Aim: 

Growth hormone (GH) plays a role in adult memory processing and hippocampus could be a target for these effects. The aim of this work was to study the acute and chronic effects of GH on working memory in adult rats tested in the 8-arm radial maze. Also, the acute effect of GH was tested in rats with impaired memory after scopolamine pre-treatment.

Methods: 

Wistar male rats (300-350g) with ad libitum feeding until 48h of testing, were treated with saline, acute GH (2 mg/kg s.c., 1h) and chronic GH (1 mg/kg s.c., twice daily for 30 days, at 8h and 20h) before radial maze tests. Then, the acute effect of the unspecific cholinergic muscarinic antagonist scopolamine (0.2 mg/kg, i.p., 15 and 75 min), and the acute effect of GH in rats pretreated with scopolamine (15 min) was also tested in the radial maze. Trials were judged complete when rats had chosen all 8 baited arms or spent 20 min in the trial. Re-entered or non entered arms were computed as errors.

Results: 

Acute and chronic GH improved task performance respect to controls (61-63% errors reduction and 14-35% reduction in trial time). Scopolamine impaired the task, increasing the number of errors (17-42%) and the time spent (31-75%). No significant change was observed when GH was administered to animals pre-treated with scopolamine.

Conclusions: 

The acute and chronic effects of GH enhancing working memory could be mediated through cholinergic mechanisms.

(Supported by SAF 2007-66878-C02-02 from MEC)