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

Takashi Suzuki, Kiyoshige Takayama, Mitsuhiko Miura

The aim of this study is to determine the distribution and projection of the medullary cardiovascular neurons that contain the neurotransmitters or the enzymes involved in cardiovascular regulation. Six male Wistar rats were used, and a mixture of WGA-HRP was injected into the depressor caudal ventrolateral medulla (D-CVLM) and the pressor rostral ventrolateral medulla(P-RVLM). Immunohistochemistry was performed to identify HRP-labelled neurons which were stained with antiserum to glutamate (GLU),glutamic acid decarboxylase(GAD),tyrosine hydroxylase(TH) or phenylethanolamine N-methyltransferase (PNMT). The investigators in this study counted all the single HRP-labeled and the double labeled neurons in the NTS, D-CVLM and P-RVLM either ipsilaterally or contralaterally to HRP injection. They found that: (1)the HRP/GLU-labeled neurons in the NTS project to both the D-CVLM and P-RVLM which indicates divergent excitatory projection, (2)the P-RVLM receives innervation from HRP/GLU- labeled neurons in the D-CVLM, while the D-CVLM receives innervation from HRP-GLU-labeled neurons in the P-RVLM indicating the mutual innervation,(3)the HRP/GAD- labeled neurons in both the CVLM and the NTS project to the P-RVLM indicating the convergent  inhibitory  projection,(4) there are projection of both  HRP/TH- and HRP/PNMT- labeled neurons  to the P-RVLM but they are much less than the HRP/GAD-labeled neurons projections to the P-RVLM .  From these results, they concluded that catecholaminergic  neurons paly a minor role in inhibition of the sympathetic activity of the RVLM neurons, the glutamatergic NTS neurons excite both the P-RVLM and D-CVLM neurons, and the GABA ergic NTS and CVLM neurons inhibit the P-RVLM neurons.