CALCITONIN-IMMUNOREACTIVE NEURONS IN THE BRAIN OF THE BULLFROG, RANA CATESBEIANA WITH SPECIAL REFERENCE TO THEIR LIQUOR-CONTACTING AND NEUROSECRETORY NATURE. AN IMMUNOCHEMICAL AND IMMUNOHISTOCHEMICAL STUDY

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Abstract
The occurrence of calcitonin[CT]-immunoreactive neurons in the brain is first demonstrated using anti-human CT antiserum. Immunoassay of the brain extracts of the bullfrog, R. catesbeiana indicates the occurrence of a CT like immunoreactivity contained in 2 neuronal systems: in neurons dispersed in the parvicellular preoptic nucleus whose beaded axons are traced towards the tuber cinereum; and in neurons in nucleus infundibularis ventralis, most of which are bipolar in structure. These bipolar neurons extend a process to reach the CSF in the 3rd ventricle and an axon either to the median eminence or to the prepotic area. The axons reaching the median eminence are beaded in shape containing the C-immunoreactive substance and apparently release it into the hypophyseal portal vessels. It is unknown whether the process to the CSF of these bipolar neurosecretory neurons might be sensory or secretory in nature. Immunochemical and immunohistochemical examinations support the view that the CT-like immunoreactivity in the bullfrog hypothalamus is authentic GT or related peptide and not a part of the precursor molecule of ACTH-.beta.-lipotropin.