Identification of roughskin newt medullary vasotocin target neurons with a fluorescent vasotocin conjugate

Abstract

Arginine8 vasotocin (AVT), a neurohypophyseal peptide in nonmammalian vertebrates, plays a key role in the regulation of social behaviors related to reproduction. In male roughskin newts (Taricha granulosa), AVT is an important facilitator of several reproductive behaviors, including courtship clasping of females. Although AVT is known to act in certain brain regions and AVT receptors have been localized to some extent, specific target neurons for this peptide have not been identified in any species. Internalization of a receptor-specific conjugate of AVT and the fluorescent dye Oregon green was used to identify AVT target cells in the medulla of male roughskin newts. Medullary neurons are of interest because they appear to mediate facilitation of clasping by AVT. Direct application of AVT-Oregon green to the fourth ventricular surface of the medulla in vivo resulted in conjugate internalization by a widespread population of medullary neurons, particularly in the medial reticular formation and nuclei of cranial nerves V, VII, VIII, IX, and X. Some fourth-ventricle ependymal cells were also labeled. Reticulospinal neurons, which play an important role in clasping, were identified by retrograde labeling with tetramethylrhodamine dextran amine. AVT-Oregon green was internalized by 72% of these neurons. These results show that AVT can directly affect a very large and diverse medullary neuronal population, which may underlie the peptide's role in multiple neuroendocrinological processes, including autonomic and behavioral regulation. Selectivity of the AVT action may arise through interactions between AVT and steroids such as corticosterone.

Localization of three types of arginine vasotocin receptors in the brain and pituitary of the newt Cynops pyrrhogaster

“…In our study, we have histochemically confirmed the presence of V1a-type receptor in these regions of the brain of C. pyrrhogaster. Medullary AVT target neurons, particularly those in the medial reticular formation and nuclei of cranial nerves, have recently been visualized by means of Oregongreen-conjugated AVT (Lewis et al 2004(Lewis et al , 2005. These neurons coincide with those exhibiting V1a-type-receptorlike immunoreactivity in the brain of C. pyrrhogaster.…”

“…The anatomical nomenclature as given in Table 2 is based on the studies of Smeets (1992a, 1992b), Lowry et al (1997), Lewis et al (2005), and Hollis et al (2006).…”

“…3k, 5m) of the mesencephalon Table 2 Distribution and relative abundance of three types of AVT receptor mRNAs and immunoreactive cells in the brain and pituitary of the newt (++ intense signal, + moderate signal, -no immunoreactivity or no mRNA hybridization signal). Anatomical nomenclature is according to Smeets (1992a, 1992b), Lowry et al (1997), Lewis et al (2005), and Hollis et al (2006) Structures…”

The distribution of an AVT V1a receptor in the brain of a sex changing fish, Epinephelus adscensionis

“…In one study, fluorescently labeled AVT was administered directly to the brain of newt and specific cell populations in the reticular formation of the hind brain were labeled and identified as areas of AVT action (Lewis et al, 2005). Similarly, only one study in fish has reported identification of AVT binding sites in the pituitary and several generalized brain regions in the seabass, Dicentrarchus labrax (Moons et al, 1989).…”

Pheromones enhance somatosensory processing in newt brains through a vasotocin-dependent mechanism

“…There are VT terminals (Lowry et al 1997) and receptors (Boyd & Moore 1991;Lewis et al 2005) in the newt medulla, although the source of those projections and the circuits through which olfactory stimuli activate them have not yet been identified. Additionally, although we did not characterize individual neuronal responses as did Rose et al (1995), and thus cannot say whether individual neurons are firing more or previously unresponsive neurons are being recruited in response to FSW, our present results are consistent with what they observed when exogenous VT was applied to the medulla, which was that neuronal responses to somatosensory stimuli typically increased.…”