Cardiovascular effects of central microinjections of apomorphin in cats

Microinjections of apomorphine (25-300 mug) were made into the lateral ventricle, dorsal nucleus of the vagus and ventromedial nucleus of the hypothalamus of cats through a stereotaxically implanted cannula-electrode. Apomorphine caused depressor and bradycardic effects without any dose-response relationship. At the above doses of apomorphine the efferent vagal discharges werr markedly increased concurrent with cardiovascular changes. Respiration was not affected except at higher doses causing depression in some experiments. Pretreatment with atropine, scopolamine or haloperidol abolished those responses. Similar results were observed with bivagotomy and midcollicular transection. Dopamine (125-100 mug), acetylcholine (10-100 mug) and norepinephrine (25-100 mug) caused similar cardiovascular changes, as in the case of apomorphine, and such effects were blocked by both specific and non-specific autonomic blackers. Thus the hypothalamus and the dorsal nucleus of the vagus appear to be inbolved in the central cardiovascular effects of apomorphine and such effects may be mediated through more than one neurotransmitter mechanisms.