SUMMARY

1
Neurosecretory phenomena are apparently ubiquitous among Metazoa.

2
In Hydra, neurosecretory products are probably involved in the control of growth and reproduction.

3
Secretory elements in the central nervous system of turbellarians probably promote fission, regeneration and reproduction.

4
The cerebral ganglia of nemertines are the source of a hormone which exercises an inhibitory influence on maturation of the gonads and the development of somatic sexual characteristics. A principle secreted by the ganglia and/or the associated cerebral organs controls weight regulation. A sex hormone controls sexual differentiation.

5
Secretory neurons may influence the production of exsheathing fluid and ecdysis in nematodes.

6
In nereid polychaetes, a single hormone which originates from the cerebral neuroendocrine system apparently promotes segment proliferation and inhibits maturation. However, in certain other polychaetes, contrasting endocrine mechanisms seem to operate.

7
In lumbricid oligochaetes, a hormone secreted by the cerebral ganglion (and possibly by other nervous centres also) promotes gonadal activity and the differentiation of somatic sexual characters. In some species the ganglion exerts an inhibitory influence on the associated processes of ‘diapause’ and posterior regeneration. The cerebral and suboesophageal ganglia are implicated in the control of osmoregulation. Cerebral neurosecretory cells in limicolous oligochaetes may influence regenerative growth and osmoregulation.

8
The cerebral ganglia of leeches secrete a gonadotrophic hormone.

9
In gastropod molluscs, hormones secreted by the cerebral ganglia, glandular ‘dorsal bodies’ and/or optic tentacles are responsible for the control of the development of the reproductive tract, and the activity of the gonads. Contrasting mechanisms are thought to operate in the different gastropod groups and there is conflicting evidence particularly with respect to the endocrine functions of the optic tentacles and the gonads. The ‘bag cells’ of the abdominal ganglion of ApZysiu secrete a hormone which induces egg-laying. Cells in the pleural and parietal ganglia probably control osmoregulation in Lymnaea.

10
The optic glands of cephalopods secrete a gonadotrophic hormone, but sex hormones are apparently absent. The functional significance of the neurovenous tissues (presumptive neurosecretory complexes of unusual character) is obscure in most cases.

11
The radial nerves of starfish are the source of a hormone which induces the production of I-methyl adenine by the follicle cells of the gonad. This second principle stimulates oocyte maturation and the shedding of male and female gametes.

12
The relevance of such information to the development of certain biological concepts and to various aspects of comparative physiology is briefly discussed.

A survey of neuroendocrine phenomena in non‐arthropod invertebrates

In Polychaeta, as in many invertebrates, reproduction is controlled by both environmental and endocrine factors. Although the effects of environmental factors on reproductive behaviour are briefly discussed, this review focuses on the endocrinology of reproduction. As Nereidae are the most intensively studied polychaetes, their epigamic monotelic strategy is discussed first in this review. Although a large number of physiological observations have been made, biochemical data have been greatly lacking until recent years, except, however, for the recent isolation of several pheromones. These substances, such as uric acid and L-cysteine gluthathione disulfide, occur widely and must be present at high concentrations in order to exert their physiological effects. Results obtained from iteroparous species are also considered. The stolonization strategy of Syllidae, the control of vitellogenesis in Nephtyidae, Phyllodocidae, Polynoidae, and Cirratulidae, and the regulation of gamete maturation in Arenicolidae an...

Endocrine and environmental control of reproduction in Polychaeta

Publisher Summary This chapter discusses the cellular dynamics in invertebrate neurosecretory systems. The chromatographic and electrophoretic microtechniques provide complete information on the range of active factors and their distribution in individual species. Assays of synthetic crustacean chromatophorotropins tend to confirm the impression derived from many partial purification schemes that unique molecules have the potential to affect several target organs. It is likely, however, that organisms possess mechanisms to control separately the responsiveness of individual targets. Such mechanisms might include: local control of target sensitivity mediated through some aspect of the intrinsic metabolism of a particular target; the antagonistic or synergistic control of some targets of a particular hormone by blood-borne factors from other sources, or by nervous input; local differences in hormone concentration occasioned by direct delivery of a hormone to some tissues and broadcast dispersal through the circulatory system to others. Studies on mollusc neurosecretory cells have demonstrated clearly that several peptides are released by the activation of a homogeneous population of neurosecretory cells. The techniques of electron microscope autoradiography have been used only sparingly in studies of invertebrate neurosecretory systems and have the potential to provide valuable information on granule processing and transport, and on the possibility of an extragranular pool of hormone or hormone-associated molecules in the axon terminals. Some invertebrate neurosecretory cells present many of the same experimental advantages for electrophysiological studies as ordinary invertebrate neurons over their counterparts in vertebrates.

Cellular Dynamics in Invertebrate Neurosecretory Systems

Identification of progesterone and 17α-hydroxyprogesterone in polychaetes (Perinereis sp.) and the effects of hormone extracts on penaeid oocyte development in vitro

Premières données quantitatives sur l'activité endocrine du cerveau des Néréidiens au cours de leur cycle sexuel

Normal and regenerative growth are partially separated from maturation, since during the later stages of maturation, growth does not occur. A mature animal almost invariably regenerates a pygidium but rarely regenerates segmental rudiments. The supraesophageal ganglion of a mature animal secretes less hormone than that of an immature animal, though it still induces a significant amount of regeneration when implanted into an immature, decerebrate host. The rate of secretion of such a ganglion is as great during the first five days after implantation into the host as it is subsequently. A single ganglion from an immature donor (in which it is known to be actively secreting) induces no regeneration when implanted into a mature host. Immature grafts, from which posterior segments have been removed, engage in virtually no segment regeneration when stitched into mature hosts. However, implantation of three ganglia removed from immature donors into each graft results in the formation of a significant but very sm...

D. W. Golding

Papers

Endocrinology, regeneration and maturation in nereis