Distribution and projection of the medullary cardiovascular control neurons containing glutamate, glutamic acid decarboxylase, tyrosine hydroxylase and phenylethanolamine N-methyltransferase in rats

Abstract

This study was aimed at showing the distribution and projection of the medullary cardiovascular control neurons that contain a standard neurotransmitter or a related enzyme in the rat. A small amount of HRP was injected into either the depressor area of the caudal ventrolateral medulla (D-CVLM) or the pressor area of the rostral ventrolateral medulla (P-RVLM). Using an immunohistochemical method, we identified HRP-labelled neurons which were stained with antiserum to glutamate (Glu), glutamic acid decarboxylase (GAD), tyrosine hydroxylase (TH) or phenylethanolamine N-methyltransferase (PNMT). Our findings are summarized as follows. (1) The Glu-containing neurons in the nucleus tractus solitararii (NTS) project to the D-CVLM ( n=279, 100% assumed as a standard value) and P-RVLM ( n=225, 81% against the standard), indicating divergent excitatory projection. (2) The GAD-containing neurons in the NTS ( n=74, 27% against the standard) and CVLM ( n=70, 25% against the standard) project to the P-RVLM, indicating the convergent inhibitory projection. (3) The projections of the TH-containing neurons from the NTS ( n=19, 7% against the standard) and CVLM ( n=4, 1% against the standard) to the P-RVLM are weaker than those of the GAD-containing neurons, suggesting that the catecholaminergic neurons play a minor role in inhibition of the sympathetic activity of the P-RVLM neurons. These results suggest that the glutamatergic NTS neurons excite both the P-RVLM and D-CVLM neurons, and the γ-aminobutyric acid (GABA)ergic NTS and CVLM neurons inhibit the sympathetic activity of the P-RVLM neurons.