Fine structure of the neurosecretory system of the vena cava in Octopus

The Gastric Ganglion of Octopus vulgaris: Preliminary Characterization of Gene- and Putative Neurochemical-Complexity, and the Effect of Aggregata octopiana Digestive Tract Infection on Gene Expression

The gastric ganglion is the largest visceral ganglion in cephalopods. It is connected to the brain and is implicated in regulation of digestive tract functions. Here we have investigated the neurochemical complexity (through in silico gene expression analysis and immunohistochemistry) of the gastric ganglion in Octopus vulgaris and tested whether the expression of a selected number of genes was influenced by the magnitude of digestive tract parasitic infection by Aggregata octopiana. Novel evidence was obtained for putative peptide and non-peptide neurotransmitters in the gastric ganglion: cephalotocin, corticotrophin releasing factor, FMRFamide, gamma amino butyric acid, 5-hydroxytryptamine, molluscan insulin-related peptide 3, peptide PRQFV-amide, and tachykinin-related peptide. Receptors for cholecystokininA and cholecystokininB, and orexin2 were also identified in this context for the first time. We report evidence for acetylcholine, dopamine, noradrenaline, octopamine, small cardioactive peptide related peptide, and receptors for cephalotocin and octopressin, confirming previous publications. The effects of Aggregata observed here extend those previously described by showing effects on the gastric ganglion; in animals with a higher level of infection, genes implicated in inflammation (NFκB, fascin, serpinB10 and the toll-like 3 receptor) increased their relative expression, but TNF-α gene expression was lower as was expression of other genes implicated in oxidative stress (i.e., superoxide dismutase, peroxiredoxin 6, and glutathione peroxidase). Elevated Aggregata levels in the octopuses corresponded to an increase in the expression of the cholecystokininA receptor and the small cardioactive peptide-related peptide. In contrast, we observed decreased relative expression of cephalotocin, dopamine β-hydroxylase, peptide PRQFV-amide, and tachykinin-related peptide genes. A discussion is provided on (i) potential roles of the various molecules in food intake regulation and digestive tract motility control and (ii) the difference in relative gene expression in the gastric ganglion in octopus with relatively high and low parasitic loads and the similarities to changes in the enteric innervation of mammals with digestive tract parasites. Our results provide additional data to the described neurochemical complexity of O. vulgaris gastric ganglion.

The proboscis apparatus of the nemertine Lineus ruber

The proboscis apparatus of the nemertine Linens ruber is divided into three segments: the anterior, middle and posterior proboscis, and in addition to these, the retractor muscle. The latter connects the caudal end of the posterior proboscis to the posterior dorsal wall of the rhynchocoel. The general arrangement of the constituent layers of the three segments of the proboscis is more or less similar: (1) inner epithelium, (2) basement membrane, (3) nerve plexus, and (4) one or two layers of muscle which are covered exteriorly by (5) basement membrane and (6) the endothelial cells. The endothelial cells are freely exposed to the rhynchocoel fluid. The inner epithelium of the anterior and posterior proboscis consists of only one type of lining cells, whereas the epithelium of the middle proboscis has many different types of cells, among which may be mentioned (1) ‘rhabdite’-forming cells, (2) ‘sensory’ cells, (3) cells with long microvilli, (4) mucussecreting cells, and (5) cells with acidophilic granules. The rhabdites of the rhabdite-forming cells are very characteristic. Two stages of the rhabdites have been seen: newly developed and mature rhabdites. In the former, the central tubular core of the structure is small and the ‘pool’ in which the rhabdite is embedded is large. In the mature rhabdite the reverse is true, i.e. the central tubular core is distended with electron-translucent secretion probably derived from the ‘pool’, since the latter is greatly reduced in size. The rhabdites are discharged in clusters into the lumen of the ‘resting’ proboscis and presumably over ‘prey’ when the proboscis is ejected. The muscles of the proboscis have ‘dual’ innervation. Aminergic and cholinergic nerve fibres, which arise from the dorsal cerebral ganglia, enter the proboscis at its anterior connexion (‘hinge’). In the aminergic nerve terminals two types of ‘synaptic vesicles’ have been resolved: vesicles of moderate density (20 to 50 nm) and dense-core vesicles (50 to 80 nm). Cholinergic terminals show typical vesicles of size 20 to 50 nm. The retractor muscle is apparently trebly innervated. ‘Synaptic contacts’ (mostly aminergic) occur at the junction of the proboscis and the retractor muscle. In addition, the retractor muscle has a probable peptidergic type of innervation. Neural terminals loaded with granules of size 140 nm, and thus comparable with other neurosecretory endings, are seen in the close vicinity of the retractor muscle. This histological evidence is supported by the observation that the muscle contracts vigorously when stimulated with oxytocin at a concentration of 0.01 unit/ml. The fluid relationships between the rhynchocoel and the vascular system, that allow the proboscis to be freely ejected and withdrawn, are discussed.

Membrane routing during exocytosis and endocytosis in neuroendocrine neurones and endocrine cells: use of colloidal gold particles and immunocytochemical discrimination of membrane compartments

The hypothesis that the retrieval of membranes of neurohypophysial neurosecretory granules (NSG) and small electron-lucent microvesicles occurs by different routes was tested by incubating neurohypophysial neurosecretosomes with colloidal gold particles of various sizes. Neurosecretosomes derived from normal Long Evans rats and incubated in media of normal ionic composition endocytosed a few small (less than 25 nm) gold particles into 40-50 nm electron-lucent microvesicles. After depolarisation, more small gold particles were found in microvesicles, and small and large (greater than 25 nm) gold particles in vacuoles. Oxytocin-containing neurosecretosomes derived from Brattleboro rats, which contain 160 nm-diameter NSG, endocytosed gold particles in a pattern indistinguishable from that of neurosecretosomes from Long Evans rats. However, neurosecretosomes derived from defective vasopressin neurones of Brattleboro rats, which contain microvesicles, small vacuoles, and a few 100 nm dense-cored vesicles, but no 160 nm NSG, endocytosed only small colloidal gold particles. Early after depolarisation the gold particles were present only in microvesicles, but later some could be found in vacuoles and lysosome-like structures. Immunogold cytochemistry using a polyclonal antiserum raised against microvesicle-rich neurosecretosomes derived from Brattleboro rats labelled microvesicles in the posterior pituitary strongly, NSG weakly, and vacuoles to a variable extent. These data together indicate that, after exocytosis, the membranes of NSG are recaptured as large vacuoles. Microvesicles are exocytosed and endocytosed separately.

Neurosecretory cells with 'synaptoid perikarya' in Helix. A definitive description of secretory release from the somata of endocrine neurones

Neurosecretory cells in the mollusc Helix have perikarya that show clear signs of adaptation for both the synthesis and the discharge of secretory material. They are characterized morphologically by juxtaposition with the neural lamella. Passage of hormone into the haemocoel is apparently facilitated in many cases by the extreme attenuation of areas of the lamella and perineurium adjacent to the perikarya and by other forms of histological differentiation. Presumptive sites of release are characterized by prominent aggregations of synaptoid vesicles and the discharge of the contents of secretory granules by exocytosis.

Effects of biogenic amines and related agonists and antagonists on the isolated heart of the common cuttlefish Sepia officinalis L

1. Effects of noradrenaline and the related compounds adrenaline, dopamine, octopamine, tyramine, clonidine and isoprenaline were studied in isolated heart preparations from the cuttlefish Sepia officinalis L. 2. All analogues produced a positive inotropic affect, with noradrenaline being the most potent substance. The chronotropic effects of the tested compounds differed widely. 3. The action of substances of the phenylethanolamine group were not antagonized by propranolol but were partly antagonized by phentolamine. 4. Serotonin and its analogues also produced cardio-excitation. These effects were blocked by cyproheptadine but not by methysergide. 5. These results indicate the presence of two different receptors in the Sepia myocardium: one type reacting with noradrenaline most effectively and a second type being stimulated by serotonin.

Anatomy and ultrastructure of the axons and terminals of neurons R3-R14 in Aplysia

Using light and electron microscopy and autoradiography, we have traced the axons of neurons R3-R14 in the parietovisceral ganglion (PVG) of Aplysia to terminal fields associated with vascular tissue. The axons are identified by their large size (15-30 micrometer diameter), extensive glial infolding, characteristic dense core vesicles (DCV; approximately 180 nm diameter), and specific, rapid uptake of 3H-glycine. Each neuron in this homogeneous group sends an axon via the branchial nerve to the pericardial region surrounding the junction of the efferent gill vein and the heart. R14 also sends axons to major arteries near the PVG. The R3-R14 axons branch extensively; we estimate that there are at least several hundred per cell. Branches along axons in the branchial nerve exit the nerve, subdivide, and end blindly in the sheath which is bathed by hemolymph. Similar blind endings from R3R14 occur in the sheath of the PVG (Coggeshall, '67). Axonal branches in the pericardial region and the special R14 axons in the arterial walls form both varicose endings near and terminals in contact with vasvular smooth muscle. All R3-R14 endings are free of glia, packed with DCV, show occasional omega-shaped profiles and rapidly take up 3H-glycine. R3-R14 manufacture specific low molecular weight peptides (Gainer and Wollberg, '74), and both the cell bodies (Iliffe et al., '77) and the germinals contain unusually high concentrations of glycine. The presence of peptides as putative neurohormones and sheath endings (neurohormonal release areas) are consistent with R3-R14 being neurosecretory (Coggeshall et al., '66). While glycine could not be a circulating hormone due to its high circulating levels (Iliffe et al., '77), glycine could act as a local chemical messenger between R3-R14 and smooth muscle. The terminal morphology of R3-R14 is consistent with these neurons having both synaptic-type and neurosecretory-type functions.

Octopus microvasculature: permeability to ferritin and carbon

The permeability of Octopus microvasculature was investigated by intravascular injection of carbon and ferritin. Vessels were tight to carbon while ferritin penetrated the pericyte junction, and was found extravascularly 1-2 min after its introduction. Vesicles occurred rarely in pericytes; fenestrae were absent. The discontinuous endothelial layer did not consitute a permeability barrier. The basement membrane, although retarding the movement of ferritin, was permeable to it; carbon did not penetrate the basement membrane. Evidence indicated that ferritin, and thus similarly sized and smaller water soluble materials, traverse the pericyte junction as a result of bulk fluid flow. Comparisons are made with the convective (or junctional) and slower, diffusive (or vesicular) passage of materials known to occur across the endothelium of continuous capillaries in mammals. Previous macrophysiological determinations concerning the permeability of Octopus vessels are questioned in view of these findings. Possible reasons for some major structural differences in the microcirculatory systems of cephalopods and vertebrates are briefly discussed.

On the structure and function of a neurohemal organ in the eye cavity of Eledone cirrosa (Cephalopoda)

The subpeduncualte lobe of the octopod brain produces a hormone that is released into the orbit. The hormone was extracted from Eledone cirrosa and assayed on the isolated perfused heart of the same species. It has a remarkable effect on amplitude, beat frequency and blood pressure; compared to equivalent extracts of posterior salivary gland it is about 70 times more effective. The substance is not a biogenic amine.