Development of somatosensory responsiveness in the basal ganglia in awake catsSchneider, J. S.; Levine, M. S.; Hull, C. D.; Buchwald, N. A.
doi: N/Apmid: 4031980
Abstract Single-unit activity was recorded from the caudate nucleus (CD), globus pallidus, and entopeduncular nucleus (GP-ENTO) in awake, partially restrained kittens. The purpose of this experiment was to assess the ability of developing basal ganglia structures to process natural facial somatosensory information and compare this function to that observed in the adult. Somatosensory responsiveness in the CD and GP-ENTO developed slowly during the first three postnatal months. Somatosensory responsiveness had three major developmental trends in these nuclei: 1) The proportion of neurons responding to facial sensory stimulation increased with age; 2) proportionally, the area of face encompassing a receptive field of a neuron was smaller in adults than in young kittens; 3) qualitatively, adultlike responses to sensory stimulation did not appear until approximately three months of age. Units responsive to facial somatosensory stimulation in kittens under three months of age were very limited in the types of information they received. No specific stimuli parameters were encoded by these neurons. At approximately three months of age, units began to respond to varied stimuli (i.e., indentation of the skin as well as to brushing stimuli) and began to encode specific stimulus parameters such as direction of movement and relative location on the face. Kitten units responsive to skin indentation showed no evidence of encoding stimulus magnitude information. This was also true for the majority of adult basal ganglia neurons tested. The present findings suggest that the functions of the basal ganglia may be altered significantly during development. With increasing age, the basal ganglia may change from primarily a relay area for relatively nonspecific sensory information to an active processor of complex afferent information. Copyright © 1985 the American Physiological Society
Body position with respect to the head or body position in space is coded by lumbar interneuronsSuzuki, I.; Timerick, S. J.; Wilson, V. J.
doi: N/Apmid: 3875695
Abstract In decerebrate cats, we have studied the response of neurons in the L3-L6 segments of the spinal cord to stimulation of neck and vestibular receptors. Neck receptors were stimulated by head rotation in labyrinthectomized cats or by body rotation with the head fixed in labyrinth-intact cats. Vestibular receptors were stimulated by whole-body tilt in the latter preparation. Most neurons were located outside the motoneuron nuclei and were arbitrarily classified as interneurons. Combinations of roll and pitch stimuli at frequencies of 0.1 or 0.05 Hz were used to determine the horizontal component of the polarization vector, i.e., the best direction of tilt, for each neuron. Two types of stimuli were used; rotation of a fixed angle of tilt around the head or body ("wobble," Ref. 22) or sinusoidal stimuli in several planes. Polarization vectors of the responses to neck stimulation were widely distributed; different neurons responded best to roll, pitch, and angles in between. For every neuron, the amplitude of the response decreased as the cosine of the angle between the direction of maximal sensitivity and the plane of the stimulus. The direction of the vector remained stable as the frequency of stimulation was varied. Neurons with different vectors had similar dynamics that resembled those of cervical interneurons (27). Many neurons responded to both neck and vestibular stimulation, although the vestibular response usually had a much lower gain. Neck and vestibular vectors were approximately opposite in direction. We suggest that neck responses originate in receptors, probably spindles, in perivertebral muscles. Each of these muscles presumably is best stretched by a particular direction of pull. It seems likely that convergence from receptors in selected muscles determines the direction of a spinal neuron's vector. Vestibular responses probably are due mainly to activity in otolith afferents. Copyright © 1985 the American Physiological Society
T2-T5 spinothalamic neurons projecting to medial thalamus with viscerosomatic inputAmmons, W. S.; Girardot, M. N.; Foreman, R. D.
doi: N/Apmid: 4031983
Abstract Spinothalamic tract neurons projecting to medial thalamus (M-STT cells), ventral posterior lateral nucleus (VPL) of the thalamus (L-STT cells), or both thalamic regions (LM-STT cells) were studied in 19 monkeys anesthetized with alpha-chloralose. Twenty-seven M-STT cells were antidromically activated from nucleus centralis lateralis, nucleus centrum medianum, or the medial dorsal nucleus. Stimulation of VPL elicited antidromic responses from 22 cells and 13 cells were activated from both VPL and medial thalamus. Antidromic conduction velocities of M-STT cells were significantly slower than those of L-STT or LM-STT cells. M-STT cells were located in laminae I, IV, V, and VII with greater numbers found in the deepest laminae. L-STT cells were located mostly in lamina IV, whereas most LM-STT cells were found in lamina V. Twenty-four of 27 M-STT cells, all L-STT cells, and all LM-STT cells received input from both cardiopulmonary sympathetic and somatic afferent fibers. WDR cells were most common among the L-STT and LM-STT groups, whereas HT cells were the most common class in the M-STT cell group. Excitatory receptive fields of M-STT cells were large, and often bilateral. Receptive fields of L-STT cells were simple and never bilateral. Receptive fields of LM-STT cells could be similar to M-STT or L-STT cells. Thirty-three percent of the M-STT cells, 37% of the L-STT cells, and 62% of the LM-STT cells had inhibitory receptive fields. Inhibition was elicited most often by a noxious pinch of the hindlimbs. Sixteen of 23 (70%) M-STT cells received C-fiber cardiopulmonary sympathetic input in addition to A-delta-fiber input. The other 7 cells received only A-delta-fiber input. Only 45% of the L-STT cells and 38% of the LM-STT cells received both A-delta- and C-fiber inputs. The maximum number of spikes elicited by A-delta-input was related to segmental locations for L-STT cells with greatest responses in T2 and lesser responses in more caudal segments; however, no such trend was apparent for M-STT cells or for responses to C-fiber input for either group. Electrical stimulation of the left thoracic vagus nerve inhibited 7 of 18 M-STT cells, 10 of 16 L-STT cells, and 6 of 12 LM-STT cells. These results are the first description of visceral input to cells projecting to medial thalamus.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1985 the American Physiological Society
Comparison of response properties of cells in the cat's visual cortex at high and low luminance levelsRamoa, A. S.; Freeman, R. D.; Macy, A.
doi: N/Apmid: 4031982
Abstract Receptive-field organization of cells in the cat's striate cortex and lateral geniculate nucleus (LGN) was investigated by using bars of light as stimuli. The aim was to determine if differences occur between conditions of high and low luminance levels. Of 72 cortical cells studied, the receptive fields of 63 were clearly different at high compared with low luminances. Units that gave on-off responses to flashed bars, for example, typically displayed on-only responses at low luminance. By far the most frequent change was that off responses were reduced or absent at low luminance levels. Of 63 cells that showed clear changes, 54 were of this type. This altered receptive-field organization appears to remain for extended periods (we have monitored the steady-state case for up to 2 h). Additional tests allow us to rule out the possible influence of overall changes in response strength and scattered light. To see if similar changes in receptive-field organization are present at the level of the LGN, we recorded from a small number of cells in the LGN (n = 10) and from an additional five afferent fibers in the cortex. In each case, there was a change in center-surround organization between high and low luminance levels similar to that previously reported for retinal ganglion cells. The excitatory responses from the surround for both on-center and off-center cells were absent at low luminance. Taken together, the results suggest that surround responses that can be elicited from ganglion cells and LGN cells make an important contribution to the receptive-field organization of cortical neurons. Changes in receptive-field organization of cortical cells are apparently not accompanied by alterations of other basic response properties. Orientation (7 cells) and spatial frequency (53 cells) selectivity remain relatively unchanged when measured at different luminances. Although optimal spatial frequency is slightly lower at low luminance levels, the low spatial frequency attenuation remains unaltered. Since receptive-field changes between high and low luminance levels suggest that a unit's classification may also vary, we examined simple and complex cell characteristics using sinusoidal gratings (65 cells). Contrary to what we had anticipated, the degree of modulation of responses was relatively independent of luminance, indicating that cell classification does not vary with stimulus luminance. Copyright © 1985 the American Physiological Society
Cervicocollic reflex: its dynamic properties and interaction with vestibular reflexesPeterson, B. W.; Goldberg, J.; Bilotto, G.; Fuller, J. H.
doi: N/Apmid: 3162006
Abstract Electromyographic activity of dorsal neck muscles elicited by sinusoidal rotations of the body and head was studied in decerebrate cats over a wide range of rotational frequencies and amplitudes. Rotation of the body with the head held fixed in space elicited a cervicocollic reflex (CCR) in the biventer cervicis, complexus, obliquus capitis inferior, rectus capitis major, and splenius muscles. As stimulus amplitude increased, CCR amplitude increased first rapidly and then more slowly, displaying two linear incremental sensitivity ranges. In contrast, the vestibulocollic reflex (VCR) elicited by whole body rotation had a minimum stimulus threshold below which no response was observed, whereas the vestibuloocular reflex (VOR) saturated at intermediate stimulus intensities. When stimulus frequency was varied, the CCR exhibited second-order dynamic behavior. At frequencies below 0.5 Hz, muscle EMG activation was in phase with peak platform angular deviation in the direction that stretched the muscle, and the gain measured as the percent modulation of EMG activity per degree of rotation remained constant. As frequency increased to 3-4 Hz, response phase advanced by 120 deg or more and gain increased with a slope approaching 40 dB/decade. The data were well-fitted by second-order transfer functions containing two zeros. Both the dynamic behavior of the CCR and its high sensitivity to small stimuli resemble the properties of muscle spindle primary afferents, suggesting that the latter may provide the major input responsible for the CCR. Dynamic properties and gains of the CCR and VCR were quite similar at frequencies between 0.2 and 3-4 Hz. Transfer functions of both reflexes contained two zeros whose time constants were correlated in a population of 11 cats, suggesting that reflex dynamics may be matched to the mechanical properties of each animal's head-neck system. Interaction of the CCR and VCR was studied under two conditions. When the head was driven by a servomotor while the body remained stationary, EMG activation by the two reflexes added linearly to produce a large response. When the body was rotated with the head allowed to counterrotate about the C1-C2 joint, the two reflexes combined linearly in an antagonistic fashion: the CCR acted to oppose head rotations produced by the VCR, thus preventing the ratio of head counterrotation to body rotation from exceeding 0.5. The data indicate that the CCR and VCR behave approximately linearly, both individually and in combination. Acting together, the two reflexes assist each other in preventing oscillation of the head on a stationary body.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1985 the American Physiological Society
Control of abdominal muscles by brain stem respiratory neurons in the catMiller, A. D.; Ezure, K.; Suzuki, I.
doi: N/Apmid: 3162005
Abstract Control of abdominal musculature by brain stem respiratory neurons was studied in decerebrate unanesthetized cats by determining 1) which brain stem respiratory neurons could be antidromically activated from the lumbar cord, from which the abdominal muscles receive part of their innervation, and 2) if lumbar-projecting respiratory neurons make monosynaptic connections with abdominal motoneurons. A total of 462 respiratory neurons, located between caudal C2 and the retrofacial nucleus (Botzinger complex), were tested for antidromic activation from the upper lumbar cord. Fifty-eight percent of expiratory (E) neurons (70/121) in the caudal ventral respiratory group (VRG) between the obex and rostral C1 were antidromically activated from contralateral L1. Eight of these neurons were activated at low thresholds from lamina VIII and IX in the L1-2 gray matter. One-third (14/41) of the E neurons that projected to L1 could also be activated from L4-5. Almost all antidromic E neurons had an augmenting firing pattern. Ten scattered inspiratory (I) neurons projected to L1 but could not be activated from L4-5. No neurons that fired during both E and I phases (phase-spanning neurons) were antidromically activated from the lumbar cord. In order to test for possible monosynaptic connections between descending E neurons and abdominal motoneurons, cross-correlations were obtained between 27 VRG E neurons, which were antidromically activated from caudal L2 and contralateral L1 and L2 abdominal nerve activity (47 neuron-nerve combinations). Only two neurons showed a correlation with one of the two nerves tested. Although there is a large projection to the lumbar cord from expiratory neurons in the ventral respiratory group caudal to the obex, cross-correlation analyses suggest that strong monosynaptic connections between these neurons and abdominal motoneurons are scarce. Copyright © 1985 the American Physiological Society
Nonspiking local interneuron in the motor pattern generator for the crayfish swimmeretPaul, D. H.; Mulloney, B.
doi: N/Apmid: 2993539
Abstract We describe a type of nonspiking premotor local interneuron (interneuron IA) in the abdominal nervous system of Pacifasticus leniusculus. All of its branches are restricted to one side of the midline. These interneurons are identifiable and occur as bilateral pairs, one neuron on each side of abdominal ganglia 3, 4, and 5. The membrane potential of interneuron IA oscillated in phase with the swimmeret rhythm, a motor pattern generated in each of these ganglia, because the neuron received postsynaptic potentials in phase with the rhythm. Sustained hyperpolarization of an individual interneuron IA initiated generation of the swimmeret rhythm in all the ganglia of a quiescent nervous system. Sustained depolarization stopped the swimmeret rhythm in all the active ganglia of a nervous system that was generating the rhythm. Currents injected into one interneuron reset the rhythm. Comparisons of the shapes of the IA interneurons in different ganglia showed that they are similar to each other and distinct from other local interneurons in these ganglia. Interneuron IA has a large integrative segment and relatively few branches that are largely restricted to the lateral neuropil, to which all other kinds of swimmeret neurons also project. We conclude that this interneuron occurs only once in each hemiganglion in abdominal segments 3, 4, and 5, and that it is identifiable. Furthermore, this interneuron is an essential component of the circuit in each hemiganglion that generates the swimmeret rhythm. The interneuron was dye coupled to a particular identifiable motor neuron and not to any other neurons. The motor neuron was not dye-coupled to any other local interneurons. The ability of this motor neuron to reset the rhythm is attributed to its being electrically coupled to interneuron IA in its ganglion. Copyright © 1985 the American Physiological Society
Synaptic potentials in motoneurons during fictive swimming in spinal Xenopus embryosRoberts, A.; Dale, N.; Evoy, W. H.; Soffe, S. R.
doi: N/Apmid: 2993537
Abstract Embryos spinalized at the 3rd to 6th postotic myotome and immobilized in 10(-4) M tubocurarine can respond to a brief skin stimulus with motor root activity suitable for swimming. Embryos spinalized at the more caudal levels give shorter episodes of fictive swimming. We have previously described the synaptic inputs to motoneurons during fictive swimming in intact embryos (23). In the present paper we look to see if similar synaptic inputs are present in spinal embryos and are therefore spinal in origin. All motoneuron firing during fictive swimming is associated with a tonic depolarization that falls away slowly once firing stops, is increased by hyperpolarizing current, and is reduced by depolarizing current. A slow depolarizing potential evoked by lower levels of skin stimulation has similar properties and rate of fall. In 1-2 mM PDA, an excitatory amino acid antagonist, only a small remnant of the depolarization remains, and motoneuron firing stops. The NMDA antagonist 50 microM APV reduces the depolarization less but also blocks firing. Motoneurons fire one spike per swimming cycle, in phase with nearby motor root discharge. Spikes are preceded by a depolarizing prepotential. This increases with hyperpolarizing current, which can block the spike to reveal an underlying depolarizing potential. In phase with motor root discharge on the opposite side of the body, motoneurons receive a midcycle inhibitory postsynaptic potential, which increases with depolarizing current, decreases with hyperpolarizing current, and is blocked by 10(-6) M strychnine. Strychnine, 5 X 10(-7) M, leads first to broadening of motor root bursts then to loss of the alternating swimming pattern of activity, which is replaced by synchronous bursts on both sides of the body. We conclude that the synaptic inputs to motoneurons during fictive swimming in spinal embryos are very similar in properties and pharmacology to those in intact embryos. These inputs, including the tonic depolarization always associated with motoneuron firing during swimming, must be at least partly spinal in origin. Copyright © 1985 the American Physiological Society
Adaptive response to ocular muscle weakness in human pursuit and saccadic eye movementsOptican, L. M.; Zee, D. S.; Chu, F. C.
doi: N/Apmid: 4031979
Abstract Eye movement deficits caused by ocular muscle weakness vary according to the position of the eye in the orbit and the direction of eye movement. We studied the ability of both the saccadic and pursuit eye-movement systems to compensate for these anisotropic deficits in four patients with ocular muscle weakness. The eye-position dependence of each patient's motor deficit was characterized by plotting the position of the weak eye against that of the normal eye (in various orbital positions) when fusion was prevented, thus giving a static eye-position curve from which relative muscle strength could be inferred. Movements of the weak eye were smaller and slower than those made by the normal eye, so that the weak eye required more time to acquire a visual target. When patients were forced to view monocularly with their weak eye for several days, both the saccadic and pursuit systems showed changes in the movements of the normal eye consistent with an increased central innervation designed to decrease the time it takes to bring the target's image onto the fovea of the weak eye and to keep it there. These adaptive changes varied with eye position and movement direction and compensated for the weak muscle in both its agonistic and antagonistic actions. Saccadic adaptation consisted of a change in the relationship between saccadic amplitude and retinal error (distance between the target's image and the fovea) to compensate for hypometria (undershoot) and a readjustment of the ratio of the phasic (pulse) and tonic (step) components of the saccadic innervation to suppress postsaccadic ocular drift. Pursuit adaptation consisted of an increase in the relationship between eye acceleration and the rate of motion of the image of the target on the retina during the initial phase of tracking as well as an increase in the velocity during tracking of a target moving at a constant velocity. These changes reflect an increase in pursuit innervation that would cause the weak eye's velocity to approach target velocity sooner. The average acceleration of the normal eye during the initial period of tracking (130 ms) increased by as much as threefold. The corresponding maximum smooth eye velocity increased so that, for example, the pursuit response to a 15 degree/s target movement could be over 50 degree/s in the normal eye. Copyright © 1985 the American Physiological Society