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PubMed1987

Intracellular recording from hippocampal CA1 interneurons before and after development of long-term potentiation.

Synaptic efficacy is modified following a brief train of high frequency stimulation (HFS) to a cell's afferent fibers (long-term potentiation, LTP). Modulation of synaptic efficacy could be achieved through changes in excitability of interneurons. To test this hypothesis, we used the in vitro hippocampal slice to record intracellularly from CA1 basket cell interneurons before and following a period of HFS to fibers in stratum radiatum. Stimulation of stratum radiatum consistently produced action potential discharge in the basket cell interneuron prior to the discharge of a population spike in stratum pyramidale. This result is consistent with findings that basket cells may receive direct excitatory afferent input from neurons extrinsic to the CA1 region, and mediate a powerful feed-forward inhibition. Interneuron responses were recorded under 3 experimental conditions, in which stimulus intensity was varied. The level of basket cell excitability, as assessed by responses to orthodromic input, was not decreased following a train of HFS. Rather, the evoked EPSP in basket cells was often enhanced following high frequency stimulation to the cell's afferent fibers. These findings support the notion that decrement in basket cell activity is not responsible for LTP in CA1 hippocampus.

Action Potentials↗
PubMed1988

The orientation of interneurones in the dorsal lateral geniculate nucleus of the rat: a quantitative study.

The orientation of the processes of 60 Golgi-impregnated interneurones in the rat dorsal lateral geniculate nucleus (dLGN) was studied quantitatively. A statistical analysis of the orientation of 238 interneuronal processes (dendrites and axon-like processes) showed that they were aligned preferentially along a dorsoventral axis through the dLGN and were predominantly oriented parallel with the outlying optic tract. Computer reconstructions of two of the Golgi-impregnated dLGN interneurones and their subsequent 3-dimensional computer rotations showed that their processes ramified in long columnar-shaped territories aligned dorsoventrally. There was little extension of these processes along the rostrocaudal axis of the nucleus. The data of this investigation provide evidence that the processes of 'inhibitory' interneurones in the rat dLGN are predominantly aligned along the dorsoventral axis, parallel with both the optic tract and with the afferent and efferent fibre tracts coursing through the nucleus.

Animals↗
PubMed1991

Sensory inhibition of flexion producing interneurons in lobster abdomen.

Mechanosensory stimulation of an abdominal swimmeret initiates a fictive extension which includes flexion inhibition. The role of flexion producing interneurons (FPIs) in this motor program was examined by recording from a pair of FPIs which excite flexor motor neuron f3. The afferent-FPI-f3 pathway includes at least 5 levels of neural activity. Since swimmeret stimulation hyperpolarizes the FPIs, and mechanosensory afferents are not known to be inhibitory, sensory interneurons must connect the afferent with the FPIs. The generalized receptive fields and long latencies of the FPI response support polysynaptic afferent-FPI connections. The poor correlation between f3FPI spikes and f3 EPSPs they evoke, and the 15 ms delay for initiation of these EPSPs, suggest that additional premotor interneurons are interposed between f3FPI and f3. Since restricted stimulation of swimmeret sensilla generates IPSPs in f3 without affecting f3FPI activity, f3FPI and f3 must be inhibited by different interneurons. Sensory evoked FPI inhibition contributes to the flexion inhibition component of the swimmeret evoked responses since hyperpolarization of f3FPI to block f3FPI spiking during spontaneous flexion activity decreases ongoing f3 spike discharge. Coupling between f3FPI and f3 activities during spontaneously initiated postural flexions supports this conclusion.

Abdomen↗
PubMed1993

A selective lesion of striatonigral neurons decreases presynaptic binding of [3H]hemicholinium-3 to striatal interneurons.

We have used the suicide transport agent, volkensin, to produce selective lesions of striatal efferent neurons projecting to the substantia nigra in the rat. In order to evaluate potential trans-synaptic effects, we examined cholinergic interneurons intrinsic to the striatum following destruction of striatonigral projection neurons by nigral injection of volkensin. There was no change in the number of large interneurons identified either by Nissl stain or by immunocytochemistry for choline acetyltransferase, indicating that volkensin was not directly toxic to this group of neurons. However, [3H]hemicholinium-3 binding to the choline re-uptake site on the presynaptic cholinergic terminals decreased. No change in [3H]hemicholinium-3 binding was seen after destruction of dopaminergic afferents with 6-hydroxydopamine. Striatonigral afferents to the cholinergic interneurons contain substance P which has been shown to stimulate acetylcholine release. The decrease in [3H]hemicholinium-3 binding may reflect loss of this afferent input. However, striatonigral neurons are an efferent target of the cholinergic interneuron as well, and a presynaptic effect due to loss of target neurons also may contribute.

Animals↗
PubMed1994

Cytochemical polarity in lateral geniculate interneurons.

To determine the cytochemical composition of presynaptic dendrites, we have examined the distribution of synapsin 1, calcium and calmodulin-dependent protein kinase II (CaM-II), microtubule-associated protein 2 (MAP-2) and spectrin in cat lateral geniculate (LGN) class III cells by immune-EM. Special attention was paid to the dendrites of these interneurons because they are both pre- and postsynaptic. The dendritic proteins MAP-2 and RBC spectrin were not observed in interneuron dendrites but these proteins were localized in relay cell dendrites. The synaptic vesicle-associated protein synapsin 1 was present in all synaptic vesicle containing profiles, including dendritic terminals. CaM-II, the major postsynaptic density protein, was found in all dendrites. Thus, the LGN interneuron dendritic compartment displays both axonal and dendritic cytochemical properties. The results suggest the possibility of unique molecular interactions in interneuron dendritic terminals.

Animals↗
PubMed1995

Modulation of frog spinal cord interneuronal activity by activation of 5-HT3 receptors.

Motoneuron membrane potentials were recorded from the ventral roots of isolated, hemisected frog spinal cords using sucrose gap techniques. The effects of the selective 5-HT3 agonist 2-methyl-serotonin (2-Me-5HT) on the changes in motoneuron membrane potential produced by dorsal root stimulation and by superfusion of excitatory amino acid agonists were evaluated. Application of 2-Me-5HT (100 microM) did not alter motoneuron membrane potential, but did substantially reduce (approximately 20%) the polysynaptic ventral root potentials evoked by dorsal root stimulation. 2-Me-5HT did not change motoneuron depolarizations generated by addition to the Ringer's solution of the excitatory amino acid agonists AMPA (10-30 microM), kainate (30 microM), or t-ACPD (100 microM), but NMDA-induced motoneuron depolarizations (100 microM) were significantly and reversibly reduced (approximately 20%) by exposure to 2-Me-5HT (100 microM). 2-Me-5HT-evoked decreases of NMDA depolarizations were blocked by the 5-HT3 antagonists ICS 205 930 (50-100 microM) and D-tubocurarine (3-10 microM), but not by MDL 72222 (20-100 microM), the 5-HT2 receptor antagonist ketanserin (10 microM), or the 5-HT1A/5-HT2A antagonist spiperone (10 microM). Two lines of evidence support the hypothesis that the effects of 2-Me-5HT are generated by an indirect mechanism involving interneurons: (1) TTX (0.781 microM) eliminated the effect of 2-Me-5HT on NMDA-induced motoneuron depolarizations, and (2) 2-Me-5HT reduced spontaneous ventral root potentials that result from interneuronal discharges. We attempted to establish the identity of a putative transmitter released by interneurons responsible for the effects on NMDA-depolarizations produced by 2-Me-5HT, but the AMPA receptor antagonist, CNQX (10 microM), the GABAA receptor antagonist, bicuculline (50 microM), the GABAB receptor antagonist, saclofen (100 microM), the opioid antagonist, naloxone (100 microM), and the adenosine antagonists, CPT (20-100 microM) and CSC (10-100 microM) did not alter 2-Me-5HT-induced reductions of NMDA-depolarizations. In sum, the site of interaction between 2-Me-5HT and NMDA appears to be at interneuronal locus, but the mechanism remains unclear.

Animals↗
PubMed1996

Brainstem interneurons necessary for vestibular influences on sympathetic outflow.

The objective of this study was to determine which general brainstem regions contain interneurons that are critical for mediating vestibulo-sympathetic responses in decerebrate cats, as a prelude for future cell recording studies. Large injections of kainic acid into the lateral reticular formation at levels caudal to the obex abolished sympathetic nerve responses elicited by electrical stimulation of the vestibular nerve. The same lesions also diminished excitatory and some inhibitory components of somato-sympathetic responses elicited by stimulation of the sciatic nerve, raising the possibility that a common pool of interneurons integrates signals from muscle, skin and the vestibular system that reflect body position in space. Large lesions of other brainstem regions containing interneurons involved in regulation of sympathetic activity, including nucleus tractus solitarius, the lateral tegmental field rostral to the obex, and the parabrachial nucleus, had no appreciable effect on the amplitude of either vestibulo-sympathetic or somato-sympathetic responses. Thus, interneurons critical for relaying vestibular and other somatic signals to descending cardiovascular-regulatory pathways appear to be located in the caudal and lateral parts of the medulla.

Animals↗
PubMed1996

Alpha 1B-adrenoceptor-mediated excitation of piriform cortical interneurons.

Pharmacological techniques have defined the existence of two different alpha 1-adrenoceptors, the alpha 1A- and alpha 1B-adrenoceptor subtypes and both of these receptors have been cloned in addition to a cloned alpha 1d-adrenoceptor. A subpopulation of interneurons in layer III of the rat piriform cortex that are excited by 5-hydroxytryptamine (5-HT) via 5-HT2A receptors are also excited by norepinephrine via alpha 1-adrenoceptors. In the present study we determined the pA2 values against the norepinephrine-mediated excitation of piriform cortical interneurons for a number of antagonists that are (1) not selective for alpha 1A- or alpha 1B-adrenoceptors (prazosin), (2) selective for alpha 1A-adrenoceptors (5-methyl urapidil, 2-(2,6-dimethoxy-phenoxyethyl)- aminomethyl-1,4-benzodioxane hydrochloride (WB 4101), benoxathian, phentolamine) and (3) selective for alpha 1B-adrenoceptors (spiperone and risperidone). The pA2 values for the antagonist blockade of norepinephrine-mediated interneuron excitation were significantly correlated to literature values for the pKi values of antagonist binding to the alpha 1B-adrenoceptor (r = 0.919) and the cloned alpha 1b-adrenoceptor (r = 0.849) but were not correlated to the pKi values of antagonist binding to the alpha 1A-adrenoceptor or the cloned alpha 1a- and alpha 1d-adrenoceptor. Thus, we conclude that this population of piriform cortical interneurons is excited by norepinephrine via alpha 1B-adrenoceptors.

Action Potentials↗
PubMed1992

Acromelic acid, a novel kainate analogue, induces long-lasting paraparesis with selective degeneration of interneurons in the rat spinal cord.

A single systemic administration of acromelic acid, a novel kainate analogue (kainoid), induces a series of characteristic behavioral changes in association with selective damage of interneurons in the caudal spinal cord in adult rats. When an effective dose of acromelic acid (5 mg/kg) was systemically administered, forced extension of hindlimbs with or without cramps appeared in all rats. In the course of the intensified hindlimb extension, 10 of 16 rats suffered from generalized convulsive seizures during which 6 rats died without apparent neuropathological change. Of 4 surviving rats that experienced seizures, two developed long-lasting spastic paraparesis which remained unchanged for at least 3 months, whereas the other two were normal in behavior on the days following the administration. In lower doses (less than 4 mg/kg), the rats transiently displayed forced extension of hindlimbs, and in a higher dose (5.5 mg/kg), all rats died during an attack of severe generalized convulsion. Neuropathological changes were observed only in the rats with persistent paraparesis, in which neuron damage was identified selectively in small interneurons in the lumbosacral cord. The morphological change of the degenerated spinal interneurons resembles that of degenerated hippocampal CA1 pyramidal cells seen after systemic administration of kainate. Large motoneurons, spinal roots, and white matter of the spinal cord were well preserved. Unlike the case of systemic administration of kainate, other structures in the central and peripheral nervous system and muscles were morphologically intact except the hippocampal CA4 and the stratum moleculare-lacnosum in which there were reactive astrocytes. The regional difference between kainate-induced and acromelate-induced neuron damage suggests that systemically administered acromelic acid, a kainoid, induces selective neuron damage through activating a particular kainate receptor subtype. The clinicopathological feature of the paraparetic rats resembles closely that of stiffman syndrome, a progressive human neurological disorder with selective loss of interneurons in the spinal cord.

Animals↗
PubMed1995

Striatal interneurones: chemical, physiological and morphological characterization.

The neostriatum is the largest component of the basal ganglia, and the main recipient of afferents to the basal ganglia from the cerebral cortex and thalamus. Studies of the cellular organization of the neostriatum have focused upon the spiny projection neurones, which represent the vast majority of neurones, but the identity and functions of interneurones in this structure have remained enigmatic despite decades of study. Recently, the discovery of cytochemical markers that are specific for each of the major classes of striatal interneurones, and the combination of this with intracellular recording and staining, has revealed the identities of interneurones and some of their functional characteristics in a way that could not have been imagined by the classical morphologists. These methods also suggest some possible modes of action of interneurones in the neostriatal circuitry.

Animals↗
PubMed1992

Induction of immediate-early gene proteins in dentate granule cells and somatostatin interneurons after hippocampal seizures.

The expression of the protein products of the immediate-early genes c-fos, Fos B, Fos-related proteins (FRAs), c-jun, jun B, jun D and krox-24 was investigated in the rat hippocampus at various times after electrically-induced hippocampal seizures. Hippocampal seizures induced all the immediate-early gene proteins in dentate granule cells with differing time-courses. In addition, Krox-24, Fos and Jun D were also induced in somatostatin-containing interneurons throughout the hippocampus and also in a small percentage of parvalbumin-containing interneurons. Thus, hippocampal seizures induce waves of immediate-early gene protein expression in dentate granule cells and a selective expression of krox-24, Fos and Jun D in hippocampal somatostatin interneurons. These results suggest that biochemical and/or morphological changes occurring in dentate granule cells and somatostatin interneurons after seizures may be regulated by immediate-early gene expression, and that these immediate-early gene proteins may be involved in seizure development in the nervous system.

Animals↗
PubMed1988

Mechanosensory interneurons (MSIs) in the crayfish 6th abdominal ganglion are inhibited by activation of other MSIs.

1. Identified mechanosensory interneurons (MSIs) in the 6th abdominal ganglion of the crayfish Procambarus clarkii have been shown to inhibit other projecting MSIs. 2. Interneurons sensitive to water-current stimulation of the tailfan, and which inhibited the tactile response of other MSIs when activated by depolarizing currents, were identified by iontophoresis of fluorescent dye. 3. Ten inhibitory interneurons have been identified, including both non-adapting, directional cells and phasic "touch" cells. 4. Inhibition triggered by activation of the identified cells was not widespread among fibers in the connectives. 5. Inhibition recorded intracellularly was mediated by compound inhibitory postsynaptic potentials of long duration (300-400 msec) and latencies of 13-15 msec, and therefore was apparently polysynaptic. 6. Depolarization and/or activity in MSIs, which modulates the stimulus response characteristics of related cells is a possible mechanism for contrast enhancement among directional or frequency-selective interneurons.

Abdomen↗
PubMed1989

Intracellular dyes mask immunoreactivity of hippocampal interneurons.

The results of several studies have suggested that local circuit neurons, or interneurons, of area CA1 of hippocampus use gamma-aminobutyric acid (GABA) as their neurotransmitter. However, when these cells were labelled by intracellular dye injection, and examined immunocytochemically with antisera raised against GABA, none of the interneurons were immunoreactive. Numerous non-injected interneurons in the same tissue section were clearly immunoreactive. These results suggest that intracellular dyes interfere with immunocytochemical staining of hippocampal interneurons.

Animals↗
PubMed1988

Intracellular staining of physiologically identified photoreceptor cells and hyperpolarizing interneurons in the teleost pineal organ.

The directly photosensory pineal organ of the rainbow trout functions primarily as a luminance detector. Its neutral output reflects the level of ambient illumination in an almost linear fashion over several orders of magnitude. It may thus transmit information about the daily light-dark cycle to central projection targets in the brain, and exert an important control over putative central oscillators. We have studied single neural elements in the explanted pineal organ of the rainbow trout by combining intracellular recording with intracellular injections of either the fluorescent dye Lucifer Yellow CH or the electron dense marker horseradish peroxidase. After physiological characterization, dye was injected, and the pineal organs were processed for fluorescence or electron microscopy. Horseradish peroxidase-injected cells were selected with light microscopy, and were serially sectioned for electron microscopy. By examining the entire series of ultrathin sections of several labeled cells the following results were obtained. (1) Intensity-graded hyperpolarization that was elicited by light stimuli of all wavelengths could be either purely monophasic at all light intensities, or monophasic at low and intermediate light intensities but with an initial peak transient at response saturation. These two types of responses could be demonstrated to emanate from photoreceptor cells. (2) In addition, an interneuron that responded to light stimulation with intensity-graded hyperpolarizations that decreased in amplitude at high light intensities was identified by analysis of serial ultrathin sections. This interneuron was situated in close opposition to a photoreceptor-like element and another interneuron, both of which contained transcellularly transferred horseradish peroxidase. Transcellular transfer of horseradish peroxidase was repeatedly observed, although in the majority of cases only single cells were labeled. Intracellular injection of Lucifer Yellow CH consistently revealed dye-coupling between photoreceptors and between (inter)neurons. The numbers of labeled elements varied between two and eight cells, after intracellular injection of one cell. The present results indicate that the net neural output of the pineal organ is the result of a relatively complicated neural circuitry, encompassing different types of photoreceptors, interneurons and projection neurons. Electrical coupling between photoreceptors, between neurons, and between photoreceptors and neurons may provide spatial signal averaging. The very slow photoreceptor responses to photic stimulation may provide temporal signal averaging.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Increase in cytoplasmic free Ca2+ elicited by noradrenalin and serotonin in cultured local interneurons of mouse olfactory bulb.

Effects of noradrenalin and serotonin on cytoplasmic free Ca2+ concentrations ([Ca2+]i) were studied by using the fluorescent indicator fura-2 in cultured local interneurons of mouse olfactory bulb. Application of noradrenalin (0.1-100 microM) caused a rapid and concentration-dependent rise in [Ca2+]i, while isoproterenol was ineffective at concentrations up to 100 microM. The noradrenalin (1 microM)-induced increase in [Ca2+]i was completely inhibited by pretreatment with alpha 1-antagonist, prazosin (100 nM), whereas the inhibitory effect of alpha 2-antagonist, yohimbine, was about 100-times less potent. Serotonin (0.1-100 microM) also caused the dose-dependent rise in [Ca2+]i, which was inhibited by serotonin2 antagonist, ketanserin. Even in the absence of the extracellular calcium, the noradrenalin- or serotonin-induced increase in [Ca2+]i was observed. These results indicate that both noradrenalin and serotonin elicit the rise in [Ca2+]i in local interneurons of the olfactory bulb. They also suggest that the rise in [Ca2+]i is mediated by alpha 1-adrenergic and serotonin2 receptors, and that the increased calcium is mainly derived from intracellular calcium storage sites. The above results provide evidence to suggest that in the olfactory bulb, noradrenergic and serotonergic centrifugal fibers exert modulatory influences on synaptic interactions between mitral/tufted cells and local interneurons by increasing cytoplasmic Ca2+ in local interneurons.

Animals↗
PubMed1994

GABAergic interneurons in the somatosensory thalamus of the guinea-pig: a light and ultrastructural immunocytochemical investigation.

This work was performed to confirm previous data reporting the presence of GABAergic interneurons in the ventrobasal complex of guinea-pig, and to investigate the intrinsic organization of this nucleus compared to that of thalamic nuclei lacking interneurons. Immunocytochemical experiments were performed on the thalamus of adult guinea-pigs perfused with mixed aldehydes using an anti-GABA serum. At light microscopy, the immunoreaction on floating Vibratome sections showed that GABAergic neurons are present only in the reticular and lateral geniculate nuclei and in the ventrobasal complex. Quantitative evaluation of their number indicated that they are 20 and 15% of the total neuronal population in lateral geniculate nucleus and ventrobasal complex, respectively, while they are less than 1% in ventrolateral nucleus. At the ultrastructural level, the postembedding immunogold procedure showed the presence, in the ventrobasal complex, of GABA-labeled profiles involved in complex synaptic arrangements similar to those found in carnivores and primates. Conversely, GABA-labeled terminals in thalamic nuclei devoid of interneurons formed exclusively axo-dendritic or axo-somatic contacts, like in rats and mice. The present data suggest that GABAergic neurons in the ventrobasal complex of guinea-pigs give rise to functionally important rearrangements of its intrinsic synaptic organization and that they represent the morphological basis for an intrinsic modulatory mechanism that is absent in other thalamic nuclei lacking inhibitory interneurons. The phylogenetic implications of these findings are also discussed in comparison to other animal species.

Animals↗
PubMed1995

Innervation of burst firing spiny interneurons by pyramidal cells in deep layers of rat somatomotor cortex: paired intracellular recordings with biocytin filling.

Intracellular recordings were obtained from a class of neuron defined electrophysiologically as burst firing interneurons in layers V and VI in slices of adult rat somatomotor cortex. Four of these cells were recovered histologically. These four cells had resting membrane potentials between -68 and -80 mV, a mean input resistance of 77 +/- 16.2 M omega (measured from the voltage deflection produced by a 100 ms, 0.5 nA hyperpolarizing pulse delivered from a membrane potential of -80 mV) and responded to injections of depolarizing current from membrane potentials negative of -70 to -75 mV with an initial burst of action potentials followed by a complex afterhyperpolarization. In response to injection of larger (0.5-1.5 nA) hyperpolarizing current pulses from membrane potentials between -60 and -70 mV, 15 of 20 burst firing cells (three of four recovered histologically) that were tested displayed delayed inward rectification, and in all 20 cells of this type, responses to large negative current pulses were followed by a rebound depolarization that could initiate action potentials. Filling of four of these cells with biocytin and subsequent histological processing revealed that they were bitufted with sparsely to medium spiny dendrites and extensive local axon ramifications. These neurons are similar to low threshold spiking cells [Kawaguchi (1993) J. Neurophysiol. 69, 416-431]. Ultrastructural examination of the axons of three cells revealed that of 53 labelled terminals studied, the majority formed synaptic contacts with dendritic shafts. Filling neurons with biocytin during paired intracellular recordings resulted in three well labelled interneurons, each of which was postsynaptic to a simultaneously recorded pyramidal neuron. In these pairs both cells were identified, but the presynaptic axon was poorly labelled in one. In one of the two pairs in which the pre- and postsynaptic neurons were fully recovered, light microscopic assessment indicated that the axon of the presynaptic pyramid formed 12 close appositions with dendrites of the postsynaptic interneuron. Six of these appositions were examined at the electron microscopic level and were identified as possible synaptic contacts. In the other pair three of six close appositions observed at the light level were verified as possible synaptic connections at the ultrastructural level. These correlated electrophysiological and anatomical studies provide the first evidence for connections from pyramid to burst firing interneurons in the neocortex and indicate that these connections can be mediated by multiple synaptic contacts. The accompanying paper describes the functional properties of these connections.

Animals↗
PubMed1992

Opioid inhibition of GABA release from presynaptic terminals of rat hippocampal interneurons.

Opiates and the opioid peptide enkephalin can cause indirect excitation of principal cortical neurons by reducing inhibitory synaptic transmission mediated by GABAergic interneurons. The mechanism by which opioids mediate these effects on interneurons is unknown, but enkephalin hyperpolarizes the somatic membrane potential of a variety of neurons in the brain, including hippocampal interneurons. We now report a new, more direct mechanism for the opioid-mediated reduction in synaptic inhibition. The enkephalin analog D-Ala2-Met5-enkephalinamide (DALA) decreases the frequency of miniature, action potential-independent, spontaneous GABAergic inhibitory postsynaptic currents (IPSCs) without causing a change in their amplitude. Thus, we conclude that DALA inhibits the action potential-independent release of GABA through a direct action on interneuronal synaptic terminals. In contrast, DALA reduces the amplitude of action potential-evoked, GABA-mediated IPSCs, as well as decreases their frequency. This suggests that the opioid-mediated inhibition of non-action potential-dependent GABA release reveals a mechanism that contributes to reducing action potential-evoked GABA release, thereby decreasing synaptic inhibition.

Action Potentials↗