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At least 91 records · Page 5Linked to original sources
PubMed1993

Effects of met-enkephalin on electrical coupling between identified neurons in the pulmonate snails, Helix and Lymnaea.

1. The effects of met-enkephalin on electrical coupling between molluscan neurons have been investigated using the isolated brains of Helix pomatia and Lymnaea stagnalis. 2. In the presence of both serotonin and met-enkephalin, non-rectifying electrical coupling is strongly facilitated between identified respiratory neurons in Helix, whilst coupling between putative, serotonin-containing, ciliomotoneurons in Lymnaea is facilitated by met-enkephalin alone. 3. Facilitation of coupling by met-enkephalin is weaker in the strongly coupled neurons, VD1/RPaD2 of Lymnaea. 4. These data suggest that met-enkephalin can modulate different groups of electrically coupled cells and may be involved in coordination of motor patterns.

Animals↗
PubMed2004

Nucleotidase activities in membrane preparations of nervous ganglia and digestive gland of the snail Helix aspersa.

Nucleotide-metabolizing enzymes play an important role in the regulation of nucleotide levels. In the present report, we demonstrated an enzyme activity with different kinetic properties in membrane preparations of the nervous ganglia and digestive gland from Helix aspersa. ATPase and ADPase activities were dependent on Ca2+ and Mg2+ with pH optima approximately 7.2 and between 6.0 and 8.0 in digestive gland and nervous ganglia, respectively. The enzyme activities present in membrane preparations of these tissues preferentially hydrolyzed triphosphate nucleotides. In nervous ganglia, the enzyme was insensitive to the classical ATPases inhibitors. In contrast, in digestive gland, N-ethylmaleimide (NEM) produced 45% inhibition of Ca(2+)-ATP hydrolysis. Sodium azide, at 100 microM and 20 mM, inhibited Mg(2+)-ATP hydrolysis by 36% and 55% in digestive gland, respectively. The presence of nucleotide-metabolizing enzymes in these tissues may be important for the modulation of nucleotide and nucleoside levels, controlling their actions on specific purinoceptors in these species.

Adenosine Diphosphate↗
PubMed2003

Evidence for a persistent Na-conductance in identified command neurones of the snail, Helix pomatia.

Neurones RPa3 and LPa3 were identified as 'command' neurones in the Helix parietal ganglia. The physiological role of these cells is the integration of sensory information before triggering withdrawal behaviour. Properties of the Na-channels are poorly understood in these neurones which produce Na(+)-dependent action potentials in Ca(2+)-free solution. Our aim was to describe the kinetic properties and TTX-sensitivity of the Na-channels of these cells, and to provide evidence for the existence of a persistent inward sodium current (I(NaP)) in them. Two-microelectrode voltage- and patch-clamp techniques were used on isolated or semi-isolated neurones. The kinetics and potential dependence of the transient inward sodium current (I(NaT)) agreed well with those obtained on other molluscan neurones. We concluded that I(NaT) present in these neurones is slow and TTX-resistant (k(D)=8 microM of TTX) and has two components with different rates of inactivation. In addition, the presence of an I(NaP) component was revealed. We showed that I(NaP) is neither an artifact nor the contribution of a Ca-channel or a 'window' current. With slow voltage ramp pulses I(NaP) could be activated and separated from I(NaT). Like I(NaT) it appeared to be TTX-resistant and Na-dependent. I(NaP) was upregulated by increased pH (8.0) and decreased by elevated extracellular Mg(2+) concentration parallel with the I(NaT). Our results suggest that I(NaP) originates from the same set of sodium channels that underlie I(NaT).

Action Potentials↗
PubMed2002

Effects of atmospheric exposure to naphthalene on xenobiotic-metabolising enzymes in the snail Helix aspersa.

Polycyclic aromatic hydrocarbons are xenobiotics whose elevated toxicity for living organisms requires to efficiently monitor air pollution, either by evaluating their levels in the environment, or by assessing their biological impacts on sentinel organisms. We investigated the effects of naphthalene exposure on some xenobiotic-metabolising enzyme activities in three organs of Helix aspersa. Particular activities depending on cytochrome P450 (ethoxyresorufin O-deethylase, EROD; ethoxycoumarin O-deethylase, ECOD; pentoxyresorufin O-dealkylase, PROD) and associated with glutathione (glutathione S-transferase, GST; glutathione peroxidase, GPX; glutathione reductase, GR) were assessed. In control animals, the P450-dependent specific activities were distributed according to the range kidney > digestive gland > mantle cavity forming tissues (MCFT). Neither ECOD nor PROD activities could be detected in MCFT. In the two other organs, the major phase I activities were due to ECOD, the level of PROD being very low or null. The glutathione-associated activities showed comparable levels in the three organs, except GPX activity that was higher in the digestive gland. Naphthalene (NAP) exposure did not affect any activity in MCFT, but it significantly decreased EROD and ECOD activities in the kidney as opposed to their increase in the digestive gland, whereas PROD activities were not influenced by the treatment. Glutathione-dependent activities were not significantly affected by NAP exposure, except for GPX which activity diminished in the digestive gland. This study demonstrates that complex detoxification pathways should exist in Helix aspersa as in mammals and that they could be used as potential biomarkers of NAP exposure.

Animals↗