Somatostatin inhibits activation of dorsal cutaneous primary afferents induced by antidromic stimulation of primary afferents from an adjacent thoracic segment in the rat.
To investigate the effect of somatostatin on the cross-excitation between adjacent primary afferent terminals in the rats, we recorded single unit activity from distal cut ends of dorsal cutaneous branches of the T10 and T12 spinal nerves in response to antidromic stimulation of the distal cut end of the T11 dorsal root in the presence and absence of somatostatin and its receptor antagonist applied to the receptive field of the recorded nerve. Afferent fibers were classified based upon their conduction velocity. Mean mechanical thresholds decreased and spontaneous discharge rates increased significantly in C and Adelta but not Abeta fibers of the T10 and T12 spinal nerves in both male and female rats following antidromic electrical stimulation (ADES) of the dorsal root from adjacent spinal segment (DRASS) indicating cross-excitation of thin fiber afferents. The cross-excitation was not significantly different between male and female rats. Microinjection of somatostatin into the receptive field of recorded units inhibited the cross-excitation. This inhibitory effect, in turn, was reversed by the somatostation receptor antagonist cyclo-somatostatin (c-SOM). Application of c-SOM alone followed by ADES of DRASS significantly decreased the mechanical thresholds and increased the discharge rates of C and Adelta fibers, indicating that endogenous release of somatostatin plays a tonic inhibitory role on the cross-excitation between peripheral nerves. These results suggest that somatostatin could inhibit the cross-excitation involved in peripheral hyperalgesia and have a peripheral analgesic effect.
Guo
Yuan
Y
Department of Physiology and Pathophysiology, Xi'an Jiaotong University School of Medicine, Xi'an, Shaanxi 710061, PR China.
Yao
Fan-Rong
FR
Cao
Dong-Yuan
DY
Pickar
Joel G
JG
Zhang
Qi
Q
Wang
Hui-Sheng
HS
Zhao
Yan
Y
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D000344:Afferent Pathways / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D000704:Analysis of Variance; D000818:Animals; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods*; D005260:Female; D006728:Hormones / Q000494:pharmacology*; D008297:Male; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D017481:Receptors, Somatostatin / Q000037:antagonists & inhibitors; D012445:Sacrococcygeal Region; D012684:Sensory Thresholds / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D012867:Skin / Q000294:innervation*; D013004:Somatostatin / Q000494:pharmacology*; D013126:Spinal Nerve Roots / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D013127:Spinal Nerves / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects
D006728:Hormones; D017481:Receptors, Somatostatin; D013004:Somatostatin