Lobeline attenuates neonatal ethanol-mediated changes in hyperactivity and dopamine transporter function in the prefrontal cortex in rats

CE-123, a novel dopamine transporter inhibitor, attenuates locomotor hyperactivity and improves cognitive functions in rat model of fetal alcohol spectrum disorders

Perinatal alcohol exposure can lead to fetal alcohol spectrum disorders (FASD), usually first diagnosed in childhood, that are characterized by hyperactivity, impulsivity and learning and memory disability, among others. To test the hypothesis that dopamine signaling is one of the main factors underlying these impairments, a new atypical dopamine transporter (DAT) inhibitor, CE-123 (1, 3 or 10 mg/kg) was assessed for its potential to overcome the ethanol-induced behavioral effects in a rat model of FASD. In the present study, neonatal rats were exposed to alcohol intubations across the neonatal period (postnatal day (PND)4-9, the third trimester equivalent of human gestation) and, after weaning, the animals (male rats) were assigned randomly to three groups. The first group was tested at PND21 (hyperactivity test). A second group was tested at PND45 (anxiety test), at PND47 (locomotor activity test), at PND49 (spatial cognitive test in the Barnes maze) and PND50 (reversal learning in the Barnes maze). The third group was tested at PND50 (dopamine receptor mRNA expression). Our results support the hypothesis that dopamine signaling is associated with FASD because the dopamine (D1, D2 and D5) receptor mRNA expression was altered in the striatum, hippocampus and prefrontal cortex in adult rats exposed to ethanol during neonatal period. CE-123 (3 and 10 mg/kg) inhibited the hyperactivity and ameliorated (10 mg/kg) the impairment of reversal learning in alcohol-exposed rats. Thus, these findings provide support that CE-123 may be a useful intervention for same of the deficits associated with neonatal ethanol exposure.

Mechanisms of context conditioning in the developing rat

The article reviews our studies of contextual fear conditioning (CFC) in rats during a period of development---Postnatal Day (PND) 17-33---that represents the late-infant, juvenile, and early-adolescent stages. These studies seek to acquire 'systems level' knowledge of brain and memory development and apply it to a rodent model of Fetal Alcohol Spectrum Disorder (FASD). This rodent model focuses on alcohol exposure from PND4-9, a period of brain development equivalent to the human third trimester, when neocortex, hippocampus, and cerebellum are especially vulnerable to adverse effects of alcohol. Our research emphasizes a variant of CFC, termed the Context Preexposure Facilitation Effect (CPFE, Fanselow, 1990), in which context representations incidentally learned on one occasion are retrieved and associated with immediate shock on a subsequent occasion. These representations can be encoded at the earliest developmental stage but seem not to be retained or retrieved until the juvenile period. This is associated with developmental differences in context-elicited expression, in prefrontal cortex, hippocampus, and amygdala, of immediate early genes (IEGs) that are implicated in long-term memory. Loss-of-function studies establish a functional role for these regions as soon as the CPFE emerges during ontogeny. In our rodent model of FASD, the CPFE is much more sensitive to alcohol dose than other commonly used cognitive tasks. This impairment can be reversed by acute administration during behavioral testing of drugs that enhance cholinergic function. This effect is associated with normalized IEG expression in prefrontal cortex during incidental context learning. In summary, our findings suggest that long-term memory of incidentally-learned context representations depends on prefrontal-hippocampal circuitry that is important both for the normative development of context conditioning and for its disruption by developmental alcohol exposure.

Chronic ethanol forced administration from adolescence to adulthood reduces cell density in the rat spinal cord

Ethanol (EtOH) consumption is a risk factor for central nervous system damage, especially during adolescence. This study aimed to investigate the possible effects of chronic EtOH forced administration on gray and white matter of the spinal cord, from adolescence to adulthood. For this, male Wistar rats were administered EtOH by gavage (6.5 g/kg/day; 22.5% w/v) from the 35th to the 90th day of life, while control animals received only distilled water. After exposure, animals were euthanized and their spinal cords processed to obtain cervical and thoracic segments for histological analyses. Quantitative analyses of total cell density and motor neurons of white and gray matter from the ventral horns were evaluated. Forced EtOH administration model showed a decrease in the motoneuron density in the spinal cord in both segments evaluated. Analyses of total cell density showed that the cervical segment was more susceptible to damages promoted by EtOH, with a significant decrease in cell density. Our results showed that chronic EtOH exposure during adolescence could promote injuries to the spinal cord, with neurodegeneration of motoneurons and other cell types present in neural parenchyma.

Prenatal Alcohol Exposure in Rodents As a Promising Model for the Study of ADHD Molecular Basis

A physiological parallelism, or even a causal effect relationship, can be deducted from the analysis of the main characteristics of the “Alcohol Related Neurodevelopmental Disorders” (ARND), derived from prenatal alcohol exposure (PAE), and the behavioral performance in the Attention-deficit/hyperactivity disorder (ADHD). These two clinically distinct disease entities, exhibits many common features. They affect neurological shared pathways, and also related neurotransmitter systems. We briefly review here these parallelisms, with their common and uncommon characteristics, and with an emphasis in the subjacent molecular mechanisms of the behavioral manifestations, that lead us to propose that PAE in rats can be considered as a suitable model for the study of ADHD.

Animal Models for Medication Development and Application to Treat Fetal Alcohol Effects

Ethanol consumption during pregnancy can have lifelong consequences for the offspring, their family and society. Fetal alcohol spectrum disorders (FASD) include a range of physical and behavioral effects with the most significant impact occurring as a result of the effects of ethanol on the developing central nervous system (CNS). To date, there are no FDA approved drugs that have been tested that prevent/reduce or specifically treat the symptoms of FASD. There are several promising lines of research from rodent models aimed at reducing the neurotoxic effects of ethanol on the developing CNS or in treating the resulting behavioral impairments but these have not yet moved to clinical testing. The current review discusses some of the most promising targets for intervention and provides a review of the past and ongoing efforts to develop and screen pharmacological treatments for reducing the effects of prenatal ethanol exposure.

Pax2-Islet1 Transgenic Mice Are Hyperactive and Have Altered Cerebellar Foliation

The programming of cell fate by transcription factors requires precise regulation of their time and level of expression. The LIM-homeodomain transcription factor Islet1 (Isl1) is involved in cell-fate specification of motor neurons, and it may play a similar role in the inner ear. In order to study its role in the regulation of vestibulo-motor development, we investigated a transgenic mouse expressing Isl1 under the Pax2 promoter control (Tg^+/−). The transgenic mice show altered level, time, and place of expression of Isl1 but are viable. However, Tg^+/− mice exhibit hyperactivity, including circling behavior, and progressive age-related decline in hearing, which has been reported previously. Here, we describe the molecular and morphological changes in the cerebellum and vestibular system that may cause the hyperactivity of Tg^+/− mice. The transgene altered the formation of folia in the cerebellum, the distribution of calretinin labeled unipolar brush cells, and reduced the size of the cerebellum, inferior colliculus, and saccule. Age-related progressive reduction of calbindin expression was detected in Purkinje cells in the transgenic cerebella. The hyperactivity of Tg^+/− mice is reduced upon the administration of picrotoxin, a non-competitive channel blocker for the γ-aminobutyric acid (GABA) receptor chloride channels. This suggests that the overexpression of Isl1 significantly affects the functions of GABAergic neurons. We demonstrate that the overexpression of Isl1 affects the development and function of the cerebello-vestibular system, resulting in hyperactivity.

Adenylyl cylases 1 and 8 mediate select striatal-dependent behaviors and sensitivity to ethanol stimulation in the adolescent period following acute neonatal ethanol exposure

Neonatal alcohol exposure in rodents causes dramatic neurodegenerative effects throughout the developing nervous system, particularly in the striatum, acutely after exposure. These acute neurodegenerative effects are augmented in mice lacking adenylyl cyclases 1 and 8 (AC1/8) as neonatal mice with a genetic deletion of both AC isoforms (DKO) have increased vulnerability to ethanol-induced striatal neurotoxicity compared to wild type (WT) controls. While neonatal ethanol exposure is known to negatively impact cognitive behaviors, such as executive functioning and working memory in adolescent and adult animals, the threshold of ethanol exposure required to impinge upon developmental behaviors in mice has not been extensively examined. Therefore, the purpose of this study was to determine the behavioral effects of neonatal ethanol exposure using various striatal-dependent developmental benchmarks and to assess the impact of AC1/8 deletion on this developmental progression. WT and DKO mice were treated with 2.5 g/kg ethanol or saline on postnatal day (P)6 and later subjected to the wire suspension, negative geotaxis, postural reflex, grid hang, tail suspension and accelerating rotarod tests at various time points. At P30, mice were evaluated for their hypnotic responses to 4.0 g/kg ethanol by using the loss of righting reflex assay and ethanol-induced stimulation of locomotor activity after 2.0 g/kg ethanol. Ethanol exposure significantly impaired DKO performance in the negative geotaxis test while genetic deletion of AC1/8 alone increased grid hang time and decreased immobility time in the tail suspension test with a concomitant increase in hindlimb clasping behavior. Locomotor stimulation was significantly increased in animals that received ethanol as neonates, peaking significantly in ethanol-treated DKO mice compared to ethanol-treated WT controls, while sedation duration following high-dose ethanol challenge was unaffected. These data indicate that the maturational parameters examined in the current study may not be sensitive enough to detect effects of a single ethanol exposure during the brain growth spurt period. Genetic deletion of AC1/8 reveals a role for these cylases in attenuating ethanol-induced behavioral effects in the neonatally-exposed adolescent.

Evaluation of mutagenic and genotoxic activities of lobeline and its modulation on genomic instability induced by ethanol

AIM

Lobeline is a natural alkaloid derived from Lobelia inflata that has been investigated as a clinical candidate for the treatment of alcoholism. In a pre-clinical trial, lobeline decreased the preference for and consumption of ethanol, due to the modulation of the nicotinic acetylcholine receptor. However, the interaction between lobeline and ethanol is poorly known and thus there are safety concerns. The present study was conducted to evaluate the mutagenic and genotoxic effects of lobeline and assess its modulation of ethanol-induced toxicological effects.

MAIN METHODS

CF-1 male mice were divided into five groups. Groups received an intraperitoneal injection of saline solution, lobeline (5 or 10mg/kg), ethanol (2.5 g/kg), or lobeline plus ethanol, once a day for three consecutive days. Genotoxicity was evaluated in peripheral blood using the alkaline comet assay. The mutagenicity was evaluated using both Salmonella/microsome assay in TA1535, TA97a, TA98, TA100, and TA102 Salmonella typhimurium strains and the micronucleus test in bone marrow. Possible liver and kidney injuries were evaluated using biochemical analysis.

KEY FINDINGS

Lobeline did not show genotoxic or mutagenic effects and did not increase the ethanol-induced genotoxic effects in blood. Lobeline also protected blood cells against oxidative damage induced by hydrogen peroxide. Biochemical parameters were not altered, indicating no liver or kidney injuries or alterations in lipid and carbohydrate metabolisms.

SIGNIFICANCE

These findings suggest that lobeline does not induce gene or chromosomal mutations, and that this lack of genetic toxicity is maintained in the presence of ethanol, providing further evidence of the safety of this drug to treat alcohol dependence.

Examination of age-dependent effects of fetal ethanol exposure on behavior, hippocampal cell counts, and doublecortin immunoreactivity in rats

Ethanol is known as a potent teratogen having adverse effects on brain and behavior. However, some of the behavioral deficits caused by fetal alcohol exposure and well expressed in juveniles ameliorate with maturation may suggest some kind of functional recovery occurring during postnatal development. The aim of this study was to reexamine age-dependent behavioral impairments in fetal-alcohol rats and to investigate the changes in neurogenesis and gross morphology of the hippocampus during a protracted postnatal period searching for developmental deficits and/or delays that would correlate with behavioral impairments in juveniles and for potential compensatory processes responsible for their amelioration in adults. Ethanol was delivered to the pregnant dams by intragastric intubation throughout 7-21 gestation days at daily dose of 6 g/kg. Isocaloric intubation and intact control groups were included. Locomotor activity, anxiety, and spatial learning tasks were applied to juvenile and young-adult rats from all groups. Unbiased stereological estimates of hippocampal volumes, the total number of pyramidal and granular cells, and double cortin expressing neurons were carried out for postnatal days (PDs) PD1, PD10, PD30, and PD60. Alcohol insult during second trimester equivalent caused significant deficits in the spatial learning in juvenile rats; however, its effect on hippocampal morphology was limited to a marginally lower number of granular cells in dentate gyrus (DG) on PD30. Thus, initial behavioral deficits and the following functional recovery in fetal-alcohol subjects may be due to more subtle plastic changes within the hippocampal formation but also in other structures of the extended hippocampal circuit. Further investigation is required.