Configural learning, spatial navigation, and amphetamine-induced activity spared with ibotenic acid but not quinolinic acid lesions of the dorsomedial thalamus in rats

The connections that the dorsomedial (MD) thalamus makes with the frontal cortex and hippocampus suggest that it should share in their functions. This study examined the role of the dorsomedial nucleus (MD) of the thalamus in learning tasks that require the use of compound cues and in amphetamine-induced locomotion. The cell-specific neurotoxins ibotenic acid and quinolinic acid were injected into MD, and the animals were tested on a configural tactile—olfactory task, on a matching-to-place task in a swimming pool, and on spontaneous and amphetamine-induced locomotion. The ibotenic acid lesions produced cell death that was relatively confined to MD, while the quinolinic acid lesions produced widespread thalamic cell death and calcium deposits. The control and the ibotenic acid groups were not different, but the quinolinic acid lesions produced significant impairments on all of the tasks. The results suggest that although the frontal cortex and hippocampus may participate in solving the tasks used in this study, the MD, despite its reciprocal connections, does not share their involvement. The quinolinic acid results suggest either that very large lesions are required to produce deficits or that other thalamic nuclei are involved in the behaviors that were measured.