Dissociating ventral and dorsal subicular dopamine D1 receptor involvement in instrumental learning, spontaneous motor behavior, and motivation

Abstract

A series of experiments investigating the role of dopamine D1 receptors in the ventral subiculum (vSUB) and dorsal subiculum (dSUB), 2 subregions of the hippocampal formation, found that D1 receptor antagonism (3.0 nmol/0.5 microl SCH-23390 bilaterally) in the vSUB impaired instrumental learning and performance, reduced break point in progressive ratio (PR) tests, and produced an intrasession decline in responding during test sessions, but had no effect on spontaneous motor or food-directed behavior. In contrast, D1 receptor blockade in the dSUB had no effect on instrumental learning, performance, PR break point, or food-directed behavior, but reduced spontaneous motor behavior. These results suggest a dissociation between the vSUB and dSUB with respect to the role of dopamine in various aspects of motivated and motor behavior. Further, D1 activation in the vSUB may be a critical component of motivational arousal associated with learned contextual cues.

Figure 1

Histological reconstructions of cannula placements in the dorsal subiculum (dSUB) and ventral subiculum (vSUB) are represented in schematic form. Histological sections were examined under light microscope and the site of the infusion estimated. Numbers beside each slide represent millimeters from bregma. Schematic diagrams are reprinted from The Rat Brain in Stereotaxic Coordinates (4th ed.), by G. Paxinos and C. Watson, pp. 206–208 (Figures 42–44), copyright 1998, with permission from Elsevier.

Figure 2

Effects of infusions of the D₁ antagonist SCH-23390 in the ventral subiculum (vSUB) and dorsal subiculum (dSUB) on instrumental learning, performance, and nose poking. Rats received infusions of SCH-23390 or vehicle prior to Sessions 1–5, prior to Session 11, and prior to Session 13 (vSUB only), but not prior to Sessions 6–10 or Session 12. Panels A and C show the mean number of lever presses per session per group (±SEM) with infusions in the vSUB or dSUB, respectively. Panels B and D show the mean number of nose pokes per session per group (±SEM) for vSUB and dSUB. No statistical reliable main effect of treatment or interaction on nose poking was found. **p < .01, compared with vehicle, revealed by Tukey post hoc comparisons.

Figure 3

The effects of SCH-23390 infusions on intrasession response rates during Sessions 11 (A) and 13 (B) for ventral subiculum (vSUB) infused rats and Session 11 (C) for dorsal subiculum (dSUB) infused rats. A and B show the mean number of lever presses per minute (±SEM) for vSUB treated rats across the 15-min sessions. No statistically significant differences were found in dSUB treated groups. *p < .05, **p < .01, compared with vehicle using Tukey post hoc comparison method.

Figure 4

Microstructural behavioral analysis of D₁ antagonism in the ventral subiculum (vSUB) and dorsal subiculum (dSUB). A and E show the mean conditional probability (±SEM) of a lever press (LP) given that a nose poke (NP) was the last recorded event—p(LP|NP)—in the vSUB and dSUB, respectively. B and F show the probability of an NP given that a reinforcer (Reinf) was the last recorded event—p(NP|Reinf). C and G show the average latency between an NP and an LP, the same dyad used to compute the p(LP|NP). D and H show the latency between a Reinf delivery and an NP, once again, the same dyad used to compute the p(NP|Reinf).

Figure 5

Effects of SCH-23390 infusions in the ventral subiculum (vSUB) and dorsal subiculum (dSUB) on Progressive Ratio 4 performance. The mean break point (±SEM) of the last ratio completed before the rat ceased responding per group is plotted for vSUB treated rats in A and for dSUB treated rats in B.

Figure 6

The effects of SCH-23390 infusions on intrasession response rates during the progressive ratio (PR) test session for ventral subiculum (vSUB) treated rats in A and for dorsal subiculum (dSUB) treated rats in B. The mean rate of responding per minute (±SEM) per group is plotted over the course of the 45-min test session.

Figure 7

Effects of SCH-23390 infusions in the ventral subiculum (vSUB) and dorsal subiculum (dSUB) on measure of food-directed and spontaneous locomotor behavior. A–F show the effects of SCH-23390 in the vSUB compared with vehicle controls (M ± SEM). No statistically reliable effects were found in vSUB treated rats. G–L show the effects of SCH-23390 infusions in the dSUB compared with vehicle. *p < .05, dependent t tests.