Progesterone facilitates the acquisition of avoidance learning and protects against subcortical neuronal death following prefrontal cortex ablation in the rat.

Following a cortical injury, neurons in areas near and connected to the site of injury begin to degenerate. The observed neuronal death may contribute to the severity of the observed behavioral impairments. The purpose of the present study was to examine if progesterone, a hormone known for its effectiveness at reducing cerebral edema, could protect against secondary neuronal death and facilitate the acquisition of an avoidance learning task in an ablation model of cortical injury. Rats served as sham controls or received bilateral ablation of the medial prefrontal cortex followed by a 10-day regimen of progesterone (4 mg/kg) or oil vehicle (1 ml/kg) beginning 1 h after cortical lesions. Progesterone-treated lesion rats showed a significant facilitation of avoidance learning compared to oil-treated lesion controls. In addition, progesterone-treated lesion animals did not differ from either progesterone- or oil-treated sham controls in avoidance learning. Anatomical analysis revealed that progesterone treatment decreased the amount of neuronal death seen in the striatum and the mediodorsal nucleus of the thalamus. The findings are consistent with the notion that progesterone is an effective neuroprotective agent and suggest that the hormone can reduce the behavioral impairments associated with frontal cortical ablation injury.

Medial prefrontal lesion deficits involving or sparing the prelimbic area in the rat.

The rat medial prefrontal cortex (PFC) is believed to play a central role in working memory and selective attention processes. More recently, it has been shown that the effects of large PFC lesions on working memory may be due to the prelimbic area of the PFC. The aim of the present study was to compare the effects of lesions of the prelimbic area with PFC lesions that involved or spared the prelimbic area on shuttlebox avoidance and radial maze learning in rats. The findings indicate that rats with PFC lesions that spared the prelimbic area were impaired at avoidance but not radial arm maze learning, whereas rats with prelimbic lesions or PFC lesions that included this area were impaired on the radial arm maze but not the avoidance learning task. Results support the notion that the medial frontal cortex of the rat is a functionally dissociable region and suggest that the prelimbic area appears to be critical for working memory, but less so for attention processes.