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At least 19 recordsLinked to original sources
PubMed1976

Anatomy of the ocellar interneurons of acridid grasshoppers. I. The large interneurons.

The anatomy of the large ocellar interneurons in the brain of five species of acridid grasshoppers of two different subfamilies (Schistocerca vaga, S. gregaria, Gastrimargus africanus, Trimerotropis pallidipennis, and Arphia conspersa) was revealed by cobalt-filling of the three ocellar nerves and subsequent reconstructions from silver-intensified (Timm's method) serial sections. Conflicts in the literature are reviewed (Tables 1, 2) and differences in the number of cells, anatomical descriptions of these cells, and nomenclature are resolved by demonstration of an identical number of large ocellar identical number of large ocellar interneurons in all five species examined (Fig. 1). There are 17 large 1st-order ocellar interneurons (Figs. 2, 3). Each of the three ocellar nerves contains the axons of seven large interneurons; four of these interneurons have axons in two ocellar nerves. The anatomy of three pairs of 2nd-order ocellar interneurons (with branches in the ocellar tracts within the brain and axons in the circum-esophageal connectives) is reconsidered in light of recent conflicts in the literature. Previous accounts by Williams (1975) of interneurons O2, O3, and PI(2):5 are corroborated and new details added (Fig. 7) by the use of a cobalt method that appears to stain these 2nd-order interneurons transsynaptically (Fig. 6).

Animals↗
PubMed1976

Anatomy of the ocellar interneurons of acridid grasshoppers. II. The small interneurons.

The anatomy of the small ocellar interneurons in the brain of the acridid grasshopper Schistocerca vaga was revealed by cobalt-filling the three ocellar nerves and subsequent reconstructions from silver-intensified (Timm's method) serial sections. In total, 61 small ocellar interneurons were repeatedly identified with arborizations in many areas of the brain and optic lobe, including in particular the posterior neuropil, ocellar tracts, protocerebral bridge, lobula, ventral bridge and tritocerebral crotch, calyces, and antenno-glomerular tracts. Each ocellar nerve contains the axons of small cells that arborize in the other two ocellar tracts; these tracts are sites of ocellar integration. Direct interactions between the ocelli and compound eyes are suggested by the projections of small ocellar interneurons into the proximal lobula. Small cell arborizations from all three ocelli are distributed actoss much of the protocerebral bridge, implying a role for the bridge as an ocellar neuropil within the brain. Four of the small interneurons could be seen in whole-mount preparations and are demonstrated to be identical in five species of acridid grasshoppers of two different subfamilies: Schistocera vaga, S. gregaria, Gastrimargus africanus, Trimerotropis pallidipennis, and Arphia conspersa.

Animals↗
PubMed1975

Nonspiking interneurons in walking system of the cockroach.

Intracellular recordings were made from the neurites of interneurons and motoneurons in the metathoracic ganglion of the cockroach, Periplaneta americana. Many neurons were penetrated which failed to produce action potentials on the application of large depolarizing currents. Nevertheless, some of them strongly excited and/or inhibited slow motoneurons innervating leg musculature, even with weak depolariziing musculature, even with weak depolarizing currents. Cobalt-sulfide-straining of these nonspiking neurons showed them to be interneurons with their neurites contained entirely within the metathoracic ganglion. Two further characteristics of these interneurons were rapid spontaneous fluctuations in membrane potential and a low resting membrane potential. One nonspiking neuron, interneuron I, when depolarized caused a strong excitation of the set of slow levator motoneurons which discharge in bursts during stepping movements of the metathoracic leg. During rhythmic leg movements the membrane potential of interneuron I oscillated with the depolarizing phases occurring at the same time as bursts of activity in the levator motorneurons. No spiking or any other nonspiking neuron was penetrated which could excite these levator motoneurons. From all these observations we conclude that oscillations in the membrane potential of interneuron I are entirely responsible for producing the levator bursts, and thus for producing stepping movements in a walking animal. During rhythmic leg movements, bursts of activity in levator and depressor motoneurons are initiated by slow graded depolarizations. The similarity of the synaptic activity in these two types of motoneurons suggests that burst activity in the depressor motoneurons is also produced by rhythmic activity in nonspiking interneurons. The fact that no spiking neuron was found to excite the depressor motoneurons supports this conclusion. Interneuron I is also an element of the rhythm-generating system, since short depolarizing pulses applied to it during rhythmic activity could reset the thythm. Long-duration current pulses applied to interneuron I in a quiescent animal did not produce rhythmic activity. This observation, together with the finding that during rhythmic activity the slow depolarizations in interneuron I are usually terminated by IPSPs, suggests that interneuron I alone does not generate the rhythm. No spiking interneurons have yet been enccountered which influence the activity in levator motoneurons. Thus, we conclude that the rhythm is generated in a network of nonspiking interneurons. The cellular mechanisms for generating the oscillations in this network are unknown. Continued.

Action Potentials↗
PubMed1977

Organization of visual inputs to interneurons of lateral geniculate nucleus of the cat.

1. Two groups of interneurons that are involved in the organization of the lateral geniculate nucleus (LGN) are described. The cell bodies of one group lie within the LGN; these units are referred to as intrageniculate. The cell bodies of the other group are found immediately above the LGN at its border with the perigeniculate nucleus; these units are referred to as perigeniculate. 2. Intrageniculate interneurons have center-surround receptive fields that resemble those of relay (principal) cells. They can be subdivided into brisk or sluggish and sustained or transient categories. They are stimulated transsynaptically from the visual cortex and have a characteristic variation in the latency of their spike response to such stimulation both at threshold and for suprathreshold stimuli. The pathway for this stimulation appears to be via cortical efferents to the LGN. Intrageniculate interneurons receive direct, monosynaptic retinal inputs, as determined by recording simultaneously from such interneurons and from the ganglion cells which provide excitatory input to them. Similar to relay cells, they are shown to have one or two major ganglion cell inputs. 3. Perigeniculate interneurons are generally binocularly innervated and give on-off responses to small spot stimuli throughout their receptive field. They respond well to rapid movement of large targets. They respond to electrical stimulation of the retina with a spike latency that falls between that of brisk transient and brisk sustained relay cells. This latency is one synaptic delay longer than that of brisk transient relay cell activation and suggests that they are excited by axon collaterals of these relay cells. Electrical stimulation of the visual cortex is also consistent with this model; the latency of the response of perigeniculate interneurons is approximately one synaptic delay longer than the latency of the response of brisk transient relay cells. 4. The interneuronal pathways described are consistent with proposed circuits that subserve the generation of IPSPs that arise in response to optic nerve and visual cortical stimulation. We now show that such inhibition has feed-forward (intrageniculate) and feed-back (perigeniculate) components that are mediated by two different classes of geniculate interneurons. It is suggested that the intrageniculate interneurons are involved in precise, spatially organized inhibition and that the perigeniculate interneurons are part of a more general, diffuse inhibitory system that modulates LGN excitability.

Animals↗
PubMed1979

Graded synaptic interactions between local premotor interneurons of the locust.

1. Graded synaptic interactions are revealed between pairs of nonspiking, local interneurons in the metathroracic ganglion of the locust. These interneurons drive motor neurons innervating muscles of a hindleg. 2. All the interactions found between the interneurons are inhibitory and one way. Synaptic transmission is effected by the graded release of chemical transmitter. Some of the connections are apparently direct. One local interneuron can, therefore, exert a graded control over the membrane potential of another local interneuron. 3. There are inhibitory connections between local interneurons that excite the same motor neuron, between local interneurons that excite antagonistic motor neurons, and between local interneurons that excite motor neurons to muscles moving different joints of a hindleg. 4. Other pairs of interneurons, which are not connected, may be driven by common synaptic inputs. Their outputs add together at the level of the motor neurons to produce effects that are greater than the sum of their individual effects. 5. It is proposed that graded interactions between these local interneurons are an essential element in the generation of motor patterns.

Electrophysiology↗
PubMed1976

Convergence on interneurones mediating the reciprocal Ia inhibition of motoneurones. III. Effects from supraspinal pathways.

Supraspinal effects were investigated in interneurones identified as mediating the disynaptic reciprocal Ia inhibition of motoneurones (referred to as Ia inhibitory interneurones). It was revealed that volleys in the vestibulospinal tract may evoke mono- and disynaptic EPSPs in interneurones monosynaptically excited from extensor muscles, i.e. extensor coupled Ia inhibitory interneurones. Flexor coupled interneurones instead received disynaptic inhibition. Volleys in the rubrospinal tract evoked a dominating polysynaptic excitation, usually mixed with inhibition, in flexor as well as extensor coupled interneurones. Disynaptic rubrospinal EPSPs and IPSPs were also revealed. The pyramidal tract also gives rise to a dominating polysynaptic excitation, usually mixed with inhibition, in flexor as well as extensor coupled Ia inhibitory interneurones. Rubrospinal and pyramidal volleys were shown to facilitate transmission in various segmental reflex pathways to the Ia inhibitory interneurones. A detailed comparison reveals a striking parallelism of segmental and supraspinal effects on alpha-motoneurones and Ia inhibitory interneurones connected to the same muscles. This considerably strengthens the hypothesis of an "alpha-gamma-linkage in the reciprocal inhibition".

Animals↗
PubMed1978

Graded synaptic transmission between local interneurones and motor neurones in the metathoracic ganglion of the locust.

1. In the metathoracic ganglion of the locust some neurones can effect changes in the membrane potential of identified post-synaptic motor neurones without themselves spiking. 2. These 'non-spiking' neurones have processes only within the metathoracic ganglion, and therefore are local intraganglionic interneurones. 3. The absence of spikes in the interneurones reflects their normal physiological state and is not due to the experimental conditions. 4. When the interneurones are depolarized by the injection of current pulses lasting several hundred milliseconds, post-synaptic motor neurones are either depolarized, or hyperpolarized, for the duration of the pulse. 5. The magnitude of the change in post-synaptic voltage is graded according to the amount of presynaptic current. 6. A number of physiological tests indicate that the graded effects upon motor neurones are mediated by chemical synaptic transmission. For example, an evoked hyperpolarization of a motor neurone can be reversed in polarity by simultaneously hyperpolarizing the motor neurone with injected current. 7. At their resting potential some interneurones tonically release sufficient transmitter to have a measurable post-synaptic effect. The injection of depolarizing and hyperpolarizing currents into these interneurones effects opposite changes in post-synaptic potential. 8. Other interneurones must be depolarized from resting potential before a post-synaptic effect is observed, and hyperpolarizing currents have no post-synaptic effect. In these interneurones it is estimated that a depolarization of only 2 mV is sufficient to effect the release of transmitter. 9. The membrane potentials of non-spiking interneurones can fluctuate by as much as 15 mV during active movements of the hind legs and individual p.s.p.s as large as 5 mV can be recorded. Therefore, summed p.s.p.s or even single ones are expected to be the electrophysiological signals effecting transmitter release from these interneurones.

Action Potentials↗
PubMed1978

[Interneurons of the motor region of the neocortex].

Interneurons of motor area in the brain cortex have been studied in cats and monkeys. The greatest attention has been paid to pyramidal interneurons, among which six cell types have been described according to their axonal composition. Unlike stellate interneurons, all types of pyramidal interneurons possess less developed axonal collaterals. Interneuronal contacts are situated on dendrites or cell bodies of middle and large long-axonal pyramids. Functional role of cortical interneurons seems to be different. Some of them are of inhibitory nature (basket cells and, perhaps, other types of long-axonal stellate neurons), others are exciting elements. The latter include short-axonal stellate neurons and, perhaps, pyramidal interneurons. While comparing the cortex in cats and monkeys, it is evident that the neocortex in monkeys, especially its lower layers, is rich in pyramidal interneurons.

Animals↗
PubMed2025

Pyramidal neurons proportionately alter the identity and survival of specific cortical interneuron subtypes.

The mammalian cerebral cortex comprises a complex neuronal network that maintains a precise balance between excitatory pyramidal neurons and inhibitory interneurons. Accumulating evidence indicates that specific interneuron subtypes form stereotyped microcircuits with distinct pyramidal neuron classes. Here we show that pyramidal neurons play an active role in this process by promoting the survival and terminal differentiation of their associated interneuron subtypes. In wild-type cortex, interneuron subtype abundance mirrors the prevalence of their pyramidal neuron partners. In Fezf2 mutants, which lack layer 5b pyramidal neurons and are expanded in layer 6 intratelencephalic neurons, corresponding subtype-specific shifts occur through two distinct mechanisms: somatostatin interneurons adjust their programmed cell death, whereas parvalbumin interneurons switch their subtype identity. Silencing neuronal activity or blocking vesicular release in L5b pyramidal neurons revealed that their communication with interneurons does not require voltage-gated synaptic activity and engages both tetanus toxin-sensitive and -insensitive pathways. Moreover, a targeted bioinformatic screen for ligand-receptor pairs displaying subtype-specific expression and reduced expression of pyramidal neuron-derived ligand in Fezf2 mutants identified candidate secreted factors and adhesion molecules. These findings reveal distinct, pyramidal neuron-driven mechanisms for sculpting interneuron diversity and integrating them into local cortical circuits.

Journal Article↗
PubMed1976

Identification and discharge patterns of spinal sympathetic interneurons.

Sympathetic interneurons, in the vicinity of the intermediolateral cell column of the cat thoracic spinal cord, were identified by determining whether the probability of spontaneously occurring unitary discharge was correlated in time with the R wave of the ECG. Fifteen units which could not be antidromically activated by stimulation of the cervical sympathetic nerve exhivited a positive post-R wave relationship. The discharge patterns of these cells were distinctly different from those of antidromically identified preganglionic neurons. The interneurons discharged spontaneously in bursts with short interspike intervals (less than 20 ms). Preganglionic neurons rarely discharged more than once during a cardiac cycle. Single shocks applied to medullary pressor sites evoked a train of spikes in the interneurons. Preganglionic units usually discharged only once to medullary pressor stimulation. Electrial activation of medullospinal inhibitory tracts suppressed the discharges of both interneurons and preganclionic units. This observation indicates that spinal inhibition is exerted at an interneuronal level within sympathoexictatory pathways. No evidence was found for the existence of inhibitory interneurons in the intermediolateral cell column. This study demonstrated that the post-R wave time interval histogram in combination with a test for antidromic activation can be used to differentiate between spinal sympathetic internuerons and preganglionic cells.

Animals↗
PubMed1977

Physiological and kinetic properties of cholinergic receptors activated by multiaction interneurons in buccal ganglia of Aplysia.

1. Neurons of Aplysia buccal ganglia contain three types of acetylcholine (ACh) receptors, each of which has been characterized by its sensitivity to inhibitors and kinetics of desensitization and by the properties of the conductance change it controls, including reversal potential, major ion, and functional consequence. The receptors are classified as depolarizing, slowly decrementing hyperpolarizing, and rapidly decrementing hyperpolarizing. Identified neurons are innervated by identified cholinergic multiaction interneurons; the form of the postsynaptic potential produced depends on the number and class of receptor found on each cell. 2. Interneuronal action potentials produce monosynaptic IPSPs by activating slowly decrementing hyperpolarizing receptors on seven cells in each ganglion. The IPSP reversal potential of 75 mV is shifted 42 mV in a depolarizing direction in Cl = free seawater. The ACh response has a reversal potential identical to that of the PSP; the PSP is blocked by 10(-4) g/ml curare but unaffected by hexamethonium. Interneuronal action potentials also produce monosynaptic EPSPs with a -14 mV extrapolated reversal potential by activating depolarizing receptors on one cell in each ganglion. This PSP is blocked by 10(-4) g/ml hexamethonium and mimicked by a Na-dependent ACh response. 3. Each interneuronal action potential also produces a diphasic depolarizing-hyperpolarizing synaptic potential in one cell in each ganglion as a result of released ACh acting on two classes of postsynaptic receptor on the same cell. One of these receptors is depolarizing; the other is a rapidly decrementing hyperpolarizing receptor. The two differ in their sensitivity to inhibitors, and the conductance changes they produce differ in their reversal potential, duration, and functional consequences. Both components can be mimicked by iontophoretic application of ACh. 4. Although the hyperpolarizing receptors on the inhibitory and diphasic follower cells have similar sensitivity to inhibitors and control similar conductance changes, they differ in their kinetics of desensitization. The hyperpolarizing receptor on the diphasic cell shows marked decrement to repeated presynaptic action potentials and to repeated iontophoretic application of ACh. This decrement is greater than that seen in either the hyperpolarizing receptor on the inhibitory follower cell or the depolarizing receptor on the dual follower cell. The shape of the PSP in the diphasic follower and its effect on firing of the cell are thus functions of both membrane potential and the degree of desensitization of the receptor. 5. Rate of desensitization is, therefore, an additional criterion for characterizing otherwise similar receptors for neurotransmitters.

Acetylcholine↗
PubMedDate not supplied

Receptor and interneuron light-adaptation in the dragonfly visual system.

Intracellular recordings show that the receptors and second-order interneurons of the dragonfly compound eye change their sensitivity in response to maintained illumination. Comparison of receptor with interneuron shows that neural mechanisms act to ensure that the modulation of interneuron membrane potential that is set up by contrast changes is independent of background intensity.

Adaptation, Physiological↗
PubMed1978

[Transformation of long reticulofugal impulse trains by interneurons monosynaptically linked to the reticulospinal tract].

Transmission of the reticulofugal activity via the interneurons localized in the ventromedial grey matter of the lumbar region and monosynaptically activated from the reticulospinal fibres was studied in anaesthetized immobilized cats. Interneurons usually generated stationary discharges when reticulospinal pathways were rhythmically stimulated with relatively low frequencies (up to 80-100/s); with further increase of stimulation frequency the discharges became non-stationary (initial high-frequency phase was followed by partial or complete discharge suppression). Maximal firing rate at the initial phase could not exceed 180-230 imp./s. The "transfer function" (the ratio of response frequency to stimulation frequency) reached 0.7-0.8 at low stimulation frequencies and decreased substantially at higher ones. Using mathematical modelling of the excitatory and post-activation inhibitory actions in these neurons, the parameters have been estimated which determine the transfer properties, of the interneuronal population relaying reticulofugal activity.

Animals↗
PubMed1978

A second sensory--motor--interneuron with neurosecretory granules in Hydra.

Using serial-sectioning techniques for conventional transmission and high-voltage electron microscopy, we characterized the ultrastructural features and synaptic contacts of the sensory cell in tentacles of Hydra. The sensory cell has an apical specialization characterized by a recessed cilium surrounded by three rodlike stereocilia. This ciliary--stereociliary complex constitutes the receptive or dendritic pole of the sensory cell. The dense filamentous cores of the stereocilia project proximally into a narrow circumciliary cytoplasmic region connected by septate junctions to marginal processes of an enveloping epitheliomuscular cell. The central cilium has a characteristic marginal flare midway along its length and a dense filamentous substructure at its base. Pairs of branched, striated rootlets extend from the axial centriole into a mitochondria-rich region of the cell. Pigment-like granules are present in the cytoplasm around the circumciliary space. The perikaryon is characterized by an elongate nucleus surrounded by a narrow rim of cytoplasm containing prominent Golgi complexes, assorted vacuoles and dense-cored vesicles, free ribosomes, short segments of rough endoplasmic reticulum, microtubules, glycogen particles, and lipid droplets. Generally, one or two thin, naked axons extend laterally from the perikaryon into the nerve net region above the myonemes of the large epitheliomuscular cells. Within the axons are found occasional aggregates of dense-cored vesicles and en passant synapses characterized by the presence of clear or dense-cored vesicles in contact with paramembranous densities and associated intracleft cross filaments. Using these ultrastructural criteria, we demonstrated for the first time that the granule-containing sensory cells have synaptic contacts with other neurons, nematocytes, and epitheliomuscular cells hence, we considered these cells to be sensory--motor--interneurons with neurosecretory granules. We hypothesize that this unique, apparently multifunctional neuron may be a modern representative of a primitive stem cell that give rise evolutionarily to the sensory cells, motor neurons, interneurons, and neurosecretory cells of higher animals.

Animals↗
PubMed1978

Interneurons of sympathetic ganglia: divergent cyclic AMP responses and morphology in cat and cow.

The biochemical properties of the small, intensely fluorescent (SIF) cells of bovine and feline superior cervical ganglia were determined by studying the cyclic AMP responses to incubation in vitro with adrenergic agonists: the morphological properties were studied by fluorescence histochemistry and electron microscopy. Incubation with 50 micron dopamine elicited cyclic AMP levels 524% of control values in the bovine ganglion, but only 152% in the feline ganglion (a value which is not statistically significant). Incubation with 50 micron isoproterenol produced an increase of 356% of control values in the cow, but no increase in the cat. SIF cells were classified into two types by fluorescence histochemistry. The bovine ganglion contained 23.7% Type I (solitary) SIF cells, and 76.3% Type II (clustered) cells, whereas the feline ganglion contained 99.5% Type II cells. Thus the feline ganglion lacks both Type I SIF cells and a dopamine receptor-adenylate cyclase complex. On the basis of biochemical and morphological evidence, we hypothesize that the Type I SIF cell is an interneuron, and infer that the lack of a response to dopamine stimulation in the feline ganglion is caused by a scarcity of interneurons in this species.

Animals↗
PubMed1979

Synaptic potentials effect the release of transmitter from locust nonspiking interneurons.

An excitatory synaptic potential in a local nonspiking interneuron of a locust is able to effect the release of chemical transmitter. The consequence is that a discrete inhibitory synaptic potential is evoked in an identified postsynaptic motoneuron. These local interactions between interneurons and motoneurons are of behavioral significance in that they ensure the correct operation of a resistance reflex.

Action Potentials↗
PubMed1978

Structural correlates of recurrent collateral interneurons producing both electrical and chemical inhibitions of the Mauthner cell.

Intracellular injections of horseradish peroxidase provided a basis for morphological identification of inhibitory interneurons belonging to the recurrent collateral network of the Mauthner cell. Their axons dilate to form unusually large bulbs surrounding the axon cap. The morphological appearance of these bulbs as well as intracellular recordings at their level indicate that they behave as nodes and serve as a final source of current for electrical inhibition of the Mauthner cell. The axon of each interneuron gives rise to two different groups of fibres which are respectively fitted for the mediation of electrical and chemical inhibitions of their target cell.

Animals↗
PubMed1979

[Effect of leucine-enkephalin on the interneuronal transmission of excitation].

In the experiments on non-anesthetized flaxedil-immobilized cats it has been shown that the injection of leucin-enkephalin (1 mg) into the lateral ventricle of the brain is followed by the inhibition of evoked potentials in the ventrolateral columns of the spinal cord and of segmental interneuronal transmission in the spinal cord as well as by the reduction of the amplitude of potentials in the S I zone of the brain cortex induced by the sciatic nerve stimulation. Naloxone (1 mg/kg, i.v.) prevented the effects of leucin-enkephalin. Methysergide pretreatment (2.5 mg/kg, i.p.) led to a decrease of leucin-enkephalin effect on the interneuronal transmission in the spinal cord. Leucin-enkephalin failed to change the amplitude of polysynaptic potentials of glosso-mandibular reflex integrated at the brain stem level.

Animals↗