER) or an equal volume of 2.1%

Sanka coffee (COF).

Table 2. Mean (�SEM) Dose of Ethanol (g/kg/day) Ingested During the 24-Hour Two-Bottle Ingestion Test

for Experiments 1 and 2

Experiment 1

Observer group

EtOH 9.45 (1.13)

H2O 5.80 (0.98)

COF 5.97 (0.99)

Experiment 2

Demonstrator dose

0.0 5.69 (0.77)

1.0 6.45 (1.10)

1.5 8.16 (0.67)

3.0 5.96 (0.75)

104 Hunt, Holloway, and Scordalakes

ethanol solution following a brief (30 min) interaction

with an intoxicated sibling. Presumably, the adminis-

tration of ethanol to the demonstrator resulted in the

elimination of unmetabolized ethanol that was dete-

cted by the observer. By experiencing these ethanol

cues in the context of social interactions, the observer

acquired suf®cient information about ethanol to guide

later voluntary choice of this drug. In contrast to the

®nding of increased ethanol ingestion in EtOH

observers, animals that had interacted with demon-

strators administered a coffee solution showed no

socially mediated change in coffee preference (but see

Galef & Stein, 1985). It is possible that the time

between administration of coffee to the demonstrator

and the interaction phase, or characteristics of the

coffee solution intubated, may have affected the

observers detecting and learning about the coffee cue

from the demonstrators.

The work of Galef and colleagues (Galef & Stein,

1985; Galef & Wigmore, 1983) has repeatedly indi-

cated that physical contact per se is not a necessary

component of this type of learning. Observers have

been found to acquire dietary information from de-

monstrators even when the animals are separated by a

wire mesh screen or when demonstrators are anesthe-

tized. There is, however, a lack of data on preweanling

and periadolescent animals. The availability for social

interactions may in fact enhance the strength of diet

acquisition in younger animals more so than in adults.

Several laboratories have shown that social interac-

tions and the opportunity for play are highly rein-

forcing to adolescent age rats. Most of the research in

this area has utilized the conditioned place preference

paradigm, in which one arm of a T-maze contains a

play partner while the alternative arm contains no

stimulus, a surrogate animal, or an animal that does

not engage in play behavior. Using variants of this

paradigm, adolescent rats have consistently been

shown to prefer the arm previously associated with

a play partner (e.g., Calcagnetti & Schechter, 1992;

Crowder & Hutto, 1992; Humphreys & Einon, 1981;

Normansell & Panksepp, 1990). In the present proce-

dure the demonstrators and observers were allowed to

physically interact following a period of social isola-

tion. It is unclear at present whether or not this

physical contact had the effect of promoting acquisi-

tion of appetitive responses toward ethanol.

EXPERIMENT 2

In Experiment 1 the EtOH demonstrators were ad-

ministered a 1.5 g/kg dose of ethanol. This dose was

chosen on the basis of a series of reports by Molina

and colleagues (Molina et al., 1989; Molina & Chotro,

1989b) indicating that 1.5 g/kg ethanol, but not lower

doses, resulted in detectable levels of ethanol orosen-

sory cues suf®cient for learning about those cues to

occur. In the Molina studies, the animal that was

administered the ethanol intragastrically was assessed

for its own learning about alcohol in terms of olfactory

preferences and alcohol intake. The results of the

present Experiment 1 indicate that another animal can

detect and learn about these cues as well. It is possible

that with the demonstrator± observer procedure doses

lower than 1.5 g/kg would be effective for producing

suf®cient elimination of ethanol to affect the alcohol

intake of an observer. The purpose of Experiment 2

was to conduct a dose ± response study to determine

(a) whether demonstrators administered a dose of

ethanol lower than 1.5 g/kg would provide suf®-

cient orosensory stimuli to promote ethanol intake

in observers and (b) whether demonstrators adminis-

tered a dose higher than 1.5 g/kg would establish

even stronger preferences for the ethanol solution in

observers. In this experiment demonstrators were

intragastrically administered 0, 1.0, 1.5, or 3.0 g/kg

ethanol.

Methods

Subjects. The subjects in this experiment were 48 pairs of same-sex sibling Sprague-Dawley-derived

rats (24 male, 24 female), representing 14 different

litters. Subjects ranged in age from 28 to 33 days on

the ®rst day of the procedure. Animals were born and

reared in the psychology department vivarium at the

College of William & Mary under conditions identical

to those described in Experiment 1. Pairs of animals

were randomly assigned to one of four conditions,

designated according to the dose of ethanol adminis-

tered to the demonstrator: 0 (n�12), 1.0 (n�12), 1.5 (n�12), or 3.0 g/kg (n�11). One pair of female subjects assigned to the 3.0 g/kg group was eliminated

from the study due to the improper intubation of the

demonstrator.

Procedure. The experimental procedure was similar to that of Experiment 1, except for a change in coffee

concentration and the dose of ethanol administered to

the demonstrators. Following 2 days of pair housing

in hanging cages, demonstrators were removed and

placed in an adjacent cage. Observers were then

water-deprived. Demonstrators were intragastrically

administered one of three doses of a 12.0% v/v ethanol

solution prepared in a tap water vehicle: 1.0, 1.5, or

3.0 g/kg. A water-intubated control group (0 g/kg) was

Periadolescent Ethanol Intake 105

administered a volume of tap water equal to the

volume administered to the 1.5 g/kg EtOH group.

Thirty minutes following intubation, the demonstrator

was placed into the observer's cage and the two

animals were allowed to interact for 30 min. The

demonstrator was again removed and the observer

was given a 24-hour test of intake of 5.6% v/v ethanol

vs. 1.8% w/v Sanka coffee. The concentration of the

coffee solution was decreased in order to reduce

baseline ethanol preference. This allowed us to more

clearly address the question of whether the preference

for ethanol established through interactions with a 3.0

g/kg demonstrator would be greater than that with a

1.5 g/kg demonstrator. The volume of each solution

ingested by the observers was recorded, and the data

were also expressed in terms of the dose of ethanol

ingested (g/kg/day).

Results

The data from this experiment are presented in Figure

2 and Table 2. As can be seen in the ®gure, observers

that had interacted with demonstrators administered

1.5 g/kg ethanol exhibited an increased intake of

ethanol vs. coffee, and therefore a higher daily dose of

ethanol consumed, replicating the results of Experi-

ment 1. However, observers that had interacted with

demonstrators administered either a lower (1.0 g/kg)

or a higher (3.0 g/kg) dose of ethanol failed to exhi-

bit a reliable change in ethanol intake. Finally, the

water observers (0 g/kg) showed approximately equal

intake of both solutions, similar to that observed in

Experiment 1.

A 4 (demonstrator dose)�2 (test solution)�2 (gender) ANOVA conducted on the intake data

revealed only a signi®cant main effect of gender [F

(1,39)�4.18, p < :05]. Generally, males ingested more ¯uid during the test than females, although there

were no differences in terms of the proportions of

ethanol and coffee. Follow-up ANOVAs [2 (demon-

strator dose)�2 (test solution)] were used to compare intakes of the 0.0 g/kg group with each of the other

groups. The only reliable demonstrator dose� test solution interaction occurred for the 1.5 g/kg obser-

vers that exhibited increased intakes of ethanol, and

reduced intakes of coffee, relative to the water (0.0 g/

kg) controls [F (1,22)�5.77, p < :05]. The analyses comparing the 0.0 with the 1.0 g/kg and 3.0 g/kg

groups, respectively, revealed no signi®cant diffe-

rences. The analyses of the ethanol dose ingested

yielded comparable results (see Table 2). The 4

(demonstrator dose) �2 (gender) ANOVA revealed no signi®cant effects or interactions. Planned t-tests,

however, indicated that the dose of ethanol ingested

by the 1.5 g/kg observer group was signi®cantly

higher than that ingested by the water control group

[t (22)�2.36, p < :05]. No other differences were statistically reliable.

Discussion

The results of Experiment 2 once again indicated that

observers that had brie¯y interacted with an intoxi-

cated sibling exhibited increased intake of ethanol

during a two-bottle choice test. Furthermore, there

was an inverted-U dose ± response relationship. Obser-

vers interacting with siblings given a 1.5 g/kg dose of

ethanol did increase their intake of ethanol; however,

observers interacting with siblings administered either

a lower (1.0 g/kg) or a higher (3.0 g/kg) dose failed to

exhibit altered ethanol ingestion.

The failure to obtain increased ethanol intake in

the low (1.0 g/kg) dose condition is likely due to

insuf®cient olfactory cues present on the breath of the

demonstrator animals. Decreased salience of these

cues would correspondingly reduce the ability of

observers to detect and/or learn about alcohol from the

demonstrators (cf. Molina & Chotro, 1989b). This

social modulation of ethanol intake can easily be

viewed within a Pavlovian conditioning perspective,

for which the ethanol olfactory cues detected on a

conspeci®c's breath serve as the conditioned stimulus

(CS) and some aspect of the social interaction serves

FIGURE 2 Mean (�SEM) intakes of ethanol and coffee (ml) by observers in Experiment 2 during a 24-hour two-

bottle choice test. Observers had previously interacted for

30 min with demonstrators that had been intragastrically

administered 0, 1.0, 1.5, or 3.0 g/kg ethanol.

106 Hunt, Holloway, and Scordalakes

as the unconditioned stimulus (US). It is well known

that characteristics of the CS, as well as the US, can

in¯uence the rate and asymptotic level of conditioning

(e.g., Pearce & Hall, 1980; Rescorla & Wagner, 1972).

If the amount of respired ethanol cues is not of

suf®cient intensity, then minimal conditioning would

be expected. Therefore, little or no conditioned res-

ponse (ethanol intake above 50%) would be expected

to occur. This is precisely what was observed in

Experiment 2.

A different explanation, however, is required to

describe the failure of the 3.0 g/kg observers to exhibit

an ethanol preference. First, it is possible that the

severely intoxicated demonstrator was capable through

some means of communicating an aversion for ethanol

to the observer (but see Galef, Wigmore, & Kennett,

1983). The post-ingestional consequences of a dose of

3.0 g/kg ethanol have been found to condition taste

aversion to a concurrently presented sucrose solution,

at least in younger animals (Hunt, Spear, & Spear,

1991). Furthermore, preweanling rats administered a

3.0 g/kg dose will subsequently avoid both ethanol

odor and taste (e.g., Molina et al., 1989). It is therefore

possible that a severely intoxicated demonstrator

could transmit cues that serve to communicate even

a weak ethanol avoidance to an observer, one that was

capable of counteracting an established preference.

A second explanation for the failure of 3.0 g/kg

observers to acquire a preference for ethanol centers

on the ability of the observers to detect the ethanol

cues from the demonstrators. Clearly if the salience of

the CS in part determines the strength of conditioning,

then the intensity of the cues resulting from this high

dose of ethanol should be even greater than those from

the 1.5 g/kg condition (Hollstedt & Rydberg, 1985;

Pohorecky & Brick, 1982). Although the concentra-

tion of these cues might in fact be greater, the question

remains as to whether the observers were actually able

to detect these cues from the demonstrator. Casual

observation of the 3.0 g/kg demonstrators indicated

an almost complete lack of movement during the

30-minute interaction period; demonstrators tended to

lie in a prone posture with their mouths directed

toward the bottom of the cage. Although quantitative

measurements of peri-oral contact between demon-

strators and observers were not made, it is possible

that the observers were unable to detect the ethanol

cues emanating from the peri-oral region of the

3.0 g/kg demonstrators. In the absence of adequate

detection of ethanol orosensory cues, the transmission

of ethanol information from demonstrator to observer

would not occur. By this account then, the failure of

these observers to exhibit modi®ed ethanol ingestion

resulted from an inability to learn about ethanol.

GENERAL DISCUSSION

Among the ways that human infants, young children,

and adolescents can be exposed to alcohol in the

context of the home and other social environments is

through the detection of ethanol in the milk of a

breast-feeding mother, long-term exposure to the odor

of ethanol, direct topical application (e.g., for relief of

teething pain), and/or the detection of respired ethanol

cues (e.g., Fossey, 1993; Mennella & Beauchamp,

1991, 1993; Noll, Zucker, & Greenberg, 1990). It has

been suggested that young children acquire informa-

tion about alcohol via such types of exposure. Noll

et al. (1990) reported that children whose parents were

heavy drinkers were more likely to correctly identify

the odor of alcohol than children whose parents drank

only moderately or not at all. Another study reported

similar results from a cohort of Scottish and British

children (Fossey, 1993). In this study, the children

were capable of correctly identifying alcohol by smell

on over 80% of the occasions presented. Whether

exposure to ethanol cues in these situations would be

suf®cient to modify a human's later choice and

acceptance of this drug is not yet known.

Such experiential factors may indeed contribute

substantially to the initiation of alcohol drinking in

children and adolescents. It is known that children of

alcoholics tend to drink more than children of non-

alcoholics (U.S. Department of Health and Human

Services, 1993). Although genetics no doubt play an

important role here, the home environment is likely to

also be extremely important. Children of alcoholics

would spend more time in contact with alcohol-

related cues, potentially affecting these children's

learning of positive responses toward this drug.

In animal studies designed to model such situations,

young rats have consistently been shown to increase

their acceptance of ethanol following each type of

exposure. These results are highly suggestive that early

experiences with alcohol cues can impact alcohol inges-

tion patterns. For example, Hunt et al. (1993) investi-

gated alcohol intake in preweanling rats following

exposure to ethanol during a bout of nursing. Pups

12 ± 16 days of age increased their intake of ethanol

after experiencing alcohol-contaminated milk in con-

junction with the opportunity to suckle. Pepino,

Kraebel, Lopez, Spear, and Molina (1998) have addi-

tionally reported that exposure to alcohol-contami-

nated milk can result in altered motor and cardiac

responsivity toward ethanol cues in preweanlings.

Bannoura et al. (1998) raised rat pups from birth to

weaning in cages that were continuously scented with

ethanol odor. These pups exhibited a clear preference

for ethanol when tested for intake after weaning,

Periadolescent Ethanol Intake 107

compared with controls not exposed to ethanol cues.

These ®ndings could re¯ect a conditioned preference

for ethanol odor experienced in the context of social

interactions with the dam and littermates, or the effect

of familiarity from long-term repeated exposure

(Bronstein & Crockett, 1976; Leon, Galef, & Behse,

1977).

Once ingested, a proportion of the ethanol dose is

distributed throughout the body in unmetabolized

form and is expired via its accumulation in the lungs.

Additional routes of nonhepatic elimination involve

salivation, urination, and perspiration (Hollstedt &

Rydberg, 1985). Regardless of the actual route of

elimination, animals are known to be capable of

detecting these cues and learning about them in a

variety of experimental preparations in which social

contact with other animals is a critical feature (e.g.,

Bannoura et al., 1998; Chotro, Kraebel, McKinzie,

Molina, & Spear, 1996; Hunt et al., 2000). Hunt et al.

reported that social interactions with an intoxicated

sibling result in enhanced intake of ethanol by pre-

weanling animals, ranging in age from 8 to 16 days.

These results, along with those of previous research

(e.g., Chotro et al., 1996) indicate that exposure to

ethanol in social contexts can play a role in modifying

a preweanling animal's responsiveness toward etha-

nol. The results of the present experiments indicate that

a periadolescent rat will also acquire information

about alcohol cues from an intoxicated sibling, and as

a result will increase its subsequent intake of an etha-

nol solution. It is, however, unclear at this time, whether

or not exposure to ethanol-derived cues in these

situations would have a relatively long-term impact on

later alcohol choice (but see Galef, 1989; Hunt et al.,

2000, Experiment 3; Strupp & Levitsky, 1984).

Clearly, research is beginning to identify ways in

which early experiences involving direct exposure to

ethanol cues in the context of the home environment

can affect young organisms' later acceptance of this

drug. Continued investigation into the nature of the

alcohol cues detected, and the mechanisms through

which various types of learning take place, may help

to further elucidate the consequences of social learn-

ing for alcohol abuse in late childhood and adoles-

cence. Moreover, the present experimental procedure

may afford a relatively simple and robust experimental

situation in which to further study the role of social

experiences with alcohol in the initiation, and possibly

also the maintenance, of excessive ethanol intake.

NOTES

This research was supported by grants AA12135 and

AA12466 from the National Institutes of Alcohol

Abuse and Alcoholism to P.S.H.. Experiment 1 was

conducted as part of the requirements for a B.S. with

honors in biological psychology by E.M.S., and

Experiment 2 was conducted as part of the require-

ments for a master's degree in psychology by J.L.H..

We are grateful to Elena Cuticelli for her assistance

with data collection.

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