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Investigating the neurohormonal basis of courtship behavior in the medicinal leech, Hirudo verbana


Neurohormones in the vasopressin/oxytocin family of peptides are responsible for eliciting social behaviors ranging from kin recognition (Ferguson et al., 2002) to pair-bonding (Winslow et al., 1993) and other aspects of reproductive behavior in various organisms (Donaldson and Young, 2008; Northrop and Erskine, 2008). In the medicinal leech, exogenous homologs of vasopressin, such as conopressin and annetocin, and the endogenous Hirudo homolog, hirudotocin (Salzet, 2007), initiate stereotyped courtship behavior in the medicinal leech Hirudo verbana. Hirudo sp. is a valuable model organism for investigating pattern generator networks due to its readily accessible central nervous system, relatively small number of neurons, many of which are well characterized, and similarities between mid-body ganglia (Macagno, 1980; Muller et al., 1981; Pearce and Friesen, 1984). Vasopressin analogs interact with a central pattern generator in the medicinal leech that initiates and maintains a variety of behaviors that play a role in reproduction (Wagenaar et al., 2010). Using immunohistochemistry, we determined that a vasopressin-like molecule was reliably present in specific identified neurons within the leech nervous system. Most of those cells are as yet uncharacterized, but one pair of large, well-known neurosecretory cells, the Leydig cells, showed a positive reaction in every ganglion. In addition, to look for potential targets of this vasopressin-like molecule, we probed ganglia with antibodies that recognize receptors for mammalian vasopressin. We discovered a set of neurons that labeled positively for vasopressin receptor 1B. In future work, we will use the results to further study the neurohormonal basis of reproductive behavior

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