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A comparative study of the effects of morphine in the dorsal periaqueductal gray and nucleus accumbens of rats submitted to the elevated plus-maze test.

Abstract：

:We studied the effects of morphine injected either systemically or into the dorsal periaqueductal gray (DPAG) or nucleus accumbens (NA) using conventional and ethological analyses of behavior of rats submitted to the elevated plus-maze test with transparent walls. Intraperitoneal morphine (0.1 mg/kg and 0.3 mg/kg) increased both standard and ethological measures, expressing general exploratory activity such as total arm entries, end-exploration, scanning, head-dipping, and rearing. Morphine 10 (7.6 microg/microl) and 30 nmol (23 microg/microl) injected into nucleus accumbens produced similar effects, which were blocked by i.p. naltrexone (2.0 mg/kg), an opioid antagonist with good affinity for mu-opioid receptors. Morphine injected into the DPAG produced either antiaversive (10 nmol) or aversive effects (30 nmol), which respectively reduced and increased entries and time spent in the open arms and behaviors associated with risk assessment (peeping out, stretched attend postures, and flat back approach). The proaversive effects were inhibited by i.p. norbinaltorphimine (2.0 mg/kg), a selective inhibitor for kappa-opioid receptors. These findings support the contention that at least some of the motivational effects of morphine may be due to activation of opioid mechanisms in nucleus accumbens, and DPAG has neural substrates for antiaversive and aversive effects of morphine. Moreover, on the basis of previous and present data obtained in this laboratory, it is suggested that stimulation of mu-opioid receptors inhibits and stimulation of kappa-receptors activates the neural substrate of aversion in the DPAG. On the other hand, the increase in exploratory behavior due to interaction of morphine with mu-opioid receptors in the nucleus accumbens may be due to the stimulation of the interface between neural substrates of motivation and motor output in this structure.

journal_name

Exp Brain Res

journal_title

Experimental brain research

authors

Anseloni VC,Coimbra NC,Morato S,Brandão ML

doi

10.1007/s002210050896

keywords:

subject

Has Abstract

pub_date

1999-11-01 00:00:00

pages

260-8

issue

eissn

0014-4819

issn

1432-1106

pii

91290260.221

journal_volume

129

pub_type

杂志文章

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A comparative study of the effects of morphine in the dorsal periaqueductal gray and nucleus accumbens of rats submitted to the elevated plus-maze test.