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At least 613 records · Page 34Linked to original sources
PubMed1984

Central projections of first-order ocellar interneurons in two orthopteroid insects Acheta domesticus and Periplaneta americana. A comparative study.

The central projections of ocellar first-order interneurons in the cricket, Acheta domesticus, and the cockroach, Periplaneta americana, were examined in silver-intensified cobalt preparations. Ten morphologically different types of ocellar interneurons among a total of 44 are recognized in the cricket, and five different types among a total of 26 in the cockroach, indicating that these species have simpler ocellar systems than those described previously in locusts. Ocellar interneurons arborize in the following regions of neuropil in both the cricket and cockroach: the ocellar foci of the posterior protocerebrum, the posterior deutocerebrum, the protocerebral bridge, the ocellar synaptic plexus, ocellar nerves and tracts, and the lobula and medulla of the optic lobes. Ocellar first-order interneurons thus project predominantly to sites where they are likely to synapse with other ocellar and optic-lobe interneurons.

Animals↗
PubMed1990

Activity of interneurons within the L4 spinal segment of the cat during brainstem-evoked fictive locomotion.

Extracellular recordings from interneurons located in the L4 spinal segment were made during fictive locomotion produced by electrical stimulation of the mesencephalic locomotor region (MLR) in the paralysed decerebrate cat. Only interneurons within the L4 segment which received group II input from quadriceps, sartorius or the pretibial flexor muscle afferents and which had axonal projections to motor nuclei in L7 were selected for analysis. During the fictive step cycle two thirds of these interneurons fired action potentials during the time of activity in the ipsilateral hindlimb flexor neurograms. These cells were also less responsive to peripheral input during the extension phase of the fictive locomotion cycle. The remaining one third of the interneurons examined were not rhythmically active during locomotion. The possible contributions of the midlumbar interneurons to motoneuron activity during locomotion are discussed.

Action Potentials↗
PubMed1991

Integration in trigeminal premotor interneurones in the cat. 2. Functional characteristics of neurones in the subnucleus-gamma of the oral nucleus of the spinal trigeminal tract with a projection to the digastric motoneurone subnucleus.

Seventy-one (n = 71) premotor interneurones have been localized by extracellular recordings within the subnucleus-gamma of the oral nucleus of the spinal trigeminal tract (NVspo-gamma) in nineteen chloralose anaesthetized cats. The neurons were antidromically activated by microstimulation (minimum = 3 microA) applied to the digastric motoneurone subnucleus of the trigeminal motor nucleus. Fifty-one (n = 51) of the interneurones were discharged from the ipsi- and nineteen (n = 19) from the contralateral digastric subnucleus. One neurone out of four tested was antidromically activated from both stimulation sites suggesting a bifurcated axon. The identified premotor neurones had a unique convergence profile of oral and perioral primary afferents. Latency calculations indicated that at least 55% of these interneurones were monosynaptically activated by low stimulus strength applied to the inferior alveolar (minimum = 1.0 T) and/or the lingual nerve (minimum = 1.0 T). The thresholds for evoking the neuronal discharges coincided statistically with those required to evoke a jaw opening reflex response by stimulation of the same nerves. It is suggested that the specific group of NVspo-gamma interneurones under different contexts mediates the disynaptic reflex and participates in the centrally and reflexly evoked "patterning" adjustments of the digastric jaw opening motoneurones during ongoing jaw movements. A companion paper reports the convergence of descending cortical, tectal and ascending cervical inputs, as well as of oro-facial and neck primary afferent inputs onto an unselected population of interneurones in the NVspo-gamma (Westberg and Olsson 1991).

Afferent Pathways↗
PubMed1991

Response of adult cat abducens internuclear interneurons to selective removal of their target motoneurons.

The morphological and physiological integrity of abducens internuclear interneurons was evaluated following chemical removal of their almost exclusive target, i.e. the contralateral medial rectus motoneuron population. Motoneuron death was induced by toxic ricin injection into the ipsilateral medial rectus muscle. The main advantage of this method is that target removal is not associated with presynaptic axon damage. The activity of identified abducens internuclear interneurons was recorded before and after target removal during spontaneous eye movements in the chronic cat preparation. Several abnormalities and a remarkable decrease in eye position and velocity sensitivities were observed in the discharge pattern of these neurons for a period of 15-20 days following target removal. After that time all recorded interneurons behaved normally. A parallel morphological study showed the absence of any abducens internuclear interneuron death. These results indicate that, after a critical period, the abducens internuclear interneuron population recovers its normal behavior following target removal with no evidence of neuronal loss.

Abducens Nerve↗
PubMed1988

Neural control of ventilation in the shore crab, Carcinus maenas. II. Frequency-modulating interneurons.

1. We have identified a class of nonspiking interneurons which can control the frequency of ventilation in a graded manner. These frequency modulating interneurons (FMis) also receive synaptic inputs in-phase with the ventilatory motor output providing a functional positive feedback loop in the ventilatory system. The class of FMis is composed of three morphologically and physiologically distinct interneurons, FMi1, FMi2 and FMi3. 2. Depolarization of FMi1 increases the rate of ventilation, while hyperpolarization decreases the rate (Fig. 1). This control is restricted to a single ventilatory central pattern generator (CPG), (Fig. 2), although FMi1 sends processes into the neuropils of both hemiganglionic CPGs (Fig. 3). 3. Hyperpolarization of FMi2 increases the rate of both ventilatory CPGs while depolarization of this cell slows and eventually arrests the rhythm (Figs. 5 and 6). FMi2 receives a synaptic input correlated with the motor output of each of the ventilatory CPGs (Fig. 4). During periods of reversed ventilation, this cell is abruptly hyperpolarized and continues to be driven in-phase with the ventilatory motor output (Fig. 7). 4. Hyperpolarization of FMi3 increases the rate of ventilation and depolarization decreases the rate of ventilation produced by both CPGs (Fig. 10). This control of the ventilatory rate by FMi3 is graded (Fig. 11). There is no apparent change in the membrane potential of FMi3 during reversed ventilation and it is morphologically distinct from FMi2. 5. FMi2 and FMi3 may be involved in the switch in ventilatory motor pattern from forward to reversed ventilation. Hyperpolarization of FMi2 and depolarization of FMi3 can elicit bouts of reversed ventilation from both CPGs (Fig. 13). 6. These results suggest that the FM interneurons act in parallel to control the frequency of ventilation and may act as integrating elements between spiking 'command' fibers in the circumesophageal connectives and the nonspiking interneurons of the ventilatory CPG.

Animals↗
PubMed1988

Ascending auditory interneurons in the cricket Teleogryllus commodus (Walker): comparative physiology and direct connections with afferents.

Ascending auditory interneurons of the cricket, Teleogryllus commodus (Walker), were investigated using simultaneous intracellular and extracellular recording in order to identify units which had previously been characterized only by extracellular recording. The morphology and physiology of the large adapting unit (LAU: Fig. 1) and of the small tonic unit (STU: Fig. 2) of Teleogryllus correspond well to those of the ascending neuron 2 (AN2) and the ascending neuron 1 (AN1) of Gryllus (Figs. 1, 2), respectively. A summary of the ascending auditory interneurons described by various authors in 5 species of crickets is presented in order to establish common identities. Physiological evidence for direct connections between auditory afferents and the ascending auditory interneurons AN1 (STU) and AN2 (LAU) is presented. Simultaneous intracellular recordings from receptors and interneurons in response to sound as well as the activity of auditory interneurons upon electrical stimulation of the tympanal nerve reveal short and constant latencies of receptor-evoked synaptic activity in AN1 (STU) and AN2 (LAU).

Animals↗
PubMed1994

An immunohistochemical study of parvalbumin containing interneurons in the gerbil hippocampus after cerebral ischemia.

We investigated postischemic changes of non-pyramidal neurons in the gerbil hippocampus 1 h - 7 days after 10 min of cerebral ischemia, with parvalbumin and microtubule-associated protein 2 (MAP2)-immunohistochemistry. Parvalbumin-immunoreactive interneurons in the hippocampus were unaffected up to 24 h after ischemia. A slight reduction of the immunoreactivity in neuronal processes was seen in the hippocampal CA1 sector 48 h after ischemia. Seven days after ischemia, a marked loss of parvalbumin-immunoreactive interneurons was observed in the hippocampal CA1 and CA3 sectors. Furthermore, reduced staining in the dentate granular and molecular layers was observed. MAP2-immunoreactive pyramidal neurons in the hippocampus were unchanged up to 48 h after ischemia. Seven days after ischemia, a severe loss of MAP2 immunoreactivity was found in the hippocampal CA1 and CA3 neurons and dentate hilar neurons. However, scattered CA1 neurons, most likely interneurons, preserved MAP2 immunoreactivity. The results demonstrate that transient cerebral ischemia can cause a loss of parvalbumin-immunoreactive interneurons in the hippocampus. Furthermore, some interneurons seem to lose parvalbumin synthesis. Although dentate granule cells are resistant to ischemia, considerable reductions of afferent input was suggested by parvalbumin staining.

Animals↗
PubMed1997

Patterns of connectivity of spinal interneurons with single muscle afferents.

A technique was developed to measure, in the anesthetized and paralyzed cat under artificial ventilation, changes of excitability to intraspinal stimulation simultaneously in two different afferent fibers or in two collaterals of the same afferent fiber. Intraspinal stimulation reduced the threshold of single muscle afferent fibers ending in the intermediate nucleus. This effect was seen with strengths below those required to activate the afferent fiber tested (1.5-12 microA), occurred at a short latency (1.5-2.0 ms), reached a maximum between 15 and 30 ms, and lasted up to 100 ms. The effects produced by graded stimulation applied at the shortest conditioning-testing stimulus time intervals increased by fixed steps, suggesting recruitment of discrete elements, most likely of last-order interneurons mediating primary afferent depolarization (PAD). The short-latency increases in excitability produced by the weakest effective intraspinal stimuli were usually detected only in the collateral closest to the stimulating micropipette, indicating that the stimulated interneurons mediating PAD have spatially restricted actions. The short-latency PAD produced by intraspinal stimuli, as well as the PAD produced by stimulation of the posterior biceps and semitendinosus (PBSt) nerve or by stimulation of the bulbar reticular formation (RF), was depressed 19-30 min after the i.v. injection of 0.5 mg/kg of picrotoxin, suggesting that all these effects were mediated by GABAergic mechanisms. The PAD elicited by stimulation of muscle and/or cutaneous nerves was depressed following the i.v. injection of (-)-baclofen, whereas the PAD elicited in the same collateral by stimulation of the RF was baclofen-resistant. The short-latency PAD produced by intraspinal stimulation was not always depressed by i.v. injections of (-)-baclofen. Baclofen-sensitive and baclofen-resistant monosynaptic PADs could be produced in different collaterals of the same afferent fiber. The results suggest that the intraspinal terminals of single muscle afferents receive synapses from more than one PAD-mediating GABAergic interneuron and that a single last-order interneuron has synaptic connections with a restricted number of intraspinal terminals and/or collaterals of the same afferent fiber. In addition, they support the existence of separate subsets of last-order baclofen-sensitive and baclofen-resistant interneurons that respond predominantly to segmental and to descending inputs. It is suggested that the restricted nature of the PAD plays an important role in the central control of the synaptic effectiveness of group I muscle afferents.

Afferent Pathways↗
PubMed2002

Differential distribution of interneurons in the neural networks that control walking in the mudpuppy (Necturus maculatus) spinal cord.

Locomotor behavior is believed to be produced by interneuronal networks that are intrinsically organized to generate the underlying complex spatiotemporal patterns. In order to study the temporal correlation between the firing of individual interneurons and the pattern of locomotion, we utilized the spinal cord-forelimb preparation from the mudpuppy, in which electrophysiological recordings of neuronal activity were achieved during walking-like movement of the forelimb induced by bath application of N-methyl- D-aspartate (NMDA). Intra- and extracellular recordings were made in the C2 and C3 segments of the spinal cord. These segments contain independent flexor and extensor centers for the forelimb movement about the elbow joint during walking. Among the 289 cells recorded in the intermediate gray matter (an area between the ventral and dorsal horns) of the C2 and C3 segments, approximately 40% of the cells fired rhythmically during "walking." The firing rates were 6.4+/-0.4 impulses/s (mean +/- SE). These rhythmically active cells were classified into four types based on their phase of activity during a normalized step cycle. About half the rhythmic cells fired in phase with either the flexor (F) or extensor (E) motoneurons. The rest fired in the transitions between the two phases (F-->E and E-->F). Longitudinal distributions of the four types of interneurons along the spinal cord were in agreement with observations that revealed distinct but overlapping flexor and extensor centers for walking. Some cells triggered short-latency responses in the elbow flexor or extensor muscles and may be last-order interneurons. These observations suggest that there is a differential distribution of phase-specific interneurons in the central pattern generator of the mudpuppy spinal cord for walking.

Action Potentials↗
PubMed2000

Areas of operation of interneurons mediating presynaptic inhibition in sacral spinal segments.

Sources of primary afferent depolarization (PAD) of skin afferents in the sural (Sur) nerve and of group-II muscle afferents in the posterior biceps and semitendinosus (PBST) nerve were compared at several sites, about 2 mm apart, within the L7-S2 segments in order to define areas of projection of sacral interneurons mediating PAD of these afferents. Just rostral to the pudendal nucleus, strong PAD of Sur afferents was evoked by stimulation of skin nerves, while stimulation of muscle nerves had only marginal effects. This indicates that sacral PAD interneurons co-excited by skin and muscle afferents operate primarily within the regions overlying the pudendal nucleus. Furthermore, PAD evoked by muscle afferents was weaker over the rostral part of the pudendal nucleus than over the caudal part of this nucleus, where hamstring afferents became its main source, both in Sur and in PBST group-II afferents. By correlating the relative strength of PAD at the levels of the rostral and caudal parts of the pudendal nucleus with the previously established input from muscle and cutaneous afferents to interneurons at these levels, it is therefore proposed that sacral PAD interneurons operate over shorter distances than indicated by previous experiments: over either rostral or caudal parts of the pudendal nucleus, i.e., about 2 mm, rather than over the whole length of this nucleus, i.e., 4-5 mm. Sacral PAD interneurons may, thus, modulate synaptic transmission to even more spatially restricted neuronal populations than previously proposed.

Action Potentials↗
PubMed2005

Modification of statocyst input to local interneurons by behavioral condition in the crayfish brain.

Posture control by statocysts is affected by leg condition in decapod crustaceans. We investigated how, in the crayfish brain, the synaptic response of local interneurons to statocyst stimulation was affected by leg movements on and off a substratum. The magnetic field stimulation method permitted sustained stimulation of statocyst receptors by mimicking body rolling. The statocyst-driven local interneurons were classified into four morphological groups (Type-I-IV). All interneurons except Type-IV projected their dendritic branches to the parolfactory lobe of the deutocerebrum where statocyst afferents project directly. Type-I interneurons having somata in the ventral-paired lateral cluster responded invariably to statocyst stimulation regardless of the leg condition, whereas others having somata in the ventral-unpaired posterior cluster showed response enhancement or suppression, depending on the cell, during leg movements on a substratum, but no response change during free leg movements off the substratum. The synaptic responses of Type-II and IV interneurons were also affected differently by leg movements depending on the substratum condition, whereas those of Type-III remained unaffected. These findings suggest that the statocyst pathway in the crayfish brain is organized in parallel with local circuits that are affected by leg condition and those not affected.

Action Potentials↗
PubMed2001

Proportional inhibition in the cricket medial giant interneuron.

Inhibitory effects on the number of wind-evoked impulses were studied in the medial giant interneuron of the cricket, Gryllus bimaculatus. The interneuron receives an inhibitory input from wind receptors on cercus ipsilateral to its soma. Using a dual channel wind stimulator, the intensity of inhibitory input was changed over 1,000-fold and effects on the number of spikes were observed. The ipsilateral inhibition reduced the number of outgoing spikes from a level elicited by excitation alone and it did so in proportion to the level of wind responsiveness displayed by each cell. A proportional coefficient of inhibition was derived and its value depended on the level of total excitation of the medial giant interneuron. The medial giant interneurons with high excitation showed a smaller value of the coefficient than those with low excitation. The proportional inhibition of the medial giant interneuron by the ipsilateral cercus suppresses the number of its spikes to a reasonable level for a wide range of stimulus intensities under natural conditions.

Animals↗
PubMed1975

Activity of interneurons mediating reciprocal 1a inhibition during locomotion.

The activity of interneurons monosynaptically excited by 1a afferents and mediating the reciprocal inhibition of motoneurons of the antagonistic muscles was recorded in mesecephalic cats. The activity was resulted during locomotion evoked by stimulation of the "locomotor region" of the mesencephalon. The neurons turned out to be active in a definite phase of the step simultaneously with that muscle which supplied them by 1a afferent input. In preparations with de-efferent hindlimbs, stimulation of the "locomotor region" evoked a periodic process in the spinal cord ("fictive" locomotion); in this case bursts of activity in the interneurons also coincided with the activity of motoneurons of corresponding muscles. Under such conditions excitation of 1a afferents by the passive stretch of the muscle or by electric stimulation of the muscle nerve studied in an increase of the activity of interneurons, which depended on the phase of the cycle. The data obtained show that during locomotion there are at least two sources of inhibition of motoneurons of antagonistic muscles; (i) the activity of 1a afferents of the active muscle, mediating by corresponding interneurons; and (ii) signals coming through the same interneurons from the central mechanisms of generating stepping movements.

Animals↗
PubMed1980

Activity of Ia inhibitory interneurons during fictitious scratch reflex in the cat.

(1) The fictitious scratch reflex was observed in decerebrate cats immobilized with Flaxedil. The activity of interneurons in the inhibitory pathways from Ia afferents to motoneurons of antagonistic muscles was recorded during scratching. The selected interneurons were supplied by Ia afferents from m. vastus, posterior biceps-semitendinosus and sartorius. (2) Almost all recorded interneurons showed periodic modulation of activity. Their maximal activity in the scratch cycle usually coincided with the maximal activity of motoneurons of those muscles from which the interneurons receive Ia afferents. Excitation of Ia afferents by passive stretch of the muscle or by electrical stimulation of the muscle nerve resulted in the increase of the interneuron activity, without changing its timing in the scratch cycle.

Afferent Pathways↗
PubMed1990

Serotonin (5-HT) induces IPSPs in pyramidal layer cells of rat piriform cortex: evidence for the involvement of a 5-HT2-activated interneuron.

In a slice preparation of rat piriform cortex, both intracellular and extracellular techniques were used to examine the pharmacological and electrophysiological actions of serotonin (5-HT). Bath application of 5-HT resulted in either depolarization (57%), hyperpolarization (34%) or no change (9%) in membrane potential of cells in the pyramidal cell layer (layer II) of piriform cortex. Additionally, when KCl-containing electrodes were used, 5-HT induced an increase in depolarizing synaptic potentials in 41% of these cells. It was concluded that these potentials were reverse inhibitory post-synaptic potentials (IPSPs) because they were blocked by bicuculline and tetrodotoxin. The induction of IPSPs by 5-HT was blocked by the 5-HT2-selective antagonist ritanserin. By recording extracellularly in the presence of 5-HT, a group of 5-HT-activated, putative interneurons was found at the border of layers II and III of piriform cortex, 5-HT but not norepinephrine activation was blocked by ritanserin. The actions of 5-HT were mimicked by the 5-HT2 agonist alpha-methyl-5-HT; the 5-HT2 partial agonist, 2,5-dimethoxy-4-methyl-amphetamine had a small agonist action of its own and blunted the effect of 5-HT. Activation of a larger group of putative interneurons by the more universal excitant N-methyl-D-aspartate showed that the 5-HT-activated interneurons represented 23% of the interneurons located on the border between layers II and III. We conclude that 5-HT induces IPSPs in layer II pyramidal cells by activating a subpopulation of interneurons at the border of layers II and III of piriform cortex.

Animals↗
PubMed1992

Convergence and segregation of septal and median raphe inputs onto different subsets of hippocampal inhibitory interneurons.

The convergence and segregation of medial septal and median raphe afferents in the innervation of different subpopulations of GABAergic interneurons was investigated in the rat hippocampal formation. Following local injections of 5,7-dihydroxytryptamine into the median raphe nucleus destroying all serotonergic neurons, iontophoretic injections of Phaseolus vulgaris leucoagglutinin (PHAL) into the medial septum resulted in anterograde labelling of axons in the hippocampus. The labelled varicose fibres made multiple contacts with calbindin D28K-, parvalbumin-, and cholecystokinin-immunoreactive interneurons. These results disproved the possibility that PHAL-labelled afferents innervating hippocampal interneurons following septal PHAL injections would have been raphe axons passing through the injection site. In the second set of experiments a double anterograde tracing technique (PHAL from the septum and biotinylated-PHAL from the median raphe) and a triple or double immunostaining procedure was used to determine the types of interneurons (calbindin D28K-, parvalbumin-, or cholecystokinin-immunoreactive) innervated by one, or the other, or both pathways. The results showed that parvalbumin-containing neurons were innervated by septal afferents but avoided by raphe axons, whereas calbindin D28K-containing cells, and to a smaller extent cholecystokinin-containing cells served as targets for both pathways. In some cases the same individual calbindin D28K- or cholecystokinin-containing neurons received multiple contacts from afferents of both septal and raphe origin. Thus, our results indicate that different subcortical nuclei modulate largely different inhibitory circuits in the hippocampal formation. However, considering the occasional convergence of the two subcortical nuclei not only onto the same type, but even onto the same individual calbindin D28K-containing interneurons, we propose that a particular inhibitory function, most probably feed-forward inhibition in the distal dendritic region, is under the control of both pathways.

Afferent Pathways↗
PubMed1993

Theory of the locomotion of nematodes: control of the somatic motor neurons by interneurons.

The only animal of which the complete neural circuitry is known at the submicroscopical level is the nematode Caenorhabditis elegans. This anatomical knowledge is complemented by functional insight from electrophysiological experiments in the related nematode Ascaris lumbricoides, which show that Ascaris motor neurons transmit signals electrotonically and not with unattenuated spikes. We developed a mathematical model for electrotonic neural networks and applied it to the motor nervous system of nematodes. This enabled us to reproduce experimental results in Ascaris quantitatively. In particular, our computed result of the velocity v approximately equal to 6 cm/s of neural excitations in the Ascaris interneurons supports the simple hypothesis that the so-called rapidly moving muscular wave is produced by a neural excitation traveling at the same speed in the interneuron as the muscular wave. In C. elegans, the computed velocity v approximately equal to 8-30 cm/s of signals in the interneurons is much larger than the observed velocity v approximately equal to 0.2 cm/s of the body wave. Therefore, the hypothesis that the muscular wave is produced by a synchronous neural excitation wave cannot hold for C. elegans. We argue that stretch receptor control is the most likely mechanism for the generation of body waves used in the locomotion of C. elegans. Extending the simulation to larger groups of neurons, we found that the neural system of C. elegans can operate purely electrotonically. We demonstrate that the same conclusion cannot be drawn for the nervous system of Ascaris, because in the long (l approximately equal to 30 cm) interneurons the electrotonic signals would be too strongly attenuated. This conclusion is not in contradiction with the experimental findings of electrotonic signal propagation in the motor neurons of Ascaris because the latter are shorter (l approximately equal to 5 cm) than the interneurons.

Animals↗
PubMed1989

Differential effects of methionine5-enkephalin on hippocampal pyramidal cells and interneurons.

While the excitatory action of opioids and opiate drugs upon pyramidal neurons in the hippocampus is well known, the mechanism by which this excitation is achieved is still argued. A popular hypothesis is that opiates reduce the activity of inhibitory interneurons, thereby indirectly exciting the pyramidal cells. To validate this idea, it is necessary to show that opiates selectively affect the population of interneurons. The present study therefore examined the effects of met-enkephalin upon pyramidal cells and interneurons located in area CA1. Extracellular action potentials were recorded using multibarrelled micropipettes. Drugs were applied locally by either pressure micro-ejection or microiontophoresis. Met-enkephalin (10(-5) M) elevated the spontaneous discharge of pyramidal cells, while interneurons were inhibited. The responses of both types of cell were blocked by the opiate antagonist naloxone. When the synaptic connections between the pyramidal cells and interneurons were disrupted by local application of magnesium or bicuculline, met-enkephalin had no effect on the pyramidal cells. However, neither magnesium nor bicuculline altered the enkephalin-induced inhibition of theta neurons. These results support the hypothesis that opioids of the enkephalin subclass, excite pyramidal cells in the hippocampus through a disinhibition mechanism.

Action Potentials↗