The response of the pineal melatonin miosynthesis to the selective MAO-A inhibitor, clorgyline, in young and middle-aged rats

Abstract

1. Clorgyline increased pineal melatonin and N-acetylserotonin (NAS) and decreased 5-hydroxyindoleacetic add (5-HIAA) content in 3 and 12 months of age male Sprague-Dawley rats kept under 12:12 h light: dark schedule. Exposure to light for 24 h before Clorgyline administration resulted in additonal elevation of NAS and melatonin.NAS and melatonin levels after clorgyline injections were significantly higher while 5-HIAA levels were significantly lower in young than in middle-aged rats. 2.The 5-HIAA/5-HT ratio (index of monoamine oxidase activity) was higher in middle-aged than in young rats suggesting the lesser degree of clorgyline-induced inhibition of MAO-A in old than in young rats. 3. It is suggested that melatonin response to a single dose of the selective MAO-A inhibitor might be used for the assessment of the aging changes of the rat (and human) pineals.