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Single shock stimulations have been applied stereotaxically and bilaterally in the region of the caudo-thalamic groove of the cat. These stimulations elicit diphasic potentials in the amygdala. Using combined methods of stimulation and lesion, it has been demonstrated that these electrical responses are due to the excitation of fibers projecting rostrally in the lateral border of the contralateral fimbria and caudally in the homologous part of the homolateral fimbria. A commissural path has been identified in the rostral part of the fimbria-fornix. Analysis of the experimental data has shown that the projection system consists of a discrete bundle of fibers which probably reaches the amygdala directly, in the dorsal part of the basal nucleus. The length of the explored portion of this pathway has been measured. The calculated conduction velocity of this amygdalopetal commissural component of the fimbria is 4.5 m/sec.
1. A cross-sectional study has been performed on 457 normal subjects to determine changes in conduction delays with age in central and peripheral motor and somatosensory pathways to the upper limb. 2. Electromagnetic stimulation was used to investigate central and peripheral conduction in motor pathways from the cortex to biceps brachii and hypothenar muscles in 308 normal human subjects aged from 32 weeks gestation to 55 years. The responses were recorded in the surface electromyogram. 3. Somatosensory potentials evoked by electrical stimulation of the median nerve have been recorded at Erb's point and over the somatosensory cortex in 149 normal subjects aged from 34 weeks gestation to 52 years to determine central and peripheral somatosensory conduction delays. 4. The conduction delays in the central components of both motor and somatosensory pathways rapidly decrease over the first 2 years after birth and thereafter remain constant at adult values. 5. The conduction delays in the peripheral components of both motor and somatosensory pathways also decrease initially but then from the age of 5 years progressively increase in proportion to arm length. 6. The threshold stimulus intensity for evoking muscle responses following electromagnetic stimulation of the cortex is high initially and falls progressively until the age of 16 years. A linear relationship exists between the threshold intensity and height for the height range 70-180 cm. 7. The threshold stimulus intensities for exciting peripheral motor and somatosensory nerves decrease up to the age of 5 years and then reach a plateau. 8. The results support the conclusion, already reported in the literature that peripheral nerves attain maximum value for fibre diameter and conduction velocity at approximately 5 years of age. 9. In contrast, it is concluded that the maximum fibre diameters in both motor and somatosensory central pathways increase in proportion to height, leading to constant central conduction delays with growth.
Calculation on a mathematical model showed that for distortion-free conduction of excitation through a net of excitatory elements (EEs) a system is necessary of optimum correlation of EEs parameters, links between them and of external influences. When these parameters are deviated from their optimum values, excitation is conducted through the net either with attenuation or with intensification (as a result of divergence and convergence of the influences of the previous layer on the following one). The background activity which is above threshold of impulse activity emergence and which is created by common effects on all EEs, prevents the revealing of the input EEs activation at the net output. Near-threshold tonic net activation facilitates excitation conduction through it. Periodic net activity facilitates excitation conduction through it only under optimum correlation of its parameters and the time of its conduction through the net. At disturbance of this condition, excitation conduction through the net is limited.
PSPs, evoked by stimulation of the ipsi- and contralateral horizontal semicircular canals (HSC) in motoneurons of neck muscles, were studied in acute experiments on cats under chloralose-nembutal anesthesia. Ipsilateral stimulation evoked EPSP with latencies ranging from 1.8 to 10.0 ms in 25 motoneurons and IPSP with latencies 1.9-3.9 ms in 10 motoneurons. Calculation of conduction time from ipsilateral canal via Deiters nucleus to neck motoneurons gives reason to consider EPSP with latencies less than 3.8 ms as disynaptic, and those with greater latencies as polysynaptic. Contralateral stimulation evoked EPSP with latencies 1.8-6.0 ms in 19 motoneurons and IPSP with latencies 3.2 and 3.9 ms in 2 motoneurons. Possible pathways conducting these influences and their functional role are discussed.
In this paper, we describe interactions between neural cells and the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) toward development of electrically conductive biomaterials intended for direct, functional contact with electrically active tissues such as the nervous system, heart, and skeletal muscle. We introduce a process for polymerizing PEDOT around living cells and describe a neural cell-templated conducting polymer coating for microelectrodes and a hybrid conducting polymer-live neural cell electrode. We found that neural cells could be exposed to working concentrations (0.01 m) of the EDOT monomer for as long as 72 h while maintaining 80% cell viability. PEDOT could be electrochemically deposited around neurons cultured on electrodes using 0.5-1 microA/mm(2) galvanostatic current. PEDOT polymerized on the electrode and surrounded the cells, covering cell processes. The polymerization was impeded in regions where cells were well adhered to the substrate. The cells could be removed from the PEDOT matrix to generate a neural cell-templated biomimetic conductive substrate with cell-shaped features that were cell attracting. Live cells embedded within the conductive polymer matrix remained viable for at least 120 h following polymerization. Dying cells primarily underwent apoptotic cell death. PEDOT, PEDOT+live neurons, and neuron-templated PEDOT coatings on electrodes significantly enhanced the electrical properties as compared to the bare electrode as indicated by decreased electrical impedance of 1-1.5 orders of magnitude at 0.01-1 kHz and significantly increased charge transfer capacity. PEDOT coatings showed a decrease of the phase angle of the impedance from roughly 80 degrees for the bare electrode to 5-35 degrees at frequencies >0.1 kHz. Equivalent circuit modeling indicated that PEDOT-coated electrodes were best described by R(C(RT)) circuit. We found that an RC parallel circuit must be added to the model for PEDOT+live neuron and neuron-templated PEDOT coatings.
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Two neurons with cell bodies symmetrically located in the abdominal ganglion and giant axons in the left (L1) and right (R1) pleurovisceral connectives of Aplysia californica were examined in vivo and in vitro. Direct stimulation of R1 and L1 in the intact animal does not elicit any observable behavior, suggesting that they are neither motoneurons nor command neurons. These cells respond in vivo to sudden onset mechanical stimulation of widespread regions of the body. R1 and L1 spikes are initiated in at least three different loci: (1) the peripheral axon in the foot, (2) the neuropil of the pleural and/or pedal ganglion, and (3) the neuropil of the abdominal ganglion. Furthermore, R1 and L1 probably have two different mechanisms for spike initiation: (1) sensory (foot), and (2) synaptic (abdominal and/or head ganglia). The different loci for spike initiation account for the bidirectional conduction of R1 and L1 spikes. As sensory (mechanoreceptor) neurons, R1 and L1 have peripheral axons in the ipsilateral posterior pedal nerve, show low threshold responses to stimulation of the ipsilateral posterior foot, they are rapidly adapting their responses do not decrease with repetition, and they are not blocked by high Mg++/low Ca++ solutions. As synaptically-driven neurons, R1 and L1 have widespread bilateral responsiveness, their responses decrease with repetition and their inputs are blocked with high Mg++/low Ca++ solutions. These neurons integrate sensory and synaptic inputs and conduct bidirectionally, however, their output connections must be specified before their behavioral function can be understood.
The escape reflex of the lobster consists of a series of tail flips resulting from alternating activity of the abdominal flexor and extensor muscles. Electromyographic (EMG) activity was recorded from the medial (DEAM) and the lateral (DEAL1) deep abdominal extensor muscles during free swimming. During the escape response, the muscles were active either synchronously or separately, at frequencies of 100-120 Hz. This activity pattern could be generated either by central programming, or by a peripheral mechanism such as frequency-dependent differential conduction block into one of the two branches of the common excitor axon (C.Ex) innervating these muscles. In order to explore the latter possibility in a living animal, we left the DEAM and DEAL1 muscles innervated only by the C.Ex from the tested segment. This was accomplished by manually cutting all other axons in the nerve under visual control. During escape responses in six successfully dissected animals, we found 27 sudden failures of the DEAM responses and only three in DEAL1. The failures were usually preceded by an increase in the delay of the response. These findings strongly suggest that conduction block occurs in the M branch innervating the DEAM under physiological conditions.