Abstract
The pedunculopontine nucleus is known as a cholinergic nucleus of the reticular activating system, participating in regulation of sleep and wakefulness. Besides cholinergic neurons, it consists of GABAergic and glutamatergic neurons as well. According to classical and recent studies, more subgroups of neurons were defined. Groups based on the neurotransmitter released by a neuron are not homogenous, but can be further subdivided. The PPN neurons do not only provide cholinergic and non-cholinergic inputs to several subcortical brain areas but they are also targets of cholinergic and other different neuromodulatory actions. Although cholinergic neuromodulation has been already investigated in the nucleus, one of its characteristic targets, the M-type potassium current has not been described yet. Using slice electrophysiology, we provide evidence in the present work that cholinergic neurons possess M-current, whereas GABAergic neurons lack it. The M-current contributes to certain functional differences of cholinergic and GABAergic neurons, as spike frequency adaptation, action potential firing frequency or the amplitude difference of medium afterhyperpolarizations (AHPs). Furthermore, we showed that high threshold membrane potential oscillation with high power, around 20 Hz frequency is a functional property of almost all cholinergic cells, whereas GABAergic neurons have only low amplitude oscillations. Blockade of the M-current abolished the oscillatory activity at 20 Hz, and largely diminished it at other frequencies. Taken together, the M-current seems to be characteristic for PPN cholinergic neurons. It provides a possibility for modulating gamma band activity of these cells, thus contributing to neuromodulatory regulation of the reticular activating system.
Highlights
The pedunculopontine nucleus (PPN) is known as one of the cholinergic nuclei of the reticular activating system
The identified tdTomato-expressing neurons were filled with biocytin, and later recovered; and confocal images were taken in order to assess their location and document their GAD2- or choline acetyltransferase (ChAT)-positivity (Figures 1A–C,I–K)
In the present project we showed that most of the cholinergic neurons of the PPN possess M-current, whereas all investigated GABAergic neurons lacked it
Summary
The pedunculopontine nucleus (PPN) is known as one of the cholinergic nuclei of the reticular activating system. The PPN is considered as a cholinergic nucleus, it is composed of non-cholinergic (i.e., GABAergic and glutamatergic) neurons, as well. Neurons of this nucleus are grouped due to their functional or morphological characteristics. According to the classical grouping based on electrophysiological properties, three types of neurons were distinguished. None of the functional groups are clearly related to morphological subgroups (Kang and Kitai, 1990; Leonard and Llinás, 1994; Steriade and McCarley, 2005)
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