MONOAMINES (NOREPINEPHRINE, DOPAMINE, SEROTONIN) IN THE RAT MEDIAL VESTIBULAR NUCLEUS - ENDOGENOUS LEVELS AND TURNOVER

Monoamine (norepinephrine, dopamine, serotonin) and metabolite endogen ous levels were determined in the rat medial vestibular nucleus (MVN) using HPLC with electrochemical detection. As a comparison, the locus coeruleus (LC) and dorsal raphe nucleus (RD) which contain the cell bo dies of MVN noradrenergic and serotoninergic neurons respectively were also analyzed. Norepinephrine (NE) and serotonin (5-HT) basal levels of MVN were high (33.8 and 39.2 pmol/mg protein respectively) but less er than in LC or RD. Great amounts of MHPG and 5-HIAA were also presen t in the MVN. The turnover of NE assessed both from the ratio MHPG/NE and by the decrease in the NE content after treatment with alpha-methy lparatyrosine was faster in the MVN (half-life: 1.5h) than in LC (half -life: 3.6h). On the other hand, the ratio 5-HIAA/5-HT was lower in th e MVN (0.58) than in the RD (0.85) indicating a smaller 5-HT turnover in the MVN. In addition, like LC and RD, the MVN contained meaningful amounts of dopamine (DA) and DOPAC. The high ratio DA!NE (0.27) sugges ts the presence of non precursor specific dopaminergic pools. However, individualized dopaminergic neurons have not yet been demonstrated. T he data are discussed in line with the possible neurotransmitter funct ion of monoamines in the MVN.