Characterization of responses of T2-T4 spinal cord neurons to esophageal distension in the rat.
1. Three hundred fifty neurons in the T2-T4 spinal segments of 38 intact, pentobarbital sodium-anesthetized, pancuronium-paralyzed male rats were examined for somatic receptive fields and responses to midthoracic esophageal distension (ED). Recordings were made at a depth of 0.1-1.45 mm from the dorsal spinal cord surface and from the midline to approximately 1.0 mm lateral. 2. Fifty-six of the 350 total neurons (16%) responded to ED, produced by air inflation of a latex balloon (0.5-1.5 ml). Most of these 56 neurons (84%) were excited by ED, and all except one were excited at a short latency (< 2 s) to stimulus onset. The response to ED in about one-half of all excited neurons terminated abruptly with termination of the stimulus; the other neurons exhibited an afterdischarge of 5 to > 80 s. Repeated ED at a constant intensity (1.25 ml, 30 s every 6 min) produced stable and reproducible responses of neurons excited by ED. Twenty-one percent of neurons that responded to ED were antidromically invaded from the spinomedullary junction. 3. Graded ED (0.5-1.5 ml, 30 s every 6 min) produced linear and accelerating stimulus-response functions in the 29 neurons tested. The mean threshold for distension, determined with a least-squares regression analysis, was extrapolated to near 0.5 ml of distending volume, and no difference in response threshold was found between neuronal groups with or without after-discharge. 4. The spontaneous activity of 7 of the 56 neurons (12.5%) that responded to ED was inhibited by the stimulus. Stimulus-response functions for four neurons inhibited by ED were intensity dependent. The spontaneous activity of these neurons was inhibited to a mean of 24.5% of the prestimulus control by 1.25 ml ED. 5. Two neurons of the total sample of 56 (3.5%) responded to ED (1.50 ml) in a biphasic excitatory-inhibitory manner. The excitatory component of excitatory-inhibitory neurons encoded the intensity of ED; the inhibitory component during the second half of ED was apparent only at greater distending volumes (1.25-1.5 ml). 6. Somatic receptive fields were found for 303/350 neurons, and 98% were located on the thorax and proximal forearm (all ipsilateral). Five neurons in T2-T4 spinal segments had their cutaneous receptive fields located on caudal parts of the body (tail, hindleg, scrotum).(ABSTRACT TRUNCATED AT 400 WORDS)
Euchner-Wamser
I
I
Department of Pharmacology, College of Medicine, University of Iowa, Iowa City 52242.
Sengupta
J N
JN
Gebhart
G F
GF
Meller
S T
ST
D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D001341:Autonomic Nervous System / Q000502:physiology; D001933:Brain Stem / Q000502:physiology; D004947:Esophagus / Q000294:innervation*; D005727:Ganglia, Spinal / Q000502:physiology; D008297:Male; D008465:Mechanoreceptors / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D009474:Neurons / Q000502:physiology; D009619:Nociceptors / Q000502:physiology; D009620:Nodose Ganglion / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000502:physiology; D012867:Skin / Q000294:innervation; D013116:Spinal Cord / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*; D014630:Vagus Nerve / Q000502:physiology