bluuebunny/crossref_metadata_2025 huggingface dataset:
Pharmacologic sensitivity of amino acid responses and synaptic activation of in vitro prepyriform neurons
Authors: Hori N. , Auker C. R. , Braitman D. J. , Carpenter D. O.
Published: December 2017

1. In an effort to identify the neurotransmitter released from terminals of the lateral olfactory tract (LOT) we have studied excitatory amino acid agonist and antagonist actions on population and single-unit responses in submerged and perfused slices of rat prepyriform cortex. Previous studies suggest that the transmitter at this synapse is either aspartate (Asp) or glutamate (Glu). 2. The field potential reflecting the monosynaptic activation of pyramidal neurons after stimulation of the LOT was reversibly depressed by bath perfusion of agonists, with an order of potency being kainic acid (KA) greater than N-methyl-DL-aspartate (NMDA) greater than homocysteic acid (HC) greater than Asp = Glu. 3. The synaptic field potential was essentially unaffected by DL-alpha-aminoadipic acid (AA), 2-amino-3-phosphonopropionic acid (APP), and DL-alpha-diaminopimelic acid (DAPA), all presumed to be selective for Asp receptors, and by L-glutamic acid diethyl ester (GDEE), presumed to be specific for Glu receptors. The field potential was depressed or abolished by 2-amino-4-phosphonobutyric acid (APB), an agent known to block Glu responses in insect muscle. 4. The effects of ionophoretic application of agonists were studied on single neurons recorded extracellularly. While there was some variability among neurons in relative agonist potency, all neurons were excited by the five agonists with relative potencies in general similar to those observed for the field potentials. 5. Responses to Glu and Asp were unaffected by AA, GDEE, and APB at concentrations up to 5 X 10(-3) M. Responses to KA, NMDA, and HC were often depressed by APB but were unaffected by the other antagonists. The excitation on stimulation of the LOT was consistently, rapidly, and reversibly blocked by APB. 6. These observations are not consistent with either Glu or Asp being the neurotransmitter of the LOT.
Lateral visual pathway of giant barnacle
Authors: Oland L. A. , French K. A. , Hayashi J. H. , Stuart A. E.
Published: December 2017

1. We have studied the responses to light, conduction down the axons, and anatomical projections of the photoreceptors of the lateral eye in the giant barnacle, Balanus nubilus. By recording intracellularly from ganglion cells that respond to visual input, we have described convergence of the lateral and median visual pathways. 2. Each lateral eye contains three photoreceptor cells, two large and one small. Cobalt filling of single large lateral receptor axons demonstrated that they end in a restricted ovoid bush on the ipsilateral side of the ganglion in approximately the same region in which the median receptors arborize. 3. The lateral receptors have dark resting potentials and responses to light similar to those previously described for the receptors of the median eye. Like the median receptors, the lateral receptors conduct visual signals decrementally, although their axons may be twice as long (14-25 mm). 4. Passing current of either polarity into either of the large receptors produced no detectable voltage change in the other cell. Action potentials elicited in either cell by stimulating it in the presence of tetraethylammonium ion were not detected in the other cell. Light-induced membrane noise in one cell did not correlate with noise in the other. Thus, like the receptors of the median eye, the large receptors of the lateral eye are not electrically coupled. 5. By shadowing each ocellus individually, we have shown that the signals from the median and lateral photoreceptors converge at the level of the second-order cells described for the median pathway. Shadowing the median or a lateral eye gave rise to synergistic responses in second-, third-, and all higher order ganglion cells studied. No cells were found that were driven solely by the lateral eyes. Thus, the lateral and median visual pathways are highly convergent.
Crossed and uncrossed visual topography in dorsal lateral geniculate nucleus of the pigmented rat
Authors: Reese B. E. , Jeffery G.
Published: December 2017

1. The representation of the retinocentric visual field within the dorsal lateral geniculate nucleus (dLGN) was assessed electrophysiologically by recording multicellular responses from anesthetized pigmented rats. Separate experiments examined the representation through either the contralateral or ipsilateral eye along the dorsoventral, mediolateral, and rostrocaudal dimensions of the nucleus. 2. The crossed projection displays an orderly representation of the visual field, mapping eccentricities out to 100 degrees from the optic disk. There is, however, a marked absence of eccentricities greater than 60 degrees representing upper nasal visual space. The uncrossed projection also displays an orderly representation of the visual field but is limited in extent to upper nasal visual space at far eccentricities of 50-90 degrees. 3. The ipsilateral projection, which represents far eccentric upper nasal visual space, occupies a region in the contralateral representation corresponding with upper nasal visual space at reduced eccentricity. It is these two regions that are considered binocularly conjugate: the temporal crescent of each eye with another crescent (the conjugate central crescent) lying between the optic disk and the temporal crescent of the opposite eye. It is suggested that the crossed and uncrossed representations are aligned in the dLGN so that projection lines for discrete regions of the binocular visual field course through the nucleus from rostroventral to caudodorsal. Although the dLGN of the rat lacks the cytoarchitecturally distinct laminae associated with the regions of afferent input from each eye, as is seen in the primate and cat dLGN, the organizing principle of apposing the representation of the visual field through each eye is similar.
Receptive-field properties in reptilian optic tectum: some comparisons with mammals
Authors: Stein B. E. , Gaither N. S.
Published: December 2017

The receptive-field properties of single cells in the optic tectum of Iguana iguana were studied using the same procedures as have been used in this laboratory in studying its mammalian homologue, the superior colliculus. Surprisingly, despite some species-specific characteristics, the range of physiological properties of tectal and superior collicular cells appeared to be strikingly similar. This observation is not consistent with the notion that functional differences between these structures evolved as a consequence of the tremendous elaboration of mammalian neocortex and its involvement in sensory processes. The internal organization of visual tectal receptive fields was observed to be very much like that described in mammals. This included a similar distribution of on-off areas, the presence of both spatial summation and spatial inhibition within the excitatory receptive-field borders, suppressive areas just beyond these borders, and a marked tendency for habituation. In addition, many cells showed distinct directional preferences that were strongly influenced by the velocity of movement through the receptive field. Furthermore, the receptive fields of bimodal and trimodal cells showed topographic correspondences as in mammals, although the sizes of the fields were often large, thereby emphasizing the lack of an exact register between modalities. In contrast to the findings in mammals, however, a preference for stationary over moving stimuli was observed in most neurons, and specializations in iguana tectal cells representing the fovea were noted that have not been described in other species. These foveal specializations include a distinct preference for stationary over moving stimuli, the absence of directional selectivity, and the presence of a majority of cells responding at light onset only. It is suggested that the similarities in the organization and response properties of cells of the optic tectum and superior colliculus reflect the retention of ancestral characteristics through various levels of vertebrate evolution. Furthermore, the subtle species differences in the properties of these cells appear to reflect adaptations to specific ecological pressures rather than general evolutionary trends.
Localization and characteristics of responses in cat medial preoptic region to stimulation of fornix
Authors: Hubbard J. I. , Mills R. G. , Sirett N. E.
Published: December 2017

Field potentials and units were recorded within the boundaries of the cat medial preoptic area (MPO) following stimulation of the fornix. The position of the recording electrode was marked by pressure injection of alcian blue dye. Stimulation of the medial and lateral aspects of the ipsilateral fornix produced a field consisting of four negative waves and a positive wave. The first and second negative waves had a short latency and duration and appeared to be produced by fornix axons in the MPO. The third negative wave had a longer duration and appeared to be generated by the monosynaptic activation of units in the MPO. The fourth negative wave had a long latency and very long duration and appeared to be generated by polysynaptic activation of neurons in the MPO. The positive wave was associated with inhibition of MPO neurons as a result of fornix excitation of inhibitory interneurons. Responses from nerve fibers in the MPO had latencies corresponding to peaks of the first and second peaks of the evoked potential. Monosynaptically evoked responses to ipsilateral fornix stimulation were recorded all over the dorsal two-thirds of the MPO. Units driven from the medial fornix lay in the periventricular nucleus. Units driven from the lateral fornix lay in the medial preoptic nucleus. Units driven from both medial and lateral fornix lay between units driven by the medial fornix medially and the lateral fornix laterally. Units driven polysynaptically from the ipsilateral fornix lay in the medial preoptic nucleus. About one-quarter of such units were also excited by stimulation of the contralateral fornix. Spontaneously discharging units were recorded all over the MPO. The geometric mean frequency was 2.1 +/- 1.7-2.8 Hz; n = 35. Fornix stimulation inhibited spontaneous units in the medial preoptic nucleus for 50-200 ms. Usually inhibition was evoked by lateral fornix stimulation or by medial or lateral fornix stimulation. Spontaneously discharging units in the periventricular nuclei were not inhibited by fornix stimulation. The position of fornix-excited units suggests they might be temperature sensitive and in female animals, play a role in controlling ovulation.
Effects of eye rotation on visually guided behavior
Authors: Presson J. , Moran J. , Gordon B.
Published: December 2017

Visually guided behavior was examined in cats reared with one eye intorted, one eye extorted, or monocular section of the extraocular muscles. Kittens from 2 to 4 mo old jumped from a tower onto a platform in a pan of water. They refused to jump or missed the platform more often when forced to use the rotated eye than when forced to use the unoperated eye. This deficit was eliminated if the non-rotated eye was sutured at the time of eye rotation. Further, when the extraocular muscles were cut but the eye was not rotated, jumping was normal. Acuity was measured using an alley box in which the cats were required to distinguish between horizontal and vertical stripes. No cats were blind when tested with the operated eye. Although not conclusive, the data suggest that the acuity of the rotated eye was slightly lower than that of the unoperated eye. The visual field of the rotated eye was also abnormal. Regardless of the direction of eye rotation, the cats appeared blind in the contralateral and lower visual quadrants. This field deficit was much less severe in animals with extraocular muscle section alone and did not occur in rotation-plus-suture animals. The visual-field deficits in the contralateral field can be explained by assuming that each collicular or cortical region always controls orienting to the same region of the visual field. We are, however, unable to explain the deficits in the lower field in terms of the mapping data from the previous paper (4).
Voltage threshold and excitability among variously sized cat hindlimb motoneurons
Authors: Pinter M. J. , Curtis R. L. , Hosko M. J.
Published: December 2017

Intracellular recording has been performed to examine whether any differences in apparent initial-segment voltage threshold exist between types F and S cat triceps surae motoneurons. Voltage threshold was estimated using orthodromic action potentials initiated by large, monosynaptic excitatory postsynaptic potentials (EPSPs) evoked by dorsal root stimulation. No significant differences in voltage threshold could be detected between types F and S motoneurons. Further, voltage thresholds did not covary with motoneuron input resistance, afterhyperpolarization duration, or the twitch contraction time of functionally isolated muscle units. Significant positive correlations were observed between voltage threshold and the motoneuron resting potential. Utilizing a compartmental neuron model, a theoretical analysis has been performed that examines the influence of specific passive membrane properties on current threshold for action potentials initiated by large, monosynaptic EPSPs. This analysis indicates that total membrane capacitance will be the primary determinant of these thresholds. Further analysis of available data suggests that active membrane properties will play a minimal role in setting these thresholds. Since specific membrane capacitance is likely to be similar among cat motoneurons, it is concluded that only size or surface area-related current threshold differences will exist among these cells for activation with brief currents such as those underlying large EPSPs. For motoneurons thus activated, it is suggested that variations in the excitatory/inhibitory balance or density of synaptic input would be the major mechanisms for producing differential recruitment thresholds among the motoneuron population. Other available evidence is discussed that indicates that factors intrinsic to the motoneurons themselves will contribute to the setting of functional recruitment thresholds for activation with longer duration currents.
Motor pool organization in monosynaptic reflexes: responses in three different muscles
Authors: Clamann H. P. , Ngai A. C. , Kukulka C. G. , Goldberg S. J.
Published: December 2017

Recruitment order of motoneurons was measured as a function of their conduction velocities in the presence of monosynaptic reflexes evoked by dorsal root stimulation. Motoneurons were studied in three cat hindlimb muscles: medial gastrocnemius (MG), plantaris (Pl), and tibialis anterior (TA). A relationship between recruitment order and unit conduction velocity (CV) was clearly seen in all three muscles. The correlation between these two variables was lower than that found in previous studies. A CV-dependent recruitment order was most clearly sen in tibialis anterior motoneuron pool; the relationship was poorest in plantaris. Recruitment order of MG motoneurons was measured and related to their conduction velocities in response to monosynaptic reflexes evoked by L7 + S1 dorsal root stimulation. Recruitment order was then retested in the presence of rostral root stimulation (largely heteronymous) alone and again in the presence of caudal root stimulation (largely homonymous) alone. Changing the composition of the afferent input changed the critical firing levels (rank order) of some motoneurons by as much as 40% and that of others, not at all. Some motoneurons became harder to recruit and others easier; changes in recruitment order were not related to conduction velocities of the units. 1a-afferent inputs are not uniformly distributed to all the motoneurons of a pool. It appears that this nonuniformity is a determining factor in establishing a recruitment order. TA, which receives the most uniformly distributed monosynaptic input, also has the most nearly size-dependent recruitment order. Fractionation of input ca induce additional nonuniformity, and results in recruitment-order changes in some motor units that are independent of their conduction velocity. It is concluded that nonuniformity of afferent inputs, whether present or induced by experiment, can produce large recruitment-order changes among individual motoneurons in a pool and that these individual motoneurons need not share a common property such as conduction velocity or recruitment threshold in response to a control input. Therefore, arguments based on reversals in recruitment order of pairs of motor units or even changes in rank order of individual motor units do not present sufficient evidence for the presence of input specifically directed to motor units sharing a particular property.
Effects of impulse frequency, PTP, and temperature on responses elicited in large populations of motoneurons by impulses in single Ia-fibers
Authors: Luscher H. , Ruenzel P. W. , Henneman E.
Published: December 2017

Excitatory postsynaptic potentials (EPSPs) were evoked in large populations of motoneurons by impulses in single Ia- and group II fibers and recorded from L7 and S1 ventral roots by means of a sucrose-gap technique and spike-triggered averaging, as previously described (33, 34). Factors known to influence conduction at branch points in peripheral nerves or transmission in the Ia projection to motoneurons were studied to determine their effects on these postsynaptic population potentials (PSPPs). When impulse frequency was plotted against the amplitude of these PSPPs, a sequence of low-frequency depression, higher frequency facilitation, and still higher frequency depression was regularly observed. Similar plots of PSPP amplitude versus impulse frequency in a small sample of group II spindle fibers did not reveal any low-frequency depression. Higher frequency facilitation and depression followed the same pattern as that produced by Ia-fibers. Early potentiation of the PSPPs was produced by applying 20 stimulating pulses at 500/s to branches of the medial gastrocnemius nerves containing single Ia-fibers. Single, posttetanic PSPPs were recorded at fixed intervals following each tetanus and averaged. A brief, initial depression followed by a rapidly declining potentiation of PSPPs was regularly observed. When the core temperature was reduced from 41 to 35 degrees C, there was an approximately linear increase in the amplitude of PSPPs. At each temperature a combination of cooling and posttetanic potentiation (PTP) elicited larger PSPPs than cooling alone. The effects of impulse frequency, PTP, and temperature on PSPPs may all be interpreted in terms of their known effects on action potentials or on conduction at branch points in peripheral nerves. Similar effects on transmission or transmission failure in the terminal arborizations of Ia-fibers would account for the influence of these factors on PSPPs. Alternatively, these same three factors might cause similar effects on PSPPs through influences they might exert on the transmitter release mechanism.
Electrophysiology of dentate gyrus granule cells
Authors: Fricke R. A. , Prince D. A.
Published: December 2017

The orthodromic synaptic responses, membrane properties, and responses of dentate gyrus granule cells (DGCs) to several convulsant agents were studied in the in vitro hippocampal slice preparation. Orthodromic stimulation via the perforant pathway (PP) evoked excitatory-inhibitory postsynaptic potentials (EPSP-IPSP) sequences in 27 of 34 DGCs studied. In the majority, only one action potential could be evoked by supramaximal orthodromic stimulation. In recordings from DGC somata, overshooting spikes could be evoked either orthodromically or by current injections. Small-amplitude, fast transients were seen in 5 of 34 DGCs. The current/voltage (I-V) characteristic of most DGCs was linear throughout a range of membrane potentials between 15 and 20 mV negative and 5 and 15 mV positive to the resting potential. At the extremes of this range nonohmic behavior was noted. Exposure of slices to agents that block IPSPs, such as penicillin, bicuculline, picrotoxin, and media containing low Cl- concentrations, eliminated PP-evoked hyperpolarizations in DGCs and prolonged the repolarizing phase of the PP EPSP. In contrast to findings in hippocampal pyramidal cells and neocortical neurons, blockade of IPSPs did not lead to the development of orthodromically evoked slow depolarizations and burst discharges. After slices were exposed to 5 mM tetraethylammonium, current pulses evoked slow spikes, which were resistant to tetrodotoxin and presumably mediated by Ca2+. Spontaneous burst discharges or bursts evoked by brief depolarizing pulses did not occur under these conditions. Substitution of Ba2+ for Ca2+ in the perfusion solution resulted in development of spontaneous slow membrane depolarizations and burst discharges in DGCs. Burst discharges could be directly evoked and spikes were prolonged and resistant to tetrodotoxin (TTX). After hyperpolarizations lasting 200-1,000 ms, associated with a conductance increase and presumably due to a Ca2+-activated K+ conductance, followed directly evoked spike trains in 5 of 20 DGCs. These data suggest that Ca2+ conductances may be evoked in DGCs under certain circumstances but are not prominent during activation of DGCs under standard in vitro recording conditions.(ABSTRACT TRUNCATED AT 400 WORDS)
Postsynaptic dorsal column pathway of the rat. I. Anatomical studies
Authors: Giesler G. J. , Nahin R. L. , Madsen A. M.
Published: December 2017

As one of a series of studies of the ascending spinal cord pathways that might be involved in nociception in the rat, we have examined the projection to the dorsal column nuclei that originates in the spinal cord dorsal horn using the retrograde transport of horseradish peroxidase (HRP). This projection in other animals has been called the postsynaptic dorsal column (PSDC) pathway. Small iontophoretic injections of HRP into the cuneate nucleus (CN) labeled more than 350 neurons in alternate sections within the ipsilateral gray matter of segments C6-8. Fewer than 25 neurons were labeled in L4-6 by injections into CN. Injections of HRP confined to the gracile nucleus (GN) labeled more than 200 neurons within a narrow band extending across the ipsilateral dorsal horn subjacent to substantia gelatinosa of L4-6. Fewer than 10 cells were labeled in C6-8 by such injections. Labeling in lumbar neurons following injections into GN was prevented by transection of the dorsal columns at T10, T8, or C2. Thus, neurons labeled by such injections ascend entirely within the dorsal columns. Lesions of the dorsal columns in C2 reduced the number of labeled neurons in the cervical cord following CN injections by approximately 90%. Combined lesions of the dorsal columns and ipsilateral dorsal lateral funiculus (DLF) reduced the number of cells labeled in C6-8 by approximately 98%. Thus, the majority of labeled neurons in the cervical enlargement project to CN via the dorsal columns; a small secondary component of the cervical projection to CN appears to ascend within the DLF. To compare the relative sizes of the projections to the dorsal column nuclei from PSDC neurons and dorsal root ganglion cells (DRG), labeled neurons were counted in the gray matter of the cervical and lumbar enlargements and the corresponding DRG. In the four animals so examined, PSDC neurons constituted over 38% of the neurons that projected to CN and approximately 30% of the cells that projected to GN. These findings indicate that the PSDC projection of the rat is capable of providing a large somatotopically organized input to the dorsal column nuclei.
Electrophysiology of lateral and dorsal terminal nuclei of the cat accessory optic system
Authors: Grasse K. L. , Cynader M. S.
Published: December 2017

Visual responses were examined quantitatively in 96 units in the lateral (LTN) and dorsal (DTN) terminal nuclei of the cat accessory optic system (AOS). The receptive fields of LTN and DTN cells were quite large, with an average diameter of approximately 60 degrees. Individual cell receptive fields, which could be as small as 30 degrees vertically by 15 degrees horizontally or as large as 100 by 100 degrees, always included the area centralis. Large, moving textured stimuli provoked optimal modulation in these cells. In response to a 100 by 80 degrees random-dot pattern moving at a constant velocity, nearly all cells in both the LTN and DTN displayed a high degree of direction selectivity. Directional response profiles were subjected to a vector analysis that generated two quantities proportional to the direction and magnitude of the major excitatory (E vectors) and inhibitory (I vectors) responses of individual cells. Directional vectors of the LTN displayed a strikingly bimodal distribution: E vectors of individual LTN cells pointed either upward (25 of 49) or downward (23 of 49). I vectors also pointed either up or down in a direction opposite to that of the E vector for the same cell. E and I vectors in both LTN and DTN units were separated by approximately 180 degrees. With few exceptions, E vectors of DTN cells pointed in a horizontal-medial direction, while DTN I vectors pointed in a horizontal-lateral direction. A relatively broad range of stimulus velocities (0.8-102.4 degrees/s) evoked maximal excitation in individual LTN units. The majority of LTN cells, however, achieved maximal excitation at velocities between 0.8 and 12.8 degrees/s. The deepest inhibition was elicited over a range of velocities from 0.2 to 102.4 degrees/s, with two major peaks at 0.8 and 12.8 degrees/s. A similar range of velocity sensitivity was observed in DTN cells: maximal excitation was obtained for stimulus velocities from 1.6 to 102.4 degrees/s, with most DTN cells showing the greatest excitatory response between 6.4 and 12.8 degrees/s. A broad range of inhibitory velocity tuning was also observed in DTN units, with most cells exhibiting the deepest inhibitory modulation at 25.6 degrees/s. The majority of LTN and DTN units were driven most effectively through the eye contralateral to the recording site. Nonetheless, a large percentage of LTN (78%) and DTN (93%) cells could be driven to some extent through both eyes. Despite this conspicuous ipsilateral eye influence, no units were found in either the LTN or the DTN that were driven solely through the ipsilateral eye.(ABSTRACT TRUNCATED AT 400 WORDS)
Convergence onto interneurons subserving primary afferent depolarization of group I afferents
Authors: Brink E. , Jankowska E. , Skoog B.
Published: December 2017

The aim of the study was to investigate whether common or independent neuronal pathways are used to evoke primary afferent depolarization (PAD) from selectively activated group Ia and Ib afferents of different muscles. To this end, the spatial facilitation of effects of various afferents, indicating convergence on the same interneurons, was used as a test. Its occurrence was assessed on dorsal root potentials (DRPs) evoked in unspecified fibers or using intra-axonal recording from identified group Ia muscle spindle afferents or group Ib tendon organ afferents. Spatial facilitation has been found in PAD pathways a) from various Ia-afferents, whether of flexors or extensors; b) from various Ib-afferents, whether of flexors or extensors; and c) from flexor Ib-afferents and flexor or extensor Ia-afferents. In contrast, no indications have been found for common pathways from extensor Ib- and any Ia-afferents under conditions that proved effective in other combinations. Latencies of those components of PAD that appeared as a result of the spatial facilitation ranged from 2 to more than 7 ms, indicating that the convergence occurred in the shortest (trisynaptic) as well as longer pathways. The same patterns of convergence have been found in PAD pathways to extensor and flexor Ia-afferents (in experiments with intraaxonal recording from these afferents). The possibility might thus be considered that some neuronal pathways are used to modulate transmission via Ia-afferents independently of their muscle origin. The same might hold true for extensor and flexor Ib-afferents. Generally, it is concluded that the minimal number of distinct neuronal populations subserving PAD of group I afferents may be two to six. Additionally, actions of cutaneous, joint, and interosseous afferents on DRPs from Ia-afferents were reexamined to further the comparison between neurons mediating PAD and those mediating postsynaptic excitation or inhibition of motoneurons. Only depression of Ia DRPs followed stimulation of these afferents at intensities of 1.5-2.0 times threshold and higher; lower threshold afferents were apparently ineffective. On the basis of lack of convergence of extensor Ib and Ia muscle afferents and of low-threshold cutaneous afferents, interneurons mediating PAD may thus be distinguished from the interneurons subserving Ib and Ia-like-Ib postsynaptic actions in motoneurons. The latter are coexcited by these three groups of afferents.
Effects of deuterium oxide and galvanic vestibular stimulation on visual cortical cell function
Authors: Reinis S. , Landolt J. P. , Weiss D. S. , Money K. E.
Published: December 2017

/he spontaneous and evoked unit activities of complex visual cortical cells were recorded from Brodmann's area 18 in immobilized, unanesthetized cats before, during, and after stimulation of the vestibular system. The vestibular system was stimulated by intravenous injection of deuterium oxide (D2O)--a noted nystagmogenic agent (14)--or by direct galvanic stimulation of the labyrinth. Measures of the receptive-field areas, poststimulus time histograms, directional preferences, and the optimal speed of the light bar stimulating the cell were obtained before and after the application of D2O. Directional preferences were determined in a novel manner, using a method derived from a hierarchical clustering technique (19). Data were collected and analyzed from a) visual cortical cells in cats with intact labyrinths, b) visual cortical cells in cats following bilateral labrinthectomies, and c) nonvisual cortical cells in cats with intact labyrinths. In cats with intact labyrinths, D2O changed the optimal length of the light bar that was able to stimulate the cortical cell as well as the path on which it evoked the response of the cell. Both values, which constitute the receptive field of the cell, changed approximately proportionately. This effect usually lasts for less than 4.5 h. The other cellular characteristics were also altered by the D2O. Galvanic stimulation of the labyrinth resembles, in its effects, the injection of D2O. In labyrinth-intact cats, the time course of area 18 spontaneous activity dramatically increased 30 min or more after D2O was administered. It peaked 2-3 h later and still had not returned to preinjection levels even 7 h after the D2O administration. In bilaterally labyrinthectomized cats, the spontaneous activity of the visual cells (and the other cellular characteristics studied) did not change following D2O administration. In nonvisual cells from labyrinth-intact cats, the spontaneous activity demonstrated a slight but significant decrease over time after D2O injection. (The other measures, however, did not change.) In pilot studies (about 2 wk prior to the electrophysiological experiments), the cats were injected with D2O. Within 8-10 min afterward, signs of positional nystagmus commenced; and within 30 min, problems in maintaining balance were noted. This continued for 7-8 h before disappearing. In the labyrinthectomized animals, such effects were not observed. These results, therefore, add support to other evidence that suggests that D2O works directly through the vestibular apparatus to produce the effects it does (and not through interference with certain cellular processes).(ABSTRACT TRUNCATED AT 400 WORDS)
Loss of set in muscle responses to limb perturbations during cerebellar dysfunction
Authors: Hore J. , Vilis T.
Published: December 2017

The properties of electromyograph (EMG) responses that enabled the arm to return accurately to target following limb perturbations were investigated in five Cebus monkeys. In particular, factors that affected the timing and magnitude of an early antagonist response that occurred prior to stretch of the antagonist muscle were examined. The early antagonist response was large and early (latency, 60 ms) when the perturbation was brief and a constant force assisted the return movement. In this situation, early contraction of the antagonist muscle was required to prevent the return movement from overshooting the target. To determine whether this early antagonist response was influenced by prior instruction (which in this case was the type of perturbation the monkey had previously received), two types of perturbations requiring different EMG responses were studied. When torque steps (duration, 2,000 ms) were expected and were applied, monkeys generated M1, M2, and M3 responses and later activity only in the agonist (the initially stretched) muscle. When torque pulses (duration, 40 ms) were expected and were applied, monkeys generated M1 and M2 responses in the agonist and an early antagonist response. EMG responses to torque pulses and steps were then compared when the type of perturbation was expected and when it was unexpected. These comparisons revealed that the early antagonist response only occurred when the monkey expected a torque pulse. Therefore, this response was dependent on set. Expectation of a torque step caused enhancement of the agonist M2 and M3 responses. These agonist and antagonist EMG responses that were dependent on set were also influenced by changes in afferent drive. Cerebellar nuclear cooling through probes implanted lateral and medial to the dentate abolished that component of EMG responses attributed to set. The residual EMG responses in agonists and antagonists appeared to be driven by stretch of their respective muscles. The results suggest that when the nature of an arm perturbation is correctly predicted, the cerebellum provides accuracy in repositioning the limb a) by adjusting the magnitude of the M2 agonist response and b) by enabling activity after a latency of 60 ms (e.g., the M3 and early antagonist response) to be switched to the agonist or antagonist as appropriate, irrespective of which muscle is being stretched. This latter mechanism provides the motor system with predictive ability.
Sensory, interneuronal, and motor interactions within Hermissenda visual pathway
Authors: Goh Y. , Alkon D. L.
Published: December 2017

The visual pathway of Hermissenda was identified by means of intracellular recordings and iontophoretic injection of the fluorescent dye lucifer yellow. This pathway consisted of five neuron types, namely, type B photoreceptors and the medial type A photoreceptor within each of the two eyes, hair cells in the two statocysts, a group of interneurons in the cerebropleural ganglia, and a putative motor neuron (MN1) in each pedal ganglion. The MN1 cells responded during illumination of the eye with increased impulse and excitatory postsynaptic potential (EPSP) activity. This response was often followed by bursting activity for higher light intensities. The medial type A photoreceptor, which was found to be inhibited by medial and intermediate type B photoreceptors, was demonstrated to excite the MN1 cell indirectly via a group of identified interneurons. Hair cells were also found to excite the MN1 cell indirectly via these interneurons. Among the ipsilateral hair cells, cephalic hair cells were least frequently found to excite the MN1 cell. Among the contralateral hair cells, on the other hand, lateral hair cells were most often found to excite the MN1 cell. Interneurons that were shown to excite the MN1 cell received excitatory input from the medial type A photoreceptor and hair cells. Our observations are consistent with the interpretation that these interactions are mediated by monosynaptic chemical synapses. Electrical stimulation of the MN1 cell with positive-current injection produced turning of the posterior half of the animal's foot to the ipsilateral direction consistent with the animal's turning behavior toward light. The visual pathway identified in this experiment was considered to have some significance in explaining, at least in part, a causal role for changes within type B photoreceptors in producing Hermissenda's modified behavior following associative conditioning.
Response properties of striate cortex neurons in cats raised with divergent or convergent strabismus
Authors: Kalil R. E. , Spear P. D. , Langsetmo A.
Published: December 2017

Recordings were made from striate cortex in five groups of cats that had been raised with strabismus produced by sectioning the extraocular muscles. These groups included animals reared with exotropia, unilateral or bilateral esotropia, and esotropia combined with lid suture of the unoperated eye. In addition, a group of esotropes was studied in which the unoperated eye was removed a few hours prior to recording. For comparison, five normal adult cats were also studied. In each of the above groups, cells were sampled in the representations of the central and peripheral visual fields in area 17 ipsilateral and contralateral to the deviated eye. We mapped the receptive field of each responsive cell, determined its ocularity, and tested it for selectivity. Confirming previous work, we found a marked loss of cortical binocularity in cats raised with strabismus. On average only 7% of the neurons that we recorded could be driven by both eyes. This percentage was relatively constant at all cortical locations that were studied and was not influenced by whether cats had been reared with exotropia, unilateral esotropia, or bilateral esotropia. The percentage of selective cells driven by the deviated eye in exotropes or esotropes did not appear to be different from normal at most cortical locations (but see 5, below). In addition, we did not observe any bias in the axial preference of selective cells in strabismic cats when compared with normal adult cats. In both exotropes and esotropes the deviated eye drove fewer cells when compared with the proportion that are driven by one eye in normal cats. In exotropes this deficit did not vary at different cortical representations of the visual field. In esotropes, however, this deficit was graded, being least in the representation of the peripheral visual field in area 17 contralateral to the deviated eye, intermediate in the representations of the central visual field in the contralateral and ipsilateral hemispheres, and greatest in the representation of the peripheral visual field in ipsilateral area 17. Furthermore, only when recording from the peripheral field representation in the ipsilateral hemisphere did we encounter significant numbers of cells driven by the deviated eye that lacked normal selectivity. Since it is possible that deprivation of the converged eye during development might account for the deficits noted above, we attempted to evaluate this factor using several independent lines of evidence. First, we could find no correlation between the angle of esotropia and the ability of the deviated eye to drive ipsilateral cortical cells representing the peripheral visual field.(ABSTRACT TRUNCATED AT 400 WORDS)
Stimulus- and amino acid-induced calcium and potassium changes in rat neocortex
Authors: Pumain R. , Heinemann U.
Published: December 2017

Local changes in extracellular concentration of calcium ions, [Ca2+]o, and potassium ions, [K+]o, elicited through ionophoretic applications of the excitatory amino acids glutamate (Glu) and aspartate (Asp) or through cortical surface stimulations were measured in the rat motor cortex using paired ion-selective microelectrodes. Glu or Asp applications produced dose-dependent decreases in [Ca2+]o from a base line of 1.25 mM to as low as 0.08 mM and increases in [K+]o from 2.8 mM to as high as 13.3 mM. These ionic changes were accompanied by negative DC potential shifts of up to 15 mV. [K+]o changes were practically constant in all cortical layers, whereas [Ca2+]o changes were variable with depth, showing two localized marked maximums. One was observed in the superficial layers, 150-300 microns below cortical surface and the second at 1,100-1,300 microns, in a region corresponding roughly to layer V. Application of tetrodotoxin (TTX) onto the cortical surface abolished stimulus-evoked ionic changes, whereas amino acid-induced [Ca2+]o changes remained practically unaltered, and [K+]o changes were reduced by 20% on average. Selective degeneration of the pyramidal tract neurons was induced by performing chronic lesions of the pyramidal tract at the bulbar level. In these conditions, laminar profiles of amino acid-induced [Ca2+]o changes were considerably altered in the corresponding motor cortex. The maximum Ca2+ changes were then reduced by two-thirds, and the [Ca2+]o signals were practically constant throughout the cortex. Local cobalt (Co2+) or manganese (Mn2+) applications could abolish amino acid-evoked [Ca2+]o changes, whereas most of the [K+]o changes persisted. gamma-Aminobutyric acid applications could decrease [Ca2+]o signals to a large extent, whereas [K+]o changes were diminished by only 15-25% on average. These results show that the putative neurotransmitters Glu and Asp induce significant changes in [Ca2+]o and [K+]o in the rat cerebral cortex and indicate the possible origin of the ion fluxes in terms of neuronal elements and ionic channels: in particular, they indicate that the major part of the amino acid-induced [Ca2+]o maximum decreases can be ascribed to Ca2+ movements through channels located very likely on the pyramidal tract neurons in the motor cortex. They also indicate that significant reductions of the extracellular space volume occur during excitatory amino acid applications.
Modification of saccadic eye movements by GABA-related substances. I. Effect of muscimol and bicuculline in monkey superior colliculus
Authors: Hikosaka O. , Wurtz R. H.
Published: December 2017

Our previous observations led to the hypothesis that cells in the substantia nigra pars reticulata (SNr) tonically inhibit saccade-related cells in the intermediate layers of the superior colliculus (SC). Before saccades to visual or remembered targets, cells in SNr briefly reduce that inhibition, allowing a burst of spikes of SC cells that, in turn, leads to the initiation of a saccadic eye movement. Since this inhibition is likely to be mediated by gamma-aminobutyric acid (GABA), we tested this hypothesis by injecting a GABA agonist (muscimol) or a GABA antagonist (bicuculline) into the superior colliculus and measured the effects on saccadic eye movements made to visual or remembered targets. An injection of muscimol selectively suppressed saccades to the movement field of the cells near the injection site. The affected area expanded over time, thus suggesting the diffusion of muscimol in the SC; the area never included the other hemifield, suggesting that the diffusion was limited to one SC. One of the monkeys became unable to make any saccades to the affected area. Saccades to visual targets following injection of muscimol had longer latency and slightly shorter amplitudes that were corrected by subsequent saccades. The most striking change was a decrease in the peak velocity of the saccade, frequently to less than half the preinjection value. Saccades to remembered targets following injection of muscimol also showed an increase in latency and decrease in velocity, but in addition, showed a striking decrease in the accuracy of the saccades. The trajectories of saccades became distorted as if they were deflected away from the affected area. After muscimol injection, the area over which spontaneous eye movements were made shifted toward the side ipsilateral to the injection. Saccades toward the contralateral side were less frequent and slower. In nystagmus, which developed later, the slow phase was toward the contralateral side. In contrast to muscimol, injection of bicuculline facilitated the initiation of saccades. Injection was followed almost immediately by stereotyped and apparently irrepressible saccades made toward the center of the movement field of the SC cells at the injection site. The monkeys became unable to fixate during the tasks; the fixation was interrupted by saccadic jerks made to the affected area of the visual field and then back to the fixation point.(ABSTRACT TRUNCATED AT 400 WORDS)
Cat lateral suprasylvian cortex: Y-cell inputs and corticotectal projection
Authors: Berson D. M.
Published: December 2017

Retinal Y-cells activate most cells in the deep layers of the cat's superior colliculus via an indirect pathway involving the occipital cortex. The lateral suprasylvian area seems to be an important source of visual input to the deep collicular strata but it is unclear whether Y-cell influences reach this extrastriate area and, hence, whether this area participates in the indirect Y-cell pathway. In this study, retinal influences on the posteromedial lateral suprasylvian area (PMLS) were studied in anesthetized cats. Responses to electrical stimulation of the optic disk (OD) and optic chiasm (OX) were recorded in single units in PMLS and in neurons of the dorsal lateral geniculate nucleus (LGNd) that were antidromically driven from PMLS. Virtually all PMLS cells (99%; 99/100) exhibited small differences (less than or equal to 0.8 ms) between OD- and OX-activation latency, indicating that they were driven by a pathway originating in rapidly conducting Y-cell axons. A small number of PMLS cells (17%; 20/118) had very short activation latencies (less than or equal to 3.2 ms from OX), comparable to those of cells in areas 17 and 18 receiving monosynaptic inputs from geniculate Y-cells. Further, LGNd cells with latency behaviors typical of Y-cells could be antidromically driven from PMLS, confirming that geniculate Y-cells project directly to PMLS. Most PMLS cells (83%; 98/118), though exhibiting small OD-OX latency differences, had absolute latencies too long to be attributed to direct inputs from geniculate Y-cells (3.3-8.5 ms from OX). Thus Y-cells in the LGNd influence most PMLS cells by way of a multisynaptic pathway. PMLS cells antidromically activated from the superior colliculus were driven only by this multisynaptic Y-cell input. Total conduction time from the retina through PMLS to the colliculus corresponds closely to the latency of the indirect Y-cell activation observed in the deep collicular layers. These results support the view that the lateral suprasylvian cortex constitutes an important source of visual input to the cat's deep collicular layers and, more generally, that the extrastriate visual cortex may figure prominently in the cortical control of gaze.