Neuroscience
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Comparative Study
Intrinsic collaterals of layer 6 Meynert cells and functional columns in primate V1.
Meynert cells are a distinct type of large neuron which project to area MT/V5 and to subcortical targets, including the superior colliculus. They have recently been shown to have extensive intrinsic collaterals spreading up to 8.0 mm within layer 6 of area V1 [J Comp Neurol 441 (2001) 134]. Using intrinsic signal imaging combined with tracer injections, this study investigates how Meynert cell collaterals are mapped in relation to the functional architecture of area V1 in macaque monkeys. ⋯ This contrasts with the same-eye bias previously reported for intrinsic collaterals of pyramidal neurons in layer 3. The suggestion is that the system of Meynert intrinsic collaterals is involved with binocular interactions over wide sectors of the visual field. This might be related to processes such as optic flow or, especially given the wide-field spread, even contour completion or interpolation.
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Although the major routes of dopamine metabolism seem to be established, at least in terminal regions such as the striatum, it is important to search for previously unknown metabolites and to investigate the relevance of previously suggested minor alternative pathways. An urgent issue is to verify and quantify the transformation of dopamine to putative toxic species, another is to further explore metabolism of dopamine located in cell bodies/dendrites, e.g. in the substantia nigra. We have developed a new method in order to widen the search for alternative metabolites of dopamine. ⋯ The method was used to evaluate the possibility that cytochrome P450 2E1 is involved in the metabolism of dopamine in the substantia nigra. Significant changes in the radioactivity pattern were induced by inhibition of the enzyme but conclusions about whether cytochrome P450 2E1 is involved in the metabolism of dopamine or not requires further studies. The method can be used to study the metabolism of dopamine and can be extended, by using other radiolabelled precursors, also to evaluate metabolism of other transmitters, e.g. serotonin.
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Comparative Study
Nociceptin/orphanin FQ knockout mice display up-regulation of the opioid receptor-like 1 receptor and alterations in opioid receptor expression in the brain.
The opioid receptor-like 1 receptor is a novel member of the opioid receptor family and its endogenous peptide ligand has been termed nociceptin and orphanin FQ. Activation of the opioid receptor-like 1 receptor by nociceptin/orphanin FQ in vivo produces hyperalgesia when this peptide is given supraspinally but analgesia at the spinal level. Nociceptin/orphanin FQ also reverses stress-induced analgesia, suggesting that the peptide has anti-opioid properties. ⋯ Mu-Receptors also showed significant differences between genotypes whilst changes in delta- and kappa- receptors were minor. In conclusion the region-specific up-regulation of the opioid receptor-like 1 receptor indicates a tonic role for nociceptin/orphanin FQ in some brain structures and may suggest the peptide regulates the receptor expression in these regions. The changes in the opioid receptor-like 1 receptor may relate to the anxiogenic phenotype of these animals but the observed change in mu-receptors does not correlate with altered morphine responses.
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Comparative Study
Brain afferents to the lateral caudal ventrolateral medulla: a retrograde and anterograde tracing study in the rat.
The ventrolateral medulla (VLM) modulates autonomic functions, motor reactions and pain responses. The lateralmost part of the caudal VLM (VLMlat) was recently shown to be the VLM area responsible for pain modulation. In the present study, the brain sources of VLMlat afferent fibers were determined by tract-tracing techniques. ⋯ The present study gives an account of the brain regions putatively involved in triggering the modulatory actions elicited from the VLMlat. These include areas committed to somatosensory processing, autonomic control, somatic and visceral motor activity and affective reactions. The findings suggest that the VLMlat may play a major homeostatic role in the integration of nociception with other brain functions.
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Comparative Study
Immunohistochemical localization of myosin Va in the adult rat brain.
Brain myosin Va (MVa) is a molecular motor associated with plastic changes during development. MVa has previously been detected in the cell body and in dendrites of neuronal cells in culture, in cells of the guinea-pig cochlea, as well as in cerebellar cells. Adult Wistar rats (n=14), 250-300 g, were perfused with standard methods for immunohistochemistry, using a polyclonal, affinity-purified rabbit antibody against MVa tail domain. ⋯ The analysis of MVa and glial fibrillary acidic protein staining in adjacent brain sections demonstrated a clear-cut neuronal labeling rather than an astroglial staining. The studies presented here represent a comprehensive map of MVa regional distribution in the CNS of the adult rat and may contribute to the basic understanding of its role in brain function and plasticity, particularly in relationship to phenomena that involve molecular motors, such as neurite outgrowth, organelle transport and neurotransmitter-vesicle cycling. It is important to highlight that this is a pioneer immunohistochemical study on the distribution of MVa on the whole brain of adult rats, a first step toward the understanding of its function in the CNS.