Responses of Neurons in the Rat Nucleus Submedius to Noxious and Innocuous Mechanical Cutaneous Stimulation

Extracellular recordings were used to characterize responses to cutaneous mechanical stimulation of 78 neurons in the rat nucleus submedius (SM). Thirty-nine of these units were activated by some type of cutaneous mechanical stimulation. Eighteen cells were activated exclusively by noxious stimuli. In 13 of these cells, responses were of swift onset and relatively rapid termination following stimulus application. In contrast, in three neurons responses were delayed both in onset and termination, and in two the response was immediate, but the markedly increased evoked activity outlasted stimulus application by 13 min. Receptive fields (RFs) of these nociceptive neurons were generally large, although none were bilateral. Four SM neurons were activated by innocuous stimuli, but their maximal response was obtained only after noxious stimulation. Responses of all of these neurons were of immediate onset and recovery, and their RFs were large (two were bilateral). Twelve SM neurons were activated maximally by innocuous stimuli. Responses of seven of these cells were immediate in onset and termination, while that of three were delayed in both onset and termination. Two of the 12 innocuous-only neurons quickly became unresponsive to repeated stimulus applications, and could be reactivated only after a rest period during which no stimuli were applied. RFs of these units were also generally large, and in three cases were bilateral. Five SM neurons responded by decreasing, or completely ceasing, their firing subsequent to noxious-only (n = 2), or innocuous-only (n = 3) stimulation. Four of these units had large RFs (two were bilateral). The remaining 39 SM neurons could not be activated by any type of mechanical cutaneous stimulation we tried.

Electrical stimulation of the ventrolateral orbital cortex (VLO) was employed to examine frontal cortical projections of 21 SM neurons. Ten of these units were activated, although all of them synaptically rather than antidromically, and two were inhibited. There was no clear-cut relationship between neuronal location, physiological type, RF site, or VLO stimulation effects among the 39 SM neurons.

These results provide further support for the involvement of SM neurons in nociceptive information signaling, and suggest additionally that the role of the nucleus is not limited to nociception but encompasses a wider range of cutaneous sensations.     

Raphe Stimulation-Evoked Modulation of Postsynaptic Responses by Neurons of the Cat Somatosensory Cortex Activated by Stimulation of Nociceptors

We studied the effects of electrical stimulation of the raphe nuclei (RN) of the cat brain on postsynaptic potentials developing in somatosensory cortex neurons activated by nociceptive influences. Intracellular records were obtained from 15 cells, which were either selectively excited by stimulation of nociceptors (intense electrical stimulation of the dental pulp) or activated by both the above nociceptive and non-nociceptive (moderate stimulations of the infraorbital nerve or thalamic ventroposteromedial nucleus, VPMN) influences. In neurons of both groups, stimulation of both nociceptive afferents and the VPMN evoked complex responses (EPSP–AP–IPSP; IPSPs were 200 to 300 msec long). In some studied cortical neurons, isolated electrical stimulation of the RN (which caused the release of serotonin, 5-HT, in the cortex) resulted in relatively short-latency synaptic excitation, while inhibition was observed in other cells. In the case where stimulation of the RN was used as conditioning influence, such stimulation (independently of the kind of the initial response to RN stimulation) led to long-latency and long-lasting suppression of all components of the synaptic reactions evoked by excitation of nociceptors. The maximum of inhibition was observed at test intervals of 300 to 800 msec. The mechanisms underlying modulatory influences coming from the 5-HT-ergic brainstem system to neurons of the somatosensory cortex, which are activated by excitation of high-threshold (nociceptive) afferent inputs, are discussed.     

The Responses of Neurons of the Somatosensory Cortex to Stimulation of the Posterior Thalamus (PO) in WAG/Rij Rats Genetically Predisposed to Absence Epilepsy

In genetically predisposed WAG/Rij rats and healthy Wistar rats, we studied functioning of the paralemniscal region of the thalamo-cortical system. The responses of neurons of the somatosensory cortex to single electrical stimulation of the posterior nucleus of the thalamus were recorded in two- to three-monthold rats within the period when the epileptic activity was not developed. We revealed lower number of shortterm inhibitory responses in WAG/Rij rats as compared to Wistar rats. This may create preconditions for the spreading of spike-wave activity in the somatosensory cortex, which is an electrophysiological sign of absence epilepsy.     

Afferent Modulation of Warmth Sensation and Heat Pain in the Human Hand

The hands of 14 normal humans were used to determine the somatotopic organization of the modulation of warmth sensation and heat pain by different forms of cutaneous stimuli. Test stimuli were 5-sec heat pulses ranging from 36° to 51°C, delivered to the fingerpads of digits 1, 2, 4, and 5 with a contact thermode. Conditioning stimuli (15 sec) bracketed the test stimuli and included vibration, noxious and innocuous heat, cold, and electrical pulses delivered to the fingerpads of digits that were adjacent or nonadjacent to the tested digits. Noxious (48° ± 1.3°C), but not innocuous (43°C), heat stimuli increased the perceived magnitude estimation of innocuous test stimuli (36–43°C) by 20–37% when delivered to adjacent, but not to nonadjacent, digits. No other conditioning stimuli had any effect on the intensity of warmth perception. In contrast, both noxious and innocuous heat or electrical conditioning reduced the magnitude estimation of noxious (50–5°C), but not innocuous, test pulses by 12–22% when delivered to adjacent digits. Conditioning of nonadjacent digits was significantly less effective. The analgesic effects of noxious and innocuous conditioning were approximately equal. Vibratory (120 Hz, 3.5 μm) and cold (15°C) conditioning stimuli were ineffective. The results are consistent with a dermatomal somatotopic organization of tactile and heat modulatory influences on warmth sensation and heat pain. The results further suggest that the neural mechanisms subserving warmth mediate a negative feedback influence on heat pain intensity.     

Effects of Stimulation of the Periaqueductal Gray and <Emphasis Type="Italic">Locus Coeruleus</Emphasis> on Postsynaptic Reactions of Cat Somatosensory Cortex Neurons Activated by Nociceptors

In cats, we studied the influences of stimulation of the periaqueductal gray (PAG) and locus coeruleus (LC) on postsynaptic processes evoked in neurons of the somatosensory cortex by stimulation of nociceptive (intensive stimulation of the tooth pulp) and non-nociceptive (moderate stimulations of the infraorbital nerve and ventroposteromedial nucleus of the thalamus) afferent inputs. Twelve cells activated exclusively by nociceptors and 16 cells activated by both nociceptive and non-nociceptive influences (hereafter, nociceptive and convergent neurons, respectively) were recorded intracellularly. In neurons of both groups, responses to nociceptive stimulation (of sufficient intensity) looked like an EPSP-spike-IPSP (the latter, of significant duration, up to 200 msec) complex. Electrical stimulation of the PAG (which could itself evoke activation of the cortical neurons under study) resulted in long-term suppression of synaptic responses evoked by excitation of nociceptors (inhibition reached its maximum at a test interval of 600 to 800 msec). We observed a certain parallelism between conditioning influences of PAG activation and effects of systemic injections of morphine. Isolated stimulation of LC by a short high-frequency train of stimuli evoked primary excitatory responses (complex EPSPs) in a part of the examined cortical neurons, while in other cells high-amplitude and long-lasting IPSP (up to 120 msec) were observed. Independently of the type of the primary response to PAG stimulation, the latter resulted in long-term (several seconds) suppression of the responses evoked in cortical cells by stimulation of the nociceptive inputs. The mechanisms of modulatory influences coming from opioidergic and noradrenergic brain systems to somatosensory cortex neurons activated due to excitation of high-threshold (nociceptive) afferent inputs are discussed.Neirofiziologiya/Neurophysiology, Vol. 37, No. 1, pp. 61–73, January–February, 2005.     

GABA-Mediated Inhibition in Cultured Neurons of the Rat Brain Cortex

In cultured pyramidal neurons of the rat brain cortex, we recorded (in the whole-cell configuration) postsynaptic currents (PSC) evoked by direct electrical microstimulation of an axon of the interneuron adjacent to the pyramidal cell. Application of 5 M bicuculline rapidly, entirely, and reversibly blocked these currents. Linear changes in the holding potential on the membrane of the postsynaptic cell resulted in linear changes in the amplitude of averaged currents. The currents underwent reversion when the holding potential was –16 mV, which was close to the reversal potential for Cl^- ions at their respective concentrations in the extra- and intracellular solutions. We conclude that the recorded currents are inhibitory PSC (IPSC) mediated by GABA release. The amplitudes of the recorded currents varied from a measurable minimum (8 pA) to more than 150 pA at a holding potential on the postsynaptic cell membrane of –80 mV. Times to peak of the high- and low-amplitude currents showed no significant differences, being about 6.4 msec on average. Decays of the current could be satisfactorily approximated by a monoexponential function with a mean time constant of 17 msec. The time constants of IPSC decay were distributed accordingly to the Gaussian law. In some cases, the amplitude distributions of IPSC were unimodal ((with a rightward asymmetry), but in most cases they were clearly polymodal. The amplitude distribution can be described by the sum of several Gaussian distributions; the distance between modes of the Gaussians was 25 ± 6 pA, on average. The obtained estimates of the amplitude of monoquantal GABA-induced IPSC in neurons of the brain cortex allow us to conclude that in various CNS regions the dimension of the vesicles in GABA-ergic synapses formed by inhibitory interneurons is identical.     

Brain-State-Dependent Modulation of Neuronal Firing and Membrane Potential Dynamics in the Somatosensory Thalamus during Natural Sleep

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Organization of the Viscerosomatic Afferent Projections to Fields 24 and 25 of the Cingulate Gyrus of the Cat Brain Cortex

We studied evoked potentials (EP) and responses of single neurons in fields 24 and 25 of the cingulate gyrus of the cat brain cortex. The responses were elicited by stimulations of a parasympathetic, a sympathetic, and a somatic nerve (the pelvic, splanchnic, and sciatic nerves). The configuration and amplitude/temporal characteristics of both EP and neuronal responses showed that the organization of the visceral and somatic afferent inputs to the cortical fields under study is to a great extent similar. Localization of the foci of maximum activity for EP within field 24 and their overlapping, the higher responsiveness of the neurons of this field to afferent volleys as compared with that in field 25, the dominance of short-latency neuronal responses in field 24, and the presence of polysensory neurons with modally specific opposite responses in this field allow us to conclude that field 24 (compared with field 25) plays a more significant role in the perception and analysis of viscerosomatic afferent information. Taking into account earlier published data that the zones of concentration of the efferent neurons (forming a descending limbico-sympathetic discharge in the L2-L3 white connective branches and a limbico-parasympathetic discharge in the pelvic nerve) are localized within field 25 and overlap each other, we discuss the functional roles of fields 24 and 25 of the cingulate gyrus in viscerosensory and visceromotor control.     

Quantum Properties of GABA Release in Cultured Neurons from the Rat Cortex

We analyzed the properties of inhibitory synaptic transmission between neurons in low-density cultures of cortical cells. Miniature, spontaneous, and evoked inhibitory postsynaptic currents were studied using a whole-cell path-clamp technique at a holding potential of -80 mV. These postsynaptic currents were identified as GABA release-activated Cl^- currents mediated by GABA_A receptors. Fitting amplitude histograms of these currents with Gaussian curves and an autocorrelation technique revealed the presence of equidistant peaks corresponding to a mean quantum size of 10 pA.     

Optogenetic Stimulation of the Corticothalamic Pathway Affects Relay Cells and GABAergic Neurons Differently in the Mouse Visual Thalamus

The dorsal lateral geniculate nucleus (dLGN) serves as the primary conduit of retinal information to visual cortex. In addition to retinal input, dLGN receives a large feedback projection from layer VI of visual cortex. Such input modulates thalamic signal transmission in different ways that range from gain control to synchronizing network activity in a stimulus-specific manner. However, the mechanisms underlying such modulation have been difficult to study, in part because of the complex circuitry and diverse cell types this pathway innervates. To address this and overcome some of the technical limitations inherent in studying the corticothalamic (CT) pathway, we adopted a slice preparation in which we were able to stimulate CT terminal arbors in the visual thalamus of the mouse with blue light by using an adeno-associated virus to express the light-gated ion channel, ChIEF, in layer VI neurons. To examine the postsynaptic responses evoked by repetitive CT stimulation, we recorded from identified relay cells in dLGN, as well as GFP expressing GABAergic neurons in the thalamic reticular nucleus (TRN) and intrinsic interneurons of dLGN. Relay neurons exhibited large glutamatergic responses that continued to increase in amplitude with each successive stimulus pulse. While excitatory responses were apparent at postnatal day 10, the strong facilitation noted in adult was not observed until postnatal day 21. GABAergic neurons in TRN exhibited large initial excitatory responses that quickly plateaued during repetitive stimulation, indicating that the degree of facilitation was much larger for relay cells than for TRN neurons. The responses of intrinsic interneurons were smaller and took the form of a slow depolarization. These differences in the pattern of excitation for different thalamic cell types should help provide a framework for understanding how CT feedback alters the activity of visual thalamic circuitry during sensory processing as well as different behavioral or pathophysiological states.     

Neurochemical Changes in Brain Induced by Chronic Morphine Treatment: NMR Studies in Thalamus and Somatosensory Cortex of Rats

To investigate the effects of chronic morphine treatment and its cessation on thalamus and the somatosensory cortex, an ex vivo high resolution (500 MHz) ¹H nuclear magnetic resonance spectroscopy (NMRS), in the present study, was applied to detect multiple alterations of neurochemicals and/or neurometabolites in the rats. Ten days of chronic morphine administration was observed to markedly increase the total amount of lactate (Lac), myo-inositol (my-Ins) (each P < 0.01) and aspartate (Asp) (P < 0.05), and significantly decrease that of glutamate (Glu) and glutamine (Gln) in the rats thalamus (each P < 0.05). In the somatosensory cortex, chronic morphine was shown to increase the level of Lac and my-Ins, and decrease that of Glu (each P < 0.05). Interestingly, the ratio of Glu/GABA was found to decrease in these two brain areas after chronic morphine treatment, and among the detectable neurochemicals in those two cerebral areas, only taurine (Tau) showed to result in a significant increment in thalamus during the process of morphine discontinuation (P < 0.05). Moreover, the alterations of multiple neurochemicals due to chronic morphine exhibited a tendency of recovery to the normal level over the course of morphine withdrawal. The results suggested that, in thalamus and the somatosensory cortex, chronic morphine administration and its cessation could induce multiple neurochemical changes, which may involve in the brain energy metabolism, activity and transition of neurotransmitters.     

Temporal Sharpening of Sensory Responses by Layer V in the Mouse Primary Somatosensory Cortex

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Responses in Primary Somatosensory Cortex of Rhesus Monkey to Controlled Application of Embossed Grating and Bar Patterns

Responses of 66 neurons in primary somatosensory cortex (SI) of three anesthetized monkeys (Macaca mulatto) were characterized with grating patterns of 550- to 2900-mm groove width (Gw) and 250-mm ridge width, and/or pairs of 3-mm-wide ridges (bars) spaced 1-20 mm apart. Surfaces were stroked across single fingertips at parametrically varied levels of force ('25-150 g) and velocity ('25-100 mm/sec). The average firing rates (AFRs) of many cells varied with Gw, but force and velocity altered response functions (e.g., from linear to plateau or inverted). Slowly adapting (SA) cells were more sensitive to force, rapidly adapting (RA) cells to velocity. Force and velocity affected all cells sensitive to Gw, which suggests that response independence (e.g., AFR correlated with Gw but not force or velocity) may require active touch

Discharge intervals of many cells replicated stimulus temporal period. This temporal fidelity in SAs far exceeded examples reported for active touch. However, discharge burst duration and AFR increased with Gw, supporting a neural rate rather than temporal code for roughness. Force and velocity altered the Gw at which some cells fired once in phase to stimulus cycle (“tuning point”). Responses to bar edges suggest cortical replication of peripheral mechanoreceptor sensitivity to skin curvature, leading to this temporal fidelity in some cortical cells. Graded RA responses to Gw without obvious stimulus temporal replication may reflect early stages of integrative processing in supra- and infragranular layers that blur obvious temporal patterning and lead to a rate code correlated with spatial variation and proportional to perceived roughness     

初级视皮层神经元响应反应与撤反应的朝向选择性

朝向选择性是初级视皮层(17区或V1)神经元的基本性质,在图形感知中起着关键作用.同时这些神经元对于持续时间大于100 ms的视觉刺激具有清晰的响应反应(Onset responses)和撤反应(Offset responses).以往的研究只关注响应反应的朝向选择性,而忽视了对撤反应的朝向选择性研究.我们比较了响应与撤反应的朝向调谐性质,大多数细胞的撤反应与响应反应基本上具有相似的最优朝向,而撤反应的朝向调谐宽度有窄于响应反应的趋势,撤反应的最优延迟普遍滞后于响应反应的最优延迟.撤反应的朝向选择性略强于响应反应和具有显著长的反应延迟提示,皮层内的反馈输入可能在形成撤反应的朝向选择性中起着作用.本研究揭示了撤反应的朝向选择性在刺激朝向的连续表征和主体在形状知觉的后期对朝向的精细区分中起着作用.     

The Effects of Localized Inactivation of Somatosensory Cortex,Area 2, on the Cat Motor Cortex

Direct corticocortical afferents to the primary motor cortex (MI) originate in area 2 and area 3a of the primary somatosensory cortex (SI). The functional and morphological characteristics of the two pathways indicate that they relay different sensory signals to MI. The role of area 2 in relaying peripheral information to the cat MI was studied using electrophysiological techniques. Neurons that responded to stimulation of peripheral receptive fields on the contralateral forepaw were identified in MI by extracellular recordings. In area 2 of SI, neurons with the same receptive field modality and location as those in MI were also identified. Field potentials to electrical stimulation of the peripheral receptive field were recorded at the somatotopically matched sites in both MI and SI. Neuronal activity at the recording site in area 2 was blocked by injection of lidocaine, a local anesthetic. Changes in MI and area 2 responses were monitored before and after inactivation of area 2. Neuronal activity near the injection site was abolished, and evoked potentials (EPs) in area 2 were considerably diminished immediately following the injection. In MI, spontaneous activity levels were altered at some sites, but overall these changes were not significant. MI EPs recorded in response to peripheral stimulation were altered, and various patterns of change were noted in the early and late phases of the EPs. Changes often occurred in only one phase of the response. In some EPs, both early and late phases changed, but the direction and magnitude of change in one phase were not always linked to such changes in the other phase. Both increases and decreases in the amplitude and the area of each phase were observed. The morphological characteristics of the projection were reviewed and related to the findings in the study. It is proposed that inherent features of the pathway may account for the variable patterns of change that were observed.     

大鼠老化过程大脑皮层及小脑神经元染色质构象分析

 本文在前文~[2]的基础上进一步以MCN和DNaseⅠ为探针研究大鼠脑神经元终末分化后不同生理时期染色质构象,结果表明:MCN酶解DNA产物PAGE显示脑老化过程大脑皮层及小脑神经元染色质核小体单体DNA分别保持在176bp和215bp水平,核小体连接DNA长度存在组织差异,但不受老化影响;<2>DNaseⅠ酶解DNA产物PAGE显示各年龄组大脑皮层及小脑神经元染色质DNA存在10bp间隔重复结构和相同的泳动区带分布特征,提示脑老化中染色质具有稳定的B型双螺旋结构和一致的螺线管卷曲形式。染色质DNaseⅠ降解率随年龄增加而降低,提示老化导致活性染色质区域减少,老化过程脑神经元染色质构象改变成为其转录功能减退的结构基础。     

纯氧或空气环境复苏对新生大鼠缺氧性大脑皮质神经元超微结构的影响

目的应用缺氧动物模型比较纯氧环境(pure oxygen environment,POE,100%氧)与空气环境(roomair environment,RAE,21%氧)复苏对新生大鼠缺氧性大脑皮质神经元超微结构的影响。方法7日龄20只SD(Sprague Dawley)乳鼠建立缺氧2.5 h模型后,分为纯氧环境组(POE)和空气环境组(RAE),每组再根据复氧后时间点分为2个亚组,即24 h组和72 h组,每亚组5只。按时间点取各组乳鼠大脑半球右侧额顶皮质行电镜样品制备,透射电镜观察。结果复氧各组均可见神经元、神经毡和细胞间隙水肿。RAE 24 h组神经元核膜结构不清,细胞器减少,线粒体肿胀、空泡化、嵴断裂;粗面内质网扩张,常呈空泡状,核糖体减少;高尔基复合体囊泡扩张;溶酶体较多。RAE 72 h组细胞器改变同前,但类似凋亡的细胞核较多,坏死细胞亦较其他组多见。POE 24 h组病变较RAE 24 h组轻。POE 72 h组细胞内线粒体及粗面内质网较丰富,病变亦比RAE 72 h组轻。结论POE复苏较RAE复苏可更能缓解缺氧致神经元超微结构的损伤、减少细胞凋亡及减轻脑水肿。提示,纯氧环境对缺氧复苏后大脑皮质神经元有一定的保护作用,并表明本动物模型适合缺氧新生大鼠大脑皮质神经元研究。     

雌激素对大鼠肾上腺皮质中Bcl-2和 Bax蛋白表达的影响

利用免疫组织化学SP法检测摘除卵巢及补充17β-雌二醇后大鼠肾上腺皮质各层Bcl-2和Bax蛋白表达的变化。结果表明,摘除卵巢后肾上腺皮质束状带和网状带Bcl-2和Bax表达都增加;球状带中Bax表达增加,而Bcl-2表达阴性。补充17β-雌二醇后,束状带和网状带中Bcl-2蛋白表达显著降低,Bax在束状带中表达极显著降低,而在网状带中没有阳性产物;在球状带中Bcl-2表达上升,而Bax表达下降。表明雌激素在肾上腺皮质各层发挥着复杂的作用。