Description of an epidemic outbrake of smallpox in Pakistan 1974

The corrective action of Thyroxine on the deficit of the synaptic density of the molecular layer of the cerebellar cortex was studed quantitatively, in the rat made hypothyroid by propylthiouracile (P.T.U.). In the normal as in the hypothyroid rat, the increase of the synaptic density does not extend over the fifth postnatal week. In the PTU treated animals, during the 2 first postnatal weeks, the administration of 0,25 mug/d during the third and 0.50 mug/d during the fourth postnatal week brings the synaptic density back to normal. In the PTU treated animals, during the 5 postnatal weeks, the administration during a week only of 0.50 mug/d of LT4 between 1 and 14 days or, of 1 mug/d between 15 and 28 days, increases, but does not return to normal the synaptic density. On the contrary, the administration of 1 mug/d of LT4 during 1 or even 2 consecutive weeks 28 days later, remains without effect on the synaptic density. After the end of the fourth postnatal week, the deficit of the synaptic density becomes irreversible.     

Marked restoration of density and total number of mature (knob-bearing) olfactory receptor neurons in rats recovering from early hypothyroid-induced growth retardation

Our recent studies have shown that restoration of thyroid function in developing hypothyroid rats results in upregulation of olfactory neurogenesis and compensatory proliferation of olfactory receptor neurons (ORN) in the olfactory epithelium (OE) (Paternostro and Meisami, Dev. Brain Res., 76 (1993) 151-161; ibid., 83 (1994) 151-162). It was not clear, however, whether the newly forming ORNs undergo complete maturational stages. To determine the effects of restoration of thyroid function on maturation of ORNs, the density and total number of mature ORNs were estimated in the OE of euthyroid and hypothyroid rats at postnatal days 1, 12, 25 and 90 and the results were compared with those in rats allowed to recover from early thyroid deficiency at weaning (day 25). As a marker for mature ORNs, and on the basis of one olfactory dendritic knob per ORN, the density and total number of the olfactory knobs were determined in the entire extent of the OE covering the nasal septum. Hypothyroidism was induced by adding propylthiouracil (PTU) to the drinking water (1 g/l) from birth until days 12, 25 or 90 of age. Recovery from hypothyroidism was induced by withdrawal of PTU at day 25, leading to restoration of thyroid function and somatic growth recovery. The density of olfactory knobs was determined in 1 microm semi-thin sections stained with toluidine blue. In the normal rats, the number of olfactory knobs (= mature ORNs) increased 8.5- and 3-fold during postnatal days 1-25 and 25-90 respectively, reaching a mean value of 4 X 10(6)/septal OE, compared to 2.8- and 1.4-fold, respectively, for the hypothyroid rats. This led to deficits of 51% and 76% in the number of mature ORNs in the 25- and 90-day-old hypothyroid rats. In rats allowed to recover, the number of mature ORNs increased 4.5-fold during postnatal days 25-90 (3 X > hypothyroid rats and 1.5 X > controls). The results indicate marked upregulation of the maturational process of the ORNs and their compensatory accretion within the OE of the recovery group. The recovery process was not complete however, as indicated by a remaining deficit of about 25% in the total number of mature ORN, compared to normal 90-day controls. Thus thyroid hormones are essential for accretion of new mature ORNs in both the suckling and postweaning rats. Also, the ORNs show a remarkable ability to recover from severe early hypothyroid-induced growth retardation and attain normal mature state.     

Neuronal cell loss in the CA3 subfield of the hippocampus following cortical contusion utilizing the optical disector method for cell counting

Unilateral cortical contusion in the rat results in cell loss in both the cortex and hippocampus. Pharmacological intervention with growth factors or excitatory neurotransmitter antagonists may reduce cell loss and improve neurological outcome. The window of opportunity for such intervention remains unclear because a detailed temporal analysis of neuronal loss has not been performed in the rodent cortical contusion model. To elucidate the time course of hippocampal CA3 neuronal death ensuing cortical contusion, we employed the optical disector method for assessing the total number of CA3 neurons at 1 and 6 hours, 1, 2, 10, and 30 days following injury. This stereological technique allows reporting of total cell numbers within a given region and is unaffected by change in the volume of the structure or cell size. A rapid and significant reduction in neurons/mm3 in the ipsilateral CA3 field was observed by 1 h following trauma. However, a significant increase in neurons/mm3 was seen at 30 days postinjury. This surprising finding is a result of CA3 volume shrinkage and redistribution of CA3 neurons. Utilization of the optical disector reveals that regardless of an increase in neurons/mm3 at 30 days following injury, CA3 cell loss reaches 41% of control animals by 1 day posttrauma and remains near that level at all subsequent time points examined. It is estimated that there are about 156,000 neurons in the CA3 region in control animals. By 1 h following cortical contusion the cell population decreases to 93,000 neurons indicating a very rapid cell loss. This suggests a window of less than 24 h for pharmacological intervention in order to save CA3 neurons following cortical contusion.     

Postischemic application of lipid peroxidation inhibitor U-101033E reduces neuronal damage after global cerebral ischemia in rats

BACKGROUND AND PURPOSE: The lipid peroxidation inhibitor U-101033E was examined for effects on cerebral blood flow (CBF), cortical tissue hemoglobin oxygen saturation (HbSo2), and neuronal damage. METHODS: Fifteen minutes of global cerebral ischemia was induced by two-vessel occlusion and hypobaric hypotension. Wistar rats (n = 25) were randomized to receive vehicle (n = 9) or 40 mg/kg U-101033E (n = 9) intraperitoneally during 2 hours of reperfusion. A sham group (n = 7) had neither ischemia nor therapy. Histology was evaluated 7 days after ischemia. RESULTS: During late hyperperfusion (at 17 minutes), vehicle-treated animals had a higher (P = 0.044) cortical tissue HbSo2 (72.0 +/- 1.4%) than did U-101033E-treated animals (65.8 +/- 2.5%). Neuronal counts in the superficial cortex layer found after 7 days correlated negatively with rCBF (r = -0.76; P < 0.001) or cortical tissue HbSo2 (r = -0.56; P = 0.028) assessed during the late hyperperfusion phase. U-101033E reduced neuronal damage in hippocampal CA1 from 64.3 +/- 9.2% to 31.2 +/- 8.4% (P = 0.020), as well as in the superficial cortical layer from 53.5 +/- 14.6% to 12.8 +/- 11.7% (P = 0.046). While animals in the vehicle group had reduced counts in all four examined cortex layers (P < 0.05 versus sham group), there was significant cortical neuron loss in the U-101033E group in only one of four areas. U-101033E had no effect on resting CBF or CO2 reactivity. CONCLUSIONS: Postischemic application of U-101033E protects hippocampal CA1 and cortical neurons after 15 minutes of global cerebral ischemia. The results indicate that free radical-induced lipid peroxidation contributes to reperfusion injury, a process that can be inhibited by antioxidants such as U-101033E.     

Galanin messenger RNA during postnatal development of the rat brain: expression patterns in Purkinje cells differentiate anterior and posterior lobes of cerebellum

Following our initial mapping of preprogalanin messenger RNA in adult brain and its presence in a subpopulation of cerebellar Purkinje neurons [Ryan M. C. and Gundlach A. C. (1996) Neuroscience 70, 709-728], the present study examined the ontogenic expression of preprogalanin messenger RNA in the postnatal rat brain focussing on the Purkinje cells of the cerebellar cortex. Using in situ hybridization histochemistry, preprogalanin messenger RNA was detected in the developing forebrain and hindbrain from postnatal day 4 to day 60 (adult). On postnatal day 4 very light hybridization signal (labelling) was observed in cells of a number of nuclei including the central amygdaloid nucleus, the medial preoptic area, paraventricular nucleus and dorsomedial hypothalamic nucleus of the forebrain while lightly-labelled cells were detected in neurons of the nucleus of the solitary tract and locus coeruleus of the hindbrain. Hybridization signal was not apparent in other nuclei until later, with positively-labelled neurons first apparent in the dorsal cochlear nucleus at postnatal day 21. The abundance of preprogalanin messenger RNA-positive neurons and the intensity of the hybridization signal increased, in most regions, until postnatal day 28 when labelling resembled that of the mature rat. Preprogalanin messenger RNA was first detected in the cerebellum on postnatal day 10 only in Purkinje cells of lobule 10 of the posterior vermis and increased in distribution throughout Purkinje cell layers of the entire cerebellar cortex by postnatal day 13. The intensity of hybridization signal in Purkinje cells varied between lobules, with Purkinje cells in lobule 10 displaying a moderate to heavy degree of labelling, while lobules 6-9 and the more posterior lobules of the hemisphere including crus 2 of the ansiform lobule, the paramedian lobule and the copula pyramis, displayed only light labelling. The intensity of labelling in the anterior vermis and the remaining lobules of the hemisphere including crus 1 of the ansiform lobule, the simple lobule, the paraflocculus and the flocculus, was homogeneously weak. By postnatal day 21, Purkinje cell labelling reached maximum intensity in all lobules. Regional differences were still apparent, however, with labelling in the posterior vermis and hemisphere ranging from moderate to heavy, with only light to moderate labelling detected in the anterior vermis. The intensity of labelling in the posterior vermis and most lobules of the hemisphere was similar from postnatal day 21 to adulthood, while, in the anterior vermis, crus 1 of the ansiform lobule and the simple lobule, the intensity of hybridization decreased slightly by postnatal day 28 and was completely absent in Purkinje cells of the adult rat. Differential expression of preprogalanin messenger RNA in Purkinje cells of the developing rat cerebellum and transient expression in certain lobules suggests that galanin gene products may have a role in both the developing and mature rat brain and that galanin gene expression may represent a useful marker for differentiating the anterior and posterior cerebellar lobes.     

Effects of neonatal freeze lesions on expression of parvalbumin in rat neocortex

Neonatal freeze lesions to the cortical plate result in focal malformations of the cerebral cortex that resemble four-layered microgyria. These malformations have been associated with local and distant changes in neuronal architecture, and have been implicated in the neocortical epileptiform discharges that can spread up to 4 mm away from the malformation itself. In an effort to assess potential changes in the development of one population of inhibitory interneurons in this malformation, we measured the density of parvalbumin-immunoreactive (ParvIR) neurons in microgyric and control cerebral cortex on postnatal days 13, 15, 21 and 64. In comparison to controls, microgyric animals exhibited a transient decrease in the expression of parvalbumin immunoreactivity in supragranular neurons, both within the malformation itself and in normal six-layered cortex up to 2 mm adjacent to it. This difference disappeared by P21. In addition, there was a permanent diminution of the density of ParvIR neurons in infragranular layers both within and immediately adjacent to the microgyrus. These results indicate that early injury to the cortical plate gives rise to both focal and more widespread changes in cortical architecture.     

Tissue plasminogen activator mRNA expression in granule neurons coincides with their migration in the developing cerebellum

Tissue plasminogen activator activity in the developing cerebellum, as quantified by zymography of cerebellar homogenates from embryonic day (E) 17 to adult mice, shows a peak of activity at postnatal day (P) 7, followed by a steady 75% decrease into adulthood. Northern blot analysis reveals a similar pattern for tissue plasminogen activator mRNA levels, which are low at E17 but increase dramatically, reaching their highest levels of specific mRNA/micrograms RNA in P1-P7 mice and declining about threefold in the adult mouse. In situ hybridization of whole mouse brain sections with a tissue plasminogen activator antisense cRNA probe shows pronounce reactivity in the cerebellum. Although some binding is associated with the cerebellar meninges, the external granule layer is devoid of tissue plasminogen activator mRNA at all ages. However, highly labeled elongated cells, which also bind antibody to neuronal nuclear antigen and are adjacent to Bergmann glial fibers (i.e., migrating granule neurons), are readily visible throughout the molecular and Purkinje layers at P7 and P14. In the adult mouse cerebellum, tissue plasminogen activator mRNA labeling is restricted to cells in the Purkinje/internal granule layers. Thus, tissue plasminogen activator gene expression is induced as granule neurons leave the external granule layer and begin their inward migration.     

Bcl-2 overexpression protects the neonatal cerebellum from ethanol neurotoxicity

The developing nervous system is extremely sensitive to ethanol, and exposure often produces a condition known as the fetal alcohol syndrome. Although mechanisms underlying developmental ethanol toxicity have long been sought, they remain poorly understood. In this study, we examined the ability of the cell death repressor gene bcl-2 to protect against ethanol neurotoxicity. Transgenic mice overexpressing bcl-2 in neurons were exposed to ethanol vapor on postnatal days 4 and 5, which is the peak period of vulnerability of cerebellar Purkinje cells to ethanol. While exposure of wild-type animals to ethanol resulted in significant loss of Purkinje cells by P5, similar exposure of homozygous and heterozygous transgenics had no effect on the number of these neurons. This study suggests that bcl-2 can protect neurons from ethanol neurotoxicity and that modulation of cell death effector or repressor gene products may play a significant role in developmental ethanol neurotoxicity.     

The developing caudate nucleus in the euthyroid and hypothyroid rat

The basal ganglia are presently implicated in learning, and thyroid deficiency induced neonatally is known to affect mentation. The effects of such a deficiency on the developing causate nucleus might be used to provide insight into structure and function of the normal subcortical brain, as well as possible influences of these extrapyramidal structures on mental retardation. Propylthiouracil was added to the diet of lactating rat dams and observations of the developing caudate nuclei of normal hypothyroid rats were made at 8, 14, 20, 30 and 42 days by using various tissue stains and Golgi-Cox preparations. Seven different types of neurons were distinguished in the caudate nucleus. Differences in the size of cell somata and the varying morphology of axons and dendrites were criteria used to make distinctions. Normally, the nucleus acquires cytoarchitectural complexity during the first three postnatal weeks. Within this period, neuron incidence increases in the caudate neuropil with age while the germinal matrix density decreases. Neuron accumulation reaches a plateau after the third week and cell migration is essentially complete at the end of the first postnatal month as shown by computer analysis of Nissl stained cell counts. Branching of cellular processes, attainment of receptor spines and complexity of the fiber network also appeared during this period. Retardation of structural development with thyroid hormone deficiency was shown by decreased numbers of neurons, inhibition of dendritic arborization, decreased numbers of dendritic spines and a reduced complexity of axonal plexuses. Thyroid deficiency delays cell migration during the first three weeks when compared to age-matched normal controls. The lack of thyroid hormone does not appear to influence the size of neuron somata, and the extent of related dendritic fields, nor does hypothyroidism affect a specific cell type population. Generalized disturbances of caudate nuclear morphological maturation are caused by the deficiency. An apparent compensatory process, including a spurt of neural growth and differentiation, takes place in the period between days 14 and 30 in the deficient animals and a seemingly "normal" caudate cytoarchitecture is seen after the third postnatal week. Quantitative data, however, show that this rapid "catch up" process is inadequate. The developmental imperfection of the caudate nucleus which persists might be a part of the underlying substrate for the mental retardation, disturbed motor performance and perceptual handicaps which are found in the human patient.     

Developmental expression of nitric oxide synthase in the rat diencephalon with special reference to the thalamic paratenial nucleus

Using immunohistochemistry and in situ hybridization the distribution of nitric oxide synthase (NOS) was investigated in the rat brain during pre- and postnatal development. At E15 weak NOS-like immunoreactivity (NOS-LI) could be seen in the differentiation field of the anterior hypothalamus. At E17 strong NOS-LI was observed in the developing neurons of the hypothalamic paraventricular nucleus, supraoptic nucleus, anterodorsal nucleus and lateral hypothalamic areas. In the thalamic paratenial nucleus a strong NOS-LI was observed in these neurons at E17, E18 and P1 with a weaker intensity at P3, P7, P9 and P15, whereas at P30 and in adult rats no NOS-positive neurons could be detected. NOS expression at E17 and P3 was verified by in situ hybridization. These results suggest that NO may have a developmental role at least in one of the regions studied, the thalamic paratenial nucleus.     

Developmental expression of the tenascin-C is altered by hypothyroidism in the rat brain

Tenascin-C is an extracellular matrix glycoprotein involved in cell adhesion and migration, and neurite outgrowth. Since these processes have been found to be under thyroid control in the developing rat brain, we have investigated the effect of congenital hypothyroidism on tenascin-C expression. At birth, in situ hybridization studies in hypothyroid rats show an abnormal up-regulation of tenascin-C in some areas (caudate-putamen, geniculate nuclei, ependymal epithelium of the lateral ventricles, hippocampus) and down-regulation in others (occipital and retrosplenial cortex, subiculum). With subsequent development, hypothyroid animals show higher tenascin-C expression also in the upper layers of the cerebral cortex and subplate, and the Bergmann glia of the cerebellum. Significantly, thyroxine treatment of hypothyroid rats led to normalization of tenascin-C levels in most areas. In agreement with the messenger RNA data, hypothyroid rats contain an uniformly higher level of immunoreactive tenascin-C protein throughout the brain, particularly in the cerebellum. Suggesting a direct cellular effect, thyroid hormone also decreases tenascin-C expression in two glial cell lines (C6, B3.1) expressing thyroid receptors. Our results show that congenital hypothyroidism causes specific alterations in the pattern of tenascin-C expression in the rat brain which may at least partially be responsible for some of the developmental disturbances observed in this syndrome.     

Expression and subcellular distribution of glutamate receptor subunits 2/3 in the developing cerebellar cortex

The expression and subcellular location of glutamate receptor subunits 2&3 was investigated in the developing postnatal cerebellum. Immunoblotting revealed that glutamate receptor subunits 2/3 is expressed in an identical pattern of immunoreactive bands of approximately 108 kDa from postnatal day zero to adult animals. Light microscopy showed that within the cerebellar cortex, GluR 2/3 immunoreactivity was essentially confined to Purkinje neurons. Strong immunostaining could be observed at postnatal days 1-3 within Purkinje cell bodies and primary dendrites. With ongoing development, the cell body and an increasingly elaborate dendritic tree was outlined by immunoreaction product. In adult animals, staining of Purkinje cell dendrites was patchy, and staining intensity of the cell body, in particular, was greatly reduced. Ultrastructural analysis revealed that during early postnatal development, immunoreaction product was localized to the cell membrane, but was not confined to postsynaptic densities. From the second postnatal week, glutamate receptor subunits 2/3 immunoreactivity was largely restricted to postsynaptic densities. These observations reveal a developmentally regulated refinement of the subcellular distribution of defining subunits of the AMPA-type glutamate receptor. The presence of membrane bond receptors prior to the formation of synapses also provides a rationale for the known transmitter-mediated modulation of Purkinje cell dendritogenesis.     

Developmental expression of testis messenger ribonucleic acids in the rat following propylthiouracil-induced neonatal hypothyroidism

Propylthiouracil- (PTU) induced transient neonatal hypothyroidism increases adult rat testis weight 80-100%; this effect involves prolongation of Sertoli cell proliferation. To gain insight into developmental effects of PTU on the testis, we used Northern analysis to examine chronological expression of Sertoli cell mRNA in postnatal rat testes from rats that were untreated (controls) or were given PTU from birth to Day 25. Treated rats showed prolonged early expression of genes associated with dividing Sertoli cells such as MIS (Müllerian inhibiting substance) and c-erbA alpha (thyroid hormone receptor). Expression of several other Sertoli cell mRNAs (androgen-binding protein [ABP], clusterin, and inhibin-beta B) was delayed, as was that of hemiferrin, a spermatid-specific mRNA. Temporal expression patterns for other mRNAs (sulfated glycoprotein [SGP]-1, transferrin, and inhibin-alpha) were similar in control and treated animals. Additionally, thyroid hormone replacement in PTU-treated animals decreased MIS and c-erbA alpha mRNA expression to control levels. The altered developmental pattern of expression of a number of major Sertoli cell genes reflects a prolonged mitogenesis and delayed maturation of Sertoli cells in neonatally hypothyroid animals. Furthermore, our results suggest that thyroid hormone may directly potentiate molecular events associated with cessation of Sertoli cell proliferation and maturation during early testis development.     

Functional change of NMDA receptors related to enhancement of susceptibility to neurotoxicity in the developing pontine nucleus

The developing neurons have been reported to be extremely susceptible to toxicity of NMDA during a restricted developmental period. Pontosubicular neuronal necrosis is a typical type of perinatal human brain lesion and often coexists with other forms of cerebral hypoxic and ischemic injuries. To determine whether functional changes of NMDA receptors related to the susceptibility to NMDA toxicity are involved in developing neurons in the pontine nucleus, we have examined the lesion produced by in vivo direct injection of NMDA into the pontine nucleus of rats at postnatal days 1-30, recorded NMDA-induced whole-cell currents from neurons in the pontine nucleus in the developing rat brainstem slices, and performed in situ hybridization for NMDA receptor subunit mRNAs in the pontine nucleus. The susceptibility to NMDA neurotoxicity peaked near postnatal day 15, and the NMDA-induced currents showed prominent reduction of the voltage-dependent block by Mg2+ near postnatal day 15. The pontine nucleus near postnatal day 15 showed distinct expression of the NMDA receptor subunit NR2C mRNA. These results suggest that the susceptibility to NMDA neurotoxicity that is enhanced in the rat pontine nucleus near postnatal day 15 is mediated by the NMDA receptor channels that are relatively insensitive to Mg2+ and that the reduction in the sensitivity of NMDA receptors to Mg2+ correlates with the expression of the NR2C. We present the possibility that functional changes in the NMDA receptor channels play a crucial role in the occurrence of developmentally specific neuronal injury.     

Embryonic and postnatal expression of four gamma-aminobutyric acid transporter mRNAs in the mouse brain and leptomeninges

The distribution of gamma-aminobutyric acid (GABA) transporter mRNAs (mGATs) was studied in mouse brain during embryonic and postnatal development using in situ hybridization with radiolabeled oligonucleotide probes. Mouse GATs 1 and 4 were present in the ventricular and subventricular zones of the lateral ventricle from gestational day 13. During postnatal development, mGAT1 mRNA was distributed diffusely throughout the brain and spinal cord, with the highest expression present in the olfactory bulbs, hippocampus, and cerebellar cortex. The mGAT4 message was densely distributed throughout the central nervous system during postnatal week 1; however, the hybridization signal in the cerebral cortex and hippocampus decreased during postnatal weeks 2 and 3, and in adults, mGAT4 labeling was restricted largely to the olfactory bulbs, midbrain, deep cerebellar nuclei, medulla, and spinal cord. Mouse GAT2 mRNA was expressed only in proliferating and migrating cerebellar granule cells, whereas mGAT3 mRNA was absent from the brain and spinal cord throughout development. Each of the four mGATs was present to some degree in the leptomeninges. The expression of mGATs 2 and 3 was almost entirely restricted to the pia-arachnoid, whereas mGATs 1 and 4 were present only in specific regions of the membrane. Although mGATs 1 and 4 may subserve the classical purpose of terminating inhibitory GABAergic transmission through neuronal and glial uptake mechanisms, GABA transporters in the pia-arachnoid may help to regulate the amount of GABA available to proliferating and migrating neurons at the sub-pial surface during perinatal development.     

Ischemia-induced neuronal cell loss is associated with loss of atypical angiotensin type-1 receptor expression in the gerbil hippocampal formation

The hippocampal formation of Mongolian gerbils expresses high amounts of atypical angiotensin II type-1 receptors. We studied the expression of these receptors by in situ hybridization using specific [35S]-labeled riboprobes and by receptor autoradiography using [125I]Sarcosine1-angiotensin II. Angiotensin II receptor mRNA was found in the pyramidal cell layer of the CA1, CA2 and CA3 subfields, with the highest expression in the CA2 subfield, and in the granular cell layer of the dentate gyrus. Angiotensin II binding was detected in the stratum oriens and stratum radiatum of the CA1 and CA2 subfields, in the stratum oriens of the CA3 subfield, and in the molecular layer of the dentate gyrus. We then studied the effect of ischemia on hippocampal angiotensin II receptor expression, 1, 4 and 15 days after bilateral occlusion of the common carotid arteries for 5 min. No changes in angiotensin II receptor mRNA or binding were detected 1 day after ischemia. Delayed, progressive loss of angiotensin II mRNA and binding occurred 4 and 15 days after ischemia, in the CA1, CA2 and CA3 subfields. The decline was faster in the CA1 subfield, and paralleled the loss of neurons after ischemia. In the dentate gyrus, angiotensin II receptor mRNA and angiotensin II binding were not changed when compared to sham operated controls. The decrease of angiotensin II receptor expression may reflect the loss of angiotensin II receptor-producing neurons rather than a down-regulation of receptor expression.     

Therapeutic motor training increases parallel fiber synapse number per Purkinje neuron in cerebellar cortex of rats given postnatal binge alcohol exposure: preliminary report

Because therapeutic approaches to fetal alcohol effects in humans have been rare, this study explored the rehabilitative effect of complex motor training on an animal model of binge drinking in the third trimester of human pregnancy. Neonatal alcohol exposure induces significant and permanent reductions in Purkinje and granule cell number accompanied by impaired motor behavior in rats. The purpose of this study was to determine: (1) whether the motor skill impairment caused by exposure to alcohol in the early postnatal period could be ameliorated by the learning of a set of complex motor tasks that had been demonstrated to cause synaptogenesis in the cerebellar cortex; and (2) the extent to which cerebellar neurons in alcohol-exposed (AE) rats exhibit synaptic plasticity. The AE group was given 4.5 g/kg/day of ethanol from postnatal days 4 to 9 via an artificial rearing procedure producing a mean peak blood alcohol level of 257 mg/dl. Control groups consisted of a gastrostomy control (GC) group, that received an isocaloric mixture of maltose/dextrin instead of ethanol, and a suckle control (SC) group, that was reared normally by dams. At approximately 6 months of age, animals from the three groups were assigned either to a rehabilitation condition (RC; that received 10 days of training on the motor tasks) or to an inactive condition (IC; where rats stayed in isolation in their cages). Although SC rats were significantly faster to complete the course in the first 5 days of training, there were no differences in ability to perform among animals from all three groups-SC, GC, and AE--at the end of the training period. Unbiased stereological techniques were used to obtain estimates of the number of parallel fiber synapses/Purkinje cell within the cerebellar paramedian lobule. Results showed that the RC rats from the SC and AE groups had significantly more synapses/Purkinje cell than corresponding IC animals. These data demonstrate that rehabilitative intervention (complex motor training) can improve motor performance impaired by postnatal alcohol exposure and that surviving Purkinje neurons retain the capacity for synaptic plasticity.