Activity of an identified histaminergic neuron, and its possible role in arousal of feeding behavior in semi-intact Aplysia

Abstract

The possible functions of histaminergic neuron C2 were studied in an isolated head preparation from which it was possible to obtain intracellular recordings while the buccal mass exhibited feeding-like responses. Application of food to the lips of the isolated head preparation elicited rhythmic buccal movements that appeared to be ingestion responses, since they moved seaweed into the buccal cavity and towards the esophagus, and their frequency and regularity was similar to the ingestion responses studied in a group of intact animals. The ingestion responses of the buccal mass consisted of 2 main phases of movement of the radula from a middle rest position: forward and return to rest, and backward and return to rest. The relative magnitudes and timing of these 2 phases were variable. Intracellular recordings from C2 in the isolated head revealed that C2 is silent when the buccal mass is quiescent, but that it can be excited into spike activity, either by mechanical stimulation of the perioral zone or by chemostimulation that results in rhythmic movement. C2 fires a burst of spikes in phase with each protraction-retraction cycle, and, if the movements continue, C2 fires even when the eliciting stimulus has been removed. Activity of the cell was usually preceded by fast depolarizing responses that appeared to be blocked axon spikes. The evidence suggests that C2 is part of a positive feedback loop that may help maintain the persistence of arousal of feeding behavior beyond the time that food stimuli are removed.

Neural Analog of Arousal: Persistent Conditional Activation of a Feeding Modulator by Serotonergic Initiators of Locomotion

“…Notably, the CC9 -10 induced depolarization may act in concert with the intrinsic anomalous rectification of the MCC (Kandel and Tauc, 1966;Weiss and Kupfermann, 1976) to further enhance the EPSPs that C2 evokes. C2 (Weiss et al, 1986b) is activated when food contacts the mouth and remains active as feeding progresses. Thus, the effects of CC9 -10 on the MCCs are not manifested unless another input is present (e.g., food).…”

“…Figure 1 A shows the distribution of serotonergic neurons on the dorsal surface of the cerebral ganglion (see also Fickbohm et al, 2001). In the anterior cluster (within the G cluster), there is a giant serotonergic neuron, the MCC, which sends its axon to the buccal ganglion and plays an important role in modulating the feeding network (Weiss et al, 1978(Weiss et al, , 1986bRosen et al, 1989). Adjacent to the MCC, there are several smaller serotonergic neurons that are often located closer to the ventral surface.…”

“…A likely possibility would be that this input would be food related. A previously identified sensory neuron activated by food is the cerebral C2 neuron, which is histaminergic (Weinreich et al, 1975;Weinreich, 1977;McCaman and Weinreich, 1985;Weiss et al, 1986a) and nitregic (Jacklet, 1995;Koh and Jacklet, 1999), is a mechanosensory neuron (Weiss et al, 1986c), is rhythmically active during feeding behavior (Weiss et al, 1986b), and provides slow EPSPs onto the ipsilateral MCC. This network organization provides us an opportunity to examine potential interactions between the two modulatory pathways, both of which act on the MCC.…”

“…The buccal mass pressure was monitored with a pressure transducer, which had a probe placed in the bubble separator. Buccal mass pressure has been shown to correspond well with feeding movements (Weiss et al, 1986b). The preparation was maintained at 14 -16°C.…”

Neuromechanics of Coordination during Swallowing inAplysia californica

“…The feeding apparatus of the animal is a grasping device that the animal uses to manipulate and ingest food (Kupfermann, 1974). Activity of individual nerve cells that control the grasper during feeding has been monitored in intact animals (Warman and Chiel, 1995), movements of the feeding musculature have been visualized in intact animals (Neustadter et al, 2002), and semi-intact preparations have been used to explore the effects of motor neuronal activity on grasper biomechanics (Weiss et al, 1986;Cropper et al, 1990;Morton and Chiel 1993b;Evans et al, 1996;Orekhova et al, 2001).…”