A function for REM sleep: regulation of noradrenergic receptor sensitivity

We hypothesize that REM sleep serves to upregulate and/or prevent downregulation of brain norepinephrine (NE) receptors. This hypothesis is based on the following observations: (1) NE neurons of the locus coeruleus (LC) are tonically active in waking and non-REM sleep, but the entire population of LC NE neurons is inactive during REM sleep. (2) Continuous presence of NE or adrenoceptor agonists downregulates NE receptors, while a reduction in NE availability upregulates these receptors. (3) The effects of REM sleep deprivation are similar to those of NE receptor downregulation. Recent biochemical studies of NE receptor sensitivity provide strong experimental support for this hypothesis. The functional consequence of enhanced NE receptor 'tone' brought about by REM sleep would be improved signal processing in diverse brain systems, thus endowing the organism with a selective advantage. This hypothesis makes a number of specific predictions which can be tested with currently available techniques, and suggests new ways of understanding the evolution and postnatal development of REM sleep.     

Long term blocking of GABA-A receptor in locus coeruleus by bilateral microinfusion of picrotoxin reduced rapid eye movement sleep and increased brain Na-K ATPase activity in freely moving normally behaving rats

Isolated studies showed that norepinephrinergic REM-OFF neurons are active throughout except during rapid eye movement (REM) sleep when they are inhibited possibly by GABA. Similarly, independent studies have also reported that during REM sleep deprivation those REM-OFF neurons continue firing, that there is increased norepinephrine (NE) in the brain and that increased levels of NE increases the Na-K ATPase activity in the brain. However, it was not known if all those changes were directly related to REM sleep deprivation, what could be the mechanism for such changes and their patho-physiological significance. To confirm the same, based on the reports, mostly from our group, it was hypothesised that GABA antagonist in the locus coeruleus (LC) should at least significantly reduce REM sleep and simultaneously increase Na-K ATPase activity in the brain. To confirm the proposed hypothesis, picrotoxin, a GABA-A receptor antagonist, was bilaterally microinjected every 6 h for 36 h into the LC of freely moving normally behaving rats and the effects on electrophysiological signals signifying sleep-wakefulness and on brain synaptosome Na-K ATPase activity were estimated. The microinjection was done with the help of a remote control pump without handling or disturbing the rats. The findings that REM sleep was significantly reduced and there was associated increase in Na-K ATPase activity confirmed our hypothesis. The results also support our modified (GABA-mediated) model of neural connections in the LC for the regulation of REM sleep. Also, this is probably the first report to simulate REM sleep deprivation using receptor antagonist.     

Locus Coeruleus Acid-Sensing Ion Channels Modulate Sleep–Wakefulness and State Transition from NREM to REM Sleep in the Rat

The locus coeruleus (LC) is one of the essential chemoregulatory and sleep–wake (S–W) modulating centers in the brain. LC neurons remain highly active during wakefulness, and some implicitly become silent during rapid eye movement (REM) sleep. LC neurons are also involved in CO₂-dependent modulation of the respiratory drive. Acid-sensing ion channels (ASICs) are highly expressed in some brainstem chemosensory breathing regulatory areas, but their localization and functions in the LC remain unknown. Mild hypercapnia increases the amount of non-REM (NREM) sleep and the number of REM sleep episodes, but whether ASICs in the LC modulate S–W is unclear. Here, we investigated the presence of ASICs in the LC and their role in S–W modulation and the state transition from NREM to REM sleep. Male Wistar rats were surgically prepared for chronic polysomnographic recordings and drug microinjections into the LC. The presence of ASIC-2 and ASIC-3 in the LC was immunohistochemically characterized. Microinjections of amiloride (an ASIC blocker) and APETx2 (a blocker of ASIC-2 and -3) into the LC significantly decreased wakefulness and REM sleep, but significantly increased NREM sleep. Mild hypercapnia increased the amount of NREM and the number of REM episodes. However, APETx2 microinjection inhibited this increase in REM frequency. These results suggest that the ASICs of LC neurons modulate S–W, indicating that ASICs could play an important role in vigilance-state transition. A mild increase in CO₂ level during NREM sleep sensed by ASICs could be one of the determinants of state transition from NREM to REM sleep.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12264-020-00625-0.     

Multiple-joint neurons in somatosensory cortex of awake monkeys

(1) The somatosensory cortex of alert monkeys, 55 neurons were found which receive convergent information from two or more adjacent joints. Most of these multiple-joint neurons were excited by postures of the hand, particularly those involved in grasping.

(2) Three basic types of joint interactions were observed. The simplest neurons (occlusion neurons) responded to postures of several different joints, but combination of the preferred postures produced no further increase in firing. The more complex cells showed summated responses to combined postures of adjacent joints, or subliminal facilitation between joints. The responses of both summation neurons and subliminal facilitation neurons were graded with joint angle, and there was an optimum or preferred position for both joints which gave the strongest response.

(3) Multiple-joint neurons may provide a neuronal substrate for extracting postural information from several different populations of kinesthetic neurons. They therefore act as feature-detecting neurons, abstracting information about specific body postures.

Properties of kinesthetic neurons in somatosensory cortex of awake monkeys

(1) To study neural mechanisms used to encode kinesthetic information in somatosensory cortex of awake monkeys, we recorded from 227 single neurons responsive to joint movement or specific postures of the forelimb or hand (kinesthetic neurons). Unit responses were characterized quantitatively with respect to: (a) firing patterns; (b) responses to ramp changes in joint position and joint velocity; and (c) responses to sinusoidal joint movements.

(2) Kinesthetic neurons were divided into 3 groups. Rapidly-adapting neurons (44%) responded only to joint movement, giving a burst of impulses proportional to velocity. They showed no tonic responses to limb posture. Two populations of tonically active neurons were observed: slowly-adapting neurons (43%) and postural neurons (13%). Both types increased their firing rates with increasing degrees of flexion or extension, showing maximum excitation at the extremes of joint position in the preferred direction. They were distinguished by their sensitivity to the velocity of movement, the size of the angle over which they respond, and the phase relation of their responses to sinusoidal joint movement.

(3) The firing rates of kinesthetic neurons in S-I cortex are functions of both joint angle and joint velocity. The importance of each component varies in the 3 classes: velocity of movement is the most important determinant of firing rates of rapidly-adapting and slowly-adapting kinesthetic neurons, and joint angle predominates the responses of postural neurons.

Three types of reticular neurons involved in the spinobulbo-spinal reflex of cats

Reticular neuron activity was recorded in 28 chloralosed cats in order to analyze the reflex arc of the spino-bulbo-spinal (SBS) reflex. Three types of reticular neurons, types I (input), II (output) and III (relay), were identified by unit discharges in response to stimulation of the sural nerve.

(1) Type I (input) neurons received spinal ascending volleys monosynaptically and responded to stimulation of the sural nerve with spikes of low amplitude and short latency. Unit spikes, however, were not produced by stimulation of the superficial radial nerve and the sensorimotor cortex. These input neurons were located in the dorsocaudal part of the medial bulbar reticular formation.

(2) Type II (output) neurons were part of the reticulospinal tract, which sends axons to the spinal cord, since these neurons exhibited antidromic spikes following stimulation of the ventrolateral funiculus of the spinal cord. Unit spikes were evoked by stimulation either to the sural or superficial radial nerves. These neurons were located in the ventrocaudal part of the medial bulbar reticular formation.

(3) Type III neurons included relay neurons. Unit spikes were evoked by stimulation of the sural nerve, superficial radial nerve and sensorimotor cortex. However, unit discharges were not obtained by antidromic stimulation to the reticulospinal tract. These neurons were distributed widely in the brain stem, both in the bulb and pons.

(4) Latency difference of unit discharges between input and output neurons was 3.5–5 msec, indicating the presence of interneurons (relays) between input and output neurons. Spikes of output neurons with 3.8–4.2 msec latency were observed following stimulation of the region where input neuron activity was found. We may conclude that three kinds of reticular neurons, input, relay and output, were involved in pathways of the SBS reflex.

Physiological identification of GABA as the inhibitory transmitter for mammalian cortical neurons in cell culture

(1) Rat cortical neurons grown in dissociated cell culture exhibit IPSPs which appear to be generated by an increase in membrane conductance to chloride.

(2) The neurons are all sensitive to GABA in micromolar concentrations and GABA mimics the inhibitory transmitter.

(3) The neurons are much less sensitive to glycine and insensitive to taurine.

(4) Bicuculline and strychnine both block essentially all IPSPs and at the same concentrations block GABA effects.

(5) It is concluded that GABA is the main, or only, inhibitory transmitter utilized by the cortical neurons in vitro. The relevance of this conclusion to in situ transmitter identification is discussed.

Effect of dopamine receptor blockade or norepinephrine synthesis inhibition on acute, ovariectomy-induced increases in pulsatile luteinizing hormone release in the rat

The initial aim of the present studies was to examine the influence of blockade of dopamine (DA) receptors with pimozide or inhibition of norepinephrine (NE) synthesis with U-14,624 on acute, ovariectomy (OVX)-induced changes in pulsatile LH release. Either treatment instituted at the time of OVX suppressed or inhibited the rapid increase in LH pulse amplitude and frequency normally occurring within 24 hr following ovarian removal on diestrus 1. While administration of pimozide at either 24 hr or 48 hr following OVX suppressed pulsatile LH release by selectively reducing LH pulse frequency, by 8 days following OVX pimozide failed to exert any effect on LH pulse frequency and therefore on pulsatile LH secretion. To determine if there was a transient critical period following OVX of at least 2 days but less than 8 when endogenous DA was excitatory to pulsatile LH release, piribedil (a DA receptor agonist) was given 24 hr following OVX. Rather than increase LH secretion, piribedil markedly suppressed pulsatile LH release indicating that DA does not stimulate LH secretion in acutely ovariectomized rats. These experiments indicate that

1. (1) NE is involved in stimulating the acute, OVX-induced increase that occurs in pulsatile LH release;

2. (2) DA receptorblockade by pimozide has a differential effect on pulsatile LH secretion which depends on the time following OVX when the compound is administered;

3. (3) this differential effect cannot be explained by a transient critical period of a few days duration following OVX during which DA is excitatory to pulsatile LH release.

Responses of long descending propriospinal neurons to natural and electrical types of stimuli in cat

Long descending propriospinal (LDP) neurons (antidromically identified) having cell bodies of origin in the cervical enlargement and projecting axons at least as far as the L2 segment were studied. Extracellular recording of responses to natural and electrical stimuli was done in high-spinal cats.

(1) A receptive field for natural stimuli was found for 123 LDP neurons. An additional 108 LDP cells were not activated by the natural stimuli used, but some of these fired spike potentials in response to electrical stimulation of peripheral nerves of the forelimb. There was no distinction between neurons activated and those not activated by natural stimuli on the basis of location or conduction velocity.

(2) The most effective natural stimuli were mechanical manipulation of the skin (both low and high threshold), movement of joints of the paw, and pressure to the deep tissues, especially to the extensor side of the arm. These modalities of stimuli were most often excitatory, but could be inhibitory as well.

(3) On the basis of modality, 4 subgroups of LDP cells were identified: those which were responsive only to mechanical-cutaneous, joint-movement, or deep-pressure stimuli, and those which responded to several of these modalities of stimuli, the multimodal group. These subgroups could not be distinguished on the basis of conduction velocity.

(4) The receptive fields varied in size from small (one digit) to large (all of a forelimb). For single LDP cells they included ones with single and/or multimodal input from one or both forelimbs and various combinations of excitation and/or inhibition. However, those in the dorsal horn had only ipsilateral receptive fields, mainly of the mechanical-cutaneous type. Cells with bilateral receptive fields were mainly located medially in the ventral gray in laminae VII and VIII.

(5) A comparison of the location of the subtypes of LDP cells revealed that neurons activated by mechanical-cutaneous stimuli were in laminae I and IV–VIII; whereas deep-pressure and multimodal activated neurons were almost exclusively in laminae VII and VIII.

(6) LDP cells receiving input from deep-pressure receptors in the extensor muscles of the arm, joint-movement, or deep-pressure receptors of the paw probably relay position or weight-bearing information about the forelimbs to the lumbosacral spinal cord. This arrangement suggests that LDP neurons function in interlimb coordination and would be active during locomotion. They probably participate also in other reflexes elicited by cutaneous and deep stimuli.

Non-dopaminergic nigrostriatal pathway

The nigrostriatal projection was studied with a retrograde tracing method (Evans blue, EB) combined with a technique for dopamine histofluorescence. The study, realized in control rats and in animals with 6-hydroxydopamine-induced lesions of the dopaminergic pathway, yielded the following results.

(1) In 3 control rats injected with 0.2 μl of a 10% solution of EB in thecenter of the caudate-putamen 1 mm anterior to the globus pallidus, 96% of all substantia nigra neurons retrogradely labelled with the dye contained dopamine fluorescence. The remaining ones (average 350 per brain) were devoid of dopamine fluorescence and predominantly found in the posterior 75% of the substantia nuigra. These last cells were confined to the upper-half of the pars reticulata.

(2) In a series of 6 animals, the cytotoxic agent 6-hydroxydopamine was injected in various locations in the vicinity of either the substantia nigra ir the nigrostriatal tract 12–15 days prior to the injections of 0.2 μl of EB in the same striatal locations as in the controls. Despite a reduction of up to 85% in the number of dopaminergic cell bodies, the substantia nigra of these rats contained the same average number of EB-labelled neurons devoid of dopamine fluorescence.

(3) Eight rats received smaller injections (0.1 μl) of EB in various striatal sites and in tqo further cases such injections were placed in the globus pallidus to determine more accurately the anatomical location of the dopamine-negative nigral neurons retrogradely labelled with the dye. Following the striatal injections, these cells were found mostly in the upper-half of the pars reticulata and were arranged in longitudinally oriented clusters whose mediolateral location depended on the striatal injection site.

Following the pallidal injections, retrogradely labelled neruons devoid of dopamine fluorescence were found in greater numbers and were located in all areas of the pars reticulata. The possibility of retrograde labelling of some nigrothalamic neurons was not entirely ruled out in these two cases.

(4) Finally 6 rats received 0.1 μl injections of EB in various parts of the parietal cortex. In these cases the substantia nigra did not contain any EB-positivedopamine-negative neurons.

These results are interpreted as evidence in support of the existence of a topographically organized non-dopaminergic nigrostriatal projection.

Hypercapnia and hypoxia: Chemoreceptor-mediated control of locus coeruleus neurons and splanchnic, sympathetic nerves

Utilizing single cell recording techniques to study brain norepinephrine (NE) neurons in the locus coeruleus (LC) and, in the same rats, registration of splanchnic nerve activity (SNA) the effects on these systems of hypercapnia and hypoxia, respectively, were studied.Hypercapnia (pCO₂ 36–103 mm Hg) caused a rapid increase in the firing rate of LC neurons as well as in SNA. This effect was directly correlated with the added amount of CO₂ in the inspired gas mixture. This finding indicates a similar chemoreceptor-mediated regulation of LC neurons and SNA. Since deafferentation of peripheral chemoreceptors did not alter the response of these systems to hypercapnia, the chemoreceptors involved must be centrally located.In hypoxia (pO₂ 105-31 mm Hg) the overall effect on LC neurons was activation, whereas SNA was reduced. These effects were, however, not dose-dependent. Peripheral receptor deafferentation abolished the activation by hypoxia, suggesting that the LC neurons are influenced also by peripheral chemoreceptors.The results indicate that the previously observed increase in brain NE turnover in hypercapnia is largely secondary to increased neuronal activity and not due to, e.g., changes in metabolic enzymes. In addition, the data implicate chemoreceptors, centrally but also peripherally located, in the regulation of brain NE neurons in the LC. The activation of these neurons in hypercapnia, generally associated with increased apprehension in man, is consistent with the notion that the LC may serve as an alarm system in the brain.     

Catecholamines and serotonin in the caudal medulla of the rat: Combined neurochemical-histofluorescence study

The distribution of monoamine transmitters among the nuclei of the caudal medulla was determined through the combined use of the Falck-Hillarp histofluorescence method for cellular localization of catecholamines and serotonin and quantitative micropunch neurochemical assays of norepinephrine (NE), dopamine (DA) and 5-hydroxytryptamine (5-HT) content using high performance liquid chromatography with electrochemical detection. These combined methods permit a direct correlation between neurotransmitter levels and fluorescent fiber and perikaryal profiles. Eight medullary nuclei were sampled:

1. (1) dorsal motor nucleus of X and ventral nucleus solitarius.

2. (2) the dorsomedial reticular formation.

3. (3) the hypoglossal nucleus.

4. (4) the ventromedial reticular formation.

5. (5) the nucleus ambiguus.

6. (6) nuclei raphe obscurus and pallidus.

7. (7) the inferior olivary nucleus.

8. (8) the descending (spinal) nucleus of V. Micropunched regions containing neurons which contribute projections to or receive sensory input from the vagus nerve were found to contain relatively high levels of NE, DA and 5-HT, consistent with the high density of catecholamine and 5-HT containing terminals observed in these nuclei.

The dorsal motor nucleus of X and ventral nucleus solitarius contained the highest levels of NE, DA and 5-HT (218 ± 10, 31 ± 2 and 75 ± 8 pmole/mg protein, respectively), whereas the lowest of these amines were found in the descending (spinal) nucleus of V (28 ± 1, 3.6 ± 0.8 and 32 ± 2 pmole/mg protein, respectively). In general the distribution of catecholamines and 5-HT determined by micropunch/microchemical assay agrees well with the distribution of monoamine terminals detected by fluorescence histochemical techniques.

Glutamatergic Neurons in the Preoptic Hypothalamus Promote Wakefulness,Destabilize NREM Sleep,Suppress REM Sleep,and Regulate Cortical Dynamics

Clinical and experimental data from the last nine decades indicate that the preoptic area of the hypothalamus is a critical node in a brain network that controls sleep onset and homeostasis. By contrast, we recently reported that a group of glutamatergic neurons in the lateral and medial preoptic area increases wakefulness, challenging the long-standing notion in sleep neurobiology that the preoptic area is exclusively somnogenic. However, the precise role of these subcortical neurons in the control of behavioral state transitions and cortical dynamics remains unknown. Therefore, in this study, we used conditional expression of excitatory hM3Dq receptors in these preoptic glutamatergic (Vglut2⁺) neurons and show that their activation initiates wakefulness, decreases non-rapid eye movement (NREM) sleep, and causes a persistent suppression of rapid eye movement (REM) sleep. We also demonstrate, for the first time, that activation of these preoptic glutamatergic neurons causes a high degree of NREM sleep fragmentation, promotes state instability with frequent arousals from sleep, decreases body temperature, and shifts cortical dynamics (including oscillations, connectivity, and complexity) to a more wake-like state. We conclude that a subset of preoptic glutamatergic neurons can initiate, but not maintain, arousals from sleep, and their inactivation may be required for NREM stability and REM sleep generation. Further, these data provide novel empirical evidence supporting the hypothesis that the preoptic area causally contributes to the regulation of both sleep and wakefulness.SIGNIFICANCE STATEMENT Historically, the preoptic area of the hypothalamus has been considered a key site for sleep generation. However, emerging modeling and empirical data suggest that this region might play a dual role in sleep-wake control. We demonstrate that chemogenetic stimulation of preoptic glutamatergic neurons produces brief arousals that fragment sleep, persistently suppresses REM sleep, causes hypothermia, and shifts EEG patterns toward a “lighter” NREM sleep state. We propose that preoptic glutamatergic neurons can initiate, but not maintain, arousal from sleep and gate REM sleep generation, possibly to block REM-like intrusions during NREM-to-wake transitions. In contrast to the long-standing notion in sleep neurobiology that the preoptic area is exclusively somnogenic, we provide further evidence that preoptic neurons also generate wakefulness.     

Conditioned and unconditioned drug effects in relapse to opiate and stimulant drug self-administration

1. 1. Humans and laboratory animals given access to opiate and stimulant drugs frequently become compulsive users of these drugs, and often, in spite of prolonged periods of abstinence, persist in drug-seeking behavior and relapse to drug-taking. Evidence suggests that such drugs act on positive appetitive systems of the brain to maintain drugtaking and that, in the absence of drugs, stimuli previously associated with the drug state might acquire the ability to arouse motivational states similar to those activated by the drugs themselves.

2. 2. In rats previously trained to self-administer cocaine or heroin intravenously, noncontingent ‘priming’ intravenous infusions of cocaine or heroin lead to reinstatement of drugtaking behavior. Priming infusions of pharmacologically related drugs and drugs with similar stimulus properties also reinstate responding.

3. 3. Application of morphine to the cell body region of dopaminergic neurons of the ventral tegmental area (VTA), a site known to support morphine self-administration, reinstates both heroin and cocaine self-administration behavior. Reinstatement is blocked by pretreatment with naltrexone. Morphine applied to several other brain areas rich in opiate receptors does not reinstate the behavior.

4. 4. Application of morphine to the VTA, a site known to support conditioned place preferences as well as self-administration, causes increased locomotion that is naloxone reversible. This locomotor activity shows sensitization upon repeated administration; an effect that is specific to the environment in which morphine is administered. Conditioned increases in activity are observed in the same environment. Neither conditioning nor sensitization develops when animals are pretreated with pimozide.

5. 5. These findings support the view that, opiates and stimulants are administered because of their effects on positive appetitive systems of the brain and that, through conditioning, stimulus events that are associated with these positive appetitive actions of opiates and stimulants acquire the ability to elicit neural states that mimic aspects of those elicited by the drugs themselves. The arousal of these states may act to reinstate (facilitate relapse) and to maintain drug-taking behavior. This positive incentive account of compulsive drug-taking and relapse differs from the ‘drive-reduction’ view that continued drug use depends primarily on efforts to reduce or avoid symptoms of withdrawal, and that conditioned stimuli associated with drugs can initiate and maintain drug-taking behavior through the elicitation of withdrawal-like, drug-opposing, conditioned responses.

The latent period of the Limulus lateral eye receptor potential: Action of chlorobutanol

Excised lateral eye retinular cells of Limulus polyphemus exposed to chlorobutanol were examined using microelectrode techniques. The effects observed were:

1. (1) a marked shortening of the receptor potential latent period;

2. (2) a decrease in the effective input resistance of retinular cells to hyperpolarizing currents;

3. (3) a reduction in magnitude of retinular cell receptor and membrane potential. The magnitude of the changes were concentration dependent and reversible and were only produced by chlorobutanol and closely related compounds. Chlorobutanol does not alter the sodium permeability of the receptor cell membrane but it may increase the rate of the process or processes occurring during the latent period of the receptor potential.

An ascending serotonergic pain modulation pathway from the dorsal raphe nucleus to the parafascicularis nucleus of the thalamus

(1) Three types of spontaneously active neurons were found in the parafascicularis (PF) nucleus of the thalamus of the rat: slow firing units (0.5–10 spikes/s), bursting units (2–5 spikes/burst in 10–20 ms, one burst every 1–2 s) and fast firing units (15–40 spikes/s). A similar population of neurons was found in the PF of rats treated with 5,7-dihydroxytryptamine (5,7-DHT), a serotonin neurotoxin.

(2) Noxious tail pinch (TP) caused 68% of the PF neurons to increase their firing rates to 242% of their initial baseline activity, while non-noxious touch stimulation failed to induce a response. In the 5,7-DHT-treated rats, TP caused 85% of the neurons in the PF to increase their firing rates to 581% of their initial baseline activity and 22% of the neurons increased their firing in response to touching the tail. Both the number of cells responding (P < 0.05) and the percentage increase (P < 0.001) were statistically greater in serotonin-depleted rats than in controls. This indicates that serotonin (5-HT) has a tonic inhibitory influence on responses to both noxious and non-noxious sensory stimuli.

(3) In control rats, electrical stimulation of the dorsal raphe nucleus (DR) decreased the firing rates of PF neurons. In contrast, the same DR stimulation induced an increase in PF firing rates during stimulation in serotonin-depleted rats and this increase in firing rates remained several seconds after cessation of stimulation. This indicates that the DR may use at least two different neurotransmitters in its projections to forebrain structures.

(4) In control rats, the TP stimulation induced an increase in firing rates of PF neurons while DR stimulation attenuated the excitation induced by TP stimulation. In serotonin-depleted rats, DR stimulation and TP both caused an increase in firing rates. This effect was not additive indicating that there may be a serotonergic projection from the DR to the PF which modifies responses to somatosensory stimuli.

(5) The inhibitory effects elicited by electrical stimulation were limited to the immediate area of the DR. Stimulation of the adjacent reticular formation 1 mm lateral to the DR produced the opposite effect, an increase in firing rate often accompanied by driven spike activity in the PF.

Role of alpha and beta adrenoceptors in locus coeruleus stimulation-induced reduction in rapid eye movement sleep in freely moving rats

Based on the results of independent studies the involvement of norepinephrine in REM sleep regulation was known. Isolated studies showed that the effect could be mediated through either one or more subtypes of adrenoceptors. Earlier we have reported that REM-OFF neurons continue firing during REM sleep deprivation and mild but continuous stimulation of locus coeruleus (LC) or picrotoxin injection into the LC, that did not allow the REM-OFF neurons in the LC to stop firing, reduced REM sleep. However, the mechanism of action and type of adrenoreceptors involved in REM sleep regulation were unknown. The possible mechanism of action has been investigated in this study. It was proposed that if LC stimulation-induced decrease in REM sleep was due to norepinephrine, adrenergic antagonist must prevent the effect. Therefore, in this study, the effects of alpha1, alpha2 and beta-antagonists, viz. prazosin, yohimbine and propranolol, respectively, and alpha2 agonist, clonidine, on LC stimulation-induced reduction in REM sleep were investigated. The results showed that stimulation of LC inhibited REM sleep by reducing the frequency of generation of REM sleep, although the duration per episode remained unaffected. This decrease in the frequency of REM sleep was blocked by beta-antagonist propranolol while the duration of REM sleep per episode was blocked by alpha1-antagonist, prazosin. Also, a critical level of norepinephrine in the system was required for the generation of REM sleep, however, a higher level may be inhibitory. Based on the results of this study and our earlier studies, an interaction between neurons, containing different neurotransmitters and their subtypes of receptors for LC-mediated regulation of REM sleep has been proposed.     

Dopaminergic neurons in the rat ventral tegmental area. III. Effects of -and -amphetamine

By use of various histochemical techniques, it was shown that both DA and non-DA cells in the VTA project to the NAc. Of these VTA-NAc output cells, the great majority were DA-containing cells. A small number of non-DA cells were encountered most frequently in the lateral part of the VTA. Correspondingly, two distinct groups of neurons, types I and II, could be identified by antidromic stimulation of the NAc. Several lines of evidence suggest that type I cells are DA-containing neurons. The evidence may be summarized as follows:

1. (1) type I cells had a slow-bursting or regular firing pattern, slow discharge rate and wide spike duration which appears to be identical to the characteristics of DA neurons originally described by Bunney et al.¹⁶;

2. (2) the great majority of these cells could be activated antidromically by stimulation of the NAc;

3. (3) the conduction velocity and absolute refractory period of type I cells are consistent with unmyelinated fine DA fibers;

4. (4) injection of 6-OHDA, but not 5,7-DHT directly in the MFB blocked antidromic responses of these cells;

5. (5) they were extremely sensitive to intravenously administered DA agonist apomorphine (ID₅₀ = 7 μg/kg); and

6. (6) direct fluorescence histochemical examination of serial sections from brains of animals in which type I cells have been identified by antidromic stimulation of the NAc showed that type I cells are most likely catecholamine-containi ng neurons. By contrast, type II cells possessed an entirely different spectrum of physiological characteristics; in addition, they showed no consistent response to apomorphine and their antidromic responses to stimulation of the NAc were not affected by 6-OHDA. It is concluded that (1) VTA output neurons consist of both DA and nonDA neurons, and (2) identified types I and II neurons in the VTA by antidromic stimulation of the NAc are DA and non-DA cells, respectively.

Interleukin-1β depresses calcium currents in CA1 hippocampal neurons at pathophysiological concentrations

Interleukin-1 is present in the central nervous system (CNS) during acute and chronic pathological processes. In the present study, we examined the interaction between recombinant human interleukin-1β (rhIL-1β) and the voltage-dependent calcium (Ca²⁺) current using the whole-cell patch clamp technique. RhIL-1β depressed the voltage-gated Ca²⁺ current in acutely dissociated guinea pig hippocampal CA1 neurons. This depression is rapid and is observed at pathophysiological concentrations ( 1.97 pg/10 μl)- Concomitant application of rhIL-1β and rhIL-1 receptor antagonist had no effect indicating neuroactive specificity of rhIL-1β. The depression of the inward Ca²⁺ current by IL-1β may play a role in:

1. 1) the regulation of neuronal excitability;

2. 2) the induction of neurological manifestations during disease; and

3. 3) in the induction and/or progression of neurodegenerative processes.