Forebrain pathways and their behavioural interactions with neuroendocrine and cardiovascular function in the rat

1. The forebrain is a major organizer of the complex behavioural, physiological and neuroendocrine responses to environmental challenges of a stressful nature.

2. Combined physiological and neuroanatomical studies suggest that a specific forebrain-brain stem network, composed of connections between the central nucleus of the amygdala, the paraventricular nucleus of the hypothalamus, the mesencephalic cuneiform nucleus, the parabrachial nucleus and the dorsal motor nucleus of the vagus nerve, may be important for integrating behavioural and physiological responses.

3. Based on studies using bilateral electrolytic lesions of the central nucleus of the amygdala, it has become clear that the central nucleus of the amygdala is one of the key structures involved in unconditioned responses to inescapable footshock. These responses include freezing behaviour, tachycardia and the release of adrenaline, noradrenaline, prolactin and corticosterone. However, this nucleus is involved only in the freezing behaviour and bradycardiac responses to conditioned emotional stress or to social defeat.

4. Both peptidergic (corticotropin releasing hormone and vasopressin/oxytocin) and aminergic (noradrenaline and dopamine) mechanisms in the central amygdala are involved in the regulation of integrated behavioural, physiological and neuroendocrine stress responses. This is indicated by studies with an infusion of an agonist and/or antagonist of the peptides or neurotransmitters into the central amygdala of freely moving rats. Sympathetic cardiac control is intensified by corticotropin releasing hormone and oxytocin, probably by inhibiting vagal output. In contrast, vagal activity is facilitated by vasopressin, noradrenaline and dopamine.