Neuroanatomical localization of κ1 and κ2 opioid receptors in rat and guinea pig brain

E. M. Unterwald, C. Knapp, R. S. Zukin

Research output: Contribution to journalArticle

111 Scopus citations

Abstract

The neuroanatomical localization of κ opioid receptors in rat and guinea pig brain was determined by quantitative in vitro receptor autoradiography. Our study shows striking differences in k1 and k2 receptor distributions both between species and within each species. In the rat brain, κ1 sites (labeled by [3H]U-69,593) are of low density and confined to a small number of structures. These include the claustrum, endopiriform nucleus, caudate putamen, nucleus accumbens, midline nuclear group of the thalamus, superficial grey layer of the superior colliculus, and central grey. κ2 sites (labeled by [3H]ethylketocyclazocine or [3H]bremazocine under conditions in which μ, δ, and κ1 binding was suppressed) are more widely distributed throughout all levels of rat brain. κ2 sites occur at high density in the caudate putamen, nucleus accumbens, amygdala, thalamus, and interpeduncular nuclei. In guinea pig brain, κ1 sites predominate and are of high density in layers I and VI of the neocortex, claustrum, endopiriform nucleus, caudate putamen, nucleus accumbens, and molecular layeer of the cerebellum. As in rat brain, κ2 sites in guinea pig are more uniformly and widely distributed throughtout the brain than are κ1 sites. The highest density of κ2 sites is in the dorsal parabrachial nucleus, interpeduncular nuclei, mammillary nuclei, and posterior thalamic nuclei. Results from this study demonstrate important interspecies differences in the distribution of κ1 and κ2 opioid receptors. In particular, κ1 receptors found in high density in layers I and VI of guinea pig neocortex and their virtual absence in the corresponding cortical layers of rat brain might mediate the enhanced analgesic response to κ opioids exhibited by guinea pigs relative to rats. The differences in neuroanatomical localization of κ1 and κ2 receptors within each species provide further support for heterogeneity in the κ opioid receptor system.

Original languageEnglish (US)
Pages (from-to)57-65
Number of pages9
JournalBrain Research
Volume562
Issue number1
DOIs
StatePublished - Oct 18 1991

Keywords

  • Autoradiography
  • Comparative neuroanatomy
  • Guinea pig brain
  • Opioid receptor
  • Rat brain
  • κ Opioid receptor subtype

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology

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