Spontaneous regeneration of the central nervous system in gastropods

Of all organs in mammals including humans, the brain has the most limited regenerative capacity after injury or damage. In spite of extensive efforts to treat ischemic/stroke injury of the brain, thus far no reliable therapeutic method has been developed. However, some molluscan species show remarkable brain regenerative ability and can achieve full functional recovery following injury. The terrestrial pulmonates are equipped with a highly developed olfactory center, called the procerebrum, which is involved in olfactory discrimination and odor-aversion learning. Recent studies revealed that the procerebrum of the land slug can spontaneously recover structurally and functionally relatively soon after injury. Surprisingly, no exogenous interventions are required for this reconstitutive repair. The neurogenesis continues in the procerebrum in adult slugs as in the hippocampus and the olfactory bulb of mammals, and the reconstitutive regeneration seems to be mediated by enhanced neurogenesis. In this review, we discuss the relationship between neurogenesis and the regenerative ability of the brain, and also the evolutionary origin of the brain structures in which adult neurogenesis has been observed.     

Detection of biogenic monoamines in the developing nervous system of Lymnaea stagnalis mollusk embryos]

Formaldehyde-induced fluorescence of intraneuronal monoamines can be demonstrated in the Lymnaea embryos from the "late veliger" stage on. Green specific fluorescence indicating the presence of a primary catecholamine occurs in two paired formations which contain a mass of fibres and varicosities. The formations are supposed to correspond to cerebral and pedal ganglia. Single fibres of the same type can be seen in the foot and other organs of the embryo.     

Effect of caponization on central nervous system monoamines in the Japanese quail

Depletion of brain regional norepinephrine (NE), dopamine (DA) after alpha methyl-paratyrosine (AMT), and serotonin (5HT) were measured in intact and caponized adult male Japanese quail (Coturnix coturnix japonica). Telencephalon, diencephalon, and cerebellum DA was depleted by AMT treatment, but brain stem was not affected. AMT-induced depletion of NE was greatest in telencephalon, diencephalon, and brain stem of capons. Neither caponization nor AMT affected brain regional 5HT. The results from this work indicate that caponization will affect catecholamine dynamics in brain regions other than the hypothalamus.     

Identification of piRNAs in the central nervous system

Piwi-interacting RNAs (piRNAs) are small noncoding RNAs generated by a conserved pathway. Their most widely studied function involves restricting transposable elements, particularly in the germline, where piRNAs are highly abundant. Increasingly, another set of piRNAs derived from intergenic regions appears to have a role in the regulation of mRNA from early embryos and gonads. We report a more widespread expression of a limited set of piRNAs and particularly focus on their expression in the hippocampus. Deep sequencing of extracted RNA from the mouse hippocampus revealed a set of small RNAs in the size range of piRNAs. These were confirmed by their presence in the piRNA database as well as coimmunoprecipitation with MIWI. Their expression was validated by Northern blot and in situ hybridization in cultured hippocampal neurons, where signal from one piRNA extended to the dendritic compartment. Antisense suppression of this piRNA suggested a role in spine morphogenesis. Possible targets include genes, which control spine shape by a distinctive mechanism in comparison to microRNAs.     

Computer-operated microspectrofluorimetry to identify formaldehyde-induced fluorophores of biogenic monoamines and precursor substances in models and tissue sections

By means of a histochemical reaction using formaldehyde vapour (Falck and Owman 1965), biogenic monoamines and precursor substances, i.e., L-DOPA, dopamine, noradrenaline, adrenaline, 5-hydroxytryptophan and 5-hydroxytryptamine, may be converted into fluorophores with specific spectral characteristics, i.e., the emission spectrum, excitation spectrum and fading curve. The registration and correction of the spectral properties and changes induced by acidification with hydrochloric acid vapour or treatment with ammonia vapour, of these formaldehyde-induced fluorophores, are performed by an automated microspectrofluorimeter, developed by modification of a Leitz MPV 2 system. This work deals with the instrumental configuration and certain methodological features in order to identify the fluorogenic biogenic monoamines and precursor substances in models and tissue sections. Registrations of excitation peak values, for the first time extended to a wavelength range from 240-460 nm, are discussed, which enable the calculation of peak ratio values 410/260, 380/320, 320/260 or 385/315, suitable as identification parameters for formaldehyde-induced fluorophores of biogenic monoamines and precursor amino acids.     

Computer-operated microspectrofluorimetry to identify formaldehyde-induced fluorophores of biogenic monoamines and precursor substances in models and tissue sections

Summary By means of a histochemical reaction using formaldehyde vapour (Falck and Owman 1965), biogenic monoamines and precursor substances, i.e., L-DOPA, dopamine, noradrenaline, adrenaline, 5-hydroxytryptophan and 5-hydroxytryptamine, may be converted into fluorophores with specific spectral characteristics, i.e., the emission spectrum, excitation spectrum and fading curve. The registration and correction of the spectral properties and changes induced by acidification with hydrochloric acid vapour or treatment with ammonia vapour, of these formaldehyde-induced fluorophores, are performed by an automated microspectrofluorimeter, developed by modification of a Leitz MPV 2 system. This work deals with the instrumental configuration and certain methodological features in order to identify the fluorogenic biogenic monoamines and precursor substances in models and tissue sections. Registrations of excitation peak values, for the first time extended to a wavelength range from 240–460 nm, are discussed, which enable the calculation of peak ratio values 410/260, 380/320, 320/260 or 385/315, suitable as identification parameters for formaldehyde-induced fluorophores of biogenic monoamines and precursor amino acids.Dedicated to Mrs. Prof. Dr. M.H.A. De Groodt-Lasseel, founder of the Institute of Histology and Microscopic Anatomy of the University of Antwerp     

Pigment-dispersing hormone-like immunoreactive neurons in the central nervous system of the gastropods, Helix pomatia and Lymnaea stagnalis

By using an antiserum raised against a crustacean #-pigment-dispersing hormone (PDH), the distribution and chemical neuroanatomy of PDH-like immunoreactive neurons was investigated in the central nervous system of the gastropod snails, Helix pomatia and Lymnaea stagnalis. The number of immunoreactive cells in the Helix central nervous system was found to be large (700-900), whereas in Lymnaea, only a limited number (50-60) of neurons showed immunoreactivity. The immunostained neurons in Helix were characterized by rich arborizations in all central ganglia and revealed massive innervation of all peripheral nerves and the neural (connective tissue) sheath around the ganglia and peripheral nerve trunks. A small number of Helix nerve cell bodies in the viscero-parietal ganglion complex were also found to be innervated by PDH-like immunoreactive processes. Hence, a complex central and peripheral regulatory role, including neurohormonal actions, is suggested for a PDH-like substance in Helix, whereas the sites of action may be more limited in Lymnaea.     

Effect of some fragments of peptide hormones on the content of biogenic monoamines from mouse brain]

The effect of some tripeptides, which are fragments of peptide hormones, and their analogs on the content of biogenic monoamines (BM) from albino mice brain was studied. It was found that thyroliberin, melanostatin and the C-terminal tripeptide of gonadoliberin activate the dophaminergic (DA-ergic) system in the forebrain of mice treated with reserpine or haloperidol, whereas the C-terminal tripeptide of gastrin acts as a synergic blocker of the DA receptors. The N-terminal tripeptides (with and without the amido group) do not affect the content of BM. No effect of the tripeptides was observed in intact animals. It is assumed that the agonistic or antagonistic effect of the tripeptides on BM is due to certain structural peculiarities of the tripeptides, e.g. the presence of the C-terminal amido group and their endogenous nature.     

Ultrastructural cytochemistry of biogenic amines in nervous tissue: methodologic improvements.

A new fixation method has been developed for localizing biogenic amines in nervous tissue. The method is a modification of the chromaffin reaction in which all fixation steps are buffered with mixtures of sodium chromate and potassium dichromate. In this way the fixation and cytochemical reaction are carried out almost simultaneously. Using the rat vas deferens as a model tissue, it was found that the preservation of electron dense (chromaffin) cores in the vesicles of adrenergic nerve terminals depended on several factors: a short primary fixation using low concentrations of aldehydes, the presence of the chromate/dichromate buffer during all fixation steps and, finally, a long incubation period in a slightly acidic (pH 6.0) solution of this buffer before postfixation in osmium tetroxide. Using this method it was possible to identify not only small and large dense-cored vesicles as storage sites for amines but also a tubular reticulum (neuronal endoplasmic reticulum), the latter especially in nerve terminals of mesenteric arteries and iris. Biogenic amines were also visualized in sympathetic ganglion cells and in the central nervous system e.g., supraependymal nerve terminals, tissues that up to now proved the most difficult in terms of amine localization. In all the tissues examined the cytochemical reaction was highly selective and present in well preserved tissue, which is a significant advance over previously available techniques. It therefore offers new opportunities for further studies on the role of biogenic amines as neurotransmitters.     

Cholinesterases and biogenic monoamines in ganglion semilunare (Gasseri)

Summary Cholinesterase distribution in trigeminal ganglion was studied in rabbits by the thiocholine method. The presence of acetylcholinesterase conditions either a) a diffusive cytoplasmatic reaction of varying intensity — from very weak to very strong — or b) an unevenly intensively distributed reaction pronounced on the periphery of ganglion cells. — The histochemical localization of biogenic monoamines was studied with the aid of the fluorescent method according to Falck and Hillarp. Green-yellow varicose terminals were found in the neighbourhood of blood vessels, between myelinized fibres, and, finally, in close vicinity of ganglion cells with which they probably form synaptic contacts.Preliminary paper read at the XVIIth Days of Physiology in Brno (Luká, Buriánek, ech 1966).