[Modification of noxious spinal stimulation on trigemino-trigeminal reflex--analysis in an in vitro brainstem-spinal cord preparation from newborn rats].
Whether reflex responses of the trigeminal motoneurons induced by the stimulation of the trigeminal sensory root (Vs) are inhibited by heterotopic noxious conditioning stimulation applied to the tail was investigated, using a novel in vitro brainstem-spinal cord preparation isolated together with the hindlimbs and tail of newborn rats. The neural activity evoked by electrical stimulation of Vs with a suction electrode was monitored from the trigeminal motor root (Vm) with a suction electrode in a recording chamber. The tail was pinched with forceps as the heterotopic noxious conditioning stimulation (tail pinch). In some experiments, a plastic septum sealed with Vaseline was used to partition the pool for the brainstem from that for the other part of the preparation. The results were as follows: (1) electrical stimulation of Vs induced a long lasting (duration: over 300 ms) positive potential with a peak-latency of about 80 ms in Vm; (2) the response was suppressed in amplitude by the tail pinch; (3) the suppressive effect of the tail pinch was blocked by bath application of naloxone (50 microM) to the brainstem chamber; and (4) removal of the mesencephalon from the preparation did not affect the suppressive effects of the tail pinch. It was concluded that the trigeminal reflex response is suppressed by noxious conditioning stimulation on the remote region, and that in this suppression opioid receptors located in the lower brainstem are involved. This in vitro preparation will be useful for investigations of the neural mechanisms underlying nociceptive modification of neural activity.
Hokazono
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Department of Dental Anesthesiology, Faculty of Dentistry, Tokyo Medical and Dental University.
D000818:Animals; D000831:Animals, Newborn; D001933:Brain Stem / Q000502:physiology*; D066298:In Vitro Techniques; D009046:Motor Neurons / Q000502:physiology; D010812:Physical Stimulation; D051381:Rats; D017208:Rats, Wistar; D011957:Receptors, Opioid / Q000502:physiology; D012018:Reflex; D013116:Spinal Cord / Q000502:physiology*; D013623:Tail / Q000502:physiology; D014276:Trigeminal Nerve / Q000502:physiology*
D011957:Receptors, Opioid