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

Abstract

The distribution and nature of 125I-atrial natriuretic peptide binding sites have been examined in the brain and pituitary gland of the toad, Bufo marinus, using tissue section autoradiography, affinity cross-linking and electrophoresis, guanylyl cyclase assays and molecular analysis of natriuretic peptide receptor C (NPR-C) and NPR-GC mRNA expression. The highest density of 125I-atrial natriuretic peptide binding sites occurred in the dorsal pallium, the habenular region, the torus semicircularis, the choroid plexus, and the pituitary gland. Less dense binding was observed in the medial pallium, the thalamic region, the hypothalamus, the optic tectum, and the interpeduncular nucleus. The natriuretic peptide receptor-C specific ligand, C-ANF, displaced the binding in all brain regions; however, some residual binding was observed in the habenular region, the hypothalamus, the choroid plexus, and the pituitary gland. In isolated brain membranes, 1 microM rat atrial natriuretic peptide increased cyclic guanosine monophosphate levels to 90% above basal. Affinity cross-linking followed by reducing electrophoresis showed that 125I-atrial natriuretic peptide bound to proteins of 65 kDa and 135 kDa respectively. Furthermore, molecular analysis demonstrated that natriuretic peptide receptor-C and guanylyl cyclase messenger ribonucleic acid are expressed in the brain. In combination with the autoradiography, the data indicated that atrial natriuretic peptide acting via specific receptors could be important in natriuretic peptide regulation of the brain.

Immunohistochemical localization of atrial natriuretic factor and autoradiographic distribution of atrial natriuretic factor‐binding sites in the brain of the cave salamander Hydromantes genei (Amphibia, Plethodontidae)

“…On the other hand, the occurrence of ANFimmunoreactive neurons in the CNS of H. genei and the fact that central administration of natriuretic peptides in mammals induces a number of effects, particularly on the cardiovascular system (Saper et al, 1980(Saper et al, , 1985, strongly suggest that, in addition to clearance receptors (C-ANF receptors), other receptors functionally coupled to guanylyl cyclase (A-ANF and/or B-ANF receptors) are also expressed in the brain. Consistently with this view, guanylyl cyclase mRNA is expressed in the brain of Bufo marinus, and guanylyl cyclase activity has been detected in the toad brain (McLeod and Donald, 2000).…”

“…Because both A-ANF and C-ANF receptors exhibit high affinity for ANF, the binding sites detected in the brain of H. genei may correspond to either receptor. The distribution of ANF-binding sites has been identified in the brain of several anuran species, including Rana ridibunda (Tong et al, 1989), Xenopus laevis (Kloas and Hanke, 1992), and Bufo marinus (McLeod and Donald, 2000). In contrast, the occurrence of ANF-binding sites and, a fortiori, the type of ANF receptors have not been investigated in any urodele species.…”

“…125 I]rANF exhibit the biochemical and pharmacological characteristics of C-ANF receptors (McLeod and Donald, 2000). On the other hand, the occurrence of ANFimmunoreactive neurons in the CNS of H. genei and the fact that central administration of natriuretic peptides in mammals induces a number of effects, particularly on the cardiovascular system (Saper et al, 1980(Saper et al, , 1985, strongly suggest that, in addition to clearance receptors (C-ANF receptors), other receptors functionally coupled to guanylyl cyclase (A-ANF and/or B-ANF receptors) are also expressed in the brain.…”

“…The A-ANF and B-ANF receptor subtypes are positively coupled to guanylyl cyclase, whereas the C-ANF receptor functions as a clearance receptor (Maack, 1992;Hagiwara et al, 1995). The distribution of ANF-binding sites exhibiting the pharmacological characteristics of the C-ANF receptor in the brain of the toad Bufo marinus has been recently described (McLeod and Donald, 2000). Finally, a novel type of ANF receptor (D-ANF receptor) has been cloned in the eel Anguilla japonica (Kashiwagi et al, 1995).…”

“…Therefore, antibodies against rat or human ANF have been employed successfully for the immunocytochemical identification of ANFrelated peptides in the brain of frog (Netchitaïlo et al, 1986(Netchitaïlo et al, , 1987Andersen et al, 1992;Feuilloley et al, 1993;Vallarino et al, 1998), toadfish McLeod and Donald, 1999), dogfish (Vallarino et al, 1990;, hagfish (Reinecke et al, 1987;, and lungfish (Vallarino et al, 1996). The distribution of ANF-binding sites has also been determined in the brain of the frog Rana ridibunda (Tong et al, 1989), the toads Xenopus laevis (Kloas and Hanke, 1992) and Bufo marinus (McLeod and Donald, 2000), and the lungfish Protopterus annectens (Vallarino et al, 1996). In amphibians however, the localization of ANF-related peptides and ANF-binding sites have been studied only in anurans and not in urodeles.…”