io6o 



HANDBOOK OF PHYSIOLOGV 



NEUROPH^■SiOLOGV II 



cm in the protocerchral resjion (ii6). Fibers from 

 these neurons pass to a gland the cells of which 

 contain an acidophilic secretory material. No neuro- 

 secretory elements are present in the Julidae (287). 

 Fibers from neurosecretory cells in tlie dorsal aspect 

 of the protocerebrum of chilopods terminate among 

 the cells of the 'glande cerebrale' and influence the 

 formation of an acidophilic secretory material (r2o). 



INSECTS. VVeyer (336) was the first to demonstrate 

 morphological evidence of neurosecretion in insects 

 (bee), while Kopec (186) was the first to demonstrate 

 the hormonal nature of extracts of insect brains. A 

 very large number of species in the rich insect group 

 has been investigated at least in preliminary fashion 

 with respect to neurosecretion. Uniformly, neuro- 

 secretory elements are found in .several segments of 

 the protocerebrum, especially in the pars intercere- 

 bralis. The subesophageal ganglion is somewhat less 

 consistent in this respect. The axons of the pars 

 intercerebralis unite to form a neurosecretory pathway 

 leading to the paired corpora allata, the corpora 

 cardiaca and a series of glands named according to 

 the species inv^estigated, the pericardial gland, the 

 prothorax gland and the peritracheal gland. Although 

 the relationship between these glands and the neuro- 

 secretory elements of the brain is not completely 

 elucidated, they do appear to be influenced by neuro- 

 secretory control in the formation of hormones con- 

 cerned with the pupal stages. Cells of the glandular 

 corpora cardiaca filled with a rich acidophilic secre- 

 tion are surrounded by axons containing much neuro- 

 secretory material (18). Extracts of the corpora 

 cardiaca affect the musculature, water content (7), 

 malpighian vessels and activity of the heart (331, 

 337), as well as pigment activity (91, 92). Neurosecre- 

 tory control of the corpora allata appears to extend 

 to fat metabolism and egg production also. In the silk 

 moth, neurosecretory cells have been demonstrated 

 in various segments of the protocerebrum as well as 

 in the frontal and subesophageal ganglia. In this 

 species also, neurosecretory pathways from the pars 

 intercerebralis terminate in the corpora allata and 

 the corpora cardiaca with discrete secretory pliases 

 correlating with the formation of the pupal stages 

 (159). In the adult, egg laying appears to be depend- 

 ent upon neurosecretory activity. The neurosecretory 

 elements in the subesophageal organ do not appear 

 to exhibit any cyclic activity or secretory phases (15, 

 57-59, 112). The prothorax gland is believed to 

 be the site of formation of those hormones concerned 

 with the pupal stages (106, 337). In Phasmida, changes 



in coloration ma\' be influenced by neurosecretory 

 pathways from the trito- and cleuterocerebrum. 

 Neurosecretory activity from the pars intercerebralis 

 appears firmly associated with growth and molting 

 and to a lesser extent with egg formation and egg lay- 

 ing (90-92). In the orders Diptera and Hymenoptera, 

 neurosecretory pathways are described from the pars 

 intercerebralis to the corpora cardiaca and corpora 

 allata (325). In C^alliphora, Thomsen has succeeded 

 in blocking the flow of neurosecretory material and 

 demonstrating its direction of flow from the pars 

 intercerebralis to the corpora cardiaca and allata (322, 

 323). Observation of living fibers from this tract indi- 

 cates that they contain a clear, characteristic bead-like 

 substance (324). E\idence of neurosecretory activity 

 has been demonstrated in the arachnoids (114, 115, 

 118), in the pycnogonida (270) and in the tunicates 

 (27, 62, 80, 250). 



CONCLUSION 



At the present time the information which would be 

 required to build up a general concept of the signifi- 

 cance of neurosecretory phenomena is still scanty. 

 Nevertheless, there can be no doubt that neurosecre- 

 tion plays an important part in the regulation of life 

 processes in both vertebrates and invertebrates. Two 

 facts have emerged as particularly striking: a) in the.se 

 two groups of animals neurosecretory processes are 

 concerned with similar functions, such as water and 

 mineral metabolism and reproduction; and b) neuro- 

 secretory substances are not species-specific, in fact 

 they are not even class-specific (318). 



Neurosecretory processes must be in\ohed in vari- 

 ous biological processes as well as acting as mediators 

 between the nervous and endocrine .systems. Of 

 particular interest is the as yet poorly understood 

 relation between the capacity of certain neurons 

 both to conduct impulses and to carry on neurosecre- 

 tion. That they can make possible hormone transport 

 to definite parts of the body must have a special 

 significance. These considerations make it not un- 

 likely that the neurosecretory processes are phylogene- 

 tically quite old ( 152, 341 ). 



T E X T S A N D REVIEWS 



Con\cgno sulla Neurosecrezione (riassunti). Piihblicaziorii ilell/i 

 Slaz'onr zoologica die .\apoli 24, Suppl. 1954. 



B.-^RGMANN, \V . Das ^wischenhirn-Hypophyiemyslnn. Berlin- 

 Heidelberg; Springer, 1954. 



CoLUN, R. Die ausseren und inneren Wechselbeziehungen des 

 Hypophysenorgancs. Ergebnisse der riiedizifiischni Gnindlagen- 

 forschung. Stuttgart : Thieme, 1956, Bd. i. 



