Effects of static muscular contraction on impulse activity of groups III and IV afferents in cats.

Static contraction of the hindlimb muscles, induced by electrical stimulation of the ventral roots, reflexly increases arterial blood pressure and heart rate. Although stimulation of groups III and IV muscle afferents is believed to cause these reflex increases, the responses of these afferents to a level of static contraction that increases arterial pressure have not yet been determined. Therefore, in barbiturate-anesthetized cats, afferent impulses arising from endings in the gastrocnemius muscle were recorded from the L7 or S1 dorsal roots, while the cut peripheral end of the L7 ventral root was stimulated. In addition, the effects of capsaicin (100-200 micrograms) and bradykinin (25 micrograms) on the activity of the groups III and IV afferents stimulated by contraction were examined. Contraction of the gastrocnemius muscle to a level equal to or greater than that needed to cause a pressor response stimulated 12 of 19 (63%) group III afferents and 13 of 19 (68%) group IV afferents. However, the discharge patterns of the group III afferents stimulated by contraction were very different from those of the group IV fibers. No relationship was found between those fibers stimulated by contraction and those stimulated by chemicals. Our results suggest that although both groups III and IV muscle afferents contribute to the reflex cardiovascular increases evoked by static exercise, group III fibers were likely to be stimulated by the mechanical effects of muscular contraction, whereas at least some group IV fibers were likely to be stimulated by the metabolic products of muscular contraction.

Anatomical localization of the cells of origin of efferent fibers in the superior laryngeal and recurrent laryngeal nerves of dogs.

Using horseradish peroxidase, we identified the cells of origin of motor fibers in the superior laryngeal and recurrent laryngeal nerves of dogs. Cells giving rise to fibers in the superior laryngeal nerve were found in the dorsal motor nucleus and the nucleus ambiguus, whereas cells giving rise to fibers in the recurrent laryngeal nerve were found in the nucleus ambiguus and nucleus retroambigualis, but usually not in the dorsal motor nucleus.

Cardiovascular responses elicited by hypothalamic stimulation in rabbits reveal a mediolateral organization.

Heart rate and blood pressure response patterns were elicited by relatively low intensity (approximately 0.2 mA) stimulation (10 s trains; 100 pulses/s; 0.25 ms pulse duration) in different regions of the hypothalamus in anesthetized rabbits. A bradycardia/depressor pattern was elicited from both anterior and posterior stimulating electrode sites in the far lateral hypothalamus. Medial sites including the ventromedial hypothalamus elicited a tachycardia/pressor pattern. A bradycardia/pressor pattern was elicited from both the anterior and posterior hypothalamus at sites between the lateral hypothalamic (bradycardia/depressor) and the medial hypothalamic (tachycardia/pressor) zones. Paralysis by injection of decamethonium in conjunction with artificial ventilation did not reveal systematic differences in cardiovascular response threshold, form, or magnitude between the paralyzed and non-paralyzed state, indicating that the cardiovascular response patterns were not secondary to changes in respiration. Bilateral vagotomy abolished the bradycardia responses evoked by hypothalamic stimulation indicating that the cardiodeceleration was mediated by the vagus nerves; vagotomy attenuated tachycardia responses indicating that the responses in part reflected a decrease in vagal restraint. Bradycardia responses to ipsilateral but not contralateral hypothalamic stimulation were attenuated or abolished when examined 10-14 days after unilateral destruction of the central nucleus of the amygdala. This indicates that the bradycardia responses elicited by hypothalamic stimulation are in part mediated by fibers of passage. Stimulation of lateral hypothalamic sites eliciting a bradycardia/depressor pattern in anesthetized rabbits, evoked mild orienting in the same animals when conscious, whereas medial hypothalamic sites producing the tachycardia/pressor response pattern in anesthetized animals elicited intense excitement with autonomic concomitants in the nonanesthetized state. The results indicate that the rabbit hypothalamus has a mediolateral organization in terms of at least some cardiovascular and behavioral responses to intracranial stimulation.