The effects of ethanol exposure during the brain growth spurt in rats

Neurobehavioral alterations induced by third-trimester gestation-equivalent ethanol exposure are inhibited by folate administration

Prenatal ethanol exposure (PEE) causes several neurobehavioral impairments in the fetus. Postnatal days (PDs) 4-9 in rodents are considered equivalent to the third trimester of gestation in humans. This period is characterized by high rates of synaptogenesis and myelination and the maturation of key structures and transmitter systems. Nutritional supplements, such as folate, have gained attention as putative treatments to mitigate detrimental effects of PEE. Folate is crucial for DNA synthesis and amino acid metabolism and heightens antioxidant defenses. The present study examined neurobehavioral effects of the concurrent administration of folate (20 mg/kg/day) and ethanol (5 g/kg/day) during PDs 4-9 in male and female Wistar rats. During PDs 16-18, the rat pups were tested for anxiety-like and exploratory activity in the light-dark box (LDB), open field (OF), and concentric square field (CSF) tests. After weaning, they were tested for sucrose preference and ethanol intake. Neonatal ethanol exposure reduced body weight in infancy but did not enhance ethanol self-administration or significantly affect performance in the OF or LDB. Neonatal ethanol exposure also reduced sucrose intake in the preference test and increased shelter-seeking in the CSF, and folate significantly inhibited these effects. The present findings suggest that folate, a treatment that is devoid of serious side effects, can ameliorate some neurobehavioral effects of PEE.

Prolonged maternal separation attenuates BDNF-ERK signaling correlated with spine formation in the hippocampus during early brain development

Maternal separation (MS) is known to affect hippocampal function such as learning and memory, yet the molecular mechanism remains unknown. We hypothesized that these impairments are attributed to abnormities of neural circuit formation by MS, and focused on brain-derived neurotrophic factor (BDNF) as key factor because BDNF signaling has an essential role in synapse formation during early brain development. Using rat offspring exposed to MS for 6 h/day during postnatal days (PD) 2-20, we estimated BDNF signaling in the hippocampus during brain development. Our results show that MS attenuated BDNF expression and activation of extracellular signal-regulated kinase (ERK) around PD 7. Moreover, plasticity-related immediate early genes, which are transcriptionally regulated by BDNF-ERK signaling, were also reduced by MS around PD 7. Interestingly, detailed analysis revealed that MS particularly reduced expression of BDNF gene and immediate early genes in the cornu ammonis 1 (CA1) of hippocampus at PD 7. Considering that BDNF-ERK signaling is involved in spine formation, we next evaluated spine formation in the hippocampus during the weaning period. Our results show that MS particularly reduced mature spine density in proximal apical dendrites of CA1 pyramidal neurons at PD 21. These results suggest that MS could attenuate BDNF-ERK signaling during primary synaptogenesis with a region-specific manner, which is likely to lead to decreased spine formation and maturation observed in the hippocampal CA1 region. It is speculated that this incomplete spine formation during early brain development has an influence on learning capabilities throughout adulthood.

Consequences of early life MK-801 administration: long-term behavioural effects and relevance to schizophrenia research

Animal models contribute significantly to advancing the understanding of schizophrenia neurobiology, in addition to being an important tool for the screening of antipsychotic potential of new compounds. However, the entire spectrum or all the symptoms manifested in schizophrenia cannot be straightforwardly reproduced in animals due to the complexity of the disorder, difference in mental capacities and behaviours, and the ability to quantify or measure the changes. Blockade of the NMDA receptor by the use of MK-801, a non-competitive NMDA receptor antagonist, during the early postnatal period has been proposed to be an experimental model which induces behavioural changes that mimic several aspects of the disorder. The long term behavioural profile arising from this early life manipulation is reviewed herein, with a specific focus on behaviours relevant to a schizophrenia-like condition. Some of the reported neurochemical changes are also compiled. Although this method may be suitable to model some aspects of schizophrenia in rodents, there are unmet areas which need to be addressed, notably the characterisation of its predictive value.

Developmental neurotoxicity of ethanol: further evidence for an involvement of muscarinic receptor-stimulated phosphoinositide hydrolysis

Various lines of evidence suggest that muscarinic receptor-stimulated phosphoinositide hydrolysis during postnatal development in the rat brain may play a relevant role in glial cell proliferation and neuronal differentiation. We have previously shown that administration of ethanol to developing rats during the brain growth spurt causes microencephaly and selectively decreases muscarinic receptor-stimulated phosphoinositide hydrolysis. In the present study we have investigated the sensitivity of the phosphoinositide system coupled to muscarinic receptors to ethanol inhibition during distinct stages of the brain growth spurt. Different groups of rats were treated for 3 days with ethanol (4 g/kg per day) on postnatal days 2-4 (initial), 6-8 or 10-12 (peak), 13-15 (final stage of the brain growth spurt). The results show that the period of maximal sensitivity to ethanol of muscarinic receptor-stimulated phosphoinositide hydrolysis coincides with the peak of the brain growth spurt and with the period of maximal efficacy of muscarinic receptor agonists to induce inositol phosphates accumulation. Interestingly, only when muscarinic receptor-stimulated phosphoinositide hydrolysis was inhibited, a significant reduction of brain weight was observed. The close parallel between inhibition of this second messenger response and reduction of brain weight suggests that the phosphoinositide system coupled to muscarinic receptors may represent a target for the neurotoxic effects of ethanol during this stage of brain development.

Delayed thermoregulatory changes in the immature rat following a single injection of ethanol

Adult rats exhibit rebound hyperthermia within 24 hr following a single injection of ethanol (EtOH). Tests were conducted to determine whether similar changes in thermoregulatory ability occur in the immature rat. Animals were administered saline or EtOH (4 g/kg BW; intraperitoneally) at 2 to 3, 8 to 9, or 14 to 15 days of age. Littermates were handled or left undisturbed with the dams to serve as controls. All rats were tested at 24 or 48 hr post-treatment to measure steady-state colonic temperature (Tco), tail skin temperature and metabolic rate (MR) at both thermoneutral and cold ambient temperatures (Tas). The youngest group exhibited no delayed change in body temperature or MR at 24 or 48 hr post-treatment with EtOH. Likewise, thermoregulatory ability of rats pretreated with EtOH at 8 or 9 or 14 to 15 days of age was not significantly different from controls when tested 24 hr post-treatment at thermoneutral Ta. In contrast, Tco of EtOH-treated rats in the two older age groups was 1 degree C above control level when tested 24 hr post-treatment at cold Ta. This Tco response can be explained by differences in heat transfer to the tail and MR. No altered response to cold Ta was found at 48 hr postinjection, indicating recovery from the EtOH effect. A single injection with EtOH at 2 to 15 days of age results in a change in Tco, which is dependent on postinjection time, age, and Ta.

Time-, concentration-, and age-dependent inhibition of muscarinic receptor-stimulated phosphoinositide metabolism by ethanol in the developing rat brain

We have previously reported that administration of ethanol (EtOH; 4 g/Kg/day) to rats from postnatal day 4 to day 10 causes microencephaly and decreases muscarinic receptor-stimulated inositol metabolism on days 7 and 10. An identical exposure to EtOH of adult rats, which resulted in similar blood EtOH concentrations, did not have any effect on the same system. Initial in vitro studies have shown the presence of a differential sensitivity to EtOH of the phosphoinositide system coupled to muscarinic receptors during development. In the present study we have expanded these findings by investigating the concentration-, time-, and age-dependent effects of EtOH on accumulation of [3H]inositol phosphates ([3H]InsPs) in brain slices. EtOH caused a dose-dependent inhibition of carbachol-stimulated phosphoinositide metabolism in cerebral cortex slices from 7 day-old rats. When the time of incubation with EtOH was increased to 90 minutes, concentrations as low as 50 mM, which are reached following in vivo administration of EtOH, significantly inhibited the muscarinic response. The effect of EtOH was rather specific for the muscarinic receptors, since, even with longer incubation times, the accumulation of [3H]InsPs induced by norepinephrine or serotonin was inhibited only at concentrations of 150-500 mM. The effect of EtOH was more pronounced in cerebral cortex, hippocampus and cerebellum, and less in the brainstem. The potency of EtOH in inhibiting carbachol-stimulated phosphoinositide metabolism was also dependent on the age of the animals. Its effect was maximal in the 7-day-old rat and less pronounced in younger and older animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental neurotoxicity of ethanol: in vitro inhibition of muscarinic receptor-stimulated phosphoinositide metabolism in brain from neonatal but not adult rats

The in vitro effects of ethanol (EtOH) on muscarinic receptor-stimulated phosphoinositide metabolism were measured in cerebral cortex slices of adult and 7-day-old rats. EtOH (500 mM) caused a significant decrease (32-43%) of maximal accumulation of [3H]inositol phosphates (InsPs) induced by carbachol, and a 2-fold increase in its EC50 in 7-day-old rats, but had no effect in adult rats. The effect of EtOH on [3H]InsPs accumulation in neonatal rats was significant at a concentration as low as 150 mM. The inhibitory effect of EtOH was maximal in cerebral cortex and hippocampus and lower in cerebellum, while no effect was observed in the brainstem. While carbachol- and acetylcholine-stimulated phosphoinositide metabolism were inhibited by EtOH, EtOH had no effect on norepinephrine-, histamine-, and serotonin-stimulated phosphoinositide hydrolysis. These results are qualitatively and quantitively similar to those previously found following in vivo administration of EtOH to developing and to adult rats, suggesting that the muscarinic receptor-stimulated phosphoinositide metabolism might represent a target for EtOH-induced developmental neurotoxicity.

Brain growth deficits following a single day of alcohol exposure in the neonatal rat

Alcohol (7.5 g/kg) was administered to neonatal rats in a single day via artificial rearing procedures, being given in four consecutive feedings spaced two hours apart on either postnatal day 4, 5, or 6. These single days of alcohol exposure resulted in high peak blood alcohol concentrations (mean peak BACs of 380, 439 and 460 mg/dl, respectively) and significantly restricted brain weight when measured on postnatal day 10. The cerebellum was affected more than total brain, forebrain or brain stem. Additionally, growth of the cerebellum was more stunted by alcohol exposure on either day 4 or 5 than when the alcohol exposure occurred on day 6. Small but significant delays in body growth occurred 1-2 days after the alcohol exposure for each group. The interference with brain growth following high BACs for a short period of time has important clinical and experimental implications related to binge drinking and the mechanisms underlying alcohol-induced effects on the developing brain.

Synaptogenesis in the hippocampal dentate gyrus: effects of in utero ethanol exposure

In animal models of Fetal Alcohol Syndrome, ethanol causes a number of changes in brain development, with many of these changes being very transient. This is especially true for the process of synaptogenesis in different brain areas. Our quantitative electron microscopic study of synaptogenesis in the molecular layer of the rat dentate gyrus supports the above statement, by demonstrating that ethanol has no effect on the appearance of synapses in the dentate gyrus during early postnatal life (10-30 days old). However, prenatal ethanol exposure does appear to affect the process of synapse turnover, which is indicated by the significantly delayed appearance of complex (curved) synapses and multiple synaptic contacts on single axonal terminals. Efficient synapse turnover is thought to be required for the normal maintenance of neuronal plasticity, which in turn ensures an animal's ability to respond to novel environments, tasks and injuries. It would seem that the prenatal neurotoxicology of ethanol may manifest itself by more subtle mechanisms at sites of structural and functional importance.

Differential deficits in regional brain growth induced by postnatal alcohol

Neonatal rats were exposed to alcohol during a period of brain development equivalent to part of the human third trimester. Rat pups were fed a milk formula containing either alcohol (9.8 g/kg/day) or isocaloric maltose/dextrin using artificial rearing techniques from postnatal days 4-10. Blood alcohol concentrations reached 345.8 +/- 15.6 mg/dl on postnatal day 6. All animals, including a group of normally reared suckle controls, were sacrificed on postnatal day 10, and the brains were perfused and processed for the Timm histochemical technique. Significant microencephaly (30% reduction in brain growth) was found in the alcohol-exposed animals. Growth deficits also were found in specific brain regions of the alcohol-exposed rats. The overall area of the hippocampus proper at a midtemporal level was reduced by 26.1% compared to controls. Sublaminae within the hippocampus were stunted as much as 40.5%. An overall reduction of 14.5% was found in the midsagittal (vermal) cerebellum. In contrast, growth of the dentate gyrus appeared much less affected (6.8% deficit) by the alcohol exposure. These data indicate that not all regions of the brain are affected equally by alcohol exposure during the third trimester equivalent.

Age-dependent susceptibility of rat cerebellar Purkinje cells to ethanol exposure

It is known that a proportion of cerebellar Purkinje cells do not complete development in the normal rat. In this study neonatal rat pups were treated at various stages of Purkinje cell development with ethanol vapour. We observed an increased rate of Purkinje cell loss at postnatal day 3, yet identically treated littermates had a normal complement of Purkinje cells compared to age-matched controls at 47 days of age. Single day ethanol exposures during Purkinje cell ontogenesis seems to accelerate a natural loss of Purkinje cells without a permanent loss persisting to adult life.