bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of hypothalamic stimulation on unit responses recorded from neurons of sensorimotor cortex of awake cats during conditioning
Authors: Woody C. D. , Kim E. H. , Berthier N. E.
Published: December 2017

1. The activity of single units of the coronal pericruciate (CPC) cortex was studied in 11 awake cats during sessions in which a click conditioned stimulus (CS) was repeatedly paired with glabella tap unconditioned stimulus (US) and hypothalamic stimulation (HS). Effects of HS on the activity of cortical units were also studied during sessions in which HS alone was delivered repeatedly every 10 s. 2. HS evoked an increase in spike activity of less than 60 ms latency in 89 of 116 units tested. 3. Repeated presentation of HS that was effective in producing rapid behavioral conditioning resulted in a characteristic reduction in the latency of discharge evoked by HS in cortical units. 4. Short-latency activation (less than 20 ms) of units of the sensorimotor cortex appeared to be characteristic of HS that led to enhanced rates of conditioned response (CR) acquisition. One of the cells responding in this way was identified as a pyramidal cell of layer V by intracellular injection of horseradish peroxidase (HRP). 5. Further analyses of activity were performed on 16 units of the CPC cortex that were followed through conditioning (or reconditioning) and extinction of the CR. After less than 10 CS-US-HS pairings, there was a selective augmentation of unit response to the CS but not of response to an explicitly unpaired discriminative stimulus (DS). Responses to the CS were not similarly augmented when presentations of HS preceded rather than followed the presentations of the CS and US. The rapid development of CS-evoked unit activity coincided with the rapid acquisition of discriminative CRs behaviorally. 6. During conditioning, the most conspicuous increases in CS-evoked unit response occurred at latencies 100 ms or more after onset of the click CS. This corresponded with the behavioral observation that the majority of eye blink CRs occurred with onset latencies longer than 100 ms.
Ionic mechanism of muscarinic cholinergic depolarization of mouse spinal cord neurons in cell culture
Authors: Nowak L. M. , Macdonald R. L.
Published: December 2017

1. Muscarinic cholinergic actions were investigated in a population of large multipolar spinal cord neurons in primary dissociated cell culture using conventional intracellular recording and single-microelectrode voltage-clamp techniques. 2. Cholinergic agonists were applied to the surface of neuronal somata by pressure ejecting drug-containing bathing medium from small blunt (2-10 microns) glass micropipettes. Atropine was applied by diffusion from large (20-30 microns) blunt micropipettes positioned near the soma. 3. Muscarine increased action-potential firing and evoked slow sustained membrane depolarization. Action potentials but not slow membrane depolarizations were eliminated by the sodium channel blocker, tetrodotoxin. Muscarine-induced depolarizing responses were unaffected by the calcium channel blocker, cadmium. 4. Depolarizing responses evoked by selective and nonselective muscarinic cholinergic agonists were dose dependent, reversibly antagonized by atropine, and did not desensitize. 5. Muscarine depolarized neurons and decreased membrane conductance during recording with both 3 M KCl- and 4 M KAc-filled intracellular recording micropipettes. When membrane potential was held constant using the single-electrode voltage-clamp technique (KCl-filled micropipettes), muscarine and gamma-aminobutyric acid (GABA) evoked inward currents at resting membrane potential. GABA-induced inward current responses were decreased by depolarization and had reversal potentials near -30 mV, consistent with GABA increasing chloride conductance. Muscarine-induced inward current responses were increased by depolarization and had extrapolated reversal potentials near -80 mV, consistent with muscarine decreasing a potassium conductance. 6. Unlike GABA-induced currents, muscarine-induced currents evoked in normal Tris-buffered saline (5 mM potassium) did not vary as a linear function of membrane potential and did not reverse polarity in six of seven neurons near potassium equilibrium potential. However, in high-potassium medium (15 mM) muscarinic responses did reverse polarity and current was linearly related to membrane potential. Thus, the apparent voltage dependence of muscarine responses was probably due to voltage dependency of the potassium conductance and not due to potassium channel rectification. 7. Preliminary evidence (37) indicates that muscarine decreases a time- and voltage-dependent potassium current in some cultured spinal cord neurons. Whether reduction of m current can completely account for muscarine postsynaptic actions in these cells remains unclear. Muscarine may also block a small population of non-voltage-dependent potassium channels in addition to reducing m current.
Alkaline and acid transients in cerebellar microenvironment
Authors: Kraig R. P. , Ferreira-Filho C. R. , Nicholson C.
Published: December 2017

1. Extracellular pH (pHo) was measured in the cerebellar cortex of the rat using a recently developed liquid membrane ion-selective micropipette (ISM). pHo was determined during stimulus-evoked neuronal activity, elevated extracellular potassium concentration, [K+]o, spreading depression (SD), and complete ischemia. In many experiments [K+]o was simultaneously determined. 2. A train of local surface stimuli (LOC) produced an initial alkaline shift in pHo from a base line of 7.20-7.30 to 7.25-7.35. This was followed by a long-lasting acid phase that reached a plateau of 7.05-7.15 after 64 s of stimulation. pHo decrease was related to stimulus frequency, intensity, and duration. 3. Superfusion with Ringer solution containing manganese ions rapidly abolished parallel fiber-induced Purkinje cell synaptic depolarization together with the alkaline shifts while enhancing the acid shifts. 4. Superfusion of the cerebellar cortex with Ringer solution containing increasingly elevated [K+] progressively lowered pHo to a plateau of 6.95-7.05. The acidification occurred in the presence of ouabain but was reversed on return to the normal [K+]o or with the addition of the glycolytic blocker, fluoride. Stimulus-evoked alkaline shifts were enhanced by K+-Ringer superfusion. These experiments suggested that the acid shift was due to the metabolic production of an anion, possibly lactate. 5. Elevation of [K+]o above 8-12 mM often produced oscillation in pHo and [K+]o with a period of about 40 s. Sometimes these oscillations ended in a spontaneous SD or SD could be evoked by stimulation. Under these conditions of raised [K+]o, the SD consisted of a very pronounced alkaline transient followed by a small, long-lasting acid shift. When SD was induced by conditioning the cerebellum with proprionate or lowered NaCl, the alkaline phase was reduced and the acid enhanced. 6. Complete ischemia began with a progressive decrease of pHo and rise in [K+]o. When [K+]o reached 12 mM, a second more rapid rise in [K+]o to 40 mM or more occurred. This was correlated with 0.1-0.2 pHo transient increase similar to that seen during SD. pHo eventually reached a plateau of 6.60-6.80, close to neutrality. 7. Superfusion with Ringer solution containing acetazolamide immediately altered pHo homeostasis by increasing base-line pHo by about 0.10 and enhanced the induced pHo changes. These results suggest that carbonic anhydrase (CA) is important for acute buffering of the brain extracellular microenvironment. 8. The above results were interpreted in terms of changes in extracellular strong ion concentration differences ( [SID]o), extracellular concentration of total weak acid ( [Atot]o) and partial pressure of CO2 (Pco2) in the brain microenvironment. The results indicate that neuronal activity produces changes in many of the constituents of the microenvironment.
Quantitative relations between color-opponent response of horizontal cells and action spectra of cones
Authors: Burkhardt D. A. , Hassin G.
Published: December 2017

1. Relations between cones and chromatic-type horizontal cells (C-cells) were investigated by intracellular recording in the retina of the walleye (Stizostedion vitreum). 2. The retina contains two classes of cones, midwave (M) and long wave (L). Their action spectra have maximum sensitivity at 533 and 605 nm, respectively, and have been measured with good precision from 400 to 750 nm. 3. C-cells generate relatively sustained depolarizing and hyperpolarizing responses to deep red (680 nm) and green (530 nm) test flashes, respectively, but prominent on and off transients are evoked by intermediate wavelengths. To minimize these temporal interactions, quantitative analysis was restricted to measurements of the apparent steady-state response amplitude. 4. Response amplitude was linearly related to flash intensity for responses that did not exceed 20% of their respective maxima. This is called the linear range. At higher levels, the nonlinear region of the Naka-Rushton relation holds approximately if input is largely confined to the hyperpolarizing or depolarizing mechanism. 5. Tests with red/green mixture flashes show that the hyperpolarizing and depolarizing inputs interact by simple summation for responses in the linear range. At higher levels, the interaction is complex. 6. Spectral-response curves (response amplitude versus wavelength for flashes of equal photon level) were determined for 16 C-cells in the linear range. The exact form of these curves varied considerably from cell to cell, reflecting differences in the relative strength of the hyperpolarizing and depolarizing mechanisms. 7. The spectral-response curves were analyzed by a simple linear model based on the action spectra of the L and M cones. Measured and predicted spectral-response curves agree closely. The only free parameter in the analysis is a scaling factor that specifies the strength of the L cone input relative to the M cone input. 8. Triphasic spectral-response curves, as predicted by the model, were found in the sauger (Stizostedion canadense). These C-cells have short-wavelength responses due to input from long-wave cones, resemble certain triphasic cells in primate retina, and differ sharply from other triphasic C-cells found in other fish retinas. 9. Although the precise synaptic mechanisms must still be identified, the present results show that the functional information transfer from cones to C-cells in the linear range can be closely approximated by simple operations of scaling, sign inversion, and simple summation. The C-cell thus effectively subtracts one cone action spectrum from the other and displays the difference in the form of the spectral-response curve.
Reorganization of connectivity in amphibian central auditory system following VIIIth nerve regeneration: time course
Authors: Zakon H. H.
Published: December 2017

In the frog, most neurons in the primary (dorsal medullary nucleus, DMN) and secondary (superior olivary nucleus, SO) auditory nuclei have V-shaped tuning curves, almost as narrowly tuned as those recorded in the nerve. Thus, the innervation pattern is such that if more than one excitatory afferent innervates a postsynaptic cell, they must all possess similar best frequencies (BFs). Similarly, binaural cells in these nuclei display matched frequency selectivities when acoustically stimulated via either ear. The VIIIth nerve was unilaterally severed and allowed to regenerate back into the DMN. At various postoperative intervals, extracellular single-unit recordings were made in the SO contralateral to the regenerated nerve, as that nucleus receives its dominant excitatory input (approximately 80%) from the contralateral side. Recordings were also made in the SO of a number of unoperated control animals. Functional reinnervation commenced between 4 and 5 wk postoperatively and by 6 wk, a normal innervation density, as judged by physiological criteria, was achieved. Single units of any best frequency represented within the frog's two auditory papillae could be recorded during earliest reinnervation. In general, the tuning curves of both monaural and binaural cells were V shaped in the 6 wk regenerates. Although many tuning curves were narrowly tuned (Q10dB greater than 1.0) as in unoperated animals, some were very broadly tuned (Q10dB less than 0.5). The mean Q10dB value for all contralaterally excited cells was 1.45 +/- 0.77 (SD), which was significantly lower than that of SO units in unoperated frogs (Q10dB = 1.66 +/- 0.52 (SD)). Binaural cells often had mismatched BFs and tuning curves. By 8 wk after nerve transection, tuning curves were as narrow as in unoperated animals (Q10dB = 1.64 +/- 0.68 (SD)), and the BFs of binaural cells evinced a greater match than at 6 wk. By 12 wk postoperatively, V-shaped tuning curves were still as narrow as in controls (Q10dB = 1.71 +/- 0.69 (SD)), and the tuning curves and BFs of binaural cells were well matched again. At all postoperative intervals, about 10% of the tuning curves in the SO of regenerates were W shaped. This was never seen in normal animals. The return of narrow V-shaped tuning curves in the majority of neurons and the recurrence of matched binaural cells in the SO are interpreted as evidence of specificity for potential postsynaptic targets in the DMN by regenerating auditory afferents.
Spatial vision in strabismic cats
Authors: Holopigian K. , Blake R.
Published: December 2017

Contrast thresholds for detection of stationary and flickering gratings were measured behaviorally for each eye of cats raised with induced convergent strabismus. The performance of the deviating eye was inferior to that of the nondeviating eye when test patterns were stationary. Flicker served to reduce the performance difference between the eyes in two cats but not in a third. These results suggest that strabismus amblyopia may not result from deficits within a single class of neurons. In all strabismic cats the contrast sensitivity of the nondeviating eye was significantly reduced relative to normal cats. These behavioral findings, including the deficits found bilaterally, correspond very well with results from cortical recordings from these and other strabismic cats presented in the preceding paper (7).
Higher order neurons in buccal ganglia of Pleurobranchaea elicit vomiting motor activity
Authors: McClellan A. D.
Published: December 2017

The buccal mass of the gastropod Pleurobranchaea is used during a regurgitation response that consists of a writhing phase interrupted by brief periodic bouts of a vomiting phase (17, 20). During transitions from writhing to vomiting, specific changes occur in the motor pattern (19, 20). Evidence is presented suggesting that at least some of the initiation or "command" neurons for vomiting reside in the buccal ganglia. The present paper examines the role of two candidate vomiting-initiation cells, the ventral white cells (VWC) and midganglionic cells (MC), in the buccal ganglia of isolated nervous systems. Stimulation of single VWCs activates a vomiting motor pattern, consisting in part of alternating buccal root activity. Furthermore, the VWCs fire in high-frequency bursts during episodes (i.e., bouts) of this same vomiting pattern. Mutual reexcitation between the VWCs and motor pattern generator (MPG) appears to produce the accelerated buildup and maintenance of vomiting rhythms. Brief stimulation of single MCs "triggers" bouts of a vomiting motor pattern, but the membrane potential of this cell is only modulated during this same pattern, at least in the isolated nervous system. It is proposed that in intact animals the MCs are activated by sensory inputs and briefly excite the VWC-MPG network, thereby turning on the mutual reexcitatory mechanism mentioned above and switching the output pattern. A general implication for gastropod research is that higher order neurons that activate buccal root activity cannot automatically be given the function of "feeding command neuron," as some cells clearly control other responses, such as vomiting.
Light adaptation in cells of macaque lateral geniculate nucleus and its relation to human light adaptation
Authors: Virsu V. , Lee B. B.
Published: December 2017

Responses of macaque lateral geniculate nucleus (LGN) cells to stimuli of different incremental intensities and wavelength compositions were studied at different levels of light adaptation from scotopic to low photopic levels. Stimuli were large in comparison with receptive-field size. Human increment thresholds were measured for comparison. The strength of responses grew in many cells from threshold up to a saturation level as a logarithmic function of incremental intensity. More complex intensity-response functions were also obtained, particularly from parvocellular layer (PCL) cells, but the shape and slope of the intensity-response function changed as a function of adaptation level only with chromatic backgrounds. As a function of adaptation level, the intensity-response functions shifted along the logarithmic abscissa but not sufficiently for a complete contrast constancy. Thus responses to any constant contrast became smaller when adaptation level decreased. The change from cone to rod responses, when possible, took place without noticeable change in shape of intensity-response functions, and much of the adaptive shift of the functions could be attributed to the change-over between rods and cones. Differences between different cells in light adaptation and dark-adapted sensitivity were large, mostly because of variation in the strength of rod input. The strongest excitatory rod inputs were found in PCL cells activated by short-wavelength light, so that the highest sensitivity at low levels of illumination occurred in blue- and blue-green-sensitive cells. The lowest increment thresholds based on cones matched the thresholds of macaque cone late receptor potentials recorded by Boynton and Whitten (3). They were also similar to human cone thresholds measured psychophysically but only for small stimulus sizes that may approximate the size of the receptive-field centers. Human sensitivity was much higher when measured with large stimulus sizes, indicating integration at post-geniculate neural levels. Light adaptation, as evaluated with respect to contrast constancy and Weber law behavior, was similarly incomplete in monkey single cells and human perception. A few cat LGN cells were studied in a control experiment; results agreed with previous findings. The light adaptation of cat cels was more complete and sensitivity higher than those observed under comparable conditions in macaque single cells and human. The maintained activity level of cells was little affected by the intensity of steady backgrounds. Thus, the steady-state hyper-polarisation of receptors was not transmitted to LGN cells.
Patterns of metabolic activity in cytoarchitectural area SII and surrounding cortical fields of the monkey
Authors: Juliano S. L. , Hand P. J. , Whitsel B. L.
Published: December 2017

The pattern of [14C]2-deoxyglucose (2-DG) labeling evoked by tactile stimuli was determined in cerebral cortical cytoarchitectural area SII and the fields that surround it (including area 7b, the retroinsular field (Ri), and the granular insular region (Ig) for a series of nine monkeys (macaca fascicularis). In all animals and for all tactile stimuli, the cortical labeling most frequently occurred in the form of patchlike aggregates of metabolically active neurons. Individual patches typically included laminae II-V, were most densely labeled in the central layers, and possessed limited tangential width. Analysis of the relations between patches of label in adjacent sections revealed that the metabolically active neurons form three-dimensional aggregates (termed modules or strips), which can extend for several millimeters. It is hypothesized that these metabolic modules may correspond to information-processing units within the cerebral cortex. Two-dimensional reconstructions of the 2-DG label in the hemispheres ipsilateral and contralateral to the somatic stimuli reveal that the strips of high metabolic activity are interspersed with regions of substantially less activity. In all cortical regions examined in this study, the strips were oriented roughly from anterior to posterior. Systematic changes in the place of the somatic stimulus led to systematic changes in the cortical location of the strips of metabolic label. Conversely, animals subjected to nearly identical tactile stimuli produced very similar patterns of metabolic activity. Comparison of the distribution of metabolic activity in area SII of the hemispheres ipsilateral and contralateral to the stimulus demonstrated that although the amount of labeling in SII ipsilateral to the stimulus was typically less than that present in SII of the contralateral hemisphere, it was both substantial and topographically highly organized. The labeling in the cytoarchitectural zones surrounding SII (i.e., 7b, Ri, and Ig), although clearly stimulus related, occupied extensively overlapping regions in all experiments even though the body regions stimulated were in widely different locations. As a result, a relative lack of topographical organization within these cortical fields is indicated.
Consistency and signal strength of respiratory neuronal activity
Authors: Orem J. , Dick T.
Published: December 2017

The concerns of this study are taxonomic. We demonstrate a defining characteristic of respiratory neuronal activity. This characteristic is the degree or size of the respiratory component in the activity of a respiratory cell. The essential feature of respiratory activity is that it occurs in phase with some portion of the respiratory cycle. Therefore, neuronal activity can be arranged within a matrix in which the columns are fractions of the respiratory cycle and the rows are breaths and, as Netick and Orem (10) have shown, this matrix can be analyzed with an analysis of variance to determine whether the activity contains a respiratory component. However, the analysis of variance indicates nothing about the size of a statistically significant respiratory component. We hypothesized that the size of the respiratory component in the activity of different respiratory cells differed among cells but was a stable characteristic of any given cell. The index used to quantify the degree of respiratory activity was eta 2, the proportion of the total variance of the activity of a respiratory neuron consisting of the variance occurring across fractions of the respiratory cycle. This index theoretically depends on a) the range of activity levels across a respiratory cycle and the dispersion of activity levels over this range (parameters signifying the strength of the respiratory signal) and b) the variability in the activity of the cell across breaths (a parameter signifying the consistency of the respiratory activity). Theoretically, eta 2 values can vary from 0.0 to 1.0 indicating, respectively, that none or all of the variability in the activity of a cell across breaths is accounted for by a respiratory effect. eta 2 was used to analyze the size of the respiratory component in the activity of 32 medullary respiratory neurons recorded during nonrapid eye movement (NREM) sleep in chronic cats. These different respiratory cells had activity patterns with eta 2 values ranging from 0.1 to 0.9. However, the activity of a given cell produced eta 2 values that were consistent from sample to sample. Therefore, the eta 2 value of the activity of a cell was a defining, stable characteristic of that cell. The eta 2 values of the activity of the cells were strongly correlated with the consistency of their discharge pattern from breath to breath (r x,y = 0.975).(ABSTRACT TRUNCATED AT 400 WORDS)
Analysis of association fiber system in piriform cortex with intracellular recording and staining techniques
Authors: Haberly L. B. , Bower J. M.
Published: December 2017

The piriform cortex of the opossum has been studied with intracellular recording and staining techniques. The experiments were designed to investigate the association fiber system, but the results have also revealed new properties of the afferent fiber system from the olfactory bulb and the inhibitory systems within the piriform cortex. Following shock stimulation of the lateral olfactory tract (LOT), the response of pyramidal cells consists of an initial excitatory postsynaptic potential (EPSP) followed by a long-lasting inhibitory postsynaptic potential (IPSP). The LOT-evoked EPSP consists of two components: an initial monosynaptic followed by a disynaptic component. The monosynaptic EPSP can be isolated by the use of conditioning LOT shocks to block the IPSP and disynaptic EPSP. The disynaptic EPSP can be demonstrated by cutting LOT fibers at the surface of the cortex to eliminate the monosynaptic EPSP and by the use of bicuculline to block the IPSP. The latency of the IPSP is sufficiently brief so that the disynaptic EPSP is blocked at presumed intrasomatic recording sites unless these experimental manipulations are carried out. In all histologically verified pyramidal cells in both layers II and III in which the appropriate tests were carried out, both mono- and disynaptic EPSP components were present. It was concluded on the basis of anatomical considerations, however, that a small number of pyramidal cells would be expected to receive only a disynaptic EPSP. Evidence that the LOT-evoked disynaptic EPSP is mediated, at least in part, by association axons was provided by direct stimulation of these fibers in layer III and by demonstrating that the EPSP is present distal to cuts that sever LOT axons. Direct stimulation of association axons in layer III evokes both a monosynaptic EPSP and a disynaptic IPSP in pyramidal cells at similar latencies. This IPSP is indistinguishable in properties from that evoked by LOT stimulation. Indirect evidence indicates that it is mediated via both feedforward and feedback mechanisms. In most neurons the association fiber-evoked EPSP is masked by the IPSP in response to single deep shocks but can be demonstrated by blocking the IPSP with a preceding LOT shock or by application of bicuculline. Intracellular injection of horseradish peroxidase (HRP) revealed that pyramidal cell axons give rise to an extensive system of local collaterals with a large number of synaptic terminal-like swellings in layer III. It is postulated that these collaterals synapse on both pyramidal and nonpyramidal cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Response properties of neurons in posterior parietal cortex of monkey during visual-vestibular stimulation. II. Optokinetic neurons
Authors: Kawano K. , Sasaki M.
Published: December 2017

Recordings have been made from single neurons in area 7a or PG (11) in alert monkeys. Studies were limited to those neurons that were activated during optokinetic stimulation in a particular direction but not during foveal pursuit of a small moving target in the dark. Neurons responding in this way were called optokinetic. There was a considerable number of passive visual neurons, which responded to the movement of a visual stimulus during visual fixation but did not respond during optokinetic nystagmus (OKN). Most optokinetic neurons (46/51) also responded during suppression of OKN and usually displayed the same directional preference (43/46). Average discharge rates during constant-velocity optokinetic stimulation in the preferred direction increased monotonically with increases in stimulus velocity in the range 0-60 degrees/s (9/9), and most (7/9) tended to saturate at higher velocities. While the monkey fixated a stationary target light in the dark, most optokinetic neurons (20/24) responded to small moving visual stimuli, and more than half of them (13/20) had the same directional preferences as during OKN. When the chair in which the monkey was seated was oscillated sinusoidally in combination with optokinetic stimulation, most optokinetic neurons seemed to fall into one of two groups; one mainly responded when the animal was oscillated inside a stationary cylinder, and the other when the chair and the lighted cylinder were moved in synchrony together. The results suggest that some of the optokinetic neurons in area 7a or PG may receive extraretinal inputs similar to those that have been suggested to impinge on visual tracking neurons.
Spike aftercurrents in R15 of Aplysia: their relationship to slow inward current and calcium influx
Authors: Lewis D. V.
Published: December 2017

Spikes in the bursting neuron, R15, are followed by depolarizing afterpotentials (35) and often by delayed hyperpolarizing afterpotentials as well. Placing the cell in a voltage clamp after a spike allows measurement of the depolarizing aftercurrent (DAC) and hyperpolarizing aftercurrent (HAC) that underlie the afterpotentials. Subthreshold depolarizations give rise to small DACs and HACs. The DAC and the slow inward current (SIC) of R15 are reduced or blocked in a similar manner by many experimental manipulations, e.g., application of dopamine, zero-calcium seawater, zero-sodium seawater, or calcium-channel blockers (Mn2+ and La3+), or cooling the cell from 21-22 degrees C to 10 degrees C. Neither the DAC nor the SIC were blocked by tetrodotoxin (100 uM) and neither was sensitive to altered extracellular potassium. Both the DAC and SIC become larger as the holding potential of the cell is progressively depolarized from -70 to -40 mV. DACs are sensitive to the injection of intracellular calcium chelators (EGTA (ethylene glycol-bis(beta-aminoethyl ether)-N,N1-tetraacetic acid) or EDTA [ethylenedinitrilo)tetraacetic acid]. DAC amplitude is approximately 90% reduced by intracellular EGTA concentration near 1mM. In contrast, the SIC is unchanged or much less affected by the calcium buffers. DACs are also more sensitive to low (1 mM) extracellular calcium than is the SIC. The HAC is also a calcium-dependent current. It is blocked by any experimental manipulation reducing calcium influx or intracellular calcium accumulation, i.e., reduced extracellular calcium, calcium-channel blockers, or intracellular EGTA. We suggest that the DAC and the SIC are carried by the same conductance mechanism. In the case of the DAC, the conductance might be activated by a rise in intracellular calcium activity accompanying the spike and, in the case of the SIC, depolarization per se may be the most important activating condition.
Inhibition of primate spinothalamic tract neurons by stimulation in periaqueductal gray or adjacent midbrain reticular formation
Authors: Gerhart K. D. , Yezierski R. P. , Wilcox T. K. , Willis W. D.
Published: December 2017

Recordings were made from spinothalamic tract (STT) cells in the lumbosacral enlargement of anesthetized monkeys. The cells were identified by antidromic activation from the contralateral ventral posterior lateral nucleus of the thalamus. Electrical stimulation at sites within the periaqueductal gray, the adjacent midbrain reticular formation, or the deep layers of the tectum were found to inhibit the activity of STT cells. In general, midbrain stimulation inhibited the background discharges and the responses of wide dynamic range cells evoked by innocuous and noxious cutaneous stimulation (29 of 37 cases). However, for six cells, midbrain stimulation preferentially inhibited the responses to noxious stimulation. The evoked responses of all 10 high-threshold cells were inhibited. In only two cases was midbrain stimulation ineffective, and no excitatory effects were observed. The mean latency to onset of inhibition resulting from midbrain stimulation was 24.9 +/- 7.2 ms (n = 35). The amount of inhibition produced by midbrain stimulation was graded with stimulus intensity. For example, trains of stimuli (333 Hz) at 50 microA produced a mean inhibition to 81.7 +/- 16.6% of control, while 200 microA resulted in a mean inhibition to 36.3 +/- 21.7%. Not only was the inhibition increased by the use of stronger current intensities, but the duration of inhibition was prolonged. Midbrain stimulation inhibited the responses of STT cells to volleys in both the A-fibers and the C-fibers of the sural nerve. However, there was a selective action in that the responses to C-fiber volleys were more strongly inhibited than were the responses to A-fiber volleys. Lesions placed in the white matter of the upper cervical spinal cord reduced the inhibition produced by stimulation in either the midbrain or the nucleus raphe magnus. The extent to which the inhibition was reduced was proportional to the extent of the cord lesions. However, even when there was an interruption of the entire lateral funiculus on the side of an STT cell and of the dorsal quadrant of the contralateral side, there was still substantial inhibition following stimulation in either brain stem site. It is concluded that while part of the inhibition is mediated by pathways descending in the dorsal lateral funiculus (DLF), at least some depends on pathways coursing through the ventral spinal cord. Inhibition of STT cells may contribute to the neuronal mechanism of the analgesia that results from stimulation in the periaqueductal gray matter in awake, behaving animals.
Primate raphe- and reticulospinal neurons: effects of stimulation in periaqueductal gray or VPLc thalamic nucleus
Authors: Willis W. D. , Gerhart K. D. , Willcockson W. S. , Yezierski R. P. , Wilcox T. K. , Cargill C. L.
Published: December 2017

Recordings were made from 132 raphe- and reticulospinal tract neurons in the medial part of the lower brain stem in 32 anesthetized monkeys. Recording sites were in the nucleus raphe magnus, the rostral nucleus raphe obscurus, and the reticular formation adjacent to the raphe. The neurons were identified by antidromic activation from the upper lumbar spinal cord. Of the population sampled, 83 cells were activated antidromically from the left dorsal lateral funiculus (DLF), 32 from the right DLF, and 17 from both sides. The mean latency for antidromic activation was 8.2 +/- 7.1 ms, corresponding to a mean conduction velocity of 22.8 m/s. No conduction velocities characteristic of unmyelinated axons were observed. Collision tests indicated that raphe-spinal axons that bifurcated to descend in both DLFs branched within the spinal cord. The effects of stimulation in the periaqueductal gray (PAG) or adjacent midbrain reticular formation were tested on 102 spinally projecting neurons in the medial medulla. Of these, 60 cells were excited, 9 cells were inhibited, 8 showed mixed excitation and inhibition, and 25 cells were unaffected. The mean latency for excitation was 11.6 ms and for inhibition, 17.8 ms. Threshold for excitation of raphe- and reticulospinal neurons ranged from 50 to 400 microA. Raphe- and reticulospinal tract cells could often (31/46 cells tested) be excited following stimulation in the ventral posterior lateral nucleus of the thalamus. The mean latency of excitation was 35.6 ms (range, 6-112 ms). Receptive fields could be demonstrated for 80 raphe- and reticulospinal cells, while 48 neurons possessed no demonstrable cutaneous receptive field. Most cells had large excitatory receptive fields, often encompassing the surface of the entire body and face. Some neurons had complex excitatory and inhibitory receptive fields, whereas other cells had large inhibitory receptive fields over much of the surface of the body and face. For most cells (52/55) with excitatory receptive fields, the only effective stimuli were noxious mechanical or noxious heat stimuli. Nonnoxious mechanical stimuli, such as brushing the skin, were capable of activating only a few (3/55) raphe- and reticulospinal neurons, and these were more effectively excited by noxious stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)
Metabolic variation among alpha-motoneurons innervating different muscle-fiber types. I. Oxidative enzyme activity
Authors: Sickles D. W. , Oblak T. G.
Published: December 2017

We have examined the oxidative metabolism of rat alpha-motoneurons innervating muscles composed predominantly of one muscle-fiber type. Intramuscular injections of horseradish peroxidase (HRP) into the tensor fasciae latae (TFL) (approximately 94% fast-twitch glycolytic fibers, FG), tibialis anterior (TA) (approximately 66% fast-twitch oxidative-glycolytic, FOG; 32% FG), and soleus (SOL) (approximately 84% slow-twitch oxidative, SO) muscles permitted identification of motoneurons innervating these muscles. gamma-Motoneurons (less than 25-micron average soma diameter) were eliminated from the sampling. The alpha-motoneurons innervating the TFL were considered as FG, those innervating the tibialis anterior as FOG, and those of the soleus as SO. Alternate 5-micron serial cryostat sections were processed for HRP and nicotinamide adenine dinucleotide-diapharase (NADH-D) (oxidative enzyme) activities. Controls were included to assure reliability of reaction product quantitation. Motoneuron pools of each muscle were characterized by their shape and location within the ventral horn. Cells identified on HRP sections as innervating each of the muscles were located on sections processed for NADH-D activity. The optical density of motoneurons in sections processed for NADH-D activity was measured with a Zeiss Zonax MPM 03 microdensitometer. The mean relative NADH-D activities (optical density) of alpha-motoneurons innervating the TFL (FG), TA (FOG), and SOL(SO) muscles were 0.261, 0.305, and 0.447, respectively. Although some overlap in distribution of enzyme activities was observed, statistical analysis indicated significant differences between the NADH-D activities of each type of alpha-motoneuron. This is the first report of any metabolic difference in alpha-motoneurons belonging to different motor-unit types.(ABSTRACT TRUNCATED AT 250 WORDS)
Morphology and synaptic relationships of physiologically identified low-threshold dorsal root axons stained with intra-axonal horseradish peroxidase in the cat and monkey
Authors: Ralston H. J. , Light A. R. , Ralston D. D. , Perl E. R.
Published: December 2017

The arborizations and synaptic relationships of intra-axonally stained horseradish peroxidase- (HRP) labeled primary afferent fibers to the dorsal horn of the cat and monkey spinal cord have been studied by light and electron microscopic methods. The light microscopic arborizations of the afferent fiber types (hair follicle afferents, pacinian corpuscle afferents, type I and type II slowly adapting afferents) are similar to those described by Brown and his colleagues (1) in the cat. The synaptic profiles formed by labeled afferents contain rounded synaptic vesicles. In serial thin sections, it was found that single dorsal root axons may make hundreds or thousands of synapses with neuronal structures of the dorsal horn. The vast majority of synaptic contacts are on the dendritic trees of dorsal horn neurons. The synapses made by these low-threshold afferent axons are almost all in the deeper laminae (III-VI) of the dorsal horn. The hair follicle afferent axons and the pacinian corpuscle afferents have numerous vesicle-containing structures that synapse on them to form either axoaxonal synapses or dendroaxonal synapses. The slowly adapting afferent axons are less often found to be postsynaptic to axons or dendrites. It is concluded that different physiological classes of primary afferent axons have different morphological characteristics, both at the light and electron microscopic level.
Neurons with unusual response and receptive-field properties in upper laminae of cat SI cortex
Authors: McKenna T. M. , Light A. R. , Whitsel B. L.
Published: December 2017

High-impedance micropipettes are used to record (both extra- and intracellularly) the electrical activity of neural elements located 550 micron or less from the pial surface of cerebral cortical areas 3a, 3b, 1, and 2 in unanesthetized cats. These elements are designated as "upper-layer SI units" and most frequently are sampled within the arm and forelimb digit sectors of areas 3b and 1. Mechanical stimulation of the skin is employed to determine the receptive field (RF) and response properties of the upper-layer units sampled. Single-shock electrical stimulation of the skin is used to obtain estimates of the minimal latency for eliciting spike discharge. Intracellular iontophoretic injection of horseradish peroxidase (HRP) is used to determine the laminar locations of the somata of the neural elements from which recordings are obtained. The receptive field (RF) and response properties of most upper-layer units sampled in areas 3b and 1 differ substantially from those of units recorded at depths greater than 550 micron from the pial surface in the same cortical fields. The members of one group of upper-layer area 3b and 1 units (U units) respond best to infrequently repeated (typically less than 0.5/s), slowly moving (1-5 cm/s) tactile stimuli. For the same units, repetitive application of slow-moving tactile stimuli to the RF typically leads to an enhancement of responsiveness accompanied by an elevation of spontaneous activity. In contrast, repetitive stimuli delivered at high velocity and at short interstimulus intervals lead to a decrease in unit responsiveness and to an absence of spontaneous activity. The members of a second group of upper-layer units (R units) respond best to moving stimuli delivered at higher velocities (5-20 cm/s), respond reliably at stimulus repetition rates well in excess of 0.5/s, and do not exhibit pronounced changes in responsiveness to repeated stimulation. The RFs of most upper-layer units (both R and U units) involve restricted regions on the contralateral upper limb, but the RFs of U units have poorly defined borders. In addition, the distribution of sensitivity within the RF of at least some U units is nonuniform and, frequently, discontinuous. Contralateral as well as ipsilateral body regions are included within the RFs for 12% of the upper-layer neurons sampled; the remainder (8%) have RFs restricted to the contralateral body.(ABSTRACT TRUNCATED AT 400 WORDS)
Intradendritic recordings from neurons of motor cortex of cats
Authors: Woody C. D. , Gruen E. , McCarley K.
Published: December 2017

The properties of neuronal spike potentials ranging from 20 to 60 mV in size were studied in stable recordings made from the motor cortex of unanesthetized, unparalyzed cats. Histologic evidence that injection of horseradish peroxidase (HRP) was confined to single neurons and appropriately high levels of potassium measured with K+ ion-sensitive electrodes indicated that these recordings were obtained from single, intracellularly penetrated neurons. Pressure injection of small volumes of 4% HRP in 1 M KC1, intracellularly, was characteristically associated with transient increases in spike size and decreases in input resistance. Recoveries of HRP-filled dendritic processes without filling of somata were obtained from penetrations giving spikes smaller than the recorded resting potential (spike-undershoot recordings). Recordings with dendritic recoveries had higher input resistances and showed greater increases in spike size during pressure injection than did recordings with both somata and dendrites recovered. The activity in response to a weak click elicited in cells with spike potentials between 20 and 40 mV was as great or greater than that elicited in cells with larger spike potentials or in extracellularly recorded units. We conclude that many stable spike-undershoot recordings of neurons of the motor cortex of awake cats reflect penetrations of dendritic processes as opposed to injury because they show a) a normal functional response to weak auditory stimuli delivered over periods of many minutes, b) a reversible increase in spike size during pressure injection of small volumes of HRP in KC1 consistent with penetration of a cable remote from the site of spike generation, and c) the frequent recovery of HRP-marked dendrites without somata.
Basal optic complex in the frog (Rana pipiens): a physiological and HRP study
Authors: Gruberg E. R. , Grasse K. L.
Published: December 2017

The basal optic projection in the frog Rana pipiens has been investigated by single-unit extracellular recording and horseradish peroxidase (HRP) histochemistry. We approached the projection from the ventral side of the brain and recorded single units in the basal optic projection proper as well as in the adjacent dorsomedial region (jointly called the basal optic complex). We found a) units responsive to stimuli moving in a vertical direction, b) an approximately equal number of units responsive to stimuli moving in a horizontal direction, and c) a smaller number of units responsive to changes in ambient light and moving stimuli without direction selectivity. Directional units display significant maintained activity and usually decrease their firing rate in response to stimulus motion in a direction opposite to that which elicits the maximal increase in firing rate. Receptive-field sizes for directional units ranged from 10 to 60 degrees. All units displayed vigorous excitatory response to a wide variety of moving stimuli within the velocity range of 0.2-10 degree/s. HRP histochemistry shows that in addition to the retina, the basal optic complex is connected to three principal areas: the ipsilateral tegmental griseum centrale, the ipsilateral dorsal ventrolateral nucleus of the anterior thalamus, and the ipsilateral posterior thalamic nucleus. In addition, a pathway was observed consisting of two groups of cells that send axons to the ipsilateral rostroventral medulla. This pathway originates a) in cells whose somata lie within the dorsomedial aspect of the basal optic complex (BOC); and b) in cells whose somata lie immediately outside the BOC in the adjacent gray, with apical dendrites extending into the BOC. Some of these fibers continue to the level of the spinal cord. Injection of HRP into the rostroventral medulla led to retrograde labeling of cells of the BOC.
Crayfish escape behavior: production of tailflips without giant fiber activity
Authors: Kramer A. P. , Krasne F. B.
Published: December 2017

The giant interneurons of the crayfish nerve cord are well-known mediators of fast tail flexions, "tailflips," that propel animals through the water away from danger. More recent studies have revealed an additional nongiant generator of tailflips. In contrast to giant tailflips, which are stereotyped, nongiant tailflips have variable form. The operating principles and portions of the neural circuitry governing nongiant tailflips were here investigated. Whereas fast flexor motor neurons (FFs) receive excitatory postsynaptic potentials (EPSPs) with large unitary components just prior to giant tailflips, excitation of the FFs during nongiant tailflips is due to summation of many small EPSPs, and these build up for about 60 ms prior to the tailflip; we call the period of excitation prior to FF firing the preflexion phase and the period during which FFs fire, the flexion phase of the tailflip. Even FFs that will not fire during a given tailflip become depolarized during preflexion and flexion periods. Throughout the preflexion and flexion periods there is activity in dorsal nerve cord axons (DCAs) that lie below the giants. Many DCAs are interneurons that excite FFs at short latency. Some DCAs fire uniquely during the preflexion phase, while some fire only during the flexion phase. Which DCAs fire is highly variable, and in some cases firing of particular DCAs can be correlated with particular forms of tailflips. Two identified DCAs, 12 and 13, that fire during the flexion phase were studied. These interneurons originate and receive their synaptic input in the second and third abdominal ganglia, respectively, and project to the last ganglion exciting FFs caudal to their ganglion of origin en route. Their pattern of synaptic input prior to and during nongiant tailflips is indistinguishable from that of FFs. Their input to FFs is weak, but when they fire they tend to promote intersegmental synchrony of FFs in the segments they feed. It appears likely to us that nongiant tailflips are synthesized from a small library of component tailflip movements that can be combined to produce a variety of complete tailflips and that the component movements are produced by a limited group of premotor interneurons, of which 12 and 13 are members.(ABSTRACT TRUNCATED AT 400 WORDS)