DISTRIBUTION OF ADRENALINE NEURONS IN THE RAT BRAIN

Electrical stimulation of the C1 region of the rostral ventrolateral medulla of the rat increases mean arterial pressure and adrenaline release in the posterior hypothalamus

By using intracerebral dialysis in combination with high performance liquid chromatography and electrochemical detection, extracellular posterior hypothalamic adrenaline, noradrenaline, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid were measured in the anaesthetized rat and changes in their levels monitored following administration of tranylcypromine and electrical stimulation of the rostral ventrolateral medulla. Tranylcypromine (10 mg/kg i.p.) administration decreased basal extracellular 3,4-dihydroxyphenylacetic acid and 5-hydroxyindole acetic acid levels with a simultaneous increase in adrenaline and noradrenaline levels. Electrical stimulation of the C1 area of the rostral ventrolateral medulla increased (+56.6%) extracellular adrenaline levels in the posterior hypothalamus with a simultaneous increase in mean arterial pressure (+48 mm Hg) compared to prestimulation control values. No change was seen in posterior hypothalamic extracellular levels of noradrenaline, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindole acetic acid during the stimulation period. Electrical stimulation of areas close to but outside the C1 region had no effect on either mean arterial pressure or posterior hypothalamic extracellular levels of the amines or the metabolites. The increase in adrenaline levels in the hypothalamus during stimulation of the C1 region supports the evidence for an adrenergic pathway from the rostral ventrolateral medulla to the hypothalamus and suggests that the increase in mean arterial pressure during electrical stimulation to the C1 region may relate to a specific increase in adrenaline levels.