G.S. Chhina

Some aspects of electroencephalographic studies in Yogis

Abstract Four Yogis who practised samadhi were investigated electroencephalographically. It was observed that their resting records showed persistent alpha activity with increased amplitude modulation during samadhi. The alpha activity could not be blocked by various sensory stimuli during meditation. Two Yogis, who could keep their hand immersed in ice cold water for 45–55 min, also showed persistent alpha activity both before and during this practice. The possible mechanism of these observation has been discussed.

Inhibition of male sexual behavior by serotonin application in the medial preoptic area

The study investigated the possible involvement of serotonin in the medial preoptic area in the regulation of sexual behavior of male rats. Injection of serotonin in the medial preoptic area resulted in an inhibition, whereas cyproheptadine (a serotonin antagonist) produced a slight facilitation, of male sexual behavior.

Alpha adrenergic system in medial preoptic area involved in sleep-wakefulness in rats

The study is aimed at investigating the possible involvement of adrenergic mechanisms in the medial preoptic area (mPOA) for modulation of sleep-wakefulness in rats. In this study, saline, norepinephrine (NE), phenoxybenzamine (PBZ) and propranolol (PROP) were injected in the mPOA in different groups of male rats during the day and night. NE and PBZ were injected, during the day and the night respectively, in some control areas adjoining the mPOA in two other groups of animals. Arousal was produced by NE, and sleep by PBZ when they were applied in the mPOA. All other procedures, including application of NE and PBZ in the control areas and beta blocker (PROP) in the mPOA, did not produce alterations in sleep-wakefulness. These findings provide support for a physiological role played by the alpha adrenergic system in the mPOA for arousal, and area specificity of action of this system.

Activity of preoptic neurons during synchronization and desynchronization

Extracellular unit activity from 29 neurons in the preoptic area was recorded together with the cortical EEG in encéphale isolé cats. A majority (55%) of neurons showed alterations in their firing rates during transient changes in the EEG. Among them, a majority (62.5%) showed an increased firing rate during synchronization and the remaining showed an increased firing rate during desynchronization of the EEG. Most neurons showed a Poisson distribution pattern of firing during both the synchronized and the desynchronized phases of the EEG. The changes in the neuronal discharge occurring together with the specific changes in the cortical EEG fits in well with the assigned role of the preoptic area in the sleep-waking cycle.

Interrelationship of thermal and sleep-wakefulness changes elicited from the medial preoptic area in rats

The study investigated the possible interrelationship between changes in sleep-wakefulness and body temperature, primarily induced by manipulation of the noradrenergic system in the medial preoptic area. Saline, norepinephrine, and its alpha- and beta-blockers were injected in the medial preoptic area and in some control areas of rats, during their sleeping and active periods. 5-Hydroxytryptamine was injected in the medial preoptic area in another group of animals. Simultaneous changes in sleep-wakefulness and the body temperature were continuously recorded. Norepinephrine produced hypothermia and arousal, whereas alpha-adrenergic blockers induced hyperthermia and sleep. These changes in body temperature and in sleep-wakefulness did not follow an identical time course. 5-Hydroxytryptamine induced hyperthermia without affecting sleep-wakefulness. It is suggested that there are different neuronal mechanisms in the medial preoptic area that bring about the drug-induced changes in temperature and sleep-wakefulness.

Cholinergic activation of medial preoptic area by amygdala for ovulation in rat

Ovulation blocked by amygdalar lesion was restored by carbachol injection into medial preoptic area (mPOA) in rats on the afternoon of proestrus. Both spontaneous and carbachol-induced ovulation was blocked by application of nicotinic and muscarinic cholinergic antagonists (mecamylamine and atropine) to mPOA. The effect was more pronounced in the latter case. The study suggests amygdalar facilitatory control of ovulation to be mediated via mPOA through the involvement of cholinergic mechanisms.

Tonic activity of medial preoptic norepinephrine mechanism for body temperature maintenance in sleeping and awake rats

The study was aimed at investigating the possible involvement of tonic activity of the adrenergic receptors in the medial preoptic area (mPOA) for maintenance of body temperature in rats. Differences in drug-induced changes in body temperatures during sleep and wakefulness--during the day and at night--were also investigated. Norepinephrine injected in the mPOA, produced a fall in body temperature, whereas phenoxybenzamine produced an increase. Saline and propranolol produced no alteration. Norepinephrine and phenoxybenzamine produced alterations in sleep-wakefulness also. These changes in sleep-wakefulness did not completely explain the thermal changes. The findings highlight the need for taking into account the basal activity and the time of application of drug in studies on thermo-regulation, using free moving animals.

Mechanism of participation of medial preotic area in the hippocampal inhibition of ovulation

Bilateral hippocampal (HPC) stimulation with anodal direct current on the afternoon of proestrus blocked spontaneous ovulation in 87.5% of the Wistar rats subjected to the experiments. The incidence of the ovulation block by this procedure was reduced to 16.7% on bilateral injection of 0.25 microgram picrotoxin into the medial preoptic area (mPOA) preceding as well as following the stimulation. Ovulation was also blocked in 53.8% of the animals by bilateral injection of 50.0 microgram GABA into mPOA, while only 20.0% animals showed a blockade of ovulation by saline injection into mPOA. These observations indicate that blockade of ovulation by HPC stimulation can be simulated by local injection of GABA into mPOA while the effect of stimulation can be blocked by local injection of picrotoxin. Thus, indicating the possibility of GABA being neurotransmitter involved at the level of mPOA for mediating the inhibitory hippocampal influence on ovulation.

Comparison of rostro-caudal brain stem influence on preoptic neurons and cortical EEG

The changes in activity of preoptic area (POA) neurons, and cortical EEG, upon stimulation of the caudal brain stem reticular formation (CBS) and the rostral brain stem reticular formation (RBS) are compared in this study. Low frequency (LF) stimulation of the CBS (which induced EEG synchronization) and the RBS (which generally did not affect the EEG) had an excitatory influence on a majority of the affected neurons of the POA. In contrast, high frequency (HF) stimulation of the CBS (which produced EEG desynchronization in many instances) and the RBS (which induced EEG desynchronization in all instances) resulted in inhibition of a majority of the affected POA neurons. A larger number of neurons responded to HF stimulation of both brain stem regions, as compared to LF stimulation. The changes induced in the POA neurons, upon stimulation of the two brain stem reticular structures, were not dependent on simultaneous changes in the cortical EEG, except during some cases of stimulation-induced EEG desynchronization.

The monkey split brain-stem: Effects on the sleep-wakefulness cycle

Abstract 1. 1. A midline split of the medio-rostral part of the pontine tegmentum (nearly at the level of n. reticularis pontis oralis) induced a profound chronic alteration of the sleep-wakefulness rhythm in monkeys. Desynchronized sleep was almost abolished (0.1–0.6% of the recording time) and EEG synchronization was strongly reduced (10–18%) both during day and night. The percentage of wakefulness remained very high (80–90%) for several days (up to 3 weeks) after the splitting operation. During spontaneous synchronization no EEG asymmetries were found. 2. 2. Parallel to a reduction of the total amount of sleep the monkeys were restless, hyperirritable, ground their teeth and looked exhuasted. They also showed a marked increase in appetite and voracity. 3. 3. Longitudinal bilateral cuts in the pons at 3–4 mm from the midline reduced the amount of synchronized and desynchronized sleep but to a lesser extent as compared with the split monkeys. In the case in which cerebellectomy only was performed no modifications of sleep-wakefulness and behaviour were observed. 4. 4. On the basis of recent histochemical (Dahlstrom and Fuxe 1964) and physiological (Jouvet and Renault 1966) evidence our results might be interpreted as being due to a lesion of the pontine raphe nuclei. However, several experimental considerations favour the hypothesis that the results in monkeys can be due to separation of pontine neurones and to section of crossing ascending fibres from the synchronizing structures of the lower brain-stem.