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  • Title: 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: Aronsson S, Enemar A.
    Journal: J Comp Neurol; 1981 Aug 10; 200(3):315-21. PubMed ID: 6115867.
    Abstract:
    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 mediana 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.
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