Poster Presentation The International Congress of Neuroendocrinology 2014

Seasonal plasticity of catecholaminergic innervation of central and peripheral auditory circuitry in a vocal fish (#132)

Paul M Forlano 1 2 , Zachary N Ghahramani 2 , Camillia Monestime 1 , Philip Kurochkin 1 , Alena Chernenko 1 , Dmitriy Milkis 1
  1. Biology, Brooklyn College, City University of New York, Brooklyn, NY, USA
  2. Graduate Program in Ecology, Evolutionary Biology and Behavior, The Graduate Center, City University of New York, New York, NY, USA

In seasonal breeding vertebrates, hormone regulation of catecholaminergic (CA) activity may function, in part, to modulate incentive salience of conspecific vocalizations. However, natural seasonal changes in CA innervation of auditory nuclei is largely unexplored, especially at the level of the peripheral auditory system. The plainfin midshipman fish, Porichthys notatus, has proven to be an excellent model to explore mechanisms underlying seasonal plasticity in audition related to reproductive social behavior. While it is well established that steroid hormones such as estrogen drive seasonal peripheral auditory plasticity in female Porichthys in order to better encode the male’s mate call, little is known of the neural substrates that underlie the motivation and behavioral response to auditory social signals (e.g., phonotaxis). Recently, we demonstrated robust catecholaminergic innervation throughout the auditory system in midshipman1. Most notably, dopaminergic neurons in the diencephalon, proposed A11 homologs, have widespread projections to central auditory circuitry including direct innervation of the saccule, the main endorgan of hearing and the cholinergic octavolateral efferent nucleus (OE) which projects to the inner ear. Here we tested the hypothesis that gravid, reproductive summer females show differential CA innervation of auditory nuclei compared to non-reproductive winter females. We utilized quantitative immunofluorescence to measure tyrosine hydroxylase immunoreactive (TH-ir) fiber density throughout central auditory nuclei and the sensory epithelium of the saccule. Reproductive females exhibited significantly greater density of TH-ir terminals on somata and dendrites of the OE. In contrast, non-reproductive females had significantly greater numbers of TH-ir terminals in the saccule. Less robust differences were found in central auditory nuclei. These data provide evidence that catecholamines may function, in part, to seasonally modulate the sensitivity of the inner ear and, in turn, the appropriate behavioral response to reproductive acoustic signals.