Alan M. Daniel

Opioid receptors modulate recovery from consummatory successive negative contrast.

Three experiments explored the role of the opioid system in consummatory successive negative contrast. In Experiment 1, rats treated with the nonspecific opioid-receptor antagonist naloxone (2mg/kg) exhibited increased suppression after a shift from 32% to 6% sucrose solution (32-->6), relative to 6-->6 unshifted controls. A similar but shorter effect was observed with the delta-opioid receptor antagonist naltrindole (1mg/kg). In Experiment 2, naloxone increased suppression after a more conventional 32-->4 sucrose shift. In Experiment 3, rats classified as expressing slow recovery from contrast (after a 32-->4 sucrose downshift) were more sensitive to naloxone in an activity test than fast-recovery rats. Whereas it was previously known that contrast was reduced by the extrinsic administration of opioid agonists, the effects reported here with antagonists provide the first evidence that the opioid system is intrinsically engaged by situations involving surprising reward loss.

Selective Effects of the δ-Opioid Receptor Agonist DPDPE on Consummatory Successive Negative Contrast.

Two experiments explored the role of the opioid system in a situation involving a surprising reduction in reward magnitude: consummatory successive negative contrast. Rats received access to 32% sucrose solution (preshift Trials 1-10) followed by 4% solution (postshift Trials 11-15). Independent groups received an injection of either the vehicle or the delta-receptor agonist [D-Ala2-,N-Me-Phe4,Gly-ol] enkephalin (DPDPE; 24 microg/kg). DPDPE attenuated the contrast effect when injected before Trial 11 but not when injected before Trial 12. An additional experiment showed that the attenuating effect of partial reinforcement on the recovery from contrast was reduced by DPDPE injections administered before nonreinforced preshift trials.

Trial-selective effects of U50,488H, a κ-opioid receptor agonist, on consummatory successive negative contrast

A series of experiments studied the effects of the kappa-opioid receptor agonist U50,488H on consummatory successive negative contrast (cSNC) in rats. In cSNC, previous experience with a 32% sucrose solution leads to greater rejection of 4% sucrose than exclusive experience with 4% sucrose. Experiments 1 and 2 revealed that U50,488H failed to influence cSNC when administered before the first downshifted trial, but either attenuated (1mg/kg) or enhanced (3 and 10mg/kg) cSNC when administered before the second downshift trial. Experiment 3 showed that U50,488H administered immediately after the first downshift trial had no effect on cSNC at the 1mg/kg dose, but tended to increase cSNC at the 3mg/kg dose. However, Experiment 4 suggested that the apparent enhancement of cSNC after 3mg/kg U50 administered posttrial 11 may have reflected the development of a conditioned taste aversion. The trial-selective attenuating effect of the low dose may reflect an anxiolytic-like property of U50,488H.

Memory interfering effects of chlordiazepoxide on consummatory successive negative contrast

Long-Evans rats downshifted from 32% to 4% sucrose solution exhibit lower consummatory behavior during downshift trials than rats exposed only to 4% sucrose. In Experiment 1, this effect, called consummatory successive negative contrast (cSNC), was attenuated by administration of the benzodiazepine anxiolytic chlordiazepoxide (CDP, 5mg/kg, ip) before the second downshift trial (Trial 12), but was not affected when CDP was administered before the first downshift trial (Trial 11). In Experiment 2, CDP administered after Trial 11 actually enhanced the cSNC effect on Trial 12. This posttrial effect of CDP was reduced by delayed administration (Experiment 3). This CDP effect was not present in the absence of incentive downshift (Experiments 4-5), or when animals were tested with the preshift incentive (Experiment 6) or after complete recovery from cSNC (Experiment 7). The posttrial CDP effect was observed after an 8-day interval between Trials 11 and 12 (Experiment 8) and when administered after Trial 12, rather than Trial 11 (Experiment 9). Experiment 10 extended the effect to Wistar rats. Because CDP is a memory interfering drug, it was hypothesized that its posttrial administration interferes with the consolidation of the memory of the downshifted incentive, thus prolonging the mismatch between expected (32% sucrose) and obtained (4% sucrose) incentives that leads to the cSNC effect.

Role of the opioid system in incentive downshift situations

Previous research has shown that opioid blockage enhances consummatory successive negative contrast (cSNC)-a suppression of consummatory behavior following a downshift from 32% to 4% sucrose solution. In Experiment 1, administration of the nonselective opioid receptor antagonist naloxone (2 mg/kg, ip) distorted the comparison between expected and received incentives. The results of Experiment 2 discarded the alternative that naloxone enhances cSNC by inducing a conditioned taste aversion. The results of Experiments 3a-3c provided no evidence that opioid administration after the first downshift trial modulated subsequent consummatory performance. The opioids tested included naloxone (2mg/kg, ip), the delta-opioid receptor selective antagonist naltrindole (1 mg/kg, ip), and the delta-opioid receptor selective agonist DPDPE (24 microg/kg, ip). The selected doses have proven in earlier experiments to be effective when administered before training. Experiments 4-5 failed to uncover any effects of posttraining opioid blockage with naloxone in an appetitive extinction task (autoshaping with lever-food pairings). These results add to our previous understanding of opioid function in situations involving incentive downshifts, suggesting a role in the comparison process that triggers cSNC, but no apparent function in memory consolidation related to the downshift event.

Effects of housing on consummatory successive negative contrast in rats : wire- bottom cages versus polycarbonate tubs

In consummatory successive negative contrast, rats that have had experience drinking 32% sucrose solution drink significantly less 4% sucrose solution than rats that have drunk only 4% solution. This contrast effect occurs reliably when rats are housed in wire-bottom cages, but it occurs significantly less frequently when rats are housed in polycarbonate tubs. Although it is unclear what causes these differences among housing conditions, the present study underscores the impact that housing conditions outside the domain of the training environment can have on behavioral outcomes.

A new model for sexual conditioning: the ring dove (Streptopelia risoria).

Sexual conditioning investigations have primarily used rats and domestic quail as subjects. Although much has been learned from such experiments, the relative simplicity of rat and quail reproductive behavior prohibits investigation of certain experimental questions about sexual conditioning. In contrast, the reproductive behavior of male and female ring doves (Streptopelia risoria) is complex, involving courtship, bonding, and parental care. In the present experiment, male ring doves that were presented with a visual conditioned stimulus paired with access to their pair-bonded mate (the unconditioned stimulus) showed sexual conditioned responding in the presence of the conditioned stimulus. These results represent the first evidence of sexual conditioning in ring doves and illustrate the potential of ring doves as a useful model for future sexual conditioning investigations.