On the neurosecretory system of Dendrobaena atheca Cernosvitov

Abstract

A rudimentary neurohaemal organ, the storage zone, has been observed in the cerebral ganglion and there appears to be another neurohaemal area in the ventral nerve cord ganglion. The storage zone is formed by the terminal ends of the axons of A cells. The chrome alum haematoxylin phloxin (CHP) and aldehyde fuchsin (AF) positive substances in the form of granules are found in this area. The cerebral ganglion is richly supplied by blood capillaries. The distal end of the axons of B cells are swollen like a bulb while in some cases the axons are united to form an axonal tract. Extra-cellular material is abundant in different parts of the nervous system. In all cell types, the perinuclear zone is the first to show activity in the secretory cycle. It appears that the nucleus may be involved in the elaboration of the neurosecretory material in the cells.Neurosecretory cells with endocrine functions have been demonstrated in most major groups of triploblastic animals. Endocrinological studies were initiated in annelids by Scharrer ('36), though the neurosecretory cells were shown but misinterpreted by Hamaker (1898). Since then, the endocrinology of annelid worms has been the subject of a large number of experimental and ultrastructural investigations. Divergent opinions continued to be expressed about the types of the neurosecretory cells actually present in Oligochaeta. Scharrer and Scharrer ('37, '45, '54) Current evidence indicates that neurosecretory material is produced in the perikaryon of the cells, passes into the axons where it is temporarily stored and then released through the axon bulb (Rothballer, '66; Scharrer, '66; Dogra, '68). The mechanism of the release of the neurosecretory material has been considerably debated in recent years (De Robertis, '62; Heller and Lederis, '62; Knowles, '62; Bern, '63). The axon bulbs have special significance for the neurosecretory neurones, which combine the function of ordinary neurones with that of glandular cells. Furthermore, unlike the ordinary neurones, the neurosecretory cells do not form synapses by terminating a t the effector organ but instead they release their hormones either directly into the blood (Clark, '59, '661, or into an intermediate structure-the storage and release organ (Scharrer, '63). It is possible that there are two secretory pathways, an intra-cellular and inter-cellular, for the transportation of the neurosecretory material elaborated by the perikaryon (Dogra, '68). With the discovery of the neurohaemal organs, a neurosecretory x-organ sinus gland system in crustacea and inter-cerebralis-cardiacum-allatum system in insects have been established but such a system is still not known for annelids.It appears that the variations in the morphology of the neurosecretory cells, different ways of synthesis of hormones in these cells and the various modes of release of hormones in the absence of a well developed storage and release organs are of common occurrence in oligochaetes. The present paper describes the structure of the various types...

Cytology and Histology of the Cerebral Neurosecretory Systems in some Tropical Earthworm Species

“…Classification of NSCs in the cerebral ganglion of earthworms has been made chiefly on the basis of cytomorphological characteristics, their distribution and staining characteristics [12,[21][22][23][24][25][26][27][28]. Some of these observations agree with one another but many others differ.…”

“…Our earlier scanning electron microscopic studies on the cerebral ganglia of earthworm, E. gammiei revealed rich distribution of blood capillaries within the neuropile [38]. Thus margin of the vascularized neuropile that receive axon terminals from the NSC groups may serve the purpose of 'plexiform neurohaemal complex' [2], rudimentary [25], incipient [27] or elementary [28] neurohaemal organ. Abundance of NSM beneath the neural lamellae following their release from the superficial cortical cells is an interesting feature of the present investigation.…”

“…Available literature indicates that A1-, A2-, A3-cells (together comprise A cells) occupying the postero-dorsal part of the cerebral ganglion of the earthworm species under study comprise the B-DSCs of Chaudhuri et.al. [26] ", dark stained cells" of Dutta and Nanda [27], and 'a' or 'A' neurosecretory cells of various investigators [21][22][23]25,26]. According to Al-Yousuf [3] A cells with its different types (A1-A5) are peptide secreting NSCs.…”

“…The B cells in the cerebral ganglia of the species understudy correspond to large and middle sized neurons [20], the 'B' or 'b' neurosecretory cells of several investigators [21][22][23]25,26] and moderately stained cells or MSCs of Chaudhuri et al [26] and Datta and Nanda [27]. Role of moderately stained cells (corresponding to B cells in the present investigation) in regulation of food intake in M. peguana and E. gammiei was reported by Chaudhuri et al [11] and Chaudhuri and Nanda [31].…”

Effects of Neuroendocrine Centers on Germ and Germline Cells in Dendrobaena atheca Cernosvitov (Annelida: Lumbricidae)

“…The segmental nerve ganglia (SNG), especially the anterior ones, do contain two important types of active NSCs. [11][12][13] Aldehyde-fuchsin (AF)-positive NSCs have also been discovered in ganglia of the vegetative nervous system (VNS) 14 in earthworms. So, the removal of the whole MNECs in earthworms does not mean at all that all NSCs have been removed.…”