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 µm) are confined to the tentacle digits and send motor axons to the M2 and M3 muscles.

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 was investigated by applying parallel retrograde Co- and Ni-lysine tracing via the olfactory and the peritentacular nerves. Their innervation patterns in the flexor muscles were studied by applying anterograde neurobiotin tracings via these nerves. The labeled neurons are clustered in eight groups in the cerebral ganglion.

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.

Lateralized memory storage and crossed inhibition during odor processing by Limax.

After odor conditioning intact Limax maximus and injecting LY into their haemocoel, labeled groups of neurons are found in either the right or left procerebral lobe but never in both procerebral lobes. This suggests that a competitive interaction occurs between right and left odor processing pathways of which the procerebral lobe is a part. We use the nerve discharge in the external peritentacular nerve evoked by applying a puff of conditioned odor to the nose to document crossed inhibition between left and right odor processing pathways.

Olfactory oscillations augment odor discrimination not odor identification by Limax CNS.

There is great interest in the function of synchronous oscillations in olfactory centers, as documented in a wide variety of species. In Limax procerebral (PC) lobe, local field potential oscillations are ongoing and altered by odor stimulation. Recordings from external peritentacular nerves (ePTNs) reveal a neural correlate of tentacle positioning, a response signifying recognition of a conditioned odor.

Ganglionic distribution of inputs and outputs of C-PR, a neuron involved in the generation of a food-induced arousal state in Aplysia.

Cerebral neuron C-PR is thought to play an important role in the appetitive phase of feeding behavior of Aplysia. Here, we describe the organization of input and output pathways of C-PR. Intracellular dye fills of C-PR revealed extensive arborization of processes within the cerebral and the pedal ganglia.

Nitric oxide, but not serotonin, is involved in acquisition of food-attraction conditioning in the snail Helix pomatia.

The effects of inhibition of nitric oxide (NO) or serotonin (injection of nitro-L-arginine methyl ester (L-NAME) or 5,6-dihydroxytryptamine (5,6-DHT), respectively) on food-attraction conditioning was investigated in Helix. Blocking NO synthase (NOS) prior to conditioning significantly impaired the food-finding ability of the snails. Food-conditioned snails, after inhibition of NOS, remained able to locate the conditioned food.

BLIND MEXICAN CAVE FISH (ASTYANAX HUBBSI) RESPOND TO MOVING VISUAL STIMULI.

In apparatus for measuring optomotor behaviour, blind Mexican cave fish, Astyanax hubbsi, increase their swimming velocity upon rotation of a striped cylinder, i.e. in response to a solely visual stimulus.

Dopaminergic neuron B20 generates rhythmic neuronal activity in the feeding motor circuitry of Aplysia.

We have identified a buccal neuron (B20) that exhibits dopamine-like histofluorescence and that can drive a rhythmic motor program of the feeding motor circuitry of Aplysia. The cell fires vigorously during episodes of patterned buccal activity that occur spontaneously, or during buccal programs elicited by stimulation of identified cerebral command-like neurons for feeding motor programs. Preventing B20 from firing, or firing B20 at inappropriate times, can modify the program driven by the cerebral feeding command-like neuron CBI-2.

Orientation of Aplysia californica to distant food sources.

The behavior of the marine mollusc Aplysia was examined under different experimental conditions designed to determine the food searching strategy of the animals. In a small, open field tank with still water, the animals took an average of 42 min to find a piece of seaweed, even though the stimulus was never located more than 30 cm away from the animal. Observations of the animals indicated that their search was not directed, without a clear tendency towards the food, and during the course of a search, they often crawled through most of the area of the tank.

Activity of identified cerebral neuron correlates with food-induced arousal in Aplysia.

Firing of the cerebral-pedal regulator neuron, C-PR, evokes a constellation of responses which are characteristic of the food-induced arousal state that occurs following exposure of Aplysia to seaweed. To provide further evidence that C-PR plays a role in generating the food-induced arousal state, extracellular recordings from the cerebral-pedal connective, which contains the axon of C-PR, were obtained in freely moving animals. The C-PR spike in the connective recorded in vivo was then identified by comparing the wave form to the obtained by firing C-PR in an in vitro preparation.

Identification and characterization of cerebral-to-buccal interneurons implicated in the control of motor programs associated with feeding in Aplysia.

We identified candidate neurons in the cerebral ganglion that regulate feeding responses mediated by the buccal ganglion. Backfilling the cerebral-buccal connectives revealed that each cerebral hemi-ganglion contains approximately 20 neurons that project axons to the buccal ganglion. Three M-cluster neurons (CBI-1, CBI-2, CBI-3) and one E-cluster neuron (CBI-4) were identified as cerebral-to-buccal interneurons (CBIs) based on position, morphology, synaptic connections, and ability to drive buccal motor programs (BMPs).

Egg laying hormone inhibits a neuron (C-PR) involved in multiple manifestations of food-induced arousal in Aplysia.

Egg laying behavior is known to suppress feeding in Aplysia, but both behaviors have common responses involving head movements and posture. Egg laying hormone (ELH) applied in vitro to the isolated nervous system of Aplysia reduces the spontaneous and the evoked activity of the C-PR, a neuron implicated in postural responses during feeding. The inhibitory effect of ELH on the C-PR appears to be mediated by interneurons primarily located in the pedal/pleural ganglia, which contain all the known direct follower cells of the C-PR.

Studies of Behavioral State in Aplysia.

This paper reviews a series of studies on the neural organization and the cellular mechanisms underlying behavioral states; in these studies, feeding behavior in Aplysia was used as a model system. Feeding in Aplysia has similarities to motivated behaviors in other animals and is modulated by a number of interesting state variables, including arousal. Food-induced arousal manifests itself in two categories of feeding behavior: (1) appetitive responses (e.

Appetitive feeding behavior of Aplysia: behavioral and neural analysis of directed head turning.

The appetitive phase of feeding behavior in Aplysia consists of a behavioral sequence in which the quiescent animal starts to locomote and then assumes a characteristic feeding posture. In this position, head-turning responses can be elicited by a localized food stimulus (seaweed) delivered to the lips or tentacles. In response to brief (open loop) stimulation with seaweed, the animal turns toward the stimulus but greatly overshoots the target.

An identified neuron (CPR) evokes neuronal responses reflecting food arousal in Aplysia.

Feeding behavior of Aplysia is associated with an arousal state characterized by a constellation of maintained behaviors and by a potentiation or depression of responses to specific stimuli. A neuron (the cerebral-pedal regulator or CPR) that has widespread actions on various systems connected with feeding has been identified. CPR excites neurons that modulate or drive (i) body posture, (ii) biting, and (iii) cardiovascular behaviors.

Morphological differences in neuromasts of the blind cave fish Astyanax hubbsi and the sighted river fish Astyanax mexicanus.

Vital staining and scanning electron microscopy were used to study the morphology of superficial neuromasts in the blind cave fish, Astyanax hubbsi, and its sighted congener, Astyanax mexicanus. In blind Astyanax the neuromasts are 80 X 50 microns in size and possess cupulae with an oval basal shape. The length of the cupula is correlated to the location of its neuromast.

A subpopulation of cerebral B cluster neurones of Aplysia californica is involved in defensive head withdrawal but not appetitive head movements.

The cerebral B cluster neurones of Aplysia californica were studied under experimental conditions designed to evoke head movements in a selective fashion: either to approach an appetitive stimulus, or to withdraw from an aversive one. Intracellular recordings indicated the presence of two types of B cluster neurones: Bn cells that had fast (narrow) spikes, and Bb cells that had slow (broad) spikes. Tactile stimulation of the tentacles, rhinophores and lips excited Bn neurones, but inhibited Bb neurones.

Flow field, swimming velocity and boundary layer: parameters which affect the stimulus for the lateral line organ in blind fish.

The data presented support the hypothesis that the flow field supplies the stimulus to the lateral line organ (LLO) in blind cave fish (Anoptichthys jordani). Two basic predictions from the theoretical analysis of the flow field were confirmed: (i) individual blind cave fish prefer particular swimming velocities, (ii) the velocity preferred depends on the cross-sectional area (CSA) of the fish, i.e.

Collision with and avoidance of obstacles by blind cave fish Anoptichthys jordani (Characidae).

Blind Mexican cave fish (Anoptichthys jordani) were released into unknown surroundings and their swimming tracks were recorded. During the first 24 h in a new tank, i.e.