Immunocytochemical localization of atrial natriuretic factor and autoradiographic distribution of atria natriuretic factor binding sites in the brain of the African lungfish,Protopterus annectens

Abstract

The localization of atrial natriuretic factor (ANF)-immunoreactive elements was investigated in the brain of the African lungfish, Protopterus annectens, by using antisera raised against rat and human ANF(1-28). Concurrently, the distribution of ANF binding sites was studied by autoradiography using radioiodinated human ANF(1-28) as a tracer. In general, there was a good correlation between the distribution of ANF-immunoreactive structures and the location of ANF binding sites in several areas of the brain, particularly in the ventral part of the medial subpallium, the rostral preoptic region, the preoptic periventricular nucleus, the caudal hypothalamus, the neural lobe of the pituitary, and the mesencephalic tectum. In contrast, mismatching was observed in the pallium (which contained a high density of binding sites and a low concentration of ANF immunoreactive elements) as well as in the lateral subpallium and the medial region of the ventral thalamus, in which a low concentration of binding sites but a high density of ANF-immunoreactive fibers were detected. The present data provide the first localization of ANF-related peptides in the brain of dipnoans and the first anatomical distribution of ANF binding sites in the brain of fish. The results show that the ANF peptidergic systems of P. annectens exhibit similarities with those previously described in the frog Rana ridibunda, supporting the existence of relationships between dipnoans and amphibians. The location of ANF-like immunoreactivity and the distribution of ANF binding sites suggest that ANF-related peptides may act as hypothalamic neurohormones as well as neurotransmitters and/or neuromodulators in the lungfish brain.

Atrial natriuretic peptide binding sites in the brain and pituitary gland of the toad, Bufo marinus : localisation and receptor characterisation

“…In contrast, there are few studies on the natriuretic peptide system of the brain of nonmammalian vertebrates. Immunohistochemical studies in lower vertebrates have shown that natriuretic peptides have a broad distribution in the brain of cyclostomes Reinecke et al 1987), elasmobranchs Vallarino et al 1990), teleosts ; dipnoans (Vallarino et al 1996) and amphibians (Netchitailo et al 1986Feuilloley et al 1993;McLeod and Donald 1999). These studies have shown that natriuretic peptides are found in the brain regions that, by homology with the mammalian brain, are important in the central control of osmoregulation.…”

“…In contrast, there are fewer studies on the distribution and characterisation of natriuretic peptide receptors in the brain. Atrial natriuretic peptide binding sites have been demonstrated in the brain of hagfish , gulf toadfish (Donald et al, unpublished), lungfish (Vallarino et al 1996) and amphibians (Tong et al 1989;Kloas and Hanke 1992). However, the types of receptors have not been characterised in the brain of any lower vertebrate.…”

“…Little or no specific binding is observed in the preoptic region of B. marinus and X. laevis, but dense binding is present in R. ridibunda; interestingly dense ANP binding was found in the preoptic area of the lungfish P. annectens. Immunohistochemistry has shown NP-IR perikarya and fibres in the preoptic region of R. ridibunda (Netchitailo et al 1986, P. annectens (Vallarino et al 1996), andB. marinus (McLeod and.…”

“…In mammals there is significant evidence to suggest natriuretic peptide receptors are present in the hypothalamic/preoptic region, and this has also been demonstrated in the brain of some non-mammalian vertebrates such as the frog, R. ridibunda (Tong et al 1989), and the lungfish, P. annectens (Vallarino et al 1996). Given this, it is possible that a low expression of NPR-GC occurs in regions such as the preoptic area of B. marinus, but that the receptors cannot be discerned using tissue section autoradiography.…”

“…Central natriuretic peptides and their receptors have been demonstrated in the brain of a number of lower vertebrate species including lungfish (Vallarino et al 1996) and amphibians (Netchitailo et al 1986Tong et al 1989;Kloas and Hanke 1992). In amphibians, anatomical studies have shown that natriuretic peptides are present in the preoptic area of the brain that is believed to be analogous to the AV3V region in mammals (Wada et al 1980;Netchitailo et al 1986Netchitailo et al , 1987.…”