| Co-Investigator(Kenkyū-buntansha) |
JODO Ei-ichi Associate, Department of Physiology, 生理学第二講座, 助手 (50211975)
OHTA Mamoru Associate, Department of Physiology, 生理学第二講座, 助手 (70191939)
ITO Seisho Assistant Professor, Dept. of Physiology, 生理学第二講座, 講師 (30004609)
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| Research Abstract |
1) Two kinds of action potentials (spikes) were recorded extracellularly in the laterodorsal tegmental nucleus (LDT) of the rat anesthetized with urethane, that is "brief spikes" and "broad spikes" , distinguished clearly with width of spikes. The latter were very similar to spikes generated by noradrenergic neurons of the locus coeruleus (LC) or serotonergic neurons of the dorsal raphe nucleus (DR). The majority of LDT neurons projecting to the forebrain sites had broad spikes, which, with an anatomical evidence, suggests that the broad-spike neurons are cholinergic.
2) The broad spikes could be recorded intracellularly from LDT neurons in in vitro slice preparation of the brainstem. (We could not perform this experiment further in order to concentrate our efforts in the below experiments.)
3) To clarify functional roles of mesopontine cholinergic neurons as a component of an activating system, single neuronal activity in the LDT of undrugged rats, whose head was fixed painlessly, was r
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ecorded along with cortical EEG and neck EMG. Activity of some LC and DR neurons was also recorded for comparison. Most of animals had been sleep-deprived for 24 hours. Observation was made only on neurons generating broad spikes, known from previous studies to be cholinergic or monoaminergic. The position of recorded neurons was marked by pontamine sky blue ejected from the glass pipette microelectrode, and was identified on sections processed for NADPH diaphorase histochemistry which stained cholinergic neurons specifically.
4) According to their firing rates during wakefulness (AW), slow wave sleep (SWS) and paradoxical sleep (PS), 46 broad-spike neurons in the LDT were classified into four groups : i) neurons most active during AW and silent during PS (some of these neurons might be serotonergic rather than cholinergic, as substantially all of 10 neurons in the LC and 9 neurons in the DR) ; ii) neurons most active during PS and silent during AW ; iii) neurons equally more active during AW and PS than SWS ; and iv) others mainly characterized by transiently facilitated activity at awaking and/or onset of PS. Neurons of groups ii and iii were the main constituent of the LDT, either group populating about 40% of the LDT neurons. In most neurons change in firing preceded EEG change, except at awaking from PS.
5) Sensory stimulation such as light touch to the tail or air puff to the face simply induced a state of firing during higher vigilance levels in some neurons, while in others the sensory stimulation evoked phasic responses habituated by repetition.
6) The results of the present and other studies suggest that i) the LDT is composed of cholinergic neurons with heterogenous characteristics in relation to sleep/wakefulness (and also to sensory responses), the majority displaying heightened activity in PS or in PS and AW, and ii) some tegmental cholinergic neurons play a pivotal role in induction and maintenance of PS, while having but a minor role in the ascending activation relevant to consciousness. Less
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