International journal of developmental neuroscience : the official journal of the International Society for Developmental Neuroscience
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Int. J. Dev. Neurosci. · Dec 2005
Comparative StudyPostnatal development of cholinergic neurons in the mesopontine tegmentum revealed by histochemistry.
Cholinergic neurons in the laterodorsal tegmental nucleus (LDT) and pedunculopontine tegmental nucleus (PPT) play a role in the regulation of several kinds of behavior. Some of them, such as locomotion, motor inhibition or sleep, show dramatic changes at a certain period of postnatal development. To understand the neural substrate for the development of these physiological functions, we studied the development of cholinergic neurons in the LDT and PPT of postnatal and adult rats using histochemical staining of NADPH-diaphorase (NADPH-d) and immunohistochemical staining of choline acetyltransferase (ChAT) and the vesicular acetylcholine transporter (VAChT). ⋯ The volume of the LDT increased during the second postnatal week. These findings indicate that cholinergic neurons in the LDT develop their cholinergic properties during the second postnatal week and mature functionally thereafter. We discuss these results in light of the several physiological functions regulated by the cholinergic neurons in the mesopontine tegmentum.
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Int. J. Dev. Neurosci. · Nov 2005
Developmental lead exposure impairs contextual fear conditioning and reduces adult hippocampal neurogenesis in the rat brain.
The effects of developmental lead exposure on the emotional reactivity, contextual fear conditioning and neurogenesis in the dentate gyrus of 60-80 days-old rats were studied. Wistar rat pups were exposed to 0.2% lead acetate via their dams' drinking water from postnatal day (PND) 1 to PND 21 and directly via drinking water from weaning until PND 30. At PND 60 and 80 the level of anxiety and contextual fear conditioning were studied, respectively. ⋯ A lower proportion of BrdU-positive cells co-expressed with the marker for mature neurons, calbindin. In contrast, the proportions of young not fully differentiated neurons and proportions of astroglial cells, generated from newly born cells, were increased in lead-exposed animals. Our results demonstrate that developmental lead exposure induces persistent inhibition of neurogenesis and alters the pattern of differentiation of newly born cells in the dentate gyrus of rat hippocampus, which could, at least partly, contribute to behavioral and cognitive impairments observed in adulthood.
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Int. J. Dev. Neurosci. · Nov 2005
The role of neurotrophins in the maintenance of the spinal cord motor neurons and the dorsal root ganglia proprioceptive sensory neurons.
The aim of this study was to approach the question of neuronal dependence on neurotrophins during embryonic development in mice in a way other than gene targeting. We employed amyogenic mouse embryos and fetuses that develop without any skeletal myoblasts or skeletal muscle and consequently lose motor and proprioceptive neurons. ⋯ To test the role of the spinal cord and dorsal root ganglia tissues in the maintenance of its neurons, we performed immunohistochemistry employing double-mutant and control tissues and antibodies against neurotrophins and their receptors. Our data suggested that: (a) during the peak of motor neuron cell death, the spinal cord and dorsal root ganglia distribution of neurotrophins was not altered; (b) the distribution of BDNF, NT-4/5, TrkB and TrkC, and not NT-3, was necessary for the maintenance of the spinal cord motor neurons; (c) the distribution of BDNF, NT-4/5 and TrkC, and not NT-3 and Trk B, was necessary for the maintenance of the DRG proprioceptive neurons; (d) NT-3 was responsible for the maintenance of the remaining neurons and glia in the spinal cord and dorsal root ganglia (possibly via TrkB).
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Int. J. Dev. Neurosci. · Feb 2005
ReviewBehavioral and cellular consequences of increasing serotonergic activity during brain development: a role in autism?
The hypothesis explored in this review is that the high levels of serotonin in the blood seen in some autistic children (the so-called hyperserotonemia of autism) may lead to some of the behavioral and cellular changes also observed in the disorder. At early stages of development, when the blood-brain Barrier is not yet fully formed, the high levels of serotonin in the blood can enter the brain of a developing fetus and cause loss of serotonin terminals through a known negative feedback function of serotonin during development. The loss of serotonin innervation persists throughout subsequent development and the symptoms of autism appear. ⋯ Paraventricular nucleus of the hypothalamus, a brain region involved in social memory and bonding, where a decrease in oxytocin was found. Both of these cellular changes could result from loss of serotonin innervation, possibly due to loss of terminal outgrowth from the same cells of the raphe nuclei. Thus, increased serotonergic activity during development could damage neurocircuitry involved in emotional responding to social stressors and may have relevance to the symptoms of autism.
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Int. J. Dev. Neurosci. · Feb 2005
Comparative StudyMaturation of cultured hippocampal slices results in increased excitability in granule cells.
The preparation of hippocampal slices results in loss of input neurons to dentate granule cells, which leads to the reorganization of their axons, the mossy fibers, and alters their functional properties in long-term cultures, but its temporal aspects in the immature hippocampus are not known. In this study, we have focused on the early phase of this plastic reorganization process by analyzing granule cell function with field potential and whole cell recordings during the in vitro maturation of hippocampal slices (from 1 to 17 days in vitro, prepared from 6 to 7-day-old rats), and their morphology using extracellular biocytin labelling technique. Acute slices from postnatal 14-22-day-old rats were analyzed to detect any differences in the functional properties of granule cells in these two preparations. ⋯ Extracellularily applied biocytin labelled dentate granule cells, and revealed sprouting and aberrant targeting of mossy fibers in cultured slices. Our results suggest that reorganization of granule cell axons takes place during the early in vitro maturation of hippocampal slices, and contributes to their increased excitatory activity resembling that in the epileptic hippocampus. Cultured immature hippocampal slices could thus serve as an additional in vitro model to elucidate mechanisms of synaptic plasticity and cellular reactivity in response to external damage in the developing hippocampus.