V. Mohan Kumar

Sleep-awake responses elicited from medial preoptic area on application of norepinephrine and phenoxybenzamine in free moving rats

The study makes an attempt to find out the action of norepinephrine (NE) and phenoxybenzamine (PB), applied at medial preoptic area (mPOA), in altering the sleep-awake responses, in free moving rats, which has not yet been reported. Effects of application of NE during day and PB during night, at mPOA, on sleep-awake responses, were compared with application of saline during identical periods. Application of NE produced arousal, whereas, PB produced the opposite effect. The findings are suggestive of the involvement of NE terminals at mPOA in normal arousal.

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.

Sleep-inducing function of noradrenergic fibers in the medial preoptic area

The aim of the investigation was to find out the role of noradrenergic (NE) terminals of the medial preoptic area (mPOA), in the regulation of sleep-wakefulness. Studies were conducted on free-moving adult male rats with chronically implanted cannulae in the mPOA. Sleep-wakefulness was assessed on the basis of EEG, EMG, and EOG recordings along with behavioral observations. Lesioning of catecholamine terminals (with 6-hydroxydopamine) in the mPOA produced an increase in quiet wakefulness. Prevention of NE fiber destruction, by pretreating the rats with imipramine, prevented this effect. This demonstrated that the increased quiet wakefulness produced by 6-OHDA was the result of NE fiber destruction. Changes in sleep-wakefulness were also assessed after microinjection of NE into the mPOA, in normal and ventral noradrenergic bundle (VNA)-lesioned rats. NE administration induced sleep in VNA-lesioned rats, and arousal in normal rats. The findings suggest that the NE terminals in the mPOA, projecting via VNA, play a role in the induction of sleep.

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.

Stereotaxic assembly and procedures for simultaneous electrophysiological and MRI study of conscious rat

A stereotaxic restraining assembly was designed and developed for simultaneous electrophysiological recordings and functional MRI (fMRI) data acquisition from a conscious rat. The design of the nonmagnetic stereotaxic apparatus facilitated the restraining of head and body of the unanesthetized conscious animal during MRI experiments. The apparatus was made of Teflon and Perspex materials with an appropriate size and shape for a 4.7 T / 40 cm animal MRI scanner. Electrodes made from nonmagnetic silver wire were implanted on the skull for recording the electroencephalogram (EEG), the electro‐oculogram (EOG), and the electromyogram (EMG), while polycarbonate screws were used for anchoring the electrode assembly. There were no major distortions or artifacts observed in the electrophysiological tracings and MR images. Electrophysiological recordings during fMRI acquisitions are useful to study different neurophysiological mechanisms of sleep and pathophysiology of seizure activity. Integration of electrophysiological recordings (with their good temporal resolution) and MRI (with its superior spatial resolution) is helpful in characterizing the functional state of different brain regions. Magn Reson Med 49:962–967, 2003.

Sensory Modulation of the Medial Preoptic Area Neuronal Activity by Dorsal Penile Nerve Stimulation in Rats

The study was aimed at finding out the influence exerted by the genital afferents on the medial preoptic area (mPOA), which plays a pivotal role in the regulation of male sex behavior. To fulfil this objective, the effects of stimulation of the dorsal penile nerve (DPN) on the activity of 82 mPOA neurons were studied. The base line firing rates of the mPOA neurons, studied by extracellular recording, ranged between 0.5 and 38.5 Hz (mean 7.18 +/- 7.91). The stimulation of the DPN (20 Hz, 0.4 msec. 70 microA) influenced 79.69% of the neurons studied. Though increased firing was the predominant influence produced (50%), decreased firing was also seen in a few (29.69%). The excited and inhibited neurons were randomly distributed within the mPOA. Neurons located in the lateral and posterior hypothalamus were not affected by the DPN stimulation. The stimulation parameters used in this study did not produce any change in the systemic arterial pressure and heart rate. The results provide electrophysiological evidence of afferent inputs from the male sex organ to the mPOA, which is an important area controlling male sex behavior.

Changes in sleep–wakefulness after 6-hydroxydopamine lesion of the preoptic area

This study was undertaken to assess the role of catecholamine fibers, terminating in the preoptic area, in regulating sleep-wakefulness in rats. Sleep-wakefulness was assessed on the basis of 24h electroencephalogram, electromyogram and electro-oculogram recordings before and after destruction of catecholaminergic terminals at the medial preoptic area by bilateral intracerebral injection of 6-hydroxydopamine (8 microg in 0.2 microl). There was a mild reduction in sleep and increase in wakefulness after the lesion. The increase in active wakefulness observed after eight days of lesion persisted even on the 12th day. In spite of the reduction in sleep, the day-night sleep ratio was not affected by 6-hydroxydopamine lesion of the preoptic area. The results indicate that the noradrenergic fibers at the preoptic area have a hypnogenic role.

Influence of ascending reticular activating system on preoptic neuronal activity.

There is evidence to suggest that the reticular activating system may have an influence on the neurons of the preoptic area (POA). We studied the responses of POA neurons and their relation to the cortical EEG, on stimulation of the midbrain reticular formation (MRF) at various frequencies, in unanesthetized, encéphale isolé cats. Stimulation of the MRF at high frequency produced inhibition of the firing rate in a majority of the responsive neurons of the POA. Stimulation of the MRF with lower frequencies, on the other hand, induced excitation in a majority of the responsive POA neurons. The possibility exists of a summation of stimuli and an involvement of structures bringing about changes in the EEG in causing the shift in the POA neuronal excitability.

Mapping of regions in the caudal brain stem that produce stimulus-bound synchronization in the cortical EEG.

This study was aimed at filling the lacunae in our knowledge regarding the localization of the regions in the caudal brain stem that bring about cortical EEG synchronization on electrical stimulation and characteristic features of synchronized waves elicited from those regions. Studies were conducted on 40 encéphale isolé cats. Stimulation of ventromedial regions of the caudal brain stem, with low frequency, elicited stimulus-bound synchronized waves in the cortex which were more prominent ispsilaterally. On the other hand, low-frequency stimulation of dorsal and lateral areas produced synchronized waves which were either equally prominent on both sides, or more prominent on the contralateral side. The loci in the brain stem that produce synchronization were very specific. The induced synchronized waves showed amplitude modulation and did not outlast the train of stimuli. The results are further confirmation of the role of caudal brain stem structures in cortical EEG synchronization. They also provide information regarding the nature of cortical synchronization elicited from these brain stem structures.