CONDITIONED PLACE PREFERENCE INDUCED BY MICROINJECTION OF 8-OH-DPAT INTO THE DORSAL OR MEDIAN RAPHE NUCLEAS

Experiments were conducted to examine the ability of the selective 5-h ydroxytryptamine (5-HT)(1A) agonist 8-hydroxy-2-(di-n-propylamino)tetr alin (8-OH-DPAT) to induce a conditioned place preference following pe ripheral injection, and direct microinjection into the dorsal or media n raphe nuclei. An unbiased place preference paradigm was used in whic h control animals showed no preference for either of two compartments differing in terms of colour (white versus black), floor texture (roug h versus smooth) and olfactory cues (no odour versus acetic acid odour ). Drug treatments were paired with access to either of the two compar tments, and saline injections were paired with access to the other com partment. Rats experiencing a low dose of 8-OH-DPAT (125 mu g/kg) with a specific compartment demonstrated a significant preference for that compartment over one paired with saline injections. The magnitude of this effect was similar to that observed in rats treated with 1.5 mg/k g d-amphetamine. A significant place preference was found in animals r eceiving injections of 8-OH-DPAT in the dorsal raphe at 0.1 mu g but n ot 1 mu. Animals also displayed a preference for the compartment paire d with 1 mu g 8-OH-DPAT injected into the median raphe; lower doses we re not effective. These results indicate that the mechanism by which 8 -OH-DPAT induces a conditioned place preference involves activation of raphe somatodendritic 5-HT1A autoreceptors, leading to a reduction in 5-HT neurotransmission. This demonstration of the rewarding propertie s of 8-OH-DPAT, together with previous results showing increased feedi ng and sexual behaviour following 8-OH-DPAT treatment, strongly sugges ts an important role for brain 5-HT systems in reward and reinforcemen t processes.