34 research outputs found
Physiological and Pharmacological Properties of Superior Tentacular Muscles Participating in Olfactory Orientation of the Land Snail, Helix Pomatia
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Novel peripheral motor neurons in the posterior tentacles of the snail responsible for local tentacle movements
Three flexor muscles of the posterior tentacles of the snail Helix pomatia have recently been described. Here, we identify their local motor neurons by following the retrograde transport of neurobiotin injected into these muscles. The mostly unipolar motor neurons (15-35 A mu m) are confined to the tentacle digits and send motor axons to the M2 and M3 muscles. Electron microscopy revealed small dark neurons (5-7 A mu m diameter) and light neurons with 12-18 (T1 type) and 18-30 A mu m diameters (T2 type) in the digits. The diameters of the neurobiotin-labeled neurons corresponded to the T1 type light neurons. The neuronal processes of T1 type motor neurons arborize extensively in the neuropil area of the digits and receive synaptic inputs from local neuronal elements involved in peripheral olfactory information processing. These findings support the existence of a peripheral stimulus-response pathway, consisting of olfactory stimulus-local motor neuron-motor response components, to generate local lateral movements of the tentacle tip ("quiver"). In addition, physiological results showed that each flexor muscle receives distinct central motor commands via different peritentacular nerves and common central motor commands via tentacle digits, respectively. The distal axonal segments of the common pathway can receive inputs from local interneurons in the digits modulating the motor axon activity peripherally without soma excitation. These elements constitute a local microcircuit consisting of olfactory stimulus-distal segments of central motor axons-motor response components, to induce patterned contraction movements of the tentacle. The two local microcircuits described above provide a comprehensive neuroanatomical basis of tentacle movements without the involvement of the CNS
Voltage-gated membrane currents in neurons involved in odor information processing in snail procerebrum
Excitatory neurotransmitters in the tentacle flexor muscles responsible for space positioning of the snail olfactory organ
Recently, three novel flexor muscles (M1, M2 and M3) in the posterior tentacles of the snail have been described, which are responsible for the patterned movements of the tentacles of the snail, Helix pomatia. In this study, we have demonstrated that the muscles received a complex innervation pattern via the peritentacular and olfactory nerves originating from different clusters of motoneurons of the cerebral ganglia. The innervating axons displayed a number of varicosities and established neuromuscular contacts of different ultrastructural forms. Contractions evoked by nerve stimulation could be mimicked by external acetylcholine (ACh) and glutamate (Glu), suggesting that ACh and Glu are excitatory transmitters at the neuromuscular contacts. Choline acetyltransferase and vesicular glutamate transporter immunolabeled axons innervating flexor muscles were demonstrated by immunohistochemistry and in Western blot experiments. Nerve- and transmitter-evoked contractions were similarly attenuated by cholinergic and glutamatergic antagonists supporting the dual excitatory innervation. Dopamine (DA, 10−5 M) oppositely modulated thin (M1/M2) and thick (M3) muscle responses evoked by stimulation of the olfactory nerve, decreasing the contractions of the M1/M2 and increasing those of M3. In both cases, the modulation site was presynaptic. Serotonin (5-HT) at high concentration (10−5 M) increased the amplitude of both the nerve- and the ACh-evoked contractions in all muscles. The relaxation rate was facilitated suggesting pre- and postsynaptic site of action. Our data provided evidence for a DAergic and 5-HTergic modulation of cholinergic nerves innervating flexor muscles of the tentacles as well as the muscles itself. These effects of DA and 5-HT may contribute to the regulation of sophisticated movements of tentacle muscles lacking inhibitory innervation
Anatomical and physiological background permitting spatial odor sensation in stylommatophoran molluscs
Earlier experiments demonstrated that in order to place protracted tentacles and thereby olfactory receptors in an appropriate position for optimal perception of odor stimuli extraordinary complex movements are required. Until recently both large scale tentacle movements and patterned tentacle movements have been attributed to the concerted involvement of the tentacle retractor muscle and muscles of tegumentum. Recently the existence of three novel muscles in the posterior tentacles of Helix has been discovered. The present review, based on experimental data obtained by our research group, outlines the anatomy, physiology and pharmacology of these muscles that enable the tentacles to execute complex movements observed during foraging both in naïve and food-conditioned snails. Our findings are also compared as far as possible with earlier and recent data obtained on innervation characteristics and pharmacology of molluscan muscles
Potassium channels in the central nervous system of the snail, Helix pomatia : localization and functional characterization
A QT-intervallum rövidtávú variabilitásának fokozódása előre jelzi a ciszaprid indukálta kamrai ritmuszavarok kialakulását [Increased short-term variability of the QT interval predicts cisapride induced ventricular arrhythmias]
PACAP modulates acetylcholine-elicited contractions at nicotinic neuromuscular contacts of the land snail
In this study, we investigate the potentiating effect of PACAP27 on cholinergic neuromuscular transmission in the recently discovered flexor muscles of the land snail, Helix pomatia. Using immunohistochemistry, we show that PACAP and PAC1 receptors are present in nerve fibers innervating the flexor muscles but not in the muscle itself. We also observed that PACAP27 exerts both pre- and postsynaptic effects on the cholinergic synapse and performed tests using a broad spectrum of chemicals in order to explore the possible intracellular pathways through which PACAP mediates its stimulatory effect. Our pharmacological data demonstrate that PACAP27 presynaptically enhances the release of acetylcholine by activating the adenylate cyclase-cAMP-PKA pathway. Postsynaptically, PACAP27 was found to enhance muscle contractility by PKC-mediated signaling pathway resulting in an increased Ca2+ release from intracellular stores. These findings suggest that regulation of Ca2+ release may contribute to the stimulatory effect of PACAP. Our data are the first demonstration of the potentiating effect of PACAP27 at the molluscan excitatory neuromuscular contact
Neuronal background of positioning of the posterior tentacles in the snail Helix pomatia
The location of cerebral neurons innervating the three recently described flexor muscles
involved in the orientation of the posterior tentacles as well as their innervation patterns were
investigated, applying parallel retrograde Co- and Ni-lysine as well as anterograde
neurobiotin tracings via the olfactory and the peritentacular nerves. The neurons are clustered
in eight groups in the cerebral ganglion and they send a common innervation pathway via the
olfactory nerve to the flexor and the tegumental muscles as well as the tentacular retractor
muscle and distinct pathways via the internal and the external peritentacular nerves to these
muscles except the retractor muscle. The three anchoring points of the three flexor muscles at
the base of the tentacle outline the directions of three force vectors generated by the
contraction of the muscles along which they can pull or move the protracted tentacle which
enable the protracted tentacle to bend around a basal pivot. In the light of earlier physiological
and the present anatomical findings we suggest that the common innervation pathway to the
muscles is required to the tentacle withdrawal mechanism whereas the distinct pathways serve
first of all the bending of the protracted posterior tentacles during foraging
Regional adaptation defines sensitivity to future ocean acidification
Physiological responses to temperature are known to be a major determinant of species distributions and can dictate the sensitivity of populations to global warming. In contrast, little is known about how other major global change drivers, such as ocean acidification (OA), will
shape species distributions in the future. Here, by integrating population genetics with experimental data for growth and mineralization, physiology and metabolomics, we
demonstrate that the sensitivity of populations of the gastropod Littorina littorea to future OA is shaped by regional adaptation. Individuals from populations towards the edges of the natural latitudinal range in the Northeast Atlantic exhibit greater shell dissolution and the inability to upregulate their metabolism when exposed to low pH, thus appearing most sensitive to low seawater pH. Our results suggest that future levels of OA could mediate
temperature-driven shifts in species distributions, thereby influencing future biogeography and the functioning of marine ecosystems