Relationship between arginine vasotocin-like and natriuretic peptide-like immunoreactive structures in the brain of the toad Bufo marinus

The distribution of natriuretic peptide-like immunoreactivity was investiga ted in the brain of Bufo marinus and compared with arginine vasotocin-like immunoreactivity using fluorescence immunohistochemistry. The antisera used were rabbit anti-porcine brain natriuretic peptide, which recognises the t hree main structural forms of natriuretic peptides, and guinea-pig antivaso pressin, which recognises arginine vasotocin. Natriuretic peptide-like immu noreactive fibres were observed in many regions of the brain, being densest in the preoptic/hypothalamic region of the diencephalon and the interpedun cular nucleus of the mesencephalon. Natriuretic peptide-like immunoreactive cell bodies were observed in the dorsal and medial pallium, the medial amy gdala, the preoptic nucleus, the ventral hypothalamus, the nucleus posterod orsalis tegmenti mesencephali, and the interpeduncular nucleus. No natriure tic peptide-like immunoreactivity was seen in the pituitary gland. The dist ribution of arginine vasotocin-like immunoreactivity was similar to that de scribed previously for other amphibian species. Numerous immunoreactive cel l bodies were present in the preoptic nucleus whilst immunoreactive fibres were observed in the preoptic/hypothalamic region as well as in extrahypoth alamic regions such as the medial amygdala and the medial pallium. Double-l abelling immunohistochemistry revealed no colocalisation of arginine vasoto cin-like and natriuretic peptide-like immunoreactivities in the same neural elements. The results suggest that natriuretic peptides and arginine vasot ocin have distinct distributions in the brain but that natriuretic peptide- like immunoreactive fibres in the hypothalamus could influence the activity of arginine vasotocin-like immunoreactive cell bodies.