Early postnatal alcohol exposure produced long-term deficits in brain weight, but not the number of neurons in the locus coeruleus

Long-Term Neurobehavioral Consequences of a Single Ketamine Neonatal Exposure in Rats: Effects on Cellular Viability and Glutamate Transport in Frontal Cortex and Hippocampus

The neonatal exposure to general anesthetics has been associated with neuronal apoptosis and dendritic spines morphologic changes in the developing brain. Ketamine, a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, is widely used in pediatric patients to induce general anesthesia, analgesia, and perioperative sedation. In the present study, we investigated short- and long-term effects of a single ketamine (20 mg/kg, s.c.) neonatal exposure at postnatal day 7 in rats on the hippocampal and frontal cortical cellular viability. Additionally, putative neurochemical alterations and neurobehavioral impairments were evaluated in the adulthood. Ketamine neonatal administration selectively decreased cellular viability in the hippocampus, but not in the frontal cortex, 24 h after the treatment. Interestingly, a single ketamine neonatal exposure prevented the vulnerability to glutamate-induced neurotoxicity in the frontal cortex of adult rats. No short- or long-term damage to cellular membranes, as an indicative of cell death, was observed in hippocampal or cortical slices. However, ketamine induced a long-term increase in hippocampal glutamate uptake. Regarding behavioral analysis, neonatal ketamine exposure did not alter locomotor activity and anxiety-related parameters evaluated in the open-field test. However, ketamine administration disrupted the hippocampal-dependent object recognition ability of adult rats, while improved the motor coordination addressed on the rotarod. These findings indicate that a single neonatal ketamine exposure induces a short-term reduction in the hippocampal, but not in cortical, cellular viability, and long-term alterations in hippocampal glutamate transport, improvement on motor performance, and short-term recognition memory impairment.

Attention-Deficit/Hyperactivity Disorder: Focus upon Aberrant N-Methyl-D-Aspartate Receptors Systems

Attention-deficit/hyperactivity disorder (ADHD) pathophysiology persists in an obscure manner with complex interactions between symptoms, staging, interventions, genes, and environments. Only on the basis of increasing incidence of the disorder, the need for understanding is greater than ever. The notion of an imbalance between central inhibitory/excitatory neurotransmitters is considered to exert an essential role. In this chapter, we first review how the default mode network functions and dysfunction in individuals diagnosed with ADHD. We also present and briefly review some of the animal models used to examine the neurobiological aspects of ADHD. There is much evidence indicating that compounds/interventions that antagonize/block glutamic acid receptors and/or block the glutamate signal during the "brain growth spurt" or in the adult animal may induce functional and biomarker deficits. Additionally, we present evidence suggesting that animals treated with glutamate blockers at the period of the "brain growth spurt" fail to perform the exploratory activity, observed invariably with control mice, that is associated with introduction to a novel environment (the test cages). Later, when the control animals show less locomotor and rearing activity, i.e., interest in the test cages, the MK-801, ketamine and ethanol treated mice showed successively greater levels of locomotion and rearing (interest), i.e., they fail to "habituate" effectively, implying a cognitive dysfunction. These disturbances of glutamate signaling during a critical period of brain development may contribute to the ADHD pathophysiology. As a final addition, we have briefly identified new research venues in the interaction between ADHD, molecular studies, and personality research.

Fetal exposure to moderate ethanol doses: heightened operant responsiveness elicited by ethanol-related reinforcers

BACKGROUND

Prenatal exposure to moderate ethanol doses during late gestation modifies postnatal ethanol palatability and ingestion. The use of Pavlovian associative procedures has indicated that these prenatal experiences broaden the range of ethanol doses capable of supporting appetitive conditioning. Recently, a novel operant technique aimed at analyzing neonatal predisposition to gain access to ethanol has been developed. Experiment 1 tested the operant conditioning technique for developing rats described by Arias and colleagues (2007) and Bordner and colleagues (2008). In Experiment 2, we analyzed changes in the disposition to gain access to ethanol as a result of moderate prenatal exposure to the drug.

METHODS

In Experiment 1, newborn pups were intraorally cannulated and placed in a supine position that allowed access to a touch-sensitive sensor. Paired pups received an intraoral administration of a given reinforcer (milk or quinine) contingent upon physical contact with the sensor. Yoked controls received similar reinforcers only when Paired pups activated the circuit. In Experiment 2, natural reinforcers (water or milk) as well as ethanol (3% or 6% v/v) or an ethanol-related reinforcer (sucrose compounded with quinine) were tested. In this experiment, pups had been exposed to water or ethanol (1 or 2 g/kg) during gestational days 17 to 20.

RESULTS

Experiment 1 confirmed previous results showing that 1-day-old pups rapidly learn an operant task to gain access to milk, but not to gain access to a bitter tastant. Experiment 2 showed that water and milk were highly reinforcing across prenatal treatments. Furthermore, general activity during training was not affected by prenatal exposure to ethanol. Most importantly, prenatal ethanol exposure facilitated conditioning when the reinforcer was 3% v/v ethanol or a psychophysical equivalent of ethanol's gustatory properties (sucrose-quinine).

CONCLUSIONS

The present results suggest that late prenatal experience with ethanol changes the predisposition of the newborn to gain access to ethanol-related stimuli. In conjunction with prior literature, this study emphasizes the fact that intrauterine experience with ethanol not only augments ethanol's palatability and ingestion, but also facilitates the acquisition of response-stimulus associations where the drug acts as an intraoral reinforcer.

Early postnatal alcohol exposure reduced the size of vibrissal barrel field in rat somatosensory cortex (SI) but did not disrupt barrel field organization

Prenatal alcohol exposure (PAE) has been shown to alter the somatosensory cortex in both human and animal studies. In rodents, PAE reduced the size, but not the pattern of the posteromedial barrel subfield (PMBSF) associated with the representation of the whiskers, in newborn, juvenile, and adult rats. However, the PMBSF is not present at birth, but rather first appears in the middle of the first postnatal week during the brain-growth spurt period. These findings raise questions whether early postnatal alcohol exposure might disrupt both barrel field pattern and size, questions that were investigated in the present study. Newborn Sprague-Dawley rats were assigned into alcohol (Alc), nutritional gastric control (GC), and suckle control (SC) groups on postnatal day 4 (P4). Rat pups in Alc and GC were artificially fed with alcohol and maltose-dextrin dissolved in milk, respectively, via an implant gastrostomy tube, from P4 to P9. Pups in the Alc group received alcohol (6.0 g/kg) in milk, while the GC controls received isocaloric equivalent maltose-dextrin dissolved in milk. Pups in the SC group remained with their mothers and breast fed throughout the experimental period. On P10, pups in each group were weighed, sacrificed, and their brains removed and weighed. Cortical hemispheres were separated, weighed, flattened, sectioned tangentially, stained with cytochrome oxidase, and PMBSF measured. The sizes of barrels and the interbarrel septal region within PMBSF, as well as body and brain weights were compared between the three groups. The sizes of PMSBF barrel and septal areas were significantly smaller (P<.01) in Alc group compared to controls, while the PMBSF barrel pattern remained unaltered. Body, whole-brain, forebrain, and hemisphere weights were significantly reduced (P<.01) in Alc pups compared to control groups. GC and SC groups did not differ significantly in all dependent variables, except body weight at P9 and P10 (P<.01). These results suggest that postnatal alcohol exposure, like prenatal exposure, significantly influenced the size of the barrel field, but not barrel field pattern formation, indicating that barrel field pattern formation consolidated prior to P4. These results are important for understanding sensorimotor deficits reported in children suffering from fetal alcohol spectrum disorder (FASD).

Neurofunctional deficits and potentiated apoptosis by neonatal NMDA antagonist administration

The early postnatal brain development, when many potentially sensitive processes occur, has been shown to be vulnerable to different pharmacological and environmental compounds. In the present investigation, four groups of neonatal NMRI male mice were administered the glutamate NMDA receptor antagonist ketamine (50 mg/kg, s.c.), or the GABA(A) receptor agonist diazepam (5 mg/kg, s.c.), or co-administered ketamine (50 mg/kg, s.c.) and diazepam (5 mg/kg, s.c.), or vehicle (0.9% saline, s.c.) on day 10 after birth. On day 11, mice from each treatment group were sacrificed and brains were taken for analysis of neuronal cell degeneration, using Fluoro-Jade staining technique. Ketamine, but not diazepam, induced a severe degeneration of cells in the parietal cortex. The opposite was observed for diazepam in the laterodorsal thalamus. The most pronounced cell degeneration was seen in parietal cortex of mice exposed to both ketamine and diazepam. At 2 months of age each treatment group was tested for motor activity and learning performance. Ketamine and ketamine + diazepam treated mice displayed severe deficits of habituation to the test chamber in the spontaneous motor activity test, marked deficits of acquisition learning and retention memory in the radial arm maze-learning task and less shift learning in the circular swim maze-learning task. This study indicates that the observed functional deficits can be related to cell degeneration induced during a critical stage of neonatal brain development. The potentiated apoptosis induced by ketamine and diazepam may have implications for the selection of drugs used in neonatal paediatric anaesthesia.

Spatial acquisition in the Morris water maze and hippocampal long-term potentiation in the adult guinea pig following brain growth spurt–prenatal ethanol exposure

Previous work has demonstrated that in the guinea pig, chronic prenatal ethanol exposure throughout gestation can result in deficits in spatial learning in the Morris water maze and impaired hippocampal long-term potentiation (LTP). The behavioural effects are known to be dose dependent because water maze deficits occur at a dose of 4 g ethanol/kg maternal body weight/day, but not at a dose of 3 g/kg/day, administered throughout gestation. It is possible that the gradual, progressive development of tolerance to ethanol throughout gestation limits ethanol toxicity, especially for lower doses of ethanol. The present study examined whether neurobehavioural deficits are produced by prenatal ethanol exposure at a dose of 3 g/kg/day, administered only during the brain growth spurt (BGS), a regimen designed to limit the development of ethanol tolerance. Pregnant guinea pigs [term, about gestational day (GD) 68] received oral administration of ethanol (1.5 g/kg maternal body weight/day on GD 43 and 44 and then 3 g/kg maternal body weight/day from GD 45 to 62), isocaloric-sucrose/pair-feeding, or water. Offsprings were studied between postnatal days (PD) 40 and 80. The maternal blood ethanol concentration (BEC) on GD 57 or 58, at 1 h after the daily dose, was 245+/-19 mg/dl (n=7). This BGS--prenatal ethanol exposure regimen did not affect spatial learning performance in the Morris water maze over a 7-day test period or in the LTP recorded in the CA1 region of the hippocampus. Thus, even when limiting the development of ethanol tolerance seen with chronic ethanol treatment throughout gestation, ethanol exposure during the BGS does not result in deficits in the behavioural and electrophysiological measures of hippocampal integrity assessed in the present study. These data indicate that in the guinea pig, the BGS may not constitute a critical period of vulnerability for ethanol-induced deficits in spatial learning or hippocampal synaptic plasticity in young adult offspring.

Neurobehavioural deficits associated with apoptotic neurodegeneration and vulnerability for ADHD

Several studies involving postnatal administration of the N-methyl-D-aspartate (NMDA) antagonists, dizocilpine (MK-801; 3 x 0.5 mg/kg, at 08.00, 16.00 and 24.00 h) on Postnatal day 11, or Ketamine (1 x 50 mg/kg) or Ethanol (1 x 2.5 g/kg, Ethanol-Low, or 2 x 2.5 g/kg, 2-h interval, Ethanol-High) on Postnatal day 10, are described. Some mice from each treatment/vehicle group were sacrificed 24 h after NMDA antagonist treatment and brain regions were taken for fluoro-jade staining analysis. Functional analysis was initiated at 60 days of age. All three treatments inducing an antagonistic action at NMDA receptors, MK-801, Ketamine and Ethanol-High induced a similar pattern of initial hypoactivity followed by marked and lasting hyperactivity in the motor activity test chambers. In each case, the basal hyperactivity level was abolished by acute treatment with a low dose of D-amphetamine (0.25 mg/kg). All three treatments, MK-801, Ketamine and Ethanol-High, induced a deficit in acquisitive performance in the radial arm maze test of instrumental learning. The deficit induced by postnatal MK-801 was abolished by acute treatment with the low dose of D-amphetamine. All three treatments, MK-801, Ketamine and Ethanol-High, resulted in normal acquisitive performance during the first three test days in the circular swim with the submerged platform maintained in a constant position, but on the fourth test day, with the platform position shifted to a different "quadrant", induced marked deficits. Fluoro-jade staining analyses indicated a devastating cell degeneration in several brain regions of mice administered NMDA antagonists postnatally, including the hippocampus, frontal cortex, parietal cortex, and cerebellum. Severe cell degeneration in the laterodorsal thalamus due to Ethanol or diazepam (5 mg/kg) appeared not to affect the different aspects of function. The pattern of dysfunctional outcome and apoptotic cell loss following postnatal NMDA antagonist treatment offers a plausible similarity to the major aspects of 'syndromatic continuity' in ADHD, hyperactivity, inattention and impulsivity, thereby providing an interesting animal model of the disorder.

Fetal alcohol exposure and temporal vulnerability: effects of binge-like alcohol exposure on the developing rat hippocampus

Children with fetal alcohol syndrome (FAS) display altered performance in tasks of learning and memory, behaviours thought to be associated with the hippocampus. Altered hippocampal structure has been reported in some FAS children; therefore, a rat model system was used to determine whether the size and numbers of pyramidal cells in regions CA1 and CA3 of the hippocampal formation and granule cells in the dentate gyrus were altered by alcohol exposure during different periods of development. Rat pups were exposed to alcohol in utero during the second trimester-equivalent (E10-20), the first two trimesters-equivalent (E1-20), during the time of hippocampal pyramidal cell neurogenesis (E16-20), part of the third trimester-equivalent (P4-9), and all three trimesters-equivalent (E1-20+P4-9). Control animals (nutritional and untreated) were reared for all treatment conditions. All pups were perfused on P10. CA1 volume, pyramidal cell density, and number were reduced in pups treated with alcohol during the third trimester-equivalent, whether unique or as exposure during all three trimesters-equivalent. CA3 volume was reduced in alcohol-treated animals across all gestational ages; however, pyramidal cell density and number in this region were only reduced in animals treated with alcohol during the third trimester-equivalent. Volume of the dentate gyrus did not appear to be affected by alcohol treatment. Granule cell density and number in this region were reduced in animals treated with alcohol during the third trimester-equivalent. The third trimester-equivalent in the rat appears to be a developmental period during which the hippocampus is particularly susceptible to the effects of alcohol consumption. The resulting damage to the hippocampus may contribute to the behavioural deficits related to learning and memory noted in children with FAS.

Alcohol and nutritional control treatments during neurogenesis in rat brain reduce total neuron number in locus coeruleus, but not in cerebellum or inferior olive

Although a significant amount of progress has been made during the past two decades in determining the effects of alcohol on brain development, there is still a gap in the literature in terms of when the neurons in the brain are more or less vulnerable to the deleterious effects of alcohol. Using a rat model system, we examined the effect of alcohol on the development of three brain regions after exposure to alcohol only during the period of neurogenesis of each specific region. Our working hypothesis was that all three regions would be equally vulnerable to alcohol-induced reductions in neuron number after exposure during neurogenesis. The Purkinje cells of the cerebellum and the neurons of the locus coeruleus and inferior olive were chosen for examination because of their functional relation to the neuroanatomical circuit for motor coordination and gait, which is disrupted in children exposed to alcohol during gestation. Groups of timed-pregnant Sprague-Dawley rats were administered alcohol or nutritional control substitute daily by gavage during the period of neurogenesis for each region, or they were given no treatments. On postnatal day 10, neuron counts were derived from the three regions of the offspring brains by using stereological cell-counting techniques. The number of neurons in the locus coeruleus was reduced in both the alcohol- and nutritional control-treated groups relative to findings for the normal control group. There was no similar reduction in neuron number in the Purkinje cells of the cerebellum, nor in the neurons of the inferior olive, among the treatment groups. These results demonstrate that the period of neurogenesis is not a uniformly vulnerable period for the three brain regions tested, and the findings support the suggestion of a possible avenue for examining the underlying explanation for why some regions are more vulnerable than other regions during various phases of neuronal development.

Hyperactivity following postnatal NMDA antagonist treatment: reversal by D-amphetamine

Three experiments were performed to study the effects of neonatal administration of glutamate receptor antagonists, on either Day 11 (dizocilpine = MK-801, 3 x 0.5 mg/kg, s.c., injected at 0800, 1600 and 2400 h) or Day 10 (Ketamine, 1 x 50 mg/kg, s.c., or Ethanol-Low, 1 x 2.5 mg/kg, or, Ethanol-High, 2 x 2.5 mg/kg, s.c., with 2-h interval) to male mice pups, on spontaneous motor behavior, habituation to a novel situation and D-amphetamine-induced activity in the adult animals. Mice administered MK-801 showed initial hypoactivity followed by hyperactivity over the later (20-40 and 40-60 min) periods of testing. Mice administered Ketamine and Ethanol-High similarly displayed an initial hypoactivity followed by hyperactivity over the later time (20-60 min) of testing. Habituation to the novel activity test chambers was reduced drastically in the MK-801 mice compared with vehicle-treated mice. Similarly, mice administered Ketamine and Ethanol-High displayed too drastically reduced habituation behavior. The low dose of D-amphetamine (0.25 mg/kg) reduced the hyperactivity of neonatal MK-801-treated mice, particularly from 30-60 min onwards, and elevated the activity level of the vehicle-treated mice. Similarly, the low dose of D-amphetamine (0.25 mg/kg) reduced the hyperactivity of neonatally Ketamine-treated and Ethanol-High-treated mice, particularly from 30-60 min onwards, and elevated the activity level of the respective vehicle-treated mice. Fluoro-jade staining per mm(2) regional brain tissue of MK-801 mice pups expressed as percent of vehicle mice pups showed also that the extensiveness of staining was markedly greater in the parietal cortex, hippocampus, frontal cortex, and lesser so in the laterodorsal thalamus. Ketamine-treated mice showed cell degeneration mainly in the parietal cortex, whereas the Ethanol-High mice showed marked cell degeneration in both the parietal and laterodorsal cortex. The present findings that encompass a pattern of regional neuronal degeneration, disruptions of spontaneous motor activity, habituation deficits and reversal of hyperactivity by a low dose of D-amphetamine suggest a model of Attention Deficit Hyperactivity Disorder that underlines the intimate role of N-methyl-D-aspartate (NMDA) receptors in the developing brain.

Abnormal postnatal ontogeny of the locus coeruleus in the epileptic mutant mouse quaking

The tonic-clonic convulsions of the quaking mutant mice have been shown to be associated with the hyperplasia of the nucleus locus coeruleus, the origin of most brain noradrenergic neurons. In the present study, the postnatal ontogeny of the locus coeruleus has been studied by tyrosine hydroxylase immunolabeling in the mutant mice quaking and their controls at postnatal days 1, 30 and 90. In the control mice, the number of immunoreactive neuronal cell bodies increased significantly in the rostral half of the locus coeruleus between birth and postnatal day 30, while it decreased significantly in the caudal half between birth and adulthood. Thus, during postnatal maturation, the distribution of locus coeruleus neurons was shifted in the rostral direction. In the quaking mutant mice, while the increase of immunolabeling between birth and postnatal day 30 was observed in the rostral half of the locus coeruleus, no diminution could be found in the caudal half between birth and adulthood. As a result, the rostral shift of tyrosine hydroxylase immunoreactivity was not observed. Consequently, in adult mice, the caudal part of the mutants locus coeruleus appeared to contain significantly more neurons than the corresponding region in the controls. These results indicate that the hyperplasia of the locus coeruleus of the quaking mice that we had previously reported results from an alteration of the postnatal maturation of this nucleus. This developmental abnormality might be a primary determinant of the inherited epilepsy of the quaking mutant mice.

Estudo estereológico das células de Purkinje cerebelares submetidas à intoxicação alcoólica em ratos Wistar

MOTIVO DO ESTUDO: Analisar o efeito do álcool sobre as células de Purkinje de ratos. MÉTODO: Ratos Wistar receberam oralmente soluções alcoólicas em diferentes concentrações 4%, 12% e 24%. Os animais foram sacrificados com 4, 8 e 12 semanas e os cerebelos foram clivados em cortes aleatórios e uniformemente isotrópicos e incluídos em parafina. Cortes de 6µm (H & E) foram analisados por estereologia. RESULTADOS: As diferenças entre a densidade por área e densidade de superfície das células de Purkinje de todos os grupos experimentais (E) e os respectivos controles (C) foram significativas. Com 12 semanas, a densidade volumétrica da célula de Purkinje diminuiu entre os grupos C e E nas concentrações de 4% e 12%, mas não para a concentração de 24%, provavelmente devido a menor ingestão de líquido pelos animais. CONCLUSÃO: O álcool exerceu efeito tóxico sobre o corpo celular da célula de Purkinje nas três concentrações estudadas a partir de 4 semanas.