Activity In Mesencephalic Reticular Formation Research Articles

Further study on 1/f fluctuations observed in central single neurons during REM sleep.

Recently, 1/f fluctuations have been discovered in the single-unit activity of mesencephalic reticular formation (MRF) neurons during REM sleep. In a previous paper, such behavior could satisfyingly be interpreted on the basis of the clustering Poisson process. The question of applicability of this model to other MRF neurons remained unanswered. The present paper reports on 1/f fluctuations in 12 MRF neurons all of which can satisfyingly be modeled by the clustering Poisson process.

The effect of iontophoretically administered GABA and glycine on the neuronal activity of mesencephalic reticular formation.

By recording the neuron unit discharges we have observed the effect of iontophoresis of gamma amino butyric acid (GABA) and glycine on the electrical activity of three different types of neurons in mesencephalic reticular formation (MRF). The results indicated that both GABA and glycine have a significant inhibitory effect on the spontaneous discharges of all three types of neurons and the pain discharges of the “pain excitatory type” neurons, and this inhibitory effect can be abolished by their corresponding antagonists, picrotoxin and strychnine. In combination with known histochemical data the results suggest that GABA and glycine might be endogenous transmitters in MRF.

The influence of intra-hippocampal gamma-aminobutyric acid on the orienting reflex

The spontaneous electrical background and evoked orienting EEG activities were tested before and after intra-hippocampal administration of gamma-aminobutyric acid (GABA) to eleven adult cats with electrodes chronically implanted in the ectosylvian and suprasylvian gyri, mesencephalic reticular formation (MRF), posterior hypothalamic area and dorsal hippocampus. Concomitantly the spontaneous and auditorily induced behaviour were observed. The results were as follows: 1. 1. The effects of intra-hippocampal GABA appeared 2 min following uni- or bilateral administration, were, mostly evident between 2 and 7 min and disappeated after 35–40 min. The rapid effect of the drug was due to its intra-hippocampal administration, which permitted avoidance of the blood-brain barrier and thus immediately induced a high concentration of GABA. 2. 2. No changes in the animals behaviour and in the electrical activity of the neocortex were observed (the neocortical arousal reaction and the potentials evoked by repetitive auditory stimulation were not altered). Thus intra-hippocampal GABA exerts its influence exclusively upon the hippocampus. 3. 3. Intra-hippocampal GABA induced changes in hippocampal activity (slight increase of spontaneous electrical activity, faster extinction of the hippocampal evoked response to repetitive auditory stimulation and depression, or even suppression, of the spontaneous or evoked arousal reaction), delayed extinction of orienting behaviour and convulsive activity in MRF. The EEG and behavioural changes were simultaneous. 4. 4. The authors assume that the alterations are due to a depressing action of the drug on hippocampal neurones. The local depressing effect is responsible for suppression of the modulating effect of the hippocampus on the MRF and therefore upon the orienting reflex.

Caudate-capsular-induced modulation of single-unit activity in mesencephalic reticular formation

Fifty-five sites in and around the caudate nucleus were stimulated at low frequencies to determine their effects on single-unit activity in the mesencephalic reticular formation. Ninety-two units in 15 acutely prepared cats were isolated. Twenty-nine units were inhibited by forebrain stimulation, 15 were excited,and 16 showed both excitation and inhibition. Excitatory influences occurred with a short latency; inhibitory effects had a longer latency. The most effective sites in producing these unit effects were located in the periphery of the caudate nucleus and in the region of the internal capsule and cortex that borders the caudate nucleus by about 1 mm. The effectiveness of a site in modulating unit activity was related to whether that site produced a spindle discharge recorded from the cortex. Ninety-two per cent of the sites that produced a spindle also produced unit effects, whereas only 31 per cent of the nonspindle sites affected units. The type of response produced in a given RF unit appeared to be a property of the unit and not of the site in the forebrain being stimulated. It was concluded that a forebrain excitatory mechanism influences mesencephalic units via a fast-conducting direct pathway; a forebrain inhibitory mechanism influences mesencephalic units via a slow-conducting or multisynaptic pathway (perhaps both); and behavioral effects produced by low-frequency caudate and capsular stimulation may be mediated by an alteration or perhaps disruption of the ongoing neuronal activity in the mesencephalic arousal system.