[Reversal of the inhibitory effect of electroacupuncture on the nociceptive response of neurons in parafascicular nucleus by naloxone and atropine in acute arthritic rats].

Rats with adjuvant arthritis were used as an animal model of pathological pain in this experiment and the nociceptive response of neurons in parafascicular nucleus (Pf) were recorded and intracerebroventricular (icv) injection of naloxone and atropine was adopted in order to investigate the effect of electroacupuncture (EA) and to analyze the neurotransmitters involved. The main results were as follows: (1) The nociceptive response of the majority of Pf neurons (29/34) in arthritic rats was significantly inhibited by EA at acupoints of "Zusanli" and "Sanyinjiao"; (2) The inhibitory effect of EA was reversed in 12/13 units by icv injection of naloxone (4 micrograms/10 microliters); (3) The inhibitory effect of EA was also reversed in 11/12 units by icv injection of atropine (5 micrograms/10 microliters) (4) The spontaneous unit discharge of Pf neurons in arthritic rats was increased after icv injection of naloxone or atropine. Experimental results suggest that EA could have an inhibitory effect on the nociceptive response of Pf neurons in arthritic rats, which might be mediated by opioid system and cholinergic system in the brain, and that opioid system and cholinergic system might have a tonic inhibitory effect on the spontaneous unit discharge of Pf neurons in arthritic rats.

[Inhibitory effects of hypothalamic arcuate nucleus or anterior pituitary stimulation on the nociceptive responses of thalamic parafascicular neurons].

The effects of hypothalamic arcuate nucleus (ARC) or anterior lobe of pituitary (AL) stimulation on the nociceptive responses of thalamic parafascicular (Pf) neurons were studied in rats with electrophysiological technique. The results showed that ARC stimulation could inhibit the nociceptive discharges of Pf neurons, namely, the immediate inhibition because of its very short latency and duration. AL stimulation could also inhibit the nociceptive discharges of Pf neurons, but this inhibition was a delayed one because of its longer latency and duration. Hypophysectomy diminished the immediate inhibition due to ARC stimulation, while ARC lesion diminished the delayed inhibition due to AL stimulation. Both kinds of inhibition were blocked by dexamethasone pretreatment. The above results suggest that neuroendocrine relationship between ARC and AL is involved in pain modulation.