Electrosensitivity of canal and free neuromast organs in a gymnotid electric fish

The posterior lateral line nerve was studied by recording singel unit activity with glass miocropipette electrodes to examine the electrosensitivity of the canal and free neuromast organs. The fibers innervating these organs has no or irregular spontaneous discharges. For a 50 msec electric pulse applied through a pair of electrodes at the two ends of the fish, almost all fibers discharged impulses during the pulse, irrespective of its polarity. The electrosensitivity for a 50 msec electric pulse was 37 mV/cm on the average. When a 0.5–1.0 msec electric pulse was used, these fibers showed no responses to it, even if it was stronger than 40 mV/cm. Responses to organ discharges were not found at all. These organs do not seem to function as electroreceptors. The canal organ was excited by water ripple and by weak water currents allied to the trunk and can be considered a mechanoreceptor. The free neuromast of the trunk was mechanically excitable, but it did not respond to moderately strong water current, and its function remains unclear.     

Axon-to-axon transmission in tullidora (buckthorn) neuropathy

Oral administration of ether extracts of the tullidora (Karwinskia humboldtiana) fruit, which contains an identified neurotoxin, produced flaccid hind limb paralysis in cats after a latency of 4 to 7 weeks. Acute experiments were conducted after the paralysis was evident. Spinal roots of lumbar and sacral segments were transected as close as possible to the spinal cord and divided into several filaments. Stimulation of some filaments distal to the transection evoked action potentials in other filaments (axon-to-axon transmission or cross talk) after a latency of at least 8 ms. Cross-talk responses frequently consisted of multiple discharges. Axon-to-axon transmission was seen only between motor axons and disappeared when hind limb nerves were transected 10 to 15 cm from the spinal cord. Twin pulses were applied to a filament at various intervals; the pulse intensity was adjusted so that the conditioning pulse was subthreshold to elicit cross talk, but the test pulse frequently elicited it (temporal facilitation). In three fully studied fibers the facilitation was prolonged to 50 to 80 ms. In some cases, no cross talk was evoked in a given filament by individual stimulation of two other filaments, but simultaneous stimulation of the same filaments did evoke cross talk (spatial facilitation). Series of periodic bursts of activity spontaneously occurred in those axons responding with multiple discharges to single stimulation of other axons. At low temperatures (about 30°C) the stimulus could trigger essentially similar series of bursts. Single motoneurons were intracellularly stimulated by brief depolarizing pulses. The action potential elicited by the stimulus was followed after several msec by a secondary train of discharges generated at the periphery (“back firing”).     

Tooth pulp-evoked activity in the spinal trigeminal nucleus caudalis of cat: comparison to primary afferent fiber, reflex, and sensory responses

Tooth pulp-evoked single-neuron responses were recorded in the spinal trigeminal nucleus caudalis of the cat. The thresholds to monopolar electric pulses of various durations (0.2 to 20 ms) were determined using a constant current stimulator. With stimulus pulse durations of 10 to 20 ms, the thresholds were comparable with those of primary afferent A-fibers, although the most sensitive primary afferent fibers had lower thresholds. Primary afferent C-fibers had higher thresholds than the postsynaptic neurons studied. The threshold for the tooth pulp-elicited jaw-opening response was obtained at a lower stimulus intensity than the liminal response in most postsynaptic neurons of this study. The threshold rise of the postsynaptic trigeminal neurons with decreasing stimulus pulse duration (from 5 to 0.2 ms) was much steeper than that of primary afferent A-fibers or jaw-opening response. The strength-duration curves for tooth pulp-elicited pain sensations in man resemble those of spinal trigeminal neurons. Sixty-two percent of the units had a threshold elevation during a noxious pinch of the tail. The results indicate that the activation of postsynaptic trigeminal neurons requires a considerable temporal summation of primary afferent impulses. The jaw reflex thresholds cannot be explained by the properties of the neurons in the subnucleus caudalis of the trigeminal tract. The results support the concept that dental pain is based on the activation of spinal trigeminal nucleus caudalis neurons receiving their input from intradental A-fibers.     

Variation in the mode of receptor cell addition in the electrosensory system of gymnotiform fish

Age-related changes in ampullary and tuberous receptor organ morphology were studied in six species of gymnotiform weakly electric fish. Cheek skin was silver-stained, whole-mounted, and viewed under Nomarski differential interference contrast optics. The ampullary receptor units of all species show an increasing number of receptor organs per afferent fiber with fish size, presumably the result of addition of newly formed receptor organs. Ampullary units composing over a dozen organs were observed in large specimens of a few species. Receptor cells were also added in the tuberous receptor system of all species, but in different ways. As previously reported for Sternopygus, small specimens of Eigenmannia had only a single tuberous receptor organ per afferent. Fish of increasing size retained a population of afferents that innervated only a single receptor organ and, in addition, had a population of afferents that innervated a cluster of receptor organs. The mean number of receptor organs per cluster increased in fish of increasing size. In addition, the mean number of sensory receptor cells per organ increased. New organs presumably derive from older ones, which divide under the stimulus of continued addition of new receptor cells. Apteronotus, Adontosternarchus, and Hypopomus all added more receptor cells to their tuberous organs. In these species, every afferent innervated only a single tuberous organ and there was no indication of division of receptor organs. Gymnorhamphichthys and Gymnotus were intermediate in that they added new receptor cells to each receptor organ, and, in larger fish, these were segregated into discrete patches within a single receptor organ. It is likely that the addition of new receptor cells aids in increasing sensitivity of both ampullary and tuberous receptors as fish grow.     

Responses of rabbit retinal ganglion cells to electrical stimulation with an epiretinal electrode

Rational selection of electrical stimulus parameters for an electronic retinal prosthesis requires knowledge of the electrophysiological responses of retinal neurons to electrical stimuli. In this study, we examined the effects of cathodal and anodal current pulses on the extracellularly recorded responses of OFF and ON rabbit retinal ganglion cells (RGCs) in an in vitro preparation. Current pulses (1 msec duration), delivered by a 125 microm electrode placed on the inner retinal surface within the receptive field of a RGC, produced both short-latency (< or =5 msec) and long-latency (8-60 msec) responses. The long-latency responses, but not the short-latency responses, were abolished upon application of the glutamate receptor antagonists CNQX and NBQX, thus indicating that the long-latency responses of RGCs are due to activation of presynaptic neurons in the retina. The latency of the long-latency response depended upon the polarity of the stimulus. For OFF RGCs, the average latency was 11 msec for a cathodal stimulus and 24 msec for an anodal stimulus. For ON RGCs, the average latency was 25 msec for a cathodal stimulus and 16 msec for an anodal stimulus. The threshold current also depended upon the polarity of the stimulus, at least for OFF RGCs. The average threshold current for evoking a long-latency response in OFF RGCs was 10 microA for a cathodal stimulus and 21 microA for an anodal stimulus. In ON RGCs, the average threshold current was 13 microA for a cathodal stimulus and 15 microA for an anodal stimulus.     

Perturbation of the direction of neurite growth by pulsed and focal electric fields

We have studied the orientation of neurite growth in the culture of embryonic Xenopus neurons in response to three types of extracellular electric fields: spatially uniform pulsed fields, focally applied steady (DC) fields, and focally applied pulsed fields. Under uniform pulsed fields, neurites showed a preferential orientation toward the cathode pole of the field in a manner similar to that previously found for DC fields. The extent of neurite orientation depended upon the duration, amplitude, and frequency of the pulse but appeared to be similar to that produced by a uniform DC field of an equivalent time-averaged field intensity. For square pulses of 5 msec duration, the minimal amplitude and frequency required to produce a detectable orientation of neurite growth over a period of 24 hr were 2.5 V/cm and 10 Hz, which correspond to a time-averaged field intensity of 125 mV/cm. Steady or pulsed focal fields were applied by passing a current through a micropipette placed near the growth cone of the neurite. Fields of negative polarity (current sink) were found to attract the growth cone, whereas fields of positive polarity (current source) were found to deflect the growth cone away from the pipette. The threshold DC current density needed at the growth cone to perturb its direction of growth within 15 min was 0.2 to 2 pA/micron2 (or 3 to 30 mV/cm); and for focal pulsed currents (pulse duration 5 msec), a typical combination of minimal pulse amplitude and frequency was 4 pA/micron2 and 10 Hz. This threshold focal current is similar to that which occurs at the synaptic cleft during active synaptic activity.     

Graded action potentials generated by neurons in rat hypothalamic slices

Preoptic neurons in rat hypothalamic slices were investigated with tight-seal whole-cell recording techniques. The main aim was to investigate the ability to generate graded, stimulus-dependent impulses. In response to rectangular current pulses, all cells generated impulses with an amplitude that to some degree depended on the stimulus strength. Stronger current steps induced impulses of larger amplitude. In 50% of the cells, a systematic variation of impulse amplitude of more than 10 mV (up to 40 mV) was recorded, implying a clear deviation from the ‘all-or-nothing’ principle. A clear variation in amplitude of spontaneous impulses was also recorded, in the whole-cell mode as well as from intact cells in the cell-attached mode.     

Relevance of stimulus duration for activation of motor and sensory fibers: implications for the study of H-reflexes and magnetic stimulation.

Electric stimuli with durations of 0.5-1.0 msec are optimal for studies of H-reflexes. It is more difficult to obtain H-reflexes with shorter duration stimuli or with magnetic stimulation. In order to understand this behavior, we studied the excitation thresholds for motor and sensory fibers in the ulnar, median and tibial nerves using both electric and magnetic stimulation. For short duration electrical stimuli (0.1 msec) the threshold for motor fibers is lower than for sensory fibers. For longer duration electric stimuli (1.0 msec) the threshold for sensory fibers is lower. For magnetic stimulation the threshold for motor fibers is much lower than for sensory fibers. Thus, stimulus duration is a critical parameter for sensory fiber excitation, and current magnetic stimulators are not optimal.     

Pulse repetition rate increases the minimum threshold and latency of auditory neurons

The effect of pulse repetition rate on auditory sensitivity of the big brown bat,Eptesicus fuscus, was studied by determining the minimum threshold, response latency and recovery cycle of inferior collicular neurons at different repetition rates under free field stimulation conditions. In general, collicular neurons shortened the response latency and increased the number of impulses monotonically or non-monotonically with stimulus intensity. They recovered at least 50% when the interpulse interval was 10–57 ms. In addition, they increased the minimum threshohold, lengthened the response latency, and reduced the number of impulses discharged to each pulse with increasing repetition rate. The increase in minimum threshold with repetition rate is partly because the neuron can not recover from previous stimulation when the interpulse interval is shortened. This increase reduces a neuron's response sensitivity and thus diminishes its number of impulses to each presented pulse. This increase also reduces the effectiveness of a given stimulus intensity which contributes to the lengthening of the neuron's response latency. Data obtained from single neuron recordings are used to highlight these observations. Implications of present findings regarding the bat's echolocation are also discussed.     

Reticular formation influence on neuronal transmission from perforant pathway through dentate gyrus

Electrical stimulation of the perforant pathway discharges granule cell synchronously, giving rise to a characteristic evoked potential in the granule cell layer termed here the evoked action potential or EAP. In freely moving rats, we applied 3 pulses of low intensity electrical stimulation to the medullary reticular formation prior to the application of the perforant path pulse. The effect of prior reticular formation stimulation was a marked augmentation of the normal EAP response to the perforant path stimulus. The augmentation was dependent on the behavioral state of the experimental animal (it occurred during slow-wave sleep but not during still, alert behavior) and was eliminated by anesthetic agents. The latency of EAP augmentation effect (minimum effective time interval between application of the reticular formation stimulus and the perforant path pulse) was 13--18 msec. In order to localize the sites in the medullary reticular formation from which EAP augmentation could be elicited, threshold currents for producing the effect were determined during dorso-ventral penetrations of a reticular formation stimulating electrode. EAP augmentation was elicited at low stimulus currents from a relatively broad region of the reticular formation. It was also noted that reticular formation stimulation which produced EAP augmentation always elicited one or more motor responses of the neck, back, face or vibrissae. Subsequent investigation of the pathways underlying these motor responses suggested that the effect of reticular formation stimulation on granule cell excitability was mediated by a polysynaptic pathway, the first segment of which was a projection to cells of nucleus gigantocellularis of the caudal medulla.     

Cellular mechanisms contributing to response variability of cortical neurons in vivo.

Cortical neurons recorded in vivo exhibit highly variable responses to the repeated presentation of the same stimulus. To further understand the cellular mechanisms underlying this phenomenon, we performed intracellular recordings from neurons in cat striate cortex in vivo and examined the relationships between spontaneous activity and visually evoked responses. Activity was assessed on a trial-by-trial basis by measuring the membrane potential (Vm) fluctuations and spike activity during brief epochs immediately before and after the onset of an evoked response. We found that the response magnitude, expressed as a change in Vm relative to baseline, was linearly correlated with the preceding spontaneous Vm. This correlation was enhanced when the cells were hyperpolarized to reduce the activation of voltage-gated conductances. The output of the cells, expressed as spike counts and latencies, was only moderately correlated with fluctuations in the preceding spontaneous Vm. Spike-triggered averaging of Vm revealed that visually evoked action potentials arise from transient depolarizations having a rise time of approximately 10 msec. Consistent with this, evoked spike count was found to be linearly correlated with the magnitude of Vm fluctuations in the gamma (20-70 Hz) frequency band. We also found that the threshold of visually evoked action potentials varied over a range of approximately 10 mV. Examination of simultaneously recorded intracellular and extracellular activity revealed a correlation between Vm depolarization and spike discharges in adjacent cells. Together these results demonstrate that response variability is attributable largely to coherent fluctuations in cortical activity preceding the onset of a stimulus, but also to variations in action potential threshold and the magnitude of high-frequency fluctuations evoked by the stimulus.     

The development of lateral-line receptors in Eigenmannia (Teleostei, Gymnotiformes). II. The electroreceptive lateral-line system

Weakly electric fish of the genus Eigenmannia were induced to spawn in conditions simulating the tropical rainy season. The skin of embryos of different ages was prepared for histological examination, and whole animals were examined by various histological methods and scanning electron microscopy. It was found that the electrosensory system develops after the first mechanoreceptive lines have formed. The tuberous and ampullary organs initially form adjacent to the lines of the lateral-line system. The tuberous organs develop at a rate 5 times higher than that of the ampullary organs. The rate of development for both classes of electroreceptors is 4 times higher on the head than on the trunk. The first tuberous organs develop on the head at day 7 and on the trunk at day 8. They increase in number and size during the growth of the fish. The ampullary organs begin to form on the head and on the most rostral part of the trunk at day 8. They are deeply sunk into the corium and have the same number of receptor cells as in adults. There are both ampullary and tuberous organs within fields of receptors that are innervated by a single nerve branch.     

Randomized double pulse stimulation for assessing stimulus frequency-dependent conduction in injured spinal and peripheral axons.

Injury compromises the ability of axons to conduct action potentials at high frequencies. To study stimulus frequency-dependent conduction in injured spinal and peripheral axons, we developed a new stimulation paradigm which applies trains of double pulses at 5 Hz and randomly varied interpulse intervals of 3, 4, 5, 8, 10, 30, 50, and 80 msec. In each double pulse, the first pulse was used to condition the response activated by the second test pulse. Responses elicited by double pulses with 80 msec intervals served as controls. The L5 dorsal root was stimulated to activate dorsal column and dorsal root compound action potentials in pentobarbital anesthetized rats. To injure the spinal cord, we compressed the cord stepwise (0.25 mm every 5 min) until action potential conduction across the compression site was abolished and then decompressed the spinal cord 10 min later. Before injury, conditioning pulses applied 3-80 msec before the test pulses did not alter dorsal column responses except for a slight amplitude augmentation at 20 msec interpulse intervals (mean +/- S. E., + 4.2 +/- 0.8%, P less than 0.02) compared to controls. Injury had 3 effects on the responses. First, it significantly reduced response amplitudes and increased response latencies at 3-5 msec interpulse intervals, i.e., responses activated with 3 msec intervals were 26.0 +/- 7.4% (P less than 0.002, paired t test, n = 6) smaller and had 108 +/- 45 microseconds (P less than 0.04) longer latency than control responses. Second, response amplitude increases at 20 msec interpulse intervals (9.0 +/- 0.7%, P less than 0.0001) significantly exceeded those observed before injury (P less than 0.02, paired t test). Third, injury accentuated response amplitude declines during the stimulus train, most prominently at 80 msec intervals. Spinal cord injury did not affect the dorsal root responses. L5 root compression injury depressed dorsal root action potentials at 3-5 msec interpulse intervals (36.9 +/- 8.4%, n = 4, P less than 0.0001) but had no other effect on the responses. Our data indicate that randomized double pulse evoked potentials are sensitive detectors of acute axonal dysfunction and can be used to quantify stimulus frequency-dependent conduction deficits in injured central and peripheral axons.     

Voltage-activated K+ currents in acutely isolated hippocampal astrocytes.

Hippocampal astrocytes were acutely isolated by papain treatment and mechanical trituration. Astrocytes were identified by their distinctive stellate morphology and immunocytochemical staining for glial fibrillary acidic protein. The electrophysiological properties of these cells were investigated using whole-cell voltage-clamp techniques. Three kinetically and pharmacologically distinct voltage-activated K+ currents were identified in most cells; they resembled the neuronal A-current, delayed rectifier, and inward rectifier. The activation threshold of the A-current was -40 mV with a time to peak that ranged from 10 msec at -20 mV to 6 msec at 100 mV. Steady-state inactivation was observed when the holding potential was positive to -100 mV. The current was half-inactivated at -60 mV and totally inactivated at -20 mV. The A-current was suppressed by 4-aminopyridine (4-AP). The delayed rectifier was activated by depolarizing pulses more positive than -40 mV and had a half time of activation that ranged from 18 msec at -20 mV to 10 msec at potentials more positive than 40 mV. This current did not inactivate during a 100 msec pulse and was suppressed by extracellular tetraethylammonium (TEA). An inwardly rectifying current was elicited by hyperpolarizing pulses more negative than -80 mV. This current was not blocked by extracellular TEA or 4-AP and was never observed in the presence of external Ba2+. Voltage-activated inward Na+ currents were never observed. Voltage-activated K+ channels may enhance the local K+ spatial buffering capabilities of the astrocyte syncytium when extracellular [K+] increases during neuronal activity.     

Effect of various stimulus parameters on electrically-induced catecholamine secretion by thin slices of bovine adrenal medulla

Summary We examined the role of various stimulus parameters in electrically-induced catecholamine secretion by thin slices of bovine adrenal medulla. The stimulus parameters examined were voltage, duration, pulse width, and frequency for square-wave monophasic pulses. As each was examined it was held constant at a selected value for the evaluation of subsequent stimulus characteristics.For 16 mm² tissue slices, catecholamine secretion was approximately linearly related to stimulus voltage over the range 20–80 volts, with a threshold of 20 V. Increasing the voltage beyond 80 V did not enhance secretion. Similarly, catecholamine secretion was dependent upon the frequency of stimulation. For stimuli delivered at 50 V for a 10-sec interval there was a four-fold increase in secretion over the frequency range 10–100/sec. Increasing pulse width at a constant voltage (50 V) over the range 0.4–2.0 msec resulted in a four-fold increase in catecholamine secretion. For pulses of 50 V, 50/sec and 0.8 msec pulse width, secretion was dependent upon the duration of the stimulus. Enhanced secretion was evident for times as short as 2 sec; between 5 and 15 sec of stimulation catecholamine secretion was linearly related to stimulus duration. Over the range 2–15 sec there was a five-fold enhancement of secretion.Electrically-induced catecholamine secretion by slices was markedly dependent upon stimulus parameters. In general, it was enhanced by increasing voltage, stimulus duration, pulse width and frequency. For most experiments a good choice of stimulus parameters appears to be 50 V, 10 sec duration, 0.8 msec pulse width delivered at a frequency of 50/sec. Maximizing all stimulus parameters resulted in a 17-fold enhancement of secretion.     

Treatment of Spastic Gait Disorders Using an "Electro-Gait-Stimulator ("Schrittstimulator") (author's transl)]

A short historical outline of electric treatment of spasticity is given. A specially developed management with a "gait-stimulator" is described. Four muscles of each lower extremity being mainly engaged in walk were electrically stimulated in the physiological sequences according to the normal gait. The used electric impulses were of a duration of 0,25 msec and an intensity up to 700 V. Using such a "gain-stimulator" in spastic-paraparetic patients a reduced spasticity has been achieved. Positive effect of this treatment has been mostly pronounced, when the programming of impulses was adjusted to the end of the expected physiological contraction of the corresponding muscles. Physiological and pathological data of the "Silent period" is proposed to be mostly involved. The application of impulses in physiological sequences seems to reactivate normal reflex - mechanisms which are disturbed by supraspinal laesion. The results indicate that the electric impulses activates muscle-sensory - organs and that impulses on these organs produce a pace-making function on the spinal cord, which lessens spasticity.     

Temporal integration of pain from electrical stimulation of the skin

Abstract

The threshold of sensation and the threshold of pain in response to electrical stimulation (impulses of 1 msec duration) of the skin on the forearm or hand in individuals without pain were compared with the thresholds of individuals with chronic pain in the range 1 to 100 pulses per second repetition rate. The threshold of sensation in patients without pain was little affected by the repetition rate of the stimulation within the range studied, and the threshold for pain decreased exponentially with increasing repetition rate. In individuals with chronic pain the threshold of sensation was similar to that of individuals without pain over the entire range of stimulus repetition rates studied, but the threshold ofpain in patients with pain was lower and less affected by the stimulus rate than it was in the individuals without pain, thus closer to the threshold of sensation. [Neural Res 1997; 19: 481-488J     

Response characteristics of tooth pulp-driven postsynaptic neurons in the spinal trigeminal subnucleus interpolaris of the cat: comparison with primary afferent fiber, subnucleus caudalis, reflex, and sensory responses

Tooth pulp-evoked single neuron responses were recorded in the spinal trigeminal subnucleus interpolaris of the cat. The thresholds to monopolar electric pulses of varying duration (0.2-20 ms) were determined using a constant current stimulator. The thresholds were comparable with those of primary afferent A-fibers, although the most sensitive primary afferent fibers have lower thresholds. The thresholds and latencies showed that none of the interpolaris neurons received their input solely from intradental C-fibers. The most sensitive subnucleus interpolaris neurons had lower thresholds than the respective subnucleus caudalis neurons studied in our previous work. The thresholds and strength-duration curves of the most sensitive interpolaris neurons and of the tooth pulp-elicited jaw-opening reflex are nearly similar, although the jaw reflex can be elicited at an intensity which is slightly lower than that needed to activate the most sensitive interpolaris neurons of the present sample. The most sensitive interpolaris neurons were activated at current intensities that were below the intensity needed to produce liminal dental pain in man, and the strength-duration curves of these neurons were flatter than the curve depicting liminal dental pain sensation in man. The relationship between stimulus intensity and response magnitude could be well described by power functions, the median exponent of which was 1.251. A conditioning stimulation of the tooth pulp at low intensity produced a short (less than 25 ms) enhancement of the response to the following test stimulus, whereas a high intensity conditioning stimulus produced a longer (greater than 40 ms) suppression of the response to the following stimulus. The threshold of 33% of the neurons was elevated during a noxious tail pinch, and this elevation was not reversed by naloxone, an opioid antagonist. The results indicate that in the trigeminal subnucleus interpolaris there are tooth pulp-driven neurons with an input from intradental A-fibers and that a considerable temporal summation of impulses from primary afferent fibers is needed to activate most of them. Human dental pain thresholds cannot be explained by the liminal response properties of the most sensitive interpolaris neurons, but they may be important in the mediation of near-threshold reflex events. It is possible, however, that the high-threshold interpolaris neurons may have a role in the mediation of sensory responses.     

Focal dorsal raphe stimulation and pinnal electrical stimulation modulate spontaneous and noxious evoked responses in thalamic neurons

This study investigated the nocieceptive responses of single neurons within the nucleus parafascicularis (PF) thalami of the rat following two modes of electrical stimulation known to induce analgesia. It was found that both focal electrical dorsal raphe stimulation (DRS) and bilateral pinnal (ear) electrical stimulation (PES) converge on the same PF neurons, affecting both the spontaneous discharges and the noxious evoked responses toward these neurons. The effects of different stimulus current intensity, frequency and pulse duration were also examined. It was found that for both DRS and PES at pulse frequency of 10 Hz and current amplitude of 10 microA are the optimal parameters to modulate both the spontaneous and the noxious evoked responses. These stimuli produced prolonged effects related to the duration of stimulation. The external (PES) low current stimulation which was delivered below the sensory threshold was as effective in modulating noxious responses as the invasive DRS in intact animals and in animals with bilateral dorsolateral-funiculus ablation. It was observed that dorsal lateral funiculus ablation (DLFx) did not modify the DRS and the PES effects. These observations further support the existence of an ascending pain modulation pathway.     

Pathways between the nucleus tractus solitarius and neurosecretory neurons of the supraoptic nucleus: Electrophysiological studies

In anesthetized cats recordings were made from hypothalamo-neurohypophysial neurons in a supraoptic nucleus (SON) of the hypothalamus. The region of the nucleus tractus solitarius in the medulla, identified electrophysiologically as the site of termination of the first relay neurons of the sinus and aortic nerves, was stimulated with single or short trains of pulses (2–3 at 200 Hz). Out of 133 SON neurons 67 were affected by such stimuli. In 14 cells (21% of ‘responsive’ neurons) the stimulus produced profound inhibition of SON neuron activity after a latency of 10–30 msec. In another 8 neurons (12%) the inhibitory effect was observed after a longer latency of over 100 msec. An increase in intensity of stimulus merely prolonged or increased the inhibitory effect without changing the response qualitatively. The other 45 (67%) SON neurons were excited by stimulation of the nucleus tractus solitarius. In a small proportion of these neurons (5 cells, 7%) the stimulus evoked discharges, even in spontaneously silent neurosecretory cells, after a latency of 10–20 msec with little fluctuation. In the remaining 40 neurons, i.e. 60% of the ‘responsive’ neurons, the excitatory effect was observed after a latency of 40–120 msec. Again, changes in intensity of stimulation did not alter the nature of this response. The results indicate that both ‘fast’ as well as ‘slow’ pathways between the nucleus tractus solitarius and SON neurons exist and impulses travelling through the latter pathway from the carotid sinus or aortic nerve affect the larger proportion of SON neurons.