Nervous System Of Cephalopods Research Articles

A newly identified enzyme from Japanese common squid Todarodes pacificus has the ability to biosynthesize d-aspartate

Amino acids exist in two chiral forms, namely L and D. Although l-amino acids are predominant in vivo, certain limited circumstances have reported the usage of d-amino acids. d-aspartate (Asp), among them, plays crucial physiological roles in living organisms and is biosynthesized from L-Asp by the enzyme named aspartate racemase (AspRase). D-Asp is known to accumulate in large amounts in the nervous system of cephalopods. To understand the function of D-Asp in nervous system in more detail, it is necessary to elucidate its metabolic pathway; however, AspRase gene has not been identified in cephalopods as in the case of mammals. In this study, we successfully identified a novel gene encoding AspRase from the optic ganglion of Japanese common squid Todarodes pacificus. Our discovery of the squid AspRase challenges the prevailing assumption that AspRases across different animals share similar structures. Surprisingly, the squid AspRase is a unique enzyme that differs significantly from known AspRases, being structurally and phylogenetically related to aspartate aminotransferase (AST) and possessing both AspRase and AST activities. The optimum pH and temperature for AspRase activity using L-Asp as a substrate are approximately 7.0 and 20 °C, respectively. Moreover, we have found that AspRase activity is enhanced in the presence of 2-oxoacids. These findings have far-reaching implications for the understanding of enzymology and suggest that yet-to-be-identified mammalian AspRases may also be phylogenetically related to AST, rather than conventional AspRases. Furthermore, our results provide valuable insights into the evolution of the D-Asp biosynthetic pathway.

Immunolocalization of choline acetyltransferase of common type in the central brain mass of Octopus vulgaris.

Acetylcholine, the first neurotransmitter to be identified in the vertebrate frog, is widely distributed among the animal kingdom. The presence of a large amount of acetylcholine in the nervous system of cephalopods is well known from several biochemical and physiological studies. However, little is known about the precise distribution of cholinergic structures due to a lack of a suitable histochemical technique for detecting acetylcholine. The most reliable method to visualize the cholinergic neurons is the immunohistochemical localization of the enzyme choline acetyltransferase, the synthetic enzyme of acetylcholine. Following our previous study on the distribution patterns of cholinergic neurons in the Octopus vulgaris visual system, using a novel antibody that recognizes choline acetyltransferase of the common type (cChAT), now we extend our investigation on the octopus central brain mass. When applied on sections of octopus central ganglia, immunoreactivity for cChAT was detected in cell bodies of all central brain mass lobes with the notable exception of the subfrontal and subvertical lobes. Positive varicosed nerves fibers where observed in the neuropil of all central brain mass lobes.

Enrico Sereni: Research on the Nervous System of Cephalopods

This essay focuses on a paradigmatic moment in neurobiological studies of invertebrates: the research on the nervous system of cephalopods carried out by Enrico Sereni at the Naples Zoological Station between 1925 and 1931. Although he remained unknown on the historiographic scenario, probably due to his early death, he contributed toItalian science of the first half of the twentieth century. In my paper particular attention will be given to Sereni's study on the pigmentary-effector, neurohumoral, and peripheral nervous systems, since they also accounted for the historical foundation of the experimental vein that, through the years, would lead John Zachary Young, Sereni's follower, to the most well-known discovery of the giant nerve fibers.

Calretinin distribution in the octopus brain: An immunohistochemical and in situ hybridization histochemical analysis

The distribution of calretinin containing neurons examined by in situ hybridization mapping was compared with that obtained by immunocytochemistry in the brain of octopus. Results revealed a close correspondence between the two types of investigations. Western blot analysis disclosed a 29 kDa protein immunostained with anti-calretinin antibody. Calretinin containing neurons were localized mainly in the cortex of octopus lobes, including the vertical, frontal, basal, buccal, palliovisceral, pedal and branchial, with variations of staining intensity and density of immunoreactive cells. The amacrine cells surrounding calretinin containing neuronal bodies of the cortex were also labeled unlike the glial cells. The close correspondence of blotting analysis, immunocytochemistry and in situ hybridization indicates with no doubt that calretinin, like other calcium-binding proteins previously studied, is also present in the nervous system of cephalopods. Furthermore, although recent findings localize calretinin also in endocrine glands, the presence of this calcium-binding protein in the brain of octopus indicates that calretinin appeared early in the phylogeny as a neuronal protein already in invertebrates.

L-Glutamate and its Ionotropic Receptors in the Nervous System of Cephalopods

In several species of cephalopod molluscs there is good evidence for the presence of L-glutamate in the central and peripheral nervous system and evidence for both classes of ionotropic receptor, AMPA/kainate and NMDA.The best evidence for glutamate being a transmitter in cephalopods comes from pharmacological, immunohistochemical and molecular investigations on the giant fibre system in the squid stellate ganglion. These studies confirm there are AMPA/kainate-like receptors on the third-order giant axon. In the (glial) Schwann cells associated with the giant axons both classes of glutamate receptor occur.Glutamate is an excitatory transmitter in the chromatophores and in certain somatic muscles and its action is mediated primarily via AMPA/kainate-like receptors, but at some chromatophores there are NMDA-like receptors.In the statocysts the afferent crista fibres are also glutamatergic, acting at non-NMDA receptors.In the brain (of Sepia) a neuronal NOS is activated by glutamate with subsequent production of nitric oxide and elevation of cGMP levels. This signal transduction pathway is blocked by D-AP-5, a specific antagonist of the NMDA receptor.Recently immunohistochemical analysis has demonstrated (in Sepia and Octopus) the presence of NMDAR2A /B - like receptors in motor centres, in the visual and olfactory systems and in the learning system. Physiological experiments have shown that glutamatergic transmission is involved in long term potentation (LTP) in the vertical lobe of Octopus, a brain area involved in learning. This effect seems to be mediated by non-NMDA receptors. Finally in the CNS of Sepia NMDA-mediated nitration of tyrosine residues of cytoskeletal protein such as alpha-tubulin, has been demonstrated.

Peptidyl-D-amino acid hydrolase from Loligo vulgaris Lam. Purification and characterization.

An enzyme, tentatively called peptidyl-D-amino acid hydrolase, has been purified from digestive juice from cecum intestine of Loligo vulgaris. The enzyme hydrolyzes peptides that have a low number of D- or L-amino acids. Proteins, polypeptides, and amino acid derivatives are not hydrolyzed. The enzyme acts as a carboxypeptidase with specificity toward small peptides. Polyacrylamide gel electrophoresis, polyacrylamide gel isoelectric focusing, and gel filtration showed the enzyme to be homogeneous. The native enzyme has Mr = 140,000 and consists of two subunits of Mr = 106,000 and 36,000, respectively. The enzyme has an isoelectric point at pH 6.1. The extinction coefficient is 336,000 at 278 nm and the absorption spectrum reveals no chromophoric cofactors. The apparent Km values for Gly-D-Ala, Gly-L-Ala, L-Ala-D-Ala, L-Ala-L-Ala, D-Leu-D-Leu, and L-Leu-L-Leu are 5.2, 7.7, 2.5, 2.8, 5.4, and 8.6 mM, respectively. The enzyme also hydrolyzes Leu-enkephalin, Met-enkephalin, and [D-Ala2] X Met-enkephalin. It has a broad pH optimum from 7.2 to 8.8 with a maximum at pH 8.0. The enzyme activity is not inhibited or increased by Co2+, Mn2+, Mg2+, Zn2+, Cu2+, and Ca2+ at a concentration of 1 mM or by guanidine chloride (50 mM)urea (3 M), and EDTA (50 mM). 50 mM CaCl2, 1 mM CdCl2, and 1 mM Pb(CH3COO)2 inhibited the enzyme activity by 5-10%. Amino acid analysis of the purified enzyme revealed an abundance of aspartic acid, glutamic acid, glycine, and valine. We hypothesize that the enzyme described here serves to hydrolyze D-amino acid peptides, which are probably present in the nervous system of cephalopods.

Identification of a calcium-binding, brain specific protein in the axoplasm of squid giant axons.

Abstract— An acidic protein has been isolated from the optic lobes of two cephalopods, Sepia officinalis and Loligo vulgaris. The protein has been obtained in pure form by fractionation with ammonium sulphate and chromatography on DEAE‐cellulose and Sephadex G 100. Its apparent molecular weight is 13,000–15,000. Glutamic and aspartic acids account for 35 per cent of the amino acid residues. The protein binds Ca2+ ions with an apparent dissociation constant of 2·5 × 10−5 M at physiological concentrations of KCI. Antibodies have been prepared against the protein purified from Sepia officinalis. By the micro‐complement fixation technique it has been shown that the protein is highly concentrated in the nervous system of cephalopods and that the amount in the axoplasm of squid giant axons is eight to nine‐fold higher than in the optic lobes of the same animal.

Nature of vesicles associated with the nervous system of cephalopods.

The epistellar body on the stellate ganglion of octopods and the parolfactory vesicles on the optic tracts of decapods have been established as potential photoreceptors on the basis of morphology (rhabdomeric processes) and biochemistry (presence of rhodopsin and vitamin A1). These organs are not to be viewed as neuroglandular, as originally suggested, but rather as possibly contributing to physiological regulation by recording photic information. Layers of nerve fibers are evident around the vesicles in silver-stained preparations, contributing to nerves with central connections. The stellate ganglion of the young Octopus has lens-like optical properties.

Ferrier Lecture - Growth and plasticity in the nervous system

Clues as to the possible nature of the processes of learning and form discrimination are provided by certain similarities between the nervous system of cephalopods and mammals. These are the presence of (1) large numbers of small neurons, (2) self-re-exciting chains of neurons, (3) arrangements for interaction of the effects proceeding from each point of a stimuated sensory surface. The optic and tactile receiving centres of Octopus both contain elaborate interlaced arrange­ments of fibres that would allow for diffusion of effects of a local stimulus and interaction of effects from different loci. There is also provision for interaction between tactile and optic information after it has been synthesized in this way. The uppermost lobe of the brain (lobus verticalis) receives the final product of this interaction and appears to have the function of conserving the information. After its removal an octopus is able to retain a learned inhibition for only a few minutes, as against many hours in the normal animal. The course of these learning processes in Octopus strongly suggests that self-regenerating cir­cuit systems are involved, but these can hardly be the only basis for the stable learning of higher animals. The study of the factors controlling the growth of regenerating nerve fibres shows that the nature of peripheral contacts made determines the size of the fibres. Evidence is also given that the size reached by nerve cells and their dendrites depends upon the amount of afferent influence that falls upon them. Every part of the nervous system is thus doubly dependent on influences it receives and on the cells that it can influence. The continual renewal of the finer branches of the fibres may well be controlled by these influences. Slight changes as a result of the combinations set up during functioning would be sufficient to alter the probable course of excitation within the nervous networks and thus to provide a stable basis for learned reactions.