Properties Of Single Neurons Research Articles

Dendritic asymmetry cannot account for directional responses of neurons in visual cortex

A simple model was proposed to account for the direction selectivity of neurons in the primary visual cortex, area V1. In this model, the temporal asymmetries in the summation of inhibition and excitation that produce directionality were generated by structural asymmetries in the tangential organization of the basal dendritic tree of cortical neurons. We reconstructed dendritic trees of neurons with known direction preferences and found no correlation between the small biases of a neuron's dendritic morphology and its direction preference. Detailed simulations indicated that even when the electrotonic asymmetries in the dendrites were extreme, as in cortical Meynert cells, the biophysical properties of single neurons could contribute only partially to the directionality of cortical neurons.

Fast optical recordings of membrane potential changes from dendrites of pyramidal neurons.

Understanding the biophysical properties of single neurons and how they process information is fundamental to understanding how the brain works. A technique that would allow recording of temporal and spatial dynamics of electrical activity in neuronal processes with adequate resolution would facilitate further research. Here, we report on the application of optical recording of membrane potential transients at many sites on neuronal processes of vertebrate neurons in brain slices using intracellular voltage-sensitive dyes. We obtained evidence that 1) loading the neurons with voltage-sensitive dye using patch electrodes is possible without contamination of the extracellular environment; 2) brain slices do not show any autofluorescence at the excitation/emission wavelengths used; 3) pharmacological effects of the dye were completely reversible; 4) the level of photodynamic damage already allows meaningful measurements and could be reduced further; 5) the sensitivity of the dye was comparable to that reported for invertebrate neurons; 6) the dye spread approximately 500 micron into distal processes within 2 h incubation period. This distance should increase with longer incubation; 7) the optically recorded action potential signals from basolateral dendrites (that are difficult or impossible to approach by patch electrodes) and apical dendrites show that both direct soma stimulation and synaptic stimulation triggered action potentials that originated near the soma. The spikes backpropagated into both basolateral dendrites and apical processes; the propagation was somewhat faster in the apical dendrites.

Electrophysiological properties of inferior olive neurons: A compartmental model.

As a step in exploring the functions of the inferior olive, we constructed a biophysical model of the olivary neurons to examine their unique electrophysiological properties. The model consists of two compartments to represent the known distribution of ionic currents across the cell membrane, as well as the dendritic location of the gap junctions and synaptic inputs. The somatic compartment includes a low-threshold calcium current (I(Ca_l)), an anomalous inward rectifier current (I(h)), a sodium current (I(Na)), and a delayed rectifier potassium current (I(K_dr)). The dendritic compartment contains a high-threshold calcium current (I(Ca_h)), a calcium-dependent potassium current (I(K_Ca)), and a current flowing into other cells through electrical coupling (I(c)). First, kinetic parameters for these currents were set according to previously reported experimental data. Next, the remaining free parameters were determined to account for both static and spiking properties of single olivary neurons in vitro. We then performed a series of simulated pharmacological experiments using bifurcation analysis and extensive two-parameter searches. Consistent with previous studies, we quantitatively demonstrated the major role of I(Ca_l) in spiking excitability. In addition, I(h) had an important modulatory role in the spike generation and period of oscillations, as previously suggested by Bal and McCormick. Finally, we investigated the role of electrical coupling in two coupled spiking cells. Depending on the coupling strength, the hyperpolarization level, and the I(Ca_l) and I(h) modulation, the coupled cells had four different synchronization modes: the cells could be in-phase, phase-shifted, or anti-phase or could exhibit a complex desynchronized spiking mode. Hence these simulation results support the counterintuitive hypothesis that electrical coupling can desynchronize coupled inferior olive cells.

Animal models for the optokinetic system of the human

We compare the neuronal and behavioural consequences of abnormal visual experience during early infancy for the optokinetic system of cat and monkey with the neuroopthalmological results in man. Optokinetic eye movements were recorded with the search coil method and electrooculography. In addition, the response properties of single neurons in the visual cortex and pretectum of anesthetized and paralyzed cats and monkeys were determined in electrophysiological experiments. Our data show that monocular deprivation and strabismus lead to an increase of asymmetry of monocular optokinetic nystagmus and a decrease in gain of slow phase optokinetic eye movements during monocular stimulation as well as to a significant decrease of binocular convergence in the oculomotor system of both cat and monkey. Although these changes are basically similar in both species they are not identical. These differential effects may be explained by structural differences. Assuming a similar neuronal substrate for the optokinetic system in all primates the monkey represents a more suitable animal model for the human visual system than the cat.

Receptive field properties of single neurons in rat primary visual cortex.

The rat is used widely to study various aspects of vision including developmental events and numerous pathologies, but surprisingly little is known about the functional properties of single neurons in the rat primary visual cortex (V1). These were investigated in the anesthetized (Hypnorm-Hypnovel), paralyzed animal by presenting gratings of different orientations, spatial and temporal frequencies, dimensions, and contrasts. Stimulus presentation and data collection were automated. Most neurons (190/205) showed sharply tuned (</=30 degrees bandwidth at half height) orientation selectivity with a bias for horizontal stimuli (31%). Analysis of response modulation of oriented cells showed a bimodal distribution consistent with the distinction between simple and complex cell types. Orientation specific interactions occurred between the center and the periphery of receptive fields, usually resulting in strong inhibition to center stimulation when both stimuli had the same orientation. There was no evidence for orientation columns nor for orderly change in optimal orientation with tangential tracks through V1. Responses were elicited by spatial frequencies ranging from zero (no grating) to 1.2 cycle/degree (c/ degrees ), peaking at 0.1 c/ degrees, and with a modal cutoff of 0.6 c/ degrees. Half of the neurons responded optimally to drifting gratings rather than flashing uniform field stimuli. Directional preference was seen for 59% of oriented units at all depths in the cortex. Optimal stimuli velocities varied from 10 to 250 degrees /s. Some units, mainly confined to layer 4, responded to velocities as high as 700 degrees /s. Response versus contrast curves (best fit with Naka-Rushton) varied from nearly linear to extremely steep (mean contrast semisaturation 50% and threshold 6%). There was a trend for cells from superficial layers to be more selective to different stimulus parameters than deeper layers cells. We conclude that neurons in rat V1 have complex and diverse visual properties, necessary for precise visual form perception with low spatial resolution.

Spatiotemporal properties of layer V neurons of the rat primary somatosensory cortex.

Animals in their natural environments actively process spatiotemporally complex sensory signals in order to guide adaptive behavior. It therefore seems likely that the properties of both single neurons and neural ensembles should reflect the dynamic nature of such interactions. During exploratory behaviors, rats move their whiskers to actively discriminate between different tactile features. We investigated whether this dynamic sensory processing was reflected in the spatial and temporal properties of neurons in layer V of the 'whisker area' in the rat primary somatosensory cortex. We found that the majority of layer V neurons had large (8.5+/-4.9 whiskers) spatiotemporal receptive fields (i.e. individual cells responded best to different whiskers as a function of post-stimulus time), and that the excitatory responses of surround whiskers formed a spatial gradient of excitation that seemed to reflect the greater use of the ventral and caudal whiskers during natural behaviors. Analyses of ensembles of layer V neurons revealed that single-whisker stimuli activated a portion of layer V that extends well beyond a single cortical column (average of 5.6 barrel cortical columns). Based on these results, we conclude that the rat primary somatosensory cortex does not appear to operate as a static decoder of tactile information. On the contrary, our data suggest that tactile processing in rats is likely to involve the on-going interactions between populations of broadly tuned neurons in the thalamocortical pathway.

Monaural response properties of single neurons in the chinchilla inferior colliculus

The responses of 274 inferior colliculus (IC) central nucleus neurons from 20 chinchillas were studied. Characteristic frequency (CF) increased as the IC was traversed in the dorsal-ventral direction. Most units had little or no spontaneous activity, with a mean threshold for response of about 30 dB SPL across all units. Tuning curve width varied between units, with a significant increase in Q 20 with increasing CF. Peri-stimulus time histogram (PSTH) types were similar to those reported for cat inferior colliculus units. Transient, sustained, pauser, and buildup types were observed, with transient responses predominating. Response area (RA) types were also similar to those of cat IC units, with most units displaying stable best frequencies across a range of stimulus intensity levels. For a few units, excitatory RA regions were surrounded by inhibitory sidebands. Nonmonotonic discharge rate vs. stimulus intensity level functions were common in all CF ranges and for all PSTH and RA types. Mean first spike latencies, however, differed across PSTH groups, owing to the temporal definitions of these PSTH shapes. Latencies of sustained units were significantly longer than those of transient units, and buildup PSTHs showed significantly longer latencies than any other group.

Single cortical neurons serve both echolocation and passive sound localization.

The pallid bat uses passive listening at low frequencies to detect and locate terrestrial prey and reserves its high-frequency echolocation for general orientation. While hunting, this bat must attend to both streams of information. These streams are processed through two parallel, functionally specialized pathways that are segregated at the level of the inferior colliculus. This report describes functionally bimodal neurons in auditory cortex that receive converging input from these two pathways. Each brain stem pathway imposes its own suite of response properties on these cortical neurons. Consequently, the neurons are bimodally tuned to low and high frequencies, and respond selectively to both noise transients used in prey detection, and downward frequency modulation (FM) sweeps used in echolocation. A novel finding is that the monaural and binaural response properties of these neurons can change as a function of the sound presented. The majority of neurons appeared binaurally inhibited when presented with noise but monaural or binaurally facilitated when presented with the echolocation pulse. Consequently, their spatial sensitivity will change, depending on whether the bat is engaged in echolocation or passive listening. These results demonstrate that the response properties of single cortical neurons can change with behavioral context and suggest that they are capable of supporting more than one behavior.

Discharge properties of single neurons in the dorsal nucleus of the lateral lemniscus of the rat

The aim of the present study was to characterize the discharge properties of single neurons in the dorsal nucleus of the lateral lemniscus (DNLL) of the rat. In the absence of acoustic stimulation, two types of spontaneous discharge patterns were observed: units tended to fire in a bursting or in a nonbursting mode. The distribution of units in the DNLL based on spontaneous firing rate followed a rostrocaudal gradient: units with high spontaneous rates were most commonly located in the rostral part of the DNLL, whereas in the caudal part units had lower spontaneous discharge rates. The most common response pattern of DNLL units to 200 ms binaural noise bursts contained a prominent onset response followed by a lower but steady-state response and an inhibitory response in the early-off period. Thresholds of response to noise bursts were on average higher for DNLL units than for units recorded in the inferior colliculus under the same experimental conditions. The DNLL units were arranged according to a mediolateral sensitivity gradient with the lowest threshold units in the most lateral part of the nucleus. In the rat, as in other mammals, the most common DNLL binaural input type was an excitatory response to contralateral ear stimulation and inhibitory response to ipsilateral ear stimulation (EI type). Pure tone bursts were in general a more effective stimulus compared to noise bursts. Best frequency (BF) was established for 97 DNLL units and plotted according to their spatial location. The DNLL exhibits a loose tonotopic organization, where there is a concentric pattern with high BF units located in the most dorsal and ventral parts of the DNLL and lower BF units in the middle part of the nucleus.

Effects of cholinergic depletion on evoked activity inthe cortex of young and aged rats

Degeneration of cholinergic neurons in the basal forebrain is a neural marker ofAlzheimers disease and is associated with perceptual and cognitive deficits. An idea that hasattracted scientific scutiny is that aging makes the brain more susceptible to neurodegenerativediseases such as Alzheimers. The purpose of this study was to compare the effects of the loss ofcholinergic input from nucleus basalis of Meynert on evoked activity in the posteromedial barrelsubfield of the somatosensory cortex in young (2–2.5 months) and aged (28–30 months) maleFisher hybrid rats. The mean firing rate and receptive fields of single neurons in the posteromedialbarrel subfield of the somatosensory cortex were examined after selective lesions of cholinergicneurons in the nucleus basalis of Meynert with an immunotoxin, IgG 192-saporin.Functional properties of single neurons in young animals were affected much moresignificantly by cholinergic depletion than those in aged animals. In cholinergic-depleted younganimals, the mean firing rate of evoked activity and receptive field of posteromedial barrel subfieldneurons were significantly decreased. Cholinergic depletion caused a 14% decrease in evokedactivity and a 33% increase in receptive field size in young animals. The mean firing rate andreceptive field of single neurons were not affected by cholinergic depletion in aged animals. It isconcluded that functional properties of cortical sensory neurons in young animals are morevulnerable to cholinergic depletion than are those of aged animals and that cholinergic depletiondoes not further impact the properties of neurons exposed to the processes of aging.

Monaural and binaural response properties of single neurons in the rat's dorsal nucleus of the lateral lemniscus

Extracellular recordings were made with microelectrodes from single neurons in the rat's dorsal nucleus of the lateral lemniscus (DNLL) and response characteristics were determined for monaural and binaural acoustic stimulation. The vast majority of DNLL neurons were narrowly tuned to sound frequency and their temporal responses to contralateral tone pulses fell into one of three broad categories: onset (57%), sustained (21%) or onset-pause-sustained (22%). Most DNLL neurons fired multiple action potentials to a single click delivered to the contralateral ear. The majority (77%) of DNLL neurons showed a monotonic increase in the number of spikes elicited by contralateral tone pulses of increasing sound pressure level; the remaining cells were weakly non-monotonic. No obvious tonotopic pattern was found in the distribution of characteristic frequency of neurons in DNLL. Most DNLL neurons exhibited either excitatory/inhibitory (74%) or excitatory/excitatory (9%) binaural response patterns. The remaining cells (17%) were monaural and driven exclusively by stimulation of the contralateral ear. The binaural neurons in DNLL were sensitive to both interaural intensity and interaural time differences as determined by presentation of dichotic tone bursts and clicks respectively. The responses of DNLL neurons could be distinguished on the basis of monaural and binaural response characteristics from those in surrounding areas including the sagulum, paralemniscal zone and the intermediate nucleus of the lateral lemniscus.

Spatial and temporal matching of receptive field properties of binocular cells in area 19 of the cat

The spatial and temporal properties of single neurons were investigated in area 19 of the cat. We evaluated the matching of binocular receptive field properties with regard to the respective strength of the ipsilateral and contralateral inputs. Results indicate that most cells in area 19 are well tuned to spatial and temporal frequencies and exhibit relatively low contrast threshold (mean=6.8%) when assessed using optimal parameters and tested through the dominant eye. Spatial resolution (mean=0.75 c/°), optimal spatial frequencies (mean=0.16 c/°) were relatively low and spatial bandwidths (mean=2.1 octaves) were broader as compared to those of cells in area 17 but comparable to those of cells in other extrastriate areas. On the other hand temporal resolution (mean=10.7 Hz), optimal temporal frequency (mean=4.5 Hz) and temporal bandwidths (mean=2.9 octaves) were higher and broader than in primary visual cortex. A significant relationship exists between most of the cell's properties assessed through either eye. For some parameters, such as spatial and temporal resolution, ocular dominance was shown to be significantly related to the extent of matching between the two eyes. For these parameters, binocular cells that exhibited a balanced ocular dominance were generally well matched with regard to the receptive field properties of each eye whereas the largest mismatches were found in cells that were more strongly dominated by one eye. These results suggest that visual input contributes to the activation of cells in area 19 in a redundant manner, possibly attesting to the multiplicity of parallel pathways to this area in the cat.

A model of the combination of optic flow and extraretinal eye movement signals in primate extrastriate visual cortex: Neural model of self-motion from optic flow and extraretinal cues

The determination of the direction of heading from optic flow is a complicated task. To solve it the visual system complements the optic flow by non-visual information about the occurrence of eye movements. Psychophysical studies have shown that the need for this combination depends on the structure the visual scene. In a depth-rich visual environment motion parallax can be exploited to differentiate self-translation from eye rotation. In the absence of motion parallax, i.e. in the case of movement towards a frontoparallel plane, extraretinal signals are necessary for correct heading perception ( Warren and Hannon, 1990). Lappe and Rauschecker (1993b) have proposed a model of visual heading detection that reproduces many of the psychophysical findings in the absence of extraretinal input and links them to properties of single neurons in the primate visual cortex. The present work proposes a neural network model that integrates extraretinal signals into this network. The model is compared with psychophysical and neurophysiological data from experiments in human and non-human primates. The combined visual/extraretinal model reproduces human behavior in the case of movement towards a frontoparallel plane. Single model neurons exhibit several similarities to neurons from the medial superior temporal (MST) area of the macaque monkey. Similar to MST cells ( Erickson and Thier, 1991) they differentiate between self-induced visual motion that results from eye movements in a stationary environment, and real motion in the environment. The model predicts that this differentiation can also be achieved visually, i.e. without extraretinal input. Other simulations followed experiments by Bradley et al. (1996), in which flow fields were presented that simulated observer translation towards a frontoparallel plane plus an eye rotation. Similar to MST cells, model neurons shift their preference for the focus of expansion along the direction of the eye movement when extraretinal input is not available. They respond to the retinal location of the focus of expansion which is shifted by the eye movement. In the presence of extraretinal input the preference for the focus of expansion is largely invariant to eye movements and tied to the location of the focus of expansion with regard to the visual scene. The model proposes that extraretinal compensation for eye movements need not be perfect in single neurons to achieve accurate heading detection. It thereby shows that the incomplete compensation found in most MST neurons is sufficient to explain the psychophysical data.

Object representation in the ventral premotor cortex (area F5) of the monkey.

Visual and motor properties of single neurons of monkey ventral premotor cortex (area F5) were studied in a behavioral paradigm consisting of four conditions: object grasping in light, object grasping in dark, object fixation, and fixation of a spot of light. The employed objects were six different three-dimensional (3-D) geometric solids. Two main types of neurons were distinguished: motor neurons (n = 25) and visuomotor neurons (n = 24). Motor neurons discharged in association with grasping movements. Most of them (n = 17) discharged selectively during a particular type of grip. Different objects, if grasped in similar way, determined similar neuronal motor responses. Visuomotor neurons also discharged during active movements, but, in addition, they fired also in response to the presentation of 3-D objects. The majority of visuomotor neurons (n = 16) showed selectivity for one or few objects. The response was present both in object grasping in light and in object fixation conditions. Visuomotor neurons that selectively discharged to the presentation of a given object discharged also selectively during grasping of that object. In conclusion, object shape is coded in F5 even when a response to that object is not required. The possible visual or motor nature of this object coding is discussed.

Reorganization in the auditory cortex of the rat induced by intracortical microstimulation: a multiple single-unit study.

Many manipulations are able to change or perturb various aspects of single neuron properties and interneuronal relationships. Changes of cerebral cortex organization have been observed in different cortical areas and at different time scales in relation to peripheral stimulation, peripheral damage, associative learning, and electrical stimulation. Here we describe studies on separable multineuron recordings in the rat's auditory cortex under two different anesthetics. Acoustic stimuli were used as a normal, physiological input, and weak electrical intracortical microstimulation (ICMS) as a perturbation that forces a rapid cortical reorganization. ICMS induced fast changes in the cortical map and in the receptive field properties of cells at the electrically stimulated and adjacent electrodes. In effect there was an enlargement of the cortical domain tuned to the acoustic frequency that had been represented at the stimulating electrode. ICMS also incremented afterdischarge responses; these consisted of an initial response to the auditory stimulus followed by less intense repetitive activity that was stimulus-time locked and had a period of 8-12 Hz, similar to that of the spontaneous synchronous activity. Cortical activity under ketamine differed from that under pentobarbital sodium, although in both situations we observed that cortical neurons were highly synchronous.

Morphological and electrophysiological properties of neurons in an area of the chick brain involved in learning

The intermediate, medial part of the hyperstriatum ventrale (IMHV) is an area of the avian forebrain which is essential for two forms of early learning in the domestic chick, We have developed an in vitro slice preparation which contains part of the IMHV and have found that the electrophysiological properties of the area show a considerable degree of plasticity, In particular, age and prior learning appear to modify the properties of single neurons recorded intracellularly. We have used the in vitro slice preparation to make intracellular recordings from 38 single neurons in the IMHV and have then dye-injected each cell to find out whether there is any relationship between electrophysiological and morphological characteristics. The basic membrane properties of each neuron were measured. Responses to standard electrical stimuli, delivered extracellularly, were also recorded, and each neuron was classified on this basis. Finally, the presence or absence of spontaneously occurring bursts of EPSPs was noted, At the end of recording biocytin was injected into the cell, After the tissue had been processed, each cell was drawn. The area of the cell body was measured, the number of dendrites was counted, and dendritec extent and branching were estimated. Each cell was also classified as ‘spiny’ or ‘non-spiny’. We found that neurons displaying one particular type of response to external stimulation possessed a well defined set of morphological and electrical properties, In addition, three parameters — electrical resistance, somatic area, and the presence or absence of dendritec spines — were related to specific subsets of anatomical and physiological characteristics. The possible relevance of these findings to the plasticity of the IMHV is discussed.

Information coding in the rodent prefrontal cortex. II. Ensemble activity in orbitofrontal cortex.

1. Neural activity was recorded from the orbitofrontal cortex (OF) of rats performing an eight-odor discrimination task that included predictable associations between particular odor pairs. A modified linear discriminant analysis was employed to characterize the population response in each trial of the task as a point in an N-dimensional activity space with the firing rate of each cell in the population represented on one of the N dimensions. The ability of the ensemble to discriminate among conditions of a variable was reflected in the tendency of population responses to cluster together in this activity space for repetitions of a given condition. We assessed coding of several variables describing the period of odor sampling, focusing on aspects of current, past, and future events reflected in single-neuron firing patterns, in ensembles composed of 22-138 cells active during the period when the rats sampled the discriminative stimulus in each trial. 2. OF ensembles performed well at discriminating variables with relevance to task demands represented in single-neuron firing patterns, specifically the physical attributes and assigned reward contingency of the current odor as well as the expectation of reward in the following trial that could be inferred from the predictable associations between particular pairs of odors. OF ensembles were able to correctly identify the identity and assigned reward contingency of the current odor in up to 52% (chance = 12.5%) and 99% (chance = 50%) of all trials, respectively, such that the observed behavioral performance required a population of 5,364 odor-responsive cells in the case of odor identity and only 40 cells in the case of valence. Expectations regarding upcoming rewards based on both assigned response contingency and associations between particular pairs of odors were correctly classified in up to 67% (chance = 20%) of all trials such that the observed level of behavioral performance required a population of 3,169 cells. 3. Other information represented in the single-neuron firing patterns, such as the identity and reward contingency of the preceding odor and specific odor-odor associations, was poorly encoded by OF ensembles. Thus neural ensembles in OF may represent only some of the information reflected in single-neuron activity. Stable coding of only the most useful and relevant information by the ensemble might emerge from the tuning properties of single neurons under the influence of the task at hand, producing in the well-trained animal the observed pattern of broad and diverse coding by single neurons and selective, task-relevant coding by neural ensembles in OF.

Acoustic response properties of single neurons in the central posterior nucleus of the thalamus of the goldfish, Carassius auratus.

Acoustic responses were recorded extracellularly from single neurons in the thalamic central posterior nucleus (CP). Spontaneous activity, best sensitivity, and sharpness of tuning (Q10dB) of CP neurons ranged from 0 to 36 spikes/s, -40 to 5 dB re: 1 dyne/cm2, and 0.18 to 1.80, respectively. The distribution of characteristic frequency (CF) was nonuniform with a mode at 195 Hz. Temporal response patterns of CP neurons (N = 60) were categorized into three groups: phasic (25%), tonic chopper-like (22%), and tonic nonchopper-like (53%) on the basis of peri-stimulus time and inter-spike interval histograms. Most CP neurons (90%) did not phase-lock to tones, and none phase-locked strongly. The properties of CP neurons are similar to those of the midbrain torus semicircularis neurons in spontaneous rates, best sensitivities, nonuniform CF distributions, and in exhibiting level-independent best frequencies. Both CP and toral neurons show a diversity of response patterns resembling those found in the mammalian central auditory system. However, CP neurons have broader tuning and less phase-locking than toral neurons, suggesting different roles in auditory processing. While peripheral frequency analysis is enhanced at the midbrain level, the integration of frequency-selective channels in the thalamus may function in the processing of wideband spectra characteristic of natural sound sources.

The action of 5-HT on calcium-dependent potassium channels and on the spinal locomotor network in lamprey is mediated by 5-HT 1A-like receptors

5-HT has a powerful modulatory action on the firing properties of single neurons as well as on locomotor activity. In lamprey, 5-HT increases the neuronal firing frequency in spinal neurons by reducing the conductance in Ca 2+-dependent K + channels (K Ca) underlying the slow afterhyperpolarization (sAHP), and it also lowers burst frequency of the spinal locomotor network. To elucidate which type of 5-HT receptor mediates these effects, different specific receptor agonists and antagonists were applied during intracellular current lamp recordings and during NMDA-induced fictive locomotion in the lamprey spinal cord in vitro preparation. The 5-HT 1A receptor agonist 8-OH-DPAT ((±)-8-hydroxy-dipropylaminotetralin hydrobromide), the 5-HT 1 receptor agonist 5-CT (5-car☐yamidotryptamine maleate) and the 5-HT 2 receptor agonist α-CH 3-5-HT (α-methylserotonin maleate) all reproduced the actions of 5-HT at both the cellular and the network levels. The effects of all agonists were completely or partially blocked by the 5-HT 1A and 5-HT 2 receptor antagonist spiperone (spiroperidol hydrochloride) while selective 5-HT 2 receptor antagonists were ineffective. The selective 5-HT 1A receptor antagonist S(−)-UH301 (S(−)-5-fluoro-8-hydroxy-dipropylaminotetralin hydrochloride) also counteracted the effect of 5-HT on the sAHP. 5-HT 3 and 5-HT 4 receptor agonists and antagonists were without effects. The intracellular coupling mechanism was not sensitive to pertussis toxin nor to the cAMP dependent protein kinase blocker (Rp)-cAMPS. These results indicate that the intracellular coupling mechanism is not likely to be due to a down regulation of adenylate cyclase activity or through a direct modulation of K + channels, as is common for 5-HT 1 receptors. The present results taken together with previous data indicates that the receptor responsible for the effects of 5-HT on the sAHP, and on the locomotor pattern generator in lamprey shares certain features, but is not identical to the mammalian 5-HT 1A receptor.

Functional properties of single neurons in the primate face primary somatosensory cortex. I. Relations with trained orofacial motor behaviors

1. We have demonstrated recently that reversible, cooling-induced inactivation of the face primary somatosensory cortex (SI) severely impairs the successful performance of a tongue-protrusion task but has relatively minor effects on the performance of a biting task. In an attempt to establish a neuronal correlate for these different behavioral relations, the present study was initiated to document the mechanoreceptive field properties of a population of face SI neurons and their activity during the tongue-protrusion and biting tasks. 2. Within SI, the representation of the face was found immediately lateral to that of the hand, and there was a clear somatotopic pattern of organization within face SI: the periorbital or nose region was located most medially in the face SI, then followed laterally in sequence the representation of the upper lip, lower lip, and intraoral area. A mechanoreceptive field (RF) was identified for 253 neurons, which included 162 "lip RF" neurons receiving mechanosensitive afferent inputs from the upper lip, lower lip, or both; 72 "tongue RF" neurons that received mechanosensitive afferent inputs from the tongue; 11 "periodontium RF" neurons receiving periodontal inputs; and 8 neurons that received inputs from other orofacial regions. 3. Nearly all (249/253) of the face SI neurons responded to light tactile stimuli, and most of them received contralateral inputs (78%) and showed a rapidly adapting (RA) response to tactile stimulation (82%). There was no significant difference in the ratio of slowly adapting (SA) to RA neurons in areas 3b and 1. 4. For 193 neurons studied in one or both of the orofacial tasks, 113 were found, on the basis of histological reconstruction, to be distributed in area 1, 61 in area 3b, and 19 in area 2. 5. The firing rate of most tongue RF (79% of 56) neurons and lip RF (60% of 93) neurons tested was significantly altered during the tongue-protrusion task. Only some (14% of 36 tongue RF neurons and 34% of the 92 lip RF neurons tested) showed a significant change in firing rate during the biting task. Three of 7 periodontium RF neurons studied in the tongue-protrusion task altered their firing rate and 5 of 10 altered their firing rate during the biting task. 6. Most of the 116 face SI neurons studied during both tasks exhibited a preferential relation to the tongue-protrusion task as distinct from the biting task, and none showed task-related activity during the biting task only.(ABSTRACT TRUNCATED AT 400 WORDS)