Cerebral CBm1 Neuron Contributes to Synaptic Modulation Appearing During Rejection of Seaweed inAplysia kurodai

Abstract

Narusuye, Kenji, and Tatsumi Nagahama. Cerebral CBM1 neuron contributes to synaptic modulation appearing during rejection of seaweed in Aplysia kurodai. J Neurophysiol 88: 2778J Neurophysiol 88: -2795J Neurophysiol 88: , 2002 10.1152/jn.00757.2001. The Japanese species Aplysia kurodai feeds well on Ulva but rejects Gelidium with distinctive rhythmic patterned movements of the jaws and radula. We have previously shown that the patterned jaw movements during the rejection of Gelidium might be caused by long-lasting suppression of the monosynaptic transmission from the multiaction MA neurons to the jaw-closing (JC) motor neurons in the buccal ganglia and that the modulation might be directly produced by some cerebral neurons. In the present paper, we have identified a pair of catecholaminergic neurons (CBM1) in bilateral cerebral M clusters. The CBM1, probably equivalent to CBI-1 in A. californica, simultaneously produced monosynaptic excitatory postsynaptic potentials (EPSPs) in the MA and JC neurons. Firing of the CBM1 reduced the size of the inhibitory postsynaptic currents (IPSCs) in the JC neuron, evoked by the MA spikes, for Ͼ100 s. Moreover, the application of dopamine mimicked the CBM1 modulatory effects and pretreatment with a D1 antagonist, SCH23390, blocked the modulatory effects induced by dopamine. It could also largely block the modulatory effects induced by the CBM1 firing. These results suggest that the CBM1 may directly modulate the synaptic transmission by releasing dopamine. Moreover, we explored the CBM1 spike activity induced by taste stimulation of the animal lips with seaweed extracts by the use of calcium imaging. The calciumsensitive dye, Calcium Green-1, was iontophoretically loaded into a cell body of the CBM1 using a microelectrode. Application of either Ulva or Gelidium extract to the lips increased the fluorescence intensity, but the Gelidium extract always induced a larger change in fluorescence compared with the Ulva extract, although the solution used induced the maximum spike responses of the CBM1 for each of the seaweed extracts. When the firing frequency of the CBM1 activity after taste stimulation was estimated, the Gelidium extract induced a spike activity of ϳ30 spikes/s while the Ulva extract induced an activity of ϳ20 spikes/s, consistent with the effective firing frequency (Ͼ25 spikes/s) for the synaptic modulation. These results suggest that the CBM1 may be one of the cerebral neurons contributing to the modulation of the basic feeding circuits for rejection induced by the taste of seaweeds such as Gelidium.

Classical Olfactory Conditioning in the Cockroach Periplaneta americana

“…In addition, in studies using the nematode Caenorhabditis elegans, the involvement of Ras/ MAPK signaling in olfaction was demonstrated (Hirotsu et al, 2000), and a secretory protein that regulates sensory integration and learning was identified (Ishihara et al, 2002). Other notable findings from our research project include the first behavioral demonstration of color vision by spiders (Nakamura and Yamashita, 2000) and identification of a cerebral neuron that contributes to synaptic modulation during taste aversion learning in Aplysia (Narusuye and Nagahama, 2002).…”

Feeding Neural Networks in the Mollusc <i>Aplysia</i>

“…It has been postulated that there is more than one type of egestive behavior in Aplysia [59,103,104]. In part, this is suggested by the fact that one type of response (i.e., active seaweed rejection) appears to be dependent on the cerebral ganglion [103][104][105], while a second type (i.e., egestion of a tube) is not [59]. As might be expected, therefore, rejection-like motor programs can be triggered in the isolated nervous system via CBI stimulation.…”

“…the neuron CBI-1. This cell has been identified and characterized in both Aplysia californica [60] and A. kurodai [105]. In A. kurodai, the designation CBM1 is used [105].…”

“…This cell has been identified and characterized in both Aplysia californica [60] and A. kurodai [105]. In A. kurodai, the designation CBM1 is used [105]. In A. californica, CBI-1 responds to touch of the tentacles, lips, and buccal mass [60].…”

“…In A. kurodai, CBM1 is specifically associated with active rejection [105]. Thus, A. kurodai feed well on one type of seaweed, i.e.…”