Selective catecholamine depletion of structures along the ventral lamina terminalis: effects on experimentally-induced drinking and pressor responses

Ablation of the periventricular tissue of the anteroventral third ventricle (AV3V) or injection of the chemical neurotoxin, 6-hydroxydopamine (6-OHDA), into the structures along the ventral lamina terminalis will produce deficits in drinking and pressor responses to exogenous angiotensin II (ANG II). Centrally-applied 6-OHDA has been shown to result in widespread depletions of both adrenergic (i.e. both noradrenaline and adrenaline-containing) and dopaminergic neurons. Questions arise, therefore, as to whether a dopaminergic or adrenergic depletion is critical and the locus where reductions must occur. The present experiment was designed to investigate the specificity of the effects of 6-OHDA administration into lamina terminalis-associated structures on ANG II-induced drinking and pressor responses. The nature of the depletion was manipulated with desmethylimipramine (DMI), a drug which blocks the uptake of 6-OHDA into adrenergic but not dopaminergic nerve terminals and thereby spares adrenergic elements. The experimental results indicate that 6-OHDA administration into structures of the ventral lamina terminalis produced ANG II response deficits and marked reductions in catecholamine histofluorescence in the regions of the injection sites. In contrast, pretreatment with DMI protected against the 6-OHDA-produced functional deficits and minimized the effects on histofluorescence. These findings are consistent with the interpretation that adrenergic but not dopaminergic neurons must be present in the structures of the ventral lamina terminalis in order to elicit normal angiotensin-induced drinking and pressor responses.