Descending modulation of thoracic visceroreceptive transmission by C1-C2 spinal neurons

Extracellular potentials of single T3 neurons were recorded in pentobarbital anesthetized male rats. Thoracic esophageal distension (ED, 0.3-0.4 ml, 20 s) and intrapericardial injection of bradykinin (BK, 10(-5) M, 0.2 ml, 1 min) were used as noxious visceral stimuli. Chemical activation of C1-C2 neurons with glutamate pledgets (1 M, 1-3 min) decreased background activity and/or excitatory responses of 26/35 (74%) neurons to ED and 34/44 (77%) neurons to BK. After spinal transection at rostral C1 in five animals, glutamate at C1-C2 still significantly reduced excitatory responses of five neurons to BK. Data showed that intraspinal descending modulation of C1-C2 neurons primarily produced descending inhibition of excitatory responses of thoracic spinal neurons to noxious visceral stimuli.