There are clear differences in the acute effects of alcohol between adolescent and adult rats. Differences at the behavioral level reflect the underlying neurobiological differences between adolescents and adults. Adolescent rats voluntarily drink more alcohol than adults. This could relate to the increased binging behavior seen in adolescent humans.

Adolescent Rats Voluntarily Drink More Alcohol than Adults

Adolescent (post natal day 28) and adult (post natal day 60) male Sprague - Dawley rats were trained with a 30 min limited access to sucrose-alcohol solutions. The data above is for 5% sucrose at 3 different alcohol concentrations. Adolescent rats also drank more alcohol when maintained on a 5% sucrose and 10% alcohol solution. Other studies have also demonstrated that adolescent rats consume more alcohol than adults. (Constructed from data in Maldonado, A.M. et al. Alcohol Clin Exp Res, 32: 1574, 2008) ©2008 NBEP
A major difference is that adolescent rats have less impairment of motor ordination following acute alcohol exposure than adults. This could be a factor in the increased binge drinking and adolescents compared to adults since loss of coordination would be one of the factors that limits alcohol intake

Adolescent Rats Have Less Impairment of Motor Coordination Following Acute Alcohol Exposure Than Adults

Adolescent (post natal day, 35-40) and adult (post natal day, 70-75) rats were given a Tilting Plane Test to measure motor coordination before and then at 15, 30, 60, 120, and 180 min after IP injection of alcohol. Adolescent rats usually have higher alcohol blood levels to the same dose of alcohol than adults so the smaller effect of alcohol on motor coordination in adolescents is due to alcohol effects on the neuromuscular system. (Constructed from data in White, A.M. et al. Pharmacology, Biochemistry & Behavior, 73: 673, 2002) ©2008 NBEP
Adolescent rats develop tolerance to alcohol more rapidly than adults, which could be a factor that would increase alcohol intake in adolescents.

Tolerance to Ethanol Develops More Rapidly in Adolescents Than in Adults

7-day ethanol pretreated adolescent rats developed greater tolerance to the effects of ethanol on body temperature than did adults, and took less time to right themselves after receiving same IP dose of ethanol (falling Blood Alcohol at recovery of righting reflex was 0.452 gm/100 ml in adolescents and 0.264 gm/100 ml in adults, p < .001). Colorectal temperature and latency to loss of righting reflex did not differ between age groups on the initial day of testing. 36 adolescent and 36 adult rats were randomly assigned to control or experimental groups and subsequently divided into subgroups receiving either 3- or 7-days of 4 g/kg ethanol (saline for controls) twice a day. 36 hours after the last pretreatment dose, all mice received a single (sedative) IP dose of 5 g/kg ethanol. Colorectal temperature was measured before and 90 min after IP dose with thermometer probe inserted a controlled distance each time. Recovery of righting reflex after IP dose was defined by rat’s ability to right itself (4 legs on floor) within 3 seconds of being placed on its back, twice in succession. (Constructed from data in Swartzwelder, H.S. et al. Alcohol, 15: 311, 1998) ©2008 NBEP
Adolescent rats are more sensitive than adults to alcohol impairment of memory of odor discrimination, indicating that alcohol can impair cognitive function more in adolescents than adults.

Alcohol Impairs Memory of an Odor Discrimination in Adolescent but not Adult Rats

Adolescent (age 28 days old) and adult (age 100-120 days old) rats learned to dig for a food reward in one type of scented sand in a cup and they learned that a different scented sand in another cup had no reward. After about 10 min training rats were immediately injected intraperitoneally with alcohol or saline. They were tested for digging 48 hours later with the two seated cups that contained no reward. Digging in the scented cup that the rats had learned contained no reward was mostly less than 2 sec and did not differ with age or alcohol. Since adolescents and adults dug the same amount of time in the scented cup that had contained a reward in the saline control, the data indicate that alcohol impairs the memory of the association between the scent and the reward. * = p <.005 compared to saline control. (Constructed from data in Land, C. and Spear, N.E. Neurobiology of Learning and Memory, 81: 75, 2004) ©2008 NBEP
In adolescent rats, alcohol selectively impairs spatial memory but not non-spatial memory. In adult rats alcohol did not impair either type of memory. This is another example of alcohol producing a selective impairment of cognitive function in adolescence, and it is key evidence for the harmful effects of alcohol in adolescence.

Alcohol Selectively Impairs Spatial Memory Acquisition in Adolescent but not Adult Rats and Alcohol Does not impair non-spatial memory in either adolescent or adult rats.

Adolescent (30 days old) and adult (65 days old) rats were given intraperitoneal alcohol at 2 doses or saline on 5 successive days, 30 min before a series of 5, 60 second trials each day. An escape platform was hidden under opaque water except in non-spatial trials a 12-inch pole identified the location of the platform. Similar results were obtained when distance swam was scored. (Constructed from data in Markwiese, B.J. et al. Alcohol Clin Exp Res, 22: 416, 1998) ©2008 NBEP
Of major importance is the finding that adolescence is associated with an increased sensitivity to alcohols as motivational affects. Thus in adolescence alcohol produces a combination of an reduced motor impairment, increasedimpairment of cognitive function and increased motivational effects.

Adolescent Rats Have Greater Alcohol-Mediated Second Order Conditioning Than Adult Rats

Male and female adolescent rats (post natal day 32, P32) and adult rats P70 received oral sucrose 5-20 min or 30-45 min following intragastric ethanol (0.5 or 2.0 g/kg) and compared controls received ethanol at least over 195 min after sucrose. One day later all rats received sucrose in a distinctive chamber and 30 min later were tested for 12 min for preference to that chamber in a 3 chamber box. Blood ethanol levels did not differ between the groups. The earlier and later times for sucrose are combined. * = Significantly different than controls and adults. (Constructed from data in Pautassi, R.M. et al. Alcoholism: Clinical & Experimental Research, 32: 1, 2008) ©2008 NBEP