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.     

Action of the octavolateralis efferent system upon the lateral line of free-swimming toadfish,Opsanus tau

Summary The activation and action of the octavolateralis efferent system was studied by chronic recordings of discharge patterns from putative efferent and single primary afferent neurons in alert, free-swimming toadfish. Efferent axons isolated in the anterior lateral line nerve showed phasic discharges following touch stimuli applied to the head or trunk and demonstrated sustained discharges to visual stimuli. Resting discharge patterns of primary afferents were categorized into irregular, burster, regular, and silent classes. Afferent discharges were often modulated by low frequency (< 1 Hz) water movement around the head generated during respiratory movements. When fish with recording electrodes implanted in the lateral line nerve were visually stimulated, modulated peak discharges and average (DC) firing rates were inhibited in irregular-type units only. Inhibition of irregular-type afferent neurons also followed visual presentation of natural prey and persisted long after prey stimuli were removed from view. The inhibitory action upon lateralis afferents when activated by biologically significant visual stimuli leads to the hypothesis that the octavolateralis efferent system functions in the peripheral processing of information carried by the lateral line in natural settings.Abbreviations DC average - IO infraorbital - IPSPs inhibitory postynaptic potentials - MXC maxillary canal - OMC operculomandibular canal - SOC supraorbital canal     

Effect of sectioning the mammillothalamic tract on neurons of limbic nuclei of the thalamus

Neuronal activity of n. AV (n = 75) and n. AD (n = 55) of the thalamus was recorded extracellularly in unanaesthetized chronic rabbits after complete transection of the mammillo -thalamic tract (MTT). Elimination of this powerful afferent system produced a surprisingly small effect upon spontaneous and evoked neuronal activity. All types of responses were preserved in both nuclei, though some increase of multimodal diffuse tonic responses and decrease of more specialized phasic and complex on-effects occurred in n. AV. In both nuclei short-latency responses (less than 14 ms) to auditory stimuli disappeared. The number of units with dynamic transformations of responses during repeated stimuli application (gradual emergence and shaping of responses, as well as their habituation) decreased 2-3-fold in both nuclei. The impulse activity travelling in MTT seems to be not critical for limbic nuclei sensory reactivity but significant for plasticity of the responses.     

Unit responses of the superior olives in bats to single and paired ultrasonic stimuli

Single unit responses in the superior olive of the greater horseshoe bat to ultrasonic stimuli with a filling frequency within the echolocation range were investigated. Some neurons were found to have three completely unconnected response regions with characteristic frequencies of 1/2 and 1/3 of the basic frequency, which was within the 80–86 kHz band. An increase in strength of the stimulus with filling frequency equal to the characteristic frequency of the neuron changed the tonic regime of activity into phasic. Presentation of two stimuli, overlapping in time, replaced the phasic regime by tonic. The frequency of the tonic response corresponded exactly to the beating frequency up to 1200 Hz (synchronization of unit discharges with each beating cycle). The synchronized tonic regime was preserved to definite strengths and filling frequencies of the two stimuli.A. A. Zhdanov State University, Leningrad. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 30–38, January–February, 1976.     

Activity of hippocampal neurons deprived of ascending brain stem connections

97 units of the hippocampal fields CA3 and CA1 were recorded extracellularly in chronic unanaesthetized rabbits after complete basal undercutting of the septum. In activity of about one third of the units slow rhythmic bursts (3,3-4,5 Hz) were present. Low frequency theta-like rhythm was present in EEG of the hippocampus. Reactivity to sensory stimuli was unusually low (46-47% of reactive units). Specific and phasic effects of stimuli, typical of the normal field CA1, were observed in both fields. The majority of the reactive neurons respond to sensory stimuli by prolonged shift of the mean frequency of discharges, by regularization of the rhythmic component, or by gradual increase of diffuse activation. Effects of suppression of activity by sensory stimuli were very rare. The data are discussed in the light of presumed difference of reinnervation by axonal sprouting in conditions of basal undercutting of the septum and complete septo-hippocampal disconnection.     

Medullary electrosensory processing in the little skate

1. Ampullary electroreceptors in elasmobranchs are innervated by fibers of the ALLN, which projects to the dorsal octavolateralis nucleus (DON). The purpose of this study is to examine the response characteristics of ALLN fibers and DON neurons to weak D.C. and sinusoidal electric field stimuli presented as local dipole fields. 2. ALLN fibers respond to presentation of D.C. fields with a phasic burst, followed by a more slowly adapting period of firing. Ascending efferent neurons (AENs) in the DON respond to stimuli with a similar initial burst, which adapts more quickly. 3. Type 1, 2, and 3 neurons are possible local interneurons or commissural DON neurons. Type 1 neurons demonstrate response properties similar to those of AENs. Type 2 cells demonstrated slowly adapting responses to excitatory stimuli, the duration of the response increased with the amplitude of the stimulus. Type 3 neurons demonstrated an increased rate of firing, but the response lacked any specific temporal characteristics. 4. ALLN fibers typically have receptive fields consisting of a single ampulla. The receptive field sizes of DON neurons exhibited varying degrees of convergence for different cell types. 5. Responses of ALLN fibers and DON neurons to weak sinusoidal stimuli demonstrated very similar frequency response characteristics for all cell types. The peak sensitivity of electrosensory neurons was between 5-10 Hz.     

In vitro and in vivo responses of saccular and caudal nucleus neurons in the grassfrog (Rana temporaria).

We present results from in vitro and in vivo studies of response properties of neurons in the saccular and caudal nuclei in the frog. In the in vitro studies the saccular nerve of the isolated brain was stimulated with electrical pulses. In the in vivo experiments, the neurons were stimulated by dorso-ventral vibrations of the intact animal. We identified six response types: (1) primary-like cells with short latencies and follow repetition rates up to 100 Hz; (2) phasic cells responding only to the first pulse in a train; (3) bursting cells firing several spikes in response to any stimulation; (4) late responders with very long latencies; (5) integrator cells showing facilitated responses, and (6) inhibitory cells inhibited by saccular nerve stimulation.The cells have comparable sensitivity and frequency characteristics to the primary fibres (BF 10-80 Hz, thresholds from 0.01 cm/s2) and enable a sophisticated analysis of vibrational stimuli.     

Relationship between functional characteristics of cat visual cortex neurons,their response to novelty,and short-term memory

In the visual cortex of unanesthetized cats, the number and frequency of discharges in response to a new stimulus differed from the subsequent responses: the first response was more intensive in 34% of the neurons, but in 30% it was inhibited. The phenomenon of short-term memory was detected in 19% of the cells: it was expressed in regeneration of the configuration of response discharges after the cessation of rhythmic stimulation. These peculiarities can be linked with functional organization of the neurons. We divided them into two groups according to their response to photic stimuli. The first group includes short-latent neurons that respond with discharges of the phasic type and that virtually or totally lack spontaneous activity. The second group consists of long-latent neurons with the tonic type of discharges and distinct spontaneous activity. In the overwhelming majority of cases, response to novelty and short-term memory were discovered in neurons of the second group. It is hypothesized that the population of neurons of the first group — having narrower afferent connections — takes part mainly in analysis of properties of a photic stimulus; the population of neurons of the second group participates in information processing at the final and highest level, on which mechanisms of memory and attention are implicated.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 6, pp. 611–617, November–December, 1970.     

Mechanosensitive enteric neurons in the myenteric plexus of the mouse intestine

Background

Within the gut the autonomous enteric nervous system (ENS) is able to sense mechanical stimuli and to trigger gut reflex behaviour. We previously proposed a novel sensory circuit in the ENS which consists of multifunctional rapidly adapting mechanosensitive enteric neurons (RAMEN) in the guinea pig. The aim of this study was to validate this concept by studying its applicability to other species or gut regions.

Methodology/Principal Findings

We deformed myenteric ganglia in the mouse small and large intestine and recorded spike discharge using voltage sensitive dye imaging. We also analysed expression of markers hitherto proposed to label mouse sensory myenteric neurons in the ileum (NF145kD) or colon (calretinin). RAMEN constituted 22% and 15% of myenteric neurons per ganglion in the ileum and colon, respectively. They encoded dynamic rather than sustained deformation. In the colon, 7% of mechanosensitive neurons fired throughout the sustained deformation, a behaviour typical for slowly adapting echanosensitive neurons (SAMEN). RAMEN and SAMEN responded directly to mechanical deformation as their response remained unchanged after synaptic blockade in low Ca⁺⁺/high Mg⁺⁺. Activity levels of RAMEN increased with the degree of ganglion deformation. Recruitment of more RAMEN with stronger stimuli may suggest low and high threshold RAMEN. The majority of RAMEN were cholinergic but most lacked expression of NF145kD or calretinin.

Conclusions/Significance

We showed for the first time that fundamental properties of mechanosensitive enteric neurons, such as firing pattern, encoding of dynamic deformation, cholinergic phenotype and their proportion, are conserved across species and regions. We conclude that RAMEN are important for mechanotransduction in the ENS. They directly encode dynamic changes in force as their firing frequency is proportional to the degree of deformation of the ganglion they reside in. The additional existence of SAMEN in the colon is likely an adaptation to colonic motor patterns which consist of phasic and tonic contractions.     

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.     

Two types of P neurons in the medullary dorsal respiratory cellular group in cats

Electrophysiological properties of P neurons localized in the medullary dorsal respiratory cellular group and of vagal afferent fibers innervating these neurons were studied in acute experiments on nembutal-anesthetized cats with preserved spontaneous respiration. P neurons were shown to form a non-homogeneous cellular population. They generated phasic discharges during the whole inspiration period, but differed in their responses to lung inflation. These findings allowed us to classify P neurons as slowly adapting and rapidly adapting units, probably activated by slowly and rapidly adapting pulmonary receptors, respectively. Sensitivity of the slowly adapting P neurons to activation by the corresponding receptors and the mechanisms underlying the participation of the two types of P neurons in the reflex feedback between the respiratory center and lungs are discussed.Neirofiziologiya/Neurophysiology, Vol. 26, No. 3, pp. 211–217, May–June, 1994.     

Temporal selectivity by single neurons in the torus semicircularis of Batrachyla antartandica (Amphibia: Leptodactylidae)

We investigated the response selectivities of single auditory neurons in the torus semicircularis of Batrachyla antartandica (a leptodactylid from southern Chile) to synthetic stimuli having diverse temporal structures. The advertisement call for this species is characterized by a long sequence of brief sound pulses having a dominant frequency of about 2000 Hz. We constructed five different series of synthetic stimuli in which the following acoustic parameters were systematically modified, one at a time: pulse rate, pulse duration, pulse rise time, pulse fall time, and train duration. The carrier frequency of these stimuli was fixed at the characteristic frequency of the units under study (n=44). Response patterns of TS units to these synthetic call variants revealed different degrees of selectivity for each of the temporal variables. A substantial number of neurons showed preference for pulse rates below 2 pulses s(-1), approximating the values found in natural advertisement calls. Tonic neurons generally showed preferences for long pulse durations, long rise and fall times, and long train durations. In contrast, phasic and phasic-burst neurons preferred stimuli with short duration, short rise and fall times and short train durations.     

Tonic and phasic receptor neurons in the vertebrate olfactory epithelium

Olfactory receptor neurons (ORNs) respond to odorants with characteristic patterns of action potentials that are relevant for odor coding. Prolonged odorant exposures revealed three populations of dissociated toad ORNs, which were mimicked by depolarizing currents: tonic (TN, displaying sustained firing, 49% of 102 cells), phasic (PN, exhibiting brief action potential trains, 36%) and intermediate neurons (IN, generating trains longer than PN, 15%). We studied the biophysical properties underlying the differences between TNs and PNs, the most extreme cases among ORNs. TNs and PNs possessed similar membrane capacitances (approximately 4 pF), but they differed in resting potential (-82 versus -64 mV), input resistance (4.2 versus 2.9 G(Omega)) and unspecific current, I(u) (TNs: 0 < I(u) 1 pA/pF). Firing behavior did not correlate with differences in voltage-gated conductances. We developed a mathematical model that accurately simulates tonic and phasic patterns. Whole cell recordings from rat ORNs in fragments (approximately 4 mm(2)) of olfactory epithelium showed that such a tissue normally contains tonic and phasic receptor neurons, suggesting that this feature is common across a wide range of vertebrates. Our findings show that the individual passive electrical properties can govern the firing patterns of ORNs.     

大鼠杏仁核簇与痛觉调制的关系

目的：研究伤害性刺激对大鼠杏仁核簇中各亚核痛反应神经元电活动的影响。方法：用串电脉冲刺激坐骨神经作为伤害性刺激,用玻璃微电极引导神经元放电。结果：杏仁核簇中多个亚核均存在痛反应神经元。伤害性刺激使痛兴奋神经元(PEN)诱发放电频率增加;使痛抑制神经元(PIN)诱发放电频率降低,并出现放电频率极低现象;两类神经元电活动相互配合。腹腔注射吗啡(10mg／kg)可以对抗伤害性刺激对痛反应神经元的作用。结论：杏仁核簇中的部分亚核在感受、整合和传递痛觉信息方面起一定作用,是中枢神经系统控制和处理痛觉信息的一个组成部分。     

Factors controlling the expansion behavior of favia favus (Cnidaria: Scleractinia): effects of light, flow, and planktonic prey

Colonies of the massive stony coral Faviafavus were exposed to different flow speeds and levels of light, and to the addition of zooplankton prey. The relative importance of each factor in controlling polyp expansion behavior was tested. The coral polyps fully expanded when they were exposed to low light intensity (0-40 micromol m(-2) s(-1)) and high flow speed (15 cm s(-1)), regardless of prey presence. They also partially expanded under low and medium light (40-80 micromol m(-2) s(-1)) at medium flow speed (10 cm s(-1)). The corals expanded their polyps only when they were exposed to light levels below compensation irradiance (Icom: light level at which photosynthesis = respiration), which was determined to be about 107 +/- 24 micromol m(-2) s. The results presented here indicate that high flow, low light, and the presence of planktonic prey induce coral expansion. There is a hierarchy of response to these stimuli, in which light level and flow speed are dominant over prey presence. Coral response to these three factors is probably due to the relative importance of gas exchange and zooplankton prey.     

Activity of rabbit's neocortical and hippocampal neurons in orienting-exploratory behavior and freezing

By plotting autocorrelation histograms, the character of impulsation of neurons in bilateral derivations from cortical visual and somatosensory areas and hippocampal field CA1 was studied in rabbits during free behavior under the influences of emotional stimuli. During active orienting-exploratory reaction of rabbits, most cortical and hippocampal neurons manifested bursting discharges and theta-frequency oscillation (predominantly 4-5 Hz in cortex and 4-5, 6-7 in hyppocampus). During freezing, as compared with active locomotor reaction, the number of neurons with equiprobabilistic discharges increased; in impulsation of neurons with periodicity, the intensity of delta-frequency oscillation increased (predominantly 2-4 Hz) but theta-frequency oscillation decreased. The number of neurons with delta-frequency oscillation during freezing was greater then in calmly sitting rabbits.     

Rhythmic activities of hypothalamic magnocellular neurons: Autocontrol mechanisms

Electrophysiological recordings in lactating rats show that oxytocin (OT) and vasopressin (AVP) neurons exhibit specific patterns of activities in relation to peripheral stimuli: periodic bursting firing for OT neurons during suckling, phasic firing for AVP neurons during hyperosmolarity (systemic injection of hypertonic saline). These activities are autocontrolled by OT and AVP released somato-dentritically within the hypothalamic magnocellular nuclei. In vivo, OT enhances the amplitude and frequency of bursts, an effect accompanied with an increase in basal firing rate. However, the characteristics of firing change as facilitation proceeds: the spike patterns become very irregular with clusters of spikes spaced by long silences; the firing rate is highly variable and clearly oscillates before facilitated bursts. This unstable behaviour dramatically decreases during intense tonic activation which temporarily interrupts bursting, and could therefore be a prerequisite for bursting. In vivo, the effects of AVP depend on the initial firing pattern of AVP neurons: AVP excites weakly active neurons (increasing duration of active periods and decreasing silences), inhibits highly active neurons, and does not affect neurons with intermediate phasic activity. AVP brings the entire population of AVP neurons to discharge with a medium phasic activity characterised by periods of firing and silence lasting 20–40 s, a pattern shown to optimise the release of AVP from the neurohypophysis. Each of the peptides (OT or AVP) induces an increase in intracellular Ca²⁺ concentration, specifically in the neurons containing either OT or AVP respectively. OT evokes the release of Ca²⁺ from IP3-sensitive intracellular stores. AVP induces an influx of Ca²⁺ through voltage-dependent Ca²⁺ channels of T-, L- and N-types. We postulate that the facilitatory autocontrol of OT and AVP neurons could be mediated by Ca²⁺ known to play a key role in the control of the patterns of phasic neurons.     

Computation of responses to color and brightness differences of neurons in the rabbit lateral geniculate nucleus

Changes in activity of 51 neurons in the rabbit lateral geniculate nucleus evoked by the replacement of eight color and eight achromatic stimuli in pairs were analyzed. It was found that neurons displayed the earliest phasic (within 50-90 ms after the replacement) and tonic response components. The earliest component strongly correlated with differences between stimuli, whereas the tonic component depended on stimuli intensity. Analysis of phasic component revealed two neuronal populations: the first group of cells was specialized for stimuli differentiation only by their intensities, and, and the second group could measure differences in colors and intensities. Neuronal perceptual spaces were reconstructed using the average of the earliest response component as a measure of differences between stimuli. Spaces of 44 neurons (86%) were two-dimensional with brightness and darkness axes. Such neurons had the same structures of space for color and achromatic stimuli. Spaces of 7 neurons (14%) were four-dimensional with two chromatic and two achromatic axes. The structures of perceptual space reconstructed from neurons in the lateral geniculate nucleus were identical to the spaces calculated from the neurons in the primary visual cortex. The structure of the perceptual space reconstructed from neuronal spikes was also similar to space calculated from the N85 visual evoked potential component recorded under similar conditions and to another space reconstructed on the basis of rabbit's instrumental learning. This fact confirmed the general principle of vector coding in the visual system. The tonic component of the most of neurons in the lateral geniculate nucleus showed a linear correlation with changes in intensities, thereby these neurons could be characterized as pre-detectors for cortical selective detectors.     

Electrical properties of neurons recorded from the rat supraoptic nucleus in vitro

The electrical properties of neurons in the supraoptic nucleus (so.n.) have been studied in the hypothalamic slice preparation by intracellular and extracellular recording techniques, with Lucifer Yellow CH dye injection to mark the recording site as being the so.n. Intracellular recordings from so.n. neurons revealed them to have an average membrane potential of -67 +/- 0.8 mV (mean +/- s.e.m.), membrane resistance of 145 +/- 9 M omega with linear current-voltage relations from 40 mV in the hyperpolarizing direction to the level of spike threshold in the depolarizing direction. Average cell time constant was 14 +/- 2.2 ms. So.n. action potentials ranged in amplitude from 55 to 95 mV, with a mean of 76 +/- 2 mV, and a spike width of 2.6 +/- 0.5 ms at 30% of maximal spike height. Both single spikes and trains of spikes were followed by a strong, long-lasting hyperpolarization with a decay fitted by a single exponential having a time constant of 8.6 +/- 1.8 ms. Action potentials could be blocked by 10(-6) M tetrodotoxin. Spontaneously active so.n. neurons were characterized by synaptic input in the form of excitatory and inhibitory postsynaptic potentials, the latter being apparently blocked when 4 M KCl electrodes were used. Both forms of synaptic activity were blocked by application of divalent cations such as Mg2+, Mn2+ or Co2+. 74% of so.n. neurons fired spontaneously at rates exceeding 0.1 spikes per second, with a mean for all cells of 2.9 +/- 0.2 s-1. Of these cells, 21% fired slowly and continuously at 0.1 - 1.0 s-1, 45% fired continuously at greater than 1 Hz, and the remaining 34% fired phasically in bursts of activity followed by silence or low frequency firing. Spontaneously firing phasic cells showed a mean burst length of 16.7 +/- 4.5 s and a silent period of 28.2 +/- 4.2 s. Intracellular recordings revealed the presence of slow variations in membrane potential which modified the neuron's proximity to spike threshold, and controlled phasic firing. Variations in synaptic input were not observed to influence firing in phasic cells.     

Slope-Based Stochastic Resonance: How Noise Enables Phasic Neurons to Encode Slow Signals

Fundamental properties of phasic firing neurons are usually characterized in a noise-free condition. In the absence of noise, phasic neurons exhibit Class 3 excitability, which is a lack of repetitive firing to steady current injections. For time-varying inputs, phasic neurons are band-pass filters or slope detectors, because they do not respond to inputs containing exclusively low frequencies or shallow slopes. However, we show that in noisy conditions, response properties of phasic neuron models are distinctly altered. Noise enables a phasic model to encode low-frequency inputs that are outside of the response range of the associated deterministic model. Interestingly, this seemingly stochastic-resonance (SR) like effect differs significantly from the classical SR behavior of spiking systems in both the signal-to-noise ratio and the temporal response pattern. Instead of being most sensitive to the peak of a subthreshold signal, as is typical in a classical SR system, phasic models are most sensitive to the signal''s rising and falling phases where the slopes are steep. This finding is consistent with the fact that there is not an absolute input threshold in terms of amplitude; rather, a response threshold is more properly defined as a stimulus slope/frequency. We call the encoding of low-frequency signals with noise by phasic models a slope-based SR, because noise can lower or diminish the slope threshold for ramp stimuli. We demonstrate here similar behaviors in three mechanistic models with Class 3 excitability in the presence of slow-varying noise and we suggest that the slope-based SR is a fundamental behavior associated with general phasic properties rather than with a particular biological mechanism.