Eyeblink classical conditioning and interpositus nucleus activity are disrupted in adult rats exposed to ethanol as neonates

Developmental alcohol exposure is exhausting: Sleep and the enduring consequences of alcohol exposure during development

Prenatal alcohol exposure is the leading nongenetic cause of human intellectual impairment. The long-term impacts of prenatal alcohol exposure on health and well-being are diverse, including neuropathology leading to behavioral, cognitive, and emotional impairments. Additionally negative effects also occur on the physiological level, such as the endocrine, cardiovascular, and immune systems. Among these diverse impacts is sleep disruption. In this review, we describe how prenatal alcohol exposure affects sleep, and potential mechanisms of those effects. Furthermore, we outline the evidence that sleep disruption across the lifespan may be a mediator of some cognitive and behavioral impacts of developmental alcohol exposure, and thus may represent a promising target for treatment.

Impairment of the context preexposure facilitation effect in juvenile rats by neonatal alcohol exposure is associated with decreased Egr-1 mRNA expression in the prefrontal cortex

The context preexposure facilitation effect (CPFE) is a variant of contextual fear conditioning in which learning about the context (preexposure) and associating the context with a shock (training) occur on separate occasions. The CPFE is sensitive to a range of neonatal alcohol doses (Murawski & Stanton, 2011). The current study examined the impact of neonatal alcohol on Egr-1 mRNA expression in the infralimbic (IL) and prelimbic (PL) subregions of the mPFC, the CA1 of dorsal hippocampus (dHPC), and the lateral nucleus of the amygdala (LA), following the preexposure and training phases of the CPFE. Rat pups were exposed to a 5.25 g/kg/day single binge-like dose of alcohol (Group EtOH) or were sham intubated (SI; Group SI) over postnatal days (PD) 7-9. In behaviorally tested rats, alcohol administration disrupted freezing. Following context preexposure, Egr-1 mRNA was elevated in both EtOH and SI groups compared with baseline control animals in all regions analyzed. Following both preexposure and training, Group EtOH displayed a significant decrease in mPFC Egr-1 mRNA expression compared with Group SI. However, this decrease was greatest after training. Training day decreases in Egr-1 expression were not found in LA or CA1 in Group EtOH compared with Group SI. A second experiment confirmed that the EtOH-induced training-day deficits in mPFC Egr-1 mRNA expression were specific to groups which learned contextual fear (vs. nonassociative controls). Thus, memory processes that engage the mPFC during the context-shock association may be most susceptible to the teratogenic effects of neonatal alcohol. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Video-based data acquisition system for use in eye blink classical conditioning procedures in sheep

Pavlovian eye blink conditioning (EBC) has been extensively studied in humans and laboratory animals, providing one of the best-understood models of learning in neuroscience. EBC has been especially useful in translational studies of cerebellar and hippocampal function. We recently reported a novel extension of EBC procedures for use in sheep, and now describe new advances in a digital video-based system. The system delivers paired presentations of conditioned stimuli (CSs; a tone) and unconditioned stimuli (USs; an air puff to the eye), or CS-alone "unpaired" trials. This system tracks the linear distance between the eyelids to identify blinks occurring as either unconditioned (URs) or conditioned (CRs) responses, to a resolution of 5 ms. A separate software application (Eye Blink Reviewer) is used to review and autoscore the trial CRs and URs, on the basis of a set of predetermined rules, permitting an operator to confirm (or rescore, if needed) the autoscore results, thereby providing quality control for accuracy of scoring. Learning curves may then be quantified in terms of the frequencies of CRs over sessions, both on trials with paired CS-US presentations and on CS-alone trials. The latency to CR onset, latency to CR peak, and occurrence of URs are also obtained. As we demonstrated in two example cases, this video-based system provides efficient automated means to conduct EBC in sheep and can facilitate fully powered studies with multigroup designs that involve paired and unpaired training. This can help extend new studies in sheep, a species well suited for translational studies of neurodevelopmental disorders resulting from gestational exposure to drugs, toxins, or intrauterine distress.

Functional MRI of Human Eyeblink Classical Conditioning in Children with Fetal Alcohol Spectrum Disorders

Prenatal alcohol exposure has been linked to a broad range of developmental deficits, with eyeblink classical conditioning (EBC) among the most sensitive endpoints. This fMRI study compared EBC-related brain activity in 47 children with fetal alcohol syndrome (FAS), partial FAS (PFAS), heavily exposed (HE) non-syndromal children, and healthy controls. All of the children had previously participated in two EBC studies conducted as part of our longitudinal study of fetal alcohol spectrum disorders. Although learning-related behavioral differences were seen in all groups during the scans, controls showed more conditioned responses (CR) than the alcohol-exposed groups. Despite lower conditioning levels relative to controls, the exposed groups exhibited extensive cerebellar activations. Specifically, children with FAS/PFAS showed increased activation of cerebellar lobule VI in session 2, while HE children showed increased activation in session 1. Continuous measures of prenatal alcohol use correlated with learning-related activations in cerebellum and frontal cortices. Only controls showed significant cerebellar activation-CR correlations in the deep nuclei and lateral lobule VI, suggesting that these key regions supporting EBC may be functionally disorganized in alcohol-exposed children. These findings are the first to characterize abnormalities in brain function associated with the behavioral conditioning deficits seen in children with prenatal alcohol exposure.

Performance in eyeblink conditioning is age and sex dependent

A growing body of evidence suggests that the cerebellum is involved in both cognition and language. Abnormal cerebellar development may contribute to neurodevelopmental disorders such as attention deficit hyperactivity disorder (ADHD), autism, fetal alcohol syndrome, dyslexia, and specific language impairment. Performance in eyeblink conditioning, which depends on the cerebellum, can potentially be used to clarify the neural mechanisms underlying the cerebellar dysfunction in disorders like these. However, we must first understand how the performance develops in children who do not have a disorder. In this study we assessed the performance in eyeblink conditioning in 42 typically developing children between 6 and 11 years old as well as in 26 adults. Older children produced more conditioned eyeblink responses than younger children and adults produced more than children. In addition, females produced more conditioned eyeblink responses than males among both children and adults. These results highlight the importance of considering the influence of age and sex on the performance when studying eyeblink conditioning as a measure of cerebellar development.

Alcohol Teratogenesis: Mechanisms of Damage and Strategies for Intervention

There are multiple mechanisms by which alcohol can damage the developing brain, but the type of damage induced will depend on the amount and developmental timing of exposure, along with other maternal and genetic factors. This article reviews current perspectives on how ethanol can produce neuroteratogenic effects by its interactions with molecular regulators of brain development. The current evidence suggests that alcohol produces many of its damaging effects by exerting specific actions on molecules that regulate key developmental processes (e.g., L1 cell adhesion molecule, alcohol dehydrogenase, catalase), interfering with the early development of midline serotonergic neurons and disrupting their regulatory-signaling function for other target brain structures, interfering with trophic factors that regulate neurogenesis and cell survival, or inducing excessive cell death via oxidative stress or activation of caspase-3 proteases. The current understanding of pathogenesis mechanisms suggests several strategic approaches to develop rational molecular prevention. However, the development of behavioral and biologic treatments for alcohol-affected children is crucial because it is unlikely that effective delivery of preventative interventions can realistically be achieved in ways to prevent prenatal damage in at-risk pregnancies. Toward that end, behavioral training that promotes experience-dependent neuroplasticity has been effective in a rat model of cerebellar damage induced by alcohol exposure during the period of brain development that is comparable to that of the human third trimester.

The impact of prenatal alcohol exposure on social, cognitive and affective behavioral domains: Insights from rodent models

Fetal Alcohol Spectrum Disorders (FASD) are characterized by deficits in working memory, response inhibition, and behavioral flexibility. However, the combination and severity of impairments are highly dependent upon maternal ethanol consumption patterns, which creates a complex variety of manifestations. Rodent models have been essential in identifying behavioral endpoints of prenatal alcohol exposure (PAE). However, experimental model outcomes are extremely diverse based on level, pattern, timing, and method of ethanol exposure, as well as the behavioral domain assayed and paradigm used. Therefore, comparisons across studies are difficult and there is currently no clear comprehensive behavioral phenotype of PAE. This lack of defined cognitive and behavioral phenotype is a contributing factor to the difficulty in identifying FASD individuals. The current review aims to critically examine preclinical behavioral outcomes in the social, cognitive, and affective domains in terms of the PAE paradigm, with a special emphasis on dose, timing, and delivery, to establish a working model of behavioral impairment. In addition, this review identifies gaps in our current knowledge and proposes future areas of research that will advance knowledge in the field of PAE outcomes. Understanding the complex behavioral phenotype, which results from diverse ethanol consumption will allow for development of better diagnostic tools and more critical evaluation of potential treatments for FASD.

Relating cerebellar purkinje cell activity to the timing and amplitude of conditioned eyelid responses

How Purkinje cell (PC) activity may be altered by learning is central to theories of the cerebellum. Pavlovian eyelid conditioning, because of how directly it engages the cerebellum, has helped reveal many aspects of cerebellar learning and the underlying mechanisms. Theories of cerebellar learning assert that climbing fiber inputs control plasticity at synapses onto PCs, and thus PCs control the expression of learned responses. We tested this assertion by recording 184 eyelid PCs and 240 non-eyelid PCs during the expression of conditioned eyelid responses (CRs) in well trained rabbits. By contrasting the responses of eyelid and non-eyelid PCs and by contrasting the responses of eyelid PCs under conditions that produce differently timed CRs, we test the hypothesis that learning-related changes in eyelid PCs contribute to the learning and adaptive timing of the CRs. We used a variety of analyses to test the quantitative relationships between eyelid PC responses and the kinematic properties of the eyelid CRs. We find that the timing of eyelid PC responses varies systematically with the timing of the behavioral CRs and that there are differences in the magnitude of eyelid PC responses between larger-CR, smaller-CR, and non-CR trials. However, eyelid PC activity does not encode any single kinematic property of the behavioral CRs at a fixed time lag, nor does it linearly encode CR amplitude. Even so, the results are consistent with the hypothesis that learning-dependent changes in PC activity contribute to the adaptively timed expression of conditioned eyelid responses.

Eyeblink Classical Conditioning in Alcoholism and Fetal Alcohol Spectrum Disorders

Alcoholism is a debilitating disorder that can take a significant toll on health and professional and personal relationships. Excessive alcohol consumption can have a serious impact on both drinkers and developing fetuses, leading to long-term learning impairments. Decades of research in laboratory animals and humans have demonstrated the value of eyeblink classical conditioning (EBC) as a well-characterized model system to study the neural mechanisms underlying associative learning. Behavioral EBC studies in adults with alcohol use disorders and in children with fetal alcohol spectrum disorders report a clear learning deficit in these two patient populations, suggesting alcohol-related damage to the cerebellum and associated structures. Insight into the neural mechanisms underlying these learning impairments has largely stemmed from laboratory animal studies. In this mini-review, we present and discuss exemplary animal findings and data from patient and neuroimaging studies. An improved understanding of the neural mechanisms underlying learning deficits in EBC related to alcoholism and prenatal alcohol exposure has the potential to advance the diagnoses, treatment, and prevention of these and other pediatric and adult disorders.

Exercise and environment as an intervention for neonatal alcohol effects on hippocampal adult neurogenesis and learning

Neonatal alcohol exposure impairs cognition and learning in adulthood and permanently damages the hippocampus. Wheel running (WR) improves hippocampus-associated learning and memory and increases the genesis and survival of newly generated neurons in the hippocampal dentate gyrus. WR significantly increases proliferation of newly generated dentate granule cells in alcohol-exposed (AE) and control rats on Postnatal Day (PD) 42 but only control rats show an increased number of surviving cells thirty days after WR (Helfer et al., 2009b). The present studies examined whether proliferation-promoting WR followed by survival-enhancing environmental complexity (EC) during adolescence could increase survival of new neurons in AE rats. On PD 4-9, pups were intubated with alcohol in a binge-like manner (5.25g/kg/day, AE), were sham-intubated (SI), or were reared normally (suckle control, SC). On PD 30 animals were assigned to WR (PD 30-42) followed by EC (PD 42-72; WR/EC) or were socially housed (SH/SH) for the duration of the experiment. All animals were injected with 200mg/kg bromodeoxyuridine (BrdU) on PD 41. In Experiment 1, survival of newly generated cells was significantly enhanced in the AE-WR/EC group in comparison with AE-SH/SH group. Experiment 2A examined trace eyeblink conditioning. In the SH/SH condition, AE impaired trace eyeblink conditioning relative to SI and SC controls. In the WR/EC condition, AE rats performed as well as controls. In Experiment 2B, the same intervention was examined using the context preexposure facilitation effect (CPFE); a hippocampus-dependent variant of contextual fear conditioning. Again, the WR/EC intervention reversed the deficit in conditioned fear to the context that was evident in the SH/SH condition. Post-weaning environmental manipulations promote cell survival and reverse learning deficits in rats that were exposed to alcohol during development. These manipulations may provide a basis for developing interventions that ameliorate learning impairments associated with human fetal alcohol spectrum disorders.

Neonatal ethanol exposure results in dose-dependent impairments in the acquisition and timing of the conditioned eyeblink response and altered cerebellar interpositus nucleus and hippocampal CA1 unit activity in adult rats

Exposure to ethanol in neonatal rats results in reduced neuronal numbers in the cerebellar cortex and deep nuclei of juvenile and adult animals. This reduction in cell numbers is correlated with impaired delay eyeblink conditioning (EBC), a simple motor learning task in which a neutral conditioned stimulus (CS; tone) is repeatedly paired with a co-terminating unconditioned stimulus (US; periorbital shock). Across training, cell populations in the interpositus (IP) nucleus model the temporal form of the eyeblink-conditioned response (CR). The hippocampus, though not required for delay EBC, also shows learning-dependent increases in CA1 and CA3 unit activity. In the present study, rat pups were exposed to 0, 3, 4, or 5 mg/kg/day of ethanol during postnatal days (PD) 4-9. As adults, CR acquisition and timing were assessed during 6 training sessions of delay EBC with a short (280 ms) interstimulus interval (ISI; time from CS onset to US onset) followed by another 6 sessions with a long (880 ms) ISI. Neuronal activity was recorded in the IP and area CA1 during all 12 sessions. The high-dose rats learned the most slowly and, with the moderate-dose rats, produced the longest CR peak latencies over training to the short ISI. The low dose of alcohol impaired CR performance to the long ISI only. The 3E (3 mg/kg/day of ethanol) and 5E (5 mg/kg/day of ethanol) rats also showed slower-than-normal increases in learning-dependent excitatory unit activity in the IP and CA1. The 4E (4 mg/kg/day of ethanol) rats showed a higher rate of CR production to the long ISI and enhanced IP and CA1 activation when compared to the 3E and 5E rats. The results indicate that binge-like ethanol exposure in neonatal rats induces long-lasting, dose-dependent deficits in CR acquisition and timing and diminishes conditioning-related neuronal excitation in both the cerebellum and hippocampus.

Long-lasting distortion of GABA signaling in MS/DB neurons after binge-like ethanol exposure during initial synaptogenesis

Using a well-established model of binge-like ethanol treatment of rat pups on postnatal days (PD) 4-9, we found that maturation of GABAA receptor (GABAAR) miniature postsynaptic currents (mPSCs) was substantially blunted for medial septum/diagonal band (MS/DB) neurons in brain slices on PD 11-16. Ethanol reduced mPSC amplitude, frequency, and decay kinetics, while attenuating or exaggerating allosteric actions of zolpidem and allopregnanolone, respectively. The impact of ethanol in vivo was long lasting as most changes in MS/DB GABAAR mPSCs were still observed as late as PD 60-85. Maturing MS/DB neurons in naïve brain slices PD 4-16 showed increasing mPSC frequency, decay kinetics, and zolpidem sensitivity that were nearly identical to our earlier findings in cultured septal neurons (DuBois et al., 2004, 2006). These rapidly developing mPSC parameters continued to mature through the first month of life then stabilized throughout the remainder of the lifespan. Finally, equivalent ethanol-induced alterations in GABAAR mPSC signaling were present in MS/DB neurons from both male and female animals. Previously, we showed ethanol treatment of cultured embryonic day 20 septal neurons distorts the maturation of GABAAR mPSCs predicting that early stages of GABAergic transmission in MS/DB neurons are vulnerable to intoxication injury (DuBois et al., 2004, 2006). Since the overall character, timing, and magnitude of GABAergic mPSC developmental- and ethanol-induced changes in the in vivo model so closely mirror chronologically equivalent adaptations in cultured septal neurons, this suggests that such parallel models of ethanol impairment of GABAergic synaptic development in vivo and in vitro should be useful for translational studies exploring the efficacy and mechanism of action of potential therapeutic interventions from the cellular to whole animal level.

Rehabilitation training using complex motor learning rescues deficits in eyeblink classical conditioning in female rats induced by binge-like neonatal alcohol exposure

BACKGROUND

Effective treatments for the behavioral and cognitive deficits in children with fetal alcohol spectrum disorders (FASD) are lacking, and translational approaches using animal models can help develop rational interventions. One such model, binge-like alcohol exposure in neonatal rats during the period of brain development comparable with that of the human third trimester, causes structural and functional damage to the cerebellum and disrupts cerebellar-dependent eyeblink classical conditioning. The eyeblink conditioning deficits first demonstrated in this rat model predicted the similar deficits subsequently demonstrated in children with FASD.

METHODS

The current study extends this translational approach by testing the hypothesis that rehabilitation training involving 20 days of training on traversal of an obstacle course (complex motor learning) would ameliorate the deficits on classical conditioning of eyeblink responses produced by the neonatal alcohol exposure. We have previously shown that this training stimulates cerebellar synaptic plasticity and improves alcohol-induced deficits on motor coordination tasks.

RESULTS

The current studies found that rehabilitation training significantly attenuated alcohol-induced deficits in acquisition of eyeblink conditioning in females but not in males. These results are consistent with normalization of cerebellar-dependent learning, at least in alcohol-exposed females.

CONCLUSIONS

These findings extend previous studies in this model suggesting that rehabilitation of adolescents with FASD using training with complex motor learning tasks could be effective in ameliorating functional impairments associated with cerebellar damage. Eyeblink classical conditioning deficits are now well documented in children with FASD and could serve as an evaluation measure to continue to develop therapeutic interventions such as complex motor learning.

Ontogeny of trace eyeblink conditioning to shock-shock pairings in the rat pup

Rats are responsive to shock from an early age, but eyeblink conditioning to a tone-conditioned stimulus (conditional stimulus; CS) paired with a shock-unconditioned stimulus (US) does not emerge until postnatal Day 20 (P20). More generalized postural responses such as conditioned freezing can occur at P16. Using the same periorbital shock as both the CS and US in a US-US conditioning paradigm previously shown to be effective in adult animals, we found that shock-shock pairings with a 200-ms trace interval resulted in eyeblink conditioning in younger animals than previously thought. Some rat pups showed conditioned eyeblink responses as early as P12, and by P18, conditioned responses were fully developed in all animals. Unpaired control subjects confirmed that responding in paired subjects was associative. Although many stimuli can act as a CS in adults, the advantage of using US-US pairings is that responses to the first US ensure young rat pups are capable of detecting the stimulus-something that may not be true when auditory or visual stimuli are used early in the development of altricial animals. The US-US pairing paradigm could be used to study the ontogeny and neural substrates of learning and memory before other sensory systems mature, and evaluate learning and memory in animal models of early developmental disorders.

Hippocampal-dependent Pavlovian conditioning in adult rats exposed to binge-like doses of ethanol as neonates

Binge-like postnatal ethanol exposure produces significant damage throughout the brain in rats, including the cerebellum and hippocampus. In the current study, cue- and context-mediated Pavlovian conditioning were assessed in adult rats exposed to moderately low (3E; 3g/kg/day) or high (5E; 5g/kg/day) doses of ethanol across postnatal days 4-9. Ethanol-exposed and control groups were presented with 8 sessions of trace eyeblink conditioning followed by another 8 sessions of delay eyeblink conditioning, with an altered context presented over the last two sessions. Both forms of conditioning rely on the brainstem and cerebellum, while the more difficult trace conditioning also requires the hippocampus. The hippocampus is also needed to gate or modulate expression of the eyeblink conditioned response (CR) based on contextual cues. Results indicate that the ethanol-exposed rats were not significantly impaired in trace EBC relative to control subjects. In terms of CR topography, peak amplitude was significantly reduced by both doses of alcohol, whereas onset latency but not peak latency was significantly lengthened in the 5E rats across the latter half of delay EBC in the original training context. Neither dosage resulted in significant impairment in the contextual gating of the behavioral response, as revealed by similar decreases in CR production across all four treatment groups following introduction of the novel context. Results suggest ethanol-induced brainstem-cerebellar damage can account for the present results, independent of the putative disruption in hippocampal development and function proposed to occur following postnatal ethanol exposure.

Biobehavioral markers of adverse effect in fetal alcohol spectrum disorders

Identification of children with fetal alcohol spectrum disorders (FASD) is difficult because information regarding prenatal exposure is often lacking, a large proportion of affected children do not exhibit facial anomalies, and no distinctive behavioral phenotype has been identified. Castellanos and Tannock have advocated going beyond descriptive symptom-based approaches to diagnosis to identify biomarkers derived from cognitive neuroscience. Classical eyeblink conditioning and magnitude comparison are particularly promising biobehavioral markers of FASD-eyeblink conditioning because a deficit in this elemental form of learning characterizes a very large proportion of alcohol-exposed children; magnitude comparison because it is a domain of higher order cognitive function that is among the most sensitive to fetal alcohol exposure. Because the neural circuitry mediating both these biobehavioral markers is well understood, they have considerable potential for advancing understanding of the pathophysiology of FASD, which can contribute to development of treatments targeted to the specific deficits that characterize this disorder.

Choline supplementation mitigates trace, but not delay, eyeblink conditioning deficits in rats exposed to alcohol during development

Children exposed to alcohol prenatally suffer from a range of physical, neuropathological, and behavioral alterations, referred to as fetal alcohol spectrum disorders (FASD). Both the cerebellum and hippocampus are affected by alcohol exposure during development, which may contribute to behavioral and cognitive deficits observed in children with FASD. Despite the known neuropathology associated with prenatal alcohol exposure, many pregnant women continue to drink (heavy drinkers, in particular), creating a need to identify effective treatments for their children who are adversely affected by alcohol. We previously reported that choline supplementation can mitigate alcohol's effects on cognitive development, specifically on tasks which depend on the functional integrity of the hippocampus. The present study examined whether choline supplementation could differentially mitigate alcohol's effects on trace eyeblink classical conditioning (ECC, a hippocampal-dependent task) and delay ECC (a cerebellar-dependent task). Long-Evans rats were exposed to 5.25 g/kg/day alcohol via gastric intubation from postnatal days (PD) 4-9, a period of brain development equivalent to late gestation in humans. A sham-intubated control group was included. From PD 10-30, subjects received subcutaneous injections of 100 mg/kg choline chloride or vehicle. Beginning on PD 32-34, subjects were trained on either delay or trace eyeblink conditioning. Performance of subjects exposed to alcohol was significantly impaired on both tasks, as indicated by significant reductions in percentage and amplitude of conditioned eyeblink responses, an effect that was attenuated by choline supplementation on the trace, but not delay conditioning task. Indeed, alcohol-exposed subjects treated with choline performed at control levels on the trace eyeblink conditioning task. There were no significant main or interactive effects of sex. These data indicate that choline supplementation can significantly reduce the severity of trace eyeblink conditioning deficits associated with early alcohol exposure, even when administered after the alcohol insult is complete. These findings have important implications for the treatment of fetal alcohol spectrum disorders.

Neonatal corticosterone administration impairs adult eyeblink conditioning and decreases glucocorticoid receptor expression in the cerebellar interpositus nucleus

Neonatal maternal separation alters adult learning and memory. Previously, we showed that neonatal separation impaired eyeblink conditioning in adult rats and increased glucocorticoid receptor (GR) expression in the cerebellar interpositus nucleus, a critical site of learning-related plasticity. Daily neonatal separation (1 h/day on postnatal days 2-14) increases neonatal plasma corticosterone levels. Therefore, effects of separation on GR expression in the interpositus and consequently adult eyeblink conditioning may be mediated by neonatal increases in corticosterone. As a first step in exploring a potential role for corticosterone in the neonatal separation effects we observed, we assessed whether systemic daily (postnatal days 2-14) corticosterone injections mimic neonatal separation effects on adult eyeblink conditioning and GR expression in the interpositus. Control uninjected animals were compared to animals receiving either daily corticosterone injections or daily injections of an equal volume of vehicle. Plasma corticosterone values were measured in a separate group of control, neonatally separated, vehicle injected, or corticosterone injected pups. In adulthood, rats underwent surgery for implantation of recording and stimulating electrodes. After recovery from surgery, rats underwent 10 daily sessions of eyeblink conditioning. Then, brains were processed for GR immunohistochemistry and GR expression in the interpositus nucleus was assessed. Vehicle and corticosterone injections both produced much larger increases in neonatal plasma corticosterone than did daily maternal separation, with the largest increases occurring in the corticosterone-injected group. Neonatal corticosterone injections impaired adult eyeblink conditioning and decreased GR expression in the interpositus nucleus, while the effects of vehicle injections were intermediate. Thus, while neonatal injections and maternal separation both produce adult impairments in learning and memory, these manipulations produce opposite changes in GR expression. This suggests an inverted U-shaped relationship may exist between both neonatal corticosterone levels and adult GR expression in the interpositus nucleus, and adult GR expression in the interpositus and eyeblink conditioning.

Impaired delay and trace eyeblink conditioning in school-age children with fetal alcohol syndrome

BACKGROUND

Classical eyeblink conditioning (EBC) involves contingent temporal pairing of a conditioned stimulus (e.g., tone) with an unconditioned stimulus (e.g., air puff). Impairment of EBC has been demonstrated in studies of alcohol-exposed animals and in children exposed prenatally at heavy levels.

METHODS

Fetal alcohol syndrome (FAS) was diagnosed by expert dysmorphologists in a large sample of Cape Coloured, South African children. Delay EBC was examined in a new sample of 63 children at 11.3 years, and trace conditioning in 32 of the same children at 12.8 years. At each age, 2 sessions of 50 trials each were administered on the same day; 2 more sessions the next day, for children not meeting criterion for conditioning.

RESULTS

Six of 34 (17.6%) children born to heavy drinkers were diagnosed with FAS, 28 were heavily exposed nonsyndromal (HE), and 29 were nonexposed controls. Only 33.3% with FAS and 42.9% of HE met criterion for delay conditioning, compared with 79.3% of controls. The more difficult trace conditioning task was also highly sensitive to fetal alcohol exposure. Only 16.7% of the FAS and 21.4% of HE met criterion for trace conditioning, compared with 66.7% of controls. The magnitude of the effect of diagnostic group on trace conditioning was not greater than the effect on short delay conditioning, findings consistent with recent rat studies. Longer latency to onset and peak eyeblink CR in exposed children indicated poor timing and failure to blink in anticipation of the puff. Extended training resulted in some but not all of the children reaching criterion.

CONCLUSIONS

These data showing alcohol-related delay and trace conditioning deficits extend our earlier findings of impaired EBC in 5-year-olds to school-age. Alcohol-related impairment in the cerebellar circuitry required for both forms of conditioning may be sufficient to account for the deficit in both tasks. Extended training was beneficial for some exposed children. EBC provides a well-characterized model system for assessment of degree of cerebellar-related learning and memory dysfunction in fetal alcohol exposed children.

Glucocorticoid receptor blockade in the posterior interpositus nucleus reverses maternal separation-induced deficits in adult eyeblink conditioning

Previously, we showed that neonatal maternal separation impaired eyeblink conditioning in adult rats. This impairment is correlated with increased glucocorticoid receptor (GR) expression in the cerebellar posterior interpositus nucleus, a critical site of learning-related plasticity. To assess whether increased GR expression is responsible for the separation-induced learning impairment, we infused a GR antagonist (mifepristone) or vehicle into the posterior interpositus during eyeblink conditioning in adult male Long-Evans rats that had undergone control rearing or neonatal maternal separation (1h/day, postnatal days 2-14). Rats received standard rearing (control) or neonatal maternal separation (separated; 1h/day on postnatal days 2-14). In adulthood, rats underwent surgery for implantation of recording electrodes in the orbicularis oculi of the left eyelid, a bipolar stimulating electrode dorsocaudal to the left eye, and an infusion guide cannula positioned over the posterior interpositus. Then, rats underwent 10 daily sessions of eyeblink conditioning. Rats in each group received either 0.2microl of mifepristone (2ng in 2% EtOH) or vehicle infusion prior to each eyeblink conditioning session. Mifepristone infusions improved conditioning in separated rats, but impaired control rats' performance. Thus, separation-induced increases in GRs may mediate the learning deficit seen in adult neonatally separated rats.

Associative plasticity in the medial auditory thalamus and cerebellar interpositus nucleus during eyeblink conditioning

Eyeblink conditioning, a type of associative motor learning, requires the cerebellum. The medial auditory thalamus is a necessary source of stimulus input to the cerebellum during auditory eyeblink conditioning. Nothing is currently known about interactions between the thalamus and cerebellum during associative learning. In the current study, neuronal activity was recorded in the cerebellar interpositus nucleus and medial auditory thalamus simultaneously from multiple tetrodes during auditory eyeblink conditioning to examine the relative timing of learning-related plasticity within these interconnected areas. Learning-related changes in neuronal activity correlated with the eyeblink conditioned response were evident in the cerebellum before the medial auditory thalamus over the course of training and within conditioning trials, suggesting that thalamic plasticity may be driven by cerebellar feedback. Short-latency plasticity developed in the thalamus during the first conditioning session and may reflect attention to the conditioned stimulus. Extinction training resulted in a decrease in learning-related activity in both structures and an increase in inhibition within the cerebellum. A feedback projection from the cerebellar nuclei to the medial auditory thalamus was identified, which may play a role in learning by facilitating stimulus input to the cerebellum via the thalamo-pontine projection.

MK-801 administration during neonatal ethanol withdrawal attenuates interpositus cell loss and juvenile eyeblink conditioning deficits

Binge-level doses of ethanol have been demonstrated to severely disrupt the cerebellum and cerebellum-dependent tasks when administered to rodent subjects during the early postnatal period. N-methyl-d-aspartic acid (NMDA) receptor-mediated excitotoxicity associated with ethanol withdrawal has been implicated as a significant component contributing to neurotoxic effects resulting from early ethanol exposure, and studies using MK-801 (dizocilpine) have reported protection from ethanol-induced damage. The present study examined whether the administration of MK-801 during ethanol withdrawal would ameliorate ethanol-associated cell death in the interpositus nucleus of the cerebellum and behavioral deficits in a cerebellar dependent task. Long Evans rat pups were treated with ethanol (5.25 g/kg) in a binge-like manner on postnatal day 6 using intragastric intubation. Subjects then received an injection of MK-801 (0.5mg/kg) or vehicle during withdrawal, 30h after ethanol exposure. Rats were then trained on an eyeblink classical conditioning task as juveniles (40 days of age), and cerebellar interpositus nucleus numbers were assessed after conditioning. Ethanol-exposed subjects exhibited reductions in neuronal populations and behavioral deficits during eyeblink conditioning. However, MK-801 administration significantly attenuated observed deficiencies, suggesting a protective effect resulting from MK-801 treatment during ethanol withdrawal. These results support the role of NMDA receptor-mediated excitotoxicity as a component mechanism by which ethanol produces teratogenicity. Additionally, our findings support previous reports that have shown correlations between dependent measures of eyeblink classical-conditioning behavior and unbiased cell counts in the interpositus nucleus.

Neonatal binge alcohol exposure produces dose dependent deficits in interstimulus interval discrimination eyeblink conditioning in juvenile rats

Alcohol consumption in neonatal rats produces cerebellar damage and is widely used to model 3rd-trimester human fetal alcohol exposure. Neonatal "binge-like" exposure to high doses of alcohol (5 g/kg/day or more) impairs acquisition of eyeblink classical conditioning (EBC), a cerebellar-dependent Pavlovian motor learning task. We have recently found impairments in interstimulus interval (ISI) discrimination--a complex task variant of EBC--in adult rats following postnatal day (PD) 4-9 alcohol exposure at doses of 3, 4, and 5 g/kg/day. Because robust developmental differences in conditioned response (CR) generation and CR latency measures are present between untreated juveniles and adults in this task, we sought to extend alcohol findings to juvenile rats (PD30). Five neonatal treatment groups were used: (1) undisturbed controls, (2) sham intubation controls, (3) 3 g/kg/day of alcohol (blood alcohol concentration {BAC}=139.9 mg/dl), (4) 4 g/kg/day of alcohol (BAC=237.3 mg/dl), or (5) 5 g/kg/day of alcohol (BAC=301.8 mg/dl). Intubations occurred over PD4-9. ISI discrimination training in juveniles (PD30-33) revealed dose-dependent CR deficits in all three alcohol-exposed groups relative to controls. Contrary to expected outcomes, CR latency measures were not significantly affected as a function of neonatal treatment. Comparison of these findings with our recent study in adults suggests that alcohol-induced impairments in ISI discrimination EBC may be greater in adults relative to juveniles. The present findings provide further evidence that ISI discrimination may provide greater sensitivity to functional deficits resulting from moderate levels of neonatal alcohol exposure relative to single-cue EBC paradigms.

Associative and non-associative blinking in classically conditioned adult rats

Over the last several years, a growing number of investigators have begun using the rat in classical eyeblink conditioning experiments, yet relatively few parametric studies have been done to examine the nature of conditioning in this species. We report here a parametric analysis of classical eyeblink conditioning in the adult rat using two conditioned stimulus (CS) modalities (light or tone) and three interstimulus intervals (ISI; 280, 580, or 880 ms). Rats trained at the shortest ISI generated the highest percentage of conditioned eyeblink responses (CRs) by the end of training. At the two longer ISIs, rats trained with the tone CS produced unusually high CR percentages over the first few acquisition sessions, relative to rats trained with the light CS. Experiment 2 assessed non-associative blink rates in response to presentations of the light or tone, in the absence of the US, at the same ISI durations used in paired conditioning. Significantly more blinks occurred with longer than shorter duration lights or tones. A higher blink rate was also recorded at all three durations during the early tone-alone sessions. The results suggest that early in classical eyeblink conditioning, rats trained with a tone CS may emit a high number of non-associative blinks, thereby inflating the CR frequency reported at this stage of training.

Neonatal alcohol-induced region-dependent changes in rat brain neurochemistry measured by high-resolution magnetic resonance spectroscopy

BACKGROUND

Maternal drinking during pregnancy can lead to a range of deleterious outcomes in the developing offspring that have been collectively termed fetal alcohol spectrum disorders (FASDs). There is interest and recognized value in using non-invasive neuroimaging techniques such as magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) to characterize, respectively, structural and biochemical alterations in individuals with FASDs. To date, however, results with MRS have been inconsistent regarding the degree and/or nature of abnormalities.

METHODS

High-resolution magic angle spinning (HR-MAS) proton ((1)H) MRS is an ex vivo neuroimaging technique that can acquire spectra in small punches of intact tissue, providing clinically relevant neurochemical information about discrete brain regions. In this study, HR-MAS (1)H MRS was used to examine regional neurochemistry in frontal cortex, striatum, hippocampus, and cerebellum of young rats previously exposed to ethanol as neonates. Key neurochemicals of interest included N-acetyl-aspartate (NAA), glutamate, GABA, glutamine, creatine, choline and myo-inositol.

RESULTS

Daily neonatal alcohol exposure from postnatal day 4 (PN4) through PN9 significantly reduced levels of NAA and taurine in the cerebellum and striatum, and induced sex-dependent reductions in cerebellar glutamate when measured on PN16. In addition, myo-inositol was significantly increased in cerebellum. The frontal cortex and hippocampus were virtually unaffected by this neonatal alcohol exposure.

CONCLUSION

Results of this research may have implications for understanding the underlying neurobiology associated with FASDs and aid in testing treatments in the future. Ongoing studies are assessing the developmental persistence of and/or maturational recovery from these changes.

Eyeblink classical conditioning in the preweanling lamb

Classical conditioning of eyeblink responses has been one of the most important models for studying the neurobiology of learning, with many comparative, ontogenetic, and clinical applications. The current study reports the development of procedures to conduct eyeblink conditioning in preweanling lambs and demonstrates successful conditioning using these procedures. These methods will permit application of eyeblink conditioning procedures in the analysis of functional correlates of cerebellar damage in a sheep model of fetal alcohol spectrum disorders, which has significant advantages over more common laboratory rodent models. Because sheep have been widely used for studies of pathogenesis and mechanisms of injury with many different prenatal or perinatal physiological insults, eyeblink conditioning can provide a well-studied method to assess postnatal behavioral outcomes, which heretofore have not typically been pursued with ovine models of developmental insults.

Impaired eyeblink conditioning in children with fetal alcohol syndrome

BACKGROUND

Eyeblink conditioning (EBC) is a Pavlovian paradigm that involves contingent temporal pairing of a conditioned stimulus (e.g., tone) with an unconditioned stimulus (e.g., air puff). Animal studies have shown that binge consumption of alcohol during pregnancy impairs EBC and that this impairment is likely mediated by a loss of neurons in the inferior olive and the cerebellar cortex and deep nuclei, as well as by a reduction in neural plasticity in the cerebellar deep nuclei.

METHODS

Short delay EBC was examined in 98 5-year-old children born to women from the Coloured (mixed ancestry) community in Cape Town, South Africa, who were recruited prenatally and are participating in the first prospective longitudinal study of children with fetal alcohol syndrome (FAS). FAS status was assessed at 5 years by expert dysmorphologists. Two sessions of 50 trials each were administered to the children; a third session was administered the following day to those children who did not meet criterion of 40% conditioned responses in session 2.

RESULTS

Not a single child with FAS met criterion for conditioning as contrasted with 75.0% of the controls. Whereas 86.7% of the controls who were conditioned met criterion by the end of Session 2, a large proportion of the relatively few alcohol-exposed nonsyndromal children who conditioned did not do so until Session 3. These alcohol effects on EBC persisted after controlling for IQ. Three of 4 microcephalic children who were not exposed to alcohol were successfully conditioned.

CONCLUSIONS

This is the first prospective study to demonstrate impaired EBC in children diagnosed with FAS. Successful EBC in a microcephalic group supports the inference that the EBC deficit is specific to prenatal alcohol exposure and a potential biomarker for diagnosis of exposed children lacking the distinctive FAS dysmorphology. Delay EBC has a high sensitivity for identifying individuals with a diagnosis of probable FAS.

Dose-dependent deficits in dual interstimulus interval classical eyeblink conditioning tasks following neonatal binge alcohol exposure in rats

BACKGROUND

Neonatal alcohol consumption in rats is widely used to model cerebellar injury arising from 3rd-trimester human fetal alcohol exposure. Binge alcohol exposure of 5 g/kg/day or more over postnatal days (PD) 4 to 9 in rats damages the cerebellum and consequently impairs classical eyeblink conditioning (EBC). The present study sought to identify deficits in EBC using doses lower than those that have been reported previously following alcohol exposure limited to PD4-9. Complex conditioned response (CR) timing tasks utilizing 2 interstimulus intervals (ISIs) were used to test the hypothesis that 3 g/kg/day of alcohol would produce early onset and early peaked CRs, whereas 4 and 5 g/kg/day would impair CR acquisition.

METHODS

Five neonatal treatment groups were used: (1) undisturbed controls, (2) sham intubation controls, (3) 3 g/kg/day of alcohol, (4) 4 g/kg/day of alcohol, or (5) 5 g/kg/day of alcohol. Intubations occurred over PD4-9. In adulthood, rats were trained using ISI discrimination (Experiment 1) or temporal uncertainty (Experiment 2) EBC tasks. In ISI discrimination, 2 distinct conditioned stimuli (CSs; tone and light) are reinforced with a periocular shock unconditioned stimulus (US) at 2 different CS-US intervals. Temporal uncertainty is identical in design with the exception that the same CS is presented at both CS-US intervals.

RESULTS

Alcohol-exposed subjects were impaired in CR acquisition in a task- and dose-dependent fashion. CR deficits were most salient in the peak amplitude measure and occurred in both tasks following alcohol exposure at 4 and 5 g/kg/day. Alcohol at a dosage of 3 g/kg/day impaired CR acquisition only in ISI discrimination. All alcohol doses failed to produce short latency CRs in either task. Alcohol-exposed subjects displayed later-onset and later-peaked CRs to the long-ISI CS in ISI discrimination relative to controls.

CONCLUSIONS

ISI discrimination training may be ideal to identify CR deficits resulting from neonatal exposure to moderate alcohol doses. Applications of this EBC task to humans may enable reliable early identification and diagnosis of individuals with fetal alcohol spectrum disorders.

Binge-like ethanol exposure during the early postnatal period impairs eyeblink conditioning at short and long CS-US intervals in rats

Binge-like ethanol exposure on postnatal days (PD) 4-9 in rodents causes cerebellar cell loss and impaired acquisition of conditioned responses (CRs) during "short-delay" eyeblink classical conditioning (ECC), using optimal (280-350 ms) interstimulus intervals (ISIs). We extended those earlier findings by comparing acquisition of delay ECC under two different ISIs. From PD 4 to 9, rats were intubated with either 5.25 g/kg of ethanol (2/day), sham intubated, or were not intubated. They were then trained either as periadolescents (about PD 35) or as adults (>PD 90) with either the optimal short-delay (280-ms) ISI, a long-delay (880-ms) ISI, or explicitly unpaired CS and US presentations. Neonatal binge ethanol treatment significantly impaired acquisition of conditioning at both ages regardless of ISI, and deficits in the acquisition and expression of CRs were comparable across ISIs. These deficits are consistent with the previously documented ethanol-induced damage to the cerebellar-brainstem circuit essential for Pavlovian ECC.

Neonatal alcohol exposure impairs acquisition of eyeblink conditioned responses during discrimination learning and reversal in weanling rats

Discrimination and reversal of the classically conditioned eyeblink response depends on cerebellar-brainstem interactions with the hippocampus. Neonatal "binge" exposure to alcohol at doses of 5 g/kg/day or more has been shown to impair single-cue eyeblink conditioning in both weanling and adult rats. The present study exposed neonatal rats to acute alcohol intubations across different developmental periods (postnatal day [PND] 4-9 or PND7-9) and tested them from PND26-31 on discriminative classical eyeblink conditioning and reversal. A high dose of alcohol (5 g/kg/day) dramatically impaired conditioning relative to controls when exposure occurred over PND4-9, but produced mild or no impairments when delivered over PND7-9. These findings support previous claims that developmental exposure period plays a critical role in determining the deleterious effects of alcohol on the developing brain. A lower dose of alcohol (4 g/kg/day) delivered from PND4-9--lower than has previously been shown to affect single-cue eyeblink conditioning--also produced deficits on the discrimination task, suggesting that discrimination learning and acquisition of responding to CS+ during reversal may be especially sensitive behavioral indicators of alcohol-induced brain damage in this rat model.

Ethanol-exposed neonatal rats are impaired as adults in classical eyeblink conditioning at multiple unconditioned stimulus intensities

Binge-like exposure to ethanol early in development results in neurotoxic impairments throughout the brain, including the cerebellum and brainstem. Rats exposed to ethanol, during a period of time commensurate with the human third trimester, also show deficits in classical eyeblink conditioning (EBC), a cerebellar-dependent associative learning procedure. The relationship between ethanol-mediated EBC deficits and the intensity of the unconditioned stimulus (US) was explored in the current study. Neonatal rats were intubated and infused with ethanol (EtOH rats), sham-intubated and given no ethanol (SI rats), or reared as unhandled controls (UC rats). As adults, all rats underwent 10 days of 350 ms delay eyeblink conditioning with a tone conditioned stimulus (CS) and one of three co-terminating periorbital shock US. The frequency and topography of the conditioned eyeblink response (CR) were impaired in EtOH rats relative to UC rats. EtOH rats produced fewer CRs, with longer onset latencies, at all US intensities. In contrast, CR amplitude was impaired in EtOH rats at the highest US intensity only. Following conditioning, the unconditioned eyeblink response (UR) was analyzed in subsets of rats from each treatment group at five US intensities. Early ethanol exposure did not impair UR peak amplitude. The deficits in CR production are proposed to result from ethanol-mediated damage within specific regions of the EBC neural circuit.

Neonatal maternal separation alters adult eyeblink conditioning and glucocorticoid receptor expression in the interpositus nucleus of the cerebellum

Neonatal maternal separation alters learning and memory. Glucocorticoids also modulate adult learning and memory, and neonatal maternal separation alters forebrain glucocorticoid receptor (GR) concentrations. We used eyeblink classical conditioning to assess the effect of neonatal maternal separation on associative learning. We assessed delay eyeblink conditioning, GR expression, and total neuron number in the interpositus nucleus, a critical site of plasticity in eyeblink conditioning, in adult rats that had undergone either standard animal facilities rearing, handling for 15 min, or maternal separation for either 15 or 60 min per day on postnatal days 2-14. At 2-3 months of age, delay eyeblink classical conditioning was assessed. Brains were processed for GR immunohistochemistry, and GR expression in the interpositus nucleus was assessed using a computer-based densitometry system. Neuron counts and nuclear volumes were obtained from an alternate series of thionin-stained sections. Maternal separation significantly impaired eyeblink conditioning in male but not female rats. Handling and maternal separation did not significantly affect interpositus neuron number and volume. However, prolonged maternal separation significantly increased GR expression in the posterior interpositus in males, and increases were correlated with eyeblink conditioning. In female rats, maternal separation and handling did not significantly alter interpositus neuron number, volume, or GR protein expression, and GR expression did not correlate with eyeblink conditioning. Thus, neonatal maternal separation produces adult deficits in eyeblink conditioning and alterations in GR expression in its neural substrate in a sex-dependent manner.

Hippocampal and cerebellar single-unit activity during delay and trace eyeblink conditioning in the rat

In delay eyeblink conditioning, the CS overlaps with the US and only a brainstem-cerebellar circuit is necessary for learning. In trace eyeblink conditioning, the CS ends before the US is delivered and several forebrain structures, including the hippocampus, are required for learning, in addition to a brainstem-cerebellar circuit. The interstimulus interval (ISI) between CS onset and US onset is perhaps the most important factor in classical conditioning, but studies comparing delay and trace conditioning have typically not matched these procedures in this crucial factor, so it is often difficult to determine whether results are due to differences between delay and trace or to differences in ISI. In the current study, we employed a 580-ms CS-US interval for both delay and trace conditioning and compared hippocampal CA1 activity and cerebellar interpositus nucleus activity in order to determine whether a unique signature of trace conditioning exists in patterns of single-unit activity in either structure. Long-Evans rats were chronically implanted in either CA1 or interpositus with microwire electrodes and underwent either delay eyeblink conditioning, or trace eyeblink conditioning with a 300-ms trace period between CS offset and US onset. On trials with a CR in delay conditioning, CA1 pyramidal cells showed increases in activation (relative to a pre-CS baseline) during the CS-US period in sessions 1-4 that was attenuated by sessions 5-6. In contrast, on trials with a CR in trace conditioning, CA1 pyramidal cells did not show increases in activation during the CS-US period until sessions 5-6. In sessions 5-6, increases in activation were present only to the CS and not during the trace period. For rats with interpositus electrodes, activation of interpositus neurons on CR trials was present in all sessions in both delay and trace conditioning. However, activation was greater in trace compared to delay conditioning in the first half of the CS-US interval (during the trace CS) during early sessions of conditioning and, in later sessions of conditioning, activation was greater in the second half of the CS-US interval (during the trace interval). These results suggest that the pattern of hippocampal activation that differentiates trace from delay eyeblink conditioning is a slow buildup of activation to the CS, possibly representing encoding of CS duration or discrimination of the CS from the background context. Interpositus nucleus neurons show strong modeling of the eyeblink CR regardless of paradigm but show a changing pattern across conditioning that may be due to the necessary contributions of forebrain processing to trace conditioning.

The effects of moderate neonatal ethanol exposure on eyeblink conditioning and deep cerebellar nuclei neuron numbers in the rat

Heavy, bingelike patterns of exposure to ethanol during a portion of the early postnatal period in the rat, a time of rodent brain development corresponding to the human third trimester, has been shown to deplete cerebellar neurons and to produce deficits in cerebellar-dependent tasks. In the current study, we examined the impact of more moderate ethanol exposure, during an extended portion of the rat third trimester equivalent, on cerebellar-dependent learning (eyeblink conditioning) and deep cerebellar nuclei neuron numbers. Neonatal rats received 0, 1, 2, or 3g/kg/day of ethanol in milk formula via a single intragastric intubation each day across postnatal days 2-11, or were left untreated. Peak BACs for ethanol-exposed rats were 50, 150, and 225 mg/dl, respectively. Rats underwent eyeblink conditioning as young adults (70 days of age) and deep cerebellar nuclei neuron numbers were assessed at 100 days of age. In Experiment 1, all rats showed normal responsiveness to periorbital stimulation prior to conditioning. The 3-g/kg/day group was impaired in eyeblink conditioning and possessed fewer deep cerebellar nuclei neurons. A trend toward impairment was observed in the 2-g/kg/day group. However, the 0-g/kg/day group was also impaired in eyeblink conditioning. In Experiment 2, the unconditioned stimulus pretest phase was eliminated, the 0-g/kg/day group learned normally, and both the 2- and 3-g/kg/day groups were again impaired. These results suggest that more moderate doses of ethanol during the rat third-trimester equivalent can produce long-term effects on the cerebellum.

Eyeblink conditioning in rats using pontine stimulation as a conditioned stimulus

Previous studies using rabbits and ferrets found that electrical stimulation of the pontine nuclei or middle cerebellar peduncle could serve as a conditioned stimulus (CS) in eyeblink conditioning (Bao, Chen, & Thompson, 2000; Hesslow, Svensson, & Ivarsson, 1999; Steinmetz, 1990; Steinmetz, Lavond, & Thompson, 1985; 1989; Steinmetz et al., 1986; Tracy, Thompson, Krupa, & Thompson, 1998). The current study used electrical stimulation of the pontine nuclei as a CS to establish eyeblink conditioning in rats. The goals of this study were to develop a method for directly activating the CS pathway in rodents and to compare the neural circuitry underlying eyeblink conditioning in different mammalian species. Rats were given electrical stimulation through a bipolar electrode implanted in the pontine nuclei paired with a periorbital shock unconditioned stimulus (US). Paired training was followed by extinction training. A subset of rats was given a test session of paired training after receiving an infusion of muscimol into the anterior interpositus nucleus. Rats given paired presentations of the stimulation CS and US developed CRs rapidly and showed extinction. Muscimol infusion prior to the test session resulted in a reversible loss of the eyeblink CR. The results demonstrate that electrical stimulation of the pontine nuclei can be used as a CS in rodents and that the CS pathway is similar in rats, rabbits, and ferrets. In addition, the loss of CRs following muscimol inactivation shows that the conditioning produced with pontine stimulation depends on cerebellar mechanisms.

Trace eyeblink conditioning in abstinent alcoholic individuals: effects of complex task demands and prior conditioning

Chronic misuse of alcohol affects an integrated neural circuit supporting the formation of associative memories acquired during eyeblink classical conditioning (R. McGlinchey-Berroth et al., 1995). The authors of this study investigated single-cue trace conditioning in amnesic and nonamnesic abstinent alcoholic individuals who either were or were not trained in a single-cue delay conditioning task. Overall, untrained alcoholic participants were severely impaired in acquisition, and alcoholic participants previously trained in single-cue delay conditioning performed similarly to untrained control participants. Individual performance in acquisition varied significantly within task but was relatively stable between the trace and delay tasks; there were nonamnesic and amnesic alcoholic participants who acquired responses at a normal rate in both delay and trace conditioning. The similarity of performances in delay and trace conditioning suggests a common source of impairment across both tasks.

Vitamin E does not protect against neonatal ethanol-induced cerebellar damage or deficits in eyeblink classical conditioning in rats

BACKGROUND

Rodent studies have shown that heavy binge-like ethanol (EtOH) exposure during the brain growth spurt [postnatal days (PD) 4-9] causes cerebellar neuronal loss and deficits in cerebellar-mediated eyeblink classical conditioning (ECC). Oxidative stress has been implicated in EtOH-mediated brain damage, and studies using vitamin E have reported amelioration of EtOH-induced tissue damage, including protection in rats against EtOH-induced cerebellar Purkinje cell (PC) loss on PD 4 to 5. The purpose of this study was to determine whether dietary supplementation with vitamin E concurrent with binge EtOH exposure on PD 4 to 9 in rats would attenuate the cerebellar cell death and ECC deficits.

METHODS

Rat pups were given one of five different neonatal treatments: (1) intubation with EtOH in milk formula (twice daily, total dose 5.25 g/kg/day), (2) intubation with EtOH in milk formula supplemented with vitamin E (12.26 mg/kg/feeding), (3) intubation with milk formula that contained vitamin E only, (4) sham intubations, or (5) normally reared unintubated controls. Between PD 26 and 33, subjects received short-delay ECC for 3 consecutive days. Unbiased stereological cell counts were performed on cerebellar PCs of left cerebellar lobules I to VI and neurons of the interpositus nucleus. In a separate study with PD 4 pups, the effects of vitamin E on EtOH-induced expression of caspase-3 active subunits were assessed using Western blot analysis.

RESULTS

EtOH-treated groups showed significant deficits in acquisition of conditioned eyeblink responses and reductions in cerebellar PCs and interpositus nucleus neurons compared with controls. Vitamin E supplementation failed to protect against these deficits. Vitamin E also failed to protect against increases in caspase-3 active subunit expression induced by acute binge EtOH exposure on PD 4.

CONCLUSIONS

In contrast to the previously reported neuroprotective potential of antioxidants on EtOH-mediated cerebellar damage, vitamin E supplementation did not diminish EtOH-induced structural and functional damage to the cerebellum in this model of binge EtOH exposure during the brain growth spurt in rats.

The effects of ethanol on the developing cerebellum and eyeblink classical conditioning

In rats, developmental ethanol exposure has been used to model the central nervous system deficits associated with human fetal alcohol syndrome. Binge-like ethanol exposure of neonatal rats depletes cells in the cerebellum, including Purkinje cells, granule cells, and deep nuclear cells, and produces deficits in simple tests of motor coordination. However, the extent to which anatomical damage is related to behavioral deficits has been difficult to estimate. Eyeblink classical conditioning is known to engage a discrete brain stem-cerebellar circuit, making it an ideal test of cerebellar functional integrity after developmental ethanol exposure. Eyeblink conditioning is a simple form of motor learning in which a neutral stimulus (such as a tone) comes to elicit an eyeblink when repeatedly paired with a stimulus that evokes an eyeblink prior to training (such as mild periorbital stimulation). In eyeblink conditioning, one of the deep cerebellar nuclei, the interpositus nucleus, as well as specific Purkinje cell populations, are sites of convergence for tone conditioned stimulus and somatosensory unconditioned stimulus information, and, together with brain stem nuclei, provide the necessary and sufficient substrate for the learned response. A series of studies have shown that eyeblink conditioning is impaired in both weanling and adult rats given binge-like exposure to ethanol as neonates. In addition, interpositus nucleus neurons from ethanol-exposed rats showed impaired activation during eyeblink conditioning. These deficits are accompanied by a permanent reduction In the deep cerebellar nuclear cell population. Because particular cerebellar cell populations are utilized in well-defined ways during eyeblink conditioning, conclusions regarding the underlying neural substrates of behavioral change after developmental ethanol exposure are greatly strengthened.

A Mouse Model of Prenatal Ethanol Exposure Using a Voluntary Drinking Paradigm

BACKGROUND

The incidence of fetal alcohol spectrum disorders is estimated to be as high as 1 in 100 births. Efforts to better understand the basis of prenatal ethanol-induced impairments in brain functioning, and the mechanisms by which ethanol produces these defects, will rely on the use of animal models of fetal alcohol exposure (FAE).

METHODS

Using a saccharin-sweetened alcohol solution, we developed a free-choice, moderate alcohol access model of prenatal alcohol exposure. Stable drinking of a saccharin solution (0.066%) was established in female mice. Ethanol then was added to the saccharin in increasing concentrations (2%, 5%, 10% w/v) every 2 days. Water was always available, and mice consumed standard pellet chow. Control mice drank saccharin solution without ethanol. After a stable baseline of ethanol consumption (14 g/kg/day) was obtained, females were impregnated. Ethanol consumption continued throughout pregnancy and then was decreased to 0% in a step-wise fashion over a period of 6 days after pups were delivered. Characterization of the model included measurements of maternal drinking patterns, blood alcohol levels, food consumption, litter size, pup weight, pup retrieval times for the dams, and effects of FAE on performance in fear-conditioned learning and novelty exploration.

RESULTS

Maternal food consumption, maternal care, and litter size and number were all found to be similar for the alcohol-exposed and saccharin control animals. FAE did not alter locomotor activity in an open field but did increase the time spent inspecting a novel object introduced into the open field. FAE mice displayed reduced contextual fear when trained using a delay fear conditioning procedure.

CONCLUSIONS

The mouse model should be a useful tool in testing hypotheses about the neural mechanisms underlying the learning deficits present in fetal alcohol spectrum disorders. Moreover, a mouse prenatal ethanol model should increase the opportunity to use the power of genetically defined and genetically altered mouse populations.

Using eyeblink classical conditioning as a test of the functional consequences of exposure of the developing cerebellum to alcohol

Exposure of the developing brain to alcohol produces profound Purkinje cell loss in the cerebellum, and deficits in tests of motor coordination. However, the precise relationship between these two sets of findings has been difficult to determine. Eyeblink classical conditioning is known to engage a discrete brainstem-cerebellar circuit, making it an ideal test of cerebellar functional integrity after developmental alcohol exposure. In eyeblink conditioning, one of the deep cerebellar nuclei, the interpositus nucleus, as well as specific Purkinje cell populations, are sites of convergence for CS and US information. A series of studies have shown that eyeblink conditioning is impaired in both weanling and adult rats given binge-like exposure to alcohol as neonates, and that these deficits can be traced, at least in part, to impaired activation of cerebellar interpositus nucleus neurons and to an overall reduction in the deep cerebellar nuclear cell population. Because particular cerebellar cell populations are utilized in well-defined ways during eyeblink conditioning, conclusions regarding specific changes in the mediation of behavior by these cell populations are greatly strengthened. Further studies will be directed towards the impact of early exposure to alcohol on the functionality of specific Purkinje cell populations, as well as towards brainstem areas that process the tone CS and the somatosensory US.

Neonatal ethanol produces cerebellar deep nuclear cell loss and correlated disruption of eyeblink conditioning in adult rats

Binge-like neonatal exposure to ethanol (EtOH) in rats, during the period of brain development comparable to that of the human third trimester, produces significant, dose-dependent Purkinje cell loss in the cerebellum and deficits in eyeblink classical conditioning. There are currently no published reports of whether neuronal loss in the cerebellar deep nuclei also results from binge-like neonatal exposure to EtOH and what the functional consequences of any cell loss might be. Since eyeblink conditioning requires cerebellar deep nuclear cells for normal learning to occur, we examined the effects of binge-like neonatal EtOH exposure on the total number of deep nuclear cells and eyeblink conditioning in adult rats. Group Ethanol (n=11) received EtOH doses of 5.25 g/kg/day on postnatal days 4-9, producing average peak blood alcohol concentrations of 363 mg/dl. Group Sham Intubated (n=11) underwent acute intragastric intubation on postnatal days 4-9 but did not receive any EtOH infusions. Group Unintubated Control (n=10) did not receive any intubations. When rats were at least 3 months old, they received either paired eyeblink conditioning or unpaired training. Following training, estimates of the total number of cerebellar deep nuclear cells were obtained using the optical fractionator, an unbiased stereological counting procedure. Rats in Group Ethanol had approximately 50% fewer deep nuclear cells compared to rats in Groups Sham Intubated and Unintubated Control, which did not differ. For 21 rats that received paired eyeblink conditioning, a highly significant correlation (+0.80) was found between the number of deep nuclear cells and learning rate in eyeblink conditioning.