Midbrain cholinergic mechanisms regulating cardiovascular responses during hypothalamic defence reaction.

1. Hind limb blood flow and arterial blood pressure were recorded during aggressive behaviour induced on electrical stimulation of the anterior hypothalamic area and the central gray, in anaesthetised cats. 2. Bilateral microinfusions of atropine sulphate (20 ug/ul) were made in the midbrain central gray, and the effect on the behavioural and cardiovascular components recorded. 3. Atropine sulphate was found to decrease the hind limb vascular conductance obtained on stimulation of the hypothalamic and the midbrain defence areas. 4. It was found that the recovery of the behavioural components of aggression required at least 1-5 days as compared to the cardiovascular components which reappeared after 3 weeks of atropine sulphate microinfusions. 5. These results suggest that although the cholinergic muscarinic mechanisms play an important role in eliciting both the behavioural and the cardiovascular responses from the same site, yet the two mechanisms may operate differently.

Midbrain cholinergic mechanisms in elicitation of hypothalamic aggressive responses in cats.

1. Electrodes were implanted stereotaxically in the central gray, and the anterolateral regions of the hypothalamus, in chronically prepared cats. 2. The affective attack behaviour elicited on electrical stimulation of the hypothalamic and the midbrain regions was recorded in the caged animals. 3. Bilateral microinfusions of atropine sulphate were given in the central gray and the effect on the midbrain and the hypothalamic responses studied. 4. Cholinergic blockade by atropine sulphate raised the threshold of many of the components of attack behaviour obtained on stimulation of the central gray, and from the anterior hypothalamic regions. 5. Muscarinic receptors may be playing an important role in the central gray regions for the modulation of the aggressive responses from the hypothalamus.