LOCALIZATION OF ANDROGEN RECEPTOR MESSENGER-RNA-CONTAINING CELLS IN AVIAN RESPIRATORY-VOCAL NUCLEI - AN IN-SITU HYBRIDIZATION STUDY

Song development and song pattern formation in oscine songbirds are in fluenced by steroid hormones such as estrogens and androgens, and the control of vocal pattern generation is mediated via a network of inter connected vocal and respiratory nuclei, The main components of the res piratory part of the network are the expiratory and inspiratory premot or nuclei, known as retroambigualis (RAm) and the rostral ventral resp iratory group (rVRG), respectively, These respiratory components play an integral role in song production either by providing the expiratory pulses of air required for each and every song syllable, or by contro lling inspiration between syllables in the form of minibreaths, and be tween phrases for major replenishments of air, Here we analyze the dis tribution of androgen receptors (AR) and estrogen receptors (ER) in th e midbrain and hindbrain of male and female zebra finches, and male ca naries and green finches, using in situ hybridization with cRNA probes of the zebra finch AR and ER. ERmRNA was not expressed in any of the respiratory-vocal nuclei of the midbrain or hindbrain, but ARmRNA was expressed in the tracheosyringeal motor nucleus (nXIIts) and in RAm an d rVRG, The size of the ARmRNA defined RAm and rVRG was similar in mal e and female zebra finches, but the size of ARmRNA defined nXIIts was slightly sexual dimorphic, Previously undescribed areas of ARmRNA expr ession outside the respiratory-vocal network in the brain stem were th e nucleus semi-lunaris and layers 10-12 of the optic tectum, ARmRNA ex pression in the respiratory-vocal nuclei of adult male songbirds, adul t female zebra finches, and juvenile zebra finches suggests that the t emporal pattern of learned and unlearned vocalizations is sensitive to androgen-dependent mechanisms mediated by RAm and rVRG. (C) 1997 John Wiley & Sons, Inc.