Primitive nervous system: Electrophysiology of inhibitory events in flatworm nerve cords

Evoked potentials from the major longitudinal nerve cords of Notoplana acticola are potentiated if the preparation is decerebrated or if certain nerves in the ventral submuscular plexus are severed. Concomitant with an increase in amplitude of the response (in some preparations over fourfold) is a decrease in latency of the response and a decrease in the threshold stimulus intensity needed to evoke activity. Evoked activity can also be depressed with moderate increases in stimulus intensity and is induced some distance from the recording site. The depressant effects can be lifted if the brain is bisected, if the contralateral nerve VI is severed close to the brain, and if the commissures between the two nerves VI are cut. The depressant effects of nerves V and VI are additive. Depression and the subsequent lifting of the inhibition occur in Ringer baths containing either normal sea water or equal mixtures of sea water and isotonic MgCl₂. The possibility of inhibitory synapses immune to high concentrations of magnesium ions is discussed.     

Primitive nervous systems: Peripheral habituation in decerebrate polyclad flatworms

The response to a vibration stimulus recorded from the cords of the ventral submuscular plexus of the polyclad flatworm, Notoplana acticola, consists of a burst of action potentials. The response can be abolished by the application of MgCl₂ to the sea water bathing the preparation. With repeated application of the stimulus, decreasing numbers of action potentials can be measured. This waning responsiveness can be dishabituated by applying a more intense vibration stimulus or with electrical shocks applied directly to the ventral nerve plexus. With electrical stimuli a number of shocks have to be applied before the response can be dishabituated. Changes in responsiveness can be measured simultaneously in a number of sites in the plexus even after the nerves between recording sites have been severed. With different interstimulus intervals the extent of habituation changes. As interstimulus intervals increase from 1 to 5 sec, there appears to be a decrease in responsiveness which recovers when interstimulus intervals become longer than 5 sec.     

Peripheral and central nervous responses evoked by small water movements in a cephalopod

Potentials were recorded from the epidermal head lines and from the CNS of young cuttlefish, Sepia officinalis, in response to weak water movements. 1. Within the test range 0.5-400 Hz a sinusoidal water movement elicits up to 4 components of response if the electrode is placed on a headline: (i) a positive phasic ON response; (ii) a tonic frequency-following microphonic response; (iii) a slow negative OFF response; and (iv) compound nerve impulses. 2. The amplitude of both the ON wave and the microphonic potential depends on stimulus frequency, stimulus amplitude and stimulus rise time. Frequencies around 100 Hz and short rise times are most effective in eliciting strong potentials. The minimal threshold was 0.06 microns peak-to-peak water displacement at 100 Hz (18.8 microns/s as velocity). 3. Change of direction of tangential sphere movement (parallel vs. across the head lines) has only a small effect on the microphonic and the summed nerve potentials. 4. Frequency and/or amplitude modulations of a carrier stimulus elicit responses at the onset and offset of the modulation and marked changes in the tonic microphonic response. 5. Evoked potentials can be recorded from the brain while stimulating the epidermal lines with weak water movements. The brain potentials differ in several aspects from the potentials of the head lines and show little or no onset or offset wave at the transitions of a frequency and amplitude modulation.     

The effect of an alerting acoustic stimulus on the heart rate, sympathetic activity and aortic baroreceptor discharge in conscious rabbits before and after naloxone administration

Blood pressure, heart rate, aortic nerve activity and cervical sympathetic discharge were recorded simultaneously in 10 rabbits. Chronic recordings were made with electrodes implanted to the uncut aortic and cervical sympathetic nerves. 1. The alerting acoustic stimulus produced a short lasting decrease in sympathetic activity with a transient bradycardia. 2. In 6 out of 8 rabbits i.v. administration of naloxone chloride (100 mg/kg) diminished or abolished early inhibitory effects evoked by acoustic stimulus. 3. The sympatho-inhibitory system involved in the startling response appears to be independent of the baroreceptor inhibitory reflex and has opposite responsiveness to naloxone. 4. A decrease in efferent sympathetic activity with no accompanying change in the aortic nerve activity suggests some central resetting of the baroreceptor-sympatho-inhibitory reflex. 5. We suggest that the observed autonomic effects following an alerting stimulus are typical for a fear-anxiety drive.     

The effect of severing the dorsal vessel on egg production in Rhodnius prolixus

Severing the dorsal vessel (DV) behind the corpus allatum (CA), or in the anterior part of the abdomen of Rhodnius prolixus, greatly reduces egg production, an effect which is abolished by the topical application of juvenile hormone l (JH l). Severing the DV in the posterior abdomen does not result in a marked reduction of egg production, although severing the alary muscles in segments V and VI has a similar effect to severing the DV in the anterior abdomen. Reduced egg production caused by severing the DV on day 8 postemergence does not occur if the nerves connecting the CA to the brain are severed on day 1 post emergence. However, egg production is reduced if the DV is severed on day 1 post emergence and the connections between the brain and the CA severed on day 8, suggesting that inhibition of the CA caused by severance of the DV requires innervation from the brain. An isolated CA implanted into an animal decapitated immediately after feeding escapes from the inhibition imposed by severance of the DV. Conversely, the CA in an insect, the head of which has been decapitated just anterior to the CA, remains inhibited. This result suggests that the head posterior to the brain must be present to maintain inhibition. It is concluded that DV severance acts on the brain via some humoral influence to impose inhibition on the CA, and that an endocrine center in the head is required in order to maintain the inhibition.     

Effect of ions on the efflux of acetylcholine from peripheral nerve

The nerves from the walking leg of lobster released acetylcholine (ACh) even when the ends were tied off, although this release was significantly increased when the nerve endings were not tied. The resting nerves were kept in sea water containing physostigmine. In absence of physostigmine no ACh was found in the surrounding fluid. Removal of Ca from the sea water reduced the release of ACh, while increased concentrations of Ca had no significant effect. Removal of Mg++ or increased Mg++ concentrations in the presence of normal Ca++ concentrations increased the release of ACh. Increased K+ concentrations had a stimulating action on the efflux of ACh. Increased or reduced Na+ concentrations had only slight effects on the release of ACh in resting lobster nerve. During the 4 hr observation period the excised nerves were still able to synthesize ACh. The choline acetylase activity was stimulated by increased concentrations of Mg++ and K+. The effects of ions on the release of ACh are similar to those reported at the junction.     

Innervation of the American cockroach salivary gland: neurophysiological and pharmacological investigations

Application of 5-hydroxytryptamine to the gland in vitro in concentrations as low as 10^?12 M effected continuous secretion of fluid. This suggests that 5-HT or a related compound may be the neurotransmitter substance. In vivo injections of p-chorophenylalanine did not affect secretion. Applications of pilocarpine and acetylcholine had only a transitory effect upon secretions. Nerve-section studies implicate the salivary duct nerves coming from the suboesophageal ganglion as motor nerves controlling secretion. The oesophageal salivary nerves from the brain were not severed due to excessive trauma. Simultaneous electrical recordings of the salivary nerves show no common activity. Nerve section demonstrates that the activity in these nerves is efferent. Central inhibition of nervous activity occurs during sensory stimulation, etc. Electrical stimulation of the salivary duct nerve in vitro effects salivary secretion for several hours; however, the loss of secretion is not due to failure of the nerves, but to unknown factors. Histological sections of the stimulated glands failed to show cytological changes.     

Renal responses to stressful environmental stimuli

The effects of stressful environmental stimuli on urinary sodium excretion in conscious dogs, rats, and humans are reviewed. Environmental stress can increase sympathetic neural outflow and decrease sodium excretion. The antinatriuretic response to environmental stress is accompanied by an unchanged renal blood flow and glomerular filtration rate, which indicates mediation via an increased renal tubular sodium reabsorption. The antinatriuresis resulting from environmental stress is associated with increased renal sympathetic nerve activity, and is abolished by surgical renal denervation. In the central nervous system, but not in the kidney, beta adrenoceptors mediate the increased renal sympathetic nerve activity and antinatriuretic responses to environmental stress. The increased renal sympathetic nerve activity and antinatriuretic responses to environmental stress are greater in spontaneously hypertensive rats (SHR) than in normotensive Wistar-Kyoto (WKY) rats. In SHR, but not WKY rats, the increased renal sympathetic nerve activity and antinatriuretic responses are enhanced by a high-sodium diet. Similarly, stressful competition in human young adult males results in an antinatriuresis only if a positive family history of hypertension is present. Thus, environmental stress can increase renal tubular sodium reabsorption via a central beta-adrenoceptor mechanism with activation of the renal sympathetic nerves in both conscious dogs and SHR. The antinatriuretic response to environmental stress is greater in rats and humans with a genetic predisposition to develop hypertension.     

Some effects of superior laryngeal nerve stimulation on sympathetic preganglionic neuron firing

Repetitive electrical stimulation of afferent fibers in the superior laryngeal nerve (SLN) evoked depressant or excitatory effects on sympathetic preganglionic neurons of the cervical trunk in Nembutal-anesthetized, paralyzed, artifically ventilated cats. The depressant effect, which consisted of suppression of the inspiration-synchronous discharge of units with such firing pattern, was obtained at low strength and frequency of stimulation (e.g. 600 mV, 30 Hz) and was absent at end-tidal CO2 values below threshold for phrenic nerve activity. The excitatory effect required higher intensity and frequency of stimulation and was CO2 independent. The depressant effect on sympathetic preganglionic neurons with inspiratory firing pattern seemed a replica of the inspiration-inhibitory effect observed on phrenic motoneurons. Hence, it could be attributed to the known inhibition by the SLN of central inspiratory activity, if it is assumed that this is a common driver for phrenic motoneurons and some sympathetic preganglionic neurons. The excitatory effect, on the other hand, appears to be due to connections of SLN afferents with sympathetic preganglionic neurons, independent of the respiratory center.     

Hypothalamic evoked potentials to vagus and sciatic nerve stimulation

Hypothalamic evoked potentials to stimulation of the cervical portion of the vagus nerve and the sciatic nerve were recorded in experiments on cats anesthetized with chloralose and immobilized with succinylcholine. When both monopolar and bipolar recording techniques were used the focus of maximal activity of both "visceral" and "somatic" evoked potentials was located in the supramammillary and posterolateral region of the hypothalamus. Responses in the tuberal and anterior hypothalamus occurred in most experiments after a longer latent period, their amplitude was lower, and they were less stable. Evoked potentials in the focus of maximal activity of the posterior hypothalamus are similar in all parameters to responses of the mesencephalic reticular formation. Evoked potentials to stimulation of the visceral nerve have a higher threshold of generation and a lower amplitude than the "somatic" responses and they are inhibited more strongly when the frequency of stimulation is increased. Evoked potentials arising in the hypothalamus in response to stimulation of the vagus and sciatic nerves are regarded as nonspecific responses of reticular type.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 253–260, May–June, 1973.     

Inhibition of oöcyte development during pregnancy in the cockroach Eublaberus posticus

The corpora allata are inhibited during pregnancy in ovoviviparous Eublaberus posticus, and yolk is not deposited in the basal oöcytes for the entire or almost the entire gestation period.Precocious oöcyte development occurs if the oötheca is removed but this can be prevented by substituting a plastic oötheca for the true egg case in the uterus. Implantation of a uterus containing an oötheca into the abdomen of a female whose oötheca is removed does not prevent precocious oöcyte development even though many of the eggs in the implant grow and stretch the donor uterus. These experiments argue against the hypothesis that an ‘agent’ from the uterine eggs or stretched uterus inhibits the activity of the corpora allata (CA), and supports the hypothesis that inhibition from the uterus is mechanical.Cyclical activity of neurosecretory cells in certain abdominal ganglia in one species of ovoviviparous cockroach has been correlated with the cyclical inhibition of the oöcytes during pregnancy. Mechanoreceptors are found in the uteri of several ovoviviparous species including Eublaberus.In Eublaberus transecting the nerve cord between various ganglia in pregnant females only results in a marked decrease in the percentage of famales showing precocious oöcyte development when the nerves posterior to the sixth abdominal ganglion are severed. However, the results are the same if these nerves are severed after removing the oötheca. It is suggested that pressure of the oötheca on mechanoreceptors in the uterus, or cessation of pressure (after removal of the oötheca), result in sensory information being transmitted to the last abdominal ganglion which affect the CA, perhaps indirectly by controlling the activity of the neurosecretory cells in various abdominal ganglia.     

Convergence of autonomic,somatic, and vestibular afferent impulses on single units of the medullary vasomotor center of the cat

Responses of vasomotor neurons of the cat medulla to electrical stimulation of the depressor nerve and of mixed nerves of the limbs and to adequate stimulation of the vestibular apparatus were investigated. Evoked unit activity was demonstrated as groups of action potentials followed by inhibition of spontaneous activity. Three types of unit responses to stimulation of the depressor nerve and somatic afferent fibers and changes in unit activity in response to vestibular stimulation are described. The features distinguishing the convergence of afferent impulses on vasomotor neurons are discussed.Institute of Medico-Biological Problems, Ministry of Health of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 460–467, September–October, 1973.     

Dissociating pleasantness and intensity with quinine sulfate/sucrose mixtures in taste

Independent experimental manipulation of subjective intensity and hedonic tone is required if one wants to study their separate effects on brain activity and behavior. This is problematic because hedonic tone and subjective intensity are related, leading to a pleasantness change each time the stimulus intensity is altered. In the present study, a solution to this problem was explored by combining a pleasant-tasting substance (sucrose) and a bad-tasting substance (quinine sulfate) into a number of different isointense mixtures. Here we show that subjective intensity as well as pleasantness can be accurately predicted, particularly in midrange, only if one corrects for mixture suppression.     

Sensory interaction with central ‘generators’ during respiration in the dogfish

Summary The activity in sensory and motor nerves of the gills was recorded from selected branches of the vagus nerve in decerebrate dogfish,Scyliorhinus canicula. Vagal motoneuronal activity was observed at the start of the rapid pharyngeal contraction and was followed by sensory nerve activity which preceded the slow expansion phase. Rhythmical vagal motoneuronal activity was still present after all movements had been prevented by curare paralysis although the frequency of the rhythm was higher than in the ventilating fish. Electrical stimulation of vagal sensory fibres had 3 effects on the ventilatory movements. (1) It evoked a reflex contraction of several gill muscles after a latency of about 11 ms. (2) It could reset the respiratory cycle because a stimulus given during expansion delayed the onset of the subsequent contraction. (3) The stimulus could entrain the rhythm if it was given continuously at a frequency close to that of ventilation. The vagal motor rhythm was disrupted by trigeminal nerve stimulation in the paralyzed fish but not if the motor rhythm was being entrained by vagal nerve stimulation. Vagal sensory activity may be important, therefore, in maintaining the stability of the generating circuits.Abbreviation LED Light emitting diode     

Acute Effects of Total or Partial Digit Denervation on Raccoon Somatosensory Cortex

The immediate effects of total or partial denervation of single digits (0-16 hr after nerve transection) on primary somatosensory cortex were studied electrophysiologically. Comparisons of response properties and cortical somatotopy were made between intact raccoons and four groups of raccoons with transection of some or all of the nerves innervating the fourth or fifth digit. Animals with all four digital nerves cut (amputation of the digit) were most different from normal. Approximately half of the penetrations in the affected cortical region showed inhibitory responses to stimulation of adjacent skin regions. These consisted of a strong response to stimulus offset and/or a suppression of spontaneous activity during indentation. Since these responses were substantially different from those recorded several months after digit amputation, additional changes in connectivity and synaptic strength must occur with chronic denervation. These inhibitory responses were not seen in animals with one, two, or three nerves cut per digit.

In the animals with partial denervation of a digit, the greatest disruption occurred when both ventral nerves to the glabrous skin were transected. This yielded cell clusters with abnormally large receptive fields, disruptions in somatotopic organization, and a decreased occurrence of low-threshold responses. If only one nerve to glabrous skin was transected, there was less change, even if it was combined with transection of both nerves to hairy skin. These results suggest that the release of inhibitory responses in a cortical digital region by amputation is prevented by the retention of even one ventral nerve. None of the denervation conditions produced large nonresponsive areas of cortex, which would have indicated a loss of all inputs.     

Early social isolation provokes electrophysiological and structural changes in cutaneous sensory nerves of adult male rats

Sensory and social deprivation from the mother and littermates during early life disturbs the development of the central nervous system, but little is known about its effect on the development of the peripheral nervous system. To assess peripheral effects of early isolation, male rat pups were reared artificially in complete social isolation (AR); reared artificially with two same‐age conspecifics (AR‐Social); or reared by their mothers and with littermates (MR). As adults, the electrophysiological properties of the sensory sural (SU) nerve were recorded. We found that the amplitude and normalized area (with respect to body weight) of the compound action potential (CAP) response provoked by single electrical pulses of graded intensity in the SU nerves of AR animals were shorter than the CAP recorded in SU nerves from MR and AR‐Social animals. The slope of the stimulus‐response curve of AR SU nerves was smaller than that of the other nerves. The histological characterization of axons in the SU nerves was made and showed that the myelin thickness of axons in AR SU nerves was significant lower (2–7µm) than that of the axons in the other nerves. Furthermore, the area and axon diameter of SU nerves of both AR and AR‐Social animals were significant lower than in MR animals. This is the first report to show that maternal and littermate deprivation by AR disturbs the development of the myelination and electrophysiological properties of axons in the SU nerve; the replacement of social cues prevents most of the effects. © 2014 Wiley Periodicals, Inc. Develop Neurobiol 74: 1184–1193, 2014     

Mesencephalic chronic electrodes in pain patients. An electrophysiological study.

Early components of lemniscal potentials after contralateral median nerve or mechanical stimulus are due to lemniscal pathways, whereas later components, after 70 msec appearing bilaterally and at higher stimulus intensities probably express extralemniscal activity. Evoked potentials in the central gray matter show much smaller amplitudes compared with somatosensory cortical evoked potentials (SSEP). The strongest component is a negative wave after 70--100 msec. Longer conditioning stimulation of the lemniscal system inhibits late components in the median nerve evoked cortical potentials. On the contrary, stimulation of the nonspecific periaqueductal gray matter produces inhibition of early components of cortical SSEP together with facilitation of late components.     

Acute effects of total or partial digit denervation on raccoon somatosensory cortex

The immediate effects of total or partial denervation of single digits (0-16 hr after nerve transection) on primary somatosensory cortex were studied electrophysiologically. Comparisons of response properties and cortical somatotopy were made between intact raccoons and four groups of raccoons with transection of some or all of the nerves innervating the fourth or fifth digit. Animals with all four digital nerves cut (amputation of the digit) were most different from normal. Approximately half of the penetrations in the affected cortical region showed inhibitory responses to stimulation of adjacent skin regions. These consisted of a strong response to stimulus offset and/or a suppression of spontaneous activity during indentation. Since these responses were substantially different from those recorded several months after digit amputation, additional changes in connectivity and synaptic strength must occur with chronic denervation. These inhibitory responses were not seen in animals with one, two, or three nerves cut per digit. In the animals with partial denervation of a digit, the greatest disruption occurred when both ventral nerves to the glabrous skin were transected. This yielded cell clusters with abnormally large receptive fields, disruptions in somatotopic organization, and a decreased occurrence of low-threshold responses. If only one nerve to glabrous skin was transected, there was less change, even if it was combined with transection of both nerves to hairy skin. These results suggest that the release of inhibitory responses in a cortical digital region by amputation is prevented by the retention of even one ventral nerve. None of the denervation conditions produced large nonresponsive areas of cortex, which would have indicated a loss of all inputs.     

Vestibular reafference shapes voluntary movement

The vestibular organs in the inner ear are commonly thought of as sensors that serve balance, gaze control, and higher spatial functions such as navigation. Here, we investigate their role in the online control of voluntary movements. The central nervous system uses sensory feedback information during movement to detect and correct errors as they develop. Vestibular organs signal three-dimensional head rotations and translations and so could provide error information for body movements that transport the head in space. To test this, we electrically stimulated human vestibular nerves during a goal-directed voluntary tilt of the trunk. The stimulating current waveform was made identical to the angular velocity profile of the head in the roll plane. With this, we could proportionally increase or decrease the rate of vestibular nerve firing, as if the head were rotating faster or slower than it actually was. In comparison to movements performed without stimulation, subjects tilted their trunk faster and further or slower and less far, depending upon the polarity of the stimulus. The response was negligible when identical stimulus waveforms were replayed to stationary subjects. We conclude that the brain uses vestibular information for online error correction of planned body-movement trajectories.