PHYSIOLOGY OF ANTERIOR HYPOPHYSIS 



273 



duck, was subsequently shown to be widely 

 characteristic of birds (Rahn and Painter, 

 1941, 18 species; Wingstrand, 1951a, 50 gen- 

 era). According to these authors the pars 

 distalis in birds comprises two histolog- 

 ically distinct parts, which they designate 

 "cephalic" and "caudal" lobes. The zonation 

 develops during embryonic life and, in 

 stained preparations of the adult gland, is 

 evident to the naked eye. A conspicuous re- 

 gional distribution of specific cell types has 

 been noted also in the anuran hypophysis 

 (Dawson, 1957) . These observations in lower 

 forms provide an evolutionary background 

 for the numerous instances of regional dis- 

 tribution of cell types described in mam- 

 malian pituitaries (Dawson, 1939, 1948; 

 Halmi, 1950, 1952; Purves and Griesbach, 

 1951a, b, 1955; Ferrer and Danni, 1954). 

 Ferrer (1957) noted a correlation between 

 the arrangement of the vascular supply to 

 the adenohypophysis in rats and the pattern 

 of distribution of basophils. Three zones 

 were recognized, each of which has a par- 

 ticular basophilic picture. Dawson (1957) 

 likewise noted a rather specific relationship 

 of cell types to the vascular pattern in the 

 frog. The observation that a pars intermedia 

 is absent in chickens (Kleinholz and Rahn, 

 1939) has been confirmed in all species of 

 birds thus far examined (Rahn and Painter, 

 1941; Wingstrand, 1951; Marshall, 1955). 



A. INNERVATION OF THE HYPOPHYSIS 



The qu^tion of the innervation of the 

 hypophysislia^HDecome a matter of critical 

 importance in the elucidation of mechanisms 

 regulating the various functions of this 

 organ, especially those of the anterior lobe. 

 Fibers of hypothalamic origin sweep down 

 the infundibulum in great numbers to end 

 mainly in the processus infundibularis and, 

 to a minor and perhajis questionable extent, 

 along the infundibular stem. Early workers 

 generally found some of these neurohy- 

 pophyseal fibers entering the pars inter- 

 media and terminating in the pars distalis, 

 but never in numbers to inspire confidence 

 in their significance. 



Vazquez-Lopez (1949, 1953) advocated 

 the view that there is an adequate anatomic 

 basis for neural control of the adenohy- 

 pophysis. Using modifications of the classi- 

 cal silver impregnation techniques of Cajal 



and Rio del Hortega, he observed presump- 

 tive nerve fibers coursing through the pars 

 distalis of the rabbit. These terminated with 

 typical nerve endings in connection with the 

 glandular cells. The fibers were claimed to 

 originate from the tractus hypophysius, 

 to cross over to the pars tuberalis in abun- 

 dance, and in fewer numbers to follow the 

 general course of the vascular elements to 

 the pars distalis. In 1952 Vazquez-Lopez 

 and Williams, reporting on their examina- 

 tion of these relationships in the rat, de- 

 scribed the presence of rather sizeable nerve 

 bundles in the marginal zone of the median 

 eminence, and in the pars tuberalis. They 

 were uncertain of the origin and course 

 of these fibers. In a study of the horse 

 Metuzals (1954), using the Bielchowsky 

 and the Gomori staining methods, traced 

 presumptive nerve fibers from the hypo- 

 thalamus to their endings in the pars 

 distalis. Of the fibers seen in the pars tu- 

 beralis, most are held by Stutinsky (1948), 

 Christ (1951), Nowakowski (1951), and 

 Benoit and Assenmacher (1951a) to be de- 

 rived from similar fibers which have been 

 observed in the marginal zone of the median 

 eminence and along the inferior aspect of 

 the neural stalk. A dense "secretomotor 

 ground plexus" specifically innervating the 

 gland cells has been described by Metuzals 

 (1956). With respect to Metuzals' prepara- 

 tions, A. J. Marshall (1955) states that they 

 "undoubtedly reveal an extensive and spe- 

 cific innervation of glandular cells in the 

 pars distalis." In the ferret, also, sparse 

 nonmyelinated nerve fibers and end organs 

 of characteristic appearance have been ob- 

 served (R. N. Smith, 1956) by a modifica- 

 tion of Ranson's pyridine-silver method. In 

 all these instances the nuclei of origin of 

 the fibers remain obscure. 



Truscott (1944) and Wingstrand (1951a) 

 among others described autonomic fibers 

 entering with and terminating along the 

 sinusoids of the anterior lobe. In the pars 

 distalis of man Hagen (1951) reported the 

 finding of extremely fine fibrillar networks, 

 which were believed to enter the pars dis- 

 talis from the capsule of the gland; and 

 Westman, Jacobsohn and Hillarp (1943) re- 

 ported the persistence of an autonomic fiber 

 system in the anterior pituitaries of rabbits 

 after cervical sympathectomy. Metuzals 



