Activity of preoptic neurons during synchronization and desynchronization

The Integration of the Maternal Care with Sleep During the Postpartum Period

Our entire life occurs in a constant alternation between wakefulness and sleep. The impossibility of living without sleep implies that any behavior must adapt to the need for sleep, and maternal behavior does not escape from this determination. Additionally, maternal behavior in mammals is a highly motivated behavior, essential for the survival of the offspring. Thus, the mother has to adapt her physiology of sleep to the constant demands of the pups, where each species will have different strategies to merge these two physiological needs. However, all studied female mammals will experience sleep disturbances at some point of the postpartum period.

A mathematical model towards understanding the mechanism of neuronal regulation of wake-NREMS-REMS states

In this study we have constructed a mathematical model of a recently proposed functional model known to be responsible for inducing waking, NREMS and REMS. Simulation studies using this model reproduced sleep-wake patterns as reported in normal animals. The model helps to explain neural mechanism(s) that underlie the transitions between wake, NREMS and REMS as well as how both the homeostatic sleep-drive and the circadian rhythm shape the duration of each of these episodes. In particular, this mathematical model demonstrates and confirms that an underlying mechanism for REMS generation is pre-synaptic inhibition from substantia nigra onto the REM-off terminals that project on REM-on neurons, as has been recently proposed. The importance of orexinergic neurons in stabilizing the wake-sleep cycle is demonstrated by showing how even small changes in inputs to or from those neurons can have a large impact on the ensuing dynamics. The results from this model allow us to make predictions of the neural mechanisms of regulation and patho-physiology of REMS.

Activation of inactivation process initiates rapid eye movement sleep

Interactions among REM-ON and REM-OFF neurons form the basic scaffold for rapid eye movement sleep (REMS) regulation; however, precise mechanism of their activation and cessation, respectively, was unclear. Locus coeruleus (LC) noradrenalin (NA)-ergic neurons are REM-OFF type and receive GABA-ergic inputs among others. GABA acts postsynaptically on the NA-ergic REM-OFF neurons in the LC and presynaptically on the latter's projection terminals and modulates NA-release on the REM-ON neurons. Normally during wakefulness and non-REMS continuous release of NA from the REM-OFF neurons, which however, is reduced during the latter phase, inhibits the REM-ON neurons and prevents REMS. At this stage GABA from substantia nigra pars reticulate acting presynaptically on NA-ergic terminals on REM-ON neurons withdraws NA-release causing the REM-ON neurons to escape inhibition and being active, may be even momentarily. A working-model showing neurochemical-map explaining activation of inactivation process, showing contribution of GABA-ergic presynaptic inhibition in withdrawing NA-release and dis-inhibition induced activation of REM-ON neurons, which in turn activates other GABA-ergic neurons and shutting-off REM-OFF neurons for the initiation of REMS-generation has been explained. Our model satisfactorily explains yet unexplained puzzles (i) why normally REMS does not appear during waking, rather, appears following non-REMS; (ii) why cessation of LC-NA-ergic-REM-OFF neurons is essential for REMS-generation; (iii) factor(s) which does not allow cessation of REM-OFF neurons causes REMS-loss; (iv) the association of changes in levels of GABA and NA in the brain during REMS and its deprivation and associated symptoms; v) why often dreams are associated with REMS.

Presence of alpha-1 norepinephrinergic and GABA-A receptors on medial preoptic hypothalamus thermosensitive neurons and their role in integrating brainstem ascending reticular activating system inputs in thermoregulation in rats

Thermal messages are relayed to the medial preoptic O-anterior hypothalamus (mPOAH) via the ascending reticular activating system (ARAS). According to previous findings that norepinephrine (NE)-ergic and GABA (gamma-amino butyric acid)-ergic inputs convey thermal information to the CNS, those neurotransmitters may be responsible for reciprocal correlation between body temperature and mPOAH warm-(WSNs) and cold-(CSNs) sensitive neuronal firing rates for thermoregulation. In this study on Wistar rats, we have characterized in vivo the role of alpha-1 NE-ergic and GABA-A receptors in the possible modulation of ARAS inputs to the thermosensitive neurons in the mPOAH. Nine WSNs, 7 CSNs and 19 thermo-insensitive neurons were recorded from mPOAH and effects of ARAS stimulation and iontophoretic application of prazosin as well as picrotoxin on those neurons were evaluated. The WSNs were excited by ARAS stimulation but inhibited by both prazosin and picrotoxin; whereas the CSNs were inhibited by ARAS stimulation and prazosin, but excited by picrotoxin. The NE excited the WSNs as well as the CSNs, while GABA had opposite effects on them, suggesting that NE and GABA interact in the mPOAH for thermoregulation. The findings unravel an intriguing possibility that in the mPOAH, GABA simultaneously acts on hetero-receptors located at pre-and post-synaptic sites, modulating the release of NE on the WSNs and CSNs for thermoregulation. Further, ARAS stimulation-induced similar excitatory and inhibitory responses of the WSNs and the CSNs support such converging inputs on these neurons for thermoregulation.

Influence of hypnogenic brain areas on wakefulness- and rapid-eye-movement sleep-related neurons in the brainstem of freely moving cats

Rapid-eye-movement (REM) sleep is normally preceded by non-REM sleep; however, every non-REM sleep episode is not followed by REM sleep. It has been proposed that, for the regulation of REM sleep, the brain areas modulating waking and non-REM sleep are likely to communicate with neurons promoting REM sleep. The former has been reported earlier, and in this study the latter has been investigated. Under surgical anaesthesia, cats were prepared for electrophysiological recording of sleep-wakefulness and electrical stimulation of caudal brainstem as well as preopticoanterior hypothalamic hypnogenic areas. Insulated microwires of 25-32 microm were used to record 52 single neuronal activities from the brainstem along with bipolar electroencephalogram, electromyogram, electrooculogram, and pontogeniculooccipital waves in freely moving, normally behaving cats. The neurons were classified into five groups based on changes in firing rates associated with different sleep-waking states compared with quiet wakefulness. Thereafter, the responses of these neurons to 1-Hz stimulation of the two non-REM sleep-promoting areas were studied. At the end of experiment, the stimulating and recording sites were histologically identified. It was observed that, among the affected neurons, the caudal brainstem non-REM sleep-promoting area excited more REM-on neurons, whereas the preopticoanterior hypothalamus hypnogenic area inhibited more awake-active neurons. Thus, the results suggest that, at the single neuronal level, the caudal brainstem non-REM sleep-modulating area, rather than the preopticoanterior hypothalamic hypnogenic area in the brain, plays a modulatory role in triggering REM sleep initiation at a certain depth of sleep.

Changes in rectal temperature and ECoG spectral power of sensorimotor cortex elicited in conscious rabbits by i.c.v. injection of GABA, GABA(A) and GABA(B) agonists and antagonists

1. In order to ascertain whether both GABA(A) and GABA(B), or only GABA(B) receptors, directly modulate thermoregulation in conscious rabbits, GABA(A)/GABA(B) agonist and antagonist agents were injected intracerebroventricularly in conscious rabbits while monitoring changes in rectal temperature (RT), gross motor behaviour (GMB) and electrocorticogram (ECoG) power spectra (ps) from sensorimotor cortices. 2. GABA (48 micromol), nipecotic acid (50 nmol), THIP (60 nmol), muscimol (18 nmol) and baclofen (8 nmol) induced hypothermia (-deltaRTmax values of 1.70+/-0.1, 1.4+/-0.2, 1.0+/-0.4, 1.1+/-0.2 and 1.6+/-0.3 degrees C, respectively), accompanied by inhibition of GMB and ECoG synchronization. THIP increased ps at delta frequency band (1.1-3.3 Hz), while GABA, nipecotic acid, muscimol and baclofen did the same at both delta and (4.6-6.5 Hz) frequency bands. ECoG ps changes were concomitant or even preceded hypothermia. 3. Bicuculline (1.8 nmol) induced hyperthermia (deltaRTmax 1.2+/-0.5 degrees C) and slight excitation of GMB, while CGP35348 (1.2 micromol) did not affect RT nor GMB. Both compounds did not affect ECoG ps. 4. Bicuculline potentiated muscimol-induced hypothermia, inhibition of GMB and synchronization of ECoG, while CGP35348 fully antagonized these effects. 5. In conclusion, the present results, while confirming the prevailing role of GABA(B), also outline a direct involvement of GABA(A) receptors in the central mechanisms of thermoregulation. Ascending inhibition towards discrete cortical areas controlling muscular activity and thermogenesis may result from GABA receptor activation in neurones proximal to the ventricles, thus contributing to hypothermia, although hypothermia-induced reduction of neuronal activity of these cortical areas cannot be ruled out.

Wakefulness-inducing area in the brainstem excites warm-sensitive and inhibits cold-sensitive neurons in the medial preoptic area in anesthetized rats

Sleep-wakefulness and body temperature are known to influence each other. The body temperature rises during wakefulness and falls during sleep. The midbrain reticular formation is one of the areas in the brainstem that induces wakefulness, while the preoptico-anterior hypothalamic area is the main thermoregulatory center in the brain. In order to understand the neural mechanism for simultaneous regulation of these functions we hypothesized that the wakefulness area in the brainstem is likely to have an opposite influence on warm- and cold-sensitive neurons in the preoptico-anterior hypothalamic area. Hence, first, the wakefulness-inducing area was identified in the brainstem by stimulating the site with high-frequency rectangular wave electrical pulses (100 Hz, 100 microA, 200 microsec for 5-8 sec) in freely behaving chronically prepared experimental rats. Then, single neuronal activity from the medial preoptico-anterior hypothalamic area was recorded and their thermosensitivity was established. Thereafter, the influence of such a confirmed wakefulness-inducing area in the brainstem on the responsiveness of the single neuronal activity of predetermined warm- and cold-sensitive neurons as well as on temperature-insensitive neurons was studied by overlapping stimulus (1 Hz, 500 microA, 200 microsec) bound responses. It was observed that the warm-sensitive neurons were excited and the cold-sensitive neurons were inhibited by stimulation of the wakefulness-inducing area in the brainstem. Most of the temperature-insensitive neurons remained unaffected. The results confirm our hypothesis and help in understanding the mechanism of simultaneous modulation of body temperature in association with changes in wakefulness at the single neuronal level.

Presence of alpha-1 adrenoreceptors on thermosensitive neurons in the medial preoptico-anterior hypothalamic area in rats

Earlier microinjection studies showed that norepinephrine in the medial preoptico-anterior hypothalamic area (mPOAH) regulates body temperature and the action is mediated through alpha-1 adrenoceptors. This study was conducted to confirm if the thermosensitive neurons in the mPOAH of rats possess alpha-1 adrenoceptors. First, the thermosensitivity of mPOAH neurons was tested and then the effects of microiontophoretic application of prazosin, alpha 1 adrenoceptor antagonist, on the firing rate of both the thermosensitive as well as the insensitive neurons were recorded. Prazosin significantly inhibited the firing rate of the thermosensitive neurons suggesting that most of the cold and warm sensitive neurons in the mPOAH possess alpha-1 adrenoceptors. These results at the single neuronal level confirm our earlier hypothesis that in the mPOAH, norepinephrine regulates body temperature by acting on alpha-1 adrenoceptors. The data also suggest that sensitivity of the mPOAH neurons to norepinephrine alter with changes in body temperature. The detailed physiological significance of the results with special reference to thermoregulation at the single neuronal level has been discussed.

Physiological characteristics of the projection pathway from the medial preoptic to the nucleus raphe magnus of the rat and its modulation by the periaqueductal gray

Anatomical studies have shown a strong projection from the medial preoptic nucleus of the hypothalamus (MPO) to both the periaqueductal gray (PAG) and nucleus raphe magnus (NRM). In this study, we examined the physiological characteristics of MPO to NRM connections and examined how blockade of neuronal transmission and of the glutamatergic system within the PAG modifies this pathway. In deeply anesthetized rats, recordings were made from NRM neurons that were identified by their response to peripheral mechanical stimulation and designated as "E", "I", or "N" if they were excited, inhibited, or not activated by noxious stimulation. In addition, cells were identified as spinally projecting if they could be antidromically activated by stimulation of the dorsolateral funiculus at the thoracic level. The responses of 204 NRM neurons to electrical and 87 cells to both chemical and electrical stimulation of MPO were recorded. The response of NRM neurons to MPO stimulation was highly dependent on the sensory class of these cells. Chemical stimulation of MPO inhibited 50% (16/32) and excited 16% (5/32) of the I-cells. In contrast, 23% (9/39) of the E-cells were inhibited and 49% (19/39) were excited by chemical stimulation of MPO. Electrical stimulation at intensities below 80 microA at 100Hz had similar effects on the two classes of cells; 62% (24/39) of the E-cells and 31% (10/32) of the I cells were excited, and 31% (12/39) of the E-cells and 59% (19/32) of the I-cells were inhibited. The excitatory response to chemical stimulation lasted for an average of 136.8+/-73.2s and inhibitory response lasted for an average of 143.8+/-102.1s. Electrical stimulation of MPO at 1Hz excited 27%, inhibited 3%, and had no effect on 70% of NRM cells. The mean latency to peak excitation was 9.6+/-6.6ms. Antidromic activation of MPO neurons by NRM stimulation showed an average latency of 6.3+/-3.4ms. Blocking the glutamatergic transmission within the PAG (by injecting kynurenic acid (KYN) into the PAG) blocked the inhibitory response of 40% (6/15) of the I-cells and inhibitory response of 43% (3/7) of the E-cells. The excitatory response of 27% (3/11) of the I-cells and the excitatory response of 14% (1/7) of the E-cells were blocked by kynurenic injection into the PAG. It is concluded that: (1) in response to chemical stimulation of MPO, the number of I-cells that were inhibited was more than three times the number of I-cells that were excited; in contrast, the number of E-cells that were excited was more than twice the number of E-cells that were inhibited. (2) The interaction between MPO and NRM can be modulated by blockade of the neuronal transmission or blockade of the glutamatergic system in the PAG. (3) Simultaneous activity of many synapses is required for activation of the MPO-NRM pathway. (4) MPO to NRM interaction is mediated by fibers with a conduction velocity of less than 1m/s.

Interactions between cholinergic and GABAergic neurotransmitters in and around the locus coeruleus for the induction and maintenance of rapid eye movement sleep in rats

The noradrenergic "REM-off" neurons in the locus coeruleus cease firing, whereas some cholinergic and non-cholinergic "REM-on" neurons increase firing during rapid eye movement sleep. A reciprocal interaction between these neurons was proposed. However, acetylcholine did not inhibit neurons in the locus coeruleus. Nevertheless, since GABA levels increase during rapid eye movement sleep and picrotoxin injections into the locus coeruleus reduced rapid eye movement sleep, it was hypothesized that GABA in the locus coeruleus might play an intermediary inhibitory role for rapid eye movement sleep regulation. Therefore, the effects of GABA or carbachol (a mixed cholinergic agonist receptor) alone, as well as an agonist of one in presence of an antagonist of the other, in the locus coeruleus were investigated on sleep-wakefulness and rapid eye movement sleep. The cholinergic agonist carbachol increased, while the muscarinic antagonist receptor scopolamine decreased, the frequency of induction of rapid eye movement sleep per hour. In contrast, GABA and picrotoxin increased and decreased, respectively, the duration of rapid eye movement sleep per episode. However, when carbachol was injected in the presence of picrotoxin or GABA was injected in the presence of scopolamine, the effect of GABA or picrotoxin was dominant. Microinjection of both scopolamine and picrotoxin in combination reduced both the frequency of initiation as well as the duration per episode of rapid eye movement sleep. From these results we suggest that in the locus coeruleus cholinergic input modulates the frequency of induction of rapid eye movement sleep and this action is mediated through GABA interneurons, whereas the length of rapid eye movement sleep per episode is maintained by the presence of an optimum level of GABA. A model of neural connections for initiation and maintenance of rapid eye movement sleep is proposed and discussed.

Daily rhythms in Fos activity in the rat ventrolateral preoptic area and midline thalamic nuclei

The present experiment investigated the expression of the nuclear phosphoprotein Fos over the 24-h light-dark cycle in regions of the rat brain related to sleep and vigilance, including the ventrolateral preoptic area (VLPO), the paraventricular thalamic nucleus (PVT), and the central medial thalamic nucleus (CMT). Immunocytochemistry for Fos, an immediate-early gene product used as an index of neuronal activity, was carried out on brain sections from rats perfused at zeitgeber time (ZT) 1, ZT 5, ZT 12.5, and ZT 17 (lights on ZT 0-ZT 12). The number of Fos-immunopositive (Fos+) cells in the VLPO was elevated at ZT 5 and 12.5 (i.e., during or just after the rest phase of the cycle). Fos+ cell number increased at ZT 17 and ZT 1 in the PVT and CMT, 180 degrees out of phase with the VLPO. A positive correlation was found between the numbers of Fos+ cells in the PVT and CMT, and Fos expression in each thalamic nucleus was negatively correlated with VLPO Fos+ cell number. The VLPO, PVT, and CMT may integrate circadian and homeostatic influences to regulate the sleep-wake cycle.

Adrenergic and cholinergic inputs in preoptic area of rats interact for sleep-wake thermoregulation

Isolated studies have shown that both norepinephrine and acetylcholine into the medial preoptico-anterior hypothalamic area tonically regulate sleep-wake and body temperature. A possible interaction between these neurotransmitters for the regulation of such functions has been investigated in this study. To study this interaction a combination of either prazosin and carbachol or, scopolamine and methoxamine was injected into the medial preoptico-anterior hypothalamic area and the effect on sleep, wake, and rectal temperature recorded simultaneously. The combination of chemicals were selected based on our previous studies where it was observed that each of the chemicals in a combination had opposite effects. It was observed that injection of the combination expressed a resultant summated effects of individual component chemicals when injected in isolation (observed in previous studies). Because effect of neither of the chemicals in the combination was dominant, the results suggest an interaction and integration of the adrenergic and cholinergic inputs in the medial preoptico-anterior hypothalamic area for the regulation of sleep-wakefulness and body temperature.

Role of cholinergic inputs to the medial preoptic area in regulation of sleep-wakefulness and body temperature in freely moving rats

The medial preoptico-anterior hypothalamic area receives adrenergic as well as cholinergic inputs. Independent studies showed that both these inputs influence sleep, wakefulness and body temperature. The role of the adrenergic inputs was studied earlier. The role of cholinergic inputs is reported here. The cholinergic agonist, carbachol, and antagonist, scopolamine, were injected into this area during the day and the night in freely moving rats and the effects on sleep-wakefulness and body temperature studied. It was observed that carbachol induced wakefulness accompanied by a fall in body temperature while scopolamine induced an opposite effect, i.e. sleep accompanied by an increase in body temperature. This suggested that the cholinergic input into the medial preoptic area is spontaneously active in regulating sleep-wakefulness and body temperature and this regulation is mediated through muscarinic receptors present in this area. The results also suggest that, contrary to the action of adrenergic inputs (which have a dissociated effect on sleep-wakefulness and body temperature), the cholinergic input is unlikely to have a dissociated effect on those functions.

Activation of ventrolateral preoptic neurons during sleep

The rostral hypothalamus and adjacent basal forebrain participate in the generation of sleep, but the neuronal circuitry involved in this process remains poorly characterized. Immunocytochemistry was used to identify the FOS protein, an immediate-early gene product, in a group of ventrolateral preoptic neurons that is specifically activated during sleep. The retrograde tracer cholera toxin B, in combination with FOS immunocytochemistry, was used to show that sleep-activated ventrolateral preoptic neurons innervate the tuberomammillary nucleus, a posterior hypothalamic cell group thought to participate in the modulation of arousal. This monosynaptic pathway in the hypothalamus may play a key role in determining sleep-wake states.

Noradrenaline inhibits preoptic sleep-active neurons through alpha 2-receptors in the rat

Effects of noradrenaline (NA) on the activity of sleep-related neurons in the preoptic area (POA) and the neighboring basal forebrain were examined in the rat. Of 36 sleep-active neurons tested, 19 were inhibited and the other 17 were unaffected by NA applied through a multibarrel pipette. The alpha 2-agonist clonidine inhibited 11 of 14 sleep-active neurons and did not affect the other 3 neurons, whereas the alpha 1-agonist methoxamine (n = 13) and the beta-agonist isoproterenol (n = 11) had no effect on any of the sleep-active neurons tested. Thus, alpha 2-receptors mediated the NA-induced inhibition. Of 22 waking-active neurons tested, NA excited 10, inhibited 1, and had no effect on the remaining 11. Methoxamine excited 4 of 13 waking-active neurons tested, whereas isoproterenol (n = 9) and clonidine (n = 4) were without effect on any of the waking-active neurons tested. Accordingly, alpha 1-receptors probably mediated the NA-induced excitation. Seventy-seven state-indifferent neurons, which lacked activity related to the sleep-waking state, and 20 paradoxical sleep-active neurons were mostly (65%-70%) insensitive to NA. These results suggest that NA promotes wakefulness by inhibiting sleep-active neurons and by exciting waking-active neurons.

Noradrenergic inputs to sleep-related neurons in the preoptic area from the locus coeruleus and the ventrolateral medulla in the rat

Responses of sleep-related neurons in the preoptic area (POA) to stimulation of the locus coeruleus (LC) and the ventrolateral medulla (VLM), components of the reticular activating system, were recorded in the unanesthetized, head-restrained rat. Single-pulse stimulation of the LC and the VLM, respectively, inhibited 50% and 54% of 30 sleep-active neurons and excited 47% and 67% of 34 waking-active neurons. The remaining neurons were mostly unaffected. Seventy-three neurons that were not related to a sleep-wake state were mostly (i.e., 73-80%) unresponsive to stimulation. The high incidence of responses by sleep-related neurons suggests that neural inputs from the LC and VLM regulate the hypnogenic mechanisms in the POA. Stimulation of the LC antidromically activated 15% of sleep-active neurons and 11% of waking-active neurons. Thus, some of the sleep-related neurons in the POA may regulate LC neurons. In a later stage of the experiment, we used isoflurane-anesthetized rats that had been used for recording sleep-related neurons. Antagonists for adrenoceptors at a concentration of 10 microM were applied to neurons through a multibarrel micropipette to examine the involvement of noradrenaline in the responses as a neurotransmitter. Application of the alpha 2-blocker, yohimbine, attenuated the inhibitory responses in all 7 neurons tested. The beta-blocker, timolol, and the alpha 1-blocker, prazosin, did not alter any of the inhibitory responses. On the other hand, timolol attenuated the excitatory responses in 4 of 7 neurons, and prazosin attenuated the excitatory responses in 5 of 12 neurons. Yohimbine did not affect the excitatory responses. Thus, the LC and the VLM probably inhibit sleep-active neurons through alpha 2-adrenoceptors and excite waking-active neurons through either beta- or alpha 1-adrenoceptors.

Selective increases in non-rapid eye movement sleep following whole body heating in rats

Afternoon body heating has been reported to increase amounts of slow wave sleep (SWS) during the subsequent night in humans. This delayed effect of body heating on SWS has not been previously studied in laboratory animals. We examined the effect of whole body heating during the last 4 h of the light period on sleep and brain temperature (Tbr) during the subsequent twelve hour period in rats. Whole body heating was accomplished by elevating ambient temperature, typically to 33-35 degrees C, which increased Tbr to 40 +/- 0.5 degrees C. This condition was compared to a sleep-matched control condition, a sleep-deprived control condition and to a baseline condition. Following heating, non-rapid eye movement sleep 2 (NREMS2 or deep NREMS) was significantly increased during the first 2 h of the recovery period compared with baseline and sleep-matched control conditions and during the first hour compared with the totally sleep-deprived condition. NREMS1 was not significantly changed by heating. Rapid eye movement sleep was not different following heating compared to the sleep-matched and sleep-deprived control conditions but was significantly increased during the first hour of the recovery period following heating compared to baseline. Tbr was significantly lower for the first 5 h and the 7th h following heating compared to all three other conditions. Possible relationships between the regulation of sleep and temperature are discussed.

Different types of norepinephrinergic receptors are involved in preoptic area mediated independent modulation of sleep-wakefulness and body temperature

The preoptic area is known to regulate sleep-wakefulness and body temperature. It was suggested earlier that though sleep-wakefulness and body temperature may affect each other, the preoptic area mediated influence on those two physiological phenomena is likely to be independent of alteration in each other. Since intrapreoptic area norepinephrine could modulate both those functions, study of that system was undertaken. It was hypothesized that since the preoptic area has different types of norepinephrinergic receptors (viz. alpha 1, alpha 2 and beta), independent modulation of those two functions was probably due to activation or inactivation of separate receptors. Hence, the effects of different agonist and antagonist of those receptors individually as well as in combination into the preoptic area were studied on those two functions in freely moving rats. The results suggest that norepinephrine induced preoptic area mediated influence on the body temperature is primarily regulated by the alpha 1 receptors while the sleep and wakefulness are regulated by alpha 2 and beta receptors, respectively. The finding should help in explaining several poorly understood observations reported earlier and it suggests that similar phenomena may possibly exist in other system involving other neurotransmitters as well.

Differential influence of medial and lateral preoptic areas on body temperature in conscious and unconscious rats

Since temperature sensitive neurons are unevenly distributed in the medial and the lateral preoptic areas, it was hypothesized that the two areas possibly would influence body temperature to a different extent. As alteration in sleep-wakefulness and body movement may affect the body temperature, experiments were conducted by reversible inactivation of those two areas, in freely moving (conscious) rats as well as in rats where changes in EEG and movement were restricted (unconscious). Results showed that the medial preoptic area is more effective in body temperature regulation. The study also revealed that the preoptic area mediated effect on body temperature regulation is not necessarily linked to simultaneous changes in sleep-wakefulness and alteration in the latter probably helps in maintaining the former within limit.

Medial preoptic area affects sleep-wakefulness independent of associated body temperature change in free moving rats

Sleep-wakefulness and body temperature may modulate each other. Though both the functions are influenced by the medial preoptic area, the mechanism of action was not clear. This study was aimed at finding out whether the tonic influence of the medial preoptic area on sleep-wakefulness was independent of or secondary to simultaneous change in body temperature. The effects of inactivation of the area by a long acting local anaesthetic, marcain, on those physiological functions were investigated during the night and the day in freely moving rats. Though medial preoptic area influenced sleep-wakefulness and body temperature simultaneously, the effect on the latter was prolonged. The results suggest that the influence on sleep-wakefulness is unlikely to be associated with simultaneously changing body temperature. However, this study fails to differentiate whether the observed effects were due to inactivation of the cell body or the fibers passing through the area.

Differential acute influence of medial and lateral preoptic areas on sleep-wakefulness in freely moving rats

The role of preoptic area (POA) in sleep-wakefulness and related EEG changes is well established. Anatomically the area is divided into medial (mPOA) and lateral (IPOA) portions having different physiological functions. Knowledge regarding the differential role, if any, of those two areas in sleep and wakefulness was lacking in the literature. Therefore, an attempt was made in this study, to investigate the same systematically. Experiments were conducted during day and night in freely moving rats. Electrophysiological parameters defining sleep and wakefulness were recorded before and after reversible inactivation of those two areas separately by microinjection of a local anaesthetic, marcain. The responses were opposite in nature depending upon the time, day or night, when the anaesthetic was applied. During the day, anaesthetization induced wakefulness while during the night, sleep was precipitated. However, anaesthetization of both the areas though induced similar qualitative response, the degree of the responses differed significantly. The results suggest that the mPOA is more effective in maintaining tonic sleep while the IPOA is more potent in the maintenance of tonic wakefulness in the normal rats. The finding supports and fits well with the existing knowledge.

The role of reticular activating system in altering medial preoptic neuronal activity in anesthetized rats

The influence of the ascending reticular activating system (ARAS) on the medial preoptic unit activity was studied in urethane anesthetized rats. Alterations in the unit activity were also correlated with cortical EEG changes. A fourth of the medial preoptic units showed alterations in their discharges with cortical EEG changes. These units were also influenced by high frequency stimulation of ARAS, which simultaneously produced EEG desynchronization. On the other hand they were generally not influenced by 1 Hz stimulation of ARAS. These results indicate that the anatomically demonstrated projections from midbrain (forming ARAS), involving very few synapses, may not be involved in the regulation of sleep-wakeful function of the medial preoptic area. Interaction of some of the inputs at the medial preoptic area is discussed.

Increase of paradoxical sleep episodes after electrical stimulation of the lateral and third ventricles in the rat

Electrical stimulation (0.3 mA in intensity, 80 Hz in frequency, 0.7 ms in signal duration) applied at 17.00 h in the lateral and third ventricles induced a significant increase of nocturnal paradoxical sleep (PS). This effect persisted for two consecutive days in both cases. Non-specific aspects involved in this effect are discussed and the results are commented on in terms of humoral processes and possible control of pineal gland activity.

Increase of multiple unit activity during slow wave sleep in the cat preoptic area

Multiple unit activities (MUA) in 307 brainstem sites were recorded by chronically implanted electrodes in cats, using a polygraph with 4 channel MUA recording units. During transition from waking to slow wave sleep, at 15 sites including the medial preoptic area (11), the diagonal band of Broca (2) and medial anterior hypothalamic area (2), consistently earlier increase of MUA in discharge rate was observed, while MUA in other areas decreased. Also, at 13 sites in these areas, a decrease in discharge rate was demonstrated during paradoxical sleep. These findings suggest a close relationship between the preoptic area and sleep mechanisms, supporting a notion that an active site for induction of slow wave sleep may reside in the preoptic area.

Neuronal firing in the pallidal region: firing patterns during sleep-wakefulness cycle in cats

Neuronal activity was investigated by extracellular microelectrodes in the pallidal region of freely moving cats during wakefulness (W), slow-wave sleep (SWS) and paradoxical sleep (PS). The firing of 150 units from 35 points was examined. On the basis of the modifications of firing rates and patterns during the sleep-wakefulness cycle, 5 groups of neurons were distinguished. Two of these groups were characterized by strong increase of firing rate in W and PS and in one of them this increase preceded the cortical activation at the SWS-PS transition by an average of 26 sec. The role played by the basal forebrain area in the regulation of the sleep-wakefulness cycle is discussed.

Influence of rostral and caudal brain stem reticular formation on thalamic neurons

Single neuronal activity was recorded from the diffuse thalamic system. Influence of the rostral desynchronizing and caudal synchronizing structures of the brain stem reticular formation on these neurons was studied. Rostral stimulation produced an increase and caudal stimulation a decrease in the thalamic unit firing. A possible mechanism by which the brain stem reticular structures influence the cortical neurons is proposed on the basis of these findings.

Influence of preoptico-anterior and posterior hypothalamus on midline thalamic neurons

The present study was aimed at understanding the influence of the posterior hypothalamus (PH) and the preoptico-anterior hypothalamus (PO-AH) on the neurons of the midline thalamus (MTh) in encéphale isolé cats. A majority of the influenced neurons of the MTh showed increased firing on stimulation of the PH. Although the number of neurons showing increased or decreased firing on PO-AH stimulation were nearly equal, stimulus bound increased firing in many neurons was followed by a prolonged decreased firing. It is likely that the hypothalamo-thalamic circuit constitutes a parallel pathway to the reticulo-thalamic circuit for alteration of the cortical EEG.

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.

Alterations in preoptic unit activity on stimulation of caudal brain stem EEG-synchronizing structures

Effects of stimulation of EEG-synchronizing structures of the caudal brain stem reticular formation with low (6 Hz) and high (100 Hz) frequencies were studied on 42 neurons of the preoptic area, in encéphale isolé cats. Though low-frequency stimulation produced excitation and inhibition, the majority of the influenced neurons of the preoptic area had effects of the former type. Cortical EEG synchronization was also induced by low-frequency stimulation of the caudal brain stem. High-frequency stimulation, on the other hand, produced inhibition in a majority of the influenced neurons and induced, mostly, desynchronization of the cortical EEG. A majority of the neurons that were inhibited on high-frequency stimulation, remained unaffected during low-frequency stimulation. The influence induced on the preoptic area neurons by low-frequency stimulation could be obtained even in the absence of cortical EEG synchronization. Changes induced on preoptic neurons by high-frequency stimulation may be partially related to induced cortical EEG desynchronization.

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.

Responses of preoptic neurons to stimulation of caudal and rostral brain stem reticular structures

Effect of stimulation (1 Hz) of rostral and caudal brain stem reticular formation was studied on 41 neurons of preoptic area in encéphale isolé cats. Primary excitation was seen on almost all the 25 neurons influenced by stimulation of either of the areas. Many of these influenced neurons received inputs from both areas and showed poststimulatory oscillations in excitability. The two brain stem reticular structures, which have antagonistic influence on cortical EEG, cortical and subcortical neuronal activity, had identical influence on preoptic area neurons when stimulated at 1 Hz.