Neuroscience
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Review of the normally occurring neuronal patterns of the hippocampus suggests that the two principal cell types of the hippocampus, the pyramidal neurons and granule cells, are maximally active during different behaviors. Granule cells reach their highest discharge rates during theta-concurrent exploratory activities, while population synchrony of pyramidal cells is maximum during immobility, consummatory behaviors, and slow wave sleep associated with field sharp waves. Sharp waves reflect the summed postsynaptic depolarization of large numbers of pyramidal cells in the CA1 and subiculum as a consequence of synchronous discharge of bursting CA3 pyramidal neurons. ⋯ It is assumed that recurrent excitation during the population burst is strongest on those cells which initiated the population event. It is suggested that the strong excitatory drive brought about by the sharp wave-concurrent population bursts during consummatory behaviors, immobility, and slow wave sleep may be sufficient for the induction of long-term synaptic modification in the initiator neurons of the CA3 region and in their targets in CA1. In this two-stage model both exploratory (theta) and sharp wave states of the hippocampus are essential and any interference that might modify the structure of the population bursts (e.g. epileptic spikes) is detrimental to memory trace formation.
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The detailed organization of the corticostriate projection has been investigated in the brain of the rat using the technique of retrograde transport of horseradish peroxidase following the placement of small, iontophoretic injections of horseradish peroxidase conjugated to lectin throughout all major regions of the striatum (caudate-putamen, nucleus accumbens and olfactory tubercle). The results demonstrate that all major regions of the cerebral cortex project to the striatum on both sides of the brain with an ipsilateral predominance. The cells of origin of both the ipsilateral and contralateral corticostriate projections lie mainly in lamina V (especially lamina Va) with very small numbers in lamina III of the neocortex and mesocortex, and in the deep laminae of the allocortex. ⋯ Within each of these major projection systems there is a further organization, with the constituent parts of each major cortical region projecting to smaller longitudinal components of the major projection fields. Each neocortical area projects to a longitudinal region of the dorsal striatum (caudate-putamen): the sensory and motor areas project topographically onto the dorsolateral striatum such that the rostral sensorimotor cortex (head areas) projects to central and ventral regions and the more caudal sensorimotor cortex (limb areas) projects to dorsal regions of the dorsolateral striatum; the visual area projects to the dorsomedial striatum; and the auditory area projects to the medial striatum. Each mesocortical area projects to a longitudinal area of the striatum: the most posteromedial mesocortex (the retrosplenial area) projects to the dorsomedial striatum; more anterior and lateral parts of the mesocortex project to more ventral parts of the striatum: and the most lateral mesocortex (the agranular insular and perirhinal areas) project to the ventrolateral striatum.(ABSTRACT TRUNCATED AT 400 WORDS)
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[125I]Iodosulpride, a highly selective and sensitive probe for dopamine D-2 receptors, was used to study the expression of these receptors in binding studies performed on membranes and serial autoradiographic sections, throughout pre- and postnatal developmental periods. D-2 receptors were first detected autoradiographically in sensory and sympathetic ganglia at the embryonic age of 12 days, i.e. much earlier than in previous studies. In membrane binding studies, D-2 receptors were found to be modulated by guanylnucleotides as early as at embryonic day 15, suggesting that they were already functionally coupled to a regulatory G protein. ⋯ In areas of dopaminergic perikarya, e.g. substantia nigra and ventral tegmental area, where they largely correspond to somatodendritic autoreceptors, D-2 receptors appeared at embryonic days 17 and 21 respectively, i.e. 3-8 days after tyrosine hydroxylase immunoreactivity, suggesting that dopamine synthesis and release is not feedback regulated by autoreceptors at initial developmental stages. In areas where D-2 receptors are present in the absence of any established dopaminergic innervation (e.g. discrete layers of the hippocampus, cerebellum, parietal cortex or in cranial nerve nuclei), they generally appeared at a late stage, i.e. during the second or even the third postnatal week. Finally, there was transient and roughly concomitant expression of both D-2 receptors and tyrosine hydroxylase immunoreactivity in some areas such as spinal ganglia or the lateral ventricle floor, consistent with a possible development function of dopamine mediated by D-2 receptors.