Extracellular Spike Recordings Research Articles

Neural Circuits Underlying Multifeature Extraction in the Retina.

Classic ON-OFF direction-selective ganglion cells (DSGCs) that encode the four cardinal directions were recently shown to also be orientation-selective. To clarify the mechanisms underlying orientation selectivity, we employed a variety of electrophysiological, optogenetic, and gene knock-out strategies to test the relative contributions of glutamate, GABA, and acetylcholine (ACh) input that are known to drive DSGCs, in male and female mouse retinas. Extracellular spike recordings revealed that DSGCs respond preferentially to either vertical or horizontal bars, those that are perpendicular to their preferred-null motion axes. By contrast, the glutamate input to all four DSGC types measured using whole-cell patch-clamp techniques was found to be tuned along the vertical axis. Tuned glutamatergic excitation was heavily reliant on type 5A bipolar cells, which appear to be electrically coupled via connexin 36 containing gap junctions to the vertically oriented processes of wide-field amacrine cells. Vertically tuned inputs are transformed by the GABAergic/cholinergic "starburst" amacrine cells (SACs), which are critical components of the direction-selective circuit, into distinct patterns of inhibition and excitation. Feed-forward SAC inhibition appears to "veto" preferred orientation glutamate excitation in dorsal/ventral (but not nasal/temporal) coding DSGCs "flipping" their orientation tuning by 90° and accounts for the apparent mismatch between glutamate input tuning and the DSGC's spiking response. Together, these results reveal how two distinct synaptic motifs interact to generate complex feature selectivity, shedding light on the intricate circuitry that underlies visual processing in the retina.

Super-Selective Reconstruction of Causal and Direct Connectivity With Application to in vitro iPSC Neuronal Networks.

Despite advancements in the development of cell-based in-vitro neuronal network models, the lack of appropriate computational tools limits their analyses. Methods aimed at deciphering the effective connections between neurons from extracellular spike recordings would increase utility of in vitro local neural circuits, especially for studies of human neural development and disease based on induced pluripotent stem cells (hiPSC). Current techniques allow statistical inference of functional couplings in the network but are fundamentally unable to correctly identify indirect and apparent connections between neurons, generating redundant maps with limited ability to model the causal dynamics of the network. In this paper, we describe a novel mathematically rigorous, model-free method to map effective—direct and causal—connectivity of neuronal networks from multi-electrode array data. The inference algorithm uses a combination of statistical and deterministic indicators which, first, enables identification of all existing functional links in the network and then reconstructs the directed and causal connection diagram via a super-selective rule enabling highly accurate classification of direct, indirect, and apparent links. Our method can be generally applied to the functional characterization of any in vitro neuronal networks. Here, we show that, given its accuracy, it can offer important insights into the functional development of in vitro hiPSC-derived neuronal cultures.

Embedding optimization reveals long-lasting history dependence in neural spiking activity.

Information processing can leave distinct footprints on the statistics of neural spiking. For example, efficient coding minimizes the statistical dependencies on the spiking history, while temporal integration of information may require the maintenance of information over different timescales. To investigate these footprints, we developed a novel approach to quantify history dependence within the spiking of a single neuron, using the mutual information between the entire past and current spiking. This measure captures how much past information is necessary to predict current spiking. In contrast, classical time-lagged measures of temporal dependence like the autocorrelation capture how long-potentially redundant-past information can still be read out. Strikingly, we find for model neurons that our method disentangles the strength and timescale of history dependence, whereas the two are mixed in classical approaches. When applying the method to experimental data, which are necessarily of limited size, a reliable estimation of mutual information is only possible for a coarse temporal binning of past spiking, a so-called past embedding. To still account for the vastly different spiking statistics and potentially long history dependence of living neurons, we developed an embedding-optimization approach that does not only vary the number and size, but also an exponential stretching of past bins. For extra-cellular spike recordings, we found that the strength and timescale of history dependence indeed can vary independently across experimental preparations. While hippocampus indicated strong and long history dependence, in visual cortex it was weak and short, while in vitro the history dependence was strong but short. This work enables an information-theoretic characterization of history dependence in recorded spike trains, which captures a footprint of information processing that is beyond time-lagged measures of temporal dependence. To facilitate the application of the method, we provide practical guidelines and a toolbox.

Model-based detection of putative synaptic connections from spike recordings with latency and type constraints.

Detecting synaptic connections using large-scale extracellular spike recordings presents a statistical challenge. Although previous methods often treat the detection of each putative connection as a separate hypothesis test, here we develop a modeling approach that infers synaptic connections while incorporating circuit properties learned from the whole network. We use an extension of the generalized linear model framework to describe the cross-correlograms between pairs of neurons and separate correlograms into two parts: a slowly varying effect due to background fluctuations and a fast, transient effect due to the synapse. We then use the observations from all putative connections in the recording to estimate two network properties: the presynaptic neuron type (excitatory or inhibitory) and the relationship between synaptic latency and distance between neurons. Constraining the presynaptic neuron's type, synaptic latencies, and time constants improves synapse detection. In data from simulated networks, this model outperforms two previously developed synapse detection methods, especially on the weak connections. We also apply our model to in vitro multielectrode array recordings from the mouse somatosensory cortex. Here, our model automatically recovers plausible connections from hundreds of neurons, and the properties of the putative connections are largely consistent with previous research.NEW & NOTEWORTHY Detecting synaptic connections using large-scale extracellular spike recordings is a difficult statistical problem. Here, we develop an extension of a generalized linear model that explicitly separates fast synaptic effects and slow background fluctuations in cross-correlograms between pairs of neurons while incorporating circuit properties learned from the whole network. This model outperforms two previously developed synapse detection methods in the simulated networks and recovers plausible connections from hundreds of neurons in in vitro multielectrode array data.

In vitro characterization of intrinsic properties and local synaptic inputs to pyramidal neurons in macaque primary motor cortex.

Primates (including humans) have a highly developed corticospinal tract, and specialized motor cortical areas which differ in key ways from rodents. Much work on motor cortex has therefore used macaque monkeys as a good animal model for human motor control. However, there is a paucity of data describing the fundamental functional architecture of primate primary motor cortex, which is best addressed with in vitro approaches. In this study we examined the cellular properties and the micro‐circuitry of the adult macaque primary motor cortex by carrying out in‐vitro intracellular recordings. We aimed to characterize the basic properties of the cortical circuitry by studying the intrinsic properties of its pyramidal neurons and their physiological interconnectivity. We studied the passive and active electrophysiological properties of pyramidal neurons in both superficial and deep cortical layers. Both superficial and deep pyramidal neurons exhibited bursting behaviour that could act as powerful excitation for downstream targets. Synaptic connections were lamina specific. Neurons in the deep layers had convergent excitatory inputs from all cortical layers whereas superficial neurons had only significant inputs from superficial layers. This sheds light on the functional architecture of the primate primary motor cortex and how its output is shaped. We also took the unique opportunity in our recording technique to characterize the relationship between intracellular and extracellular spike waveforms, with implications for cell‐type identification in studies in awake behaving monkey. Our results will aid the interpretation of primate studies into motor control involving extracellular spike recordings and electrical stimulation in primary motor cortex.

Evidence Supporting a Role for Autonomic Modulation of C‐Low Threshold Mechanoreceptors

C‐low threshold mechanoreceptors (LTMRs) are a functionally distinct class of cutaneous sensory fibers believed to facilitate the sensing and coding of pleasurable touch. These afferents have also been implicated in neuropathic pain states including allodynia, in which normally innocuous tactile stimuli elicit painful sensations. The mechanisms that mediate changes in C‐LTMR function are incompletely understood. Autonomic activity has been implicated in the maintenance of various pain syndromes, yet increases in autonomic neural activity do not seem to influence the firing properties of cutaneous nociceptors. Autonomic modulation of cutaneous C‐LTMRs may contribute to allodynia and neuropathic pain, but this has not been studied. We developed an in vitro isolated truncal skin‐nerve preparation to study the recruitment properties of C‐LTMRs following optical stimulation of skin (TH::CHR2 mice) and the actions of modulatory transmitters when bath applied to the subcutaneous interior side of the skin. Extracellular spike recordings were obtained from dorsal cutaneous nerves. Optogenetic recruitment of C‐LTMRs was temperature sensitive with lower temperatures recruiting more units. Recruited C‐LTMRs had typical conduction velocities (ranging from 0.35 to 0.5 m/s) and an average spike half‐width of 0.53 ms (+/− 0.2ms). We assessed fatigability in response to repetitive optical stimuli at 10 Hz. Consistent with previous reports C‐LTMRs were highly fatigable, especially at higher temperatures. Application of acetylcholine resulted in increased spontaneous afferent activity, reduced C‐LTMR recruitment, and increased fatigability. Application of the cholinesterase inhibitor neostigmine also depressed C‐LTMR recruitment. Norepinephrine also decreased recruitment and increased fatigability but reduced the incidence of spontaneous activity. The norepinephrine transport inhibitor clomipramine also reduced C‐LTMR recruitment. Serotonin did not result in changes to recruitment or fatigability of C‐LTMRs, but increased spontaneous activity. However, the serotonin transport inhibitor citalopram did reduce C‐LTMR recruitment. Similarly, dopamine administration had no effect, but application of the dopamine transport inhibitor buproprion depressed C‐LTMR recruitment. We conclude that C‐LTMR activity can be modified by neuromodulatory transmission and studies are underway to further characterize this effect.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Alpha7 Nicotinic Acetylcholine Receptors Play a Predominant Role in the Cholinergic Potentiation of N-Methyl-D-Aspartate Evoked Firing Responses of Hippocampal CA1 Pyramidal Cells.

The aim of the present study was to identify in vivo electrophysiological correlates of the interaction between cholinergic and glutamatergic neurotransmission underlying memory. Extracellular spike recordings were performed in the hippocampal CA1 region of anesthetized rats in combination with local microiontophoretic administration of N-methyl-D-aspartate (NMDA) and acetylcholine (ACh). Both NMDA and ACh increased the firing rate of the neurons. Furthermore, the simultaneous delivery of NMDA and ACh resulted in a more pronounced excitatory effect that was superadditive over the sum of the two mono-treatment effects and that was explained by cholinergic potentiation of glutamatergic neurotransmission. Next, animals were systemically treated with scopolamine or methyllycaconitine (MLA) to assess the contribution of muscarinic ACh receptor (mAChR) or α7 nicotinic ACh receptor (nAChR) receptor-mediated mechanisms to the observed effects. Scopolamine totally inhibited ACh-evoked firing, and attenuated the firing rate increase evoked by simultaneous application of NMDA and ACh. However, the superadditive nature of the combined effect was preserved. The α7 nAChR antagonist MLA robustly decreased the firing response to simultaneous application of NMDA and ACh, suspending their superadditive effect, without modifying the tonic firing rate increasing effect of ACh. These results provide the first in vivo electrophysiological evidence that, in the hippocampal CA1 region, α7 nAChRs contribute to pyramidal cell activity mainly through potentiation of glutamatergic signaling, while the direct cholinergic modulation of tonic firing is notably mediated by mAChRs. Furthermore, the present findings also reveal cellular physiological correlates of the interplay between cholinergic and glutamatergic agents in behavioral pharmacological models of cognitive decline.

Measurement of phase resetting curves using optogenetic barrage stimuli

BackgroundThe phase resetting curve (PRC) is a primary measure of a rhythmically firing neuron's responses to synaptic input, quantifying the change in phase of the firing oscillation as a function of the input phase. PRCs provide information about whether neurons will synchronize due to synaptic coupling or shared input. However, PRC estimation has been limited to in vitro preparations where stable intracellular recordings can be obtained and background activity is minimal, and new methods are required for in vivo applications. New methodWe estimated PRCs using dense optogenetic stimuli and extracellular spike recording. Autonomously firing neurons in substantia nigra pars reticulata (SNr) of Thy1-channelrhodopsin 2 (ChR2) transgenic mice were stimulated with random barrages of light pulses, and PRCs were determined using multiple linear regression. ResultsThe PRCs obtained were type-I, showing only phase advances in response to depolarizing input, and generally sloped upward from early to late phases. Secondary PRCs, indicating the effect on the subsequent ISI, showed phase delays primarily for stimuli arriving at late phases. Phase models constructed from the optogenetic PRCs accounted for a large fraction of the variance in ISI length and provided a good approximation of the spike-triggered average stimulus. Comparison with existing methodsCompared to methods based on intracellular current injection, the new method sacrifices some temporal resolution. However, it should be much more widely applicable in vivo, because only extracellular recording and optogenetic stimulation are required. ConclusionsThese results demonstrate PRC estimation using methods suitable for in vivo applications.

Separation of electrophysiologically distinct neuronal populations in the rat hippocampus for neuropharmacological testing under in vivo conditions.

Microiontophoresis combined with extracellular spike recording is an excellent method for investigating local neuropharmacological effects under in vivo conditions. However, its application has recently become relatively rare in neuroscience research. Now, we aimed to revisit microiontophoresis and demonstrate that it provides valuable data about the pharmacophysiology of neurons and local neuronal networks, in vivo. Extracellular recordings were performed through the central recording channel of multibarrel carbon-fiber microelectrodes in the CA1 pyramidal layer of the hippocampus of anesthetized rats, while N-methyl-D-aspartate (NMDA) was locally administrated by means of microiontophoresis through the surrounding micropipettes of the microelectrode. Various separation procedures were used to distinguish putative pyramidal cells and interneurons. Quality of separation was verified by electrophysiological parameters. After the delivery of NMDA in the vicinity of the examined neurons, firing rate of putative pyramidal cells was increased with a significantly higher grade then that of putative interneurons. The present results in line with previous data indicate that pyramidal cells are more responsive to pharmacological manipulation through NMDA receptors, also confirming the reliability of the separation of different types of neurons in in vivo microiontophoretic experiments.

The Balance of Excitatory and Inhibitory Synaptic Inputs for Coding Sound Location

The localization of high-frequency sounds in the horizontal plane uses an interaural-level difference (ILD) cue, yet little is known about the synaptic mechanisms that underlie processing this cue in the inferior colliculus (IC) of mouse. Here, we study the synaptic currents that process ILD in vivo and use stimuli in which ILD varies around a constant average binaural level (ABL) to approximate sounds on the horizontal plane. Monaural stimulation in either ear produced EPSCs and IPSCs in most neurons. The temporal properties of monaural responses were well matched, suggesting connected functional zones with matched inputs. The EPSCs had three patterns in response to ABL stimuli, preference for the sound field with the highest level stimulus: (1) contralateral; (2) bilateral highly lateralized; or (3) at the center near 0 ILD. EPSCs and IPSCs were well correlated except in center-preferred neurons. Summation of the monaural EPSCs predicted the binaural excitatory response but less well than the summation of monaural IPSCs. Binaural EPSCs often showed a nonlinearity that strengthened the response to specific ILDs. Extracellular spike and intracellular current recordings from the same neuron showed that the ILD tuning of the spikes was sharper than that of the EPSCs. Thus, in the IC, balanced excitatory and inhibitory inputs may be a general feature of synaptic coding for many types of sound processing.

Masked excitatory crosstalk between the ON and OFF visual pathways in the mammalian retina

A fundamental organizing feature of the visual system is the segregation of ON and OFF responses into parallel streams to signal light increment and decrement. However, we found that blockade of GABAergic inhibition unmasks robust ON responses in OFF α-ganglion cells (α-GCs). These ON responses had the same centre-mediated structure as the classic OFF responses of OFF α-GCs, but were abolished following disruption of the ON pathway with L-AP4. Experiments showed that both GABA(A) and GABA(C) receptors are involved in the masking inhibition of this ON response, located at presynaptic inhibitory synapses on bipolar cell axon terminals and possibly amacrine cell dendrites. Since the dendrites of OFF α-GCs are not positioned to receive excitatory inputs from ON bipolar cell axon terminals in sublamina-b of the inner plexiform layer (IPL), we investigated the possibility that gap junction-mediated electrical synapses made with neighbouring amacrine cells form the avenue for reception of ON signals. We found that the application of gap junction blockers eliminated the unmasked ON responses in OFF α-GCs, while the classic OFF responses remained. Furthermore, we found that amacrine cells coupled to OFF α-GCs display processes in both sublaminae of the IPL, thus forming a plausible substrate for the reception and delivery of ON signals to OFF α-GCs. Finally, using a multielectrode array, we found that masked ON and OFF signals are displayed by over one-third of ganglion cells in the rabbit and mouse retinas, suggesting that masked crossover excitation is a widespread phenomenon in the inner mammalian retina.

Synaptic inputs and timing underlying the velocity tuning of direction-selective ganglion cells in rabbit retina

There are two types of direction-selective ganglion cells (DSGCs) identified in the rabbit retina, which can be readily distinguished both morphologically and physiologically. The well characterized ON-OFF DSGCs respond to a broad range of image velocities whereas the less common ON DSGCs are tuned to slower image velocities. This study examined how the synaptic inputs shape the velocity tuning of DSGCs in an isolated preparation of the rabbit retina. The receptive-field properties were mapped by extracellular spike recordings and compared with the light-evoked excitatory and inhibitory synaptic conductances that were measured under voltage-clamp. The synaptic mechanisms underlying the generation of direction selectivity appear to be similar in both cell types in that preferred-direction image motion elicits a greater excitatory input and null-direction image motion elicits a greater inhibitory input. To examine the temporal tuning of the DSGCs, the cells were stimulated with either a grating drifted over the receptive-field centre at a range of velocities or with a light spot flickered at different temporal frequencies. Whereas the excitatory and inhibitory inputs to the ON-OFF DSGCs are relatively constant over a wide range of temporal frequencies, the ON DSGCs receive less excitation and more inhibition at higher temporal frequencies. Moreover, transient inhibition precedes sustained excitation in the ON DSGCs, leading to slowly activating, sustained spike responses. Consequently, at higher temporal frequencies, weaker excitation combines with fast-rising inhibition resulting in lower spike output.

Neuronal connectivity inference from spike trains using an empirical probabilistic causality measure

To fully understand the computational properties of aneural network, it is crucial to know the network's connec-tivity. Unfortunately, connectivity inference using easilyaccessible data such as extracellular spike recordings is adifficult task. The difficulty arises mainly from problemsrelated with causality, polysynaptic (indirect) connectiv-ity, inhibition and variable time delays, just to name afew. Different methods have been proposed for connectiv-ity inference using, for example, mutual information[1,2], partial directed coherence [3], direct neuronaldynamics parameters fitting [4] or parameter estimationusing Bayesian approaches [5]. However, we argue thatmost of these methods are too complex to implement,hard to apply to spike times series or simply do not pro-vide appropriate estimations using benchmark syntheticdata.Here we present an alternative method that takes directlythe series of spike times from multiple sources and pro-duces a probabilistic connectivity matrix, wherein eachentry provides a confidence level for the existence of aconnection (excitatory or inhibitory) for a particularsource/target pair. Instead of using measures which aredirectly or indirectly related to correlations, our methodintroduces an empirical measure of causality that workson top of spike time probability distributions obtainedfrom the spike times series. This approach allows us tocope with variable time delays, causality, inhibitory con-nections and provides an estimate for the degree of con-nection (monosynaptic, disynaptic, etc.). Our methodincludes heuristics but only one parameter needs to be set:the causality time window. This value defines the maxi-mum time delay between two events that are said to berelated and is used to constrain the causality search space.Our method has been tested using synthetic data fromsimulations where the neuronal connectivity is known

A method for determining neural connectivity and inferring the underlying network dynamics using extracellular spike recordings

In the present paper we propose a novel method for the identification and modeling of neural networks using extracellular spike recordings. We create a deterministic model of the effective network, whose dynamic behavior fits experimental data. The network obtained by our method includes explicit mathematical models of each of the spiking neurons and a description of the effective connectivity between them. Such a model allows us to study the properties of the neuron ensemble independently from the original data. It also permits to infer properties of the ensemble that cannot be directly obtained from the observed spike trains. The performance of the method is tested with spike trains artificially generated by a number of different neural networks.

Employing ICA and SOM for spike sorting of multielectrode recordings from CNS

For classification of action potential shapes in multineuron recordings, we present a spike sorting system employing independent component analysis (ICA) and an unsupervised artificial neural network (Kohonen’s self-organizing map, SOM). We focus on how ICA in the first stage of the spike sorting system can be used to address specific problems arising in recordings using multielectrode arrays in the CNS. Using real data recorded from the pontine nuclei in rats and simulated data, we evaluate the performance of several ICA algorithms to remove cross-talk between electrodes using data from continuous recording (or simulation). When using cut-out data, the standard format of extracellular spike recordings, new problems emerge and robust algorithms are needed. We demonstrate that several ICA algorithms show a good performance on cut-out data from multielectrode array recordings (simulated and real data). In tetrode recordings the same neuron is purposely recorded by several electrodes simultaneously and we show, how independent component analysis can be used in this case to identify redundant information and hence to compress relevant information, improving subsequent clustering of a SOM.

Auto-spermatophore extrusion reveals that the reproductive timer functions in the separated terminal abdominal ganglion in the male cricket.

Auto-spermatophore extrusion is a kind of spermatophore extrusion without genital coupling in the male cricket. It rarely occurred in intact males paired with a female, while it frequently occurred in all the males with the connectives cut under restraint and dissection. The time interval (SPaSE) between spermatophore preparation and auto-spermatophore extrusion was found to be comparable to that (RS2) of the time-fixed sexually refractory stage measured by the calling song. According to extracellular spike recording, the dorsal pouch motoneuron (mDP), which singly innervates the dorsal pouch muscles and is responsible for spermatophore extrusion, showed a burst discharge in association with auto-spermatophore extrusion with an interval similar to RS2 in males with the connectives transected between the 6th abdominal ganglion and the terminal abdominal ganglion (TAG) after spermatophore preparation. These results strengthened our previous conclusion that the reproductive timer for RS2 is located in the TAG, and demonstrated that it functions normally even in the TAG separated from the rest of the central nervous system.

Improved methods for construction of carbon fibre electrodes for extracellular spike recording

Microelectrodes using single carbon fibres as the conducting element have been used since 1979 for electrophysiological measurements in vivo and in vitro. However, there is still considerable discussion about the manufacture of these electrodes, and no overall agreement as to the best way to minimise electrode noise. In this article we describe some revised methods for carbon fibre electrode manufacture, which we believe, gives the lowest noise performance for spike recording in vivo.

Visual responses and connectivity in the turtle pretectum.

1. Using an isolated turtle brain preparation, we made extracellular spike recordings in the dorsal midbrain during visual stimulation. Single units were isolated by their response to a slow-moving full-field visual pattern imaged on the contralateral retina. This stimulus elicits responses from the basal optic nucleus (BON) and the cerebellar cortex using a similar preparation. Direction and speed tuning were then analyzed, as well as the size and position of the receptive field. 2. In one brain stem region, anterior to the optic tectum and deep to the dorsal surface, all of the visually responsive neurons were direction sensitive (DS) to contralateral retinal stimulation. The location and properties of these cells indicate that they are in the mesencephalic lentiform nucleus (nLM). Anterograde transport of intravitreally injected horseradish peroxidase revealed that this pretectal nucleus receives direct input from the contralateral eye. 3. All but 2 of the 48 cells of the nLM were strongly DS. The most effective stimulus was a slowly moving complex visual pattern that drifted nasally in the contralateral visual field. Brief flashes of spots, patterns, or diffuse light were much less effective. Receptive fields were large and usually (9 of 13 cells) centered in the superior visual field near the horizon and nasal to the blind spot. 4. The visual responses of nLM cells were compared to those of cells in the superficial layers of the optic tectum. In contrast to nLM, the responses of tectal cells were heterogeneous and frequently not DS. Neither tectum or nLM cells had much spontaneous spike activity during darkness or stationary patterns. On the other hand, visual responses of nLM cells were very similar to those of the BON, where neurons also had low spontaneous activity, preferred slow-moving patterns, and were DS. However, nLM and BON exhibit different distributions of preferred directions. Most nLM cells preferred temporal-to-nasal motion, whereas BON cells preferred almost any direction, although few preferred the nasal direction. nLM cell responses were not affected by removal of the ventral brain stem including the BON. 5. The visual properties of nLM cells recorded in vitro were very similar to those that were recorded in intact turtles.(ABSTRACT TRUNCATED AT 400 WORDS)

Flow of excitation within rat barrel cortex on striking a single vibrissa.

1. Extracellular spike recordings were made from single cells in various layers of barrel cortex in adult rats anesthetized with urethan. Response magnitude and latency differences to brief 1.14 degrees deflections of mystacial vibrissae of center (principal) and surround receptive-field vibrissae were measured. Latency differences for pairs of cells in the same penetration to stimulation of the principal vibrissa were also collected. In separate experiments the domains of layer IV cells were mapped for their influence by a single vibrissa and their latencies to this vibrissa were recorded. In all experiments precise locations of layer IV cells in each penetration were identified using dye-lesioning and cytochrome oxidase staining of tangential sections. 2. The results suggest that principal vibrissa data are relayed radially in a column of neurons before parallel relay to adjacent columns. To the principal vibrissa, layers IV and Vb neurons discharged earliest, with layers II and III on average 2 and 3 ms later, respectively. Serial relay from layers IV to III to II was suggested to be the most common event. Although layer Va cells fired next, a single-column organization is not suggested for them because differences in latency or response magnitude to their principal and immediate surround vibrissae were not significant. Layer II, III and IV cells showed no statistical difference in latency to the nearest surround vibrissa but fired significantly later than to their principal input. 3. Because, from our previous studies, surround receptive fields of barrel cells in rat S1 cortex appear to be constructed intracortically, these data suggest a parallel column-column relay for their construction. Horizontal relay between barrels occurred first within the septae between barrels. Mean intracortical transmission velocities were calculated at approximately 0.05 m/s for column-column information transfer.

Neurotransmitters Regulating Vestibular Commissural Inhibition in the Cat

The present study focuses on the transmitters which control the vestibular neural activity and, in particular, those which regulate commissural inhibition. Extracellular spike recordings were taken from single vestibular neurons of decerebrate cats. Seven-barreled electrodes were used. The barrels, except for the central one, were filled with several transmitter candidates and their specific inhibitors. After isolation of a type I neuron, the chemicals were iontophoretically applied to examine their effects on the activity of the neuron. The results were as follows: i) GABA and glycine markedly decreased spontaneous firing of the neurons, while serotonin did not change the activity. ii) Bicuculline abolished the inhibitory effects of GABA on the neurons. iii) Strychnine also abolished the effects of glycine, iv) Commissural inhibition caused by electrical stimulation of the contralateral labyrinth was not abolished by the application of strychnine but was abolished by bicuculline. We concluded that 1) vestibular type 1 neurons are controlled by GABAergic and glycinergic neurons, and that 2) the commissural inhibition is activated by the GABAA receptor, but not by the GABAB receptor.