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On the structural and phyletic origin of the aminergic nerves of the hypophysis of frog tadpoles ( Rana temporaria ) with special reference to pars distalis
Author(s) -
Aronsson Stig,
Enemar Anders
Publication year - 1981
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.902000303
Subject(s) - biology , phyletic gradualism , anatomy , rana , pituitary gland , hypothalamus , median eminence , neuroscience , endocrinology , hormone , biochemistry , phylogenetics , gene
With the aid of lesion experiments and the Falck‐Hillarp fluorescence technique, it is shown that the aminergic nerves of the hypophysis, including pars distalis, originate in the caudal hypothalamus and reach the gland via a fibre tract in the floor of tuber cinereum. However, some contribution to the eminentia cmediana from the preoptic area could not be excluded. A vasomotor function of the pars distalis nerves is unlikely. Based on a comparative survey the hypothesis is put forward, that the pars distalis nerves, which disappear during the metamorphic climax, are remnants of an aminergic innervation existing together with a hypophyseal portal system as a functional link between brain and pituitary in the fish‐like ancestor of amphibians. Aspects are given on the problem of why a direct pars distalis innervation has neither been retained nor evolved during evolution of tetrapods.