C. Dean et al., DISTRIBUTION AND COLOCALIZATION OF 5-HYDROXYTRYPTAMINE, THYROTROPIN-RELEASING-HORMONE AND SUBSTANCE-P IN THE CAT MEDULLA, Neuroscience, 57(3), 1993, pp. 811-822
This study demonstrates the co-existence of three neurochemicals in ve
ntral medullary neurons of the cat utilizing fluorescence immunohistoc
hemistry. Neurons containing 5-hydroxytryptamine. thyrotropin-releasin
g hormone and substance P were identified within the rostrocaudal exte
nt of the medulla, specifically within the raphe pallidus and raphe ma
gnus and in the reticular formation of the ventrolateral medulla in th
e nucleus paragigantocellularis lateralis. Within the raphe pallidus t
he majority of 5-hydroxytroptamine-containing neurons were co-localize
d with thyrotropin-releasing hormone and substance P. However, in the
raphe magnus the majority of stained neurons contained 5-hydroxytrypta
mine and thyrotropin-releasing hormone but were devoid of substance P.
In the ventrolateral medulla two major populations of neurons were id
entified rostral to the inferior olivary nuclei, one containing 5-hydr
oxytryptamine and thyrotropin-releasing hormone, while a more lateral
group contained substance P alone. More caudally, at the level of the
inferior olives, the majority of 5-hydroxytryptamine-containing cells
also displayed immunoreactivity for thyrotropin-releasing hormone and
substance P. A consistent finding in both the ventromedial and ventrol
ateral regions of the medulla was a population of 5-hydroxytryptamine-
containing cells which did not stain for either thyrotropin-releasing
hormone or substance P. The functional role of co-localized neurochemi
cals remains unknown but co-existence of neurotransmitter substances i
n medullary neurons may allow for specific and multiple actions in the
spinal cord.