Neurosecretory System in Earthworms - A Less Studied Research Area in Invertebrates
Research Aspects in Biological Science Vol. 5,
5 July 2022
,
Page 83-95
https://doi.org/10.9734/bpi/rabs/v5/6912F
Abstract
Ernst Scharrer (1905-1965) and Berta Scharrer (1906-1995) for the first time developed the concept of neurosecretion between 1928 and 1937. The “tear drop” like neurosecretory cell is neuronal in structure and glandular in function. The neurosecretory products (neurosecretion/neurohormone) are proteinaeous in nature which is consistent with the ultra structure of the cells. Typically neurosecretory materials are transported via axon and discharged to the blood capillaries.
The distribution, structure, and functions of neurosecretory cells in the central nervous system of distinct earthworm species, regardless of their ecological categories, are more or less comparable in different earthworm species. In tropical earthworms, the central nervous system reveals two main types of neurosecretory cells: deeply stained A type cells (outer cortical tier of deeply stained AF positive cells with distinct axonal processes) and lightly stained B type cells (lying in between A type cells and central fibrous neuropile).The central nervous system neurosecretory cells peripherally are surrounded by neural lamella and epineurium. The core (medulla) of the central nervous system is made up of vascularised and fibrous neuropile. In addition to A and B cells, an “islet” of cells neurosecretory cells called S cells or Hubl cells are present at the base of circum esophageal connectives of subesophageal ganglia. Both A and B cells secrete (neurohormone) at the "zone of accumulation," a highly vascularized fibrous neuropile that can be thought of as a "elementary neuro-haemal organ." Food intake, osmoregulation, thermal acclimation, regeneration, copulation, cocoon creation, and oogenesis are all influenced by neurosecretion in Oligochaetes.
- Earthworm
- neurosecretion
- neurosecretory cells
- elementary neurohaemal organ
- AF stain