Changes in phrenic activity and heart rate elicited by localized stimulation of amygdala and adjacent structures

Abstract

1. 1. Respiratory and cardiac effects of localized repetitive stimulation of the amygdala and adjacent structures (630 points) have been studied by recording the integrated activity of the phrenic nerve and the cardiotachogram, in bivagotomized cats, with spinal cord sectioned at T 4, maintained under Flaxedil and ventilated artificially. Electrocorticogram and the activity of the parasympathetic accommodative ocular fibers were recorded and the variations of the pupil diameter were observed. 2. 2. The phrenic responses were analyzed and classified in 16 distinct patterns, which were grouped in two functional categories corresponding to increased ventilation (“activation” patterns) and decreased ventilation (“deactivation” patterns) (Fig. 1). 3. 3. The topographical results are summarized in Fig. 3, which shows a good correlation between the respiratory and cardiac effects obtained from the various amygdaloid subdivisions and a clear functional differentiation of these subdivisions. 4. 4. Respiratory “deactivation”, mainly characterized by a decrease of the slope of the integrated inspiratory discharges, and frequently associated with cardio-deceleration, was obtained when stimulating the lateral part of the central nucleus, the lateral nucleus, the parvo-cellular part of the basal nucleus, the peri-amygdaloid cortex and the putamen. 5. 5. Respiratory “activation” and cardio-acceleration could only be elicited from restricted amygdaloid areas. The most interesting effects were obtained from the magno-cellular part of the basal nucleus (amygdaloid area for the “defence reaction”). Stimulation applied in this area (and also in the anterior amygdaloid area) provokes an immediate respiratory deactivation and cardio-deceleration, followed by a delayed respiratory activation and cardio-acceleration associated with delayed incrementing cortico-ocular responses (Gary Bobo and Bonvallet 1970). It is suggested that the two phases of these respiratory and cardiac responses are respectively related to the “attentive” and to the “defensive” stages of the defence reaction. 6. 6. Immediate respiratory activation and cardio-acceleration were elicited by stimulation of the ansa lenticularis. These responses are probably due to excitation of amygdalofugal fibers running through the medial amygdalo-hypothalamic component of the ventral amygdalofugal pathway (Valverde 1965), which would mediate the responses originating in the basal nucleus. 7. 7. Evidence was obtained that the cardio-acceleration elicited from amygdala is mainly due to increase of sympathetic tone and that the cardio-deceleration results from both a decrease of sympathetic tone and an increase of vagal cardiac control. 8. 8. Phasic excitatory or inhibitory responses of the phrenic nerve, evoked by stimulation of the putamen and of the dorsal part of the amygdala are described. They are interpreted as the result of excitation of fibres de passage.