G. A. Oganesyan

Effects of Memantine on Convulsive Reactions and the Organization of Sleep in Krushinskii–Molodkina Rats with an Inherited Predisposition to Audiogenic Convulsions

Krushinskii–Molodkina rats, which have a genetic predisposition to audiogenic convulsions, are used as a natural animal model for studies of the actions of anticonvulsants. It is important to understand the extent to which changes in glutamatergic synaptic transmission is involved in the mechanisms producing convulsive states and in the functional organization of the sleep–waking cycle in rats of this strain. The present report describes experiments addressing this, in which i.m. doses of 5 and 10 mg/kg of a noncompetitive NMDA glutamate receptor antagonist of the memantine type were given at different times (30 min, 1, 2, and 3 h) before presentation of sound stimuli (sine-wave tones at 8 kHz, 90 dB). Effects on the latent periods of the initial motor excitation, the appearance of clonic convulsions of different intensities, and, finally, tonic convulsions with limb and tail extension were evaluated. The greatest attenuation of convulsive seizures, to a level consisting only of motor excitation, was obtained in 60% of the rats between 1 and 2 h after administration. There were no differences between the effects of doses of 5 and 10 mg/kg. When doses were given 3 h before sound provocation, convulsive reactions became more marked than at 2 h, though they were nevertheless more marked than in controls. Krushinskii–Molodkina rats with chronically implanted electrodes for recording brain electrical activity were used to study the effects of memantine on the organization of sleep. These experiments showed that the rats’ sleep during the first hour after dosage consisted only of short episodes of superficial slow-wave sleep, and that even this sleep disappeared completely 54.4 ± 4.9 and 39.9 ± 5.2 min after administration of the agent at doses of 5 and 7 mg/kg, respectively. Rats showed a complete absence of sleep for 2 and 2.5 h, respectively, after which episodes of slow-wave sleep reappeared. The first episodes of REM sleep was seen in rats only after 3.3 ± 0.2 and 3.7 ± 0.2 h after memantine injections. The appearance of these episodes provided evidence that the effects of memantine on the activity of the somnogenic system of the animals’ brains were complete and that recovery of the normal organization of the sleep–waking cycle had started. The synchronicity and codirectionality of the blocking action of memantine on sleep organization and measures of audiogenic convulsions in Krushinskii–Molodkina rats is evidence for the involvement of glutamatergic synapses with NMDA receptors in both the regulation of the somnogenic systems and the pathogenesis of epileptiform manifestations in rats.

The Dopaminergic System of the Telencephalo-Diencephalic Areas of the Vertebrate Brain in the Organization of the Sleep–Waking Cycle

The aim of the present work was to study the involvement of the dopaminergic system of the telencephalic and diencephalic areas of the vertebrate brain in the organization of the sleep–waking cycle in cold-blooded and warm-blooded vertebrates. Immunohistochemical studies of tyrosine hydroxylase content, this being the key enzyme in dopamine synthesis, in the striatum, supraoptic and arcuate nuclei, and zona incerta of the hypothalamus of sturgeon and mammals (rats) of three age groups (14 and 30 days and adults), in conditions of tactile and sleep-deprivation stressors. In fish, transient stress was followed by the detection of tyrosine hydroxylase-immunoreactive cells in all parts of the brain. In prolonged stress, tyrosine hydroxylase-immunoreactive cells and fibers were not found in the forebrain, though they were well represented in the hypothalamic nuclei. In 14-day-old rat pups, 2-h sleep deprivation increased the tyrosine hydroxylase content of fibers in the caudate nucleus and cells in the zona incerta of the hypothalamus, while 30-day-old animals subjected to 6-h sleep deprivation showed increases in tyrosine hydroxylaseimmunoreactive material contents in cells in the paraventricular nucleus and decreases in the quantity in fibers. In adult rats, the arcuate nucleus and zona incerta showed decreases in the content of tyrosine hydroxylase-immunoreactive material on the background of sleep deprivation, with increases during postdeprivation sleep. These data are discussed in the light of the phylo- and ontogenetic development of the neurosecretory and neurotransmitter functions of the dopaminergic system in the evolutionarily ancient diencephalic and evolutionarily young telencephalic areas of the vertebrate brain as major systems triggering and maintaining the functional states of the body during the sleep–waking cycle.

The dopaminergic nigrostriatal system in sleep deprivation in cats

The dynamics of changes in electrophysiological measures of the sleep-waking cycle were analyzed in Wistar rats after 6 h of sleep deprivation by gentle waking and subsequent 9-h post-deprivation sleep. A delayed sleep “overshoot” reaction was observed 2.5–3 h after sleep deprivation, as a moderate increase in the proportions of slow-wave and fast-wave sleep in the sleep-waking cycle. Immunohistochemical studies were performed in relation to changes in the sleep-waking cycle, with the aim of identifying changes in the quantities of immunoreactive dopamine D1 and D2 receptor material and tyrosine hydroxylase, the key enzyme in dopamine synthesis in the nigrostriatal system. In conditions of sleep deprivation, the caudate nucleus showed increases in the quantities of dopamine D1 and D2 receptor material, while there was a simultaneous decrease in the amount of immunoreactive material in the substantia nigra. Post-deprivation sleep was accompanied by decreases in the quantities of immunoreactive D1 receptor material and increases in D2 receptor material in the caudate nucleus, with an increase in the quantity of immunoreactive tyrosine hydroxylase in the substantia nigra. These data provide evidence of the active role of the dopaminergic nigrostriatal system which, along with other CNS transmitter systems, supports telencephalic-diencephalic interactions, in the sleep-waking cycle.

On the influence of prenatal hypoxia on formation of the orexinergic system and sleep–wake cycle in early ontogenesis of rats

The role of orexin in the organization of the sleep–wake cycle (SWC) is well known. The aim of this study was to examine the timing of the orexinergic system formation in rat postnatal ontogenesis and to assess the role of orexin A in the SWC organization under normal conditions and after prenatal hypoxia undergone on days 14 and 19 of embryogenesis. The SWC was investigated in 30-day-old rats with electrodes implanted into the somatosensory and occipital cortex. Immunoreactivity within the orexigenic structures of the lateral hypothalamus was analyzed. It was shown that in control 14-day-old animals the orexinergic structures were in their formative stage, whereas in 30-day-old rats they were already as formed as in adults. In 14-day-old rats, prenatal hypoxia evoked retarded formation of the orexinergic system. In 30-day-old animals, hypoxia undergone in the prenatal period increased the activity of the orexinergic system, which was higher in animals exposed to hypoxia on day 19 than on day 14 of gestation. In 30-day-old rats, these changes were reflected in the SWC formation in the form of shorter slow-wave sleep, more fitful sleep and increased number of transitions from slow- to fast-wave sleep. The results obtained are discussed in the light of the adaptive-compensatory role of the orexigenic system in postnatal ontogenesis after prenatal damage to the central nervous system.

Peculiarities of Formation of the Wakefulness—Sleep Cycle in Ontogenesis of Rats

Electrophysiological changes in the wakefulness—sleep cycle were studied in early postnatal ontogenesis of rat pups. EEG was recorded and its spectral power was determined, as well as spatial-temporal synchronization between the brain cortex zones (visual and sensomotor) and hippocampus in the process of sleep at various periods of ontogenesis. These data were compared with the literature data on studying of cytoarchitectonics and ultrastructure of rat neocortex as well as on formation of neuronal activity and maturation of transmitter systems at the same periods. Based on time of formation of interneuronal and interstructural connections and of maturation of transmitter systems, 3 stages of functional development of sleep in ontogenesis were identified: the first stage—undifferentiated sleep, the interneuronal connections are absent; the second stage—partially differentiated sleep, interneuronal connections function and control from subcortical structures appears; the third stage—differentiated sleep, clear division into sleep phase, additional control from all three transmitter systems: noradrenergic, cholinergic, and serotoninergic, action of the latter providing inhibitory mechanisms in CNS.

Regulation of Apoptosis in Nonapeptidergic Neurons of Rat Hypothalamus by Catecholamines in Experiments in vitro

Effects of noradrenaline (NA) and dopamine (DA) on apoptosis of nonapeptidergic neurons of supraoptic (SON) and paraventricular (PVN) nuclei of hypothalamus of male Wistar rats was studied in experiments in vitro. Incubation of hypothalamic sections in the medium with added NA was shown to induce an increase of the amount of pro-apoptotic protein caspase-9 in the nonapeptidergic neurons of the SON and PVN. A comparison of the level of neuronal NO-synthase with the level of caspase-9 expression in these neurons allows concluding that NA leads to initiation of apoptosis in neurons of the SON with mediation by nitric oxide (NO). In the PVN, the NA-induced initiation of apoptosis does not depend on the NO level. Addition of DA to the incubation medium results in an increase of the caspase-9 amount only in PVN neurons regardless of the NO content. The absence of neuronal death after the NA-induced increase of the caspase-9 level in the cells of SON and PVN seems to be due to increased expression of the anti-apoptotic protein bcl-2. Protection of the PVN neurons from death after addition of DA to the incubation medium is probably independent of the expression level of bcl-2. Thus, in the nonapeptidergic neurons of the SON and PVN, which are related by origin and by performed functions, modulation of the process of apoptosis by elevated concentrations of NA and DA is realized by different mechanisms.

Effects of uni- and bilateral destructions of the caudate nucleus head by kainic acid on electroencephalogram in the wakefulness—sleep cycle in wistar rats

Changes in characteristics of the wakefulness—sleep cycle were studied in Wistar rats after a uni- and bilateral destruction of the head of nucleus caudatus by kainic acid that produces a selective destruction of neuronal elements but does not damage conducting pathways passing through this structure. It is established that changes of the cycle after injections of the acid did not last long (not more than 4 days) and were due to the presence of foci of paroxysmal activity resulted from a strong excitatory effect of this selective neurotoxin. It is revealed that the consequences of the bilateral injury of the nucleus caudatus were less pronounced and easier tolerated by animals than those of the unilateral one. The appearance of spindle-like discharges on rat EEG during the fast wave sleep was observed after the unilateral but not the bilateral destruction. A possible role in the genesis of this activity played by a disbalance in the work of the system of the caudate inhibitory control of the activity of non-specific thalamic nuclei is discussed.

The effect of motion sickness on the sleep–wake cycle in rats exposed to prenatal hypoxia

This study is a follow-up to our previous research of the phenomenology and mechanisms of motion sickness (MS) and its relationship with changes in the sleep–wake cycle (SWC). We report data on the effect of MS on the SWC in 30-day-old intact rats and those exposed to prenatal hypoxia on days 13 and 19 of gestation. In all animal groups, MS was shown to decrease significantly the waking time and increase that of paradoxical sleep (PS). A link between hypothalamic MS and SWC regulatory mechanisms was revealed, and the role of this teamwork in the development of the sopite syndrome, which may be a sole manifestation of MS in some animals and man, was suggested. It was established that hypoxic exposure on day 19 of gestation had a greater damaging effect on the thalamocortical sleep-regulating structures than that on day 13, when it is only the hypothalamic-hippocampal slow-sleep regulatory systems that were found to be affected. Against this background, MS appreciably suppresses the brain excitatory systems that maintain wakefulness (supposed to be the ascending reticular activating system) and enhances those activating systems that regulate PS. It is exactly prenatal hypoxic exposure of rats on day 19 of gestation that enabled demonstrating the role of the evolutionarily young thalamocortical system in PS control.

Effects of Electrical Stimulation of the Oral Reticular Nucleus of the Pons on the Background of Different States in the Sleep–Waking Cycle in Krushinskii–Molodkina Rats

The effects of electrical stimulation of the oral reticular nucleus of the pons on behavior and brain activity in different states of the sleep–waking cycle were studied in Krushinskii–Molodkina rats, which have an inherited predisposition to audiogenic convulsions. Electrical stimulation of this structure at a frequency of 7 Hz on the background of deep slow-wave sleep induced a transition from slow- to fast-wave sleep. Analogous stimulation during fast-wave sleep had no effect on the electrogram patterns or spectra of the hippocampus or the visual, auditory, or somatosensory areas of the cortex and did not interrupt this state, though it did induce an almost twofold increase in the duration of its individual episodes. Electrical stimulation of the nucleus at 7 Hz during waking or shallow slow-wave sleep had no effect on behavior or electrogram patterns or spectral characteristics in the study structures and did not induce transition from one stage of the cycle to another. The results obtained here show that the state of the animals in the sleep–waking cycle is an important variable on which the effects of electrical stimulation of the oral reticular nucleus of the pons depend.

Effects of Stimulation of the Inferior Colliculi in Krushinskii–Molodkina Rats

The effects of chemical and electrical stimulation of the central nucleus of the inferior colliculus on the generation and formation of convulsive manifestations and on the organization of sleep were studied in Krushinskii–Molodkina rats with an inherited predisposition to audiogenic convulsions. Microinjection of quinolinic acid (10 μg in 1 μl of distilled water) or electrical stimulation at a frequency of 70 Hz generated paroxysmal manifestations in the form of intense rotatory movement acts, similar to “wild running” of animals in the initial convulsion-free stage of audiogenic seizures. This provides grounds for suggesting that in Krushinskii–Molodkina rats the inferior colliculi are part of the neural network responsible for the generation and execution of the running stage during the formation of convulsive responses to sound stimuli. Application of these stimuli was also followed by a decrease in the total duration of fast-wave sleep during the poststimulus period. Conversely, electrical stimulation of the inferior colliculi at a frequency of 7 Hz on the background of deep slow-wave sleep induced episodes of fast-wave sleep in the rats; after 3–4 sessions of this stimulation producing this effect, there was an almost two-fold increase in the total duration of fastwave sleep during the post-stimulus period due to an increase in the number but not the duration of these episodes. These results provide evidence that the inferior colliculi in rats may have a modulatory effect on the functioning of the fast-wave sleep triggering system.