Abstract
Neuronal unit activities responded to noxious stimulation were recorded extracellulary with metal microelectrodes from brainstem reticular formation in rats. The various types of responses in unit discharges to noxious stimulation were observed and classified to 1) the responses were limitted to stimulation periode (Type I), 2) the responses occured beyond stimulation periode (Type II), 3) combination of Type I and Type II. The responses to noxious stimulation were characterized by increase or decrease in firing rate.
Therefore, the elemental types of responses were Type I excitatory (I ex), Type II inhibitory (I in) Type II excitatory (II ex) and Type II inhibitory (II in) . Combined responses of two types were I ex+II ex, I ex+II in, I in+II ex and I in+II in
Acupuncture stimulation inhibited the noxous responses in 40 of 81 noxious responded neurons. In I+II neurons, I or II response alone, or both I and II responses were inhibited by acupuncture stimulation.
Electric stimulation of periaqueduct central gray (PAG) changed unit discharge rate in about half of noxious responded neurons. PAG-stimulation inhibited the noxious responded brainstem neurons in which firing rate were not changed by PAG stimulation. This inhibition last for long time beyond stimulation periode. Naloxone did not antagnize the inhibition during PAG stimulation, but antagnize the inhibition after termination of PAG stimulation.
Above observations indicate that 1) I and II responses were caused by afferent impulses of different orgins which convergence in recorded neurons. and this difference was a basis of above classification of noxious responses. 2) acupuncture inhibtion might be presynaptic inhibition since one of two kinds of noxious responses was inhibited by acupuncture stimulation in some neurons.
Inhibition of after termination of PAG stimulation was mediated by endogenous morphine like factor (MLF), while inhidition during PAG stimulation might be mediated by direct descending inhibitory system with other neurotransmitter than MLF.
