Brainstem projections to the ventromedial medulla in cat: Retrograde transport horseradish peroxidase and immunohistochemical studies

Stimulation of the nucleus magnocellularis (NMC) of the medulla produces ch anges in locomotion, muscle tone, heart rate, and blood pressure. Glutamate rgic input has been found to modulate muscle tone, whereas cholinergic inpu t has been found to mediate cardiovascular changes produced by stimulation of the NMC. The current study was designed to identify the brainstem affere nts to NMC by using retrograde transport of wheat germ agglutinin and horse radish peroxidase (WGA-HRP) combined with glutamate and choline acetyltrans ferase (ChAT) immunohistochemical and nicotinamide adenine dinucleotide pho sphate-diaphorase (NADPH-d) histochemical techniques. Fifty nanoliters of 2 .5% WGA-HRP were microinjected into the NMC in the cat. A heavy density of WGA-HRP-labeled neurons was found in the ipsilateral mesencephalic reticula r formation (MRF), periaqueductal gray, Kolliker-Fuse nucleus, and pontis c entralis caudalis (PoC), in the contralateral pontis centralis oralis (PoO) , and bilaterally in the nucleus paragigantocellularis lateralis. A moderat e density of retrogradely labeled neurons was found in the ipsilateral side of the nuclei parvocellularis, retrorubral (RRN), PoO, and vestibular comp lex, in the contralateral PoC and nucleus gigantocellularis, and bilaterall y in the inferior vestibular nucleus. Retrograde KRP/glutamate-positive cel ls could be found throughout the brainstem, with a high percentage in RRN, PoO, PoC, and MRF. Double-labeled WGA-HRP/ChAT neurons were found in the pe dunculopontine nucleus. Double-labeled WGA-HRP/NADPH-d-positive neurons cou ld be seen in many nuclei of the brainstem, although the number of labeled neurons was small. The dense glutamatergic projections to the NMC support t he hypothesis that rostral brainstem glutamatergic mechanisms regulate musc le activity and locomotor coordination via the NMC, whereas the pontine cho linergic projections to the NMC participate in cardiovascular regulation. P ublished 1999 Wiley-Liss, Inc.dagger.