title: Blocking the ghrelin receptor type 1a in the rat brain impairs memory encoding.
abstract: Studies have shown that intracerebral administration of ghrelin hormone affects learning and memory in different experimental models of learning. However, the effect of antagonism of ghrelin receptor type 1a (GHS-R1a) on different stages of learning has not been investigated. In this study the effect of intracerebroventricular (i.c.v) injection of a GHS-R1a selective antagonist (d-Lys-3-GHRP-6) was examined on acquisition and consolidation of learning in the passive avoidance task. In total, 72 male Wistar rats weighing 230-280g were randomly distributed into 9 groups of 8 each. Animals underwent stereotaxic surgery and cannulated in their right ventricle. One week after surgery, the rats received different doses of d-Lys-3-GHRP-6 (0.2, 2, 20 and 80nM/5μl; i.c.v) 10min before, or (2, 20 and 80nM/5μl; i.c.v) immediately after training. The control groups received solvent of the drug. Twenty four hours later in the test day, memory retrieval was assessed. Pre-training injection of d-Lys-3-GHRP-6 decreased step-through latency (STL) and increased number of step-throughs into the dark compartment (NST) in a dose-dependent manner, but failed to be statistically significant. It also increased time spent in the dark compartment (TDC), significantly and in a dose-dependent manner. Post-training injection of d-Lys-3-GHRP-6 decreased step-through latency and increased time spent in the dark compartment and number of step-throughs into the dark compartment, significantly and in a dose-dependent manner. The results indicate that antagonism of the GHS-R1a in the rat brain impairs memory encoding on both acquisition and consolidation stages. Further studies are required to elucidate the main brain regions affected by the antagonist.
authors.affiliation: Division of Animal Sciences, Department of Biology, Faculty of Sciences, University of Isfahan, Isfahan, Iran. Electronic address: siamak.beheshti@yahoo.com.
authors.forename: Siamak
authors.initials: S
authors.lastname: Beheshti
authors.affiliation: Division of Animal Sciences, Department of Biology, Faculty of Sciences, University of Isfahan, Isfahan, Iran.
authors.forename: Shahrzad
authors.initials: S
authors.lastname: Shahrokhi
mesh_terms: D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology*; D001921:Brain / Q000187:drug effects / Q000502:physiology*; D008297:Male; D000069077:Memory Consolidation / Q000187:drug effects / Q000502:physiology*; D011939:Mental Recall / Q000187:drug effects / Q000502:physiology*; D009842:Oligopeptides / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D054440:Receptors, Ghrelin / Q000819:agonists / Q000502:physiology*
chemical_list: C520836:GHRP-6, Lys(3)-; D009842:Oligopeptides; D054440:Receptors, Ghrelin
keywords: Ghrelin; Memory; Passive avoidance task