Journal of neurophysiology
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Comparative Study
Quantitative comparison of inhibition of visceral and cutaneous spinal nociceptive transmission from the midbrain and medulla in the rat.
1. The descending inhibition of neuronal responses by focal electrical stimulation or glutamate microinjections in the periaqueductal gray (PAG) or rostral ventromedial medulla (RVM) was quantitatively studied on 61 spinal neurons in halothane-N2O-anesthetized paralyzed rats. Thirty-six neurons were located in the medial L6-S1 spinal cord and were consistently and reproducibly excited by distension of the descending colon and rectum (75 mmHg). ⋯ Neuronal intensity coding to both graded heating of the hindfoot and graded colorectal distension was montonus and accelerating and could be expressed as linear stimulus-response functions (SRFs) in the temperature and pressure ranges studied (46-52 degrees C, 25-100 mmHg). Stimulation in the PAG modulated the SRFs differently than did stimulation in the RVM. Stimulation in the PAG decreased the slope of the SRFs without affecting the units' thresholds of response, thus influencing the gain control of both cutaneous and visceral nociception in the spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)