Catecholamines and serotonin in the caudal medulla of the rat: combined neurochemical-histofluorescence study.

The distribution of monoamine transmitters among the nuclei of the caudal medulla was determined through the combined use of the Falck-Hillarp histofluorescence method for cellular localization of catecholamines and serotonin and quantitative micropunch neurochemical assays of norepinephrine (NE), dopamine (DA) and 5-hydroxytryptamine (5-HT) content using high performance liquid chromatography with electrochemical detection. These combined methods permit a direct correlation between neurotransmitter levels and fluorescent fiber and perikaryal profiles. Eight medullary nuclei were sampled: (1) dorsal motor nucleus of X and ventral nucleus solitarius, (2) the dorsomedial reticular formation, (3) the hypoglossal nucleus, (4) the ventromedial reticular formation, (5) the nucleus ambiguus, (6) nuclei raphe obscurus and pallidus, (7) the inferior olivary nucleus and (8) the descending (spinal) nucleus of V. Micropunched regions containing neurons which contribute projections to or receive sensory input from the vagus nerve were found to contain relatively high levels of NE, DA and 5-HT, consistent with the high density of catecholamine and 5-HT containing terminals observed in these nuclei. The dorsal motor nucleus of X and ventral nucleus solitarius contained the highest levels of NE, DA and 5-HT (218 +/- 10, 31 +/- 2 and 75 +/- 8 pmole/mg protein, respectively), whereas the lowest of these amines were found in the descending (spinal) nucleus of V (28 +/- 1, 3.6 +/- 0.8 and 32 +/- 2 pmole/mg protein, respectively). In general the distribution of catecholamines and 5-HT determined by micropunch/microchemical assay agrees well with the distribution of monoamine terminals detected by fluorescence histochemical techniques.