Forebrain mapping of secretoneurin‐like immunoreactivity and its colocalization with isotocin in the preoptic nucleus and pituitary gland of goldfish

Abstract

Secretoneurin, a 33-34 amino acid neuropeptide derived from the proteolytic processing of the secretogranin-II precursor protein, is reasonably well conserved in evolution. Goldfish secretoneurin shares >75% similarity overall with other vertebrate secretoneurin sequences. The secretoneurin peptide has numerous functions that include neuroinflammation, neurotransmitter release, and neuroendocrine regulation. A detailed description of the central distribution of secretoneurin immunoreactivity is only known for the rat. Using our polyclonal antibody against the central, conserved core of the secretoneurin peptide we studied the distribution of secretoneurin-like immunoreactivity in the goldfish brain. Secretoneurin immunoreactivity was found in the olfactory bulb, entopeduncular nucleus, preoptic nucleus, lateral part of the lateral tuberal nucleus, posterior periventricular nucleus, nucleus of the posterior recess, the nucleus of the saccus vasculosus, and nucleus isthmi. Secretoneurin-immunoreactive fibers were found in the dorsal part of the dorsal telencephalon, ventral and lateral parts of the ventral telencephalon, periventricular preoptic nucleus, pituitary, and the ventrocaudal aspect of the nucleus of the lateral recess. The most conspicuous secretoneurin immunoreactivity was found in the magnocellular and parvocellular cells of the preoptic nucleus that project to the pituitary. Double-labeling studies indicated coexpression with isotocin, the fish homolog of mammalian oxytocin. Clear colabeling for secretoneurin and isotocin in fibers terminating in the neurointermediate lobe suggests that secretoneurin maybe coreleased with isotocin. Previous work indicates that secretoneurin stimulates the release of luteinizing hormone from the goldfish anterior pituitary. Our findings further support a reproductive role for secretoneurin and related peptides, given the importance of oxytocin family peptides in reproductive behavior in vertebrates.

The secretogranin-II derived peptide secretoneurin modulates electric behavior in the weakly pulse type electric fish, Brachyhypopomus gauderio

“…#T-5021, Peninsula Labs, Santa Carlos, CA, USA). This antiserum has been previously used to identify IST-positive cells in goldfish (Canosa et al, 2011). The anti-OXT antiserum (1:2500 to 1:60,000) was preabsorbed overnight (4°C) with 10-100 lM of synthetic IST (AbD Serotec, Raleigh, NC, USA).…”

“…The following primary antibodies were used: (1) anti-goldfish SN (rabbit or mouse polyclonal; Zhao et al, 2009). These SN antisera were generated against the most conserved central portion of vertebrate SN and have been extensively validated (Canosa et al, 2011;Zhao et al, 2009). To confirm the specificity of the immunostaining, control sections were incubated with SN antisera (1:1000) pre-adsorbed overnight (4°C) with 5 lM of synthetic goldfish SNa.…”

“…The bioactive peptide SN arises from the proteolytic processing of the $600 amino acid secretogranin-II (SgII) precursor protein by specific prohormone convertases in several tissues. In goldfish, SN-like immunoreactive (SN-ir) fibers and nerve terminals were visualized in the periventricular preoptic nucleus, pituitary and the ventrocaudal aspect of the nucleus of the lateral recess (Canosa et al, 2011). The most conspicuous SN-ir was found in the magnocellular and parvocellular cells of the preoptic nucleus that project heavily to the neural lobe of the goldfish pituitary (Canosa et al, 2011).…”

“…In goldfish, SN-like immunoreactive (SN-ir) fibers and nerve terminals were visualized in the periventricular preoptic nucleus, pituitary and the ventrocaudal aspect of the nucleus of the lateral recess (Canosa et al, 2011). The most conspicuous SN-ir was found in the magnocellular and parvocellular cells of the preoptic nucleus that project heavily to the neural lobe of the goldfish pituitary (Canosa et al, 2011). It has been reported in goldfish and mouse that native SN peptides stimulate luteinizing hormone release in vitro, thus revealing a role in the control of vertebrate reproduction (Zhao et al, 2006(Zhao et al, , 2010(Zhao et al, , 2011.…”

“…Importantly, the neuropeptide secretoneurin (SN) is co-localized with AVT and isotocin (IST; fish homolog of tetrapod OXT) in the preoptic area (POA) and neurointermediate lobe of the goldfish pituitary (Canosa et al, 2011) and in the AVP/OXT neurons in the rat . Given the importance of AVT/IST in the modulation of social behaviors (Goodson and Bass, 2001;Goodson and Thompson, 2010) and the clear effects of AVT on EOD in B. gauderio (Perrone et al, 2010(Perrone et al, , 2014, we have investigated the distribution and action of SN in this species.…”