Jean Cerf

Multiple Sclerosis: Serum Factor Producing Reversible Alterations in Bioelectric Responses

Serums obtained from patients during acute exacerbations of multiple sclerosis produce a reversible depression of polysynaptic reflex responses when applied to the isolated spinal cord of the frog. Motoneuron discharges initiated by monosynaptic activation through an axosomatic spinal pathway are much less affected than reflex discharges. The active factor in serum appears to depend on the presence of complement.

A low-cost timing device for increasing the versatility of physiological stimulators ☆

Abstract A versatile and inexpensive timing device suitable for driving standard stimulators and associated equipment used in neurophysiological experiments is described. Using this device as a building block, systems generating relatively complex stimulation patterns may easily be assembled. It delivers, as required, a square gate pulse of variable duration (1 msec-2 min), a brief trigger pulse with an adjustable delay (1 msec-2 min), or repetitive pulses at a variable frequency (0.005–600 Hz). The output voltage is adequate for triggering or modulating commercial stimulators, including older but still widely used vacuum-tube models. The device itself can be controlled by external signals.

A holder for rapid filling of micropipette electrodes by centrifugal action

SummaryA holder has been designed to house a glass micropipette for highspeed spinning in a centrifuge. Using this device, fine-tipped microelectrodes can be filled individually with the desired electrolyte, within minutes after their fabrication.

Préamplificateur pour microélectrodes, avec étages de gain à transistors

Abstract The paper describes a preamplifier (A) designed for intracellular or extracellular recordings of bioelectric potentials with high resistance microelectrodes. The high-impedance input stage uses a subminiature penthode, and can be switched from a conventional cathode-follower circuit (for extracellular recording) to an “inverted triode” electrometer type circuit (for intracellular recording). Two following stages equipped with low-noise transistors provide a high overall gain (800 × for extracellular and 35 × for intracellular recordings), sufficient for driving any low-gain C-R oscilloscope without additional amplification. When recording intracellularly, stray input capacity and capacity to ground of the microelectrode are neutralized by negative capacitance adjustable by positive feedback, thus improving transient response. Table I summarizes the operating characteristics of the circuit. A calibrating device (B) can be used in conjunction with the preamplifier.

Deux procédésde modulation de luminosité du spot pour l'oscillographie cathodique de potentiels bioélectriques☆

Abstract The paper describes a two-section electronic device for better recording of rapid bioelectric phenomena on the cathode-ray oscillograph screen. In section A (fig. 2), proportional brightening of the trace during transient phenomena is achieved by application of a suitable positive voltage to the cathode-ray tube grid (Z input). This voltage, proportional to the increase in writing-speed of the spot, is obtained by differentiation of the input signal. In section B (fig. 3), intensity modulation is produced by a positive square voltage applied to the grid. The square pulse is delivered by a one-shot multivibrator, triggered by the phenomenon under observation. This same device, used as a negative pulse-generator driven by an external oscillator, may produce intensity-modulated timing markers which blank the trace at known intervals. The use of either beam-intensifying device described is discussed in the paper.

Neurostimulateur multiple à impulsions rectangulaires et sorties isolêes

Abstract The paper describes a multi-channel stimulator delivering the following electrical siǵnals through separate outputs: ( a ) two brief rectangular pulses of variable duration, separated by a chosen interval; ( b ) repeated (tetanizing) pulses of variable frequency and train-duration; ( c ) a d.c. polarizing stimulus of variable duration. A built-in trigger circuit, hand-controlled or self-firing at a chosen frequency, delivers positive pulses driving the sweep of a ccthode-ray oscillograph used in connection with the stimulator. The same pulses trigger the different circuits generating stimulating signals, each through a separate delay unit introducing a measurable time lag. Thus, proper delay adjustment in each channel enables synchronisation with the oscillograph sweep of the various available electrical stimuli, delivered in any desired sequence. A versatile rectangular-wave generator has been designed, and extensively applied to the entire apparatus construction. This basic circuit assumes every stage operation (trigger stage; stimulus delay, frequency, and duration stages); with minor adjustments it is made to work, according to each function, either as a one-shot or as a free-running multivibrator. Exclusive use, in the stimulator design, of similar units greatly simplifies construction and servicing. Moreover, owing to the symmetrical operation of these circuits, the power supply has a constant load and must not be regulated. Each channel of the stimulator is linked to the physiological preparation through a radiofrequency coupling. The pulses from the output stages are the source of plate power for H.F. oscillators, and the radio oscillations produced transmitted to receiver coils. The induced voltages, demodulated and filtered, reflect the original signals from each channel but are electrically isolated.

A simple device for driving the Grass oscilloscope recording camera by electrical signals.

The device described is a simple circuit functioning as a normally open switch controllable by electrical signals. It has several modes of operation, permitting full use of the different capabilities of the C4 camera (single frames, repetitive frames, moving film). Depending on the mode, either short triggering pulses or rectangular gating signals of adjustable duration are needed for driving the circuit. A square wave stimulator, for instance, can be used to deliver the appropriate signals.