Efferent neurons and suspected interneurons in S-1 forelimb representation of the awake rabbit: receptive fields and axonal properties

1990 ◽  
Vol 63 (6) ◽  
pp. 1477-1498 ◽  
Author(s):  
H. A. Swadlow
Keyword(s):  
Receptive Field ◽  
Receptive Fields ◽  
Sensory Stimulation ◽  
Spontaneous Firing ◽  
Firing Rates ◽  
Axonal Conduction ◽  
Receptive Field Properties ◽  
Conduction Velocities ◽  
Efferent Neurons ◽  
Stimulation Of

1. Receptive-field properties of antidromically identified efferent neurons within the cutaneous forelimb representation of primary somatosensory cortex (S-1) were examined in fully awake rabbits. Efferent neurons studied included callosal neurons (CC neurons, n = 52), ipsilateral corticocortical neurons (C-IC neurons, n = 48) that project to or beyond the second somatosensory cortical area (S-2), and corticofugal neurons of layer 5 (CF-5 neurons, n = 97) and layer 6 (CF-6 neurons, n = 59) that project to and/or beyond the thalamus. 2. An additional class of neurons was studied that was not activated antidromically from any stimulus site, but which responded synaptically to electrical stimulation of the ventrobasal (VB) thalamus with a burst of three or more spikes at frequencies of 600 to greater than 900 Hz. Most of these neurons also responded synaptically to stimulation of S-2 and the corpus callosum. The action potentials of these neurons were much shorter (mean = 0.45 ms) than those of efferent neurons (mean = 0.95 ms). Such properties have been associated with interneurons found throughout the central nervous system, and these neurons are thereby referred to as suspected interneurons (SINs). 3. CF-5 neurons differed from CC, C-IC, and CF-6 neurons in their spontaneous firing rates, axonal properties, and receptive-field properties. Whereas CF-5 neurons had a mean spontaneous firing rate of 5.5 spikes/s, CC, C-IC, and CF-6 neurons had mean values of less than 1/s. Axonal conduction velocities of CF-5 neurons were much higher (mean = 12.92 m/s) than either CC (mean = 2.15 m/s), C-IC (mean = 1.31 m/s), or CF-6 (mean = 2.53 m/s) neurons. A decrease in antidromic latency (the "supernormal" period) that was dependent on prior impulse activity was seen in the great majority of CC, C-IC, and CF-6 neurons but was either minimal or absent in CF-5 neurons of comparable conduction velocity. A higher proportion of CF-5 neurons (98%) responded to peripheral sensory stimulation than did either CC (75%), C-IC (71%), or CF-6 (51%) neurons. CF-6 and C-IC neurons that did not respond to sensory stimulation had significantly lower axonal conduction velocities and spontaneous firing rates than those that responded to such stimulation. 4. Cutaneous receptive fields were seen in most neurons that could be driven by peripheral stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Efferent neurons and suspected interneurons in motor cortex of the awake rabbit: axonal properties, sensory receptive fields, and subthreshold synaptic inputs

1994 ◽  
Vol 71 (2) ◽  
pp. 437-453 ◽  
Author(s):  
H. A. Swadlow
Keyword(s):  
Motor Cortex ◽  
Receptive Field ◽  
Receptive Fields ◽  
Sensory Stimulation ◽  
Spontaneous Firing ◽  
Firing Rates ◽  
Axonal Conduction ◽  
Conduction Velocities ◽  
Efferent Neurons ◽  
Stimulation Of

1. Properties of antidromically identified efferent neurons within the cortical representation of the vibrissae, sinus hairs, and philtrum were examined in motor cortex of fully awake adult rabbits. Efferent neurons were tested for both receptive field and axonal properties and included callosal (CC) neurons (n = 31), ipsilateral corticocortical (C-IC) neurons (n = 34) that project to primary somatosensory cortex (S-1), and corticofugal neurons of layer 5 (CF-5) (n = 33) and layer 6 (CF-6) (n = 32) that project to and/or beyond the thalamus. Appropriate collision tests demonstrated that substantial numbers of corticocortical efferent neurons project an axon to both the corpus callosum and to ipsilateral S-1. 2. Suspected interneurons (SINs, n = 37) were also studied. These neurons were not activated antidromically from any stimulus site but did respond synaptically to electrical stimulation of the ventrolateral (VL) thalamus and/or S-1 with a burst of three or more spikes at frequencies from 600 to > 900 Hz. All of these neurons also responded synaptically to stimulation of the corpus callosum. The action potentials of these neurons were much shorter in duration (mean = 0.48 ms), than those of efferent neurons (mean = 0.90 ms). 3. CF-5 neurons differed from CC, C-IC, and CF-6 neurons in their spontaneous firing rates, axonal properties, and receptive field properties. Whereas CF-5 neurons had a mean spontaneous firing rate of 4.1 spikes/s, CC, C-IC, and CF-6 neurons all had mean values of < 1 spike/s. Axonal conduction velocities of CF-5 neurons were much higher (mean = 12.76 m/s) than either CC (1.47 m/s), C-IC (0.97 m/s), or CF-6 (mean = 1.96 m/s) neurons. A decrease in antidromic latency (the "supernormal" period) followed a single prior impulse in most CC, C-IC, and CF-6 neurons but was minimal or absent in CF-5 neurons. Although all but two CF-5 neurons responded to peripheral sensory stimulation, many CC (35%), C-IC (59%), or CF-6 (66%) neurons did not. CC, CF-5, and CF-6 neurons that did not respond to sensory stimulation had significantly lower axonal conduction velocities and spontaneous firing rates than those that responded to such stimulation. 4. Sensory receptive fields of neurons in motor cortex were considerably larger than those observed in S-1 but were similar in size to those seen in secondary somatosensory cortex (S-2).(ABSTRACT TRUNCATED AT 400 WORDS)

Efferent neurons and suspected interneurons in second somatosensory cortex of the awake rabbit: receptive fields and axonal properties

1991 ◽  
Vol 66 (4) ◽  
pp. 1392-1409 ◽  
Author(s):  
H. A. Swadlow
Keyword(s):  
Receptive Field ◽  
Corpus Callosum ◽  
Somatosensory Cortex ◽  
Sensory Stimulation ◽  
Spontaneous Firing ◽  
Firing Rates ◽  
Axonal Conduction ◽  
Conduction Velocities ◽  
Efferent Neurons ◽  
Stimulation Of

1. Receptive-field properties of antidromically identified efferent neurons within the representation of vibrissae and sinus hairs above the mouth were examined in secondary somatosensory cortex (S-2) of fully awake adult rabbits. Efferent neurons studied included callosal neurons (CC neurons, n = 88), ipsilateral corticocortical neurons (C-IC neurons, n = 51) that project to primary somatosensory cortex (S-1), and corticofugal neurons of layer 5 (CF-5 neurons, n = 63) and layer 6 (CF-6 neurons, n = 42) that project to and/or beyond the thalamus. Appropriate collision tests demonstrated that substantial numbers of corticocortical efferent neurons (21 of 113 tested) project an axon to both the corpus callosum and to ipsilateral S-1. 2. Suspected interneurons (SINs, n = 62) were also studied. These neurons were not activated antidromically from any stimulus site but did respond synaptically to electrical stimulation of the ventrobasal (VB) thalamus with a burst of three or more spikes at frequencies of 600 to greater than 900 Hz. Most of these neurons also responded synaptically to stimulation of S-1 and the corpus callosum. The action potentials of these neurons were much shorter (mean, 0.49 ms) than those of efferent neurons (mean, 1.01 ms). 3. CF-5 neurons differed from CC, C-IC, and CF-6 neurons in their spontaneous firing rates, axonal properties, and receptive-field properties. Whereas CF-5 neurons had a mean spontaneous firing rate of 5.7 spikes/s, CC, C-IC, and CF-6 neurons all had mean values of less than 1/s. Axonal conduction velocities of CF-5 neurons were much higher (mean, 11.90 m/s) than either CC (mean, 2.63 m/s), C-IC (mean, 0.86 m/s), or CF-6 (mean, 1.73 m/s) neurons. A decrease in antidromic latency (the "supernormal" period), which was dependent on prior impulse activity, was seen in most CC, C-IC, and CF-6 neurons but was minimal or absent in CF-5 neurons of comparable conduction velocity. Although all CF-5 neurons responded to peripheral sensory stimulation, many CC (52%), C-IC (49%), and CF-6 (55%) neurons did not. CC and CF-6 neurons that did not respond to sensory stimulation had significantly lower axonal conduction velocities and spontaneous firing rates than those that responded to such stimulation. Whereas no CC, C-IC, or CF-6 neuron responded synaptically to callosal stimulation, 43% of CF-5 neurons (and 78% of SINs) did so respond. Similar differences in synaptic responsivity to stimulation of S-1 were seen in these populations.(ABSTRACT TRUNCATED AT 400 WORDS)

Efferent neurons and suspected interneurons in binocular visual cortex of the awake rabbit: receptive fields and binocular properties

1988 ◽  
Vol 59 (4) ◽  
pp. 1162-1187 ◽  
Author(s):  
H. A. Swadlow
Keyword(s):  
Receptive Field ◽  
Receptive Fields ◽  
Visual Area ◽  
Orientation Tuning ◽  
Spontaneous Firing ◽  
Firing Rates ◽  
Axonal Conduction ◽  
Conduction Velocities ◽  
Efferent Neurons ◽  
Stimulation Of

1. In fully awake rabbits the stability of the two eyes was monitored and was sufficient to enable receptive-field analysis of antidromically identified efferent neurons and suspected interneurons in the binocular segment of visual area 1. Efferent neurons analyzed included callosal efferent neurons (CC neurons, n = 52), neurons projecting to visual area 2 (CV2 neurons, n = 35), corticotectal neurons (CT neurons, n = 43), and corticogeniculate neurons (CG neurons, n = 51). Six additional neurons projected a branching axon to both the corpus callosum and visual area 2. 2. Most CC and CV2 neurons were found in layer 2-3 and had receptive fields of the simple type. Only two corticocortical neurons with complex receptive fields were found. Orientation tuning ranges of CC and CV2 simple cells were similar and end stopping was prevalent in both CC (62%) and CV2 (45%) neurons. Axonal conduction velocities of CC and CV2 neurons were low (mean = 3.5 and 1.4 m/s, respectively) and visually nonresponsive CC neurons (19%) had conduction velocities that were significantly lower than visually responsive neurons. Spontaneous firing rates of corticocortical neurons were low (mean less than 1 spike/s) and these neurons responded to a lower range of stimulus velocities than did corticofugal neurons. 3. Most CG neurons had simple receptive fields and none had a complex field. Orientation tuning ranges of these neurons were comparable to those of CC and CV2 neurons, but a significantly smaller proportion (12%) were end stopped. Both spontaneous firing rates (mean = less than 1 spike/s) and axonal conduction velocities (mean = 2.4 m/s) of CG neurons were low and, as was found for CC neurons, visually nonresponsive CG neurons (25%) had significantly lower conduction velocities than did visually responsive neurons. 4. CT neurons had receptive fields that were predominantly complex (37%), motion/uniform (28%), or simple (26%). Conduction velocities (mean = 10.9 m/s) and spontaneous firing rates (mean = 7 spikes/s) of CT neurons of all receptive-field types were much higher than those of CC, CV2, and CG neurons. 5. An additional class of neurons was studied that responded synaptically at a short latency to electrical stimulation of the dorsal lateral geniculate nucleus (LGNd) with a burst of three or more spikes at frequencies of 600-900 Hz. These neurons showed a high degree of synaptic convergence, also responding synaptically with a high-frequency burst of spikes to stimulation of both visual area 2 and the corpus callosum.(ABSTRACT TRUNCATED AT 400 WORDS)

Corticogeniculate neurons, corticotectal neurons, and suspected interneurons in visual cortex of awake rabbits: receptive-field properties, axonal properties, and effects of EEG arousal

1987 ◽  
Vol 57 (4) ◽  
pp. 977-1001 ◽  
Author(s):  
H. A. Swadlow ◽  
T. G. Weyand
Keyword(s):  
Electrical Stimulation ◽  
Visual Cortex ◽  
Receptive Field ◽  
Receptive Fields ◽  
Spontaneous Firing ◽  
Visual Responses ◽  
Firing Rates ◽  
Axonal Conduction ◽  
Conduction Velocities ◽  
Stimulation Of

The intrinsic stability of the rabbit eye was exploited to enable receptive-field analysis of antidromically identified corticotectal (CT) neurons (n = 101) and corticogeniculate (CG) neurons (n = 124) in visual area I of awake rabbits. Eye position was monitored to within 1/5 degrees. We also studied the receptive-field properties of neurons synaptically activated via electrical stimulation of the dorsal lateral geniculate nucleus (LGNd). Whereas most CT neurons had either complex (59%) or motion/uniform (15%) receptive fields, we also found CT neurons with simple (9%) and concentric (4%) receptive fields. Most complex CT cells were broadly tuned to both stimulus orientation and velocity, but only 41% of these cells were directionally selective. We could elicit no visual responses from 6% of CT cells, and these cells had significantly lower conduction velocities than visually responsive CT cells. The median spontaneous firing rates for all classes of CT neurons were 4-8 spikes/s. CG neurons had primarily simple (60%) and concentric (9%) receptive fields, and none of these cells had complex receptive fields. CG simple cells were more narrowly tuned to both stimulus orientation and velocity than were complex CT cells, and most (85%) were directionally selective. Axonal conduction velocities of CG neurons (mean = 1.2 m/s) were much lower than those of CT neurons (mean = 6.4 m/s), and CG neurons that were visually unresponsive (23%) had lower axonal conduction velocities than did visually responsive CG neurons. Some visually unresponsive CG neurons (14%) responded with saccadic eye movements. The median spontaneous firing rates for all classes of CG neurons were less than 1 spike/s. All neurons synaptically activated via LGNd stimulation at latencies of less than 2.0 ms had receptive fields that were not orientation selective (89% motion/uniform, 11% concentric), whereas most cells with orientation-selective receptive fields had considerably longer synaptic latencies. Most short-latency motion/uniform neurons responded to electrical stimulation of the LGNd (and visual area II) with a high-frequency burst (500-900 Hz) of three or more spikes. Action potentials of these neurons were of short duration, thresholds of synaptic activation were low, and spontaneous firing rates were the highest seen in rabbit visual cortex. These properties are similar to those reported for interneurons in several regions in mammalian central nervous system. Nonvisual sensory stimuli that resulted in electroencephalographic arousal (hippocampal theta activity) had a profound effect on the visual responses of many visual cortical neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Neural Mechanisms of Spatial Selective Attention in Areas V1, V2, and V4 of Macaque Visual Cortex

1997 ◽  
Vol 77 (1) ◽  
pp. 24-42 ◽  
Author(s):  
Steven J. Luck ◽  
Leonardo Chelazzi ◽  
Steven A. Hillyard ◽  
Robert Desimone
Keyword(s):  
Visual Cortex ◽  
Receptive Field ◽  
Selective Attention ◽  
Receptive Fields ◽  
Simultaneous Presentation ◽  
Neural Mechanisms ◽  
Spontaneous Firing ◽  
Firing Rates ◽  
Behavioral Paradigm ◽  
Sensory Responses

Luck, Steven J., Leonardo Chelazzi, Steven A. Hillyard, and Robert Desimone. Neural mechanisms of spatial selective attention in areas V1, V2, and V4 of macaque visual cortex. J. Neurophysiol. 77: 24–42, 1997. Many neurons in extrastriate visual cortex have large receptive fields, and this may lead to significant computational problems whenever multiple stimuli fall within a single field. Previous studies have suggested that when multiple stimuli fall within a cell's receptive field, they compete for the cell's response in a manner that can be biased in favor of attended stimuli. In the present study we examined this role of attention in areas V1, V2, and V4 of macaque monkeys with the use of a behavioral paradigm in which attention was directed to one of two stimulus locations. When two stimuli were presented simultaneously inside the cell's receptive field (which could be accomplished only in areas V2 and V4), we found that the cell's response was strongly influenced by which of the two stimuli was attended. The size of this attention effect was reduced when the attended and ignored stimuli were presented sequentially rather than simultaneously. In addition, the effects became very weak and inconsistent in these areas when only one of the two stimuli was located inside the receptive field. Attention thus modulated sensory responses primarily when two or more simultaneous stimuli competed for access to a neuron's receptive field. As in areas V2 and V4, attention did not modulate sensory responses in area V1 when only a single stimulus was inside the receptive field. In addition, the small receptive fields in this area precluded the simultaneous presentation of attended and ignored stimuli inside the receptive field, making it impossible to determine whether attention effects would be observed under the conditions that led to consistent attention effects in areas V2 and V4. Spontaneous firing rates in areas V2 and V4 were found to be 30–40% higher when attention was directed inside rather than outside the receptive field, even when no stimulus was present in the receptive field. Spontaneous firing rates also varied according to the particular location within the receptive field that was attended. These shifts in spontaneous activity may reflect a top-down signal that biases responses in favor of stimuli at the attended location.

Neurons in the rat spinal trigeminal complex driven by corneal nociceptors: receptive-field properties and effects of noxious stimulation of the cornea

1993 ◽  
Vol 70 (6) ◽  
pp. 2370-2378 ◽  
Author(s):  
M. A. Pozo ◽  
F. Cervero
Keyword(s):  
Receptive Field ◽  
Receptive Fields ◽  
Noxious Stimulation ◽  
Caudal Part ◽  
Receptive Field Properties ◽  
Electrophysiological Recordings ◽  
Afferent Inputs ◽  
Lateral Area ◽  
Made In ◽  
Stimulation Of

1. A survey of the receptive-field properties of neurons in the spinal trigeminal complex driven by stimulation of corneal afferents has been carried out. The afferent inputs to these neurons from the cornea and from the adjacent skin were studied as well as changes in the excitability of the cells and in the size of their receptive fields after thermal noxious stimulation of the cornea. 2. Single-unit electrophysiological recordings were made in pentobarbitone anesthetized rats from 54 neurons all of which were activated by mechanical stimulation of the ipsilateral cornea. Seventeen of these neurons were activated only by corneal stimulation and the other 37 had an additional cutaneous receptive field in the periorbital skin. Of the 37 neurons with a cutaneous receptive field, 29 were activated exclusively by noxious stimulation of the skin (Class 3) and the remaining 8 were driven by both innocuous and noxious cutaneous stimuli (Class 2). 3. All of the neurons were located in the ventro-lateral area of a region of the spinal trigeminal complex between +0.5 mm and -1.0 mm from the obex. This area corresponds to the most caudal part of subnucleus interpolaris, the transition zone between interpolaris and caudalis and the rostral half of subnucleus caudalis. Most neurons were located in the superficial layers of this part of the spinal trigeminal complex. No differences were observed between the locations of the recording sites of neurons with an exclusive corneal input and those with a corneal and a cutaneous receptive field.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptive-field properties and neuronal connectivity in striate and parastriate cortex of contour-deprived cats

1976 ◽  
Vol 39 (3) ◽  
pp. 613-630 ◽  
Author(s):  
W. Singer ◽  
F. Tretter
Keyword(s):  
Electrical Stimulation ◽  
Receptive Field ◽  
Visual Experience ◽  
Receptive Fields ◽  
Direction Selectivity ◽  
Connectivity Pattern ◽  
Area 18 ◽  
Efferent Connections ◽  
Receptive Field Properties ◽  
Areas 17 And 18

An attempt was made to relate the alterations of cortical receptive fields as they result from binocular visual deprivation to changes in afferent, intrinsic, and efferent connections of the striate and parastriate cortex. The experiments were performed in cats aged at least 1 jr with their eyelids sutured closed from birth.The results of the receptive-field analysis in A17 confirmed the reduction of light-responsive cells, the occasional incongruity of receptive-field properties in the two eyes, and to some extent also the loss of orientation and direction selectivity as reported previously. Other properties common to numerous deprived receptive fields were the lack of sharp inhibitory sidebands and the sometimes exceedingly large size of the receptive fields. Qualitatively as well as quantitatively, similar alterations were observed in area 18. A rather high percentage of cells in both areas had, however, preserved at least some orientation preference, and a few receptive fields had tuning properties comparable to those in normal cats. The ability of area 18 cells in normal cats to respond to much higher stimulus velocities than area 17 cells was not influenced by deprivation.The results obtained with electrical stimulation suggest two main deprivation effects: 1) A marked decrease in the safety factor of retinothalamic and thalamocortical transmission. 2) A clear decrease in efficiency of intracortical inhibition. But the electrical stimulation data also show that none of the basic principles of afferent, intrinsic, and efferent connectivity is lost or changed by deprivation. The conduction velocities in the subcortical afferents and the differentiation of the afferents to areas 17 and 18 into slow- and fast-conducting projection systems remain unaltered. Intrinsic excitatory connections remain functional; this is also true for the disynaptic inhibitory pathways activated preferentially by the fast-conducting thalamocortical projection. The laminar distribution of cells with monosynaptic versus polsynaptic excitatory connections is similar to that in normal cats. Neurons with corticofugal axons remain functionally connected and show the same connectivity pattern as those in normal cats. The nonspecific activation system from the mesencephalic reticular formation also remains functioning both at the thalamic and the cortical level.We conclude from these and several other observations that most, if not all, afferent, intrinsic, and efferent connections of areas 17 and 18 are specified from birth and depend only little on visual experience. This predetermined structural plan, however, allows for some freedom in the domain of orientation tuning, binocular correspondence, and retinotopy which is specified only when visual experience is possible.

Changes in the response properties of neurons in the ventroposterior lateral thalamic nucleus of the raccoon after peripheral deafferentation

1996 ◽  
Vol 75 (6) ◽  
pp. 2441-2450 ◽  
Author(s):  
D. D. Rasmusson
Keyword(s):  
Receptive Field ◽  
Thalamic Nucleus ◽  
Receptive Fields ◽  
Field Size ◽  
Mechanical Stimuli ◽  
Sensory Pathways ◽  
Average Latency ◽  
Somatotopic Map ◽  
Almost All ◽  
Stimulation Of

1. Single neurons in the ventroposterior lateral thalamic nucleus were studied in 10 anesthetized raccoons, 4 of which had undergone amputation of the fourth digit 4-5 mo before recording. Neurons with receptive fields on the glabrous skin of a forepaw digit were examined in response to electrical stimulation of the “on-focus” digit that contained the neuron's receptive field and stimulation of an adjacent, “off-focus” digit. 2. In normal raccoons all neurons responded to on-focus stimulation with an excitation at a short latency (mean 13 ms), whereas only 63% of the neurons responded to off-focus digit stimulation. The off-focus responses had a longer latency (mean 27.2 ms) and a higher threshold than the on-focus responses (800 and 452 microA, respectively). Only 3 of 32 neurons tested with off-focus stimulation had both a latency and a threshold within the range of on-focus values. Inhibition following the excitation was seen in the majority of neurons with both types of stimulation. 3. In the raccoons with digit removal, the region of the thalamus that had lost its major peripheral input (the “deafferented” region) was distinguished from the normal third and fifth digit regions on the basis of the sequence of neuronal receptive fields within a penetration and receptive field size as described previously. 4. Almost all of the neurons in the deafferented region (91%) were excited by stimulation of one or both adjacent digits. The average latency for these responses was shorter (15.3 ms) and the threshold was lower than was the case with off-focus stimulation in control animals. These values were not significantly different from the responses to on-focus stimulation in the animals with digit amputation. 5. These results confirm that reorganization of sensory pathways can be observed at the thalamic level. In addition to the changes in the somatotopic map that have been shown previously with the use of mechanical stimuli, the present paper demonstrates an improvement in several quantitative measures of single-unit responses. Many of these changes suggest that this reorganization could be explained by an increased effectiveness of preexisting, weak connections from the off-focus digits; however, the increase in the proportion of neurons responding to stimulation of adjacent digits may indicate that sprouting of new connections also occurs.

Somatosensory cortical efferent neurons of the awake rabbit: latencies to activation via supra--and subthreshold receptive fields

1996 ◽  
Vol 75 (4) ◽  
pp. 1753-1759 ◽  
Author(s):  
H. A. Swadlow ◽  
T. P. Hicks
Keyword(s):  
High Speed ◽  
Receptive Fields ◽  
Cortical Cell ◽  
Sensory Stimulation ◽  
Inhibitory Response ◽  
Postsynaptic Potentials ◽  
Peripheral Stimulation ◽  
Efferent Neurons ◽  
Excitatory Component ◽  
Peripheral Sensory

1. Latencies to peripheral sensory stimulation were examined in four classes of antidromically identified efferent neurons in the primary somatosensory cortex (S1) of awake rabbits. Both suprathreshold responses (action potentials) and subthreshold responses were examined. Subthreshold responses were examined by monitoring the thresholds of efferent neurons to juxtasomal current pulses (JSCPs) delivered through the recording microelectrode (usually 1-3 microA). Through the use of this method, excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) were manifested as decreases and increases in threshold, respectively. Efferent populations examined included callosal (CC) neurons, ipsilateral corticocortical (C-IC) neurons, and descending corticofugal neurons of layer 5 (CF-5) and layer 6 (CF-6). Very brief air puffs (rise and fall times 0.6 ms) were delivered to the receptor periphery via a high-speed solenoid valve. 2. Whereas all CF-5 neurons had demonstrable suprathreshold excitatory and/or inhibitory responses to peripheral stimulation, most CC, C-IC, and CF-6 neurons did not. CC and CF-6 neurons that yielded no suprathreshold response to the stimulus had lower axonal conduction velocities than those that did respond (P < 0.0001 in both cases). However, subthreshold receptive fields could be demonstrated in many of the otherwise unresponsive CC (81%), C-IC (88%), and CF-6 (43%) neurons. The subthreshold responses usually consisted of an initial excitatory component (a decrease in the threshold to the JSCP) and a subsequent long-duration (> 80 ms) inhibitory component. A few neurons (1 CC, 1 C-IC, and 5 CF-6) showed an initial short latency inhibitory response in the absence of any excitatory component. 3. Some CC and C-IC neurons yielded supra- and/or subthreshold responses to peripheral stimulation at latencies of 6.1-7 ms. All such neurons were found at intermediate cortical depths (thought to correspond to deep layer 2-3 through layer 5). It is argued that such latencies are indicative of monosynaptic activation via thalamic afferents. Very superficial CC and C-IC neurons, and all CF-6 neurons responded to latencies of > 7 ms. All CF-5 neurons responded to latencies of > 8 ms, although many were found at the same depth as the deeper CC and C-IC neurons that responded at monosynaptic latencies. These results indicate that cortical cell type as well as laminar position are important factors that determine the sequence of intracortical neuronal activation after peripheral sensory stimulation.

scholarly journals Cutaneous stimulation evokes long-lasting excitation of spinal interneurons in the turtle

1990 ◽  
Vol 64 (4) ◽  
pp. 1134-1148 ◽  
Author(s):  
S. N. Currie ◽  
P. S. Stein
Keyword(s):  
Spinal Cord ◽  
Receptive Field ◽  
Action Potential ◽  
Receptive Fields ◽  
Neural Mechanisms ◽  
Cutaneous Afferents ◽  
Cutaneous Stimulation ◽  
Single Action ◽  
Single Action Potential ◽  
Stimulation Of

1. We demonstrated multisecond increases in the excitability of the rostral-scratch reflex in the turtle by electrically stimulating the shell at sites within the rostral-scratch receptive field. To examine the cellular mechanisms for these multisecond increases in scratch excitability, we recorded from single cutaneous afferents and sensory interneurons that responded to stimulation of the shell within the rostral-scratch receptive field. A single segment of the midbody spinal cord (D4, the 4th postcervical segment) was isolated in situ by transecting the spinal cord at the segment's anterior and posterior borders. The isolated segment was left attached to its peripheral nerve that innervates part of the rostral-scratch receptive field. A microsuction electrode (4-5 microns ID) was used to record extracellularly from the descending axons of cutaneous afferents and interneurons in the spinal white matter at the posterior end of the D4 segment. 2. The turtle shell is innervated by slowly and rapidly adapting cutaneous afferents. All cutaneous afferents responded to a single electrical stimulus to the shell with a single action potential. Maintained mechanical stimulation applied to the receptive field of some slowly adapting afferents produced several seconds of afterdischarge at stimulus offset. We refer to the cutaneous afferent afterdischarge caused by mechanical stimulation of the shell as "peripheral afterdischarge." 3. Within the D4 spinal segment there were some interneurons that responded to a brief mechanical stimulus within their receptive fields on the shell with short afterdischarge and others that responded with long afterdischarge. Short-afterdischarge interneurons responded to a single electrical pulse to a site in their receptive fields either with a brief train of action potentials or with a single action potential. Long-afterdischarge interneurons responded to a single electrical shell stimulus with up to 30 s of afterdischarge. Long-afterdischarge interneurons also exhibited strong temporal summation in response to a pair of electrical shell stimuli delivered up to several seconds apart. Because all cutaneous afferents responded to an electrical shell stimulus with a single action potential, we conclude that electrically evoked afterdischarge in interneurons was produced by neural mechanisms in the spinal cord; we refer to this type of afterdischarge as "central afterdischarge." 4. These results demonstrate that neural mechanisms for long-lasting excitability changes in response to cutaneous stimulation reside in a single segment of the spinal cord. Cutaneous interneurons with long afterdischarge may serve as cellular loci for multise

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