Role of the Basal Forebrain Neurons in Cortical Activation and Behavioural State Regulation

some news about Basal Forebrain from Poland

Marian H. Lewandowski

Dear Kazue !
Thank you very much for the information about INABIS'98. It was really good idea to organize such not conventional meeting. CONGRATULATION.
I would like also to send some news obout mesencephalic reticular formation (MRF) and basal forebrain (BF) from my lab. As you probably remeber my papers (Exp. Brain Res. 96: 1-8, 1993 and Brain Res. 706: 233-236, 1996)we have found that electrical stimulation of MRF leads to a transient faciliation of cortical processing mediated by cholinergic afferents from the BF. The facilitation was critically dependent on the time interval between MRF and sensory stimulation, being effective only within a narrow delay window between 70-150ms. Our recent experiments with extracellular single unit recording in BF of anesthetized rats and cats reveals that the most common response to MRF-stimulation is a prolonged inhibition, sometimes followed by a weak rebound excitation occuring after 100-250ms. However, following MRF-stimulation, subsequent electrical activation of the LGN can induce a robust excitation of BF neurons when applied within the time window for effective reticular facilitation. This combinatorial interaction was always paralelled by a preceeding inhibition induced by MRF-stimulation. According to the previous findings that revealed the presence of the low-threshold calcium conductance in cholinergic neurons of the BF, we conclude that MRF-stimulation hyperpolarize cholinergic BF neurons, leading to an activation of the LTCC. After activation of the current, subsequent sensory stimulation can induce a strong excitation, probably via corticofugal feedback to BF. Injection of ethosuximide into BF reversibly blocks reticular facilitation without significantly affecting baseline responses to LGN-stimulation.

Marian H. Lewandowski

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