Postnatal regulation by monoamines of vasopressin expression in the neuroendocrine hypothalamus of MAO-A-deficient mice.

We studied the influence of noradrenaline (NA) and serotonin (5-HT) on arginine-vasopressin (AVP) expression in the mouse neuroendocrine hypothalamus during the postnatal period. We used 11-day-old transgenic Tg8 mice knock-out for the monoamine oxidase A gene, which are characterized by increased amounts of NA (two-fold) and 5-HT (nine-fold) in the brain compared with wild-type littermates. AVP expression, determined by enzyme immunoassay and in situ hybridization, was increased in the suprachiasmatic nucleus (SCN), decreased in the supraoptic nucleus (SON), and unchanged in the paraventricular nucleus of Tg8 mice compared with wild-types. Inhibiting NA synthesis by injecting alpha-methylparatyrosine to Tg8 mice, AVP levels were decreased in the SCN but increased in the SON. Moreover, the administration of parachlorophenylalanine, a 5-HT synthesis inhibitor, was associated with increased AVP contents in the SCN only. Together, these data show a marked region-specific sensitivity of AVP expression to NA and 5-HT during the postnatal period in the mouse hypothalamus.