Shunji Izawa

Activity of neurons in the nucleus of the solitary tract of rats: effect of osmotic and mechanical stimuli

Patch-clamp recordings were used to examine the osmosensitivity and mechanosensitivity of neurons in the caudal part of the nucleus tractus solitarius in coronal slices from rat brain. Firing rates and membrane potentials were measured as slices were exposed to perfusate which varied in its osmolality and/or sodium concentration. In all cells tested, the responses to change in the sodium concentration of perfusate were duplicated by osmolality changes of sucrose or mannitol. When nucleus tractus solitarius cells were tested with changes in pressure applied via the pipette, responses to positive or negative pressure paralleled their responses to osmotic stimulation. We suggest that a mechanosensitive receptor exists on osmosensitive neurons within the nucleus tractus solitarius, and this receptor may be responsible for changes in the firing rate and membrane potential which occur in the nucleus tractus solitarius neurons.

Dopamine Receptor Presence in the Rat Area Postrema Identified by RT-PCR, Immunohistochemistry, and In Situ Hybridization

Abstract Dopamine (DA) is a major central nervous system (CNS) neurotransmitter with many important physiological activities. Investigations into the neuroanatomy and neurologic functions of the dopaminergic neural systems have generated much debate. Regarding neuroanatomy, physiological and pharmacological criteria have divided DA receptors into D1 and D2 subtypes. The genes encoding these subtypes have been cloned and classified into a D1 subfamily encompassing D1 and D5 receptors and a D2 subfamily with D2, D3, and D4. Based on the sequences of the cloned receptors, we prepared antibodies and riboprobes to elucidate the expression of the corresponding proteins and mRNAs in the rat area postrema (AP) by immunohistochemistry and in situ hybridization (ISH). The AP was obtained from adult male Sprague-Dawley rats undergoing brain surgery, and tissue samples were used for RT-PCR, immunohistochemistry, and ISH. The results showed that D2 and D5 receptors and their mRNAs exist in the rat AP. On the other hand, D1, D3, and D4 receptors and their mRNAs were not detected.