[Application of medical-purpose knitted fabric STRUVA 23 in office surgery for varicosity].

The article proffered herein discusses a possibility of using groin-high stockings STRUVA 23 in women operated on for uncomplicated varicosity of the lower limbs in outpatient conditions by means of modern minimally invasive techniques. Analyzing the postoperative-period course in a total of 15 women making use of conventionally employed elastic bandages, as compared with 20 women wearing the woven medical-purpose stoking pulled on the postoperative leg clearly showed apparent advantages of the latter type of compression, thus enabling the authors to safely recommend the stockings STRUVA 23 for application in office surgery.

Acetylcholine becomes the major excitatory neurotransmitter in the hypothalamus in vitro in the absence of glutamate excitation.

Glutamate and GABA are two major fast neurotransmitters (excitatory and inhibitory, respectively) in the CNS, including the hypothalamus. They play a key role in the control of excitation/inhibition balance and determine the activity and excitability of neurons in many neuronal circuits. Using neuronal cultures, whole-cell recording, Ca(2+) imaging, and Northern blots, we studied the compensatory regulation of neuronal activity during a prolonged decrease in glutamate excitation. We report here that after a chronic (6-17 d) blockade of ionotropic glutamate receptors, neurons in hypothalamic cultures revealed excitatory electrical and Ca(2+) synaptic activity, which was not elicited in the control cultures that were not subjected to glutamate blockade. This activity was suppressed with acetylcholine (ACh) receptor antagonists and was potentiated by eserine, an inhibitor of acetylcholinesterase, suggesting its cholinergic nature. The upregulation of ACh receptors and the contribution of ACh to the control of the excitation/inhibition balance in cultures after a prolonged decrease in glutamate activity were also demonstrated. Enhanced ACh transmission was also found in chronically blocked cerebellar but not cortical cultures, suggesting the region-specific character of glutamate-ACh interactions in the brain. We believe that in the absence of glutamate excitation in the hypothalamus in vitro, ACh, a neurotransmitter normally exhibiting only weak activity in the hypothalamus, becomes the major excitatory neurotransmitter and supports the excitation/inhibition balance. The increase in excitatory ACh transmission during a decrease in glutamate excitation may represent a novel form of neuronal plasticity that regulates activity and excitability of neurons during the glutamate/GABA imbalance.

Early synaptogenesis in vitro: role of axon target distance.

In contrast to some previous reports suggesting a delay in synapse formation in vitro, we found that under ideal conditions, most hippocampal and hypothalamic rat neurons were synaptically coupled after 3 or 4 days in vitro. Synaptophysin immunocytochemistry revealed strongly stained presynaptic boutons by 3 days in vitro. Studies with time-lapse laser confocal imaging of FM1-43 revealed that axonal boutons were recycling their synaptic vesicles, an indication of synapse formation, as early as 3 days after plating. To test the hypothesis that neurite outgrowth was enhanced in high-density cultures, thereby increasing the probability of synapse formation, neurons were transfected with the jellyfish green fluorescent protein (GFP) gene. After 2 days in high-density cultures, green fluorescent neurites were about three times longer than in sister neurons plated in low-density cultures. Even in single dishes, GFP-transfected cells in contact with other neurons had neurites that were at least three times longer and grew faster than more isolated cells. Neurons grew longer neurites (+51%) when growing on surface membranes of heat-killed neurons than on polylysine, underlining the importance of plasma membrane contact. Calcium imaging with fura-2 and whole cell recording showed that both GABA and glutamate presynaptic release occurred after 3 or 4 days in vitro in high-density cultures but was absent in low-density cultures at this time. Together, these morphological, cytochemical, and physiological data suggest that the distance an axon must grow to find a postsynaptic partner plays a substantial role in the timing of synapse formation. Although other factors in vitro may also play a role, the distance to a postsynaptic target, which defines the interval during which an axon grows to its target, can probably account for much of the difference in timing of synapse formation previously reported in vitro. A short intercell distance may increase the concentration of limited amounts of trophic factors available to a nearby cell, and once contact is made, a neuronal membrane provides a superior substrate for neuritic elongation.

Presynaptic and postsynaptic actions and modulation of neuroendocrine neurons by a new hypothalamic peptide, hypocretin/orexin.

A new orexigenic peptide called hypocretin (orexin) has recently been described in neurons of the lateral hypothalamus and perifornical area. The medial and lateral hypothalamus have been loosely called satiety and feeding centers of the brain, respectively. Approximately one-third of all medial and lateral hypothalamic neurons tested, but not hippocampal neurons, show a striking nanomolar sensitivity to hypocretin. As studied with calcium digital imaging with fura-2, hypocretin raises cytoplasmic calcium via a mechanism based on G-protein enhancement of calcium influx through plasma membrane channels. The peptide has a potent effect at both presynaptic and postsynaptic receptors. Most synaptic activity in hypothalamic circuits is attributable to axonal release of GABA or glutamate. With whole-cell patch-clamp recording, we show that hypocretin, acting directly at axon terminals, can increase the release of each of these amino acid transmitters. Two hypocretin peptides, hypocretin-1 and hypocretin-2, are coded by a single gene; neurons that respond to one peptide also respond to the other. In addition to its effect on feeding, we find that this peptide also regulates the synaptic activity of physiologically identified neuroendocrine neurons studied in hypothalamic slices containing the arcuate nucleus, suggesting a second function of hypocretin in hormone regulation. The widespread distribution of hypocretin axons, coupled with the strong response to the peptide at both presynaptic and postsynaptic sites, suggests that the peptide probably modulates a variety of hypothalamic regulatory systems and could regulate the axonal input to these regions presynaptically.

Dopamine inhibition: enhancement of GABA activity and potassium channel activation in hypothalamic and arcuate nucleus neurons.

Dopamine (DA) decreases activity in many hypothalamic neurons. To determine the mechanisms of DA's inhibitory effect, whole cell voltage- and current-clamp recordings were made from primary cultures of rat hypothalamic and arcuate nucleus neurons (n = 186; 15-39 days in vitro). In normal buffer, DA (usually 10 microM; n = 23) decreased activity in 56% of current-clamped cells and enhanced activity in 22% of the neurons. In neurons tested in the presence of glutamate receptor antagonists D,L-2-amino-5-phosphonovalerate (AP5; 100 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10 microM), DA application (10 microM) revealed heterogeneous effects on electrical activity of cells, either hyperpolarization and decrease in activity (53% of 125) or depolarization and increase in spontaneous activity (22% of 125). The DA-mediated hyperpolarization of membrane potential was associated with a decrease in the input resistance. The reversal potential for the DA-mediated hyperpolarization was -97 mV, and it shifted in a positive direction when the concentration of K+ in the incubating medium was increased, suggesting DA activation of K+ channels. Because DA did not have a significant effect on the amplitude of voltage-dependent K+ currents, activation of voltage-independent K+ currents may account for most of the hyperpolarizing actions of DA. DA-mediated hyperpolarization and depolarization of neurons were found during application of the Na+ channel blocker tetrodotoxin (1 microM). The hyperpolarization was blocked by the application of DA D2 receptor antagonist eticlopride (1-20 microM; n = 7). In the presence of AP5 and CNQX, DA (10 microM) increased (by 250%) the frequency of spontaneous inhibitory postsynaptic currents (IPSCs) in 11 of 19 neurons and evoked IPSCs in 7 of 9 cells that had not previously shown any IPSCs. DA also increased the regularity and the amplitude (by 240%) of spontaneous IPSCs in 9 and 4 of 19 cells, respectively. Spontaneous and DA-evoked IPSCs and inhibitory postsynaptic potentials were blocked by the gamma-aminobutyrate A (GABA(A)) antagonist bicuculline (50 microM), verifying their GABAergic origin. Pertussis toxin pretreatment (200 ng/ml; n = 15) blocked the DA-mediated hyperpolarizations, but did not prevent depolarizations (n = 3 of 15) or increases in IPSCs (n = 6 of 10) elicited by DA. Intracellular neurobiotin injections (n = 21) revealed no morphological differences between cells that showed depolarizing or hyperpolarizing responses to DA. Immunolabeling neurobiotin-filled neurons that responded to DA (n = 13) showed that GABA immunoreactive neurons (n = 4) showed depolarizing responses to DA, whereas nonimmunoreactive neurons (n = 9) showed both hyperpolarizing (n = 6) and depolarizing (n = 3) responses. DA-mediated hyperpolarization, depolarization, and increases in frequency of postsynaptic activity could be detected in embryonic hypothalamic or arcuate nucleus neurons after only 5 days in vitro, suggesting that DA could play a modulatory role in early development. These findings suggest that DA inhibition in hypothalamic and arcuate nucleus neurons is achieved in part through the direct inhibition of excitatory neurons, probably via DA D2 receptors acting through a Gi/Go protein on K+ channels, and in part through the enhancement of GABAergic neurotransmission.

Local synaptic release of glutamate from neurons in the rat hypothalamic arcuate nucleus.

1. The hypothalamic arcuate nucleus (ARC) contains neuroendocrine neurons that regulate endocrine secretions by releasing substances which control anterior pituitary hormonal release into the portal blood stream. Many neuroactive substances have been identified in the ARC, but the existence of excitatory neurons in the ARC and the identity of an excitatory transmitter have not been investigated physiologically. 2. In the present experiments using whole-cell current- and voltage-clamp recording of neurons from cultures and slices of the ARC, we demonstrate for the first time that some of the neurons in the ARC secrete glutamate as their transmitter. 3. Using microdrop stimulation of presynaptic neurons in ARC slices, we found that local axons from these glutamatergic neurons make local synaptic contact with other neurons in the ARC and that all evoked excitatory postsynaptic potentials could be blocked by the selective ionotropic glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10 microM) and D,L-2-amino-5-phosphonovalerate (AP5; 100 microM). To determine the identity of ARC neurons postsynaptic to local glutamatergic neurons, we used antidromic stimulation to reveal that many of these cells were neuroendocrine neurons by virtue of their maintaining axon terminals in the median eminence. 4. In ARC cultures, postsynaptic potentials, both excitatory and inhibitory, were virtually eliminated by the glutamate receptor antagonists AP5 and CNQX, underlining the functional importance of glutamate within this part of the neuroendocrine brain. 5. GABA was secreted by a subset of ARC neurons from local axons. The GABAA receptor antagonist bicuculline released glutamatergic neurons from chronic inhibition mediated by synaptically released GABA, resulting in further depolarization and an increase in the amplitude and frequency of glutamate-mediated excitatory postsynaptic potentials.

Dopamine enhancement and depression of glutamate-regulated calcium and electrical activity in hypothalamic neurons.

1. The neurotransmitter dopamine is found throughout the hypothalamus both in cell bodies and in axons originating from intra- and extrahypothalamic sources. To study the mechanisms of action of dopamine on cultured rat hypothalamic neurons, particularly in relation to Ca2+ regulation, we used Ca2+ digital imaging with fura-2 and whole cell patch-clamp recording. We focused on the modulatory actions of dopamine on glutamate. 2. Dopamine administration had little or no independent effect on intracellular Ca2+. However, in the presence of tetrodotoxin to block action potentials and action-potential-dependent transmitter release, dopamine (10 microM for 2-3 min) caused an increase in glutamate-evoked Ca2+ rises in 22% of 64 neurons and depressed glutamate-evoked Ca2+ rises in an equal number of neurons. Shorter exposure to dopamine reduced the number of responding cells. 3. Dopamine application to neurons with an elevated Ca2+ due to synaptic release of glutamate (in the absence of tetrodotoxin) generally caused a decrease in Ca2+ levels (40% of 106 neurons), but sometimes increased cytosolic Ca2+ (10% of 106 neurons). That dopamine influenced cells differently in conditions of spontaneous activity compared with evoked activity may be due to dopamine effects on presynaptic receptors detected under conditions of ongoing synaptic release of glutamate. 4. Dopamine modulation of glutamate responses was detected at early stages of neuronal development (embryonic day 18 after 2 days in vitro) and also after 60 days in vitro. 5. The D1, D2, and D3 dopamine receptor agonists SKF38393, quinpirole, and 7-OH-DPAT (+/- 7 hydroxy-dipropylaminotetralin) caused a reduction in Ca2+ levels raised by endogenous glutamate release or evoked by exogenous glutamate application. 6. To block the actions of dopamine released by hypothalamic neurons, D1 and D2 dopamine receptor antagonists were used. As with dopamine, dopamine antagonists had no effect on intracellular Ca2+ during glutamate receptor blockade. In the absence of glutamate receptor block, the D1 antagonist SCH23390 (1 microM) reduced Ca2+ in responding cells; in contrast, the D2 antagonist eticlopride (1 microM) generated a delayed increase in Ca2+ levels. 7. Dopamine is known to activate second messengers through G proteins independent of changes in membrane potential or input resistance. Whole cell recording was used to demonstrate that, parallel to the modulation of Ca2+, dopamine exerted a dramatic change in glutamate-mediated electrical activity, generally depressing activity and hyperpolarizing the membrane potential (8 of 15 neurons). In a smaller number of neurons (5 of 15), dopamine enhanced glutamate-mediated excitatory activity. 8. Dopamine-evoked changes in membrane potential were in part mediated through modulation of glutamate actions. Dopamine depressed glutamate-evoked currents in a dose-dependent fashion, with Hill slopes in individual neurons ranging from 0.3 to 0.6. Dopamine could also evoke a direct hyperpolarizing action on hypothalamic neurons in the presence of tetrodotoxin or glutamate receptor blockers, at least in part by opening K+ channels. 9. Glutamate plays an important role as a primary excitatory transmitter within the hypothalamus. Our data support the hypothesis that a major mechanism of dopamine's influence on hypothalamic neurons involves the modulation of glutamate's excitatory action, mostly by inhibition. This is consistent with the hypothesis that modulation of glutamate activity may be an important mechanism of dopamine action throughout the nervous system.

Neuropeptide Y-mediated long-term depression of excitatory activity in suprachiasmatic nucleus neurons.

A brief exposure to light can shift the phase of mammalian circadian rhythms by 1 hr or more. Neuropeptide Y (NPY) administration to the hypothalamic suprachiasmatic nucleus, the circadian clock in the brain, also causes a phase shift in circadian rhythms. After a phase shift, the neural clock responds differently to light, suggesting that learning has occurred in neural circuits related to clock function. Thus, certain stimuli can produce effects that last for an extended period, but possible mechanisms of this long-term effect have not been previously examined at the cellular level. Here, we report that NPY caused a long-term depression in both electrical activity and intracellular calcium levels of neurons, as studied with whole-cell patch-clamp recording and Fura-2 digital imaging. In contrast to the immediate (1 sec) recovery after relief from glutamate receptor blockade, a brief single application of NPY (100 nM) depressed cytosolic Ca2+ for > 1 hr. The mechanism of this long-term calcium depression, a form of cellular learning, is dependent on the simultaneous release of glutamate and activation of NPY receptors, because both the extended response to NPY and any aftereffect were blocked by coapplication of glutamate receptor antagonists. Postsynaptic actions of NPY, mediated by both Y1- and Y2-like receptors, were short term and recovered rapidly. The primary site of long-term NPY actions may be on presynaptic glutamatergic axons, because the frequency of miniature excitatory postsynaptic currents in the presence of tetrodotoxin was reduced by transient exposure to NPY in both cultures and slices.

Adenosine pre- and postsynaptic modulation of glutamate-dependent calcium activity in hypothalamic neurons.

1. Within the hypothalamus, adenosine has been reported to influence temperature regulation, sleep homeostasis, and endocrine secretions. The effects of adenosine on hypothalamic neurons have not been studied at the cellular level. Adenosine (5 nM-30 microM) showed no influence on intracellular Ca2+ or electrical activity in the presence of glutamate receptor antagonists D-2-amino-5-phosphonovalerate and 6-cyano-7-nitroquinoxaline-2,3-dione; consequently, we examined the role of adenosine in modulating the activity of glutamate in cultured hypothalamic neurons (n > 1,700) with fura-2 Ca2+ digital imaging and whole cell patch-clamp electrophysiology in the absence of glutamate receptor block. 2. When glutamate receptors were not blocked, adenosine (1-30 microM) and the selective adenosine A1 receptor agonist N6-cyclopentyl adenosine (CPA; 5 nM-1 microM) caused a large reduction in intracellular Ca2+ and electrical activity, suggesting that glutamate neurotransmission was critical for an effect of adenosine to be detected. Neuronal Ca2+ levels were reversibly depressed by CPA (50 nM), with a maximum depression of 90%, and these effects were blocked by coadministration of the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). 3. Ca2+ levels in immature neurons before the time of synaptogenesis were not affected by adenosine. Adenosine A1 receptor activation suppressed glutamate-mediated Ca2+ activity in neurons in vitro 8 to 73 days. 4. Adenosine (1 or 10 microM) caused a hyperpolarization of membrane potential and a reduction of large postsynaptic potentials arising from endogenously released glutamate. The administration of low concentrations of CPA (5 nM) decreased the frequency of glutamate-mediated, neuronally synchronized Ca2+ transients and the frequency of postsynaptic potentials. 5. To compare the relative effects of adenosine on hypothalamic neurons with cells from other brain regions, we assayed the effects of CPA on glutamate-mediated Ca2+ in hippocampal and cortical cultures. CPA (50 nM) reversibly depressed glutamate-mediated Ca2+ rises in hypothalamic neurons by 35%, compared with 54% in hippocampal neurons and 46% in cortical neurons. 6. If it does play a functional role, adenosine should be released by hypothalamic cells. In some neurons the adenosine A1 receptor antagonists cyclopentyltheophylline or DPCPX caused an increase in intracellular Ca2+, suggesting that adenosine was secreted by hypothalamic cells, tonically depressing glutamate-enhanced neuronal Ca2+. 7. To determine whether adenosine could exert a postsynaptic effect, we coapplied it with glutamate agonists in the presence of tetrodotoxin. Within subpopulations of hypothalamic neurons, adenosine and CPA either inhibited (18% of total neurons) or potentiated (6% of total neurons) responses to glutamate, N-methyl-D-aspartate, and kainate by > or = 20%. 8. In contrast to the modest effects found in neurons, responses of hypothalamic astrocytes to the application of glutamate or the metabotropic glutamate receptor agonist (+/-)-trans-1-amino-1,3-cyclopentanedicarboxylic acid were strongly potentiated by adenosine (mean +225%) and CPA. 9. Together, these findings suggest that adenosine exerts a major presynaptic effect and a minor postsynaptic effect in the modulation of glutamate neurotransmission in the hypothalamus, where it can play a significant role in blocking a large part of the glutamate-induced Ca2+ rise. In the absence of glutamate transmission, adenosine has relatively little effect on either neuronal intracellular Ca2+ or electrical activity.

Internal Ca2+ stores involved in anoxic responses of rat hippocampal neurons.

1. During whole-cell recordings from CA1 neurons of rat brain slices with electrodes containing only KMeSO4 and Hepes, brief anoxia (2-3 min) consistently evoked a hyperpolarization (delta V approximately 14 mV) and reduction in input resistance (delta R approximately -20%). 2. As in previous intracellular recordings, Dantrolene sodium (10 microM) suppressed the anoxic delta V and delta R, confirming the release of internal Ca2+ is a major component of the anoxic response. 3. To identify the relevant intracellular Ca2+ store, other blockers of Ca2+ release were applied either externally (in the bath) or internally, by addition to the contents of the recording electrode. 4. The anoxic hyperpolarization was abolished or much reduced by heparin (10-20 micrograms ml-1, internal), thapsigargin (10 microM, external), Ruthenium Red (50 microM, internal) and external procaine (0.5-2 mM), but not by internal procaine (0.5-1 mM) or ryanodine (10 microM, external). 5. The anoxic fall in resistance was also abolished or reduced by heparin, thapsigargin and external procaine, but not by ryanodine, internal procaine or Ruthenium Red. 6. In addition, external procaine (0.5-2 mM) eliminated the early (transient) depolarization and reduced the post-anoxic hyperpolarization by 60 +/- 22%. 7. None of these agents consistently changed the resting potential, but the input resistance was significantly increased by Dantrolene and external procaine. 8. In view of the marked effects of heparin and thapsigargin, but not ryanodine and internal procaine, we conclude that the anoxic response seen in such whole-cell recordings is initiated predominantly by Ca2+ release from an internal store that is InsP3 sensitive rather than Ca2+ sensitive. 9. Comparable but less pronounced effects of external procaine were seen during intracellular recordings with 3 M KCl-containing electrodes. The dose-dependent suppression of various features of the anoxic response by external procaine (EC50 approximately 0.2 mM) is presumed to be mediated by a superficial membrane trigger or modulating site.

[The effect of thyrotropin-releasing hormone on the activity of the septal neurons in brain slices from hibernating and active susliks Citellus undulatus]. / Vliianie tirotropin-rilizing gormona na aktivnost' septal'nykh neironov v srezakh mozga giberniruiushchikh i aktivnykh suslikov Citellus undulatus.

Effects of thyrotropin-releasing hormone (TRH) on spontaneous and evoked activity were tested in the medial septum--diagonal band neurons (MS--DB complex) in the slices taken from the brain of hibernating (HS) and waking (WS) ground squirrels. Administration of TRH (0.1 microM) into the flow of incubating medium increased the frequency of spontaneous activity of all the MS--DB neurons in HS and of the majority of neurons in the WS. However, in the septal slices of HS this increase was significantly more pronounced. The excitatory influence of TRH on the units was preserved in conditions of synaptic blockade. In the neurons from other structures in the brain slices of both HS and WS groups TRH did not affect usually the level of spontaneous discharges. When studying the responses of the MS--DB neurons to electrical stimulation of medial forebrain bundle, it was found that application of TRH led to disappearance of responses in a half of units in both groups of animals. The existence of the forebrain modulatory TRH-system which participates post- and, probably, presynaptically in regulation of the MS--DB neuronal activity is suggested. The role of TRH and of MS--DB in neural control of hibernation is discussed.

State-dependent and state-independent effects of thyrotropin-releasing hormone on medial septum neuronal activity in the brain slices of waking and hibernating ground squirrels.

Effects of thyrotropin-releasing hormone on spontaneous activity and responses to medial forebrain bundle stimulation were tested in the units of the medial septum-diagonal band complex in slices taken from the brain of hibernating and waking ground squirrels. Administration of thyrotropin-releasing hormone (0.1 microM) into the flow of incubating medium increased the frequency of spontaneous activity of all the medial septum-diagonal band complex neurons in hibernating ground squirrels and of the majority of neurons in the waking ground squirrels. However, in the septal slices of hibernating ground squirrels this increase was significantly more pronounced. In addition, the neuropeptide slightly increased the frequency of bursts in the majority of cells with rhythmic burst activity. The excitatory influence of thyrotropin-releasing hormone on the units was preserved in conditions of synaptic blockade. In neurons from other structures (lateral septum, medial preoptic area, hippocampus) in the brain slices of both hibernating and waking ground squirrels, thyrotropin-releasing hormone did not usually affect the level of spontaneous discharges. When studying the responses of the medial septum-diagonal band complex neurons to electrical stimulation of medial forebrain bundle it was found that application of thyrotropin-releasing hormone (0.1 microM) led to the disappearance of responses in 50 and 44% of units in the hibernating and waking ground squirrels, respectively; in the rest of the neurons a disturbance of stability and probability of responses was observed. The existence of a modulatory thyrotropin-releasing hormone system which participates post-, and, probably, presynaptically in the regulation of the medial septum-diagonal band complex neuronal activity is suggested. The role of thyrotropin-releasing hormone and of medial septum-diagonal band complex in the neural control of hibernation/euthermic waking cycle is discussed.

[The excitability of neurons of the medial septal area in brain slices from hibernating and active Citellus undulatus susliks]. / Vozbudimost' neironov medial'noi oblasti septuma v srezakh mozga giberniruiushchikh i aktivnykh suslikov Citellus undulatus.

Spontaneous and evoked neuronal activity of the medical septum-diagonal band complex (MS-DB) has been investigated in slices from the brain of hibernating and active ground squirrels, as well as guinea pigs. In all experimental groups, the majority of the MS-DB neurones exhibited high regular of rhythmic burst spontaneous activity which persisted even after synaptic blockade in half of the neuronal population. Under the same conditions, the activity of the surrounding structures was completely suppressed. The density of the spontaneously active neurones in the slices, as well as the mean frequency of discharges in the MS-DB of hibernating ground squirrels, were significantly higher than in active ground squirrels and guinea pigs. Stimulation of the medial forebrain bundle evoked initial suppression of the activity in the majority of MS-DB units; in many of them, the suppression was followed by a burst discharge. Neurones with background rhythmic burst activity always reacted by resetting the spontaneous bursts. In total, 50-60% of the MS-DB neurones in active ground squirrels and guinea pigs reacted by post-inhibitory bursts, whereas in hibernating animals these responses were observed nearly in all neurones. Threshold values of the stimulating current were lower in hibernating animals; the intraburst density of spikes was increased.

[A comparative analysis of the functional stability (based on electrophysiological criteria) of slices of the suslik and guinea pig brains maintained under deep hypothermia]. / Sravnitel'nyi analiz funktsional'noi sokhrannosti (po élektrofiziologicheskim kriteriiam) srezov mozga suslikov i morskikh svinok pri soderzhanii v glubokoi gipotermii.

The effect of prolonged deep cooling has been investigated in hippocampal and septal slices from the brain of hibernating and active ground squirrels, as well as of the guinea pigs. The slices were kept at low temperatures (2-4 degrees C) for various periods of time (from several hours to 6 days) and were periodically tested in a warm (31 degrees C) incubation medium. Hippocampal field potentials (mainly of the field CA1) and spontaneous activity of single neurones of the medial septum were recorded. Significant differences were observed in the recovery of functional activity of the slices after their preparation as well as after cooling between experimental groups of animals. Slices from hibernating ground squirrels retained their activity for 7-9 days, those from active ones--for 6-7 days, whereas slices from guinea pigs did not recover their functional activity after cooling for more than 1-2 days.

Modelling the regulation of theta-rhythm by increasing afferent inflow in septal slices.

We recorded the neuronal activity of the medial region of the septum (MS-DB) intracellularly in guinea-pig septal slices. Electrical stimulation of the diagonal band (DB) evoked a low-threshold initial period of inhibition in the cells (20-280 msec in various cells). When the intensity of the stimulation was increased, this inhibitory phase shortened gradually or in a step-wise fashion, remaining unaltered in a portion of the cells with brief (40-50 msec) inhibition. The duration of the inhibition stabilized within a range of 30-60 msec. Many cells with single-spike background activity switched to generating post-inhibitory bursts at various levels of stimulation by current. Cells of the MS-DB with background rhythmical bursts always responded by phase locking to the stimulus. As a result, 58% of all of the cells of the MS-DB generated relatively short-latency, synchronized bursts when the level of afferent inflow was increased.

Functional stability of the brain slices of ground squirrels, Citellus undulatus, kept in conditions of prolonged deep periodic hypothermia: electrophysiological criteria.

The brain of hibernating animals, controlling the physiological functions during the hibernation cycles, is itself subject to deep cooling during bouts of hibernation. This suggests its high tolerance to deep hypothermia. Effects of prolonged deep cooling were investigated in hippocampal and septal slices, taken from the brains of three groups of animals: hibernating ground squirrels, actively waking ground squirrels, and guinea-pigs. The slices were kept at a low temperature (2-4 degrees C) for various periods of time (from several hours up to six days) and periodically tested in warm (31 degrees C) incubation medium. The hippocampal field potentials (mainly of field CA1), as well as spontaneous activity of single neurons of hippocampus and medial septum were recorded. For comparative purposes mean amplitudes of population spikes and mean frequency of spontaneous neuronal discharge were used. Significant differences between the experimental groups were observed in recovery of functional activity of the slices after their dissection from the brain, as well as after deep cooling. In both cases re-establishment of neuronal activity in ground squirrels occurred more rapidly, than in guinea-pigs. The most dramatic was the difference in maximal time of survival of the slices under conditions of deep cooling. Independently of periodicity of the electrophysiological testing in warm medium, the slices taken from hibernating squirrels retained their activity for seven to nine days, the slices of waking ground squirrel hippocampus survived up to six to seven days, while those of guinea-pis did not recover their functional activity after cooling for more than one to two days.(ABSTRACT TRUNCATED AT 250 WORDS)

Paradoxical state-dependent excitability of the medial septal neurons in brain slices of ground squirrel, Citellus undulatus.

Spontaneous and evoked neuronal activity of the medial septum-diagonal band complex was investigated extracellularly in slices, taken from the brain of the three groups of animals: hibernating ground squirrels, waking ground squirrels, and guinea-pigs. All slices were incubated at 31-32 degrees C. The slices of the ground squirrels' brain were retested after keeping them for 15-36 h in the refrigerator at 2-4 degrees C. In all experimental groups the majority of the medial septum-diagonal band complex neurons had high regular or rhythmic burst spontaneous activity, which in half of the neuronal population persisted in conditions of synaptic blockade. The low-frequency irregular activity of the surrounding structures (lateral septum, caudate, accumbens, medial preoptic area) was completely suppressed in these conditions. The density of the spontaneously active neurons in the slices, as well as the mean frequency of discharges in the medial septum-diagonal band complex of hibernating ground squirrels, was significantly higher than that in waking ground squirrels and guinea-pigs. Stimulation of the medial forebrain bundle evoked initial suppression of activity in majority of the medial septum-diagonal band complex units; in many of them the suppression was followed by a burst discharge. The neurons with background rhythmic burst activity always responded by resetting the spontaneous bursts. In total, about 50-60% of the medial septum-diagonal band complex neurons of waking ground squirrels and guinea-pigs responded by post inhibitory bursts to the stimulation of medial forebrain bundle, while in hibernating ground squirrels such responses were observed in nearly all neurons. The threshold values of the stimulating current were significantly lower in the hibernating ground squirrels' group, the mean duration of the initial suppression was shorter, the intraburst density of spikes and/or duration of the bursts was increased. Thus, evaluation of spontaneous and evoked activity on the basis of various criteria revealed surprising similarity between the two groups of active animals, while the activity and excitability of the medial septum-diagonal band complex neurons was approximately doubled in the hibernating animals. This difference between active and hibernating ground squirrels was preserved during retesting after deep and prolonged cooling of the slices. The experiments demonstrate paradoxical stable increase of activity and excitability of the medial septum-diagonal band complex neurons in the hibernating ground squirrels.(ABSTRACT TRUNCATED AT 250 WORDS)

[The modelling of theta rhythm regulation by an increasing afferent inflow in septal slices in vitro]. / Modelirovanie reguliatsii teta-ritma vozrastaiushchim afferentnym pritokom na septal'nykh srezakh in vitro.

The aim of the work was the modelling in vitro of the condition of increased afferent inflow, which in the intact septum results in an increase of population of theta-bursting units, their synchronization and shift to a higher frequency of the bursts, with corresponding changes in the hippocampal electrical activity. Neuronal activity was recorded extracellularly in the medial septal nucleus and vertical limb of the nucleus of diagonal band (MS-DB) in guinea pig septal slices. Electrical stimulation in the medial part of horizontal limb of DB evokes initial period of suppression of spontaneous activity in 85% of the neurones. This low-threshold, rapid inhibition has variable duration (20-280 ms) in different units at low intensities of the stimulating current. With increased intensities of stimulation this inhibitory phase in majority of units is gradually or by steps shortened, though in some units with initial short inhibition it is not changed. As a result the variability of initial inhibitory period between units is decreased and centered around 30-60 ms. Many units with single-spike background activity developed postinhibitory burst responses at various levels of stimulating current. The spontaneously bursting MS-DB units always responded by resetting of their background bursts. In total 58% of all recorded neurones generated evoked bursts under condition of increased afferent inflow.

[The role of GABA-ergic regulation in organizing spontaneous and evoked activity of the septal neurons]. / Rol' GAMKergicheskoi reguliatsii v organizatsii spontannoi i vyzvannoi aktivnosti septal'nykh neironov.

Effects of GABA, pentobarbital and picrotoxin upon spontaneous and evoked activity of neurones of the medial septal nucleus and the nucleus of the diagonal band (MS-DB) were investigated in the guinea pig septal slices. GABA and pentobarbital have similar effect upon all neurones, but the cells with a regular single spike and rhythmic burst activity of pacemaker type were less sensitive to their inhibitory influence. Picrotoxin affects neither frequency, nor pattern of activity. Electrical stimulation of the medial forebrain bundle evoked initial suppression of activity in majority of the neurones (74%); the remaining cells reacted mainly with an initial burst. GABA and pentobarbital increased the duration of the initial inhibition and revealed it in all cells with initial excitation in the control state. Picrotoxin did not influence this type of response, but revealed initial short-latency bursts in the cells with inhibitory effect in control state. The experiments show double nature of the effect of afferent stimulation controlling the activity of the MS-DB neurones. The mechanism of synchronization of the rhythmic activity in MS-DB, resulting in generation of the hippocampal theta-rhythm, is discussed.