Neuronal activity recorded extracellularly in chronically decentralized in situ canine middle cervical ganglia

Abstract

In chronically decentralized in situ middle cervical ganglia of 10 dogs, 279 spontaneously active neurons were identified. One hundred and ten (39%) of these were spontaneously active during specific phases of the cardiac cycle, primarily during systole, and the activity of nearly half of these cardiovascular-related neurons was modified by gentle mechanical distortion of the vena cavae, heart, or thoracic aorta. Another 60 (22%) of the identified neurons had respiratory – related activity, but the activity of only 2 of them was modified by gentle mechanical distortion of pulmonary tissue. Twenty-nine of the other 109 identified neurons were activated by gentle mechanical distortion of localized regions of the neck, ventral thoracic wall, or ventral abdominal wall. Because of the presence of activity in the chronically decentralized middle cervical ganglion, these data infer that some afferent neurons are located in the thoracic autonomic nervous system. Some middle cervical ganglion neurons were activated by single 1–4 ms stimuli delivered to a nerve connected to the ganglion. During repetitive stimuli delivered at 0.5 Hz none were activated after a fixed latency following the stimuli. Many more neurons were activated by 10- to 200-ms trains of 1–4 ms stimuli delivered with interstimulus intervals of 1–10 ms. The majority of these neurons could still be activated electrically after the administration of cholinergic and adrenergic pharmacological blocking agents. As the spontaneously active neurons, as well as those which were not spontaneously active, which were recorded were not consistently activated by single 1–4 ms stimuli delivered individually to every nerve connected to the middle cervical ganglion, they presumably did not project axons into these nerves and thus are presumed not to be afferent or efferent postganglionic neurons but rather to be local circuit neurons. It is concluded that local circuit neurons in the middle cervical ganglion are involved in regulating cardiovascular, respiratory, and other tissues and can function independent of neurons in the central nervous system.