Using choline acetyltransferase (ChAT) immunocytochemistry and acetylcholinesterase (AChE) histochemistry, we investigated regional and laminar differences in cholinergic innervation in the cerebral cortex, hippocampus, amygdala, and thalamus of mice. In mice, unlike rats, the patterns of ChAT-immunostained and AChE-positive fibers are virtually identical in the cortex and are organized in a trilaminar pattern with cholinergic processes prominent in layers I and IV and within the lower portion of layer V and upper segment of layer VI. ChAT-immunoreactive cells were not seen in cortex. In the amygdala, the basolateral nucleus showed the highest density of cholinergic processes. In the hippocampus, a thin, dense band of ChAT-labeled processes was present in the inner segment of the molecular layer of the dentate gyrus and within the stratum oriens of CA1-3, adjacent to the basal aspect of pyramidal cells. Within the thalamus, anteroventral, mediodorsal (lateral portion), intralaminar, and reticular nuclei showed high densities of cholinergic processes. The results of this study provide the basis for examining the effects of transgenes and age on forebrain cholinergic systems.

No abstract

No abstract

Autism is a developmental brain disorder characterized by deficits in social interaction, language and behavior. Brain imaging studies demonstrate increased cerebral cortical volumes and micro-and macroscopic neuroanatomic changes in children with this disorder. Alterations in forebrain serotonergic function may underlie the neuroanatomic and behavioral features of autism. Serotonin is involved in neuronal growth and plasticity and these actions are likely mediated via serotonergic and glutamatergic receptors. Few animal models of autism have been described that replicate both etiology and pathophysiology. We report here on a selective serotonin (5-HT) depletion model of this disorder in neonatal mice that mimics neurochemical and structural changes in cortex and, in addition, displays a behavioral phenotype consistent with autism. Newborn male and female mice were depleted of forebrain 5-HT with injections of the serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), into the bilateral medial forebrain bundle (mfb). Behavioral testing of these animals as adults revealed alterations in social, sensory and stereotypic behaviors. Lesioned mice showed significantly increased cortical width. Serotonin immunocytochemistry showed a dramatic long-lasting depletion of 5-HT containing fibers in cerebral cortex until postnatal day (PND) 60. Autoradiographic binding to high affinity 5-HT transporters was significantly but transiently reduced in cerebral cortex of 5,7-DHT-depleted mice. AMPA glutamate receptor binding was decreased at PND 15. We hypothesize that increased cerebral cortical volume and sensorimotor, cognitive and social deficits observed in both 5-HT-depleted animals and in individuals with autism, may be the result of deficiencies in timely axonal pruning to key cerebral cortical areas.

Multiple brain disorders that show serotonergic imbalances have a developmental onset. Experimental models indicate a role for serotonin as a morphogen in brain development. To selectively study the effects of serotonin depletions on cortical structural development and subsequent behavior, we developed a mouse model in which a serotonin neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), is injected into the medial forebrain bundle (mfb) on the day of birth. Littermates with saline injections into the mfb and age matched mice served as controls. This study characterized the extent and duration of serotonergic denervation after the selective neonatal lesion and investigated effects on exploratory behavior, spatial learning and anxiety in mice of both sexes. We report significant decreases in the serotonergic (5-HT) innervation to cortex and hippocampus, but not to subcortical forebrain structures in 5,7-DHT-lesioned mice. The depletion of 5-HT fibers in cortical areas was long lasting in lesioned mice but autoradiographic binding to high affinity 5-HT transporters was only transiently reduced. Male but not female lesioned mice reduced their exploration significantly in response to spatial rearrangement and object novelty, suggesting increased anxiety in response to change but normal spatial cognition. Our data show that developmental disruptions in the serotonergic innervation of cortex and hippocampus are sufficient to induce permanent, sex specific, behavioral alterations. These results may have significant implications for understanding brain disorders presenting with cortical morphogenetic abnormalities and altered serotonin neurotransmission, such as autism, schizophrenia and affective disorders.

No abstract

No abstract

The purpose of this study was to examine the behavioral performance in adult mice which, as neonates, had received lesions to cortically projecting, cholinergic basal forebrain neurons. The nucleus basalis magnocellularis (nBM) provides the primary cholinergic innervation to cerebral cortex. Lesions in the nBM in neonatal mice result in transient cholinergic denervation and persistent abnormalities in cortical morphology and cytoarchitecture. These cortical abnormalities resemble pathologies observed in a number of developmental disabilities in humans, including Down Syndrome. Balb/CByJ mice received lesions to the nBM 12-24 hr after birth; littermates served as controls. Behavioral testing began 8 weeks after the lesion and included assessments of spontaneous motor activity, retention (a passive avoidance task) and cognition (the Morris swim task). Following behavioral testing, a subset of mice was killed for Nissl and acetylcholinesterase (AChE) histology. The cortical morphology in these brains was evaluated and ranked by the experimenter, who was blind to the lesion and behavioral studies. The lesioned mice exhibited increased spontaneous activity as compared to littermate controls. The lesioned mice were also severely impaired in performance of the retention and cognitive task; they showed decreased passive avoidance retention latencies and increased swim maze latencies as compared to controls. The brains of all of the lesioned mice exhibited cortical morphological abnormalities that ranged from slight to severe. Cortical AChE intensity and distribution in the brains of the lesioned mice, however, were comparable to those of controls. In correlation studies of behavioral and morphological data, motor activity did not correlate with either passive avoidance retention or swim maze latencies. Additionally, cortical cytoarchitectural abnormalities did not correlate with motor activity. Cortical cytoarchitectural abnormalities did, however, correlate with both passive avoidance and swim maze latencies, i.e. severely abnormal cortical morphology predicted low passive avoidance retention latencies and high swim maze latencies. These data indicate that cortical cytoarchitectural abnormalities resulting from nBM lesions in neonates correlate with impairments on the cognitive task, but not with the activity measures, in adult mice. Thus, in this lesion model, and by extrapolation in developmental disabilities in humans, structural changes in the cortex which result from transient disruption of cortical cholinergic innervation may lead to persistent cognitive impairments in adulthood.