Diurnal rhythms of behavior and brain mRNA expression for arginine vasotocin, isotocin, and their receptors in wild Amargosa pupfish (Cyprinodon nevadensis amargosae)

Abstract

Amargosa pupfish (Cyprinodon nevadensis amargosae) occupy remote desert habitats that vary widely in environmental conditions from day to night. In this study, die! patterns of behavior were documented for pupfish in their natural habitat, and examined relative to changes in the abundance of mRNAs encoding prepro-arginine vasotocin (pro-VT), prepro-isotocin (pro-IT), three distinct vasotocin receptors (VIal, Vla2, and V2), and an isotocin receptor (ITR) in the brain. The behavior of wild pupfish varied diurnally, with frequent aggression from 12:00 to 15:00 hand courtship and spawning most common between 15:00 and 19:00h. Transcript abundance for pro-VT in the brain also changed diurnally with mRNA levels highest at night when the pupfish were least active. Transcripts encoding VT and IT receptors, however, exhibited distinct die! patterns, with Vla2 receptor transcripts showing sex-specific diurnal changes, but V2 receptor and ITR receptor mRNAs varying similarly for males and females. VIal and pro-IT transcript abundance were constant over day-night in both sexes. These results document diurnal variation in mRNAs encoding pro-VT and the Vla2, V2, and ITR receptors in the pupfish brain, and provide evidence that die! regulation of Vla2 receptor transcript abundance differs between males and females.

Arginine Vasotocin, Isotocin and Nonapeptide Receptor Gene Expression Link to Social Status and Aggression in Sex‐Dependent Patterns

“…If social context influences not only VT production by the POA, but also the type and relative abundance of VT receptors expressed in the brain -as appears to be the case given our finding here that relationships between VT receptor gene expression and individual variation in behaviour were dependent on social status and sex -then the behavioural effects of VT might be expected to vary depending on an individual's recent social interactions or experience with social stressors (e.g., losing an agonistic interaction). And, if one considers that hypothesis in the light of previous observations that VT receptor gene expression in the fish brain can be influenced by other environmental factors such as photoperiod and environmental salinity [36,50], that complexity might explain why consistent relationships between neural VT system phenotype and behaviour have been challenging to identify across fish species without a more coordinated examination of how social interactions, reproductive status, and environmental experiences (e.g., salinity, recent…”

“…However, since only three VT receptors (v1a1, v1a2 and v2a) had been identified previously from C. nevadensis pupfish [36,50], we also amplified and sequenced a partial cDNA encoding the v2b receptor from this species prior to evaluating how VT or IT receptor gene expression in the brain links to aggression.…”

“…The resulting RNA was DNase I treated (TURBO DNA-free Kit, Ambion) and quantified using a P300 NanoPhotometer (Implen, Inc.) (260:280 ratios > Quantitative real-time RT-PCR (qRT-PCR) was conducted according to the guidelines outlined by Bustin and coworkers [57]. Primers for Taqman probe qRT-PCR assays were designed to protein coding regions of the partial cDNAs for each gene (OnLine Supplemental Table 1) [36,50]. Primers and probes designed to partial cDNAs encoding elongation factor-1α (ef-1α) (GenBank accession no.…”

“…All fish were collected between the hours of 13:00 and 16:00 to eliminate any effects of photoperiod on gene expression patterns in the VT and IT systems [50]. Fish were euthanized using MS222 immediately after capture, weighed and measured (large males: Brain tissue was subdivided macroscopically for the analysis of relative gene transcript abundance in three regions: telencephalon, hypothalamus, and hindbrain/brainstem.…”

Brain levels of arginine–vasotocin and isotocin in dominant and subordinate males of a cichlid fish

“…In fish these nonapeptides are produced by neurons localized in the parvocellular and magnocellular nuclei of the preoptic area, that project both to the neurohypophysis, where AVT/IT are released in the systemic circulation, and to multiple extrahypothalamic regions, namely the ventral telencephalon, the thalamus and the mesencephalon (Goodson and Bass, 2001;Goodson et al, 2003;Holmqvist and Ekstrom, 1995;Thompson and Walton, 2009). The functionality of the wide extrahypothalamic projections is confirmed by the presence of AVT/IT receptors in most brain regions, in particular the AVT V1a receptor (Hausmann et al, 1995;Kline et al, 2011;Lema, 2010;Lema et al, 2010).…”