Effect of electric stimulation of cortical portions of the limbic system on the activity of neurons of the anterior thalamic nuclei in the rabbit

Effects of electrical stimulation of the subiculum (SB) and posterior limbic cortex (PLC) were studied extracellularly in the anteroventral (AV) and anterodorsal (AD) limbic thalamic nuclei of awake chronic rabbits. Stimulation of SB and PLC evoked in some AV neurones discharges of 1-2 spikes. Gradual potentiation and low frequency of following (up to 10-15 Hz) were characteristic of these responses. Activity of the majority of AV cells was suppressed by stimulation with appearance of inactivation bursts, "neuronal spindles" and modulation on delta-frequencies. Spike responses were evoked by SB and (rarely) by PLC stimulation only in a certain class of AD neurones which tentatively are regarded as relay cells. The neurones with high-frequency, low-amplitude discharges (putative inhibitory interneurones) reacted to stimulation of PLC and to a lesser extent of SB by prolonged series of spikes (150 ms--2s). Stimulation of PLC exerted prolonged influence upon neuronal responses to sensory stimuli.     

Responses of dorsal and ventral thalamic neurons to visual stimulation in Emys orbicularis tortoises]

Extracellular studies have been made on the background activity and reactions to visual stimuli in neurons of nucleus rotundus and nucleus suprapeduncularis of the thalamus in the tortoise E. orbicularis. Reactions of on-off type to diffuse light flashes were recorded predominantly in both of the nuclei, whereas specific reactions to movement stimuli were found in the neurons of n. rotundus. The receptive area of the neurons in both of the nuclei involves all the visual field of one or both of the eyes. The structure of the receptive area of the neurons of n. suprapeduncularis is relatively homogeneous, whereas the receptive area of the neurons in n. rotundus exhibits a zone with an increased excitability under the horizontal meridian. After a damage of tectum opticum, the heterogeneity of the receptive areas and the specific responses to movement in cells of n. rotundus disappeared, while thresholds of the reactions increased. In the neurons of n. suprapeduncularis homogeneous structure of the receptive area remained unaffected, the thresholds of the reactions being increased as well.     

Descending influences from the lateral hypothalamus and amygdala converge onto medullary taste neurons

The lateral hypothalamus (LH) and the central nucleus of the amygdala (CeA) exert an influence on many aspects of ingestive behavior. These nuclei receive projections from several areas carrying gustatory and viscerosensory information, and send axons to these nuclei as well, including the nucleus of the solitary tract (NST). Gustatory responses of NST neurons are modulated by stimulation of the LH and the CeA, and by several physiological factors related to ingestive behavior. We investigated the effect of both LH and CeA stimulation on the activity of 215 taste-responsive neurons in the hamster NST. More than half of these neurons (113/215) were modulated by electrical stimulation of the LH and/or CeA; of these, 52 cells were influenced by both areas, often bilaterally. The LH influenced more neurons than the CeA (101 versus 64 cells). Contralateral stimulation of these forebrain areas was more often effective (144 responses) than ipsilateral (74). Modulatory effects were mostly excitatory (102 cells); 11 cells were inhibited, mostly by ipsilateral LH stimulation. A subset of these cells (n = 25) was examined for the effects of microinjection of DL-homocysteic acid (DLH), a glutamate receptor agonist, into the LH and/or CeA. The effects of electrical stimulation were completely mimicked by DLH, indicating that cell somata in and around the stimulating sites were responsible for these effects. Other cells (n = 25) were tested for the effects of electrical stimulation of the LH and/or CeA on the responses to taste stimulation of the tongue (32 mM sucrose, NaCl and quinine hydrochloride, and 3.2 mM citric acid). Responses to taste stimuli were enhanced by the excitatory influence of the LH and/or CeA. These data demonstrate that descending influences from the LH and CeA reach many of the same cells in the gustatory NST and can modulate their responses to taste stimulation.     

Involvement of Right STS in Audio-Visual Integration for Affective Speech Demonstrated Using MEG

Speech and emotion perception are dynamic processes in which it may be optimal to integrate synchronous signals emitted from different sources. Studies of audio-visual (AV) perception of neutrally expressed speech demonstrate supra-additive (i.e., where AV>[unimodal auditory+unimodal visual]) responses in left STS to crossmodal speech stimuli. However, emotions are often conveyed simultaneously with speech; through the voice in the form of speech prosody and through the face in the form of facial expression. Previous studies of AV nonverbal emotion integration showed a role for right (rather than left) STS. The current study therefore examined whether the integration of facial and prosodic signals of emotional speech is associated with supra-additive responses in left (cf. results for speech integration) or right (due to emotional content) STS. As emotional displays are sometimes difficult to interpret, we also examined whether supra-additive responses were affected by emotional incongruence (i.e., ambiguity). Using magnetoencephalography, we continuously recorded eighteen participants as they viewed and heard AV congruent emotional and AV incongruent emotional speech stimuli. Significant supra-additive responses were observed in right STS within the first 250 ms for emotionally incongruent and emotionally congruent AV speech stimuli, which further underscores the role of right STS in processing crossmodal emotive signals.     

Atrioventricular conduction with and without AV nodal delay: two pathways to the bundle of His in the rabbit heart

The electrophysiological properties of atrioventricular (AV) nodal dual pathways have traditionally been investigated with premature stimuli delivered with right atrial pacing. However, little is known about the functional characteristics of AV nodal inputs outside of this context. Superfused rabbit triangle of Koch preparations (n = 8) and Langendorff-perfused hearts (n = 10) were paced throughout the triangle of Koch and mapped electrically and optically for activation pattern, electrogram and optical action potential morphologies, stimulation thresholds, and stimulus-His (S-H) intervals. Optical mapping and changes in His electrogram morphology were used to confirm the activation pathway. Pacing stimuli >or=2 mm above the tricuspid valve caused fast-pathway activation of the AV node and His with a threshold of 2.4 +/- 1.6 mA. An area directly below the coronary sinus had high thresholds (8.6 +/- 1.4 mA) that also resulted in fast-pathway excitation (P < 0.001). S-H intervals (81 +/- 19 ms) for fast-pathway activation remained constant throughout the triangle of Koch, reflecting the AV delay. Stimuli applied <2 mm from the tricuspid valve resulted in slow pathway (SP) excitation or direct His excitation (4.4 +/- 2.2 mA threshold; P < 0.001 compared with fast pathway). For SP/His pacing, S-H intervals showed a strong dependence on the distance from the His electrode and were significantly lower than S-H intervals for fast-pathway activation. SP/His pacing also displayed characteristic changes in His electrogram morphology. In conclusion, optical maps and S-H intervals for SP/His activation suggest that AV conduction via SP bypasses the compact AV node via the lower nodal bundle, which may be utilized to achieve long-term ventricular synchronization.     

Unit responses of the cat somatosensory cortex to stimulation of the reticular and anteroventral thalamic nuclei

Responses of 189 neurons of the somatosensory cortex to stimulation of the nonspecific reticular (R) and anteroventral (AV) nuclei of the thalamus were studied in cats anesthetized with thiopental and immobilized with tubocurarine. In the series of experiments with stimulation of R and, for comparison, of the specific ventral posterolateral nucleus (VPL), 132 neurons were recorded, of which 22 (16.7%) did not respond to stimulation of these nuclei, 77 (58.3%) responded only to stimulation of VPL, and 33 (25%) responded to stimulation of both VPL and R. In the series of experiments in which AV was stimulated, 57 neurons were recorded. Eight (14.8%) responded to neither stimulus and 25 (43.1%) responded only to stimulation of VPL; 24 responded to stimulation of AV (42.1%), and of these, 10 also responded to stimulation of VPL. A characteristic feature of unit responses in the somatosensory cortex to stimulation of the nonspecific nuclei was the irregularity of the responses and their longer latent period. Only five cells responded sooner to stimulation of the nonspecific nuclei than to stimulation of VPL. Responses of the nonspecific nuclei to stimulation appeared clearly only if the stimulation was repetitive. Preliminary stimulation of R blocks the response to stimulation of VPL during the subsequent 40–60 msec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol.4, No.4, pp. 384–390, July–August, 1972.     

Neuronal responses evoked in the bulbar respiratory center by stimulation of the anterior ventral and mediodorsal thalamic nuclei

The effects of rhythmical low- and high-frequency stimulation of specific nonsensory anterior ventral and associative mediodorsal thalamic nuclei (AV and MD, respectively) on the activity of neuronal units in the medullary ventral respiratory nucleus were studied in acute experiments on anesthetized, spontaneously breathing cats. Both inhibitory and excitatory influences on spike activity of inspiratory and expiratory neurons were found, with suppression effects being markedly predominant. Thresholds for inspiratory neuronal responses were lower as compared with those for expiratory cells. Electrical AV stimulation mainly produced an inhibitory effect on the activity of nonspecific reticular neurons (without respiratory activity), whereas during MD stimulation activating effects on these neurons dominated. Possible mechanisms underlying the realization of thalamorespiratory influences are discussed.Neirofiziologiya/Neurophysiology, Vol. 25, No. 3, pp. 218–223, May–June, 1993.     

Comparative characteristics of the neuronal activity of the anterodorsal and anteroventral nuclei in thalamus slices from guinea pigs

Extracellular investigation of neurons of the anterodorsal (AD) and anteroventral (AV) nuclei in the incubated slices of the thalamus of guinea pigs and rabbits revealed unusual properties of the AD units. They responded only to electrical stimuli of considerable duration (1-5 ms) by multispike initial bursts or by prolonged (1-15 s) high frequency phasic discharges. Summation of effects of successive stimuli following with intervals of 2-30 s was necessary for development of phasic discharges. Prolonged refractory state (up to 2-15 s) followed the discharges. They were blocked in low Ca2+, high Mg2+ medium and facilitated in a medium with high concentration of K+. The nature of unusual properties of AD neurons, not present in the neighbouring AV nucleus, are discussed.     

Lesions of the anteroventral third ventricle region exaggerate neuroendocrine and thermogenic but not behavioral responses to a novel environment

Mild psychological stressors provoke an acute rise in core temperature (T(C)), stimulate the hypothalamo-pituitary-adrenocortical (HPA) axis, and induce various stress-related behaviors. In the present study, we examined the effect of ablation of the anteroventral third ventricle region (AV3V) on both physiological and behavioral responses to a novel environment. T(C) was monitored in male Sprague-Dawley rats, with either sham or AV3V lesions, during a 5-h exposure to a novel environment. Trunk blood was collected, in a second group of rats, for the assessment of plasma levels of ACTH and corticosterone. Novelty-induced grooming and rearing behaviors were assessed in a third group of animals. T(C) was elevated in all animals after 30 min in the novel environment, but the rise was exaggerated in rats with AV3V lesions ( approximately 0.5 degrees C). AV3V-lesion rats maintained a higher core temperature for 2 h before it returned to the same level as the control group. Plasma levels of ACTH and corticosterone were also exaggerated in the AV3V lesion group after 30 min in a novel environment. In contrast to the physiological responses, the behavioral measures of grooming and rearing revealed no differences between the groups. The results from the current study suggest that neurons within the AV3V region exert an inhibitory influence on the HPA axis and fever developed in response to stressful psychological stimuli. They also confirm that the physiological and hormonal components of the stress response are independent of certain behavioral measures of stress.     

Tonic GABAergic inhibition of taste-responsive neurons in the nucleus of the solitary tract

The effects of gamma-aminobutyric acid (GABA) and the GABAA receptor antagonist bicuculline methiodide (BICM) on the activity of taste- responsive neurons in the nucleus of the solitary tract (NST) were examined electrophysiologically in urethane-anesthetized hamsters. Single neurons in the NST were recorded extracellularly and drugs (21 nl) were microinjected into the vicinity of the cell via a multibarrel pipette. The response of each cell was recorded to lingual stimulation with 0.032 M NaCl, 0.032 M sucrose, 0.0032 M citric acid and 0.032 M quinine hydrochloride (QHCl). Forty-six neurons were tested for the effects of GABA; the activity of 29 cells (63%) was inhibited by 5 mM GABA. Whether activity was elicited in these cells by repetitive anodal current stimulation (25 microA, 0.5 s, 0.1 Hz) of the tongue (n = 13 cells) or the cells were spontaneously active (n = 13 cells), GABA produced a dose-dependent (1, 2 and 5 mM) decrement in activity. Forty- seven NST neurons were tested for the effects of BICM on their responses to chemical stimulation of the tongue; the responses of 28 cells (60%) were enhanced by 10 mM BICM. The gustatory responses of 26 of these cells were tested with three concentrations (0.2, 2 and 10 mM) of BICM, which produced a dose-dependent increase in both spontaneous activity and taste-evoked responses. Nine of these neurons were sucrose- best, seven were NaCl-best, eight were acid-best and two responded best to QHCl. The responses to all four tastants were enhanced, with no difference among neuron types. For 18 cells that were tested with two or more gustatory stimuli, BICM increased their breadth of responsiveness to their two most effective stimuli. These data show that approximately 60% of the taste-responsive neurons in the rostral NST are inhibited by GABA and/or subject to a tonic inhibitory influence, which is mediated by GABAA receptors. The modulation of these cells by GABA provides a mechanism by which the breadth of tuning of the cell can be sharpened. Modulation of gustatory activity following a number of physiological changes could be mediated by such a GABAergic circuit.      

The effect of disconnecting the hippocampus from the septum on the activity of septal neurons]

Extracellular recording of neuronal activity was performed in the medial and lateral septal nuclei (MS and LS) in unanaesthetized rabbits after coagulation of septo-hippocampal connections. The MS neuronal activity had many pathological features. The LS activity was normal in every respect. Spontaneous activity, reactivity to sensory stimuli and main characteristics of responses to sensory stimuli were preserved in LS (and in a part of MS neurones). Sensory effects were augmented in intensity and duration, the number of neurones in LS with theta-bursts increased twofold, theta-bursts were more regular, than in control animals. These effects may be explained by an increase of ascending RF influences, which is supported by the fact of outstanding similarity between sensory and reticular effects in septal neurones after hippocampal disconnection. The number of units with inhibition of activity in response to sensory stimuli decreased, habituation of responses was absent. That means that hippocampal influences are necessary for the organization of inhibitory phenomena in the septum, and, above all, for processes of gradual habituation.     

Role of the anteroventral third ventricle region in fever in sheep

Ablation of the anteroventral third ventricle (AV3V) region, which includes the organum vasculosum laminae terminalis (OVLT), blocks the febrile response of guinea pigs to systemically injected endotoxin; by contrast, discrete lesions of the OVLT transiently enhance fever in rabbits and rats. To assess whether separate subdivisions of the AV3V may mediate these different effects, the thermal responses to Escherichia coli lipopolysaccharide (LPS, 0.25 micrograms/kg, i.v.) were measured in eight sheep before and 12-13 days after placement of lesions at various levels within the AV3V. The responses of four of these sheep to crude homologous endogenous pyrogen (EP, 1-2 mL, i.c.v.) were also evaluated. Additionally, five other sheep were tested with LPS 2-8 months postlesion. All the experiments were performed at thermoneutrality. Sheep were used because most of the frontal wall of their 3V forms an elongated OVLT consisting of an avascular body and a vascular base. The animals were classified postmortem according to the extent of tissue ablated. Lesion overlap analyses showed that (i) medial lesions which extended from the floor of the 3V to the anterior commissure and laterally into adjacent preoptic periventricular tissue were associated with significantly depressed fever after LPS (n = 2); (ii) comparable lesions, but which excluded the ventral portion of the AV3V, i.e., the base of the OVLT, did not alter the magnitude of the febrile response to LPS (n = 4); (iii) lesions of the lateral walls of the 3V and (or) of the adjacent medial preoptic and anterior hypothalamic areas but excluding the frontal 3V wall also did not affect fever height after LPS (n = 7).(ABSTRACT TRUNCATED AT 250 WORDS)     

Osmotic regulation of estrogen receptor-beta expression in magnocellular vasopressin neurons requires lamina terminalis

Estrogen receptor-beta (ER-beta) expression in rat magnocellular vasopressin (VP) neurons of the supraoptic and paraventricular nuclei (SON and PVN, respectively) becomes undetectable after 72 h of 2% NaCl consumption. To test the hypothesis that osmosensitive mechanisms that originate in the region of the organum vasculosum lamina terminalis (OVLT) control ER-beta expression in the SON and PVN, animals were water deprived after electrolytic lesions were performed on the area anterior to the ventral third ventricle (AV3V). Such lesions prevent osmotic stimulation of VP release. Four weeks after surgery, male rats [lesioned (n = 16) or sham (n = 14)] were water deprived for 48 h or allowed water ad libitum. Water deprivation eliminated ER-beta-immunoreactivity (-ir) in SON and magnocellular PVN of sham-lesioned animals. Fos-ir was evident in these neurons, and plasma osmolality (Posm) and hematocrit (Ht) were significantly elevated compared with the sham-hydrated rats (Posm, 304 +/- 1 vs. 318 +/- 2 mosmol/kgH2O; P < 0.001; Ht, 49.6 +/- 0.6 vs. 55.0 +/- 0.9%; P < 0.001). ER-beta expression was comparable in sham-hydrated, AV3V-hydrated, and 6 of 8 AV3V-dehydrated rats despite significant increases in Posm in both groups (AV3V hydrated, 312 +/- 2; AV3V dehydrated, 380 +/- 10 mosmol/kgH2O; P < 0.001). OVLT was not ablated in the AV3V-dehydrated rats in which ER-beta was depleted. Fos-ir was low or undetectable in SON in the AV3V-hydrated animals despite elevated Posm values. In AV3V-dehydrated rats, Fos-ir was significantly less than in sham-dehydrated animals but was significantly increased compared with the sham-hydrated group. This could reflect activation by nonosmotic parameters that do not inhibit ER-beta expression. These data support the hypothesis that inhibition of ER-beta expression in the SON by osmotic stimulation is mediated by osmoreceptive neurons in the lamina terminalis.     

Changes in neuronal activities in the two ventral posterior medial thalamic nuclei in an experimental model of trigeminal pain in the rat by constriction of one infraorbital nerve

The present study analyzes the activity of 120 neurons recorded in the two ventro-postero-medial (VPM) nuclei of the thalamus in a rat model of trigeminal neuropathic pain. Twenty-eight rats were tested 2 weeks after a chronic constriction injury (CCI) of the infraorbital nerve (IoN). These animals exhibited violent pain-related reactions to extremely weak mechanical stimuli applied to the lesioned and, to a lesser extent, unlesioned IoN territories. The activities of neurons recorded in the VPMc (n = 80) and VPMi (n = 40), contralateral and ipsilateral to the injured nerve, respectively, were compared with those of 62 neurons recorded in the VPM of ten normal rats (VPMn). The neuronal background activity was higher in the VPM of CCI-IoN rats than in normal rats (about 4 vs 1 spike/s). The proportion of neurons which were driven by mechanical stimulations applied contralaterally to their recording site, was comparable in the three VPM (63-70%), but the effective stimulus modality differed significantly between the normal and the lesioned rats. In particular, the number of neurons driven by vibrissa or guard hair movements dramatically decreased in the VPM of CCI-IoN rats, mainly in the VPMc (67% of neurons with a receptive field (RF) in the VPMn vs 12% in the VPMc). Inversely, a consistent number of neurons in both the VPMc and VPMi were driven by other stimulus modalities applied to the IoN territory (moderate pressure for VPMc neurons, pinch or pinprick for both VPMc and VPMi neurons). The responses so induced were especially intense and included afterdischarges. In contrast to the VPMn neurons, the RFs of both the VPMc and VPMi neurons included two vibrissae at least, and were occasionally discontinuous and multimodal, including both vibrissae and cutaneous areas for VPMc units. The bilateral changes in VPM responsiveness and in behavior suggest the involvement of central processing of sensory information, which are set off by the CCI-IoN. The putative mechanisms and functional implication of the changes in the VPM neuronal activities are discussed.     

Neural coding in the chick cochlear nucleus

Physiological recordings were made from single units in the two divisions of the chick cochlear nucleus-nucleus angularis (NA) and nucleus magnocellularis (NM). Sound evoked responses were obtained in an effort to quantify functional differences between the two nuclei. In particular, it was of interest to determine if nucleus angularis and magnocellularis code for separate features of sound stimuli, such as temporal and intensity information. The principal findings are: 1. Spontaneous activity patterns in the two nuclei are very different. Neurons in nucleus angularis tend to have low spontaneous discharge rates while magnocellular units have high levels of spontaneous firing. 2. Frequency tuning curves recorded in both nuclei are similar in form, although the best thresholds of NA units are about 10 dB more sensitive than their NM counterparts across the entire frequency range. A wide spread of neural thresholds is evident in both NA and NM. 3. Large driven increases in discharge rate are seen in both NA and NM. Rate intensity functions from NM units are all monotonic, while a substantial percentage (22%) of NA units respond to increased sound level in a nonmonotonic fashion. 4. Most NA units with characteristic frequencies (CF) above 1000 Hz respond to sound stimuli at CF as 'choppers', while units with CF's below 1000 Hz are 'primary-like'. Several 'onset' units are also seen in NA. In contrast, all NM units show 'primary-like' response. 5. Units in both nuclei with CF's below 1000 Hz show strong neural phase-locking to stimuli at their CF. Above 1000 Hz, few NA units are phase-locked, while phase-locking in NM extends to 2000 Hz. 6. These results are discussed with reference to the hypothesis that NM initiates a neural pathway which codes temporal information while NA is involved primarily with intensity coding, similar in principle to the segregation of function seen in the cochlear nucleus of the barn owl (Sullivan and Konishi 1984).     

Differential Pavlovian conditioning in the mollusc Pleurobranchaea

The present differential Pavlovian conditioning experiments on the sea slug Pleurobranchaea californica extend conditioning described in a preceding paper and provide the conditioning foundation for studies reported in another accompanying paper comparing learned behavior in whole animals with the behavior and motor patterns of electrophysiological preparations. All animals received two appetitive-conditioned stimuli (CSs), one derived from beer (Sbr) and the other derived from squid muscle (Ssq), in different temporal relationships to an electric shock unconditioned stimulus (UCS). Two groups of animals were run concurrently. One group (n = 19) received Sbr as the CS+ in close temporal pairing with the UCS, and Ssq as the CS- explicitly unpaired with the UCS (Sbr +/Ssq-). The second group (n = 20) received the opposite contingencies (Sbr-/Ssq+). All animals received only one day of conditioning involving 5 trials with an intertrial interval of 2 h. There were two replicate experiments, each involving about half of the total n, and each yielding similar results as the sum we report here. Before conditioning, animals exhibited feeding behavior (extension of the proboscis and bite-strike responses) to both stimuli at similar low thresholds. Conditioning produced long-term behavioral changes in all animals throughout the 4.5-day postconditioning observation period. However, only the Sbr+/Ssq- animals consistently exhibited the appropriate differentially conditioned food-aversion behavior which consisted of strong withdrawal and high-threshold feeding responses to Sbr, and low-threshold feeding responses to Ssq. We discuss the possibility that such differences between Sbr+/Ssq- and Sbr-/Ssq+ conditioning may arise either from inherent differences in the responses of the animals to Sbr and Ssq, or, as seems more likely to us, from training and testing effects produced by differences in the compositions of the two stimuli.     

Estimation of color and brightness differences by neurons in the rabbit superior colliculus

Changes in activity of 83 neurons in the rabbit colliculus superior evoked by the replacement of eight color and eight achromatic stimuli in pairs were analyzed. It was found out that neurons displayed the early and late phasic responses (within 50-90 and 120-300 ms respectively, after the replacement) and long-term tonic response component, which depended on stimuli intensity. Analysis of phasic component revealed three neuronal groups. The first group (n=25, 30%) selected on the basis of the earliest component, was specialized to differentiate stimuli only by intensities. The perceptual spaces of these neurons reconstructed on the basis of spike discharge in the earliest response were two-dimensional. The second group of neurons (n=16, 19%) selected on the basis of the late phasic component demonstrated four-dimensional structure of perceptual space. Neurons of the third group (n=4, 5%) possessed a two-dimensional structure of perceptual space reconstructed by the analysis of the early component, whereas analysis of the late response revealed a four-dimensional structure. We suggest that information about differences between stimuli in color and intensity coming from cortical neurons is necessary for the reconstruction of four-dimensional space. The structure of perceptual spaces reconstructed on the basis of phasic responses of neurons in the colliculus superior was similar to the spaces of neurons in the primary visual cortex and lateral geniculate nucleus. The structure of perceptual space reconstructed on the basis of neuronal spikes was also similar to the space calculated from the N85 component of the visual evoked potential recorded under similar conditions. This finding confirms the general principle of vector coding in the visual system.     

Effects of sleep-wake state on the genioglossus vs.diaphragm muscle response to CO(2) in rats.

The effects of sleep on the ventilatory responses to hypercapnia have been well described in animals and in humans. In contrast, there is little information for genioglossus (GG) responses to a range of CO(2) stimuli across all sleep-wake states. Given the notion that sleep, especially rapid eye movement (REM) sleep, may cause greater suppression of muscles with both respiratory and nonrespiratory functions, this study tests the hypothesis that GG activity will be differentially affected by sleep-wake states with major suppression in REM sleep despite excitation by CO(2). Seven rats were chronically implanted with electroencephalogram, neck, GG, and diaphragm electrodes, and responses to 0, 1, 3, 5, 7, and 9% CO(2) were recorded. Diaphragm activity and respiratory rate increased with CO(2) (P < 0.001) across sleep-wake states with significant increases at 3-5% CO(2) compared with 0% CO(2) controls (P < 0.05). Phasic GG activity also increased in hypercapnia but required higher CO(2) (7-9%) for significant activation (P < 0.05). Further studies in 15 urethane-anesthetized rats with the vagi intact (n = 6) and cut (n = 9) showed that intact vagi delayed GG recruitment with hypercapnia but did not affect diaphragm responses. In the naturally sleeping rats, we also showed that GG activity was significantly reduced in non-REM and REM sleep (P < 0.04) and was almost abolished in REM even with stimulation by 9% CO(2) (decrease = 80.4% vs. wakefulness). Such major suppression of GG activity in REM, even with significant respiratory stimulation, may explain why obstructive apneas are more common in REM sleep.     

Phase reset affects auditory-visual simultaneity judgment

We continuously receive the external information from multiple sensors simultaneously. The brain must judge a source event of these sensory informations and integrate them. It is thought that judging the simultaneity of such multisensory stimuli is an important cue when we discriminate whether the stimuli are derived from one event or not. Although previous studies have investigated the correspondence between an auditory-visual (AV) simultaneity perceptions and the neural responses, there are still few studies of this. Electrophysiological studies have reported that ongoing oscillations in human cortex affect perception. Especially, the phase resetting of ongoing oscillations has been examined as it plays an important role in multisensory integration. The aim of this study was to investigate the relationship of phase resetting for the judgment of AV simultaneity judgement tasks. The subjects were successively presented with auditory and visual stimuli with intervals that were controlled as SOA_50% and they were asked to report whether they perceived them simultaneously or not. We investigated the effects of the phase of ongoing oscillations on simultaneity judgments with AV stimuli with SOAs in which the detection rate of asynchrony was 50 %. It was found that phase resetting at the beta frequency band in the brain area that related to the modality of the following stimulus occurred after preceding stimulus onset only when the subjects perceived AV stimuli as simultaneous. This result suggested that beta phase resetting occurred in areas that are related to the subsequent stimulus, supporting perception multisensory stimuli as simultaneous.     

味觉刺激引起大鼠臂旁核神经元抑制性反应

本研究以轻度麻醉的大鼠为对象,应用细胞外微电极记录技术,观察并分析了脑桥臂旁核抑制性味觉神经元的自发活动及其对NaCl、HCl、盐酸奎宁（quinine HCl,QHCl））和蔗糖等四种基本味觉刺激的反应。共分析了18个具有自发活动的抑制性味觉神经元,自发放电频率分布在0．2～5．5Hz之间,平均放电频率（2．15±0．31）Hz。18个神经元中,1个神经元对单一味觉刺激呈抑制性反应,其余17个神经元对两种或两种以上的基本味觉刺激发生抑制性反应,且抑制具有潜伏期短、持续时间较长等特征。抑制持续时间5～80S,部分神经元表现为后抑制效应。根据神经元对四种基本味觉刺激呈抑制性反应的程度,将其分为NaCl优势神经元（n=8）,HCl优势神经元（n=3）,QHCl优势神经元n=3）和蔗糖优势神经元n=4）。其中NaCl优势神经元的反应谐宽最高（0．945）。这些神经元对欣快或厌恶刺激的区别能力较低。结果提示,在脑桥臂旁核存在对味觉刺激起抑制性反应的神经元,这些味觉神经元可能在味觉的调制及对欣快和厌恶刺激的编码中发挥重要的作用。