Experimental Brain Research

, Volume 145, Issue 1, pp 64–75

Atypical on-, off- and neutral cells in the rostral ventromedial medulla oblongata in rat

Research Article

DOI: 10.1007/s00221-002-1093-x

Cite this article as:
Schnell, C., Ulucan, C. & Ellrich, J. Exp Brain Res (2002) 145: 64. doi:10.1007/s00221-002-1093-x

Abstract

It is generally assumed that the response pattern of on-, off- and neutral cells in the rostral ventromedial medulla (RVM) to noxious stimulation is independent of stimulation site. But recent studies have shown that a remarkable number of RVM neurons do not have whole-body receptive fields. These so-called atypical neurons were extracellularly recorded in lightly anaesthetized rats. The receptive fields to noxious thermal and mechanical stimulation applied to the tail, the extremities and the craniofacial region were determined in 57 RVM neurons. In 24 atypical off-cells, 12 on-cells and 21 neutral cells, the response pattern evoked by noxious pinch to the nose, forehead and ear most frequently differed from the responses to noxious tail heat. The modulatory effects of intravenously administered morphine were examined in 21 cells. In contrast to the general assumption that morphine activates off-cells, inhibits on-cells and has no effect on neutral cells, in atypical RVM neurons 5 of 6 off-cells, 2 of 6 on-cells and 5 out 9 neutral cells showed a different response pattern to systemical administration of morphine. The results show that a RVM cell classification that is exclusively based on the behaviour to noxious tail heat can neither sufficiently predict the response pattern to different noxious stimuli, especially in the craniofacial region, nor reliably predict the modulatory effect of morphine in RVM neurons. The fact that the neutral cells responded in an off or on manner to noxious stimulation different from noxious tail heat and that morphine modulated activity in many neutral cells suggests that these cells are probably subtypes of on- and off-cells.

Keywords

Analgesia Brainstem Morphine Pain modulation Receptive fields Rat 

Copyright information

© Springer-Verlag 2002

Authors and Affiliations

  1. 1.Department of Physiology and Experimental PathophysiologyFriedrich Alexander University of Erlangen-NurembergErlangenGermany
  2. 2.Department of Experimental and Clinical PharmacologyFriedrich-Alexander-University of Erlangen-NurembergErlangenGermany