TOPOLOGY AND IMMUNOHISTOCHEMISTRY OF PROTON-SENSITIVE NEURONS IN THE VENTRAL MEDULLARY SURFACE OF RATS

We aimed to clarify the topology and immunohistochemistry of CO2/H+-se nsitive neurons in the ventral medullary surface (VMS), the central ch emoreceptor area in rats. Inhalation of 3 and 7% CO2 in air significan tly decreased pH in arterial blood and increased p(a)CO(2), which caus ed hyperpneic and tachypneic responses. Following inhalation of 3 and 7% CO2 in air for 5 min, the density of c-Fos-immunonactive (IR) neuro ns increased stepwise not only in the 3rd-5th divisions of the VMS (be tween the caudal end of the nucleus corporis trapezoidei and the cauda l end of the area postrema), but also in the rostroventromedial medull a (RVMM). Following inhalation of 7% CO2 in air for 5 min, glutamate-, glutamic acid decarboxylase (GAD)-, calcineurin-and cAMP-IR neurons w ere found not only in the VMS, but also in the RVMM. The topology of t hese neurons was similar to that of the c-Fos-IR neurons. No immunorea ctivity was found for serotonin, substance P, somatostatin, cholecysto kinin-octapeptide, methionine-enkephalin, choline acetyltransferase, t yrosine hydroxylase, phenylethanolamine N-methyltransferase, NO-syntha se, S-100, calbindin-D, calmodulin, or parvalbumin. The densities of c -Fos-, glutamate-, GAD-, calcineurin-and cAMP-IR neurons were almost z ero in the Ist division of the VMS, but became higher along the 2nd-4t h divisions of the VMS. Regression lines of the density against the 1s t-4th divisions of the VMS were significantly linear. These results in dicate that H+-sensitive neurons are common in the 4th-5th divisions o f the VMS, and that they are glutamatergic, GABAergic, and containing calcineurin and cAMP. (C) 1998 Elsevier Science B.V.