bluuebunny/crossref_metadata_2025 huggingface dataset:
Segmental reflex action in normal and decerebrate cats
Authors: Hoffer J. A. , Leonard T. R. , Cleland C. L. , Sinkjaer T.
Published: December 2017

1. The objective of this study was to evaluate the action of the stretch reflex on the ankle extensor muscles of normal and decerebrate cats. 2. Experiments were performed on nine freely standing, unrestrained cats and repeated after decerebration at the premammillary level. The length, force, and electromyograph (EMG) of the soleus (SOL) and lateral gastrocnemius (LG) muscles were recorded with the use of implanted transducers and electrodes. 3. The left ankle joint was unexpectedly and reproducibly dorsiflexed by briefly stimulating the common peroneal (CP) nerve with electrodes within an implanted nerve cuff. The ensuing twitch contractions of the ankle dorsiflexor muscles stretched the ankle extensor muscles by 0.3-2.0 mm. Lidocaine was infused into another nerve cuff proximal to the stimulation site, to reversibly block the central propagation of evoked volleys in the CP nerve. 4. Reflex action before and after decerebration was measured from the responses to perturbations of similar amplitude and duration delivered at approximately matched background values of muscle length and force. In most cats the temperature of the hindlimb was monitored with an implanted thermistor and was restored to normal values with radiant heat after decerebration. 5. A stretch imposed on the tonically active ankle extensor muscles immediately caused a considerable rise in the force recorded from the triceps tendon. Within 30-40 ms the triceps force peaked, reaching a value 10-20 N greater than background, and then rapidly declined while the extensor muscles were still lengthening. The initial rise in force preceded any change in triceps EMG. It was attributed to the intrinsic viscoelasticity of the stretched muscles and tendons. After decerebration the magnitude and timing of the initial force peak did not change. 6. A short-latency reflex EMG burst was typically recorded from both the SOL and LG muscles, starting 11-17 ms after stimulus onset. After decerebration the area of the reflex EMG burst increased in all nine cats, typically by a factor of 2 or 3. 7. After decerebration a second, smaller increase in force was typically observed starting 60-80 ms after onset of stretch. This later force rise, interpreted to be of reflex origin, was rarely apparent in normal cats. 8. Decerebration introduced consistent modifications in postural behavior that were revealed by pushing down on the back of quietly standing cats. In normal cats, after brief pushes that stretched the ankle extensor muscles by 1-2 mm, the EMG, force, and length quickly stabilized near their initial values.(ABSTRACT TRUNCATED AT 400 WORDS)
Scratch responses in normal cats: hindlimb kinematics and muscle synergies
Authors: Kuhta P. C. , Smith J. L.
Published: December 2017

1. Scratch responses evoked by a tactile stimulus applied to the outer ear canal were characterized in nine adult cats. Chronic electromyographic (EMG) electrodes were surgically implanted in selected flexor and extensor muscles of the hip, knee, and ankle joints to determine patterns of muscle activity during scratching. In some trials EMG records were synchronized with kinematic data obtained by digitizing high-speed cine film, and in one cat, medial gastrocnemius (MG) tendon forces were recorded along with EMG. For analysis the response was divided into three components: the approach, cyclic, and return periods. Usually scratch responses were initiated with the cat in a sitting position, but in some trials the animal initiated the response from a standing or lying posture. 2. During the approach period the hindlimb ipsilateral to the stimulated ear was lifted diagonally toward the head by a combination of hip and ankle flexion with knee extension. Hindlimb motions during the approach period were associated with sustained EMG activity in hip-flexor, knee-extensor (occasionally), and ankle-flexor muscles. Initial hindlimb motions were typically preceded by head movements toward the hindpaw, and at the end of the approach period, the head was tilted downward with the stimulated pinna lower than the contralateral ear. During the return period movements were basically the reverse of the approach period, with the hindpaw returning to the ground and the head moving away from the hindlimb. 3. During the cyclic period the number of cycles per response varied widely from 1 to 60 cycles with an average of 13 cycles, and cycle frequency ranged from 4 to 8 cycles/s, with a mean of 5.6 cycles/s. During each cycle the paw trajectory followed a fairly circular path, and the cycle was defined by three phases: precontact, contact, and postcontact. On average the contact phase occupied approximately 50% of the cycle and was characterized by extensor muscle activity and extension at the hip, knee, and ankle joints. The hindpaw contacted the pinna or neck at the base of the pinna throughout the contact phase, and paw contact typically resulted in a rostral motion of the head as the hindlimb extended. 4. The postcontact phase constituted approximately 24% of scratch cycle and was usually initiated by the onset of knee flexion. Ankle and then hip flexion followed knee flexion, and flexor muscles were active during the postcontact phase as the paw was withdrawn from the head. The precontact phase constituted approximately 26% of scratch cycle and was initiated by knee joint extension and knee-extensor activity.(ABSTRACT TRUNCATED AT 400 WORDS)
Cation current activated by hyperpolarization in a subset of rat nucleus accumbens neurons
Authors: Uchimura N. , Cherubini E. , North R. A.
Published: December 2017

1. Intracellular recordings were made from neurons in slices of rat nucleus accumbens in vitro. Membrane currents were measured in the potential range -60 to -120 mV with the use of a single-electrode, voltage-clamp amplifier. 2. A minority of neurons (28/285) was identified that had resting membrane potentials almost 20 mV less negative than the majority of the cells. These cells, but not the majority, had an inward current that activated slowly when the cells were hyperpolarized from -60 to -120 mV. The time constant of activation was approximately 3 s at -70 mV and 100 ms at -120 mV. 3. This inward current was completely blocked by external cesium (2 mM) but unaffected by barium. The current was reduced in solutions containing low-sodium concentration and increased in solutions with high-potassium concentration; its reversal potential was estimated to be -36 mV. 4. It is concluded that two types of neuron can be distinguished in the rat nucleus accumbens on the basis of the presence or absence of a cation current activated by hyperpolarization. This current (IH, also called If and IQ) causes the neurons to have less-polarized resting potentials than the majority of nucleus accumbens neurons.
Lesions of nonvisual inputs affect plasticity, norepinephrine content, and acetylcholine content of visual cortex
Authors: Gordon B. , Mitchell B. , Mohtadi K. , Roth E. , Tseng Y. , Turk F.
Published: December 2017

1. The depletion of both norepinephrine (NE) and acetylcholine (ACh) in the visual cortex can decrease plasticity. This decrease in plasticity, although dramatic under some circumstances, fails to occur under others. 2. We depleted cortical NE and ACh in 35- to 42-day-old kittens by making a lesion of the white matter behind the cingulate gyrus. One eye was sutured on the day of the lesion. We recorded from the visual cortex 7 days or 2-3 mo later and used the influence of the deprived eye on the cortical cells as a measure of plasticity. 3. We measured NE content by high-pressure liquid chromatography (HPLC) and inferred ACh depletion from depletion of choline acetyltransferase (ChAT) activity. NE depletion averaged 60% in the successfully depleted animals. Depletion of ChAT activity was consistent with NE depletion. 4. When recording occurred 7 days after the lesion and the sutured eye was contralateral to the lesion, plasticity was decreased on the side with the lesion; 70% of the cells were driven by the deprived eye. On the control, uninjured side only 15% of the cells were driven by the deprived eye. 5. In two circumstances the lesion did not cause a decrease in plasticity. In animals with suture ipsilateral to the lesion, the cortex remained plastic. In these animals only 26% of the cells in the hemisphere with the lesion were driven by the deprived eye. The cortex also retained its plasticity if the contralateral eye remained sutured for several months after the lesion, even though there was no recovery from NE and ACh depletion. 6. We conclude that depletion of NE and ACh does decrease plasticity; that is, it protects the deprived eye from losing its ability to drive cortical cells, at least for a short period of time. Depletion protects only the normally dominant contralateral pathway; the ipsilateral visual pathway remains plastic. 7. Perhaps the importance of the side of the deprived eye can be explained by assuming that depletion of NE and ACh removes facilitatory input. This would decrease the ability of cortical cells on the side with lesion to potentiate the input from the nondeprived eye relative to the deprived eye; that is, it would decrease the molecular deprivation (MD) effect. A removal of facilitation would also increase the visual input required to drive cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Cardiopulmonary sympathetic afferent excitation of lower thoracic spinoreticular and spinothalamic neurons
Authors: Ammons W. S.
Published: December 2017

1. Responses of spinoreticular (SRT) and spinothalamic (STT) neurons located in the T7-T9 segments to cardiopulmonary sympathetic afferent (CPS) stimuli were studied in 27 cats that were anesthetized with alpha-chloralose. 2. CPS stimulation excited 32 SRT and 10 STT neurons. Each neuron was also excited by stimulation of the left greater splanchnic nerve (SPL) and had a somatic receptive field that was most commonly located on the upper abdomen and over the lower rib cage. An additional 12 SRT and 3 STT neurons received input from SPL and somatic structures but failed to respond to CPS stimulation. 3. CPS stimulation evoked early responses (23 cells) or both early and late responses (19 cells) that had average latencies of 12.7 +/- 1.8 and 88.2 +/- 13.1 (SE) ms, respectively. Latencies of responses to SPL stimulation were significantly shorter and averaged 8.1 +/- 0.9 and 46.1 +/- 7.1 ms. Magnitudes of early responses to SPL stimulation were significantly greater than responses to CPS stimulation; however, late responses were not different. 4. Responses to CPS stimulation were inhibited by a prior conditioning stimulus applied to SPL. Greatest inhibition occurred at a conditioning-test interval of 40 ms, and inhibition lasted for at least 300 ms. Inhibition of responses to SPL stimulation could be evoked by conditioning stimuli applied to CPS; however, the inhibition was significantly less than that evoked by SPL stimulation on responses to CPS stimulation. 5. Thirty-eight neurons were tested for responses to injection of bradykinin (4 micrograms/kg) into the left atrium. Discharge rate of 17 cells increased from 5 +/- 2 to 12 +/- 4 Hz. Four cells were tachyphylactic to repeated injections. Injections of bradykinin into the thoracic aorta did not significantly alter cell activity. Bilateral cervical vagotomy had no effect on responses to intracardiac bradykinin. 6. The results indicate that lower thoracic SRT and STT neurons are excited by CPS stimuli including noxious stimulation of the heart. However, comparison of these responses with previously reported responses of upper thoracic SRT and STT neurons indicate that there is a decrease in effectiveness of CPS stimuli from upper to lower thoracic segments. Convergence of CPS and abdominal inputs onto lower thoracic pain pathways could explain abdominal pain that is occasionally associated with cardiac disease.
Characteristics of midbrain control of spinal nociceptive neurons and nonsomatosensory parameters in the pentobarbital-anesthetized rat
Authors: Sandkuhler J. , Willmann E. , Fu Q. G.
Published: December 2017

1. GABAergic mechanisms in the midbrain periaqueductal gray (PAG) have been proposed to control the activity of descending antinociceptive systems and defensive behavior. Here, the effect of neuronal disinhibition by gamma-aminobutyric acid (GABAA) receptor blockade at midbrain sites on spinal neuronal responses to noxious and innocuous skin stimulation was quantitatively characterized. It was compared with the effect of direct neuronal excitation by glutamate microinjections or electrical stimulation at identical sites. Changes in mean arterial blood pressure and other nonsomatosensory responses were also assessed. 2. Responses of 101 multireceptive lumbar spinal dorsal horn neurons to noxious radiant skin heating (50 degrees C, 10 s), innocuous skin brushing, and electrical stimulation of primary afferent A- and C-fibers were recorded in deeply pentobarbital-anesthetized rats. The mean blood pressure was continuously monitored in one carotid artery, and other nonsomatosensory parameters, such as frequency and depth of spontaneous respiration and contractions of abdominal and facial muscles, were classified according to their relative intensity into five groups. 3. A fine, multibarrel glass pipette was constructed for monopolar electrical stimulation and microinjection of the GABAA receptor antagonist bicuculline (40, 200, or 400 pmol), or glutamate (10–50 nmol), or Fast Green dye in 50 or 100 nl at identical sites in the midbrain. 4. Bicuculline microinjections into discrete regions of the PAG selectively abolished spinal neuronal responses to noxious skin stimulation but did not affect brush-evoked responses or responses to electrical A-fiber stimuli. This antinociception was often, albeit not necessarily, accompanied by tachypnoea and abdominal and facial muscle contractions and changes--mostly increases--in mean arterial blood pressure. Injections into other areas of the PAG and adjoining ventral tegmentum (VT) were less effective. The vast majority of injection sites in the lateral tegmentum (LT) were ineffective. 5. Glutamate microinjections at midbrain sites to detect areas of origin of descending antinociceptive neurons were characterized by a high incidence (greater than 50%) of false-negative results, as bicuculline was shown to be effective at numerous glutamate-insensitive sites. Glutamate microinjections into some sites of the PAG and adjoining VT reduced, but did not abolish, spinal neuronal responses to noxious skin heating. Injections into the LT were ineffective. 6. The efficacy of electrical stimulation at midbrain sites on spinal nociceptive responses had no predictive value for the effect of glutamate or bicuculline.(ABSTRACT TRUNCATED AT 400 WORDS)
Physiological properties of neurons in the mouse superior olive: membrane characteristics and postsynaptic responses studied in vitro
Authors: Wu S. H. , Kelly J. B.
Published: December 2017

1. The physiological properties of cells in the superior olivary complex (SOC) were studied in 400-microns brain slices taken through the mouse auditory brain stem. Coronal sections were prepared from fresh brain tissue and were placed fully submerged in an oxygenated saline solution. The boundaries of the medial nucleus of the trapezoid body (MNTB), the lateral superior olive (LSO), and the fibers of the trapezoid body were visualized through a dissecting microscope, and micropipettes filled with 4 M potassium acetate were inserted into the LSO or MNTB. 2. Bipolar stimulating electrodes were placed along the trapezoid body usually at the midline decussation and at a location just lateral to the LSO. This arrangement allowed for stimulation of the trapezoid body both contralateral and ipsilateral to the SOC. Synaptic potentials were elicited by delivering brief (0.1 ms) current pulses to the fibers of the trapezoid body. In some cases the integrity of the fibers was confirmed by transport of horseradish peroxidase (HRP) after extracellular microinjections at various locations along the pathway. The HRP reaction product revealed active transport within the trapezoid body and characteristic synaptic and terminal morphology in the MNTB and LSO. The MNTB contained primarily large-diameter fibers terminating in specialized endings (the calyces of Held), whereas the LSO contained mainly small-diameter fibers and punctate terminal boutons. 3. Membrane characteristics of cells in MNTB and LSO were determined by injecting current into the cell and measuring the corresponding voltage change. Neurons in LSO exhibited a roughly linear relation between voltage and intracellularly injected current. Negative current resulted in a graded hyperpolarization of the cell membrane, and positive current resulted in a graded depolarization that led to the production of action potentials. The number of action potentials was directly related to the strength of the current injected. In contrast, the neurons in MNTB had current-voltage relations that were strongly nonlinear around resting potential. The injection of negative current led to graded hyperpolarization, but injection of positive current produced a limited depolarization that resulted in either a single large action potential or an action potential followed by several spikes with greatly reduced amplitude. 4. Excitatory postsynaptic potentials (EPSPs) could be elicited in LSO by ipsilateral stimulation of the trapezoid body and in MNTB by contralateral stimulation. In response to repeated stimulation, some cells in LSO exhibited temporal summation, that is, a series of slightly subthreshold current pulses produced postsynaptic potentials that combined to elicit action potentials.(ABSTRACT TRUNCATED AT 400 WORDS)
Basal ganglia motor control. III. Pallidal ablation: normal reaction time, muscle cocontraction, and slow movement
Authors: Mink J. W. , Thach W. T.
Published: December 2017

1. Inactivation of the portions of globus pallidus pars interna (GPi) containing the greatest concentration of wrist-related neurons was achieved in two rhesus monkeys with microinjections of muscimol (temporary) and kainic acid (permanent). 2. After muscimol injection, there was onset within 30 s of 1) tonic and phasic coactivation of wrist flexors and extensors; 2) slightly greater activation of the flexors, giving a flexor bias in postural holds and the endpoint of movements; and 3) slowness of all movements with a prolonged movement time. Nevertheless, 4) movements made by lessening prior loaded muscle activity (to move in the direction of the load) were slower than movement made by increasing muscle activity (to move against the direction of the load). Despite marked slowing of all movements, there was 5) a normal reaction time for movement onset. Finally, there was 6) a reduced amplitude of most movements. Open room behavior included 7) spiraling contralateral to the lesion while walking. Effects were reproducible (12 injections), were apparent for 7-8 h and were usually completely gone by the next day's testing. 3. After kainic acid injection, there was a period of mixed effects, followed by a period of permanent defects (observed for up to 24 days) that duplicated the temporary effects of muscimol. 4. By contrast, muscimol inactivation of the cerebellar dentate nucleus resulted in 1) a prolonged reaction time and 2) an increased variability of movement trajectory, but 3) without change in movement time or peak velocity. Open room behavior included overshoot in reaching for fruit with the forelimb ipsilateral to the injection. 5. From the facts that normal pallidal neurons fire constantly, that pallidal neurons inhibit their target neurons, and that the muscimol effect was immediate, we conclude that the release of the target neurons from the tonic inhibition allowed them to fire in patterns that promoted a maintained state of cocontraction of agonist and antagonist muscles. From the fact that movement time was prolonged, we conclude that the maintained state of neural activity that caused the muscle cocontraction interfered with the commands for voluntary movement, which were generated by other mechanisms. From the fact that reaction time for movement onset was normal, we conclude that the pallidal neurons may play little or no role in the voluntary initiation of these movements, which are instead generated by other structures that include the anterior cerebral cortex and the lateral cerebellum.
Long-term potentiation of nicotinic transmission by a heterosynaptic mechanism in the stellate ganglion of the cat
Authors: Bachoo M. , Polosa C.
Published: December 2017

1. In the anesthetized, scopolamine-treated cat, the compound action potential (CAP) evoked by a single supramaximal shock to the third thoracic white ramus (T3WR) was recorded in the inferior cardiac nerve (ICN). The CAP was depressed in a dose-dependent manner by the intravenous administration of the nicotinic antagonist hexamethonium (C6). 2. During steady intravenous infusion of C6, which reduced the amplitude of the CAP by 80-90%, a short train of stimuli (few seconds, 10-40 Hz) to the sympathetic trunk just below T4WR potentiated the CAP for periods of tens of minutes to 1-2 h (heterosynaptic long-term potentiation, LTP). An LTP of similar time course was obtained when both train and single shock were applied to T3WR (homosynaptic LTP). Magnitude and duration of the heterosynaptic LTP were dependent on number, frequency, and intensity of the stimuli. No LTP was produced by a train to the ICN. Heterosynaptic LTP was also observed in the absence of C6. Because of the limited subliminal fringe of the test input under this condition, the LTP was of small magnitude. Heterosynaptic LTP also of the heart rate (HR) response to a test stimulus was observed after a conditioning train. 3. The conditioning train produced a displacement to the right of the dose-response curve for C6. The intravenous dose of C6 required for 50% attenuation of the test CAP increased from 0.84 +/- 0.15 (SE) mg/kg pretrain to 2.56 +/- 0.46 mg/kg posttrain (n = 5, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Electrotonic structure of olfactory sensory neurons analyzed by intracellular and whole cell patch techniques
Authors: Pongracz F. , Firestein S. , Shepherd G. M.
Published: December 2017

1. Experimental studies employing whole cell patch recordings from freshly isolated olfactory sensory neurons of the salamander (Ambystoma tigrinum) yield much higher estimates of specific membrane resistance (Rm) than studies using conventional intracellular recordings from in situ neurons. Because Rm is critical for understanding information transfer in these cells, we have used computational methods to analyze the possible reasons for this difference. 2. Compartmental models were constructed for both the in situ and isolated neurons, using SABER, a general-purpose simulation program. For Rm in the in situ cell, we used a high value of 100,000 omega.cm2, as estimated in the whole cell recordings from isolated cells. A shunt across the cell membrane caused by the penetrating microelectrode was simulated by several types of shunt mechanisms, and its effects on lowering the apparent value of resting membrane potential (MP), input resistance (RN), and membrane time constant (tau m) and increasing the electrotonic length (L) were analyzed. 3. A good approximation of the electrotonic properties recorded intracellularly was obtained in the in situ model with high Rm combined with an electrode shunt consisting of Na and K conductances. A raised K conductance (1-5 nS) helps to maintain the resting MP while contributing to the increased conductance, which lowers RN and shortens the apparent tau m toward the experimental values. 4. Combined shunt resistances of 0.1-0.2 G omega (5-10 nS) gave the best fits with the experimental data. These shunts were two to three orders of magnitude smaller than the values reported from intracellular penetrations in muscle cells and motoneurons. This may be correlated with the smaller electrode tips used in the recordings from these small neurons. We thus confirm the prediction that even small values of electrode shunt have relatively large effects on the recorded electrotonic properties of small neurons, because of their high RN (2-5 G omega). 5. We have further explored the effects on electrotonic structure of a nonuniform Rm by giving higher Rm values to the distally located cilia compared with the proximal soma-dendritic region, as indicated by recent experiments. For the same RN, large increases in ciliary Rm above 100,000 omega.cm2 can be balanced by relatively small decreases below that value in soma-dendritic Rm. A high ciliary Rm appears to be a specialization for transduction of the sensory input, as reported also in photoreceptors and hair cells.
Characterization of sodium current in developing rat diencephalic neurons in serum-free culture
Authors: Park C. C. , Ahmed Z.
Published: December 2017

1. Dissociated, synchronized (G1 phase of cell cycle), and birth-dated fetal rat diencephalic neurons were grown in a serum-free defined medium. The gigaseal whole-cell voltage-clamp technique was used to measure the inward Na+ currents (INa) from morphologically identified bipolar neurons. The earliest expressed somatic INa has been characterized and compared with that present at a later date. 2. The identity of the INa was established on the basis of its reversal potential and reversible blockade by tetrodotoxin (TTX). Close agreement between the measured reversal potentials (68.5 +/- 1.3 and 38.3 +/- 2.4 mV, mean +/- SE) and calculated Nernst equilibrium potentials (64.6 and 34.7 mV) at two different bath Na+ concentrations (120 and 35 mM, respectively) suggests that the channels are highly selective for Na+. 3. The peak INa density increased from 47.7 +/- 2.9 pA/pF in younger neurons (5-6 days in culture) to 93.9 +/- 6.4 pA/pF in older neurons (12-13 days in culture). The activation voltage and the voltage for peak current were also shifted by 10 mV in the hyperpolarizing direction, from -30 and +10 mV in younger neurons to -40 and 0 mV in older neurons, respectively. However, the reversal potential did not change (69.2 +/- 2.3 and 68.5 +/- 1.3 mV in younger and older neurons, respectively). 4. In older neurons the steady-state inactivation parameters (V1/2, the voltage at which inactivation was 50% of maximum, and kh, the voltage at which there is an e-fold change in inactivation) were significantly altered. V1/2 was shifted from -41.5 +/- 2.3 to -48.8 +/- 1.8 mV, and kh was increased from 6.2 +/- 0.5 to 8.9 +/- 0.4 mV. However, the time course of activation and the rates of inactivation and recovery from inactivation were unchanged. 5. In both groups, the INa decays were best described by a sum of two exponentials. The corresponding time constants were voltage dependent. Also, the amplitudes of the two components were differentially affected by membrane potential and niflumic acid. 6. The extrapolated amplitudes of both the fast and the slow components of INa were larger in older neurons, but the ratio of the amplitudes of the two components did not change with age. The voltage dependencies of the time constants of both components were altered. 7. We conclude that INa in fetal rat diencephalic neurons grown in a defined medium with only essential nutrients undergoes in vitro changes in current density and in some, but not all, kinetic parameters.(ABSTRACT TRUNCATED AT 250 WORDS)
Synchronized GABAergic IPSPs recorded in the neocortex after blockade of synaptic transmission mediated by excitatory amino acids
Authors: Aram J. A. , Michelson H. B. , Wong R. K.
Published: December 2017

1. Intracellular and extracellular recordings were carried out in guinea pig neocortical slices to examine the effects of blockade of excitatory amino acid (EAA) synaptic transmission on population discharges elicited by 4-aminopyridine (4-AP; 50-100 microM). 2. After the introduction of 4-AP, two distinct types of rhythmic spontaneous field potentials were recorded in neocortical slices. Type I consisted of multiple spike discharges lasting 20-90 s. These events occurred at a frequency of 0.4-0.2/min. Type II were single field potential spikes (3-6 s in duration) occurring at a higher frequency (2-4/min). 3. Blockade of amino acid-mediated excitatory synaptic transmission with D-2-amino-5-phosphonovaleric acid (D-AP5; 10-30 microM) or 3-(2-carboxypiperazin-4-yl)propyl-l-phosphonic acid (CPP, 10 microM) and 6-cyano-7nitroquinoxaline-2,3-dione (CNQX; 10 microM) abolished the first type of 4-AP-induced field potential, whereas type II events persisted. 4. Type II field events, occurring in the presence of EAA blockers, were further characterized by paired recordings. Events recorded along an axis orthogonal to the pia surface occurred simultaneously without measurable delay. Recordings made along a plane parallel to the pia surface showed that type II discharges propagated over distances of greater than or equal to 3 mm at an estimated velocity of 7.5 mm/s. 5. Intracellular recordings show that during type II field discharges all cells exhibited phasic depolarizations or hyperpolarizations, depending on the resting membrane potential. When resting potentials were more depolarized than -68 mV, events became mostly hyperpolarizing.(ABSTRACT TRUNCATED AT 250 WORDS)
Coding the sweet taste in the nucleus of the solitary tract: differential roles for anterior tongue and nasoincisor duct gustatory receptors in the rat
Authors: Travers S. P. , Norgren R.
Published: December 2017

1. A variety of chemicals that humans describe as sweet drive neurons in the nucleus of the solitary tract (NST) of the rat more vigorously when applied to the taste receptors associated with the nasoincisor ducts (NID) than when applied to taste receptors on the anterior tongue (AT). 2. The differential effects of sweet stimuli applied to the AT and NID also are evident in the set of across-neuron correlations produced by these stimuli. The psychophysical similarity among the sweet stimuli is better accounted for by responses to stimulation of the NID than by responses to stimulation of the AT (mean correlation between pairs of sweet stimuli = +0.70 for the NID, +0.44 for the AT). 3. Disaccharides or polysaccharides of glucose, i.e., maltose (0.3 M) and Polycose (0.1 M), are poor stimuli on the NID, evoking responses only 17.8 and 26.7% as great as the response elicited by sucrose (0.3 M), an optimal stimulus for this receptor subpopulation. This suggests that Polycose and maltose interact with receptor sites distinct from those with an affinity for sweet stimuli. Polycose and maltose also are ineffective stimuli on the AT, evoking responses only 11.8 and 4.9% as large as the response evoked by an optimal stimulus for this receptor subpopulation, a mixture of electrolytes (0.3 M NaCl, 0.03 M HCl, and 0.01 M quinine HCl). 4. The relative effectiveness of the sweet sugars in driving NST neurons (sucrose greater than fructose greater than glucose) correlates with their order of effectiveness in generating preference behavior in the rat.(ABSTRACT TRUNCATED AT 250 WORDS)
The raccoon lateral cervical nucleus: a single-unit analysis
Authors: Simone D. A. , Pubols B. H.
Published: December 2017

1. Properties of 90 lateral cervical nucleus (LCN) neurons responsive to light tactile stimulation of ipsilateral body surfaces were examined in pentobarbital sodium-anesthetized raccoons. Peripheral receptive fields (RFs) of 60 of these lay totally or partially on glabrous skin of the forepaw. There were 71 neurons antidromically activated from the contralateral thalamic ventro-basal complex (VB) or medial lemniscus. Results were compared with previous findings in the raccoon spinocervical tract (SCT) and the dorsal column-medial lemniscal system (DC-MLS). 2. RFs located on glabrous skin of the digits were significantly smaller than those located on glabrous skin of the palm. All RFs, whether on glabrous skin of the forepaw or elsewhere, tended to be larger than those of either SCT or DC-MLS neurons. LCN units with glabrous forepaw RFs tended to be located ventrally within the nucleus. 3. Of those LCN neurons for which the RFs lay totally or partially on glabrous skin of the forepaw, relative numbers that were rapidly adapting (RA; 77%) versus slowly adapting (SA; 23%) were comparable with those found in the SCT and in VB. Relative numbers of LCN neurons that were classed as light touch (87%) versus multireceptive (13%) were comparable with those found in the SCT. 4. In contrast to both the SCT and VB, but in common with the prethalamic DC-MLS, indentation velocity coding functions of both RA and SA units fell within homogeneous groupings, power function exponents for RA units tending to be steeper than those for SA units (range of b = 0.710 - 0.919 vs. 0.448 - 0.883). 5. It is concluded that the raccoon spinocervicothalamic system (SCTS) as a whole lacks the "modality and place specificity" associated with the DC-MLS. Although the SCTS probably makes significant contributions to properties of VB neurons, these properties primarily reflect those of neurons of the DC-MLS.
Taste-responsive neurons of the glossopharyngeal nerve of the rat
Authors: Frank M. E.
Published: December 2017

1. Taste sensibilities of neurons in mammalian glossopharyngeal nerves have been inadequately studied, although they innervate the majority of taste buds and may provide unique taste information. 2. Extracellular responses of glossopharyngeal neural units to taste stimuli infused into foliate or vallate papillae were recorded in anesthetized rats. A 0.3-ml/min infusion of stimuli into papillae resulted in short-latency, 5-s nerve-impulse rates that approached 10 times the response rates observed using less invasive means of stimulation. 3. Sucrose, Na saccharin, NaCl, NH4Cl, KCl, HCl, citric acid, acetic acid, MgSO4, and quinine.HCl were effective stimuli for glossopharyngeal neurons at concentrations that have behavioral significance. 4. Response spectra for individual neural units with either foliate or vallate receptive fields fell into three clusters. Forty-six percent were A units that responded most strongly to acids and chloride salts, NH4Cl being the most effective; neither quinine nor sucrose was effective. Twenty-three percent were S units that responded to sugars and saccharin; quinine, salts, and acids were not effective. Thirty-one percent were Q units that responded to quinine; neither NaCl, HCl, nor sucrose was effective stimulus for these fragile units. 5. Glossopharyngeal A neural units were more sensitive to 1 mM HCl than were electrolyte-sensitive H units of the chorda tympani, although both respond generally to salts and acids. Units relatively specific for sodium salts (N units), which are common in the chorda tympani nerve, were not found in the glossopharyngeal nerve, which explains losses in sodium-specific behavior after cutting only the chorda tympani nerve. 6. Q units were the only glossopharyngeal neural units that responded significantly to quinine, and units with similar response spectra do not occur in the chorda tympani nerve. Q units probably mediate aversive reflexes to quinine that are eliminated by cutting only the glossopharyngeal nerve. Glossopharyngeal S neural units were more sensitive to sucrose and are more common than their counterparts in the chorda tympani, although it is not known how they might compare with sugar-sensitive units in the greater superficial petrosal nerve. 7. These data strongly suggest that posterior taste bud fields innervated by the glossopharyngeal nerve are specialized for functions different from those of anterior taste bud fields innervated by the facial nerve.
Neurogenic hyperalgesia: psychophysical studies of underlying mechanisms
Authors: LaMotte R. H. , Shain C. N. , Simone D. A. , Tsai E. F.
Published: December 2017

1. Psychophysical studies were made, in humans, of the sensory characteristics and underlying mechanisms of the hyperalgesia (often termed “secondary hyperalgesia”) that occurs in uninjured skin surrounding a local cutaneous injury. The hyperalgesia was characterized by lowered pain thresholds and enhanced magnitude of pain to normally painful stimuli. The “injury” was produced by a single intradermal injection of 10 microliters of 100 micrograms of capsaicin, the algesic substance in hot chili peppers. 2. On injection of capsaicin into the volar forearm, the subjects experienced intense burning pain, accompanied immediately by the formation of three areas of hyperalgesia surrounding the injection site. The largest mean area (55 cm2) was hyperalgesic to a normally painful punctate stimulation of the skin. Nested within this was an area of tenderness to gentle stroking (38 cm2) and a much smaller area of hyperalgesia to heat (2 cm2). An area of analgesia to pinprick, approximately 4 mm in diameter and centered on the injection site, developed within minutes and typically disappeared within 24 h. The hyperalgesia to heat and to stroking disappeared within 1-2 h, whereas the hyperalgesia to punctate stimuli, although gradually decreasing in area, lasted from 13 to 24 h. 3. The radial spread of the mechanical hyperalgesia (to punctate and stroking stimuli) away from the injury was dependent on neural activity and not produced, for example, by algesic substances transported away from the injury. The injection of capsaicin into a small area of anesthetized skin did not produce hyperalgesia in the surrounding, unanesthetized skin. Also, the hyperalgesia in normal skin readily crossed a tight arm band that blocked the circulation of blood and lymph. 4. The spread of mechanical hyperalgesia away from the injury was peripherally mediated via cutaneous nerve fibers because it was blocked by a thin mediolateral strip of cutaneous anesthesia placed 1 cm away from the capsaicin injection site. Hyperalgesia developed normally on the capsaicin side of the strip but not on the other side. 5. Heat stimulation of the skin that produced pain that was equivalent in magnitude and time course to that produced by an injection of capsaicin (10 micrograms) resulted in much smaller areas of mechanical hyperalgesia. It was postulated that there exist special chemosensitive primary afferent nerve fibers that are more effective in producing mechanical hyperalgesia than are the known thermo- and mechanosensitive nociceptive nerve fibers. 6. Once developed, the mechanical hyperalgesia became only partially dependent on peripheral neural activity originating at the site of injury.(ABSTRACT TRUNCATED AT 400 WORDS)
Neurogenic hyperalgesia: the search for the primary cutaneous afferent fibers that contribute to capsaicin-induced pain and hyperalgesia
Authors: Baumann T. K. , Simone D. A. , Shain C. N. , LaMotte R. H.
Published: December 2017

1. A local cutaneous injury can produce primary hyperalgesia within the injured area and secondary hyperalgesia in the normal surrounding skin. An intradermal injection of capsaicin in humans causes intense pain and hyperalgesia to heat and to mechanical stimuli in the surrounding skin. Psychophysical studies in humans supported the conclusions that the hyperalgesia was predominantly the secondary type and depended on one set of neurons sensitizing another (“neurogenic hyperalgesia”) and that the latter set of neurons is located in the central and not the peripheral nervous system. To further test this hypothesis and to search for peripheral neural mechanisms contributing to the pain and neurogenic hyperalgesia from a local injury, we performed neurophysiological experiments in the monkey (Macaca fascicularis) and recorded the responses of cutaneous primary afferent fibers to an intradermal injection of capsaicin and to mechanical and heat stimuli delivered before and after the injection. 2. Most C- and A-fiber mechanoheat-sensitive nociceptive afferent fibers (CMHs and AMHs, respectively) responded too weakly or transiently to capsaicin to account quantitatively for the magnitude of capsaicin pain. Of the known primary afferents tested with capsaicin injections, only the responses of heat-selective nociceptors could potentially account for the pain measured psychophysically in the human. In addition, a novel type of primary afferent--tentatively termed “chemonociceptive”--may have contributed as well. 3. Nociceptive fibers did not become sensitized to either mechanical or heat stimulation after an injection of capsaicin either outside, adjacent to, or inside the receptive field (RF); any changes that occurred could not explain the hyperalgesia to mechanical or heat stimuli observed in humans. 4. The depressed responsiveness ("desensitization") of both myelinated and unmyelinated nociceptive fibers in the monkey to heat and/or mechanical stimulation of the injection site after capsaicin was injected inside their RFs correlated with the analgesia observed at the capsaicin injection site in the human. 5. Capsaicin, topically applied to the RF in a vehicle of dimethyl sulfoxide or alcohol, excited CMHs and AMHs and enhanced the responses of some of these fibers to heat and/or to stroking the skin. In some cases, similar results were produced by the vehicle alone. However, capsaicin and not the vehicle lowered the thresholds of some CMHs to heat. Thus the sensitization of CMHs contributes to the primary hyperalgesia known to occur within the area of skin directly exposed to topically applied capsaicin.(ABSTRACT TRUNCATED AT 400 WORDS)
Excitatory effects of ACPD receptor activation in the hippocampus are mediated by direct effects on pyramidal cells and blockade of synaptic inhibition
Authors: Desai M. A. , Conn P. J.
Published: December 2017

1. Phosphoinositide hydrolysis-linked excitatory amino acid (EAA) receptors (ACPD receptors) are selectively activated by the glutamate analogue trans-1-amino-1,3-cyclopentanedicarboxylic acid (trans-ACPD). Regional analysis of trans-ACPD-induced phosphoinositide hydrolysis indicates that this response is greater in the hippocampus than in other brain regions. Therefore we designed a series of studies aimed at testing the hypothesis that activation of this receptor modulates synaptic function in the hippocampal region. 2. We report that trans-ACPD dramatically altered field population spikes at each of the three major synapses in the hippocampal trisynaptic circuit at concentrations that are effective in activating phosphoinositide hydrolysis. At the perforant path-dentate gyrus synapse, bath application of trans-ACPD resulted in a decrease in the amplitude of field population spikes. In contrast, trans-ACPD markedly enhanced field population spike amplitude at the mossy fiber-CA3 synapse and the Schaffer collateral-CA1 synapse. In area CA1, but not area CA3, trans-ACPD also induced generation of multiple population spikes. 3. Simultaneous field potential recordings from the s. pyramidale and s. radiatum in area CA1 revealed that the effect of trans-ACPD on population spikes in this region was not accompanied by an increase in the initial slope of the field EPSP. This suggests that the effect of trans-ACPD was not mediated by a presynaptic action but must be mediated by direct effects on CA1 pyramidal cells or by a decrease in synaptic inhibition. 4. trans-ACPD had a number of direct excitatory effects on CA1 pyramidal cells. These included 1) cell depolarization (with an increase in input resistance), 2) inhibition of the slow afterhyperpolarization, and 3) blockade of spike frequency adaptation. trans-ACPD also had effects on CA1 pyramidal cells that were not excitatory in nature. These included an increase in the threshold for initiation of calcium spikes and an increase in interspike interval during prolonged current injection. None of these effects were mimicked by an ACPD analogue that does not activate the ACPD receptor (trans-methanoglutamate), nor were they blocked by kynurenate, a nonselective EAA receptor antagonist that does not block the ACPD receptor.(ABSTRACT TRUNCATED AT 400 WORDS)
Differential antagonism of transmitter release by subtypes of omega-agatoxins
Authors: Bindokas V. P. , Venema V. J. , Adams M. E.
Published: December 2017

1. The omega-agatoxins from Agelenopsis aperta spider venom are a diverse group of voltage-sensitive calcium channel antagonists. Subtypes of omega-agatoxins are distinguished as type I (omega-Aga-IA, omega-Aga-IB, and omega-Aga-IC), type II (omega-Aga-IIA and omega-Aga-IIB), and type III (omega-Aga-IIIA and omega-Aga-IIIB). All except type III toxins block calcium channels in insect motor nerve terminals and in neuronal cell bodies at nanomolar concentrations. 2. The potency and maximum level of block of the excitatory junctional potential (EJP) by omega-agatoxins are dependent on the extracellular calcium concentration ([Ca]o). Saturating concentrations of type I or II omega-agatoxins block 97-99% of the evoked EJP in low [Ca]o (0.75 mM) saline. A remnant of the EJP (1-3%) that persists after toxin exposure suggests that a small amount of voltage-dependent calcium entry is toxin resistant. When [Ca]o is elevated to 5 mM, this resistant component increases dramatically, revealing differences between type I and type II block. Under these conditions, 60-70% of the EJP is resistant to type I toxins and approximately 20% is resistant to type II toxins. 3. Sequential application of type I and II toxins in high [Ca]o leads to enhanced block of the EJP, suggesting that type I and II omega-agatoxins may block calcium channels by different mechanisms. 4. Type I and type II omega-agatoxins also block calcium channels in the somata of locust dorsal unpaired median (DUM) neurons. In agreement with studies on neuromuscular transmission, block of barium action potentials is incomplete after either type I or type II toxin exposure and combined application of the toxins results in enhanced block. 5. Partial calcium channel antagonism by type I and type II toxins could be explained either by altered kinetics of toxin-modified channels or by selectivity for different subtypes of presynaptic calcium channels.