Arcuate nucleus of hypothalamus involved in analgesic action of l-THP.
OBJECTIVE
To study the role of the arcuate nucleus of hypothalamus in analgesic action of l-tetrahydropalmatine (l-THP).


METHODS
The horseradish peroxidase (HRP) retrograde tracing, HRP retrograde tracing combined with immunohistochemistry, lesion of nucleus, tail-flick test, and intra-PAG injection were used in the present study.


RESULTS
HRP retrograde tracing results showed that the striatum or accumbens nucleus connect with PAG by two pathways: 1) striatum or accumbens nucleus-->arcuate nucleus-->PAG; 2) striatum or accumbens nucleus-->habenula-->PAG. It was found that neurons in the arcuate nucleus projecting to PAG were mainly beta-endorphin neurons as observed by HRP retrograde tracing combined with immuno-histochemistry. After lesion of the arcuate nucleus, the analgesic action of l-THP (40 mg.kg-1, i.p.) was abolished, while lesion of the habenula had no such effect. Moreover, intra-PAG injection of naloxone (2, 3 micrograms) could markedly attenuate the analgesic action of l-THP (40 mg.kg-1, i.p.) in a dose-dependent manner.


CONCLUSIONS
beta-Endorphin neurons in the arcuate nucleus play an important role in the analgesic action of l-THP.
Hu
J Y
JY
Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 200031, China.
Jin
G Z
GZ
D018712:Analgesics, Non-Narcotic / Q000494:pharmacology*; D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000502:physiology*; D001600:Berberine Alkaloids / Q000494:pharmacology*; D007031:Hypothalamus / Q000502:physiology*; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism / Q000502:physiology; D010487:Periaqueductal Gray / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D001615:beta-Endorphin / Q000378:metabolism
D018712:Analgesics, Non-Narcotic; D001600:Berberine Alkaloids; D009270:Naloxone; C014215:tetrahydropalmatine; D001615:beta-Endorphin