Amygdaloid influences on brain‐stem neurones in the rabbit.

Abstract

SUMMARY1. Electrical stimulation of the central nucleus of the amygdala in the urethane or a-chloralose anaesthetized rabbit evokes a bradyeardia with a rapid onset and a concomitant fall in arterial blood pressure.2. Extracellular neuronal activity was recorded in the ipsilateral nucleus tractus solitarius and dorsal vagal nucleus whilst stimulating the ipsilateral central nucleus of the amygdala, the aortic and vagus nerves.3. A total of 213 neurones were activated by stimulation of at least one of these inputs. 93 of these neurones received a marked excitatory input from the central nucleus with a wide range of latencies (2-100 ms). 50 of these cells also received inputs from either the aortic or vagus nerves, or both.4. The activity of42 vagal preganglionic neurones was recorded in the dorsal vagal nucleus of which 22 had properties typical of cardioinhibitory neurones. 9 of these vagal motoneurones received inputs from the central nucleus with latencies between 2 and 100 ms. Of these, 5 had physiological properties indicating they were cardioinhibitory neurones.5. We conclude that neurones in the nucleus tractus solitarius and dorsal vagal nucleus can be influenced by descending inputs arising from the central nucleus of the amygdala. Some of these neurones are also likely to be influenced by afferents innervating the thoracic viscera and arterial baroreceptors. The implications of these observations on the role of forebrain-brain-stem interactions in cardiovascular control are discussed.

Annual review prize lecture. Central nervous mechanisms contributing to cardiovascular control.

“…12). Similar facilitatory interactions have been observed in the absence of GABAA receptor antagonists in the rabbit when the CEN was stimulated (Cox, Jordan, Moruzzi, Schwaber, Spyer & Turner, 1985;see Fig. 14) and these observations correlated well with the fact that CEN activation in the conscious rabbit evokes a 'playing dead' response that includes bradyeardia and systemic hypotension (Applegate, Kapp, Underwood & McNall, 1983).…”

Baroreceptor inputs to the nucleus tractus solitarius in the cat: modulation by the hypothalamus.

“…In contrast, in the rabbit on stimulating within the central nucleus of the amygdala, which is involved in the expression of affective behaviour, a facilitatory interaction between the effects of such stimulation and baroreceptor inputs has been demonstrated (see Pascoe, Bradley & Spyer, 1987). In this species the appropriate convergence of excitatory input has been observed in neurones of the NTS (Cox et al 1986). The behavioural response in the rabbit involves a marked bradycardia as part of a 'playing-dead' (Applegate, Kapp, Underwood & McNall, 1983) response unlike the defence response of the cat (Timms, 1981).…”

Cardiovascular and phrenic nerve responses to stimulation of the amygdala central nucleus in the anaesthetized rabbit.

“…Indeed, in a double-labelling study in the rabbit Higgins & Schwaber (1981) showed that the descending c.n. projection to the nucleus tractus solitarius overlapped the region of termination of aortic baroreceptor afferents and recent electrophysiological evidence (Cox, Jordan, Moruzzi, Schwaber, Spyer & Turner, 1986) has demonstrated that baroreceptor-sensitive neurones in the rabbit nucleus tractus solitarius and dorsal vagal nucleus can be influenced by stimulation of the c.n. This work was supported by grants from the Medical Research Council.…”