Journal of Neurophysiology

Deadwyler, S. A.; West, J. R.; Cotman, C. W.; Lynch, G. S.

doi: N/Apmid: 162942

Abstract The electrophysiological properties of the commissural projections to the dentate gyrus of the rat were investigated using extracellular field-potential and unit-recording techniques. The following conclusions with respect to those investigations were obtained: 1) The CA3c/CA4 region of the contralateral hippocampus proved to be the most effective site for eliciting the commissural field potentials in the dentate gyrus dorsal and ventral leaves. 2) The location of the short-latency negative field potential in the molecular layer of the dentate gyrus was restricted to a region 50-100 mum distal to the granule cell layers corresponding to the inner one-third of the granule cell dendrites. 3) The negative field potential proved to satisfy a number of criteria for the extracellular representation of the summed EPSPs of synchronously activated granule cells. 4) The excitatory nature of the commissural projections to the dentate was confirmed by the short-latency driving of units recorded from the granule cell layers. 5) A comparison of both commissural and entorhinal cortical stimulation procedures showed the field potentials elicited by the different convergent anatomical systems to be localized within different regions of the dentate molecular layer. 6) The distribution of commissural potentials along the septotemporal axis of the dentate gyrus indicated that stimulation sites homotopic to the recording electrode in the contralateral CA3c/CA4 region were the most effective in eliciting these potentials. 7) These findings were discussed with reference to the mode of activation of the dentate granule cells by the commissural system with specific comparison to the larger and apparently more powerful projections from the entorhinal cortex. Copyright © 1975 the American Physiological Society

Knighton, R. W.

doi: N/Apmid: 1078578

Abstract 1. To show conclusively that the electrically evoked retinal response (EERG) is in fact an electrically evoked component of the usual ERG, it is necessary to show that the two responses have the same intraretinal pattern of current generators. A method for determining when two responses have the same origin has been developed. This method utilizes measurements from a single microelectrode penetrating the retina. 2. The method was sensitive enough to detect differences in the origins of two responses when they were present. 3. The EERG had the same intraretinal origin as the PII component of the ERG, and thus is the PII component evoked by electricity rather than by light. 4. The hypothesis that electrical stimuli act on the synaptic terminals of the photoreceptor cells predicts that electrical current will evoke components of the ERG. The fact that the EERG is an electrically evoked component of the ERG fulfills that prediction. Copyright © 1975 the American Physiological Society

Foreman, R. D.; Applebaum, A. E.; Beall, J. E.; Trevino, D. L.; Willis, W. D.

doi: N/Apmid: 162940

Abstract The responses of spinothalamic tract neurons were studied by extra- and intracellular recordings from the lumbosacral spinal cord in anesthetized rhesus monkeys (Macaca mulatta). The neurons were identified by antidromic activation from the contralateral diencephalon. They were then classified by the mildest form of mechanical stimulation applied to the ipsilateral hindlimb. The effects of electrical stimulation of the nerve(s) supplying the receptive field were investigated. Graded electrical stimulation revealed that the threshold responses of spinothalamic tract neurons excited by weak mechanical stimuli occurred when the largest afferent fibers were activated. On the other hand, neurons that required intense mechanical stimulation for their excitation tended to have higher thresholds to electrical stimulation. Some spinothalamic tract cells were shown to receive monosynaptic excitatory connections from peripheral nerve fibers, although polysynaptic connections may generally be more important. An input from unmyelinated afferent fibers was demonstrated. It is concluded the primate spinothalamic tract neurons receive a rich convergent input from a variety of cutaneous receptors. The experiments provide some evidence for the most likely types of receptors. Copyright © 1975 the American Physiological Society

Knighton, R. W.

doi: N/Apmid: 1078579

Abstract 1. Transretinal direct current modifies the amplitude and waveform of the frog's electroretinogram (ERG). Outward current (that flowing from vitreous to sclera) depresses the ERG while inward current enhances it. Outward current causes an apparent reversal of the polarity of the positive off-response (d-wave) of the ERG. 2. A true reversal does not actually occur. Rather, the outward current unmasks a negative off-response by depressing the positive off-response. 3. The positive off-response and the b-wave can be completely abolished by strong outward current, but cannot be reversed. 4. Treatment with ammonia abolishes the negative off-response, leaving a positive off-response which is affected by current in exactly the same way as the normal positive off-response. 5. Two possible mechanisms by which the current could be affecting the amplitude of the positive off-response would require that its amplitude be reversed for strong outward current. The absence of such reversal rejects these mechanisms. Copyright © 1975 the American Physiological Society

Pearson, K. G.; Fourtner, C. R.

doi: N/Apmid: 162945

Abstract Intracellular recordings were made from the neurites of interneurons and motoneurons in the metathoracic ganglion of the cockroach, Periplaneta americana. Many neurons were penetrated which failed to produce action potentials on the application of large depolarizing currents. Nevertheless, some of them strongly excited and/or inhibited slow motoneurons innervating leg musculature, even with weak depolariziing musculature, even with weak depolarizing currents. Cobalt-sulfide-straining of these nonspiking neurons showed them to be interneurons with their neurites contained entirely within the metathoracic ganglion. Two further characteristics of these interneurons were rapid spontaneous fluctuations in membrane potential and a low resting membrane potential. One nonspiking neuron, interneuron I, when depolarized caused a strong excitation of the set of slow levator motoneurons which discharge in bursts during stepping movements of the metathoracic leg. During rhythmic leg movements the membrane potential of interneuron I oscillated with the depolarizing phases occurring at the same time as bursts of activity in the levator motorneurons. No spiking or any other nonspiking neuron was penetrated which could excite these levator motoneurons. From all these observations we conclude that oscillations in the membrane potential of interneuron I are entirely responsible for producing the levator bursts, and thus for producing stepping movements in a walking animal. During rhythmic leg movements, bursts of activity in levator and depressor motoneurons are initiated by slow graded depolarizations. The similarity of the synaptic activity in these two types of motoneurons suggests that burst activity in the depressor motoneurons is also produced by rhythmic activity in nonspiking interneurons. The fact that no spiking neuron was found to excite the depressor motoneurons supports this conclusion. Interneuron I is also an element of the rhythm-generating system, since short depolarizing pulses applied to it during rhythmic activity could reset the thythm. Long-duration current pulses applied to interneuron I in a quiescent animal did not produce rhythmic activity. This observation, together with the finding that during rhythmic activity the slow depolarizations in interneuron I are usually terminated by IPSPs, suggests that interneuron I alone does not generate the rhythm. No spiking interneurons have yet been enccountered which influence the activity in levator motoneurons. Thus, we conclude that the rhythm is generated in a network of nonspiking interneurons. The cellular mechanisms for generating the oscillations in this network are unknown. Continued. Copyright © 1975 the American Physiological Society

Shibata, M.; Bures, J.

doi: N/Apmid: 1110377

Abstract Reverberation of cortical spreading depression (CSD) around a circular obstacle (thermocoagulation lesion) in the frontal cortex of anesthetized rats was elicited by appropriately timed and spaced applications of KCl. The probability of continued reverberation was increased by a pyrrolopyrimidine drug BW 58-271 (10 mg/kg) from 0.93 to 0.98. Three methods of reverberation arrest were tested: a) CSD propagation was blocked by an interfering CSD wave which was initiated in the rear of the reverberating wave, passing through a narrow segment of the circular pathway, and collided with the reverberating wave on the opposite side of the obstacle; b) CSD propagation through a part of the circular pathway was blocked by a 10-min application of 10% MgCl2 on the exposed cortical surface; c) 1-min asphyxia stopped RCSD by increasing the overall refractoriness of cortical tissue. Least reliable was the interference method which stopped reverberation, even with optimum timing, only in 42% of the trials. The magnesium blockade was reliable but slow, the reverberation stopping only 30 min after MgCl2 application. Asphyxia evoked in any phase of the reverberation cycle stopped RCSD reliably and immediately. The results obtained with the interference method confirm the predictions of the mathematical model of impulse reverberation in sheets of excitable tissue. Anoxia seems best suited for practical control of CSD reverberation in functional decortication studies. Copyright © 1975 the American Physiological Society

Knighton, R. W.

doi: N/Apmid: 1078577

Abstract 1. Brief pulses of electrical current passed through the frog's eye cup from sclera to vitreous (inward current) evoked large, vitreous positive slow potentials of retinal origin. Brief pulses of outward current evoke no response. 2. This electrically evoked retinal response (EERG) increased sharply in amplitude as the strength of the stimulus was increased. 3. Strength-duration curves showed that the stimulating pulse was integrated with a time constant ranging from 14 to 36 ms. The time constant was a function of the amplitude chosen as a criterion. 4. The EERG was abolished by chemical agents which abolish the PII component of the ERG (KCl, NH3, aspartate). 5. The waveform of the EERG returned to the base line with exactly the same time course as the PII component of the ERG, both when the PII was evoked by flashes of light and when it was evoked by flashes of darkness. 6. These results can be explained in terms of the hypothesis that electrical stimuli act on the synaptic terminals of the photoreceptor cells. Copyright © 1975 the American Physiological Society

Naka, K.; Garraway, N. R.

doi: N/Apmid: 45934

Abstract The morphology of the catfish horizontal cells is comparable to that in other fish retinas. The external horizontal cells contact cone receptors and are stellate in shape; the intermediate horizontal cells are even more so and contact rod receptors. The internal horizontal cells constitute the most proximal layer of the inner nuclear layer and may possibly be, in reality, extended processes from the other two horizontal cell types. Bipolar cells resemble those in other teleost retinas: the size and shape of their dendritic tree encompass a continuous spectrum ranging from what is known as the small to the large bipolar cells. The accepted definition of amacrine cells is sufficiently vague to justify our originating a more descriptive and less inferential name for the (axonless) neurons in the inner nuclear layer which radiate processes throughout the inner synaptic layer. These starbust and spaghetti cells vary considerably in the character and extent of their dendritic spread, but correlates exist in other vertebrate retinas. Ganglion cells are found not only in the classical ganglion layer but displaced into the inner nuclear layer as well. Several types can be distinguished on the basis of cell geometry and by the properties of their dendritic tree. Not all of the categorization corresponds with previous descriptions; our findings suggest that some reorganization may be necessary in the accepted classification of cells in the proximal areas of the vertebrate retina. A subtle yet remarkable pattern underlies the entire structure of the catfish retina; there exists a definite gradient of size within a particular class of cells, and of configuration among the subclasses of a specific cell type. It remains to be seen if these morphological spectra bear any functional consequences. The fact that the structure of the catfish retina most closely resembles those of other phylogenetically ancient animals, such as the skate and the dogfish shark, testifies to its primitive organization; morphological and functional mechanisms discernible in this simple system may, therefore, be applicable to the retinas of higher ordered vertebrates. Copyright © 1975 the American Physiological Society

Abrahams, V. C.; Rose, P. K.

doi: N/Apmid: 162939

Abstract Unit recordings were made in the superior colliculus of cats anesthetized with chloralose and with Pentothal. Electrical stimulation of extraocular muscle afferents and neck muscle afferents excited more units in the superior colliculus than did a variety of moving and stationary visual stimuli. Units responding to neck muscle afferent stimulation fell into three populations; one population firing with a short latency and following stimulus presentation up to 1/s, a second population with a long latency and following stimulus presentation at frequencies lower than 15/min, and a third population exhibiting paired firing. The latencies and firing patterns of the third population combined the characteristics of each of the first two patterns. It is suggested that these characteristics of unit discharges stem from the existence of two pathways from neck muscle afferents to the superior colliculus. The projection is predominantly bilateral. Units responding to neck muscle afferent stimulation are distributed throughout the superior colliculus on the basis of their latencies. Long-latency responses predominate in the superficial layers of the superior colliculus and short-latency responses, while more common in the intermediate and deep layers, predominate in the tegmentum. Extraocular muscle afferent projections to the superior colliculus constitute the single richest projection found in these experiments. While the response patterns and latencies are similar to those of the neck muscle afferents, long-latency responses are the most common and dominate in all collicular regions. Few units in the tegmentum could be excited by extraocular muscle afferents. Both extraocular muscle and neck muscle afferents show considerable convergence with one another and with retinal afferents within the superior colliculus. Cells of origin of the tectospinal tract were identified within the superior colliculus and tegmentum by antidromic excitation from the upper cervical cord. These cells were distributed predominantly within the intermediate and deep layers of the superior colliculus, and sparsely in the superficial layers and tegmentum. Almost 50% of the cells of origin of the tectospinal tract receive a convergent input from extraocular muscle and neck muscle afferents and from the retina. About 30% of the cells were inexcitable to the stimuli employed in these experiments. The significance of these projections is discussed with respect to superior collicular function in the cat and i Copyright © 1975 the American Physiological Society

Luschei, E. S.; Goodwin, G. M.

doi: N/Apmid: 162941

Abstract Monkeys were trained to produce a low, steady biting force for 0.5-2.5 s, and then a rapid forceful bite in response to a visual stimulus. After large bilateral lesions of the precentral face area, monkeys emitted repetitive forceful bites on the apparatus, but could not perform the force-holding task. They eventually relearned the task, but the force exerted was never as steady as it was prelesion, and often oscillated at about 2 and/or 5-6 Hz. After retraining, two animals with large bilateral lesions of the face area produced median RT responses equal to or only slightly longer than their prelesion performance, indicating that neural pathways not involving the precentral cortex can mediate quick visual RT responses. The variability of RTs was permanently increased, probably as a result of the persistent unsteadiness of the force-holding response. Incomplete bilateral lesions of the precentral face area, a complete unilateral lesion of that area, and bilateral lesions adjacent regions of cortex produced either mild, transient difficulties with the biting taks, or no problems at all. The results indicate that the precentral cortex has a role in the control of voluntary jaw movements. Lesions caused difficulty in controlling, but not producing, closing jaw movements, thereby suggesting that this role is predominantly to inhibit jaw-closing motoneurons or the systems that excite them. Electrical stimulation studies of the face area of the precentral cortex of the unanesthetized monkey point to the same conclusion. Copyright © 1975 the American Physiological Society