0145-60081981220 1 -0270$03.0010 zyxwvutsrqpon A1 COHO1 ISM' CLlNlCAl AN11 EXPERIMENTAI RESEARCH Vol. 22, No. 1 Febmaxy 1998 RAPID COMMUNICATION Neonatal Ethanol Exposure Impairs Eyeblink Conditioning in Weanling Rats zy Mark E. Stanton and Charles R. Goodlett Eyeblink conditioningdepends on an identied brainstem-cerebellar circuit and may be useful in functional studies of early cerebellar damage produced by neurotoxicants. The present study asked whether binge-like neonatalethanol exposure that damages the cer- ebellum would also result in eyeblink conditioning deficits. On post- natal day (PND) 23 to PND24, three groups of Long-Evans rat pups were tested for eyeblink conditioning: (1) zyxwvut -OH, a group that re- ceived intragastric administration of 5.25 g/kg/day of ethanol on PNW through PND9 via artificial rearing; (2) GC, a gastrostomy con- trol group that received calorically matched milk formula on those days; and (3) SC, suckle controls that were reared normallywith their dams. Eyeblink conditioning was severely impaired in the ethanol- treated group relative to the GC and SC groups, which did not difter. This impairment did not reflect sensory, motor, or motivational ef- fects of ethanoltreatment, because startle responses to the auditory conditionedstimulus and reflexive eyeblink responses to the uncon- ditioned stimulus did not differ across the three treatment groups. These results suggest that neonatal binge ethanol exposure dis- rupted brain development in a manner that selectively impaired as- sociative processes involved in eyeblink conditioning, consistent with alcohol-induced damage to the brainstem-cerebellar circuit necessary for this form of learning. Key Words: Fetal Alcohol Syndrome, Developmental Neurotoxic- zyxwvu ity, Classical Conditioning, Associative Learning, Cerebellum. ASED ON estimates of incidence and prevalence of B fetal alcohol syndrome and the more broadly defined alcohol-related neurodevelopmental defects (ARNDs), prenatal exposure to ethanol is a leading known cause of mental retardation and developmental di~abilities.'-~ It is well established that developmental exposure to ethanol produces deficits in learning and memory in both humans zyxwvu From the Neurotoxicology Division (MD-74B) (M. E.S.), US. Environ- mental Protection Agency, Research Triangle Park, North Carolina; and the Department of Psychology, (C.R G.), Indiana University-Purdue University at Indianapolis, Indianapolis, Indiana. Received for publication October 16, 1997; accepted November 11, 1997 This study was supported in part by the National Institute on Alcohol Abuse and Alcoholism Grant AA09596 (to C.R.G.). This article has been reviewed by the National Health and Environmental Effects Research Lab- oratory, US. Environmental Protection Agency, and approved for publica- tion. Mention of trade names or commercial products does not constitute endorsement or recommendation zyxwvutsrqpo for use. Reprint requests: Mark E. Stanton, Ph.D., Neurotoxicology Division (MD- 74B), U.S. Environmental Protection Agency, Research Triangle Park, NC 27711. Copyright zyxwvutsrqp 0 1998 by The Research Society on Alcoholism. zyxwvut 270 and laboratory animal^.^-^ Understanding these deficits in terms of causal relationships between exposure scenario, neurological insult, and behavioral impairment, and in terms of how these relationships compare in humans versus animal models, remain important frontiers of research on ARNDs.~,~ In humans, neuropathologicaly,'oand recent neuroimag- ing studies" have shown that prenatal ethanol exposure impairs the normal development of several brain struc- tures. Among these, the cerebellum seems to be a major target.I2 Animal model studies using early postnatal etha- nol exposure have also shown that the neonatal rat cere- bellum is particularly vulnerable to damage by binge-like ethanol exp~sure.'~-~' In terms of brain development, this early postnatal period of the "brain growth spurt" in rats roughly corresponds to that of the human third trimes- ter.16,17 Massive reductions in cerebellar size and in Pur- kinje and granule cell numbers in cerebellar cortex result from binge-like daily exposure on postnatal day (PND) 4 through PND9 in the rat, reaching as much as 45% loss of Purkinje cells when daily peak blood ethanol concentra- tions exceed 250 mg/dl.'s-24 These cerebellar effects of ethanol exposure in neonatal rats are remarkably consistent with recently described reductions in cerebellar size in magnetic resonance imaging studies of children exposed to ethanol prenatally.12 Deficits in motor performance, balance, and coordina- tion have been reported in children exposed to ethanol and seem to be one expression of ethanol- induced cerebellar damage. Impairments on tests of motor function (rotarod, parallel bar, and walking gait) have also been demonstrated after neonatal ethanol exposure and generally have been correlated with cerebellar growth def- icits and Purkinje cell 10ss.20,24,28-31 Cerebellar damage may also play an important role in some of the deficits in associative learning that are ob- served after prenatal exposure in humans. The cerebellum is essential for certain forms of mammalian associative learning, the best studied being classical conditioning of the eyeblink reflex, which has been extensively characterized both behaviorally and neurobiologically and is known to depend on an identified brainstem-cerebellar c i r c ~ i t . ~ ~ - ~ Alcohol zyxw Clin Exp Res, Val 22, No I, 1998: pp 270-275