GABA-induced inactivation of dorsal midline thalamic subregions has distinct effects on emotional behaviors

Abstract

The paraventricular nucleus of the thalamus (PVT) is a key node integrating information about emotion and relaying output to other limbic structures influencing motor behavior. With recent studies showing the anterior (aPVT) and posterior (pPVT) subregions of this nucleus to have different anatomical connections and functions in ingestive behavior, the present study investigated whether they also make different contributions to emotional behaviors. Rats were microinjected in the aPVT or pPVT with saline vehicle or the GABAB+GABAA agonists, baclofen+muscimol (bac+mus; 0.3+0.03nmol), to inhibit neural activity and were then tested between-subject for differences in emotional behavior. In a novel activity chamber, bac+mus significantly reduced locomotor activity, with this change somewhat larger after injection in the pPVT than the aPVT. In a familiar activity chamber, bac+mus again reduced locomotor activity but induced similar changes after injection in the aPVT and pPVT. In an elevated plus maze, bac+mus significantly decreased open arm time and entries, although this was observed only after injection in the pPVT. Thus, while both PVT subregions are necessary for general locomotor activity, the pPVT appears to have a greater function in both novelty-induced activity and anxiety-like behavior, indicating that this subregion makes a greater contribution than the aPVT to reactions to stressful stimuli.

Keywords: Baclofen; Elevated plus maze; Locomotor activity; Muscimol; Novelty; Paraventricular nucleus of the thalamus.

Fig. 1

Baclofen+muscimol (bac+mus, 0.3+0.03 nmol in 0.3 µl) compared to saline vehicle (0.3 µl) reduces novelty-induced locomotor activity when injected into the anterior paraventricular thalamus (aPVT) (bac+mus: n = 8, saline: n = 7) or posterior paraventricular thalamus (pPVT) (bac+mus: n = 7, saline: n = 7), causing a greater decrease when injected into the pPVT. ***p < 0.001, **p < 0.01, *p < 0.05 vs. respective saline; +p < 0.05 vs. aPVT bac+mus.

Fig. 2

Baclofen+muscimol (bac+mus, 0.3+0.03 nmol in 0.3 µl) compared to saline vehicle (0.3 µl) reduces locomotor activity in a familiar activity chamber, with similar effects observed after injection into the anterior paraventricular thalamus (aPVT) (bac+mus: n = 8, saline: n = 7) and posterior paraventricular thalamus (pPVT) (bac+mus: n = 7, saline: n = 7). **p< 0.01, *p< 0.05 vs. respective saline.

Fig. 3

Baclofen+muscimol (bac+mus, 0.3+0.03 nmol in 0.3 µl) compared to saline vehicle (0.3 µl) increases anxiety-like behavior in an elevated plus maze when injected into the posterior paraventricular thalamus (pPVT) (bac+mus: n = 7, saline: n = 7), but not the anterior paraventricular thalamus (aPVT) (bac+mus: n = 7, saline: n= 7). **p< 0.01, *p< 0.05 vs. respective saline.

Fig. 4

Injection sites (black dots) of baclofen+muscimol (0.3+0.03 nmol in 0.3 µl) or saline vehicle (0.3 µl) for animals included in the analyses. A. Sites in the anterior paraventricular thalamus (aPVT) (N = 15). B. Sites in the posterior paraventricular thalamus (pPVT) (N = 14). Adapted :from [18], with permission :from Elsevier.