The effect of the timing of ethanol exposure during early postnatal life on total number of Purkinje cells in rat cerebellum

Curcumin alters motor coordination but not total number of Purkinje cells in the cerebellum of adolescent male Wistar rats

OBJECTIVE

The present study aimed at investigating the effects of curcumin on the motor coordination and the estimate of the total number of cerebellar Purkinje cells of adolescent Wistar rats exposed to ethanol.

METHODS

The total of 21 male Wistar rats aged 37 d old were divided into three groups, namely ethanol, ethanol-curcumin, and control groups. The ethanol group received 1.5 g/kg ethanol injected intraperitoneally and water given per oral; the ethanol-curcumin group received 1.5 g/kg ethanol injected intraperitoneally and curcumin extract given per oral; the control group received saline injection and oral water. The treatment was carried out daily for one month, after which the motor coordination performance of the rats was examined using revolving drum apparatus at test days 1, 8, and 15. The rats were finally sacrificed and the cerebellum of the rats was further processed for stereological analysis. The estimate of the total number of Purkinje cells was calculated using physical fractionator method.

RESULTS

The ethanol-curcumin group performed better than both ethanol and control groups in the motor coordination ability at day 8 of testing (P< 0.01). No Purkinje cell loss was observed as a result of one month intraperitoneal injection of ethanol.

CONCLUSION

Curcumin may exert beneficial effects on the motor coordination of adolescent rats exposed to ethanol via undetermined hormetic mechanisms.

Differential effects of neonatal maternal separation on the expression of neurotrophic factors in rat brain. II: Regional differences in the cerebellum versus the cerebral cortex

This study was conducted in order to examine the effects of early postnatal maternal separation stress on the age-dependent fluctuations in the expression levels of neurotrophic factor ligands and receptors in the developing cerebellum. Wistar rats were separated from their mothers for 3 h each day during postnatal days (PND) 10 to 15. The expression level of mRNA for brain-derived neurotrophic factor (BDNF), tyrosine kinase receptor B (TrkB), insulin-like growth factor-1 (IGF-1), and type-1 IGF receptor (IGF-1R) were evaluated in the cerebellum on PND16, 20, 30, and 60 with real-time RT-PCR. The mRNA levels of cerebellar BDNF in maternally separated rats were increased on PND16, while the other variables showed no significant alterations at any of the time points examined. However, the effects of an identical maternal separation on the cerebral cortex were previously reported to be completely different. These results indicate regional differences in the responses of neurotrophic factor ligands/receptors between the cerebellum and cerebral cortex. Given that neurotrophic factors play important roles in brain development, alterations in these factors may interrupt normal brain development and ultimately, lead to functional disruptions.

Morphological evidence of an altered process of synaptic transcytosis in adult rats exposed to ethanol

AIMS

The effects of ethanol exposure on synaptic structure were investigated in the nucleus of solitary tract (NST) in rats, using the horse-radish peroxidase (HRP) method.

METHODS

Eight-week-old experimental rats were allowed free access to a liquid diet containing ethanol for 3 weeks, while controls were given an isocaloric diet. Some of the control and experimental animals were given an injection of wheat germ agglutinin conjugated with HRP (WGA-HRP) into the vagus nerve toward the end of the treatment period. After the treatment, the neuropil region of the NST was examined under an electron microscope.

RESULTS

We observed that a few terminals were characterized by deep indentation of axodendritic membranes into the post-synaptic neurons. This appeared to be similar to that commonly seen in exocrine glands. Interestingly, the indented portion often contained various sizes of vacuoles and flattened cisternae. HRP-reaction product (RP) transported to terminals was recognized easily as an electron-dense lysosomal substance when lead citrate staining was omitted. Terminals containing HRP-RP also revealed quite a similar structure with indentation of axodendritic membranes as described earlier. The results are considered to confirm that terminals forming 'apocrine-like structures' observed in the ethanol-fed animals with no injection of WGA-HRP originate from afferent fibers of the vagus nerve.

CONCLUSION

The present study suggests the possibility that the alteration of the synaptic structure induced by ethanol exposure can lead to the neuronal transcytosis of materials including proteins which is different from the normal vesicular exocytosis involved in chemical synaptic transmission.

Effects of early postnatal exposure to ethanol on retinal ganglion cell morphology and numbers of neurons in the dorsolateral geniculate in mice

BACKGROUND

The adverse effects of fetal and early postnatal ethanol intoxication on peripheral organs and the central nervous system are well documented. Ocular defects have also been reported in about 90% of children with fetal alcohol syndrome, including microphthalmia, loss of neurons in the retinal ganglion cell (RGC) layer, optic nerve hypoplasia, and dysmyelination. However, little is known about perinatal ethanol effects on retinal cell morphology. Examination of the potential toxic effects of alcohol on the neuron architecture is important because the changes in dendritic geometry and synapse distribution directly affect the organization and functions of neural circuits. Thus, in the present study, estimations of the numbers of neurons in the ganglion cell layer and dorsolateral geniculate nucleus (dLGN), and a detailed analysis of RGC morphology were carried out in transgenic mice exposed to ethanol during the early postnatal period.

METHODS

The study was carried out in male and female transgenic mice expressing yellow fluorescent protein (YFP) controlled by a Thy-1 (thymus cell antigen 1) regulator on a C57 background. Ethanol (3 g/kg/d) was administered to mouse pups by intragastric intubation throughout postnatal days (PDs) 3 to 20. Intubation control (IC) and untreated control (C) groups were included. Blood alcohol concentration was measured in separate groups of pups on PDs 3, 10, and 20 at 4 different time points, 1, 1.5, 2, and 3 hours after the second intubation. Numbers of neurons in the ganglion cell layer and in the dLGN were quantified on PD20 using unbiased stereological procedures. RGC morphology was imaged by confocal microscopy and analyzed using Neurolucida software.

RESULTS

Binge-like ethanol exposure in mice during the early postnatal period from PDs 3 to 20 altered RGC morphology and resulted in a significant decrease in the numbers of neurons in the ganglion cell layer and in the dLGN. In the alcohol exposure group, out of 13 morphological parameters examined in RGCs, soma area was significantly reduced and dendritic tortuosity significantly increased. After neonatal exposure to ethanol, a decrease in total dendritic field area and an increase in the mean branch angle were also observed. Interestingly, RGC dendrite elongation and a decrease in the spine density were observed in the IC group, as compared to both ethanol-exposed and pure control subjects. There were no significant effects of alcohol exposure on total retinal area.

CONCLUSIONS

Early postnatal ethanol exposure affects development of the visual system, reducing the numbers of neurons in the ganglion cell layer and in the dLGN, and altering RGCs' morphology.

Ethanol exposure of neonatal rats does not increase biomarkers of oxidative stress in isolated cerebellar granule neurons

Oxidative stress is a candidate mechanism for ethanol neuropathology in fetal alcohol spectrum disorders. Oxidative stress often involves production of reactive oxygen species (ROS), deterioration of the mitochondrial membrane potential (MMP), and cell death. Previous studies have produced conflicting results regarding the role of oxidative stress and the benefit of antioxidants in ethanol neuropathology in the developing brain. This study investigated the hypothesis that ethanol neurotoxicity involves production of ROS with negative downstream consequences for MMP and neuron survival. This was modeled in neonatal rats at postnatal day 4 (P4) and P14. It is well established that granule neurons in the rat cerebellar cortex are more vulnerable to ethanol neurotoxicity on P4 than at later ages. Thus, it was hypothesized that ethanol produces more oxidative stress and its negative consequences on P4 than on P14. A novel experimental approach was used in which ethanol was administered to animals in vivo (gavage 6g/kg), granule neurons were isolated 2-24h post-treatment, and ROS production and relative MMP were immediately assessed in the viable cells. Cells were also placed in culture and survival was measured 24h later. The results revealed that ethanol did not induce granule cells to produce ROS, cause deterioration of neuronal MMP, or cause neuron death when compared to vehicle controls. Further, granule neurons from neither P4 nor P14 animals mounted an oxidative response to ethanol. These findings do not support the hypothesis that oxidative stress is obligate to granule neuron death after ethanol exposure in the neonatal rat brain. Other investigators have reached a similar conclusion using either brain homogenates or cell cultures. In this context, it is likely that oxidative stress is not the sole and perhaps not the principal mechanism of ethanol neurotoxicity for cerebellar granule neurons during this stage of brain development.

Effect of prenatal exposure to diclofenac sodium on Purkinje cell numbers in rat cerebellum: A stereological study

Diclofenac sodium (DS) is commonly used as a non-steroidal anti-inflammatory drug. Although several adverse effects are clearly established, it is still unknown whether prenatal exposure to DS has an effect on the development of the cerebellum. In this study, we investigated the total number of Purkinje cells of the cerebellum in a control group and in a DS-treated group of male rats using a stereological method. The DS in a dose of 1 mg/kg daily was intraperitoneally injected to the drug-treated group of pregnant rats beginning from the 5th day after mating for a period of 15 days during pregnancy. Physiological serum at 1 ml dose was intraperitoneally injected to the control group of pregnant rats at the same period. After delivery, male offspring were obtained and each main group was divided into two subgroups that were 4-week-old (4W-old) and 20-week-old (20W-old). Our results showed that the total number of Purkinje cells in offspring of drug-treated rats was significantly lower than in the offspring of control animals. These results suggest that the Purkinje cells of a developing cerebellum may be affected by administration of DS during the prenatal period.

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.

Effect of chronic ethanol ingestion on Purkinje and Golgi cell firing in vivo and on motor coordination in mice

As motor coordination impairment is a common symptom of acute and chronic alcohol intoxication, different studies have been conducted on cerebellar Purkinje cell sensitivity to ethanol since Purkinje cell firing constitutes the final integrative output of the cerebellar cortex. However, the effects of chronic ethanol ingestion on Purkinje firing and other cerebellar neurons such as Golgi cells remain unknown. Here, we studied the extracellular discharge of Purkinje and Golgi cells in four groups of non-anesthetized mice drinking ad libitum either 0%, 6%, 12% or 18% ethanol isocallorically compensated with sucrose 25% during a 3-month period. No difference in Golgi cell firing was found with respect to ethanol consumption. The only group that presented significant differences in Purkinje cell firing compared to the other groups was the 18% ethanol-drinking group. These mice presented decreased simple spike and complex spike firing and increased complex spike duration and pause. The 18% ethanol-drinking group was also the only one to present a slight but significant motor coordination impairment (evaluated by rotarod and runway) in naïve task. No motor coordination impairment was noticed in task learned before ethanol consumption. These results suggest that chronic high doses of ethanol are necessary to produce Purkinje cell firing alterations and measurable motor coordination impairment in naïve task. These alterations in Purkinje cell firing did not affect the ability to learn or to recall a motor coordination task.

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.

Effects of alcohol exposure during early life on neuron numbers in the rat hippocampus. I. Hilus neurons and granule cells

We previously showed that 16-day-old rats exposed to a relatively high dose of ethanol at 10-15 postnatal days of age have fewer neurons in the hilus region of the hippocampus compared with controls. Dentate gyrus granule cell numbers, however, showed no statistically significant changes attributable to the ethanol treatment. It is possible that some of the changes in brain morphology, brought about as a result of the exposure to ethanol during early life, may not be manifested until later in life. This question has been further addressed in an extension to our previous study. Wistar rats were exposed to a relatively high daily dose of ethanol on postnatal days 10-15 by placement in a chamber containing ethanol vapour, for 3 h/day. The blood ethanol concentration was found to be approximately 430 mg/dl at the end of the period of exposure. Groups of ethanol-treated (ET), separation control (SC), and mother-reared control (MRC) rats were anaesthetised and killed either at 16 or 30 days of age by perfusion with phosphate-buffered 2.5% glutaraldehyde. The Cavalieri principle and the physical disector methods were used to estimate, respectively, the regional volumes and neuron cell numerical densities in the hilus and granule cell regions of the dentate gyrus. The total numbers of neurons in the hilus region and granule cell layer were computed from these estimates. It was found that 16-day-old animals had 398,000-441,000 granule cells, irrespective of group. The numbers of granule cells increased such that by 30 days of age, rats had 487,000-525,500 granule cells. However, there were no significant differences between ethanol-treated rats and their age-matched controls in granule cell numbers. In contrast, ethanol-treated rats had slightly but significantly fewer neurons in the hilus region than did control animals at 16 days of age, but not at 30 days of age. Therefore, it appears that a short period of ethanol exposure during early life can have effects on neuron numbers of some hippocampal neurons, but not others. The effects on hilar neuron numbers, observed as a result of such short periods of ethanol treatment, appeared to be transitory.

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.

The effect of the timing of prenatal X-irradiation on Purkinje cell numbers in rat cerebellum

Exposure of the developing brain to X-irradiation in utero is known to cause various deleterious consequences. We have previously reported the effects of prenatal X-irradiation on the development of the cerebral cortex in rats. We have now extended this study to examine the effects of such X-irradiation on the development of the cerebellum. Wistar rats were exposed to 1.5 Gy X-irradiation either on days 14, 15 or 16 of gestation (E14, E15, E16). Sham-irradiated animals were used as controls. At seven postnatal weeks of age, male rats from each group were deeply anesthetized and killed by intracardiac perfusion with 2.5% glutaraldehyde in 0.1 M phosphate buffer. The unbiased stereological procedure known as the fractionator method was used to estimate the total number of Purkinje cells in the cerebellum of each animal. Body and cerebellar weights from E14 and E15, but not E16 irradiated rats showed significant deficits compared to control animals. Rats irradiated on E16 and control rats had about 285100-304800 Purkinje cells in the cerebellum. There was no significant difference between these values. However, E14 and E15 irradiated animals had about 117500 and 196300 Purkinje cells, respectively. These estimates were significantly different from those observed in both control and E16 irradiated rats. Given that the phase of division of Purkinje cell progenitors is mainly between E14-E15 and the phase of differentiation and migration is between E16-E20, it is concluded that the vulnerable period of the Purkinje cells to X-irradiation closely overlaps the phase of division of progenitors.

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.

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

Neonatal exposure to ethanol in rats, during the period of brain development comparable to that of the human third trimester, produces significant, dose-dependent cell loss in the cerebellum and deficits in coordinated motor performance. These rats are also impaired in eyeblink conditioning as weanlings and as adults. The current study examined single-unit neural activity in the interpositus nucleus of the cerebellum in adults following neonatal binge ethanol exposure. Group Ethanol received alcohol doses of 5.25 g/kg/day on postnatal days 4-9. Group Sham Intubated underwent acute intragastric intubation on postnatal days 4-9 but did not receive any infusions. Group Unintubated Control (from separate litters) did not receive any intubations. When rats were 3-7 mo old, pairs of extracellular microelectrodes were implanted in the region of the interpositus nucleus. Beginning 1 wk later, the rats were given either 100 paired or 190 unpaired trials per day for 10 d followed by 4 d of 100 conditioned stimulus (CS)-alone trials per day. As in our previous study, conditioned response acquisition in Group Ethanol rats was impaired. In addition, by session 5 of paired acquisition, Group Sham Intubated and Group Unintubated Control showed significant increases in interpositus nucleus activity, relative to baseline, in the CS-unconditioned stimulus interval. In contrast, Group Ethanol failed to show significant changes in interpositus nucleus activity until later in training. These results indicate that the disruption in eyeblink conditioning after early exposure to ethanol is reflected in alterations in interpositus nucleus activity.

Developmental instability of the cerebellum and its relevance to Down syndrome

It has been recognized for many years that cerebellar abnormalities are frequently observed in association with Down syndrome (DS). An important question to be asked about these and other findings in DS is whether their occurrence (i) is attributable to specific loci on the triplicated chromosome or chromosomal segment or (ii) derives from exaggerated responses secondary to the genetic imbalance resulting from trisomy (Ts). Recently, similar cerebellar alterations were observed in subjects with DS and in Ts65Dn mice (Baxter et al., 2000), mice segmentally trisomic for a portion of chromosome 16, which is homologous for loci on the long arm of human chromosome 21. It was concluded by these authors that the occurrence of similar cerebellar changes in DS and in the DS mouse model resulted from triplication of these homologous loci in the two trisomic organisms, i.e. cerebellar development is affected similarly by homologous loci in each species. They wrote that their study of Ts65Dn mice "correctly predicts an analagous pathology in humans". . . and that. . . "The candidate region of genes on chromosome 21 affecting cerebellar development in DS is therefore delimited to the subset of genes whose orthologs are at dosage imbalance in Ts65Dn mice, providing the first localization of genes affecting a neuroanatomical phenotype in DS." Findings described in this review suggest otherwise--that cerebellar findings in DS and in the Ts65Dn mouse are a result of exaggerated vulnerability in general of the cerebellum to disturbing events and that liability to expression of response(s) is exacerbated by trisomy. This conclusion is based on the following: (i) the cerebellum has an extended postnatal development; (ii) numerous genetic, environmental, epigenetic and metabolic conditions express cerebellar changes similar to those observed in Down syndrome; (iii) most if not all chromosomal imbalance syndromes express similar cerebellar abnormalities; (iv) the cerebellum is particularly sensitive to diverse toxic agents which may act prenatally, postnatally and/or in the mature organism; and (v) cerebellar abnormalities similar to those found in Ts65Dn mice have been described in Ts19 mice which have no segments homologous to any segment of human chromosome 21. An unavoidable conclusion from the review is that triplication of specific loci on 21q is an unlikely explanation for the cerebellar findings in DS. A simple positive control, in which the effect of triplication of loci other than those in question on a specific phenotype, should be used in experiments comparing human and experimental trisomies. As pointed out many years ago by Lorke and his coworkers (Lorke et al., 1989; Lorke, 1994; Lorke and Albrecht, 1994) similar phenotypic findings in the presence of different trisomies in the same species would suggest that the trisomic state itself rather than the gene content of a particular trisomy is responsible for the genesis of traits at issue.