Additional evidence that L-5-hydroxytryptophan discrimination models a unique serotonin receptor

Area of Science:

• Neuroscience
• Pharmacology
• Behavioral Science

Background:

• The role of central serotonin (5-HT) in mediating drug cues is complex.
• Previous studies showed 5-HT antagonists did not block the L-5-HTP discriminative cue.

Purpose of the Study:

• To further investigate the role of central serotonin (5-HT) in mediating the L-5-hydroxytryptophan (L-5-HTP) discriminative cue.
• To examine the pharmacological properties of the 5-HT receptor involved in the L-5-HTP cue.

Main Methods:

• Rats were trained to discriminate L-5-HTP (35 mg/kg) combined with RO 4-4602.
• Tested the effects of 5-HT antagonists mianserin and BC-105 (pizotyline) on the L-5-HTP cue.
• Measured regional brain levels of 5-HT, norepinephrine, and dopamine.

Main Results:

• Only BC-105 (pizotyline) completely blocked the L-5-HTP cue in a dose-dependent and surmountable manner.
• L-5-HTP administration significantly increased central 5-HT levels, correlating with behavioral responses.
• Brain catecholamine levels showed minimal changes and no correlation with L-5-HTP dose or behavioral response.

Conclusions:

• The L-5-HTP discriminative cue is mediated by a central 5-HT receptor.
• This receptor exhibits distinct pharmacological properties compared to those identified in other 5-HT behavioral models.
• Findings support a unique central 5-HT receptor mediating the L-5-HTP cue.