Innervation of the dorsal body cells of Helix aspersa: Immunocytochemical evidence for the presence of FMRF amidelike substances in nerves and synapses

Neuronal pathways of three neurosecretory cells from the lateral lobes in Helisoma (Mollusca): innervation of the dorsal body

The neurite distribution of three large neurosecretory cells, namely one canopy cell and two lateral-lobe cells from each lateral lobe of the cerebral ganglia in Helisoma duryi were studied by thick and thin plastic serial sections. These cells from only the right lateral lobe innervate the dorsal body. Neurites from the canopy cell innervate the cell-bodies whereas those from the lateral-lobe cells innervate the cell-processes of the dorsal body. Neurosecretory granules from these neurites are released at their sites of innervation. The neurites of the optic nerve form synapses with lateral-lobe cell(1), and synapse-like contacts with lateral-lobe cell(2) while a neurite of each canopy cell is found within its collateral optic nerve. Based on the anatomy of the lateral-lobe nerve cells and the optic nerve, it is argued that the stimulatory effect of long days on the dorsal body and on egg production is mediated through the lateral-lobe cells and the canopy cell.

Ultrastructural analysis of the dorsal body gland of the terrestrial snail Megalobulimus abbreviatus (Becquaert, 1948)

The ultrastructure of the reproductive gland, dorsal body (DB), of Megalobulimus abbreviatus was analysed. Electron microscope immunohistochemistry was used to detect FMRFamide-like peptides in the nerve endings within this gland. Nerve backfilling was used in an attempt to identify the neurons involved in this innervation. In M. abbreviatus, the DB has a uniform appearance throughout their supraesophageal and subesophageal portions. Dorsal body cells have several features in common with steroid-secreting gland cells, such as the presence of many lipid droplets, numerous mitochondria with tubular cristae and a developed smooth endoplasmic reticulum cisternae. Throughout the DB in M. abbreviatus numerous axonal endings were seen to be in contact with the DB cells exhibiting a synaptic-like structure. The axon terminals contained numerous electron-dense and scanty electron-lucid vesicles. In addition, the DB nerve endings exhibited FMRFamide immunoreactive vesicles. Injection of neural tracer into the DB yielded retrograde labelling of neurons in the metacerebrum lobe of the cerebral ganglia and in the parietal ganglia of the subesophageal ganglia complex. The possibility that some of these retrograde-labelled neurons might be FMRFamide-like neurons that may represent a neural control to the DB in M. abbreviatus is discussed.

A new biological activity for the neuropeptide FMRFamide: experimental evidence for a secretagogue effect on amylase secretion in the scallop Pecten maximus

FMRFamide immunoreactivity in the digestive tract of the bivalve mollusc Pecten maximus was investigated by immunocytochemistry. Positive FMRFamide-like immunoreactivity was detected in nerve fibres in close contact with exocrine alpha amylase secreting cells. Physiological studies on enzymatically dissociated cells of the stomach-digestive gland complex demonstrated the involvement of FMRFamide and analogues in the control of alpha amylase release from the cells. The FMRFamide-induced secretion was shown to be time- and dose-dependent. In contrast to most naturally occurring vertebrate secretagogues which are hormones, FMRFamide appears to work in our in vitro system as a paracrine factor.

Immunogold labelling of serotonin-like and FMRFamide-like immunoreactive material in neurohaemal areas on abdominal nerves of Rhodnius prolixus

The ultrastructure of neurohaemal areas on abdominal nerves of the blood-sucking bug Rhodnius prolixus was investigated. Four types of axon terminals were found, distinguished by the morphology of their neurosecretory granules. By use of post-embedding immunogold labelling, granules in Type I axon terminals were shown to contain serotonin-like immunoreactive material, and granules in Type II axon terminals were shown to contain FMRFamide-like immunoreactive material. There was no colocalization of these materials. It is suggested that Type III terminals contain peptidergic diuretic hormone, which has previously been reported to be present in electron-dense neurosecretory granules in this neurohaemal area. The identity of material in Type IV terminals is unknown.

Isolation of FMRFa-like peptides from the DB-containing connective tissue of Helix aspersa

The endocrine dorsal bodies (DB) of Helix aspersa are innervated by axons from the central nervous system, which establish synapse-like structures (SLS) with the DB cells. Previous immunocytochemical studies suggested the presence of FMRFa-like substances in nerves of the DB area and in SLS. This paper reports on biochemical attempts undertaken in order to investigate the nature of these substances: the use of HPLC and RIA confirms the presence of three FMRFa-like peptides in the DB-containing connective tissue among which one is probably the FMRFa itself.