Vasotocin Innervation and Modulation of Vocal-Acoustic Circuitry in the Teleost Porichthys notatus JAMES L. GOODSON AND ANDREW H. BASS* Department of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853 ABSTRACT Arginine vasotocin (AVT) and its mammalian homologue arginine vasopressin (AVP) modulate reproduction-related and other social behaviors in a broad range of vertebrate species. These functions of AVT/AVP may be in part achieved through the modulation of sensorimotor integration, although experimental evidence supporting this hypothesis re- mains limited. In the present experiments, we demonstrate (1) AVT innervation of candidate vocal-acoustic brain regions, and (2) AVT modulation of vocal-motor physiology in the plainfin midshipman fish (Porichthys notatus), which uses vocalizations in both mate attraction and agonistic contexts. AVT distribution was compared with known vocally active brain regions and to central auditory and vocal pathways. AVT-immunoreactive fibers and putative ter- minals descend almost exclusively from the preoptic area and are found in two primary candidate sites for vocal-acoustic integration - the anterior tuberal hypothalamus and paralemniscal midbrain tegmentum. AVT immunoreactivity is also located in several other vocally active regions, including the ventral tuberal nucleus, periaqueductal gray, and para- ventricular regions of the isthmus and rostral hindbrain. The parvocellular preoptic area itself is also vocally active, although thresholds are substantially higher than for other regions. The functional significance of AVT input to vocal-acoustic regions was demonstrated in the paralemniscal midbrain where local delivery of AVT modulated electrically evoked, rhythmic vocal-motor output, which precisely mimicked natural vocalizations. AVT produced dose-dependent inhibitions of parameters associated with call initiation (burst latency and number of vocal-motor bursts elicited) but not of vocal-motor patterning (fundamental fre- quency and burst duration). Together, these findings provide support for the proposal that AVT modulates sensorimotor processes underlying social/acoustic communication. J. Comp. Neurol. 422:363–379, 2000. © 2000 Wiley-Liss, Inc. Indexing terms: vasopressin; auditory; midbrain; sex differences; communication; fish The neuropeptide arginine vasotocin (AVT; nonmam- mals) and its mammalian homologue, arginine vasopres- sin (AVP) are key components of coordinated behavioral expression, as a variety of anatomic and behavioral find- ings now implicate these peptides in the modulation of a wide diversity of sex-typical and species-specific behaviors (e.g., sexual, aggressive, pair-bonding, vocal, and parental behaviors). AVT/AVP distributions and behavioral func- tions are also often steroid- and/or seasonally dependent. Across all vertebrate classes, AVT/AVP cell bodies are found in the preoptic area-anterior hypothalamus (POA- AH), a sensorimotor integration center that also regulates numerous physiologic and hormonal processes by means of its control of the pituitary gland (for reviews and/or extensive treatments of the findings discussed above, see de Vries and Miller, 1998; Engelmann et al., 1996; Good- son, 1998b; Lowry et al., 1997; Moore, 1992; Moore and Lowry, 1998; Young et al., 1998). Whereas AVT/AVP distributions and behavioral func- tions have been extensively studied with regard to sex, species, and endocrine variables, potential roles for AVT/ AVP in the modulation of sensorimotor functions have been investigated relatively less. Most extensively studied Grant sponsor: National Institutes of Health; Grant number: F32 NS- 0443; Grant sponsor: National Science Foundation; Grant number: IBN 9421319. *Correspondence to: Andrew H. Bass, Department of Neurobiology and Behavior, Mudd Hall, Cornell University, Ithaca, NY 14853. E-mail: ahb3@cornell.edu Received 8 December 1999; Revised 25 February 2000; Accepted 25 February 2000 THE JOURNAL OF COMPARATIVE NEUROLOGY 422:363–379 (2000) © 2000 WILEY-LISS, INC.