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Effect of medial prefrontal subregions electrical stimulation on the neuronal activity of the primary visual cortex and basal forebrain.

Nguyen HN, Huppé-Gourgues F, Vaucher E (2013) Effect of medial prefrontal subregions electrical stimulation on the neuronal activity of the primary visual cortex and basal forebrain. Neuroscience 2013 Abstracts 639.04. Society for Neuroscience, San Diego, CA.

Summary: The cholinergic system and the medial prefrontal cortex (mPFC) play an important role in visual attention through the modulation of neuronal responses in the primary visual cortex (V1). The mPFC doesn’t project directly to V1, but does project to the horizontal limb of the diagonal band of Broca (HDB), which contains cholinergic neurons and projections to V1. Here, we investigated a possible involvement of the mPFC subregions in the activation of basal forebrain cholinergic neurons to enhance cholinergic transmission in V1. The different subregions of the mPFC, the anterior cingulate (Cg1), the prelimbic (PrL) and the infralimbic (IL) cortices, have anatomical and functional differences. Therefore the objective of this study was to determine if electrical stimulation of the different regions of the PFC activated V1 neurons in mice and if this activation was mediated through the HDB cholinergic pathway. The neuronal activity was evaluated by early gene c-Fos immunoreactivity in V1 and HDB after unilateral electrical stimulation of mPFC subregions (trains of 100 Hz for 0.3s every 2s, 50 μA, 30 mins) provided through a tungsten electrode in urethane anesthetized mice (n=4 mice per subregion). After the mPFC stimulation, mice were kept in darkness for 1h and brains were harvested after 4% paraformaldehyde intracardiac perfusion. The c-Fos expression was quantified on 35 µm coronal brain sections in V1 and HDB: an equivalent threshold was applied to all microphotographs and a c-Fos automated particle analysis tools was used (ImageJ). Moreover, the effect of the selective lesion of cholinergic fibers by the immunotoxin mu p75-saporin (1 μg/μl injections) was evaluated. The results show that electrical stimulation of PrL (Mann-Whitney U, p=0.021) and IL (p=0.021) cortices significantly induced a higher expression of c-Fos neurons in V1 of the stimulated hemisphere, but not in the HDB. Electrical stimulation of Cg1 did not elicit V1 nor HDB c-Fos immunoreactivity (p=0.248). Furthermore, selective lesions of basal forebrain cholinergic neurons did not eliminate the IL-induced c-Fos expression in the ipsilateral V1. Therefore, the mPFC stimulation seems to activate V1 neurons without the contribution of the HDB cholinergic neurons. This suggests there is a functional link between the mPFC and V1 independent from HDB cholinergic projections.

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