Temporal Modulation of Spatial Borders in Rat Barrel CortexSheth, Bhavin R.; Moore, Christopher I.; Sur, Mriganka
doi: N/Apmid: 9425214
Abstract Sheth, Bhavin R., Christopher I. Moore, and Mriganka Sur. Temporal modulation of spatial borders in rat barrel cortex. J. Neurophysiol . 79: 464–470, 1998. We examined the effects of varying vibrissa stimulation frequency on intrinsic signal and neuronal responses in rat barrel cortex. Optical imaging of intrinsic signals demonstrated that the region of cortex activated by deflection of a single vibrissa at 1 Hz is more diffuse and more widespread than the territory activated at 5 or 10 Hz. With the use of two different paradigms, constant time of stimulation and constant number of vibrissa deflections, we showed that the optically imaged spread of activity is more discrete at higher stimulation frequencies. We combined optical imaging with multiple electrode recording and confirmed that the neuronal response to individual vibrissa stimulation at the optically imaged center of activity is greater than the response away from the imaged center. Consistent with the imaging data, these recordings also showed no response to a second vibrissa deflection at 5 Hz at a peripheral recording site, though there was a significant response to a second vibrissa deflection at 1 Hz at the same peripheral site. These findings demonstrate that vibrissa stimulation at higher frequencies leads to more focused physiological responses in cortex. Thus the spread of activation in rat barrel cortex is modulated in a dynamic fashion by the frequency of vibrissa stimulation. Footnotes Address for reprint requests: M. Sur, Dept. of Brain and Cognitive Sciences, MIT, E25-235, Cambridge, MA 02139. Copyright © 1998 the American Physiological Society
Dopaminergic Modulation of NMDA-Induced Whole Cell Currents in Neostriatal Neurons in Slices: Contribution of Calcium ConductancesCepeda, Carlos; Colwell, Christopher S.; Itri, Jason N.; Chandler, Scott H.; Levine, Michael S.
doi: N/Apmid: 9425179
Abstract Cepeda, Carlos, Christopher S. Colwell, Jason N. Itri, Scott H. Chandler, and Michael S. Levine. Dopaminergic modulation of NMDA-induced whole cell currents in neostriatal neurons in slices: contribution of calcium conductances. J. Neurophysiol. 79: 82–94, 1998. The present experiments were designed to examine dopamine (DA) modulation of whole cell currents mediated by activation of N -methyl- d -aspartate (NMDA) receptors in visualized neostriatal neurons in slices. First, we assessed the ability of DA, D 1 and D 2 receptor agonists to modulate membrane currents induced by activation of NMDA receptors. The results of these experiments demonstrated that DA potentiated NMDA-induced currents in medium-sized neostriatal neurons. Potentiation of NMDA currents occurred at three different holding potentials, although it was more pronounced at −30 mV. It was mediated by D 1 receptors, because it was mimicked by D 1 agonists and blocked by exposure to a D 1 antagonist. Activation of D 2 receptors produced inconsistent effects on NMDA-induced membrane currents. Either decreases, increases, or no effects on NMDA currents occurred. Second, we examined the contributions of intrinsic, voltage-dependent conductances to DA potentiation of NMDA currents. Blockade of K + conductances did not prevent DA enhancement of NMDA currents. However, voltage-activated Ca 2+ conductances provided a major contribution to DA modulation. The dihydropyridine L-type Ca 2+ channel blockers, nifedipine, and methoxyverapamil (D−600), markedly reduced but did not totally eliminate the ability of DA to modulate NMDA currents. The D 1 receptor agonist SKF 38393 also enhanced Ba 2+ currents in neostriatal neurons. Together, these findings provide evidence for a complex interplay between DA, NMDA receptor activation and dihydropyridine-sensitive Ca 2+ conductances in controlling responsiveness of neostriatal medium-sized neurons. Footnotes Address for reprint requests: M. S. Levine, Mental Retardation Research Center, 760 Westwood Plaza, University of California, Los Angeles, CA 90024-1759.
PET Study of Pointing With Visual Feedback of Moving HandsInoue, Kentaro; Kawashima, Ryuta; Satoh, Kazunori; Kinomura, Shigeo; Goto, Ryoi; Koyama, Masamichi; Sugiura, Motoaki; Ito, Masatoshi; Fukuda, Hiroshi
doi: N/Apmid: 9425182
Abstract Inoue, Kentaro, Ryuta Kawashima, Kazunori Satoh, Shigeo Kinomura, Ryoi Goto, Masamichi Koyama, Motoaki Sugiura, Masatoshi Ito, and Hiroshi Fukuda. PET study of pointing with visual feedback of moving hands. J. Neurophysiol. 79: 117–125, 1998. This study was conducted to determine where in the human brain visual feedback of hand movements is processed to allow accurate pointing. Regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) and H 2 15 O in nine normal volunteers while performing one control and two reaching tasks. In all tasks, visual stimuli were presented on a head mounted display (HMD). A target board was placed in front of the subjects bearing six red light-emitting diodes (LEDs) aligned on a circle with a green LED at its center. The center green LED and one of the six red LEDs, randomly selected, were repeatedly switched on and off, alternatively. In the control task, subjects were instructed to gaze at the lit LED. In the two reaching tasks, the reaching with visual feedback (RwithF) task and the reaching without visual feedback (RwithoutF) task, they had to point to the lit red LED with their right index fingers. In the RwithF task, their right hands were visible on the HMD before touching the target, whereas in the RwithoutF task, they were not visible. For each subject, subtraction images of each reaching task minus the control and the RwithF task minus the RwithoutF task were calculated after transformation of PET images into the standard brain shape with an adjustable computerized brain atlas. These subtraction rCBF images were then averaged among the subjects, and significant changes of rCBF were identified. Significant increases in rCBF not only in the RwithF task minus control image but also in the RwithF task minus the RwithoutF task image were observed in the supramarginal cortex, the premotor cortex and the posterior cingulate cortex of the left hemisphere, the caudate nucleus and the thalamus of the right hemisphere, and the right cerebellum and vermis. These results indicate that the supramarginal cortex, the premotor cortex, and the posterior cingulate cortex of the left hemisphere and the cerebellum are involved in integrating visual feedback of hand movements and execution of accurate pointing. Footnotes Address for reprint requests: R. Kawashima, Dept. of Nuclear Medicine and Radiology, IDAC, Tohoku University, 4-1 Seiryocho, Aobaku, Sendai 980-77, Japan. Copyright © 1998 the American Physiological Society
Interaction of the Two Frontal Eye Fields Before Saccade OnsetSchlag, J.; Dassonville, P.; Schlag-Rey, M.
doi: N/Apmid: 9425177
Abstract Schlag, J., P. Dassonville, and M. Schlag-Rey. Interaction of the two frontal eye fields before saccade onset. J. Neurophysiol. 79: 64–72, 1998. A normal environment often contains many objects of interest that compete to attract our gaze. Nevertheless, instead of initiating a flurry of conflicting signals, central populations of oculomotor neurons always seem to agree on the destination of the next saccade. How is such a consensus achieved? In a unit recording and microstimulation study on trained monkeys, we sought to elucidate the mechanism through which saccade-related cells in the frontal eye fields (FEF) avoid issuing competing commands. Presaccadic neuronal activity was recorded in one FEF while stimulating the contralateral FEF with low-intensity currents that evoked saccades. When an eye-movement cell was isolated, we determined: the movement field of the cell, the cell's response to contralateral FEF microstimulation, the cell's response when the evoked saccade was in the preferred direction of the cell (using the collision technique to deviate appropriately the evoked saccade vector), and the cell's response to a stimulation applied during a saccade in the cell's preferred direction, to reveal a possible inhibitory effect. Complete results were obtained for 71 stimulation-recording pairs of FEF sites. The unit responses observed were distributed as follows: 35% of the cells were unaffected, 37% were inhibited, and 20% excited by contralateral stimulation. These response types depended on the site of contralateral stimulation and did not vary when saccades were redirected by collision. This invariant excitation or inhibition of cells, seemingly due to hardwired connections, depended on the angular difference between their preferred vector and the vector represented by the cells stimulated. By contrast, 8% of the cells were either activated or inhibited depending on the vector of the saccade actually evoked by collision. These results suggest that the consensus between cells of oculomotor structures at the time of saccade initiation is implemented by functional connections such that the cells that command similar movements mutually excite each other while silencing those that would produce conflicting movements. Such a rule would be an effective implementation of a winner-take-all mechanism well suited to prevent conflicts. Footnotes Address reprint requests to J. Schlag. Present address of P. Dassonville: VA Medical Center, Brain Sciences Center (11B), 1 Veterans Dr., Minneapolis, MN 55417. Copyright © 1998 the American Physiological Society
Axon Conduction and Survival in CNS White Matter During Energy Deprivation: A Developmental StudyFern, Robert; Davis, Peter; Waxman, Stephen G.; Ransom, Bruce R.
doi: N/Apmid: 9425180
Abstract Fern, Robert, Peter Davis, Stephen G. Waxman, and Bruce R. Ransom. Axon conduction and survival in CNS white matter during energy deprivation: a developmental study. J. Neurophysiol. 79: 95–105, 1998. We investigated the postnatal development of axon sensitivity to the withdrawal of oxygen, glucose, or the combined withdrawal of oxygen + glucose in the isolated rat optic nerve (a CNS white matter tract). Removal of either oxygen or glucose for 60 min resulted in irreversible injury in optic nerves from adult rats, assessed by loss of the evoked compound action potential (CAP). Optic nerves at ages 45 min caused the selective loss of late CAP components; this was not seen with oxygen deprivation. The amplitude of the early component recovered to 94.8% of control after 60 min of glucose withdrawal, although total CAP area recovered to only 42.3%. Combined oxygen + glucose withdrawal for 60 min produced a greater degree of permanent CAP loss than 60 min of glucose or oxygen withdrawal individually in optic nerves from rats older than P4. Younger than P4 optic nerves showed no permanent loss of function from 60 min of combined oxygen + glucose withdrawal. Unexpectedly, optic nerves from P21–P49 rats recovered significantly less after all three conditions than adult opticnerves (>P50). It is probable that this period of final myelination corresponds to a time of heightened metabolic activity in white matter. The tolerance of CNS white matter to energy deprivation can be categorized into four stages that are correlated with specific developmental features: premyelination (P0–P4), highly tolerant to anoxia, aglycemia and combined anoxia/aglycemia; early myelination (P5–P20), partially tolerant of anoxia and aglycemia but not to combined anoxia/aglycemia; late myelination (P21–P49), very low tolerance of anoxia, aglycemia and combined anoxia/aglycemia; and mature (>P50), low tolerance of anoxia, aglycemia and combined anoxia/aglycemia. The relative resistance of optic nerve function to glucose withdrawal in the presence of oxygen, compared with glucose withdrawal in the absence of oxygen, is presumably due to the presence of oxygen-dependent energy reserves such as astrocytic glycogen, amino acids. and phospholipids. Footnotes Address for reprint requests: R. Fern, Dept. of Neurology, University of Washington, Box 356465, Seattle, WA 98195.
Interdependence of Spatial Properties and Projection Patterns of Medial Vestibulospinal Tract Neurons in the CatPerlmutter, S. I.; Iwamoto, Y.; Baker, J. F.; Peterson, B. W.
doi: N/Apmid: 9425197
Abstract Perlmutter, S. I., Y. Iwamoto, J. F. Baker, and B. W. Peterson. Interdependence of spatial properties and projection patterns of medial vestibulospinal tract neurons in the cat. J. Neurophysiol. 79: 270–284, 1998. Activity of vestibular nucleus neurons with axons in the ipsi- or contralateral medial vestibulospinal tract was studied in decerebrate cats during sinusoidal, whole-body rotations in many planes in three-dimensional space. Antidromic activation of axon collaterals distinguished between neurons projecting only to neck segments from those with collaterals to C 6 and/or oculomotor nucleus. Secondary neurons were identified by monosynaptic activation after labyrinth stimulation. A three-dimensional maximum activation direction vector (MAD) summarized the spatial properties of 151 of 169 neurons. The majority of secondary neurons (71%) terminated above the C 6 segment. Of these, 43% had ascending collaterals to the oculomotor nucleus (VOC neurons), and 57% did not (VC neurons). The majority of VOC and VC neurons projected contralaterally and ipsilaterally, respectively. Most C 6 -projecting neurons could not be activated from oculomotor nucleus (V-C 6 neurons) and projected primarily ipsilaterally. All VO-C 6 neurons projected contralaterally. The distributions of MADs for secondary neurons with different projection patterns were different. Most VOC (84%) and contralaterally projecting VC (91%) neurons had MADs close to the activation vector of a semicircular canal pair, compared with 54% of ipsilaterally projecting VC (i-VC) and 39% of V-C 6 neurons. Many i-VC (44%) and V-C 6 (48%) neurons had responses suggesting convergent input from horizontal and vertical canal pairs. Horizontal and vertical gains were comparable for some, making it difficult to assign a primary canal input. MADs consistent with vertical-vertical canal pair convergence were less common. Type II yaw or type II roll responses were seen for 22% of the i-VC neurons, 68% of the V-C 6 neurons, and no VOC cells. VO-C 6 neurons had spatial properties between those of VOC and V-C 6 neurons. These results suggest that secondary VOC neurons convey semicircular canal pair signals to both ocular and neck motor centers, perhaps linking eye and head movements. Secondary VC and V-C 6 neurons carry more processed signals, possibly to drive neck and forelimb reflexes more selectively. Two groups of secondary i-VC neurons exhibited vertical-horizontal canal convergence similar to that present on neck muscles. The vertical-vertical canal convergence present on many neck muscles, however, was not present on medial vestibulospinal neurons. Spatial transformations achieved by the vestibulocollic reflex may occur in part on secondary neurons but further combination of canal signals must take place to generate compensatory muscle activity. Footnotes Present address of Y. Iwamoto: Dept. of Physiology, Institute for Basic Medical Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305, Japan. Present address of and address for reprint requests: S. I. Perlmutter, Regional Primate Research Center, University of Washington, Box 357330, Seattle, WA 98195. Copyright © 1998 the American Physiological Society
Two Types of Intrinsic Oscillations in Neurons of the Lateral and Basolateral Nuclei of the AmygdalaPape, Hans-Christian; Paré, Denis; Driesang, Robert B.
doi: N/Apmid: 9425192
Abstract Pape, Hans-Christian, Denis Paré, and Robert B. Driesang. Two types of intrinsic oscillations in neurons of the lateral and basolateral nuclei of the amygdala. J. Neurophysiol. 79: 205–216, 1998. Intracellular recordings in the guinea pig and cat basolateral amygdaloid (BL) complex maintained as slices in vitro revealed that a subpopulation of neurons (79%) in the lateral (AL) and basolateral (ABl) nuclei generated two types of slow oscillations of the membrane potential upon steady depolarization from resting potential. The cells were of a stellate or pyramidal-like shape and possessed spiny dendrites and an axon leaving the local synaptic environment, and thus presumably represented projection neurons. Similar oscillatory activity was observed in projection neurons of the cat AL nucleus recorded in vivo. Oscillatory activity with a low threshold of activation (low-threshold oscillation, LTO) appeared as rhythmic deflections (amplitudes, 2–6 mV) of the membrane potential positive to −60 mV. Fast Fourier transformation (FFT) demonstrated a range of frequencies of LTOs between 0.5 and 9 Hz, with >80% occurring at 1–3.5 Hz and an average at 2.3 ± 1.1 Hz. LTOs were more regular after pharmacological blockade of synaptic transmission and were blocked by tetrodotoxin (TTX). Blockade of LTOs and Na + spikes revealed a second type of oscillatory activity (high-threshold oscillation, HTO) at depolarizations beyond −40 mV, which was capable of triggering high-threshold spikes. HTOs ranged between 1 and 7.5 Hz, with >80% occurring at 2–6 Hz and an average at 5.8 ± 1.1 Hz. HTOs vanished at a steady membrane polarization positive to −20 mV. Current versus voltage relations obtained under voltage-clamp conditions revealed two regions of negative slope conductance at −55 to −40 mV and at around −30 mV, which largely overlapped with the voltage ranges of LTOs and HTOs. TTX abolished the first region of negative slope conductance (−55 to −40 mV) and did not significantly influence the second region of negative slope conductance. Neuronal responses to maintained depolarizing current pulses consisted of an initial high-frequency discharge (up to 100 Hz), the frequency of which depended on the amplitude of the depolarizing current pulse, followed by a progressive decline (“adaptation”) toward a slow-rhythmic firing pattern. The decay in firing frequency followed a double-exponential function, with time constants averaging 57 ± 28 ms and 3.29 ± 1.85 s, and approached steady-state frequencies at 6.3 ± 2.9 Hz ( n = 17). Slow-rhythmic firing remained at this frequency over a wide range of membrane polarization between approximately −50 and −20 mV, although individual electrogenic events changed from Na + spikes and underlying LTOs to high-threshold spikes and underlying HTOs. Rhythmic regular firing was only interrupted at an intermediate range of membrane polarization by the occurrence of spike doublets. In conclusion, the integrative behavior of a class of neurons in the BL complex appears to be largely shaped by the slow-oscillatory properties of the membrane. While LTOs are likely to synchronize synaptic signals near firing threshold, HTOs are a major determinant for the slow steady-state firing patterns during maintained depolarizing influence. These intrinsic oscillatory mechanisms, in turn, can be assumed to promote population activity at this particular frequency, which ranges well within that of the limbic theta (Θ) rhythm and the delta (δ) waves in the electroencephalogram during slow-wave sleep. Footnotes Address for reprint requests: H.-C. Pape, Institut für Physiologie, Medizinische Fakultät, Otto-von-Guericke-Universität, Leipziger Str. 44,D-39120 Magdeburg, Germany.
Binocular Cross-Orientation Suppression in the Cat's Striate CortexWalker, Gary A.; Ohzawa, Izumi; Freeman, Ralph D.
doi: N/Apmid: 9425194
Abstract Walker, Gary A., Izumi Ohzawa, and Ralph D. Freeman. Binocular cross-orientation suppression in the cat's striate cortex. J. Neurophysiol. 79: 227–239, 1998. When a cortical cell is activated by an optimal sinusoidal grating, its response can be attenuated by a superimposed second grating oriented orthogonally to the optimal stimulus. This effect is known as cross-orientation suppression (COS). In previous work, monocular characteristics have been explored and interocular tests have been conducted in an attempt to locate the origin of the suppression. In this study, we have recorded extracellularly from cortical cells to investigate the binocular characteristics of COS. Our hypothesis is that binocular disparity influences the strength of the effect. Our results do not support this supposition. We find that binocular COS is as strong as monocular COS, but disparity changes are of no consequence. We also conducted interocular tests in which the optimal grating and the orthogonal mask were seen by separate eyes. Although most interocular effects were weak, they were present in almost every cell and spanned a wide range of suppression strengths. We also tested the effect of asynchronous presentation of optimal and orthogonal gratings. These temporal offsets did not affect the strength of COS. We conclude that the suppressive mechanism underlying COS is primarily monocular and acts prior to the convergence of the two monocular streams. Footnotes Address for reprint requests: R. D. Freeman, University of California, 360 Minor Hall, Berkeley, CA 94720-2020. 1 Extracellular techniques do not allow us to make a distinction between true suppression and withdrawal of excitation. Therefore, in this paper we use the terms suppression and inhibition interchangeably. 2 In this experiment, monocular suppression refers to the suppression obtained by presenting an orthogonal grating to one eye while providing binocular excitation with an optimal grating. 3 In this section we use “monocular suppression” to describe the condition in which the optimal and masking stimuli are presented to one eye while the other eye views a blank screen (Fig. 1 F ). This should be distinguished from the condition of binocular stimulation with an optimal grating combined with a masking stimulus in one eye (Fig. 1 D ).
Calcium-Activated Potassium Conductances in Retinal Ganglion Cells of the FerretWang, Guo-Yong; Robinson, David W.; Chalupa, Leo M.
doi: N/Apmid: 9425186
Abstract Wang, Guo-Yong, David W. Robinson, and Leo M. Chalupa. Calcium-activated potassium conductances in retinal ganglion cells of the ferret. J. Neurophysiol. 79: 151–158, 1998. Patch-clamp recordings were made from isolated and intact retinal ganglion cells (RGCs) of the ferret to examine the calcium-activated potassium channels expressed by these neurons and to determine their functional role in the generation of spikes and spiking patterns. Single-channel recordings from isolated neurons revealed the presence of two calcium-sensitive potassium channels that had conductances of 118 and 22 pS. The properties of these two channels were shown to be similar to those ascribed to the large-conductance calcium-activated potassium channel (BK Ca ) and small-conductance calcium-activated potassium channel (SK Ca ) channels in other neurons. Whole cell recordings from isolated RGCs showed that apamin and charybdotoxin (CTX), specific blockers of the SK Ca and BK Ca channels, respectively, resulted in a shortening of the time to threshold and a reduction in the hyperpolarization after the spike. Addition of these blockers also resulted in a significant increase in spike frequency over a wide range of maintained depolarizations. Similar effects of apamin and CTX were observed during current-clamp recordings from intact alpha and beta ganglion cells, morphologically identified after Lucifer yellow filling. About 20% of these neurons did not exhibit a sensitivity to either blocker, suggesting the presence of functionally distinct subgroups of alpha and beta RGCs on the basis of their intrinsic membrane properties. The expression of these calcium-activated potassium channels in the majority of alpha and beta cells provides a means by which the activity of these output neurons could be modulated by retinal neurochemicals. Footnotes Address reprint requests to G.-Y. Wang.