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PubMed1995

Integration in trigeminal premotor interneurones in the cat. 3. Input characteristics and synaptic actions of neurones in subnucleus-gamma of the oral nucleus of the spinal trigeminal tract with a projection to the masseteric motoneurone subnucleus.

A population of last-order interneurones within the rostrodorsal part of the oral nucleus of the spinal trigeminal tract (NVspo-gamma) has been investigated in 21 chloralose anaesthetised cats. The neurones were identified by their antidromic (AD) response to microstimulation (median current 9 microA, range 3-39 microA) of the ipsior the contralateral masseteric subnucleus of the trigeminal motor nucleus. Fifty-one of 113 interneurones tested were discharged from the ipsilateral and eight from the contralateral motor nucleus. The average conduction time was 0.50 ms from the ipsilateral and 0.74 ms from the contralateral motoneurone pool. Conduction velocities of the axons ranged from 2.0 to 14.0 ms. The pattern of primary afferent input onto the selected neurones was analysed by graded electrical stimulation of dissected trigeminal nerves. Low-threshold afferents innervating the intraoral mucosa including the tongue and the perioral skin of the lower lip were the most effective inputs, as judged from both the frequency of occurrence and from the latencies of the evoked spike discharges. Ninety-six percent of the neurones responded to stimulation of the inferior alveolar nerve (Alv inf) and 83% responded to stimulation of the lingual nerve (Ling). The median threshold strength required to evoke the Alv inf and the Ling responses was 1.7 T (range 1.0-3.6 T) and 1.3 T (range 1.0-5.0 T), respectively. The median latency to spike discharges evoked by the Alv inf was 2.0 ms (range 1.3-4.8 ms) and to the Ling it was 2.5 ms (range 1.4-7.0 ms). Action potentials elicited by stimulation of the masseteric and digastric nerves were observed in 40% and 10% of the neurones, respectively. These responses, which had median latencies of more than 8 ms (range 4.7-16.0 ms), were only seen at stimulation intensities above 2 T (range 2.5-25 T). An input from the maxillary whisker nerve was seen in only one case. Postspike averages of the extracellular field potentials within the trigeminal motoneurone subnuclei evoked by interneuronal spikes were made in a subsample of 51 NVspo-gamma neurones activated by iontophoresis of L-glutamic acid. Excitatory synaptic effects within the masseteric subnucleus were observed in eight cases. An inhibitory effect was seen in one case. One specific neurone gave an excitatory extracellular field potential within the digastric motoneurone subnucleus. This interneurone was AD activated from the digastric, but not from the masseteric subnucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1985

Control of locomotion in marine mollusc Clione limacina. IV. Role of type 12 interneurons.

Type 12 interneurons in pedal ganglia of Clione limacina exerted a strong influence upon the locomotor generator during "intense" swimming. These neurons generated "plateau" potentials, i.e. their membrane potential had two stable states: the "upper" one when a neuron was depolarized, and the "down" one, separated by 30-40 mV. The interneurons could remain in each state for a long time. Short depolarizing and hyperpolarizing current pulses, as well as excitatory and inhibitory postsynaptic potentials, could transfer the interneurons from one state to another. When the pedal ganglia generated the locomotory rhythm, type 12 neurons received an EPSP and passed to the "upper" state in the V2-phase of a locomotor cycle. They remained at this state until the beginning of the D1-phase when they received an IPSP and passed to the "down" state. The EPSP in type 12 neurons was produced by type 8d neurons, and the IPSP by type 7 neurons. Type 12 neurons exerted inhibitory influences upon many neurons active in the V1 and V2 phases, and excitatory influences upon the D-phase interneurons (type 7). The functional role of type 12 neurons was to limit the activity of neurons discharging in the V-phase of a locomotory cycle. In addition, they enhanced the excitation of the D-phase neurons and promoted, thus, the transition from the V-phase to the D-phase.

Animals↗
PubMed1977

A pharmacological study of the inhibition of ventral group Ia-excited spinal interneurones.

In cats anaesthetized with pentobarbitone a pharmacological investigation was made of the inhibition by volleys in afferent fibres and ventral roots of physiologically identified Ia interneurones in the ventral horn. The recurrent inhibition of Ia interneurones by Renshaw cells, and the "mutual" inhibition between Ia interneurones, were suppressed by electrophoretic strychnine and are presumably mediated by glycine. Short latency and duration inhibitions by impulses in muscle and cutaneous afferents were also suppressed by strychnine. Electrophoretic GABA inhibited the firing of Ia interneurones and the effects of bicuculline methochloride suggested that this amino acid mediates longer latency and duration inhibition produced by afferent impulses of muscle and cutaneous origin.

Action Potentials↗
PubMed1988

Common interneurones mediating cortical and tectal excitation of abducens motoneurones in the cat.

Tectal and cortical effects on abducens motoneurones were examined with intracellular recording techniques in cats under chloralose anaesthesia. Abducens motoneurones exhibited disynaptic EPSPs after stimulation of the contralateral superior colliculus and cerebral peduncle. The tectal disynaptic EPSPs were observed invariably in all motoneurones tested, while the peduncular EPSPs were observed only in 40% of motoneurones after stimulation of the contralateral cerebral peduncle. However, the tectal disynaptic EPSPs were consistently facilitated by conditioning peduncular stimulation in all motoneurones tested. These results indicated that the disynaptic excitatory tecto-abducens and cortico-abducens pathways shared common premotor interneurones. The common interneurones which mediated the tectal and cortical disynaptic excitation of abducens motoneurones were explored in the pons. These interneurones were identified by the criteria that they were fired monosynaptically from both the tectum and the cerebral peduncle and were activated antidromically from the abducens nucleus. Systematic threshold mapping for the antidromic activation in and around the abducens nucleus indicated that they gave off many collateral branches in the nucleus. Such neurones were found in the nucleus reticularis pontis caudalis, being distributed in the area extending 0.8-3 mm rostral to the rostral pole of the abducens nucleus, 1.3-2.7 mm deep from the dorsal surface of the brain stem, and 0.8-1.8 mm lateral from the midline. The present experiments strongly suggest that a group of neurones in the paramedian pontine reticular formation make direct excitatory connexions with abducens motoneurones and play a role of common interneurones that transmit both tectal and cortical commands.

Abducens Nerve↗
PubMed1993

Respiratory interneurons of the lower cervical (C4-C5) cord: membrane potential changes during fictive coughing, vomiting, and swallowing in the decerebrate cat.

The possible roles of interneurons in the C4-C5 cervical spinal cord in conveying central drives to phrenic motoneurons during different behaviour patterns were investigated using intracellular recordings in decerebrate, paralysed, artificially ventilated cats. Eleven cells were tentatively classified as respiratory interneurons since they: (i) could not be antidromically activated from the ipsilateral whole intrathoracic phrenic nerve, and (ii) exhibited large membrane potential changes during eupnea (7.3 mV +/- 3.6, range 2-13.5 mV) or non-respiratory behaviour patterns. Six neurons depolarized in phase with phrenic discharge; four others depolarized during the expiratory phase; one neuron exhibited depolarization during the end of both expiration and inspiration. A variety of responses was observed during fictive coughing, vomiting, and swallowing. The results are consistent with C4-C5 expiratory interneurons conveying inhibition to phrenic motoneurons during different behaviour patterns. The responses of inspiratory and multiphasic neurons suggest that the roles of these interneurons are mode complex than simply relaying central excitatory or inhibitory drive to phrenic motoneurons.

Animals↗
PubMed1988

Modulation of activity in sensory neurons and wind-sensitive interneurons by cercal displacement in the cockroach.

1. The cockroach Periplaneta americana can modify the sensory activity received by its central nervous system from the cerci, paired abdominal wind-responsive appendages. Medial displacement of the cerci produces a reduction in the number of sensory action potentials (AP's) elicited by a wind stimulus (Fig. 2) (Libersat et al. 1987; Golstein and Camhi 1988). This movement occurs naturally, for example during flying. 2. This sensory reduction is present when measured as the integral of extracellularly recorded activity as well as when counting the number of AP's larger than a threshold voltage just larger than the background noise (Fig. 2C). 3. Histological results confirm prior physiological experiments suggesting that the reduction may be produced by mechanical forces on the sensory nerve, rather than synaptically (Fig. 4). 4. The wind-response of interneurons is significantly diminished by the sensory reduction when measured either extra- or intracellularly (Figs. 5, 6). Cells affected include identified ventral and dorsal giant interneurons (GI's), which carry directional information about wind from the abdominal cerci to the more anterior portions of the nervous system, and are involved in flying (Camhi 1980; Ritzmann 1984; Comer 1985). 5. The reduction in the interneuronal response was unaffected by the elimination of input from descending central pathways, and input from a cercal chordotonal organ that senses cercal position and inhibits some of the GI's (Fig. 5). Thus, the reduction in wind-evoked sensory activity can itself account for the modulation of interneuron activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1983

Resistance of hippocampal CA-1 interneurons to 20 min of transient cerebral ischemia in the rat.

The aim of this morphological study was to determine the vulnerability of hippocampal interneurons to ischemia in the adult rat. Two types of interneurons situated in the CA-1 stratum orients were investigated, the larger basket cells close to stratum pyramidale and the smaller basket cells close to the alveus. Male Wistar rats were subjected to 20 min of transient cerebral ischemia by means of 4-vessel occlusion and perfusion fixed 1, 2, 4, or 21 days later. In both Golgi-impregnated and in routinely stained sections the pyramidal cells and interneurons in the hippocampal CA-1 region were examined and counted. The study clearly demonstrated the selective vulnerability of the CA-1 pyramidal cells, as no ischemic cell damage to or loss of interneurons was found.

Animals↗
PubMedDate not supplied

Afferent control of cortically evoked reactions of spinal cord ventral horn interneurons.

The reactions of interneurons of the ventral horn (L6,7) of the spinal cord in response to stimulation of the motor zone of the cortex and of afferents of the hind limbs were investigated intra- and extracellularly in experiments on cats. It was demonstrated that cortically evoked reactions of the interneurons are modulated by the preceding afferent wave. Three types of effects were distinguished: intensification, suppression, and biphasic changes. Facilitation is brief (not more than 30-35 msec); the duration of suppression varied from 60-100 msec to 300-400 msec. A correlation between the effect of afferentation and the latent period of the cortically evoked reaction was established: facilitation was observed among the short-latency reactions; long-latency reactions were inhibited as a rule. Inhibition was more clearly manifested: for the responses from the ipsilateral than the contralateral hemisphere; during the conditioning of the contralateral afferents, than during the conditioning of the ipsilateral; of the high-threshold afferents than of the low-threshold. The mechanisms of afferent control of descending activity and the role of "polysynaptic loops" in the processes of the afferentation as a supplementary modulator of the excitability of motoneurons are discussed. It is proposed, on the basis of the analysis of the data obtained (the absence of IPSP in the interneurons investigated, etc.), that a principal role in the suppression of descending activity belongs to the mechanism of presynaptic inhibition, as well as to the disfacilitation caused by it (the decrease in depolarization and the increase in the critical discharge level) in the interneurons themselves due to the blocking of the background afferent influx from other inputs.

Animals↗
PubMed1990

Topography and ultrastructure of commissural interneurons that may establish reciprocal inhibitory connections of the Mauthner axons in the spinal cord of the tench, Tinca tinca L.

This study was made to identify the inhibitory interneurons belonging to the spinal circuitry activated by the Mauthner axons in the tench (Tinca tinca L.). The histological investigations were focused on a segmental pair of commissural interneurons that were reconstructed in toto from their distinguishing topographical and ultrastructural features. These features are: (a) the adendritic soma located 100-150 microns dorsal to the central canal; (b) the first node of Ranvier which is precommissural and connected to the ipsilateral Mauthner axon via gap junction; (c) the second node of Ranvier, from which two first-order branches arise postcommissurally each supplying roughly the rostral and caudal half of the contralateral spinal cord segment; (d) their second-order branches, which arise at intervals that correspond closely to those of the Mauthner axon collaterals; (e) the postsynaptic targets of the second-order branches, which are exclusively all the motoneurons and interneurons innervated by the contralateral Mauthner axon; (f) the axon terminals of these branches, which contain F-type vesicles, form Gray type-2 synapses, and abut either on the initial segment or on the first node of Ranvier of the target neurons. Thus, it appears that this segmental interneuron has all the appropriate features that could provide the structural basis for the reciprocal fast-acting inhibitory coupling underlying the startle reflex elicited by the Mauthner neurons in response to auditory stimuli.

Animals↗
PubMed2001

Stridulatory pattern generation in acridid grasshoppers: metathoracic interneurons in Stenobothrus rubicundus (Germar 1817).

Stridulation was elicited in tethered gomphocerine grasshoppers of the species Stenobothrus rubicundus in order to identify interneurons of the stridulation pattern generator, and describe their morphological and physiological properties. Nine types of such neurons could be found and characterized; eight of those could additionally be compared to corresponding neuron types previously known from other species. As shown in detail for one selected type, the neurons of the stridulation pattern generator are very similar in their anatomical appearance, and possess similar physiological qualities at least in two species with similar stridulation patterns. Stridulation interneurons of species with largely different stridulatory motor patterns have a similar morphology, but show a different activation timing throughout the stridulation. Nevertheless, special properties such as resetting or initiation capability of certain stridulation interneurons seem to be conserved throughout the species. The results suggest that the stridulation pattern generator of different species consists of a uniform set of interneurons that change their activity pattern to produce species-specific song movements.

Animals↗
PubMed2001

Presynaptic effects of biogenic amines modulating synaptic transmission between identified sensory neurons and giant interneurons in the first instar cockroach.

Intracellular recording was used to investigate the modulatory effects of serotonin and octopamine on the identified synapses between filiform hair sensory afferents and giant interneurons in the first instar cockroach, Periplaneta americana. Serotonin at 10(-4) mol l(-1) to 10(-3) mol l(-1) reduced the amplitude of the lateral axon-to-ipsilateral giant interneuron 3 excitatory postsynaptic potentials. and octopamine at 10(-4) mol l(-1) increased their amplitude. Similar effects were seen on excitatory postsynaptic potentials in dorsal giant interneuron 6. Several lines of evidence suggest that both substances modulate the amplitude of excitatory postsynaptic potentials by acting presynaptically, rather than on the postsynaptic neuron. The fitting of simple binomial distributions to the postsynaptic potential amplitude histograms suggested that, for both serotonin and octopamine, the number of synaptic release sites was being modulated. Secondly, the amplitudes of miniature excitatory postsynaptic potentials recorded in the presence of tetrodotoxin were unaffected by either modulator. Finally, recordings from contralateral giant interneuron 3, which has two identifiable populations of synaptic inputs, showed that each modulator had a more pronounced effect on excitatory postsynaptic potentials evoked by the lateral axon than on those evoked by the medial axon. Immunocytochemistry confirmed that neuropilar processes containing serotonin are present in close proximity to these synapses.

Animals↗
PubMed2003

Cajal-Retzius cells, inhibitory interneuronal populations and neuropeptide Y expression in focal cortical dysplasia and microdysgenesis.

Focal cortical dysplasia (FCD) and microdysgenesis (MD) are likely to represent abnormalities of radial neuronal migration during cortical development. We investigated the distribution of reelin-positive Cajal-Retzius cells, known to be important in the later stages of radial neuronal migration and cortical organization, in 12 surgical cases of both MD and FCD. Quantitation revealed significantly higher numbers of these cells in MD cases compared to controls. As the majority of cortical interneurones arise via tangential rather than radial migration, we studied the distribution and morphology of inhibitory interneuronal subsets immunolabelled for calbindin, parvalbumin and calretinin within these malformations. Frequent findings were a reduction of inhibitory interneurones in the region of FCD and abnormally localised hypertrophic or multipolar calbindin-positive interneurones in both FCD and MD. Neuropeptide Y immunostaining showed a striking increase in the density of the superficial plexus of fibres in both MD and FCD cases in addition to labelling of dysplastic neurones, which may represent an adaptive anti-convulsant mechanism to dampen down seizure propagation.

Adolescent↗
PubMed2000

Differential activation of ATP-sensitive potassium channels during energy depletion in CA1 pyramidal cells and interneurones of rat hippocampus.

In the hippocampus, pyramidal cells are more vulnerable than granule cells and interneurones to energy depletion during hypoxia and ischaemia. The aim of the present study was to explore whether this difference is related to the lower expression of adenosine 5'-triphosphate-sensitive potassium (K(ATP)) channels in pyramidal cells compared to other hippocampal neurones. Hippocampal slices were prepared from 10- to 13-day-old rats, and CAI pyramidal cells and interneurones of the stratum radiatum were visually and electrophysiologically identified. Energy depletion was produced by removing glucose from the bath or by inhibiting mitochondrial metabolism using rotenone. In the perforated-patch configuration, both protocols elicited outward currents in only a minority of the pyramidal cells but in most of the interneurones. The currents started to develop 9-57 min after glucose deprivation and 4-16 min after rotenone application and reversed near the K+ equilibrium potential. Bath-applied diazoxide (0.3 mM), an opener of K(ATP) channels, could activate additional currents. The sulphonylureas tolbutamide (0.5 mM) or glibenclamide (20 microM), two blockers of K(ATP) channels, totally inhibited the currents induced by energy depletion and activated by diazoxide. The results demonstrate the differential activation of K(ATP) channels during energy depletion in pyramidal cells and interneurones, and suggest that channel activation is neuroprotective against the deleterious effects of energy depletion.

ATP-Binding Cassette Transporters↗
PubMed2006

Possible mechanisms of the involvement of dopaminergic cells and cholinergic interneurons in the striatum in the conditioned-reflex selection of motor activity.

A possible mechanism for the involvement of cholinergic interneurons in the striatum and dopaminergic cells in the substantia nigra in the selection from among several types of motor activity during learning is proposed. Selection is triggered by simultaneous increases in the activity of dopaminergic neurons and a pause in the activity of cholinergic interneurons in response to the conditioned signal. The appearance of the pause may facilitate activation of GABAergic interneurons in the striatum and the action of dopamine on D2 receptors on cholinergic interneurons. Differently directed changes in dopamine and acetylcholine levels synergistically modulate the efficiency of corticostriatal inputs, such that the rules for modulation of the "strong" and "weak" inputs are opposite in sign. The subsequent reorganization of neuron activity in the cortex-basal ganglia-thalamus-cortex circuit leads to increased activity in those cortical neurons providing "strong" innervation to the striatum with simultaneous decreases in the activity of neurons providing "weak" innervation to the striatum, which may underlie the selection of the movement reaction, in which the neocortex is involved. It follows from this model that if the delay between the conditioned and unconditioned stimuli is not longer than the latent period of the reactions of dopaminergic and cholinergic cells (about 100 msec), selection of movement activity in response to the conditioned signal and learning is hindered.

Acetylcholine↗
PubMed1984

Spontaneous dorsal root potentials arise from interneuronal activity in the isolated frog spinal cord.

Spontaneous dorsal root potentials (sDRPs) were recorded from the dorsal roots of the isolated frog spinal cord using sucrose gap techniques. sDRPs were always negative (depolarizing) in sign and ranged in size from about 100 microV to 6.0 mV. The largest sDRPs were 25-40% of the amplitude of DRPs evoked by stimulation of adjacent dorsal roots. Hypoxia or accumulation of extracellular K+ ions did not appear responsible for the generation of this spontaneous activity since exposing the cord to unoxygenated Ringer's solution decreased sDRPs and K+-sensitive microelectrodes indicated that only small changes in extracellular K+ (approximately 0.15 mM) were produced coincidently with the largest sDRPs. Chemically-mediated synaptic transmission was found to be necessary for the production of sDRPs because the addition of Mn2+ or Mg2+ ions or tetrodotoxin to the Ringer's solution or reduction of its Na+ concentration blocked sDRPs, whereas application of 4-aminopyridine enhanced them. It did not seem that a direct action of GABA on afferent fiber terminals was responsible for the generation of spontaneous potentials since an increase in sDRPs was seen after: application of the GABA antagonists, bicuculline and picrotoxin; exposure to the glutamic acid decarboxylase inhibitor, semicarbazide (which significantly reduced the concentration of GABA in the cord); and lowering of the external Cl- concentration. Similarly taurine is probably not significant since the taurine antagonist, TAG, increased the amount of spontaneous activity. On the other hand, (--)-baclofen, which is thought to reduce excitatory amino acid release, D,L-alpha-aminoadipic acid, alpha, epsilon-diaminopimelic acid, and 2-amino-4-phosphonobutyric acid, which are believed to be selective postsynaptic excitatory amino acid antagonists, and [D-Pro2-D-Phe7-D-Trp9]-substance P, a postsynaptic blocker of the action of substance P, markedly and reversibly reduced sDRPs. Experiments were performed on isolated cords without supraspinal or afferent input; therefore sDRPs must be generated by intraspinal structures. It would seem that interneurons are responsible because addition of mephenesin or pentobarbital--compounds which inhibit polysynaptic reflex transmission involving interneurons--reduced the production of sDRPs. sDRPs may result from the action of excitatory transmitters such as L-glutamate, L-aspartate, or substance P released by interneuronal firing in the spinal cord. Moreover, because sDRPs were increased by application of yohimbine, corynanthine and propanolol and reduced by haloperidol, such interneurons may be under descending control of adrenergic and dopaminergic fibers.

Afferent Pathways↗
PubMed1985

Activation of spinal cord interneurons which process inputs from the femoral-saphenous vein.

Recordings were made from single spinal cord interneurons which could be activated by electrical stimulation of afferents terminating in the wall of the femoral-saphenous vein. Interneurons were either excited or both excited and inhibited by venous afferent stimulation. Most of the venous afferent-driven interneurons could also be driven by electrical activation of A-alpha beta muscle and cutaneous afferents. Stimulation of several different muscle nerves drove single interneurons.

Animals↗
PubMed1986

Pathway of the blink reflex in the brainstem of the cat: interneurons between the trigeminal nuclei and the facial nucleus.

Blink reflex responses evoked by electrical stimulation of the supraorbital nerve were examined using cats and the pathway of the blink reflex in the brainstem was elucidated. Both early response (ER) and late response (LR) were mediated by the main sensory trigeminal nucleus and the spinal trigeminal nucleus. However, a lesion of the main sensory trigeminal nucleus had less effect on the blink reflex than a lesion of the spinal trigeminal nucleus. The ER was mediated not only by the shorter disynaptic pathway of 3 neurons through the trigeminal nerve, the trigeminal nuclei and the facial nucleus but also by a polysynaptic pathway of 4 neurons. The interneurons were located between the trigeminal nuclei and the facial nucleus. Some of these interneurons participated in the production of both ER and LR. The area of the brainstem responsible for ER and LR of the blink reflex was the reticular formation from the rostral part of the medulla to the pons except the medial area around the median sulcus. The LR interneurons were distributed more widely than the ER interneurons.

Animals↗
PubMed1987

Septohippocampal and commissural pathways antagonistically control inhibitory interneurons in the dentate gyrus.

Available evidence suggests that a portion of the septohippocampal pathway may form inhibitory synapses on inhibitory interneurons in the dentate gyrus. In contrast, a portion of the commissural input from the contralateral hilus may form excitatory synapses on inhibitory interneurons. To ascertain whether these pathways synapse onto a common population of interneurons, a series of pulses were applied and their effects on perforant path evoked, granule cell population spikes were measured. The population spike was markedly reduced when the perforant path pulse was preceded by a pulse to the contralateral hilus. This inhibition was markedly reduced, however, when a medial septal pulse was applied either prior to, or within 3 ms after the commissural pulse. The disinhibition was critically dependent on the temporal relationship between the medial septal and commissural pulse, and not on the medial septal-perforant path relationship. This finding suggests that the septohippocampal pathway inhibits the interneurons through which the commissural pathway is able to inhibit granule cells.

Animals↗