Mu- and delta-opioid receptor binding peaks and kappa-homogeneity in the molecular layers of rat hippocampal formation.
The sublaminar binding profiles of (D-Ala-NMe-Phe-Gly-ol)-enkephalin (DAGO), (2-D-penicillamine), 5-D-penicillamine)-enkephalin (DPDPE), and dynorphin A(1-8) (DYN) were studied in the CA1 subfield and dentate gyrus of rat hippocampal formation. Binding was assayed on cryomicrotome sections using coverslip autoradiographic and single grain counting techniques. DAGO, an agonist for mu-sites, had peak binding in the stratum pyramidale with a secondary peak in the distal part of the stratum radiatum. Binding of DAGO in the dentate gyrus was homogeneous. DPDPE, a delta-site agonist, also had peak binding in the stratum pyramidale, but there was no secondary peak in the molecular layer of the hippocampus. In the dentate gyrus, DPDPE binding was highest in the inner one-third of the molecular layer immediately adjacent to the granular cell layer. The endogenous opioid DYN had a laminar binding profile that mimicked that of DAGO. However, when tritiated DYN was coincubated with unlabeled DAGO and DPDPE, as much as 90% of DYN binding was blocked and remaining binding was homogenous though a small peak remained in the stratum pyramidale. The secondary peak of DAGO binding in the stratum radiatum corresponds to an area previously determined to contain processes immunoreactive for enkephalin and gamma aminobutyric acid. This correspondence suggests that opioid compounds may mediate disinhibition of the distal dendrites of hippocampal pyramidal neurons. In addition, DYN binding patterns indicate that its action in rat hippocampus is likely by both mu- and delta-receptors.
Plager
M D
MD
Department of Anatomy, Boston University School of Medicine, MA 02118.
Vogt
B A
BA
D000818:Animals; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D008297:Male; D011712:Pyramidal Tracts / Q000166:cytology / Q000378:metabolism; D051381:Rats; D011957:Receptors, Opioid / Q000378:metabolism*; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu
D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu