MELATONIN BINDING-SITES IN SCIURID AND HYSTRICOMORPH RODENTS - STUDIES ON GROUND-SQUIRRELS AND GUINEA-PIGS

Little is known about the distribution of binding sites for the pineal hormone melatonin in non-myomorph rodents. We used 2-[(125)]iodomelat onin (IMEL) to analyze the distribution, affinity, and specificity of binding sites in the golden-mantled ground squirrel, a sciurid rodent that reportedly lacks IMEL binding sites in the brain. Specific bindin g was found not only in the pars tuberalis, but also in several telenc ephalic and diencephalic areas including the hypothalamic suprachiasma tic region. The affinity and specificity of IMEL binding are comparabl e to those reported in other rodents. IMEL binding studies in a hystri comorph rodent, the guinea pig, revealed high concentrations of recept or in the nucleus accumbens and dorsolateral thalamus. Central melaton in binding sites have now been demonstrated in species of all three ro dent families. The heterogeneous distribution of melatonin receptors a ppears similar in the species studied, and no evidence is found to lin k IMEL binding sites at any particular locus to photoperiodic, circann ual, or non-seasonal breeding patterns.