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The neural pathway of galanin in the hypothalamic arcuate nucleus of rats: Activation of beta‐endorphinergic neurons projecting to periaqueductal gray matter
Author(s) -
Sun YanGang,
Gu XingLong,
Yu LongChuan
Publication year - 2007
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.21396
Subject(s) - galanin , periaqueductal gray , arc (geometry) , nociception , endocrinology , chemistry , medicine , hypothalamus , arcuate nucleus , antagonist , microinjection , opioid receptor , neuropeptide , opioid , neuroscience , midbrain , receptor , central nervous system , biology , geometry , mathematics
We have previously shown that microinjection of galanin into the arcuate nucleus of hypothalamus (ARC) produced antinociceptive effects in rats (Sun et al., 2003a). In this study, the neural pathway of galanin from ARC to midbrain periaqueductal gray (PAG) in nociceptive modulation was investigated. The hindpaw withdrawal latencies (HWLs) with noxious thermal and mechanical stimulation were assessed by the hotplate and the Randall Selitto tests. Intra‐ARC administration of 0.1, 0.5, or 1 nmol of galanin induced significant increases in HWLs of rats. The galanin‐induced increases in HWLs were inhibited by injection of 10 μg of the opioid receptor antagonist naloxone or 1 nmol of the mu‐opioid receptor antagonist beta‐funaltrexamine (beta‐FNA) into PAG, suggesting that the antinociceptive effects induced by intra‐ARC injection of galanin occur via the neural pathway from ARC to PAG. Furthermore, our results demonstrate that the galaninergic fibers directly innervated the beta‐endorphinergic neurons in ARC by immunofluorescent methods. Taken together, our results suggest that galanin produces antinociceptive effects in the ARC of rats by activating the beta‐endorphinergic pathway from ARC to PAG. © 2007 Wiley‐Liss, Inc.