Figure 1.
Schematic presentation of the neural circuitry underlying taste aversion training in the Lymnaea CNS.
The signals of the CS and US are associated in the CGC. Rectangles and circles indicate interneurons and motor neurons, respectively. At synapses, open circles and closed circles indicate excitatory monosynaptic inputs and inhibitory monosynaptic inputs, respectively. The N1M, N2 and N3t cells form part of the feeding CPG. The EPSPs recorded in the B1 and B3 motor neurons can be used for monitoring the changes in the synaptic connections of CGC-N3t and N3t-N1M, respectively.
Figure 2.
Learning scores by taste aversion training.
After the CS was paired 10 times with the US in the taste aversion-training session, the feeding response to the CS was significantly reduced (**P<0.01) at the posttest of 10 min, compared to those observed for the backward-conditioned and naive control snails. In all cases in the pretest session, there were no significant differences (P>0.05) in the feeding response of the taste aversion-trained snails, backward-conditioned or naive control snails. TA, BW and naive indicate taste aversion-trained snails, backward-conditioned snails and naive control snails. The numbers of snails used were 55, 48 and 28 for the taste aversion-trained snails, backward-conditioned snails and naive control snails, respectively.
Figure 3.
Evoked compound EPSPs in the B1 motor neuron by activation of the CGC.
The data correspond to the strength of the CGC-N3t synaptic connection. A. Typical recordings of evoked compound B1 EPSPs. Left: a recording from a taste aversion-trained snail; right: a recording from a backward-conditioned snail. Upper: recordings of evoked compound B1 EPSPs; lower: recordings of spikes of the CGCs. We adjusted the magnitude of the depolarizing current to elicit about 10 spikes in the CGC during a 1-s current injection and monitored the compound EPSP evoked by this activation. B. There were no significant differences (P>0.05) in the B1 EPSPs of the taste aversion-trained snails, backward-conditioned and naive control snails. TA, BW and naive indicate taste aversion-trained snails, backward-conditioned snails and naive control snails. The numbers of EPSP recordings used were 74, 47 and 49. These data were accumulated at 3 to 6 h after the training, by 5 recordings for the isolated CNSs prepared from the 18 taste aversion-trained snails, 10 backward-conditioned snails and 13 naive control snails, respectively.
Figure 4.
Spontaneous single EPSP in the B3 motor neuron.
The data correspond to the strength of the N3t-N1M synaptic connection. A. Typical recordings of spontaneous B3 EPSPs. Left: a recording from a taste aversion-trained snail; right: a recording from a backward-conditioned snail. B. The EPSPs recorded in the B3 motor neurons from the taste aversion-trained snails were significantly larger (**P<0.01 and *P<0.05) than those observed for the backward-conditioned and naive control snails, respectively. There was no significant difference (P>0.05) in the EPSPs between the backward-conditioned and naive control snails. TA, BW and naive indicate taste aversion-trained snails, backward-conditioned snails and naive control snails. The numbers of EPSP recordings used were 64, 65 and 86. These data were accumulated at 3 to 6 h after the training for the isolated CNSs prepared from the 7 taste aversion-trained snails, 10 backward-conditioned snails and 10 naive control snails, respectively.