Article Figures & Data
Figures
- Figure 1.
HEX blocked the EPSP in B51 produced by AT4 stimulation in ganglia preparations. The magnitude of the CS-evoked synaptic input to B51 was quantified while B51 was current-clamped at −60 mV. A, Representative intracellular recordings from B51 during AT4 nerve stimulation. AT4 stimulation typically produced a complex PSP in B51 (Pretest) with an initial inhibitory phase followed by a delayed excitatory phase. The EPSP was selectively blocked by HEX (100 μm) and recovered following washout (Washout). B, Measurement of the peak IPSP and EPSP at two different doses of hexamethonium. The dashed line represents the baseline potential in B51 (i.e., − 60 mV) before stimulation of AT4. B1, No significant difference was observed between the peak EPSPs induced by consecutive AT shocks in the absence of HEX (0 μm). In contrast, the 10 μm dose of hexamethonium produced a significant effect (p < 0.05, Friedman test). A post hoc analysis revealed a significant block of the EPSP (p < 0.05, Newman–Keuls test), which recovered (p < 0.05, Newman–Keuls test) following the washout. The 100 μm dose of hexamethonium also produced a significant effect (p < 0.05, Friedman test). A post hoc analysis revealed a significant block of the EPSP (p < 0.05, Newman–Keuls test), which recovered (p < 0.05, Newman–Keuls test) following the washout. B2, No significant difference was observed between the peak values of the IPSP at each dose of hexamethonium.
- Figure 2.
Development of the single-cell analog of classical conditioning. For each cell, the burst threshold, input resistance, and response to ACh were measured before (PreTest), immediately after (Post-Test, 0 h), and 24 h after (Post-Test, 24 h) the single-cell analog of classical conditioning. For the US, both DA and chloro-APB (D1R agonist) were tested. A1, A2, Representative intracellular recordings from B51 illustrating the measurement of the burst threshold. In these two examples, the burst threshold increased in the paired group from 0.6 nA initially to 0.9 nA immediately after training and to 1.0 nA 24 h after training (A1), whereas the threshold decreased slightly from 0.7 nA initially to 0.6 nA 24 h after training in the unpaired control group (A2). A3, Summary data. A significant difference was observed among the three groups (ACh paired with DA, unpaired, and ACh paired with D1R agonist) immediately after conditioning (p < 0.05, Kruskal–Wallis test). A post hoc analysis revealed a significant increase in the burst threshold in the group that received ACh paired with DA compared with either the unpaired control (p < 0.05, Newman–Keuls test) or the group that received ACh paired with the D1 agonist (p < 0.05, Newman–Keuls test). The increase in the burst threshold was still present 24 h after conditioning in the ACh paired with DA group, compared with the unpaired group (p < 0.05, Mann–Whitney test). B1, B2, Representative measurements of the input resistance of B51. B3, Summary data. No significant differences were observed between the three groups (ACh paired with DA, unpaired, and ACh paired with D1R agonist) immediately after conditioning or between the two groups (ACh paired with DA, and unpaired) 24 h after conditioning. C1, C2, Representative intracellular recordings from B51 illustrating the responses to ACh delivery. C3, Summary data. A significant difference was observed among the three groups immediately after conditioning (p < 0.05, Kruskal–Wallis test). A post hoc analysis revealed a significant increase in the ACh response in the group that received ACh paired with DA compared with either the unpaired control (p < 0.05, Newman–Keuls test) or the group that received ACh paired with the D1R agonist (p < 0.05, Newman–Keuls test). The increase in the ACh response persisted 24 h after conditioning in the ACh paired with DA group, compared with the unpaired group (p < 0.05, Mann–Whitney test).
- Figure 3.
Putative model of the mechanisms underlying operant and classical conditioning in neuron B51. Operant conditioning: In this model, the operant is represented by a plateau potential. In turn, the plateau potential produces an accumulation of Ca2+ in B51, which can lead to the activation of PKC. The PKC then phosphorylates adenylyl cyclase (AC) and primes AC for enhanced synthesis of cAMP. The reinforcement is mediated by DA. Because a D1R agonist can support operant conditioning in the single-cell analog, the DA in this model of operant conditioning binds to D1R and likely acts via AC to increase the production of cAMP. If a plateau potential immediately precedes the reinforcement and AC was phosphorylated by PKC, then the production of cAMP is greater than what would occur after either behavior alone or DA alone. After a sufficient number of contingent reinforcements, the increased levels of cAMP would activate PKA sufficiently to increase the excitability of B51. Classical conditioning: In this model, the US is mediated by DA, and the CS is mediated by ACh. Because D1R agonist did not support classical conditioning, the DA in this classical conditioning model binds to a D2-like receptor. The site of convergence between the US and CS has yet to be determined. Similarly, the effector molecules downstream from the CS and US are unknown. Nevertheless, when pairing of the CS and US occurs repeatedly a decrease in excitability is produced as well as an enhanced response to ACh in B51. Finally, the analogs of operant and classical conditioning induce long-term changes in B51. Consistent with the induction of long-term memory, the analog of operant conditioning induced the phosphorylation of CREB1. However, the processes responsible for long-term classical conditioning are unknown. Red components of the model are associated with operant conditioning, and green components are associated with classical conditioning. Yellow components represent sites of convergence between either the operant and reinforcement, or the CS and US. Blue components represent sites that overlap between operant and classical conditioning. Arrows represent an enhancement or positive interaction, whereas filled circles represent an inhibition or negative interaction.
