Galanin immunoreactivity is sexually polymorphic in neuroendocrine and vocal‐acoustic systems in a teleost fish

Abstract

Galanin is a peptide that regulates pituitary hormone release, feeding, and reproductive and parental care behaviors. In teleost fish, increased galanin expression is associated with territorial, reproductively active males. Prior transcriptome studies of the plainfin midshipman (Porichthys notatus), a highly vocal teleost fish with two male morphs that follow alternative reproductive tactics, show that galanin is upregulated in the preoptic area-anterior hypothalamus (POA-AH) of nest-holding, courting type I males during spawning compared to cuckolding type II males. Here, we investigate possible differences in galanin immunoreactivity in the brain of both male morphs and females with a focus on vocal-acoustic and neuroendocrine networks. We find that females differ dramatically from both male morphs in the number of galanin-expressing somata and in the distribution of fibers, especially in brainstem vocal-acoustic nuclei and other sensory integration sites that also differ, though less extensively, between the male morphs. Double labeling shows that primarily separate populations of POA-AH neurons express galanin and the nonapeptides arginine-vasotocin or isotocin, homologues of mammalian arginine vasopressin and oxytocin that are broadly implicated in neural mechanisms of vertebrate social behavior including morph-specific actions on vocal neurophysiology in midshipman. Finally, we report a small population of POA-AH neurons that coexpress galanin and the neurotransmitter γ-aminobutyric acid. Together, the results indicate that galanin neurons in midshipman fish likely modulate brain activity at a broad scale, including targeted effects on vocal motor, sensory and neuroendocrine systems; are unique from nonapeptide-expressing populations; and play a role in male-specific behaviors. Abbreviations: ac, anterior commissure; AH, anterior hypothalamus; AT, anterior tuberal nucleus of hypothalamus; Cc, cerebellar crest; Cg, granule cell layer of the corpus of the cerebellum; Cm, molecular layer of the cerebellum; CP, central posterior nucleus; Cpost, posterior commissure; D, area dorsalis of telencephalon; Dc, central zone of D; Dd, dorsal zone of D; DIL, diffuse nucleus of the inferior lobe; DiV, diencephalic ventricle; Dl, lateral zone of D; Dm, medial zone of D; Dm-p, posterior division of Dm; DOdm, dorsomedial division of descending octaval nucleus; DOri/I, rostral intermediate/intermediate division of descending octaval nucleus; DPo, dorsal posterior nucleus of the thalamus; Hb, habenula; Hd, dorsal zone, periventricular hypothalamus; HoCo, horizontal commissure; HV, hindbrain ventricle; Hv, ventral zone, periventricular hypothalamus; IP, isthmal paraventricular nucleus; IS, isthmal auditory-vocal nucleus; LH, lateral hypothalamus; ll, lateral lemniscus; MED, cell plate of medial octavolateralis nucleus; MLF, medial longitudinal fasciculus; MV, midbrain ventricle; nLL, nucleus of the lateral lemniscus; OB, olfactory bulb; OEN, octaval efferent nucleus; On, olfactory nerve; Opn, optic nerve; PAG, periaqueductal ...

Mating Behavioral Function of Preoptic Galanin Neurons Is Shared between Fish with Alternative Male Reproductive Tactics and Tetrapods

“…1B; Foran et al, 1997;Foran and Bass, 1998). The POA contains the primary population of galanin neurons in the midshipman brain (Tripp and Bass, 2020). Here, most POA Gal neurons were observed in the anterior parvocellular POA, though some are in the posterior parvocellular and magnocellular POA.…”

To hum or not to hum: Neural transcriptome signature of courtship vocalization in a teleost fish

“…Only a single transcript related to hormone signaling, pro-FMRFamide-related neuropeptide FF was differentially expressed between humming and non-humming midshipman males. This result was surprising because the POA-AH has dense expression of neuropeptides and hormone receptors—including arginine-vasotocin (AVT) and isotocin (teleost homologues of mammalian arginine-vasopressin and oxytocin, respectively) and their receptors, galanin, stress-related peptides (corticotropin-releasing hormone and urocortin-3), somatotropin, androgen and estrogen receptors, the enzyme aromatase which converts testosterone to estradiol, as well as a receptor for the hormone melatonin, which promotes vocalization 8,15,18,19,39,40,43–46 . Further, hormone signaling was the single significantly enriched GO term in our study of the POA-AH during spawning 15 .…”

“…We used RNA-sequencing (RNAseq) to identify transcriptional changes that occur during humming in both the VMN and POA-AH of type I male midshipman. We found that the vocally active behavioral state of humming is characterized by differential expression of a suite of functionally important genes supporting synaptic transmission, ion channels and transport, hormone signaling, and metabolism and antioxidant activity—categories that have been the focus of earlier studies of vocalization in midshipman or have been associated with courtship vocalization 5,15,18,19 . We also found that the circadian genes period3 ( per3 ) and circadian locomotor output cycles kaput-like ( Clock ) were differentially expressed between humming and non-humming males in the VMN and POA-AH, respectively; an unexpected but exciting result given that midshipman vocalization is under circadian control 8 .…”

Male-predominant galanin mediates androgen-dependent aggressive chases in medaka

“…This raises the question of the role of these neurons in such non-parental species. Curiously, studies in several teleost species have consistently shown that males have many more MPOA Gal neurons than females ( Cornbrooks and Parsons, 1991 ; Rao et al, 1996 ; Rodríguez et al, 2003 ; Tripp and Bass, 2020 ). This contrasts with the situation in mammals, where either there is no sex difference in the number of these neurons, or the direction of the sex difference (if any) varies among species and even within strains in mice ( Bloch et al, 1993 ; Park et al, 1997 ; Mathieson et al, 2000 ; Wu et al, 2014 ).…”

“…Based on this distinctive feature, Gal neurons in the teleost MPOA are assumed to be involved in some male-biased behavior. Indeed, studies in midshipman fish ( Porichthys notatus ) have shown that MPOA Gal neurons are activated during mating, thereby suggesting that they have a role in mating behavior ( Tripp and Bass, 2020 ; Tripp et al, 2020 ). To our knowledge, however, no attempt has been made to directly test these ideas.…”