Neuroscience
-
Taste receptor cells are primary sensory receptors utilized by the nervous system to detect the presence of gustatory stimuli in the oral cavity. These cells are particularly heterogeneous and may be divided into various subtypes based on morphological, histochemical, or physiological criteria. One example is the heterogeneous expression of neuropeptides, such as cholecystokinin and vasoactive intestinal polypeptide. ⋯ More remarkable was the observation that these two peptides displayed almost identical expression patterns with these signal transduction molecules, suggesting that peptides are not randomly expressed with relation to signal transduction molecules. This observation supports the hypothesis that peptides may play roles in transduction. Further physiological exploration will be required to elucidate the nature of these roles.
-
Comparative Study
Three-dimensional chemoarchitecture of the basal forebrain: spatially specific association of cholinergic and calcium binding protein-containing neurons.
The basal forebrain refers to heterogeneous structures located close to the medial and ventral surfaces of the cerebral hemispheres. It contains diverse populations of neurons, including the cholinergic cortically projecting cells that show severe loss in Alzheimer's and related neurodegenerative diseases. The basal forebrain does not display any cytoarchitectural or other structural features that make it easy to demarcate functional boundaries, a problem that allowed different investigators to propose different organizational schemes. ⋯ At a smaller scale, the different cell types within the cholinergic space occupy overlapping high-density cell clusters that are either chemically uniform or mixed. However, the cell composition of these high-density clusters is regionally specific. The proposed scheme of basal forebrain organization, using cell density or density relations as criteria, offers a new perspective on structure-function relationship, unconstrained by traditional region boundaries.
-
Comparative Study
Deeply located granule cells and mitral cells undergo apoptosis after transection of the central connections of the main olfactory bulb in the adult rat.
The main olfactory bulb (MOB) is the first relay station of the olfactory system: it receives afferents from sensory neurons and sends efferents to the primary olfactory cortex. The MOB also receives many centrifugal afferents from various regions. Transection of peripheral afferents to the MOB has been reported to induce cell death in granule cells. ⋯ The majority of the degenerating and TUNEL-positive cells were located in the deep, rather than the superficial, GCL. Immunohistochemistry for activated caspase-9 further supported the occurrence of apoptotic cell death in the mitral and deeply located granule cells. These results indicate that not only axotomized mitral cells, but also deeply located granule cells that were not directly injured, underwent apoptosis after transection of the central connections, and suggest that sensitivities to transection of the central connections differ among granule cells according to their depth in the GCL.
-
Current evidence suggests that behavioral sensitization to the chronic administration of levodopa (L-DOPA) to dopamine-depleted animals involves a plasticity of GABA-mediated signaling in output regions of the basal ganglia. The purpose of this study was to compare in adult rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion the effects of an acute or chronic (for 3 or 7 days) injection of L-DOPA on mRNA levels encoding for glutamic acid decarboxylase (GAD65 and GAD67) in the striatum and GABA(A) receptor alpha1, beta2 and gamma2 subunits in the substantia nigra, pars reticulata (SNr), by in situ hybridization histochemistry. In addition, immunostaining levels for the alpha1 subunit were examined in the SNr. ⋯ In addition, alpha1 immunostaining in the SNr was significantly decreased in rats injected for 7 days but not for 3 days or acutely with L-DOPA. Our results demonstrate that a chronic administration of L-DOPA results in a progressive increase in GAD and decrease in GABA(A) receptor expression in the striatum and SNr, respectively. They provide further evidence that behavioral sensitization and dyskinesia induced by a chronic administration of L-DOPA in an experimental model of Parkinson's disease is paralleled by a plasticity of GABA-mediated signaling in the SNr.
-
The present study was conducted to test the hypothesis that the peripheral 5-hydroxytryptamine (5-HT)2A receptor is involved in inflammatory hyperalgesia and production of noxious stimulus-induced neuronal activity at the level of the spinal cord dorsal horn. Intraplantar (i.pl.) injection of carrageenan dramatically reduced paw withdrawal latency to noxious heat (47 degrees C) and caused paw swelling. Pretreatment with ketanserin, a selective antagonist of 5-HT2A receptor, in the hindpaw produced dose-dependent inhibition of the hyperalgesia (0.5, 3 and 5 mug; i.pl.) with full relief at 5 mug. ⋯ Ketanserin (5 mug) markedly reduced carrageenan-induced FLI in all laminae of the dorsal horn. However, blockade of peripheral 5-HT1A receptors by (N-2-[4-(2-methoxyphenyl-1-piperazinyl] ethyl]-N-2-pyridinylcyclohexanecarboxamide at maximally effective doses (30 and 100 mug; i.pl.) did not alter carrageenan-induced hyperalgesia, edema or expression of FLI. The present study provided evidence at cellular level that the peripheral 5-HT2A receptor is preferentially involved in the development of thermal hyperalgesia in the carrageenan model of inflammation.