Suprachiasmatic nuclei monoamine metabolism of glucose tolerant versus intolerant hamsters

A critical role for temporal organization of dopaminergic and serotonergic activities within the suprachiasmatic nuclei (SCN) in the regulation of peripheral glucose metabolism has been postulated. This study employed in vivo microdialysis to investigate the temporal extracellular profiles of dopamine and serotonin metabolites in the SCN of freely behaving naturally glucose tolerant and intolerant Syrian hamsters. Microdialysis samples from the right SCN of awake, glucose tolerant or intolerant hamsters held on 14 h daily photoperiods were collected every 2 h over a 24 h period and assayed via HPLC for the metabolites of dopamine: homovanillic acid (HVA) and serotonin (5-hydroxyindolacetic acid, 5-HIAA). Among glucose tolerant hamsters, daily rhythms of SCN HVA and 5-HIAA were observed with coincident plateaus throughout the nocturnal phase of the day (both p<0.01). Relative to glucose tolerant hamsters, glucose intolerant animals exhibited a loss in the daily rhythm of SCN HVA (p<0.0001) and 5-HIAA (p<0.02) due to marked reductions (70%) throughout the 24 h period in HVA levels and comparative decreases (35%) in nocturnal peak levels of 5-HIAA. These findings demonstrate that daily profiles of extracellular dopamine and serotonin activities in the SCN, known to influence glucose metabolism, differ between glucose tolerant and intolerant hamsters.