Relation of exploratory behavior of rats in elevated plus-maze to brain receptor binding properties and serum growth hormone levels

Abstract

Forty-five male Wistar rats were selected according to their behavior in the elevated plus-maze. They were separated as follows: animals with low exploratory activity (`anxious'), an `intermediate' group and animals having high exploratory activity (`non-anxious'). Various receptor binding studies and hormonal assays were also performed in these selected rats. The affinity of 5-hydroxytryptamine 5-HT 2A receptors in the frontal cortex was lower in the `anxious' rats compared to home-cage controls and `non-anxious' animals. Moreover, the number of cholecystokinin (CCK) receptors in the hippocampus was significantly elevated in the `anxious' group compared to home-cage control animals. The blood levels of growth hormone (GH) were significantly lower in the `non-anxious' rats compared to `anxious' counterparts. In conclusion, it seems likely that the decreased exploratory activity of rats is related to the increased 5-hydroxytryptamine (5-HT) and CCK mediated neurotransmission in the brain. The different serum levels of GH in the selected rats probably reflect alterations in the activity of 5-HT and CCK.