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.