Journal of Neurophysiology

Harris, D. M.; Dallos, P.

doi: N/Apmid: 479921

Abstract 1. Responses of single fibers were obtained from the auditory nerve of chinchillas. Tone-burst stimuli consisted of a masking stimulus followed by a probe stimulus. Forward masking of a fiber's response is defined as a reduction in the magnitude of the probe-evoked response caused by the addition of the masking stimulus. 2. The recovery of probe response magnitude as a function of the time interval between masker offset and probe onset (delta T) follows an exponential time course. A relationship between the time course or magnitude of poststimulus recovery and the characteristic frequency (CF) of a fiber was not detected. 3. The iso-forward masking contour near the threshold of the masking effect across masker frequencies approximates a fiber's frequency threshold curve (FTC). In other words, forward masking tuning curves are essentially the same as frequency threshold curves. 4. The frequency dependence of forward masking is compared to that of two-tone suppression. Tonal stimuli outside the boundaries of a fiber's FTC that produce two-tone suppression are ineffective forward maskers. Certain frequency/intensity combinations within the FTC may produce both suppression and forward masking and tones within the remaining area of the FTC produce no suppression but are effective forward maskers. 5. Both the time course and the magnitude of the forward masking effect are dependent on the discharge rate evoked by the masker regardless of the masker's absolute level or spectral content. An increase in masker-evoked excitation causes an increase in time constant and a greater reduction in probe response magnitude, rd. The function relating rd to masker level parallels the firing rate/masker level function up to 40 dB above response threshold. 6. A decrease in masker duration from 100 ms leads to a decrease in both rd and the time constant of recovery. There is no significant difference between the 100 and 200 ms duration conditions. 7. Forward masking in single fibers is related to the period of poststimulus recovery of spontaneous activity, a component of a fiber's response pattern to the masker, and this component is tentatively identified as a period of recovery from short-term adaptation. Copyright © 1979 the American Physiological Society

Tazaki, K.; Cooke, I. M.

doi: N/Apmid: 479918

Abstract 1. Tetrodotoxin-resistant, active responses to depolarization of the large cardiac ganglion cells were studied in semi-isolated preparations from the crab, Portunus sanguinolentus. Impulse activity was monitored with extracellular electrodes, simultaneous recordings from two or three large cells were made with intracellular electrodes, and current was passed via a bridge or second intracellular electrode. Preparations were continuously perfused with saline containing 3 x 10(-7) M tetrodotoxin (TTX). 2. About 20 min after introduction of TTX, small-cell impulses and resultant EPSPs in large cells cease, while rhythmic, spontaneous bursting of large cells continues. A pacemaker depolarization between bursts and slow depolarizations underlying the impulse bursts are prominent at this time. Shortly after, spontaneous burst rate slows, and at ca. 25 min, the ganglion becomes electrically quiescent. 3. In the quiescent, TTX-perfused ganglion, injection of depolarizing current into any one of the large cells results in active responses. At current strengths of sufficient intensity and duration (e.g., 20 nA, 20 ms; 5 nA, 500 ms) to depolarize a large cell by ca. 10 mV from resting potential (-53 mV, avg), the graded responses become regenerative and of constant form, provided the stimulation rate is less thna 0.15/s. Such responses have been termed "driver potentials." At more rapid rates, thresholds are increased and responses reduced. 4. Driver potentials of anterior large cells reach peak amplitudes of ca. 20 mV (to -32 mV), have maximum rates of rise of 0.45 V/s and of fall of 0.2 V/s, and a duration of ca. 250 ms. They are followed by hyperpolarizing afterpotentials, a rapidly decaying one (1 s) to -58 mV, followed by a slowly decaying one (7.5 s), -55 mV. Responses of posterior large cells are smaller (16 mV) and slower; the site of active response may be at a distance from the soma. 5. The ability of elicit near-synchronous responses and the identity of amplitude and form of responses among anterior cells and of posterior cells, regardless of which cell receives depolarizing current, indicates that all cells undergo active responses and are stimulated by electrotonic spread of depolarization. 6. The responses involve a conductance increase since memses during a driver potential are much reduced. 7. Depolarization by steady current increases the absolute threshold, decreases the maximum depolarization of the peak, and slows rates of rise and fall. Hyperpolarization increases rates of rise and fall; the absolute value reached by the peak depolarization is unchanged. Hyperpolarization reduces the amplitude of the rapid after-potential relative to the displaced resting potential. 8. Hyperpolarizing current pulses imposed during the rise and peak of driver-potential responses are followed by redevelopment of a complete response. Sufficiently strong hyperpolarization can terminate a response. The current strength needed to terminate a response decreases the later during the response the pulse is given... Copyright © 1979 the American Physiological Society

Schiller, P. H.; Malpeli, J. G.; Schein, S. J.

doi: N/Apmid: 113508

Abstract 1. In order to examine the composition of the geniculostriate input to the superior colliculus, microelectrode recordings were undertaken in this structure of the rhesus monkey while parvocellular or magnocellular laminae of the LGN were reversibly inactivated by injecting minute quantities of lidocaine or MgCl2. 2. The inactivation of magnocellular laminae disrupted the visually driven activity of most cells in the topographically corresponding areas of the colliculus, but not in the superficial retinotectal recipient zone. The inactivation of parvocellular lamina had no effect on the visually driven activity of collicular cells. 3. Several controls were carried out to rule out the possibility of intervention with fibers of passage. We ascertained that the LGN injections did not affect the direct retinotectal pathway by comparing the effect of such inactivation with the effect produced by reversibly cooling visual cortex. These two manipulations yielded similar results: cells in the most superficial regions of the superior colliculus were unaffected by both cortical cooling and by magnocellular injections, while below this region the response of collicular cells was reduced or eliminated in both cases. 4. These results suggest that the indirect visual pathway to the superior colliculus via cortex is activated selectively by the broad-band system, which is relayed through magnocellular LGN. The color-opponent system does not appear to have a corticotectal input sufficient to drive collicular cells independently. Copyright © 1979 the American Physiological Society

Mayeri, E.; Brownell, P.; Branton, W. D.; Simon, S. B.

doi: N/Apmid: 39121

Abstract 1. The bag cells are a group of neuroendocrine cells located in the abdominal ganglion of Aplysia. Accumulated evidence suggests they synthesize and release egg-laying hormone (ELH), a peptide that induces egg laying. In this and the following paper (37) we describe five types of prolonged neural responses in cells of the isolated abdominal ganglion that are produced by stimulated bag cell activity. 2. Prolonged, 5- to 40-min bursts of spike activity were triggered in the normally silent bag cells by local stimulation of one of the bag cell clusters with brief, 0.6- to 2-strains of pulses. This local stimulation minimized the possible effects of the stimulus on other ganglion cells and initiated bag cell activity similar to what has been recorded in intact animals at the initiation of egg laying. 3. Following onset of triggered bag cell activity there is an increase in the amplitude of the bursting pacemaker potential in cell R15 that results in augmented bursting activity in this autoactive cell for up to 3 h. The increase begins in less than 1 min and reaches a maximim after 8--20 min. In two other bursting pacemaker cells, L3 and L6, there is a second type of response, slow inhibition, consisting of a smoothly graded hyperpolarization that begins in 5--14 s, reaches a peak value of 10--20 mV after 30 s, and results in a decrease in the spontaneous spike activity of these cells for 3 h or longer. Both types of responses are contingent on the occurrence of bag cell activity, they depend on prolonged bag cell activity for their normal expression, and they occur in the absence of the fast interactions characteristic of conventional synapses. 4. The results reveal at the level of intracellular recordings prolonged actions of peptide-secreting neuroendocrine cells on the central nervous system. The role of ELH as a putative mediator of one or more of these actions is discussed. Copyright © 1979 the American Physiological Society

Burrows, M.

doi: N/Apmid: 225447

Abstract 1. Graded synaptic interactions are revealed between pairs of nonspiking, local interneurons in the metathroracic ganglion of the locust. These interneurons drive motor neurons innervating muscles of a hindleg. 2. All the interactions found between the interneurons are inhibitory and one way. Synaptic transmission is effected by the graded release of chemical transmitter. Some of the connections are apparently direct. One local interneuron can, therefore, exert a graded control over the membrane potential of another local interneuron. 3. There are inhibitory connections between local interneurons that excite the same motor neuron, between local interneurons that excite antagonistic motor neurons, and between local interneurons that excite motor neurons to muscles moving different joints of a hindleg. 4. Other pairs of interneurons, which are not connected, may be driven by common synaptic inputs. Their outputs add together at the level of the motor neurons to produce effects that are greater than the sum of their individual effects. 5. It is proposed that graded interactions between these local interneurons are an essential element in the generation of motor patterns. Copyright © 1979 the American Physiological Society

Rosen, S. C.; Weiss, K. R.; Kupfermann, I.

doi: N/Apmid: 225449

Abstract 1. The cells of two clusters of small neurons on the ventrocaudal surface of each hemicerebral ganglion of Aplysia were found to exhibit action potentials following tactile stimuli applied to the skin of the head. These neurons appear to be mechanosensory afferents since they possess axons in the nerves innervating the skin and tactile stimulation evokes spikes with no prepotentials, even when the cell bodies are sufficiently hyperpolarized to block some spikes. The mechanosensory afferents may be primary afferents since the sensory response persists after chemical synaptic transmission is blocked by bathing the ganglion and peripheral structures in seawater with a high-Mg2+ and low-Ca2+ content. 2. The mechanosensory afferents are normally silent and are insensitive to photic, thermal, and chemical stimuli. A punctate tactile stimulus applied to a circumscribed region of skin can evoke a burst of spikes. If the stimulus is maintained at a constant forces, the mechanosensory response slowly adapts over a period of seconds. Repeated brief stimuli have little or no effect on spike frequency within a burst. 3. Approximately 81% of the mechanoafferent neurons have a single ipsilateral receptive field. The fields are located on the lips, the anterior tentacles, the dorsal portion of the head, the neck, or the perioral zone. Because many cells have collateral axons in the cerebral connectives, receptive fields elsewhere on the body are a possibility. The highest receptive-field density was associated with the lips. Within each area, receptive fields vary in size and shape. Adjacent fields overlap and larger fields frequently encompass several smaller ones. The features of some fields appear invariant from one animal to the next. A loose form of topographic organization of the mechanoafferent cells was observed. For example, cells located in the medial cluster have lip receptive fields, and most cells in the posterolateral portion of the lateral clusters have tentacle receptive fields. 4. Intracellular stimulation of individual mechanoafferents evokes short and constant-latency EPSPs in putative motor neurons comprising the identified B-cell clusters of the cerebral ganglion. On the basis of several criteria, these EPSPs appear to be several criteria, these EPSPs appear to be chemically mediated and are monosynaptic. 5. Repetitive intracellular stimulation of individual mechanoafferent neurons at low rates results in a gradual decrement in the amplitude of the EPSPs evoked in B cluster neurons. EPSP amplitude can be restored following brief periods of rest, but subsequent stimulation leads to further diminution of the response. 6. A decremented response cannot be restored by strong mechanical stimulation outside the receptive field of the mechanoafferent or by electrical stimulation of the cerebral nerves or connectives... Copyright © 1979 the American Physiological Society

Mayeri, E.; Brownell, P.; Branton, W. D.

doi: N/Apmid: 582605

Abstract 1. A survey of identified cells of the abdominal ganglion of Aplysia was undertaken to determine the extent of bag cell influence in the ganglion. Bursts of bag cell spike activity lasting 5--40 min were elicited by brief, 0.6- to 2 s local stimulation while recording simultaneously from bag cells and other ganglion cells with intracellular electrodes. 2. Slow inhibition occurs in giant cell R2, neurosecretory cells R3-R14, and ink-gland motoneurons, L14A, B, C. The cells remain hyperpolarized for from 15 to 60 min. 3. Transient excitation occurs in mechanoreceptor cells L1 and R1. The cells are strongly depolarized by a slow excitatory potential that lasts for about 10 min and produces spike activity for 3--7 min. 4. Prolonged excitation occurs in some cells of the LB and LC identified cell clusters. The cells are depolarized and spike activity is increased for 3 h or more. 5. A biphasic response occasionally occurs in the command interneuron L10. Inhibition of this cell lasts 10--15 min and is followed by excitation for several hours. Excitation is accompanied by facilitation of synaptic potentials for 40--60 min in cells innervated by L10; the facilitation apparently results from the increase in L10 firing rate. 6. The results indicate that the bag cells have multiple types of actions and affect large numbers of ganglion neurons. All effects have the slowly graded onsets and prolonged durations to be expected of hormonally mediated interactions. 7. Previous studies have indicated that in intact animals the bag cell burst discharge initates a stereotyped egg-laying behavioral pattern that persists for several hours (3, 27). The present data support the hypothesis that certain elements of egg-laying behavior and homeostasis are regulated by a direct action of the bag cells on the central nervous system. Copyright © 1979 the American Physiological Society

Harris, D. A.; Henneman, E.

doi: N/Apmid: 479923

Abstract 1. Single units of the plantaris pool were isolated in ventral root filaments of decerebrate cats and their critical firing levels (CFLs) were determined. Motoneurons of similar size were compared in firing rate (FR) during repetitive stimulation of the plantaris nerve to establish control values and also during added stimulation of various inhibitory nerves (sural, hamstrings, or peroneal). 2. Criteria, based on maximal firing rate, were developed whereby certain pairs of units of similar size could be reliably classified into different types. 3. A second, independent set of criteria was formulated by which the same pair of units could be classified according to their responses to added inhibitory inputs. 4. The ability to distinguish motoneurons consistently by more than one set of criteria reinforces the evidence that different physiological types of units exist within a single motoneuron pool. 5. The findings indicate that different types of cells either receive different densities of input from certain inhibitory sources or that they react differentially to the same amounts of these inputs. Copyright © 1979 the American Physiological Society

Yoshida, S.; Matsuda, Y.

doi: N/Apmid: 479922

Abstract 1. Dorsal root ganglion (DRG) cells were dissected from the adult mouse with their peripheral nerves, and electrophysiological and morphological studies were performed. 2. The peripheral nerves were stimulateradish peroxidase (HRP) was injected into the cell body, and the size of stained cell body and axon, together with the state of myelination, were examined. 4. F-neurons, whose somatic spike is a tetrodotoxin (TTX)-sensitive Na spike, had a large or medium-sized cell body with a myelinated axon, and shoed a fast conduction velocity (A fibers). 5. A-neurons, whose somatic spike is a TTX-resistant Na spike, had a small cell body with an unmyelinated axon, and showed a slow conduction velocity (C fibers). 6. Most H-neurons, whose somatic spike is a TTX-resistant combined Na-Ca spike, proved to have conduction velocity and morphological features similar to A-neurons, whereas the rest of them had features similar to F-neurons. 7. A roughly linear correlation was exhibited between each pair of cell body size, axon diameter, and conduction velcoity. 8. Spike conduction along axons to cell bodies were blocked in all neurons either by an elimination of Na ions from the medium or by an application of TTX. 9. The possibility of transmission of different information by different DRG cells and the developmental differentiation of sensory neurons are discussed. Copyright © 1979 the American Physiological Society

Forssberg, H.

doi: N/Apmid: 479924

Abstract 1. Tactile stimuli to the paw consisting of a stick making contact or an air puff aimed at the dorsum were used to study the phasic influence of locomotor activity on the reflex pattern elicited in extensor and flexor muscles and on the induced compensatory movements in intact cats. The resulting movements and reflex pattern are called "stumbling corrective reactions." 2. The basic reflex pattern and movements of the stumbling corrective reaction are: a) if the stimulus occurs during the swing phase, a short-latency activation of the flexor muscles, which induces an additional flexion of the limb lifting the paw over the obstacle; b) if the stimulus occurs during the support phase, an inhibition followed by an excitation of the extensor muscles, which neither increase nor decrease the extension. However, the stimulus evokes an increased flexor activity in the succeeding swing phase, which induces a brisker flexion. 3. Tactile stimuli to the proximal part of the limb or to the belly in front of the knee evoked the same type of phase-dependent compensatory reactions. Such reactions would presumably be beneficial for the animal to avoid high obstacles that impede movement. 4. A nonnoxious electrical stimulus (typically 2 mA; 1 ms) applied to the dorsum of the paw was used to study systematically the reflex pattern of the stumbling corrective reaction. Two pathways were defined to the knee flexor (semitendinosus). One early burst was evoked at about 10 ms and one later at about 25 ms after the stimulus. Short inhibitory pathways and longer excitatory pathways (20-50 ms) projected to the extensor nuclei. A short-latency (10 ms) excitatory pathway to the ankle extensor (lateral gastrocnemius) was also activated. 5. A painful electrical stimulus applied to the dorsum of the paw evoked large flexor responses during the whole step cycle. During the support phase the locomotion was disrupted as the supporting limb was withdrawn. 6. The results demonstrate that intact cats are able to compensate rapidly for unpredicted perturbations and that the reflex pattern and the induced corrective movements are adapted to the locomotor activity so that functionally meaningful movements are evoked in each phase of the step cycle. 7. The evoked reflexes and their modulation are consistent with those previously found in chronic spinal cats during walking and in paralyzed spinal cats performing "fictive locomotion." It is suggested that the same spinal pathways are used, and that they are controlled by the spinal "locomotor generator." Copyright © 1979 the American Physiological Society