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At least 55 records · Page 3Linked to original sources
PubMed1981

The time courses of intracellular free calcium and related electrical effects after injection of CaCl2 into neurons of the snail, Helix pomatia.

Controlled quantities of 100 mM aqueous CaCl2 solutions were pressure injected into voltage-clamped neurons with a resolution of 10(-11) 1. Ca2+-selective microelectrodes monitored the time course of changes in [Ca2+]i. At a membrane potential of -50 mV CaCl2 quantities in the range of 1% of the cell volume induced an inward current, associated with a conductance increase and having an equilibrium potential between -20 and +20 mV, which accompanied the rise in [Ca2+]i. An artifactual origin of the inward current by the injection procedure or by calcium screening of membrane sites could be excluded. The calcium-induced hyperpolarizing conductance, producing an outward current at -50 mV, followed the inward current and reached maximum during the late decline in [Ca2+]i. In most cases its development was separated from the inward current by an intermediate relative decrease of the membrane conductance. Neither of the two transient conductance increases showed a particular dependence on voltage. Renewed Ca2+ injection quickly decreased the calcium-induced hyperpolarizing conductance for several seconds. Ca2+ injections below 0.05% of the cell volume mostly produced pure outward currents or hyperpolarizing responses. Partial substitution of extracellular CaCl2 by NiCl2 decreased the hyperpolarizing response but not the initial inward current. The immediate effects of increased [Ca2+]i are activation of a depolarizing conductance and the partial block of the late hyperpolarizing conductance. The latter is probably produced through intermediate steps after increasing [Ca2+]i.

Animals↗
PubMedDate not supplied

Processing of mechano- and chemosensory information in the lip nerve and cerebral ganglia of the snail Helix pomatia L.

Neurophysiologists have long been seeking simple model systems in which to analyze the neuronal mechanisms underlying the organization of behavior. The feeding behavior of molluscs has proved to be one of the most useful simple systems for the analysis of cyclical motor patterns, the interactions of central pattern generating interneurons, and the role of sensory inputs in the initiation and maintenance of the behavior. Considerable progress has been made in one or both of the first two aspects of this research in Lymnaea, Helisoma, Limax, Planorbarius, Pleurobranchaea, and Tritonia (for reviews see [3, 7, 8, 15]), and more recently, in Aplysia [39] and Planorbis [1]. The role of mechano- and chemosensory inputs in the organization of the feeding behavior was studied in at least twenty molluscan species (for a review see [3]). However, in only less than half of them was the analysis extended to the effect of tactile and chemical inputs on identified neurons in the buccal and cerebral ganglia which contain the feeding circuitry (Aplysia: [12, 22, 36, 41]; Pleurobranchaea: [9, 16, 17]; Tritonia: [2]; Helisona: [21]; Limax: [11, 14, 35]: Helix: [6, 19, 24-26, 32, 38]). In the present work I would like to review our earlier findings on the processing of mechano and chemosensory information in the lip nerves and cerebral ganglia of Helix pomatia L. These findings were published in a series of papers between 1982 and 1987 [19, 20, 24-26]. The results reviewed here prepared the way for the development of new lines of research in our laboratory on the plasticity and serotonergic modulation of feeding in this widely used experimental animal [27, 40].

Animals↗
PubMedDate not supplied

Influence of oxytocin on identified neurons of the brain of the snail Helix pomatia L.

The responses of identified neurons induced by the effect of perfusion with a solution of oxytocin were investigated in this study. Depolarizing, hyperpolarizing, and modulating types of responses were found. It is hypothesized that these responses are associated in the majority of instances with the system of cyclic nucleotides.

Acetylcholine↗
PubMed2005

Modulation of heart activity during withdrawal reflexes in the snail Helix aspersa.

The beating activity of the molluscan heart is myogenic, but it is influenced by nervous signals of central origin. Previous studies have demonstrated changes in cardiac output during feeding and other behaviors. Here, we describe a short latency, transient cardiac response that accompanies withdrawal reflexes. When evoked by electrical stimulation of peripheral nerves, the response was detected within one or two heartbeats. Beat amplitudes increased on average 11.6%, and inter-beat intervals decreased on average 2.1%. The mean duration of the response was 28.1 s. A transient inhibitory phase often preceded the excitatory response. Results from testing various nerves and tissues show that the cardiac responses invariably occur whenever contractions of the tentacle retractor muscle are elicited. Even stimulation of the ovotestis and the kidney elicit responses despite their protected locations within the mantle cavity. Three excitatory cardioactive neurons are identified in the central nervous system of Helix aspersa, and their involvement in the reflex response is documented. The results suggest that the heart output is initially inhibited to relax the hydroskeleton and thereby aid withdrawal movements. A delayed increase in cardiac output then facilitates the re-inflation, hence eversion, of the withdrawn body parts.

Adaptation, Physiological↗