sigTOOL: A MATLAB-based environment for sharing laboratory-developed software to analyze biological signals.

This paper describes a software package, named sigTOOL, for processing biological signals. The package runs in the MATLAB programming environment and has been designed to promote the sharing of laboratory-developed software across the worldwide web. As proof-of-concept of the design of the system, sigTOOL has been used to build an analysis application for dealing with neuroscience data complete with a user-friendly graphical user interface which implements a range of waveform and spike-train analysis functions. The interface allows many commonly used neuroscience data file formats to be loaded (including those of Alpha Omega, Cambridge Electronic Design, Cyberkinetics Inc., Molecular Devices, Nex Technologies and Plexon Instruments). Waveform analysis functions selectable from the interface support waveform averaging (mean and median), auto- and cross-correlation, power spectral analysis, coherence estimation, digital filtering (feedback and feedforward) and resampling. Spike-train analyses include interspike interval distributions, Poincaré plots, event auto- and cross-correlations, spike-triggered averaging, stimulus driven and phase-related peri-event time histograms and rasters as well as frequencygrams. User-developed additions to sigTOOL that are archived and distributed electronically will be added to the sigTOOL interface on-the-fly, without the need to modify the core sigTOOL code. Full sigTOOL functionality will be provided to support the user-developed code, including the ability to record a user action history for batch processing of files and support for exporting the results of analyses to external graphics editing software and spreadsheet-based data processing packages.

Chondroitinase ABC-mediated plasticity of spinal sensory function.

Experimental therapeutics designed to enhance recovery from spinal cord injury (SCI) primarily focus on augmenting the growth of damaged axons by elevating their intrinsic growth potential and/or by nullifying the influence of inhibitory proteins present in the mature CNS. However, these strategies may also influence the wiring of intact pathways. The direct contribution of such effects to functional restoration after injury has been mooted, but as yet not been described. Here, we provide evidence to support the hypothesis that reorganization of intact spinal circuitry enhances function after SCI. Adult rats that underwent unilateral cervical spared-root lesion (rhizotomy of C5, C6, C8, and T1, sparing C7) exhibited profound sensory deficits for 4 weeks after injury. Delivery of a focal intraspinal injection of the chondroitin sulfate proteoglycan-degrading enzyme chondroitinase ABC (ChABC) was sufficient to restore sensory function after lesion. In vivo electrophysiological recordings confirm that behavioral recovery observed in ChABC-treated rats was consequent on reorganization of intact C7 primary afferent terminals and not regeneration of rhizotomized afferents back into the spinal cord within adjacent segments. These data confirm that intact spinal circuits have a profound influence on functional restoration after SCI. Furthermore, comprehensive understanding of these targets may lead to therapeutic interventions that can be spatially tailored to specific circuitry, thereby reducing unwanted maladaptive axon growth of distal pathways.

Long-range projections of Adelta primary afferents in the Lissauer tract of the rat.

Electrical microstimulation has been used to activate fine myelinated primary afferents running within the Lissauer tract. Stimulation of the tract at the L2/L3 border produced antidromic volleys which were recorded on the dorsal roots of more caudal spinal segments. Antidromic volleys were present in all cases for roots as far caudal as the S2 segment (L3, n=12; L4, n=6; L5, n=6; L6, n=9; S1, n=3; S2, n=6; observations in a total of 15 rats). These fibres were collaterals of primary afferents with conduction velocities in the dorsal root of up to 17.3+/-2.3 ms(-1) (mean+/-S.D., n=6; range 14-20 ms(-1)). Conduction velocities within the Lissauer tract were slower; the fastest contributing fibres had conduction velocities of 9.2+/-2.2 ms(-1) (range 6-12 ms(-1)). Lesions of the Lissauer tract caudal to the stimulation site abolished the volleys on roots lying caudal to the lesion. Most previous works have suggested that primary afferents project in the Lissauer tract for only one or two spinal segments. The present study shows that some fibres project rostrally for up to seven spinal segments (L2-S2).

Local and diffuse mechanisms of primary afferent depolarization and presynaptic inhibition in the rat spinal cord.

Two types of dorsal root potential (DRP) were found in the spinal cord of urethane-anaesthetized rats. Local DRPs with short latency-to-onset were evoked on roots close to the point of entry of an afferent volley. Diffuse DRPs with a longer latency-to-onset were seen on more distant roots up to 17 segments from the volley entry zone. The switch to long latency-to-onset occurred abruptly as a function of distance along the cord and could not be explained by conduction delays within the dorsal columns. Long-latency DRPs were also present and superimposed on the short-latency DRPs on nearby roots. Both local and diffuse DRPs were evoked by light mechanical stimuli: von Frey hair thresholds were

Pulser: user-friendly, graphical user-interface based software for controlling stimuli during data acquisition with Spike2 for Windows.

This paper describes software that runs in the Spike2 for Windows environment and provides a versatile tool for generating stimuli during data acquisition from the 1401 family of interfaces (CED, UK). A graphical user interface (GUI) is used to provide dynamic control of stimulus timing. Both single stimuli and trains of stimuli can be generated. The pulse generation routines make use of programmable variables within the interface and allow these to be rapidly changed during an experiment. The routines therefore provide the ease-of-use associated with external, stand-alone pulse generators. Complex stimulus protocols can be loaded from an external text file and facilities are included to create these files through the GUI. The software consists of a Spike2 script that runs in the host PC, and accompanying routines written in the 1401 sequencer control code, that run in the 1401 interface. Handshaking between the PC and the interface card are built into the routines and provides for full integration of sampling, analysis and stimulus generation during an experiment. Control of the 1401 digital-to-analogue converters is also provided; this allows control of stimulus amplitude as well as timing and also provides a sample-hold feature that may be used to remove DC offsets and drift from recorded data.

Laminar distribution of GABAA- and glycine-receptor mediated tonic inhibition in the dorsal horn of the rat lumbar spinal cord: effects of picrotoxin and strychnine on expression of Fos-like immunoreactivity.

Inhibitory mechanisms are essential in suppressing the development of allodynia and hyperalgesia in the normal animal and there is evidence that loss of inhibition can lead to the development of neuropathic pain. We used Fos expression to map the distribution of tonically inhibited cells in the healthy rat lumbar spinal cord. In a control group, Fos-like immunoreactive (Fos-LI) cells were rare, averaging 7.5+/-2.2 cells (mean+/-SEM; N=13 sections) per 20 microm thick section of dorsal horn. This rose to 103+/-11 (mean+/-SEM; N=20) in picrotoxin-treated rats and to 88+/-11 (mean+/-SEM; N=18) in strychnine-treated rats. These changes were significant (ANOVA; P<0.001). There were marked regional variations in the distribution of Fos-LI cells between picrotoxin- and strychnine-treated animals. Picrotoxin induced a significant increase in the number of Fos-LI cells throughout the dorsal horn (lamina I-VI) while strychnine significantly elevated Fos-like immunoreactivity only in deep laminae (III-VI). For both picrotoxin and strychnine, the increase in Fos-like immunoreactivity peaked in lamina V (at 3579+/-319 and 3649+/-375% of control, respectively; mean+/-SEM) but for picrotoxin an additional peak was observed in the outer part of lamina II (1959+/-196%). Intrathecal administration of both GABAA and glycine receptor antagonists has been shown elsewhere to induce tactile allodynia. The present data suggest that this allodynia could arise due to blockade of tonic GABAA and glycine-receptor mediated inhibition in the deep dorsal horn. GABAA antagonists also induce hypersensitivity to noxious inputs. The blockade of tonic inhibition in the superficial dorsal horn shown here may underlie this hyperalgesia.

Brief and prolonged effects of Lissauer tract stimulation on dorsal horn cells.

Increased excitability of dorsal horn neurones may play a critical role in producing some pain states and there is evidence that the excitability of neurones lying throughout the dorsal horn is subject to regulation by cells in its most superficial laminae. This paper examines the effect on dorsal horn cell receptive fields and excitability of the specific activation of Lissauer's tract, a tract containing propriospinal axons which arise from cells in the substantia gelatinosa and which project to the substantia of neighbouring spinal segments. Experiments were carried out on anaesthetised spinal rats in the L3-4 spinal segments with microelectrode stimulation on the surface of the Lissauer tract (LT) and microelectrode recording of single cells or small groups of cells that responded to gentle brushing on the skin. Single shocks or brief trains of low-level stimuli to the LT produced a characteristic long-latency dorsal root potential (DRP) on the L3 dorsal root and a brief burst of firing in superficial cells with no stimulation of primary afferents. Generally, this was accompanied by no excitation of deeper dorsal horn cells but commonly by a period of inhibition, often followed by facilitation. We then turned to the effect of long periods (30-90min) of continual LT stimulation because we had seen hints of prolonged facilitation of the deeper cells after periods of such stimulation. Trains of 5 stimuli separated by 2ms and repeated every 200ms were used with individual pulses of 200 micros duration and less than 10 microA amplitude. This resulted in a shift of the effect on deep cells from primarily inhibition to mainly facilitation. We then examined in detail the effect of these long periods of LT stimulation on the size of receptive fields (RFs) of dorsal horn cells first on single units and then by repeated mapping of the RFs of small groups of cells. Control periods of 60min with no LT stimulation produced no significant RF changes but 30, 60 or 90min of LT stimulation produced successively greater expansions of RFs. When the LT stimulus was turned off after 1h, the RFs remained expanded for at least 2h. The spike height of these cells remained unchanged. The effect was not influenced by the NMDA antagonist MK801 but was imitated by the GABA(A) antagonist picrotoxin. It is concluded that the prolonged expansion of RFs could not be produced by modulation of descending control since the animals had spinal transections. Neither was it dependent on an NMDA-sensitive mechanism. With these data it is not possible to conclude whether the mechanism is pre-synaptic, post-synaptic or both. It is proposed that the most likely explanation is a decrease in the normal tonic inhibition operated in part by a GABA dependent mechanism. This phenomenon may play a role in prolonged pathological states of increased spinal cord excitability.