Activation of Long Descending Propriospinal Neurons in Cat Spinal Cord

Isolated mammalian spinal cord has been shown capable of generating locomotor activity. Propriospinal systems assumed to coordinate fore- and hindlimb activity are poorly understood. This study characterizes the long descending propriospinal (LDP) neurons in terms of the location of the somas and their peripheral inputs by direct neuronal recording. Anatomical studies using axonal retrograde transport of horseradish peroxidase from the lumbar to the cervical spinal cord as a tracer first described these neurons. Two hundred and thirty-one LDP neurons were identified in electrophysiological experiments. Of these, 123 responded to natural stimulation, and about 50% of the others were activated only by electrical stimulation. The majority of cells were located in laminae VII and VIII in agreement with anatomical data. The most effective stimuli were mechanical stimulation of skin, deep pressure to subcutaneous tissues, and paw joint movement. Bot excitatory and inhibitory responses were observed

How We Look: Studies of Oculomotor-System Neural Connections

The neural connections of the reticular formation (RF) with the vestibular nuclei (8V) and the ascending medial longitudinal fasciculus (MLF) were studied, because many neurons in these structures carry eye-movement and head-movement (vestibular) signals and are only one or two synaptic connections removed from eye motorneurons. We used stimulating electrodes placed in specific brainstem structures and a single-neuron recording microelectrode in anesthetized or decerebrate cats. Connections were determined when the neurons were excited either forwards (orthodromically) or backwards (antidromically) by a shock. Four classes of neurons were studied. One neuronal class in the pontine RF projects axons into the ascending ipsilateral MLF; these axons terminate in the midbrain. Some of these cells receive excitation from both vestibular nerves and are probably involved in the vestibulo-ocular reflex. Another class of RF neurons projects to either the ipsilateral or the contralateral 8V. A third class located amidst lateral-rectus motorneurons in the VIth nucleus projects into the contralateral ascending MLF and excites medial-rectus motorneurons for the contralateral eye so that the two eyes move horizontally in the same direction. A fourth class located in and just beneath the 8V receives monosynaptic input from the vestibular nerve and projects into the contralateral MLF. The possible roles for these neurons in controlling eye movements are discussed. Abbreviations: MLF: medial longitudinal fasciculus; RF: reticular formation; 3: oculomotor (IIIrd cranial nerve) nucleus; 4: trochlear (IVth cranial nerve) nucleus; 6: abducens (VIth cranial nerve) nucleus; 8V: vestibular nuclear complex of the VIIth cranial nerve

Computer Pattern Recognition of Action Potentials

A general method of pattern recognition was applied to the problem of recognizing extracellularly-recorded neuronal action potentials in the presence of noise and other pulses. A PDP1 1/23 performed the calculations. There were four stages: 1.) A bandpass filter attenuated noises; 2.) the data input program digitized the signal every 55 μsec. If the signal exceeded a threshold, 12 samples of the signal and the time were written onto the disk; 3.) the pulse discriminating program recognized an action potential by fitting the 12 points with this function: v(t) = (a + bt + ct² ) exp(-t/Ƭ). For each pulse the computer determined values of the parameters giving the best fit through use of the least squares technique. For acceptance, the total pulse height and the position of the zeroes of v(t) must fall within limits; 4.) occasionally a pulse may be missed or an extra one recorded. The computer displayed the complete pulse train and the operator moved a cursor to insert or delete pulses