bluuebunny/crossref_metadata_2025 huggingface dataset:
Three serotonin responses in cultured mouse hippocampal and striatal neurons
Authors: Yakel JL , Trussell LO , Jackson MB
Published: March 2018

Serotonin (5-HT) produced 3 different types of responses in neurons of mouse hippocampal and striatal cell cultures. These 3 responses have been characterized in terms of their pharmacological specificity, physiological mechanism, and dependence on cytoplasmic components. The most frequently observed response was inhibitory and was the result of a receptor-mediated activation of an inwardly rectifying potassium conductance. Typically, the response peaked within 1–3 sec of agonist application and did not exhibit desensitization. 5-Methoxy-N,N- dimethyltryptamine also produced this response in both striatal and hippocampal cultures and had no effect on the other 5-HT currents observed in this study. The selective 5-HT agonists--8-hydroxy-2-(di-n- propylamino)-tetralin, 1-(m-chlorophenyl) piperazine, and 1-(2- methoxyphenyl) piperazine--did not activate this outward current response. Methysergide did not block the 5-HT-activated outward current and often acted as an agonist. The response was lost in low-series- resistance recordings which facilitate solution exchange between the patch electrode and the cell. The loss of this response was prevented by using high-resistance patch electrodes, which retard this exchange. The 2 other responses described in this study were excitatory. They were seen less often than the inhibitory response. One of the excitatory responses was fast, with a time to peak of approximately 200 msec and a duration of 2–4 sec. The other was slow, with a time to peak of 7–10 sec and a duration of approximately 30–40 sec. Both of these responses were accompanied by a conductance increase. The fast excitatory response reversed at depolarized potentials and desensitized with a rate that varied with voltage. Metoclopramide and d-tubocurarine completely and reversibly blocked this fast excitatory response, while methysergide had no effect. The fast excitatory response was not lost during intracellular dialysis of cells in cultures from either striatum or hippocampus. In cultures from both brain regions, the slow excitatory response was blocked by methysergide. The slow excitatory response was lost even in patch-clamp recordings with high-resistance electrodes. This response was similar to responses to dopamine, norepinephrine, and forskolin, all of which are known to activate adenylate cyclase in the CNS.
The EGPs: the eclosion hormone and cyclic GMP-regulated phosphoproteins. II. Regulation of appearance by the steroid hormone 20- hydroxyecdysone in Manduca sexta
Authors: Morton DB , Truman JW
Published: March 2018

Two proteins (the EGPs) in the CNS of the tobacco hornworm Manduca sexta are phosphorylated by the action of the neuropeptide eclosion hormone (EH), which triggers ecdysis behavior (Morton and Truman, 1986, 1988). The onset of sensitivity to EH requires prior exposure to the steroid hormone 20-hydroxyecdysone (20-HE). A series of steroid removal and replacement experiments indicates that the EGPs are also regulated by 20-HE with a time course that is similar to that seen for the 20-HE regulation of behavioral sensitivity to EH. This suggests that the steroid regulation of EH sensitivity is due to the regulation of the EGPs. The appearance of the EGPs requires not only the presence of 20- HE, but also its subsequent removal. The appearance of the EGPs can be blocked in vivo and in vitro by maintaining artificially elevated levels of 20-HE, but only up to a particular time in development. The ending of this steroid-sensitive period occurs 4 hr before the normal appearance of the EGPs, consistent with the hypothesis that the EGPs are synthesized de novo in response to the removal of 20-HE.
Unmyelinated cutaneous afferent neurons activate two types of excitatory amino acid receptor in the spinal cord of Xenopus laevis embryos
Authors: Sillar KT , Roberts A
Published: March 2018

The trunk and tail skin of Xenopus laevis embryos near the time of hatching is innervated by the mechanoreceptive free nerve endings of Rohon-Beard neurons, a homogeneous class of cutaneous primary afferent fibers. Rohon-Beard neurons have cell bodies and axons in the dorsal spinal cord, where they monosynaptically excite a population of dorsolaterally situated interneurons (Clarke and Roberts, 1984). EPSPs can be recorded in these dorsolateral interneurons following electrical stimulation of the unmyelinated neurites of Rohon-Beard neurons in the skin. The EPSPs are dual component, consisting of separate fast and slow potentials that are usually evoked synchronously and that closely resemble those described previously in Xenopus and lamprey motoneurons (Dale and Roberts, 1985; Dale and Grillner, 1986). The excitation of dorsolateral interneurons by Rohon-Beard neurons is reduced by the bath application of excitatory amino acid antagonists. Kynurenic acid suppresses both the fast and slow components of the EPSPs, while both (+/-)-2-amino-5-phosphonovaleric acid (APV) and 1 mM magnesium reduce the slow component but have little or no effect on the peak amplitude of the EPSPs. These data suggest that Rohon-Beard neurons release an excitatory amino acid neurotransmitter, which acts simultaneously at both N-methyl-D-aspartate (NMDA) and non-NMDA receptor types. This is the first direct demonstration of dual-component excitatory amino acid- mediated synaptic transmission from cutaneous primary afferent neurons in the vertebrate spinal cord. The bath application of the agonists NMDA, kainate, or quisqualate in salines containing 1 microM TTX depolarized the interneurons and reduced their input resistance, which suggests that the interneurons possess all 3 types of excitatory amino acid receptor. Kynurenic acid strongly inhibits responses to NMDA and kainate, but is relatively less effective against the larger responses of quisqualate in this system.
Development of cholinergic retinal neurons from embryonic chicken in monolayer cultures: stimulation by glial cell-derived factors
Authors: Hofmann HD
Published: March 2018

In recent years evidence has indicated that, like the PNS, the development of the CNS is influenced by neuronotrophic polypeptide factors. In the present study, cultures of dissociated retinal neurons from 8-d-old chicken embryos were used to investigate the role of neuronotrophic factors (NTF) in the development of the neural retina. CAT, which in vivo is located in amacrine cells of the retina, served as a marker for studying the in vitro development of cholinergic retinal neurons. Differentiation of cholinergic cells under control conditions was indicated by a 10-fold increase of enzyme activity during a 7-d culture period. Addition of media conditioned by high- density retinal cultures resulted in a further stimulation of CAT activity by 100–400%. The CAT-stimulating activity was associated with a high-molecular-weight component of the retina conditioned medium (RCM) and was sensitive to protease treatment, but was not affected by other hydrolytic enzymes. The putative cholinergic factor was secreted by retinal cultures virtually free of neurons, suggesting that it is mainly produced by Muller cells. CAT-stimulating activity was also present in extracts from embryonic chicken retinae and medium conditioned by rat retinal cultures. NGF, anti-NGF antiserum, extracts from chicken brain tissues, and a number of other extracts and conditioned media, all known to contain neuronotrophic activities, were found to have no influence on cholinergic development in chicken retinal cultures. An extract from non-retinal eye tissue containing ciliary neuronotrophic factor (CNTF) stimulated CAT activity to the same extent as did RCM.
Stratum lacunosum-moleculare interneurons of hippocampal CA1 region. II. Intrasomatic and intradendritic recordings of local circuit synaptic interactions
Authors: Lacaille JC , Schwartzkroin PA
Published: March 2018

Simultaneous intracellular recordings were obtained from stratum lacunosum-moleculare (L-M) interneurons and CA1 cells, and their local circuit synaptic interactions were examined. Synaptic interactions with pyramidal cells were evaluated in both intrasomatic and intradendritic pyramidal cell recordings. Stimulation of L-M interneurons evoked small- amplitude IPSPs in 21% of intrasomatic (9/42 cell pairs) and in 26% of intradendritic (11/43) pyramidal cell recordings. The IPSP mean peak amplitude was 0.91 mV for intrasomatic and 0.67 mV for intradendritic recordings. IPSPs had slow onset and decay (approximately 80–90 msec), decreased in amplitude with membrane hyperpolarization, and were not associated with any apparent change in input resistance. No physiologic evidence of synaptic connections was found from pyramidal cells to L-M interneurons. Inhibitory synaptic interactions were also seen between L- M interneurons and stratum pyramidale interneurons (2 of 4 cell pairs). The IPSPs recorded in pyramidale interneurons were similar to the IPSPs recorded in pyramidal cells. During simultaneous recordings, L-M interneurons were activated at a shorter latency, i.e., in a feedforward manner with respect to pyramidal cells. Thus, L-M interneurons may mediate feedforward inhibition of CA1 pyramidal cells. The L-M interneuron-evoked IPSPs in pyramidal cells share some characteristics of the late IPSP recorded in CA1 pyramidal cells and may therefore contribute to this component of the IPSP.
Autoradiographic localization of voltage-dependent sodium channels on the mouse neuromuscular junction using 125I-alpha scorpion toxin. I. Preferential labeling of glial cells on the presynaptic side
Authors: Boudier JL , Jover E , Cau P
Published: March 2018

Alpha-scorpion toxins bind specifically to the voltage-sensitive sodium channel in excitable membranes, and binding is potential-dependent (Catterall, 1984). The radioiodinated toxin II from the scorpion Androctonus australis Hector (alpha ScTx) was used to localize voltage- sensitive sodium channels on the presynaptic side of mouse neuromuscular junctions (NMJ) by autoradiography using both light and electron microscopy. Silver grain localization was analyzed by the cross-fire method. At the light-microscopic level, grain density over NMJ appeared 6–8x higher than over nonjunctional muscle membrane. The specificity of labeling was verified by competition/displacement with an excess of native alpha ScTx. Labeling was also inhibited by incubation in depolarizing conditions, showing its potential- dependence. At the electron-microscopic level, analysis showed that voltage-sensitive sodium channels labeled with alpha ScTx were almost exclusively localized on membranes, as expected. Due to washout after incubation, appreciable numbers of binding sites were not found on the postsynaptic membranes. However, on the presynaptic side, alpha ScTx- labeled voltage-sensitive sodium channels were localized on the membrane of non-myelin-forming Schwann cells covering NMJ. The axonal presynaptic membrane was not labeled. These results show that voltage- sensitive sodium channels are present on glial cells in vivo, as already demonstrated in vitro (Chiu et al., 1984; Schrager et al., 1985). It is proposed that these glial channels could be indirectly involved in the ionic homeostasis of the axonal environment.
Effects of the external ions and metabolic poisoning on the constriction of the squid giant axon after axotomy
Authors: Gallant PE
Published: March 2018

After transecting the squid giant axon in the presence of an artificial external medium, which was composed of the ions normally present in squid blood, the cut ends of the axon constrict. This constriction could be completely blocked by cutting the axon in the presence of an artificial internal medium composed of the ions normally present inside the axon. By interchanging the ions in the internal medium with those in the external medium, it was determined that constriction was stimulated by the high concentrations of calcium, chloride, and magnesium ions present in the external medium and inhibited by the high concentrations of potassium ion in the internal medium. Constriction could also be inhibited by 2,4-dinitrophenol and cyanide. Softening of axoplasm and elution of the axoplasmic proteins at the cut end of the axon also occurred in the external medium. This softening and elution may be necessary for constriction since constriction occurred only in those media that also induced axoplasmic softening and elution. Softening and elution are not sufficient for constriction, however, since high potassium, 2,4-dinitrophenol, and cyanide inhibited constriction without inhibiting the softening or elution of axoplasm.
Functional anatomy of macaque striate cortex. I. Ocular dominance, binocular interactions, and baseline conditions
Authors: Tootell RB , Hamilton SL , Silverman MS , Switkes E
Published: March 2018

A series of experiments was carried out using 14C-2-deoxy-d-glucose (DG) in order to examine the functional architecture of macaque striate (primary visual) cortex. This paper describes the results of experiments on uptake during various baseline (or reference) conditions of visual stimulation (described below), and on differences in the functional architecture following monocular versus binocular viewing conditions. In binocular “baseline” experiments, monkeys were stimulated either (1) in the dark, (2) with a diffuse gray screen, or (3) with a very general visual stimulus composed of gratings of varied orientation and spatial frequency. In all of these conditions, DG uptake was found to be topographically uniform within all layers of parafoveal striate cortex. In monocular experiments that were otherwise similar, uptake was topographically uniform within the full extent of the eye dominance strip, in all layers. Certain other visual stimuli produce high uptake in the blobs, and still another set of visual stimuli (including high-spatial-frequency gratings) produce highest uptake between the blobs at parafoveal eccentricities, even in an unanesthetized, unparalyzed monkey. Eye movements per se had no obvious effect on striate DG uptake. Endogenous uptake in the blobs (relative to that in the interblobs) appears higher in the squirrel monkey than in the macaque. The pattern of DG uptake produced by binocular viewing was found to deviate in a number of ways from that expected by linearly summing the component monocular DG patterns. One of the most interesting deviations was an enhancement of the representation of visual field borders between stimuli differing from each other in texture, orientation, direction, etc. This “border enhancement” was confined to striate layers 1–3 (not appearing in any of the striate input layers), and it only appeared following binocular, but not monocular, viewing conditions. The border enhancement may be related to a suppression of DG uptake that occurs during binocular viewing conditions in layers 2 + 3 (and perhaps layers 1 and 4B), but not in layers 4Ca, 4Cb, 5 or 6. Another major class of binocular interaction was a spread of neural activity into the “unstimulated” ocular dominance strips following monocular stimulation. Such an effect was prominent in striate layer 4Ca, but it did not occur in layer 4Cb. This “binocular” spread of DG uptake into the inappropriate eye dominance strip in 4Ca may be related to the appearance of orientation tuning and orientation columns in that layer. No DG effects were seen that depended on the absolute disparity of visual stimuli in macaque striate cortex.
The synaptic vesicle proteins synapsin I and synaptophysin (protein P38) are concentrated both in efferent and afferent nerve endings of the skeletal muscle
Authors: De Camilli P , Vitadello M , Canevini MP , Zanoni R , Jahn R , Gorio A
Published: March 2018

Synapsin I and synaptophysin (protein p38) are 2 major protein components of the membranes of small synaptic vesicles of virtually all presynaptic nerve endings. Synapsin I, a phosphoprotein regulated by both Ca2+ and cAMP, is a peripheral protein of the cytoplasmic surface of the vesicle membrane. It is thought to anchor the vesicle surface to the cytoskeleton of the terminal and to play a regulatory role in neurotransmitter release. Synaptophysin is an intrinsic transmembrane glycoprotein. We report here that both proteins are present and concentrated also in afferent nerve endings, which provide the sensory innervation of the skeletal muscle and of the tendon. The distribution of both antigens in sensory nerve endings is consistent with their localization on the microvesicles that have been described in such endings. Thus, our results suggest the existence of important biochemical, and possibly functional, similarities between small synaptic vesicles of presynaptic nerve endings and microvesicles of sensory endings. Such findings provide new clues to the understanding of the physiology of sensory endings.
Modulation of calcium current and diverse K+ currents in identified Hermissenda neurons by small cardioactive peptide B
Authors: Acosta-Urquidi J
Published: March 2018

The molluscan neuropeptides, small cardioactive peptides A and B (SCPA,B), are known to modulate the responses of many molluscan central and peripheral target cells (see review by Lloyd, 1986), but their full range of physiological actions remains unknown. External application of SCPB (1–10 microM) modified diverse ionic conductances in a set of giant identifiable neurons in the brain of the marine mollusk Hermissenda crassicornis. SCPB caused a transient depolarization and increased input resistance that enhanced or promoted cell firing. Under voltage-clamp, SCPB reduced a “background” residual current (IR), reduced early transient K+ current (IA), reduced a delayed K+ current (IK(V], and enhanced ICa, IBa, and a Ca2+-activated K+ current, IK(Ca). In tetraethylammonium chloride (TEA) saline, SCPB enhanced the amplitude and duration and reduced the threshold of evoked Ca and Ba spikes. Immunocytochemical staining techniques have localized an endogenous SCPB-like peptide in numerous somata and their neurites in the nervous system of Hermissenda (Longley and Longley, 1985; Watson and Willows, 1986). These data are consistent with a role for SCPB as a neurotransmitter/neurohormone modulator of neuronal excitability in Hermissenda. A neurotransmitter role for endogenous SCPs has been proposed for a synaptic pair of cultured neurons in the Aplysia buccal ganglion (Lloyd et al., 1986). SCPB has been implicated in the control of feeding motor output in Aplysia (Sossin et al., 1986) and Tritonia (Willows and Watson, 1986), and in the presynaptic facilitation of sensory neurons mediating the gill and siphon defensive withdrawal reflex in Aplysia (Abrams et al., 1984).
Neurofilament protein synthesis in DRG neurons decreases more after peripheral axotomy than after central axotomy
Authors: Greenberg SG , Lasek RJ
Published: March 2018

Cytoskeletal protein synthesis was studied in DRG neurons after transecting either their peripheral or their central branch axons. Specifically, the axons were transected 5–10 mm from the lumbar-5 ganglion on one side of the animal; the DRGs from the transected side and contralateral control side were labeled with radiolabeled amino acids in vitro; radiolabeled proteins were separated by 2-dimensional (2D) PAGE; and the amounts of radiolabel in certain proteins of the experimental and control ganglia were quantified and compared. We focused on the neurofilament proteins because they are neuron-specific. If either the peripheral or central axons were cut, the amounts of radiolabeled neurofilament protein synthesized by the DRG neurons decreased between 1 and 10 d after transection. Neurofilament protein labeling decreased more after transection of the peripheral axons than after transection of the central axons. In contrast to axonal transections, sham operations or heat shock did not decrease the radiolabeling of the neurofilament proteins, and these procedures also affected the labeling of actin, tubulin, and the heat-shock proteins differently from transection. These results and others indicate that axonal transection leads to specific changes in the synthesis of cytoskeletal proteins of DRG neurons, and that these changes differ from those produced by stress to the animal or ganglia. Studies of the changes in neurofilament protein synthesis from 1 to 40 d after axonal transection indicate that the amounts of radiolabeled neurofilament protein synthesis were decreased during axonal elongation, but that they returned toward control levels when the axons reached cells that stopped elongation.(ABSTRACT TRUNCATED AT 250 WORDS)
Light- and electron-microscopical study of phosphoprotein B-50 following denervation and reinnervation of the rat soleus muscle
Authors: Verhaagen J , Oesteicher AB , Edwards PM , Veldman H , Jennekens FG , Gispen WH
Published: March 2018

The neuron-specific phosphoprotein B-50 was originally identified as a phosphoprotein in synaptic plasma membranes isolated from adult brain tissue. In this paper we study the reinnervation of the soleus muscle, a target muscle of sciatic nerve axons, using affinity-purified anti-B- 50 antibodies. Light-microscopical evaluation of the reinnervation process revealed that the period of muscle fiber reinnervation corresponds closely with the time in which high B-50 immunoreactivity was observed in the nerve fibers that invade the muscle and in the newly formed neuromuscular junctions. Upon completion of reinnervation, B-50 immunoreactivity decreased. In the newly innervating terminals, B- 50 was associated with presynaptic vesicular structures and with the presynaptic plasma membrane. In intact mature neuromuscular junctions, virtually no B-50 immunoreactivity could be detected with either light- or electron-microscopic procedures. These observations corroborate the association of high levels of B-50/GAP43 during axon outgrowth and support the concept that B-50 may be a key molecule in the reconstruction of axonal structures. We also observed an unexpected transient increase in B-50 immunoreactivity in the degenerating neuromuscular junctions. This observation cannot be explained in terms of increased neuronal synthesis of B-50, since the degenerating axon processes have been completely disconnected from their cell bodies. Thus, our evidence implies that a rise of B-50 immunoreactivity can be associated with stages of neuronal degeneration as well as with those of neuronal differentiation and axon outgrowth.
Mechanism of calcium-dependent inactivation of a potassium current in Aplysia neuron R15: interaction between calcium and cyclic AMP
Authors: Kramer RH , Levitan ES , Wilson MP , Levitan IB
Published: March 2018

In the preceding paper (Kramer and Levitan, 1988), we presented evidence that an inwardly rectifying K+ current (IR) is inactivated by Ca2+ influx accompanying spontaneous bursting activity in the Aplysia neuron R15. In this paper we examine the mechanism that enables Ca2+ to inactivate IR. Since IR is enhanced by cyclic AMP in neuron R15 (Drummond et al., 1980; Benson and Levitan, 1983), we examined the Ca2+- dependent inactivation of IR after application of either serotonin (5- HT), the adenylate cyclase activator forskolin, or a membrane-permeable cAMP analog, all agents that increase cAMP and hence the magnitude of IR. Even though more active IR channels are available under these conditions, less Ca2+-dependent inactivation is observed. This is contrasted with the Ca2+-dependent inactivation of the voltage-gated Ca2+ current (ICa). Elevating cAMP enhances ICa in R15 and also increases its Ca2+-dependent inactivation. Hence the mechanisms whereby Ca2+ inactivates IR and ICa appear to differ from each other. Elevating internal Ca2+ by repeatedly depolarizing the neuron suppresses the response of IR to brief applications of 5-HT, and speeds the relaxation of the response, suggesting that Ca2+ can interfere with the cAMP- dependent activation of IR. One biochemical site where Ca2+ can reduce cellular cAMP is by activating the Ca2+/calmodulin-sensitive form of phosphodiesterase. We have detected such enzyme activity in homogenates of Aplysia abdominal ganglia and extracts of single R15 somata. Inhibitors of the phosphodiesterase activity suppress the Ca2+- dependent inactivation of IR. Finally, we have used a radioimmunoassay to measure cAMP in individual R15 somata, and have found that R15 neurons hyperpolarized for prolonged periods contain more cAMP than do R15 neurons allowed to burst, consistent with the hypothesis that Ca2+ influx reduces cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)
Seizures induce dramatic and distinctly different changes in enkephalin, dynorphin, and CCK immunoreactivities in mouse hippocampal mossy fibers
Authors: Gall C
Published: March 2018

Light microscopic immunocytochemical techniques were used to evaluate the influence of recurrent limbic seizure activity on the immunoreactivity for 3 neuropeptides--enkephalin, dynorphin, and cholecystokinin (CCK)--contained within the mouse hippocampal mossy fiber axonal system. Seizures were induced either by the placement of a small unilateral electrolytic lesion in the dentate gyrus hilus or by intraventricular injection of kainic acid. Both treatments induce epileptiform activity in hippocampus lasting several hours. Four days after either lesion placement or injection of 0.05–0.1 microgram kainic acid, immunoreactivity for all 3 peptides was altered throughout the intact mossy fiber system, bilaterally, but in distinctly different ways: enkephalin immunoreactivity (ENK-I) was dramatically elevated, dynorphin immunoreactivity was reduced, and CCK immunoreactivity (CCK- I) was either severely reduced or completely absent in the mossy fiber system. ENK-I was also clearly increased in other areas, including the lateral septum, the entorhinal cortex, and within the entorhinal (perforant path) efferents to temporal hippocampus. In contrast, the loss of CCK seemed restricted to the mossy fiber system in that immunostaining appeared normal in scattered hippocampal perikarya, within the dentate gyrus commissural system, as well as within other limbic structures. Four days after injections of 0.2 or 0.25 microgram kainic acid, mossy fiber ENK-I was greatly elevated, dynorphin immunoreactivity was reduced, but, unlike the situation with lower kainic acid doses, CCK-I was only modestly reduced in the mossy fibers and was clearly reduced in other hippocampal systems as well. These data indicate that epileptiform physiological activity differentially affects the regulation of 3 neuroactive peptides contained within the hippocampal mossy fiber system and suggest a mechanism through which seizurelike episodes can have a lasting influence on the operation of specific hippocampal circuitries.
Spatial distribution of Ca currents in molluscan neuron cell bodies and regional differences in the strength of inactivation
Authors: Thompson S , Coombs J
Published: March 2018

The spatial distribution of Ca current in molluscan neuron cell bodies was studied using a large patch method in combination with 2- microelectrode voltage clamp. The method has a spatial resolution equal to about 0.1% of the cell body area. Ca current is not uniformly distributed. The current density varies between patches, changing by as much as a factor of 2.5 over a distance of 20 micron, and there is evidence that Ca current occurs in “hot spots” involving a few hundred channels. The current density increases in a moderately steep gradient from the soma cap, opposite the axon, toward the axon hillock. Ca currents in patches from different regions of the soma are qualitatively different. Currents near the soma cap do not inactivate or inactivate weakly during depolarization, while currents of equal density nearer the axon hillock exhibit pronounced inactivation. The strength of inactivation increases in parallel with the gradient in current density, but local differences in current density, or in the number of active Ca channels, do not explain the variability in inactivation. Inactivating and noninactivating Ca currents could not be distinguished on the basis of activation or deactivation kinetics, voltage dependence of activation, or sensitivity to hyperpolarizing conditioning pulses. Also, the amplitude of noninactivating current near the soma cap is reduced by intracellular Ca injection showing that, like the whole-cell current, Ca current in this region is subject to Ca-dependent inactivation. The data favor the hypothesis that these cells express only one type of Ca channel. Differences in the strength of inactivation may result from local differences in cytoplasmic Ca buffering, local modification of Ca channels in a way that changes their sensitivity to Ca-dependent inactivation, or local differences in the availability of cytoplasmic factors or enzymes that are necessary for inactivation.
Cerebral correlates of depressed behavior in rats, visualized using 14C- 2-deoxyglucose autoradiography
Authors: Caldecott-Hazard S , Mazziotta J , Phelps M
Published: March 2018

14C-2-Deoxyglucose (2DG) was used to investigate changes in the rate of cerebral metabolism in 3 rat models of depressed behavior. The models had already been established in the literature and were induced by injections of alpha-methyl-para-tyrosine, withdrawal from chronic amphetamine, or stress. We verified that exploratory behaviors were depressed in each model and that an antidepressant drug, tranylcypromine, prevented the depressed behavior in each model. 2DG studies revealed that the rate of regional glucose metabolism was elevated bilaterally in the lateral habenula of each of the 3 models. Regional metabolic rates were reduced in each model in the dorsal medial prefrontal cortex, anterior ventral nucleus of the thalamus, and inferior colliculus. Forebrain global metabolic rates were also reduced in each of the models. Tranylcypromine prevented the elevated rate of lateral habenula metabolism seen in each of the models alone but did not significantly affect the rates of global metabolism. Our findings of identical metabolic changes in each of the models indicate that these changes are not idiosyncratic to a particular model; rather, they correlate with a generalizable state of depressed exploratory behavior in rats.
Developmental changes in K+-selective channel activity during differentiation of the Purkinje neuron in culture
Authors: Yool AJ , Dionne VE , Gruol DL
Published: March 2018

The cerebellar Purkinje neuron cultured from 20 d rat embryos is electrically inexcitable when immature, and acquires excitable membrane properties according to a programmed developmental sequence, thus providing a useful model for investigating mechanisms of CNS neuronal development. Using conventional patch-clamp techniques, we have characterized the the predominant classes of active K+-selective channels at a range of ages encompassing the entire developmental process from 5 to 29 d in vitro (DIV), and have shown pharmacologically that these channels are important contributors to the patterns of spontaneous activity generated by the Purkinje neurons. The 4 predominant classes of K+ channels that are active during steady-state depolarizing voltage commands are identified by unit conductances as the 27, 44, 70, and 100 pS channels, and show differences in several properties, including voltage dependence, sensitivity to tetraethylammonium chloride (TEA), mean open time, and time of appearance during development. Intracellular current-clamp recordings show that physiological maturation of the Purkinje neuron entails increases in the firing rate, the diversity of spike events that comprise spontaneous activity, and the sensitivity of spontaneous activity to disruption by the K+ channel blocker TEA. This increase in sensitivity to TEA correlates with the new expression of activity of the larger-conductance TEA-sensitive classes of K+ channel (70 and 100 pS types). These data show that developmental regulation of the activity of K+-selective channels contributes significantly to the ionic mechanisms that underlie the developmental transitions in spontaneous activity patterns in the Purkinje neuron.
Inhibition in kainate-lesioned hyperexcitable hippocampi: physiologic, autoradiographic, and immunocytochemical observations
Authors: Franck JE , Kunkel DD , Baskin DG , Schwartzkroin PA
Published: March 2018

Following kainate lesions of hippocampal subfield CA3, the remaining CA 1 pyramidal cells become hyperexcitable. This lesion is of interest because, morphologically, it resembles the damage often seen in cases of temporal lobe epilepsy; it may provide insight into the consequences of such cell loss in humans. The hyperexcitability in CA 1 is associated with a loss of both early and late IPSPs. At long postlesion latencies (2–4 months) inhibition shows partial recovery and the hyperexcitability subsides. The intent of the present work was to determine if alterations in CA 1 excitability and functional inhibition postlesion are correlated with changes in morphologic and physiologic indicators of inhibitory interneuron function or with alterations in binding sites for inhibitory transmitters. Using GAD immunocytochemistry, we found no acute or chronic lesion-induced decrease in numbers of CA 1 interneurons or in qualitative characteristics of the pericellular distribution of their terminals in CA 1 stratum pyramidale. Intracellular recordings from identified cells in CA 1 indicated that putative interneurons were viable in hyperexcitable tissue. It was further observed that “recovery” in tissue studied 2–4 months postlesion primarily involved the early IPSP; the late IPSP failed to reappear. Quantitative in vitro autoradiographic analysis of 3H-flunitrazepam--a marker for the early IPSP associated GABAA receptor complex--indicated that hyperexcitability was associated with an increase in GABAA receptor number in CA 1; receptor binding returned to normal at long postlesion latencies as the early IPSP returned and hyperexcitability subsided. Finally, hyperexcitable pyramidal cells were found to retain their responsivity to exogenously applied GABA. These data indicate that much of the cellular machinery necessary for inhibition is retained in CA 1, despite lesion-induced hyperexcitability. We suggest that the acute loss of the IPSP after kainate lesion is due to a transient disconnection between inhibitory and excitatory elements in CA 1 and/or to a loss of normal afferent drive from CA3 onto some CA 1 interneurons. We further suggest that incomplete recovery can be explained by abnormalities that occur as neuroplastic rearrangements in response to deafferentation of CA 1. The relevance of these studies to human hippocampal necrosis and to other models of focal epilepsy is discussed.
Feedforward inhibition of the rat entorhinal cortex and subicular complex
Authors: Finch DM , Tan AM , Isokawa-Akesson M
Published: March 2018

We used in vivo intracellular recording techniques in order to provide evidence about the source of postsynaptic inhibition in the rat entorhinal cortex and subicular complex. Several different structures in the basal forebrain and hippocampus were electrically stimulated in order to activate inhibition by different pathways. This allowed a test of 2 different neuronal circuit models: feedback inhibition, in which recurrent collaterals from principal cell axons excite a local population of inhibitory neurons, and feedforward inhibition, in which excitatory afferents activate the inhibitory neurons. In both models, inhibitory cell axons branch and contribute to the inhibition of a population of principal cells. In the feedback model, a good correlation between antidromic and inhibitory response latencies is predicted. The feedforward model predicts independent antidromic and inhibitory response latencies. In one particular model of feedforward inhibition, afferents excite both local inhibitory cells and principal cells. This model predicts a high correlation between principal cell EPSP and IPSP latencies. The results showed no consistent relationship between the presence of antidromic action potentials and the presence of inhibition in response to stimulation of different sites. In addition, there was no correlation between antidromic and inhibitory response latencies. These results provide no clear support for the feedback model of inhibition. By contrast, there was a highly significant correlation between the latency of principal cell EPSPs and IPSPs, in support of a feedforward model of inhibition. Response latencies of candidate inhibitory neurons were also consistent with the feedforward model. The results provide evidence that an excitatory relay function of the entorhinal cortex and subicular complex is modified temporally by local, extrinsically activated inhibitory circuits.
Stable and metastable cytoskeletal polymers carried by slow axonal transport
Authors: Filliatreau G , Denoulet P , de Nechaud B , Di Giamberardino L
Published: March 2018

The proteins carried by the slow axonal transport in the rat sciatic motor axons were radiolabeled by injecting 35S-methionine into the spinal cord, and the distribution of their solubility through the 2 main components of slow transport (SCa and SCb) was considered. For this purpose, a cytoskeleton-stabilizing buffer was designed in which a pellet enriched in macromolecular and polymeric structures was separated from the solubilized proteins. The monomer/polymer ratios for tubulin were quantified in the 2 rate components. Our results indicate that 90% of the total tubulin was carried with SCa. Of this, 75% was in a polymeric state, versus only 50% of the tubulin carried with SCb. The monomeric tubulin recovered in the soluble fraction was concomitantly transported with the polymerized microtubules, suggesting that it might represent metastable regions of these microtubules. The insoluble and soluble fractions of the transported actin were measured. Actin was mostly (70%) transported with SCb. Of this, more than 80% was recovered in the soluble fraction, but we cannot say whether it was in a monomeric or polymeric state, nor if it was transported free or bound to a structure solubilized during fractionation. The other 30% of the actin, most of it transported with SCa, was recovered in the polymer- enriched fraction, probably bound to a stabilized polymer, such as the microtubules.(ABSTRACT TRUNCATED AT 250 WORDS)
Habituation in Stentor: a response-dependent process
Authors: Wood DC
Published: March 2018

The contractile protozoan Stentor coeruleus habituates during repetition of the mechanical stimulus used to elicit the initial contractions. This decrement in response probability was found to be highly correlated with a reduction in receptor potential amplitude, while the amplitude of the action potentials that triggered the contractions did not change. When mechanical stimulation elicited receptor potentials and not action potentials, the receptor potential did not habituate significantly. Conversely, action potentials repetitively elicited by current pulses habituated animals to mechanical stimuli. Similarly, voltage steps used to simulate action potentials produced pronounced decrements in receptor currents recorded from voltage-clamped cells, while mechanical stimulation produced only small decrements. Thus, habituation depends primarily on action potential production, while mechanical stimulation itself makes a much smaller, but significant, contribution. The temporal relation between mechanical stimuli and action potentials, when both occur, is inconsequential in determining the rate and degree of habituation produced.
Modulation of cone horizontal cell activity in the teleost fish retina. I. Effects of prolonged darkness and background illumination on light responsiveness
Authors: Yang XL , Tornqvist K , Dowling JE
Published: March 2018

The effects of prolonged (greater than 2 hr) darkness and background illumination on the light responsiveness of cone horizontal cells were examined in isolated, superfused white perch retinas. In retinas from fish maintained in complete darkness for more than 2 hr, cone horizontal cells had a resting membrane potential of about -18 mV, and they generated only slow, low-amplitude (3-4 mV) responses even when stimulated with bright flashes. Following the presentation of dim background light, the cone horizontal cells slowly hyperpolarized and thereafter remained at a more hyperpolarized level (about -25 mV). Concurrently, their light responses were dramatically enhanced in size, and response amplitudes to bright flashes eventually increased to about 50 mV. This was accompanied by noticeable changes in response waveforms; following light exposure, the responses became faster and showed initial on-transients. The increase in cone horizontal cell responsiveness was graded with intensity of the background light. A similar enhancement in response amplitudes of cone horizontal cells occurred after presenting bright flashes repetitively at intervals of 9 sec. This background sensitization phenomenon was observed in both L- and C-type cone horizontal cells. When light-sensitized isolated retinas were maintained in darkness for long periods (greater than 30 min), the light responsiveness of cone horizontal cells gradually decreased. The changes in membrane potential and response waveform were opposite to those that occurred when prolonged dark-adapted retinas were exposed to background lights; the cells depolarized by 5–7 mV and light-evoked responses became slower. Effects of background illumination on rod-driven horizontal cells were examined as well. Rod horizontal cells were about 2 log units more sensitive to white light than were cone horizontal cells. When recorded in prolonged dark- adapted retinas, rod horizontal cells showed large responses (approximately 50 mV), which could not be further enhanced by background illumination. Cone horizontal cell responsiveness in the carp retina was also depressed by prolonged darkness and increased by illumination in a fashion similar to that observed in the white perch retina. The change in response amplitude was only about 2-fold in carp compared with 5- to 10-fold changes observed in white perch. These results indicate that the light responsiveness of cone horizontal cells in the teleost retina is suppressed in prolonged darkness and that background lights release the cells from suppression.(ABSTRACT TRUNCATED AT 400 WORDS)
Modulation of cone horizontal cell activity in the teleost fish retina. III. Effects of prolonged darkness and dopamine on electrical coupling between horizontal cells
Authors: Tornqvist K , Yang XL , Dowling JE
Published: March 2018

The effects of prolonged darkness and dopamine on the coupling between horizontal cells in the isolated, superfused white perch retina were studied. Two assays of coupling were employed; area versus amplitude relationships (area-response curves) and the diffusion of the fluorescent dye Lucifer yellow from intracellularly injected cells to neighboring cells. In prolonged dark-adapted retinas, area-response curves were difficult to determine because of the small light responses; however, light-evoked responses did not increase in size when light spots were larger than 0.8 mm in diameter. Following the presentation of dim background illumination that partially sensitized the retina, responses to light spots of various sizes were enhanced and an area-response curve could be constructed. Subsequent presentation of moderate background illumination that more fully sensitized the retina resulted in reduced responses to small spots (less than 1.6 mm in diameter) and enhanced responses to large spot or full-field stimuli. In retinas exposed to moderate background illumination, Lucifer yellow injected intracellularly into cone horizontal cells diffused into many neighboring horizontal cells. The coupled cells were very similar in morphology, suggesting they were of the same type. In prolonged dark- adapted retinas, on the other hand, the dye was usually restricted to the injected cell and a few adjacent cells. These results indicate that coupling between cone horizontal cells is modulated by prolonged darkness and background illumination. Following dopamine (50 microM) application, in both 6-OHDA-treated and untreated retinas, changes in area-response curves of cone horizontal cells were observed just opposite to those that occurred when prolonged dark-adapted retinas were exposed to background illumination. That is, following 5 min application of dopamine to the retina, responses to small spots (less than 2 mm in diameter) increased in size while responses to larger spots decreased in amplitude compared with control responses. Following 20 min of superfusion with dopamine, the recorded responses were very small, and an accurate area-response curve could not be determined. Following dopamine application to light-sensitized retinas, Lucifer yellow was restricted to the injected cells or to the injected cell and a few neighboring cells. The results suggest that the modulation of coupling between cone horizontal cells by prolonged darkness and background illumination may be mediated by dopamine. Spatial properties of rod horizontal cells were also examined.(ABSTRACT TRUNCATED AT 400 WORDS)
Chronic treatment with dopamine receptor antagonists: behavioral and pharmacologic effects on D1 and D2 dopamine receptors
Authors: Hess EJ , Norman AB , Creese I
Published: March 2018

Rats were treated for 21 d with the selective D1 dopamine receptor antagonist SCH23390, the selective D2 dopamine receptor antagonist spiperone, the nonselective dopamine receptor antagonist cis- flupentixol, or a combination of SCH23390 and spiperone. In addition, a group of rats received L-prolyl-L-leucyl-glycinamide (PLG) for 5 d after the 21 d chronic spiperone treatment. Chronic treatment with SCH23390 resulted in a significant increase in D1 dopamine receptor density with no change in the D2 dopamine receptor density. Conversely, spiperone treatment resulted in a significant increase in D2 dopamine receptors and no change in D1 dopamine receptor density. PLG treatment had no effect. SCH23390 plus spiperone treatment resulted in a significant increase in both D1 and D2 dopamine receptor densities. However, although in vitro cis-flupentixol has an equal affinity for D1 and D2 dopamine receptors, only the D2 dopamine receptor density increased after chronic treatment with cis-flupentixol. In vivo treatment with the protein-modifying reagent N-ethoxycarbonyl-2-ethoxy- 1,2-dihydroquinoline (EEDQ), which irreversibly inactivates D1 and D2 dopamine receptors, was used to investigate the paradoxical, selective D2 dopamine receptor up-regulation induced by cis-flupentixol treatment. In vivo treatment with cis-flupentixol before EEDQ administration prevented the D1 and D2 dopamine receptor reductions induced by EEDQ. However, cis-flupentixol protected, in a dose- dependent manner, a greater percentage of D2 dopamine receptors than of D1 dopamine receptors from EEDQ-induced modification. These data indicate that, in vivo, cis-flupentixol preferentially interacts with D2 dopamine receptors and could explain why only D2 dopamine receptors were up-regulated following chronic treatment with cis-flupentixol. Rats were tested for their cataleptic response to the administered drug over the course of the chronic drug treatment. Catalepsy scores of rats receiving spiperone decreased over the course of treatment, with a significant reduction in catalepsy occurring by treatment day 5. The profound catalepsy observed in rats receiving SCH23390 did not change over the 21 d of treatment. Rats receiving cis-flupentixol demonstrated tolerance to its cataleptogenic effects, with a significant reduction in catalepsy observed by treatment day 7. During the 3 week treatment, the time between drug injection and a full cataleptic response to cis- flupentixol increased from 20 to 60 min, suggesting a tolerance to the D2, but not D1, dopamine receptor antagonism by cis- flupentixol.(ABSTRACT TRUNCATED AT 400 WORDS)