In cats anesthetized with sodium pentobarbital, microelectrode recordings were made from single neurons in the posterior thalamic region of termination of the spinothalamic tract (medial magnocellular division of the medial geniculate) and adjoining mesencephalic reticular formation, to determine if they receive input of visceral as well as of somatic origin. Of 309 units encountered, 136 (44%) demonstrated viscerosomatic convergence by responding to electrical stimulation of the greater splanchnic nerve as well as a somatic nerve (superficial radial and/or posterior tibial). Of 125 units tested, 42 (34%) had large somatic receptive fields spanning two or more limbs. Most of these responded best to intense skin stimuli (pressure, pinch, sometimes noxious heating). The remaining 83 had receptive fields restricted to part of one limb, and most of these responded to weak stimuli (e.g., hair movement, light tap) with no increment in responses to stronger stimuli. To determine if neurons in this region respond to intense visceral stimulation, the small intestine was distended by inflation of a balloon catheter which was inserted into a fistulated portion of the jejunum. Of 134 units with splanchnic nerve input, 28 responded to intestinal distension. Nine units responded only during the inital phase of distension. The other 19 units responded for all or part of the stimulus duration. Each of these 19 units tested had large somatic receptive fields, and most responded best to strong stimuli (e.g., pinch). In addition, they typically had thresholds for electrical stimulation of the splanchnic nerve which were well above threshold for the viscerointercostal reflex, suggesting that the input was mediated by Aδ-C fibers.
|Original language||English (US)|
|Number of pages||11|
|State||Published - 1980|
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