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PubMed1983

The organization of flexion-evoking interneurons in the abdominal nerve cord of the crayfish, Procambarus clarkii.

Intracellular recording and dye injection was used to investigate the flexion-evoking interneurons in the isolated abdominal nerve cord of the crayfish, Procambarus clarkii. The interneurons described in this study have all of the characteristics of cells called flexion command fibers in earlier works. These interneurons show cell bodies in all of the abdominal ganglia, all are interganglionic, and those with posteriorly directed axons enter the terminal caudal ganglion. Some cells were found in as many as eight different preparations, supporting the idea that these interneurons are identified cells. In addition to presenting evidence for identities, evidence was obtained for serial homology in this premotor system. A summary of the general organization of the flexion premotor apparatus is offered. It consists primarily of parallel elements (command interneurons) that are either bipolar or monopolar whose axonal projections course to the terminal caudal ganglion or rostrally into the thoracic region, perhaps into the cerebral ganglion. When activated singly, these parallel elements do not recruit additional interneurons but there are data to suggest that several of these elements could act in concert and interact in a low-gain fashion to produce coordinated positioning behavior.

Action Potentials↗
PubMed2005

GABAergic and glutamatergic inhibition of nonspiking local interneurons in the terminal abdominal ganglion of the crayfish.

Nonspiking local interneurons in the terminal abdominal ganglion of the crayfish Procambarus clarkii receive inhibitory inputs from mainly glutamatergic spiking local interneurons and GABAergic nonspiking interneurons. In this study, the inhibitory responses of nonspiking interneurons to local application of glutamate and GABA into the neuropil were compared. Glutamate and GABA injection mediated the hyperpolarization of the nonspiking interneurons with an increase in membrane conductance. The glutamate-mediated membrane hyperpolarization was reversed by injection of 1 or 2 nA hyperpolarizing current. By contrast, more than 3 nA hyperpolarizing current was frequently necessary to reverse the GABA-mediated hyperpolarization. Bath application of a chloride channel blocker, 50 microM picrotoxin (PTX), reduced the glutamate-mediated hyperpolarization, but had no effect on the GABA-mediated hyperpolarization. The GABA-mediated hyperpolarization was not consistently affected by bath application of low chloride solution. These results suggest that the glutamate-mediated inhibition was related to the gating of a Cl(-) conductance, while the GABA-mediated inhibition was not. Electrical stimulation of sensory afferents innervating the exopodite elicited ipsps in uropod opener motor neurons. These sensory-evoked ipsps were also PTX-insensitive, suggesting GABAergic nonspiking interneurons could be the predominant premotor elements in organizing the uropod motor control system.

Animals↗
PubMed2002

Synaptic inputs onto spiking local interneurons in crayfish are depressed by nitric oxide.

We have analyzed the action of nitric oxide on the synaptic inputs of spiking local interneurons that form part of the local circuits in the terminal abdominal ganglion of the crayfish, Pacifastacus leniusculus. Increasing the availability of NO in the ganglion by bath applying the NO donor SNAP, or the substrate for its synthesis, L-arginine, caused a depression of synaptic inputs onto the interneurons evoked by electrically stimulating mechanosensory neurons in nerve 2 of the terminal ganglion. Conversely, reducing the availability of NO by bath application of an NO scavenger, PTIO, and an inhibitor of nitric oxide synthase, L-NAME, increased the amplitude of the evoked potentials. These results suggest that elevated NO concentration causes a depression of the synaptic inputs to spiking local interneurons. To determine whether these effects could be mediated through an NO/cGMP signaling pathway we bath applied a membrane permeable analogue of cGMP, 8-br-cGMP, which decreased the amplitude of the inputs to the interneurons. Bath application of an inhibitor of soluble guanlylyl cyclase, ODQ, produced an increase in the amplitude of the synaptic inputs. Our results suggest that NO causes a depression of synaptic inputs to spiking local interneurons probably by acting through an NO/cGMP signaling pathway. Moreover, application of NO scavengers modulates the inputs to these interneurons, suggesting that NO is continuously providing a powerful and dynamic means of modulating the outputs of local circuits.

Action Potentials↗
PubMed1991

Intracellular recordings from nonspiking interneurons in a semiintact, tethered walking insect.

Nonspiking interneurons were investigated in a tethered, walking insect, Carausius morosus, that was able to freely perform walking movements. Experiments were carried out with animals walking on a lightweight, double-wheel treadmill. Although the animal was opened dorsally, the walking system was left intact. Intracellular recordings were obtained from the dorsal posterior neuropil of the mesothoracic ganglion. Nonspiking interneurons, in which modulations of the membrane potential were correlated with the walking rhythm, were described physiologically and stained with Lucifer Yellow. Interneurons are demonstrated in which membrane potential oscillations mirror the leg position or show correlation with the motoneuronal activity of the protractor and retractor coxae muscles during walking. Other interneurons showed distinct hyperpolarizations at certain important trigger points in the step cycle, for example, at the extreme posterior position. Through electrical stimulation of single, nonspiking interneurons during walking, the motoneuronal activity in two antagonistic muscles--protractor and retractor coxae--could be reversed and even the movement of the ipsilateral leg could be influenced. The nonspiking interneurons described appear to be important premotor elements involved in walking. They receive, integrate, and process information from different leg proprioceptors and drive groups of leg motoneurons during walking.

Animals↗
PubMed1994

Relative survival of striatal projection neurons and interneurons after intrastriatal injection of quinolinic acid in rats.

An excitotoxic process mediated by the NMDA type glutamate receptor may be involved in striatal neuron death in Huntington's disease (HD). To explore this possibility, we have injected an NMDA-receptor-specific excitotoxin, quinolinic acid (QA), into the striatum in adult rats and 2-4 months postlesion explored the relative patterns of survival for the various different types of striatal projection neurons and interneurons and for the striatal efferent fibers in the different striatal projection areas. The perikarya of specific types of striatal neurons were identified by neurotransmitter immunohistochemical labeling or by retrograde labeling from striatal target areas, while the striatal efferent fiber plexuses were identified by neurotransmitter immunohistochemical labeling. The pattern of survival for the perikarya of each neuron type as a function of distance from the center of the injection site was determined, and the relative survival of each type was compared. For the fibers in target areas, computer-assisted image analysis was used to determine the degree of fiber loss for each projection target. In the study of perikaryal vulnerability, we found that the somatostatin-neuropeptide Y (SS/NPY) interneurons were the most vulnerable to QA and the cholinergic neurons were invulnerable to QA. The perikarya of all projection neuron types (striatopallidal, striatonigral, and striato-entopeduncular) were less vulnerable than the SS/NPY interneurons and more vulnerable than the cholinergic interneurons. Among projection neuron perikarya, there was evidence of differential vulnerability, with striatonigral neurons appearing to be the most vulnerable. Examination of immunolabeled striatal fibers in the striatal target areas indicated that striato-entopeduncular fibers better survived intrastriatal QA than did striatopallidal or striatonigral fibers. The apparent order of vulnerability observed in this study among projection neurons and/or their efferent fiber plexuses and the invulnerability observed in this study of cholinergic interneurons is similar to that observed in HD. The vulnerability of the SS/NPY interneurons to QA is, however, in stark contrast to their invulnerability in HD. The results thus suggest that although the excitotoxin hypothesis of striatal neuron death in HD has merit, QA injections into adult rat striatum do not strictly mimic the outcome in HD. This suggests that either adult rats are not a completely suitable subject for mimicking HD or the HD excitotoxic process does not involve a freely circulating excitotoxin such as QA.

Animals↗
PubMed2000

Transient global ischemia in rats yields striatal projection neuron and interneuron loss resembling that in Huntington's disease.

The various types of striatal projection neurons and interneurons show a differential pattern of loss in Huntington's disease (HD). Since striatal injury has been suggested to involve similar mechanisms in transient global brain ischemia and HD, we examined the possibility that the patterns of survival for striatal neurons after transient global ischemic damage to the striatum in rats resemble that in HD. The perikarya of specific types of striatal interneurons were identified by histochemical or immunohistochemical labeling while projection neuron abundance was assessed by cresyl violet staining. Projectionneuron survival was assessed by neurotransmitter immunolabeling of their efferent fibers in striatal target areas. The relative survival of neuron types was determined quantitatively within the region of ischemic damage, and the degree of fiber loss in striatal target areas was quantified by computer-assisted image analysis. We found that NADPHd(+) and cholinergic interneurons were largely unaffected, even in the striatal area of maximal damage. Parvalbumin interneurons, however, were as vulnerable as projection neurons. Among immunolabeled striatal projection systems, striatoentopeduncular fibers survived global ischemia better than did striatopallidal or striatonigral fibers. The order of vulnerability observed in this study among the striatal projection systems, and the resistance to damage shown by NADPHd(+) and cholinergic interneurons, is similar to that reported in HD. The high vulnerability of projection neurons and parvalbumin interneurons to global ischemia also resembles that seen in HD. Our results thus indicate that global ischemic damage to striatum in rat closely mimics HD in its neuronal selectivity, which supports the notion that the mechanisms of injury may be similar in both.

Animals↗
PubMed1990

Olfactory interneurons in the brain of the larval sphinx moth Manduca sexta.

1. The physiology and morphology of olfactory interneurons in the brain of larval Manduca sexta were studied using intracellular recording and staining techniques. Antennal olfactory receptors were stimulated with volatile substances from plants and with pure odorants. Neurons responding to the stimuli were investigated further to reveal their response specificities, dose-response characteristics, and morphology. 2. We found no evidence of specific 'labeled-lines' among the odor-responsive interneurons, as none responded exclusively to one plant odor or pure odorant; most olfactory interneurons were broadly tuned in their response spectra. This finding is consistent with an 'across-fiber' pattern of odor coding. 3. Mechanosensory and olfactory information are integrated at early stages of central processing, appearing in the responses of some local interneurons restricted to the primary olfactory nucleus in the brain, the larval antennal center (LAC). 4. The responses of LAC projection neurons and higher-order protocerebral interneurons to a given odor were more consistent than the responses of LAC local interneurons. 5. The LAC appears to be functionally subdivided, as both local and projection neurons had arborizations in specific parts of the LAC, but none had dendrites throughout the LAC. 6. The mushroom bodies and the lateral protocerebrum contain neurons that respond to olfactory stimulation.

Animals↗
PubMed1993

Local interneurons and information processing in the olfactory glomeruli of the moth Manduca sexta.

Intracellular recordings were made from the major neurites of local interneurons in the moth antennal lobe. Antennal nerve stimulation evoked 3 patterns of postsynaptic activity: (i) a short-latency compound excitatory postsynaptic potential that, based on electrical stimulation of the antennal nerve and stimulation of the antenna with odors, represents a monosynaptic input from olfactory afferent axons (71 out of 86 neurons), (ii) a delayed activation of firing in response to both electrical- and odor-driven input (11 neurons), and (iii) a delayed membrane hyperpolarization in response to antennal nerve input (4 neurons). Simultaneous intracellular recordings from a local interneuron with short-latency responses and a projection (output) neuron revealed unidirectional synaptic interactions between these two cell types. In 20% of the 30 pairs studied, spontaneous and current-induced spiking activity in a local interneuron correlated with hyperpolarization and suppression of firing in a projection neuron. No evidence for recurrent or feedback inhibition of projection neurons was found. Furthermore, suppression of firing in an inhibitory local interneuron led to an increase in firing in the normally quiescent projection neuron, suggesting that a disinhibitory pathway may mediate excitation in projection neurons. This is the first direct evidence of an inhibitory role for local interneurons in olfactory information processing in insects. Through different types of multisynaptic interactions with projection neurons, local interneurons help to generate and shape the output from olfactory glomeruli in the antennal lobe.

Animals↗
PubMed1989

Anatomical and physiological observations on the organization of mechanoreceptors and local interneurons in the central nervous system of the wandering spider Cupiennius salei.

In the wandering spider Cupiennius salei, the functional neuroanatomy of leg mechanosensory receptor neurons and interneurons associated with a single leg neuromere was investigated by combined intracellular recording and Lucifer yellow ionophoresis. Trichobothria axons that selectively respond to air currents and to low-frequency airborne vibrations have arborizations restricted to ventral regions of the appropriate leg neuromere. Receptor afferents that respond selectively to substrateborne vibrations are distributed ventrally in the corresponding leg neuromere and extend into certain interganglionic tract neuropiles. Golgi impregnation and intracellular dye filling show that local interneurons originate in ventral sensory neuropiles of leg neuromeres and ascend dorsally to terminate amongst dendrites of motor neurons. Local interneurons generally show higher thresholds for vibration stimuli than do receptors. Local interneurons typically receive inputs from one or several types of receptors. Some respond to stimulation of a single leg, others respond to stimulation of several legs on the same side of the body. The functional morphology of the receptor afferents is correlated with known physiological characteristics of slit sensilla and trichobothria. logical characteristics of slit sensilla and trichobothria. Structure and activity of the local interneurons are compared with analogous interneurons in other arthropods.

Acoustic Stimulation↗
PubMed1994

Critical parameters of the spike trains in a cell assembly: coding of turn direction by the giant interneurons of the cockroach.

Cockroaches (Periplaneta americana) respond to air displacement produced by an approaching predator by turning and running away. A set of 4 bilateral pairs of ventral giant interneurons is important in determining turn direction. Wind from a given side is known to produce more spikes, an earlier onset of the spike trains, and different fine temporal patterning, in the ipsilateral vs the contralateral set of these interneurons. Here we investigate which of these spike train parameters the cockroach actually uses to determine the direction it will turn. We delivered controlled wind puffs from the right front, together with intracellular injection of spike trains in a left ventral giant interneuron, under conditions where the animal could make normally directed turning movements of the legs and body. In trials where our stimuli caused the left side to give both the first spike and more total spikes than the right, but where our injected spike train included none of the normal fine temporal patterning, 92% of the evoked turns were to the right-opposite of normal (Figs. 4-6). In trials where the left side gave the first spike, but the right side gave more spikes, 100% of the turns were to the left--the normal direction (Figs. 8, 9). Comparable results were obtained when each of the left giant interneurons 1, 2 or 3 were electrically stimulated, and when either weak or stronger wind puffs were used. Stimulating a left giant interneuron electrically in the absence of a wind puff evoked an escape-like turn on 9% of the trials, and these were all to the right (Fig. 9). These results indicate that fine temporal patterning in the spike trains is not necessary, and information about which side gives the first spike is not sufficient, to determine turn direction. Rather, the key parameter appears to be relative numbers of action potentials in the left vs the right group of cells. These conclusions were supported by similar experiments in which extracellular stimulation of several left giant interneurons was paired with right wind (Figs. 11, 12).

Action Potentials↗
PubMed1995

The hybrid modulatory/pattern generating N1L interneuron in the buccal feeding system of Lymnaea is cholinergic.

This study examines neurotransmission between identified buccal interneurons in the feeding system of the snail Lymnaea stagnalis. We compare the pharmacology of the individual synaptic connections from a hybrid modulatory/pattern generating interneuron (N1L) to a pattern generating interneuron (N1M) with that from a modulatory interneuron (SO) to the same follower cell (N1M). The pharmacological properties of the N1L to N1M and the SO to N1M connections closely resemble each other. Both interneurons produce fast cholinergic EPSPs as judged by the blocking effects of cholinergic antagonists hexamethonium, d-tubocurarine and the cholinergic neurotoxin AF-64A. A slower, more complex but non-cholinergic component of the synaptic response is also present after stimulating either the presynaptic N1L or SO interneurons. This second component of the postsynaptic response is not dopaminergic, on the basis of its persistence in the presence of dopaminergic antagonists ergometrine and fluphenazine and the dopaminergic neurotoxin MPP+. We conclude that, although there has been an evolutionary divergence in function, the modulatory SO and the hybrid modulatory/pattern generating N1L are pharmacologically similar. Neither of them contributes directly to dopaminergic modulation of the feeding activity. These neurons also resemble the N1M protraction phase pattern generating neurons which are cholinergic (Elliott and Kemenes, 1992).

Animals↗
PubMed2004

Multilevel inhibition of feeding by a peptidergic pleural interneuron in the mollusc Lymnaea stagnalis.

The pleural interneuron PlB is a white neuron in the pleural ganglion of the snail Lymnaea. We test the hypothesis that it inhibits neurons at all levels of the feeding system, using a combination of anatomy, physiology and pharmacology. There is just one PlB in each pleural ganglion. Its axon traverses the pedal and cerebral ganglia, running into the buccal ganglia. It has neuropilar branches in the regions of the cerebral and buccal ganglia where neurons that are active during feeding also branch. Activation of the PlB blocks fictive feeding, whether the feeding rhythm occurs spontaneously or is driven by a modulatory interneuron. The PlB inhibits all the neurons in the feeding network, including protraction and retraction motoneurons, central pattern generator interneurons, buccal modulatory interneurons (SO, OC), and cerebral modulatory interneurons (CV1, CGC). Only the CV1 interneuron shows discrete 1:1 IPSPs; all other effects are slow, smooth hyperpolarizations. All connections persist in Ca(2+)/Mg(2+)-rich saline, which reduces polysynaptic effects. The inhibitory effects are mimicked by 0.5 to 100 micromol l(-1) FMRFamide, which the PlB soma contains. We conclude that the PlB inhibits neurons in the feeding system at all levels, probably acting though the peptide transmitter FMRFamide.

Action Potentials↗
PubMed2004

Octopamine-containing (OC) interneurons enhance central pattern generator activity in sucrose-induced feeding in the snail Lymnaea.

In the pond snail Lymnaea stagnalis octopamine-containing (OC) interneurons trigger and reconfigure the feeding pattern in isolated CNS by excitation of the central pattern generator. In semi-intact (lip-mouth-CNS) preparations, this central pattern generator is activated by chemosensory inputs. We now test if sucrose application to the lips activates the OC neurons independently of the rest of the feeding central pattern generator, or if the OC interneuron is activated by inputs from the feeding network. In 66% of experiments, sucrose stimulated feeding rhythms and OC interneurons received regular synaptic inputs. Only rarely (14%) did the OC interneuron fire action potentials, proving that firing of OC interneurons is not necessary for the sucrose-induced feeding. Prestimulation of OC neurons increased the intensity and duration of the feeding rhythm evoked by subsequent sucrose presentations. One micromolar octopamine in the CNS bath mimicked the effect of OC interneuron stimulation, enhancing the feeding response when sucrose is applied to the lips. We conclude that the modulatory OC neurons are not independently excited by chemosensory inputs to the lips, but rather from the buccal central pattern generator network. However, when OC neurons fire, they release modulatory octopamine, which provides a positive feedback to the network to enhance the sucrose-activated central pattern generator rhythm.

Animals↗
PubMed1999

Motor pattern switching in the heartbeat pattern generator of the medicinal leech: membrane properties and lack of synaptic interaction in switch interneurons.

The motor program for heartbeat in the medicinal leech is produced by a central pattern generator that regularly switches between two alternative coordination states. A pair of switch heart interneurons reciprocally alternate between rhythmically active and inactive states to effect these switches. During spontaneous switches in the activity state of switch interneurons, there was no correlation between the duration of a particular activity state and beat period, indicating that the timing networks for the switch cycle and the beat cycle are relatively independent. Simultaneous recordings from two switch heart interneurons showed that a perturbation in the electrical activity of one does not influence switching of the other and that there is no synaptic interaction between them. Using voltage clamp, we characterized an L-like Ca2+ current (measured as Ba2+ currents), inactivating and non-inactivating K+ currents, a persistent Na+ current, and a hyperpolarization-activated inward current in switch interneurons. Dynamic clamp experiments show that "subtraction" of an artificial switch leak conductance (described previously by Gramoll et al. 1994) from a switch interneuron when it is in the inactive state causes it to display activity associated with the active state. We discuss how the switch leak conductance may interact with the intrinsic currents of switch interneurons to control their activity state.

Animals↗
PubMed2005

Interneuron deficits in patients with the Miller-Dieker syndrome.

Lissencephaly is characterized by a thickened cortex and loss of gyri, resulting in the brain having a smooth surface. Patients with lissencephaly frequently exhibit epilepsy and mental retardation, conditions often associated with a defect in inhibitory neurons. While lissencephaly has traditionally been considered a disorder of radial migration, recent data indicate interneurons migrate non-radially, while projection neurons migrate radially. To determine if an interneuron defect, and therefore a non-radial migration defect, exists in patients with lissencephaly, we studied the calretinin-expressing interneuron subpopulation in the brains from two fetuses and two children with lissencephaly and a deletion involving 17p13 deletion (Miller-Dieker syndrome) along with age-matched controls. Our data indicate fetuses with the Miller-Dieker syndrome have a significant (tenfold) reduction in the number of calretinin-expressing interneurons present, whereas minimal reductions in the number of calretinin-expressing interneurons are present in children with this disorder. These data parallel those seen in the Lis1(+/-) mouse model of human lissencephaly, and are consistent with a non-radial cell migration defect in humans. Thus, when considering the pathogenesis of human lissencephaly and the clinical manifestations in these patients, defects in both non-radial cell migration (inhibitory interneurons) and radial migration (excitatory projection neurons) must be considered.

Analysis of Variance↗
PubMed1998

Quantitative analysis of inputs to somatostatin-immunoreactive descending interneurons in the myenteric plexus of the guinea-pig small intestine.

Somatostatin immunoreactivity occurs in a specific subgroup of cholinergic descending interneurons in the myenteric plexus of the guinea-pig small intestine. In the present work, we made light- and electron-microscopic investigations of chemically defined inputs to these neurons, in order that the origins of the connections of other neurons with them could be deduced. Somatostatin-immunoreactive synapses and close contacts were found on the cell bodies and filamentous processes of somatostatin neurons; these were 84% of all inputs. It is thus confirmed that this class of interneuron forms chains that project anally. Descending interneurons with immunoreactivity for nitric oxide synthase provided 14% of inputs to somatostatin-immunoreactive descending interneurons. An antiserum against a calcium-binding protein, calbindin, was used as marker for the majority of intrinsic primary afferent neurons, AH/Dogiel type II neurons; this class of neurons provided only 2.5% of the inputs to somatostatin-immunoreactive descending interneurons. We conclude that somatostatin-immunoreactive descending interneurons are involved in the conduction of impulses distally along the full length of the small intestine, but receive only a minor input from calbindin-immunoreactive primary afferent neurons.

Animals↗
PubMed1995

Interneurones of the supratrigeminal area mediating reflex inhibition of trigeminal and facial motorneurones in the rat.

Whether sensory information from the inferior alveolar nerve is mediated by different types of interneurones in the supratrigeminal area (Su5) and whether different types of these interneurones have different inhibitory actions on jaw-closing motor neurones of the trigeminal motor nucleus was investigated. The intracellular responses of periodontal afferents in the mesencephalic trigeminal nucleus, Su5 interneurones and jaw-closing motor neurones were studied in response to graded, single-shock stimulation of the ipsilateral inferior alveolar nerve. It was found that the inhibitory action of afferent inflow from the inferior alveolar nerve to jaw-closing motor neurones is possibly mediated by two types of Su5 interneurones (T-I and T-II). These Su5 neurones were discriminated on the basis of their firing characteristics. The findings also indicated that: (1) T-I neurones are responsible for short-latency, low-threshold inhibitory postsynaptic potentials (IPSPs) observed in the trigeminal motor nucleus neurones; (2) T-II interneurones mainly contribute to the amplitude of these IPSPs at higher stimulus strengths; (3) the late part of plateau IPSPs in the jaw-closing motor neurones is induced by a characteristic firing of T-II neurones. It was also shown that afferent inflow from the inferior alveolar nerve, probably mediated by collaterals of T-I and T-II interneurones, also evokes IPSPs in neurones of the intermediate subnucleus of the facial motor nucleus. The characteristics of these IPSPs resemble those of the IPSPs recorded in the jaw-closing motor neurones.

Action Potentials↗
PubMed1990

Contralaterally projecting lamina VIII interneurones in middle lumbar segments in the cat.

Peripheral input to lamina VIII interneurones was investigated by using extracellular and/or intracellular records from them. The interneurones were located in the L4-L5 spinal segments and projected to contralateral motor nuclei in the L7 segment. They constituted a non-homogeneous population but their input from muscle afferents (mainly group II afferents of quadriceps, flexor digitorum longus and pretibial flexors and group I afferents of triceps surae and hamstring nerves) and from cutaneous and joint afferents resembled the input to ipsilaterally projecting laminae V-VII interneurones of the same segments rather than the input to more caudally located lamina VIII interneurones. Since the ipsilaterally projecting laminae V-VII interneurones with such an input might be involved in locomotion, it is proposed that this is also the case for the contralaterally projecting lamina VIII midlumbar interneurones, especially those excited by stimuli applied in the cuneiform nucleus (mesencephalic locomotor region).

Animals↗