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

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

Neurons Controlling Aplysia Feeding Inhibit Themselves by Continuous NO Production

Neural activity can be affected by nitric oxide (NO) produced by spiking neurons. Can neural activity also be affected by NO produced in neurons in the absence of spiking?Applying an NO scavenger to quiescent Aplysia buccal ganglia initiated fictive feeding, indicating that NO production at rest inhibits feeding. The inhibition is in part via effects on neurons B31/B32, neurons initiating food consumption. Applying NO scavengers or nitric oxide synthase (NOS) blockers to B31/B32 neurons cultured in isolation caused inactive neurons to depolarize and fire, indicating that B31/B32 produce NO tonically without action potentials, and tonic NO production contributes to the B31/B32 resting potentials. Guanylyl cyclase blockers also caused depolarization and firing, indicating that the cGMP second messenger cascade, presumably activated by the tonic presence of NO, contributes to the B31/B32 resting potential. Blocking NO while voltage-clamping revealed an inward leak current, indicating that NO prevents this current from depolarizing the neuron. Blocking nitrergic transmission had no effect on a number of other cultured, isolated neurons. However, treatment with NO blockers did excite cerebral ganglion neuron C-PR, a command-like neuron initiating food-finding behavior, both in situ, and when the neuron was cultured in isolation, indicating that this neuron also inhibits itself by producing NO at rest.Self-inhibitory, tonic NO production is a novel mechanism for the modulation of neural activity. Localization of this mechanism to critical neurons in different ganglia controlling different aspects of a behavior provides a mechanism by which a humeral signal affecting background NO production, such as the NO precursor L-arginine, could control multiple aspects of the behavior

Neural correlates of higher-order integration between multiple behaviors in Aplysia Final scientific report

Available from TIB Hannover: DtF QN1(65,9) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEGerman-Israeli Foundation for Scientific Research and Development (GIF), Oberschleissheim (Germany)DEGerman

Novel triplet of flexor muscles in the posterior tentacles of the snail, Helix pomatia

The anatomy of three novel flexor muscles in the posterior tentacles of Helix pomatia is described. The muscles originate from the ventral side of the sensory pad and are anchored at different sites in the base of the tentacle stem. The muscles span the tentacle and always take the length of the stem which depends on the rate of tentacle protrusion indicating that the muscles are both contractile and extremely stretchable. The three anchoring points at the base of the stem determine three space axes along which the contraction of a muscle or the synchronous contraction of the muscles can move the tentacle in space