Distribution and quantification of corticotropin‐releasing hormone (CRH) in the brain of the teleost fish Oreochromis mossambicus (tilapia)

Abstract

The recent characterization of the corticotropin-releasing hormone (CRH) prehormone of the fish tilapia (Oreochromis mossambicus) showed that more variation exists between vertebrate CRH amino acid sequences than recognized before. The present study investigates whether the deviating composition of tilapia CRH coincides with an atypical distribution of CRH in the brain. For this purpose we applied immunohistochemistry, as well as radioimmunoassay (RIA) quantification in brain slices. The results are plotted in a new atlas and reconstruction of the tilapia brain. The largest population of CRH-immunoreactive (ir) neurons is present in the lateral part of the ventral telencephalon (Vl). Approximately tenfold less CRH-ir neurons are observed in the preoptic and tuberal region. The CRH-ir neurons observed in the preoptic region are parvocellular and do not, or hardly, display arginine-vasotocin (AVT) immunoreactivity. CRH-ir neurons are also present in the glomerular layer of the olfactory bulb, in the periventricular layer of the optic tectum, and caudal to the glomerular nucleus. A very dense plexus of CRH-ir terminals is located in the most rostral part of the dorsal telencephalon. This region has not been described in other teleosts and is in the present study subdivided into the anterior part of the dorsal telencephalon (Da) and the anterior part of the laterodorsal telencephalon (Dla). High densities of CRH-ir terminals were observed in and around Vl, in the tuberal region, around the rostral part of the lateral recess, and in the caudal part of the vagal lobe. In the pituitary, CRH-ir terminals are concentrated in the neuro-intermediate lobe. Overall, the immunohistochemical and quantitative data correlated well, as the RIA CRH profile in serial 160-microm slices revealed four peaks, which corresponded with major ir-cell groups and terminal fields. Our results strongly suggest that the CRH-ir cells of Vl project to the rostro-dorsal telencephalon. Consequently, they may not be primarily involved in regulation of pituitary cell types but may subserve other functions. The presence of a CRH-containing Vl-Da/Dla projection seems to be restricted to the most modern group of teleosts, i.e., the Acanthopterygians. Further anatomic indications for non-pituitary-related functions of CRH are found in the vagal lobe and the optic tectum of tilapia. Although the low CRH content of the preoptic region reported here for tilapia may be typical for unstressed fish, the fact remains that remarkably few CRH-ir neurons are involved in regulating the pituitary. Overall, the CRH distribution in the brain of tilapia is more widespread than previously reported for other teleosts.

Heads or tails? Stressor-specific expression of corticotropin-releasing factor and urotensin I in the preoptic area and caudal neurosecretory system of rainbow trout

“…Although the presence of CRF in the POA has been reported in many teleost species, the overall expression pattern of CRF in the CNS of rainbow trout appears to differ substantially from the distribution observed in tilapia (Oreochromis mossambicus) where the primary site of CRF immunoreactive cells is in the lateral part of the ventral telencephalon (Pepels et al 2002). In accordance with the strong in situ hybridization signal previously observed in the CNSS of rainbow trout , our distribution survey identified the CNSS as an equally important site of CRF gene expression as the POA.…”

Experimental hyperthyroidism and central mediators of stress axis and thyroid axis activity in common carp (Cyprinus carpio L.)

“…Instead, CRH is the thyrotropic factor (Larsen et al 1998). CRH has a widespread distribution in the teleostean brain; hypophysiotropic CRH-positive neurons have been identified in the NPO, and the nucleus lateralis tuberis (NLT) and nucleus recessi lateralis (NRL) in the hypothalamus (Matz & Hofeldt 1999, Pepels et al 2002, Huising et al 2004. Matz & Hofeldt (1999) showed that, in Chinook salmon (Oncorhynchus tshawytscha), CRH-immunoreactive fibers, originating from the preoptic region and NLT, terminate with boutonlike swellings in the proximity of TSH-ir cells in the pituitary pars distalis.…”

Sequences, expression patterns and regulation of the corticotropin-releasing factor system in a teleost

“…CRF, CRFBP, and both CRF receptor types are expressed in the brain and pituitary in A. burtoni and in the other teleosts (Olivereau and Olivereau, 1988;Arai et al, 2001;Pepels et al, 2002;Pepels and Balm, 2004;Alderman and Bernier, 2007;Alderman et al, 2008) suggesting that CRF acts in the central nervous system along with its role in the HPI axis. The present of CRFBP and both types of CRF-Rs, not CRF mRNA in the pituitary gland implicates that the outside CRF neurons, possibly in the hypothalamus innervate the pituitary via CRF receptors and the ligands are regulated by CRFBP.…”