bluuebunny/crossref_metadata_2025 huggingface dataset:
Localization and organization of the central pattern generator for hindlimb locomotion in newborn rat
Authors: Cazalets JR , Borde M , Clarac F
Published: April 2018

An in vitro preparation of newborn rat isolated brainstem/spinal cord was used in order to locate the spinal network responsible in mammals for producing patterned locomotor activity. The spinal cord was partitioned by building Vaseline walls at various lumbar levels. When a mixture of serotonin and N-methyl-D,L-aspartate was bath applied to the upper lumbar cord (L1/L2 segments), rhythmic locomotor-like activity was induced and recorded in all the lumbar segments (from L1 to L5). Conversely, when the mixture of transmitters was bath applied to the lower lumbar cord, only tonic activity was induced in the lower lumbar segments. Intracellular recordings performed on motoneurons revealed that during elicited L1/L2 locomotor-like activity, they received a rhythmic synaptic drive that was often below the threshold for spiking, because the excitability of the neurons was too low. When the L1/L2 segments were isolated, their burst production capacities remained. The network located at the L1/L2 level was found to be responsible not only for generating the rhythm but also for organizing its alternating pattern. We demonstrated that the rhythmic synaptic drive that the motoneurons receive during locomotor-like activity comes directly from the L1/L2 network and that there is no relay at the segmental level. We conclude from our study that the network that organizes locomotion in the newborn rat is not segmentally distributed but is restricted to a specific part of the cord. This finding has important consequences, since it means that it is now feasible to study the activity of the rhythmic spinal network independently from that of the motoneurons.
The Shaker-like potassium channels of the mouse rod bipolar cell and their contributions to the membrane current
Authors: Klumpp DJ , Song EJ , Ito S , Sheng MH , Jan LY , Pinto LH
Published: April 2018

RT PCR on mRNA from enzymatically dissociated, isolated bipolar cells showed that these neurons express the Shaker-like K+ channels Kv1.1, Kv1.2, and Kv1.3. Immunohistochemical localization showed each channel to have a unique subcellular distribution: Kv1.1 immunoreactivity was detected in the dendrites and axons terminal, whereas Kv1.2 and Kv1.3 subunits were localized to the axon and the postsynaptic membrane of the rod ribbon synapse, respectively. Whole-cell patch-clamp recordings indicated that the activation voltage of the delayed rectifier current of the isolated bipolar cell and the inhibitory constants for current blockade by TEA, 4-AP, and Ba2+ were similar to these same properties measured for Kv1.1 expressed in oocytes. However, the TEA and 4-AP inhibitory constants for the bipolar cell current differed from the inhibitory constants for Kv1.2 or Kv1.3. These results suggest that the current of the isolated rod bipolar cell is most similar to Kv1.1 but that all three channels may function in the intact retina to allow complex modulation of retinal synaptic signals.
In vitro classical conditioning of abducens nerve discharge in turtles
Authors: Keifer J , Armstrong KE , Houk JC
Published: April 2018

In vitro classical conditioning of abducens nerve activity was performed using an isolated turtle brainstem-cerebellum preparation by direct stimulation of the cranial nerves. Using a delayed training procedure, the in vitro preparation was presented with paired stimuli consisting of a 1 sec train stimulus applied to the auditory nerve (CS), which immediately preceded a single shock US applied to the trigeminal nerve. Conditioned and unconditioned responses were recorded in the ipsilateral abducens nerve. Acquisition exhibited a positive slope of conditioned responding in 60% of the preparations. Application of unpaired stimuli consisting of CS-alone, alternate CS and US, or backward conditioning failed to result in conditioning, or resulted in extinction of CRs. Latencies of CR onset were timed such that they occurred midway through the CS. Activity-dependent uptake of the dye sulforhodamine was used to examine the spatial distribution of neurons labeled during conditioning. These data showed label in the cerebellum and red nucleus during conditioning whereas these regions failed to label during unconditioned responses. Furthermore, the principal abducens nucleus labeled heavily during conditioning. These findings suggest the feasibility of examining classical conditioning in a vertebrate in vitro brainstem-cerebellum preparation. It is postulated that the abducens nerve CR represents a behavioral correlate of a blink- related eye movement. Multiple sites of conditioning are hypothesized, including the cerebellorubral circuitry and brainstem pathways that activate the principal abducens nucleus.
Central endogenous opioid inhibition of supraoptic oxytocin neurons in pregnant rats
Authors: Douglas AJ , Neumann I , Meeren HK , Leng G , Johnstone LE , Munro G , Russell JA
Published: April 2018

Naloxone increases oxytocin secretion in pregnant rats, suggesting restraint by endogenous opioids but we have previously reported that oxytocin nerve terminals in the neural lobe become desensitized to opioid actions in late pregnancy. Therefore, we sought evidence for opioid inhibition on oxytocin cell bodies and their inputs at this time. In conscious 21 d pregnant rats naloxone increased the number of neurons expressing Fos (an indicator of neuronal activity) in the supraoptic nucleus (SON) but had no effect on 16 d pregnant or virgin rats. Release of oxytocin within the SON, measured by microdialysis in conscious rats, was also increased by naloxone in late pregnancy but not before. Nor-binaltorphimine, a specific kappa- opioid antagonist, did not increase Fos or affect oxytocin release within the SON in any group. In anesthetized rats the firing rate of SON neurons was recorded and oxytocin neurons identified by an excitatory response to intravenous cholecystokinin. Naloxone potentiated the cholecystokinin- induced firing rate response on day 21 of pregnancy but not in 16 d pregnant or virgin rats. Blood sampling in anesthetized rats showed that naloxone also increased the oxytocin secretory response to cholecystokinin in late pregnant rats. We conclude that in late pregnancy, after day 16, endogenous opioids inhibit oxytocin neurons either directly, on their cell bodies, or presynaptically on inputs. These endogenous opioids do not act through kappa- opioid receptors since nor-binaltorphimine was ineffective, but may act via mu-opioid receptors. Thus, the opioids restrain premature oxytocin secretion until parturition when there is a high demand for it.
GABA neurotransmission in the hypothalamus: developmental reversal from Ca2+ elevating to depressing
Authors: Obrietan K , van den Pol AN
Published: April 2018

GABA is the primary inhibitory transmitter of the adult hypothalamus, synthesized by many neurons and found in 50% of the presynaptic boutons. GABA causes a decrease in Ca2+ in mature hypothalamic neurons in vitro by depressing cellular activity through opening Cl- channels. Despite the early expression of GABAA receptors in the embryonic hypothalamus (E15), the cellular function of GABA in the developing hypothalamus has received little attention. In the present study the role of GABA in modulating intracellular Ca2+ in developing hypothalamic neurons was studied with fura-2 digital imaging. GABA (0.5- 500 microM) applied to embryonic hypothalamic neurons elicited a dramatic and rapid increase in intracellular Ca2+ This Ca2+ rise could be completely blocked by the GABAA antagonist bicuculline (20 microM) and persisted in the presence of tetrodotoxin (1 microM). The Ca2+ elevation induced by GABA was greater than that of equimolar concentrations of the excitatory transmitter glutamate in early development. The number of E15 neurons that responded to GABA with a Ca2+ rise increased during the first few days of culture, reaching 78% after 4 d in vitro. The Ca2+ rise was 87% blocked by cadmium (100 microM) and 85% blocked by nimodipine (1 microM), indicating that the mechanism of Ca2+ increase was primarily via L-type voltage operated Ca2+ channels. Addition of bicuculline to synaptically coupled cultures caused a significant decrease in Ca2+ 4–10 d after culturing, indicating hypothalamic neurons were secreting GABA at an early age of development, and that sufficient GABA was released to elicit an increase in Ca2+. This effect was seen even after blocking all glutamatergic activity with glutamate receptor antagonists. In contrast, GABA elicited no Ca2+ rise in older neurons (> 18 d in vitro), and the action of bicuculline reversed and caused a large increase in Ca2+ in spontaneously active neurons. Similar findings were obtained in cultures enriched in GABAergic neurons from the suprachiasmatic nucleus. To determine if the Ca2+ stimulating role of GABA on developing neurons was restricted to the hypothalamus and a few other regions, or whether it might exist throughout the brain, we examined the Ca2+ responses in cultured olfactory bulb, cortex, medulla, striatum, thalamus, hippocampus, and colliculus. The majority (75%) of developing neurons from each region showed a Ca2+ rise in response to GABA. Together these data suggest that GABA elevates Ca2+ in developing, but not mature, neurons from the hypothalamus and all other brain regions examined.
Induction of interleukin-6 in axotomized sensory neurons
Authors: Murphy PG , Grondin J , Altares M , Richardson PM
Published: April 2018

RNA from rat dorsal root ganglia was analyzed in search of potentially beneficial cytokines that are induced in dorsal root ganglia by nerve injury. By reverse transcription, the PCR, and Southern blotting, interleukin-6 mRNA was detected during development but not in normal adult dorsal root ganglia, reappeared within 1 d of sciatic nerve transection, was maximally increased after 2 and 4 d, and decreased below the threshold of detection within 1 week. By RNase protection assay, interleukin-6 mRNA was consistently present in RNA from dorsal root ganglia removed from rats 4 d following transection but not in control dorsal root ganglia. Interleukin-6 bioactivity was also present in dorsal root ganglia following nerve injury. By in situ hybridization, interleukin-6 mRNA was localized within large and medium- sized axotomized neurons. In summary, some sensory neurons respond to axotomy with a brisk transient increase in synthesis of interleukin-6. Injury to the sciatic nerve also induced mRNAs for interleukin-1 beta and tumor necrosis factor-alpha in dorsal root ganglia. The inductions of interleukin-1 beta and tumor necrosis factor-alpha mRNAs were later and more sustained than that of interleukin-6 mRNA. The cellular sources of these two cytokines have not been defined.
Expression and in vitro function of beta 1-integrin laminin receptors in the developing avian ciliary ganglion [published erratum appears in J Neurosci 1996 Nov 1;16(21):7097-8]
Authors: Weaver CD , Yoshida CK , de Curtis I , Reichardt LF
Published: April 2018

In chick development, ciliary ganglion (CG) neurons go through a period of axon extension from approximately embryonic day (E)4 to E8, followed by a period of synaptogenesis and neuronal cell death. By examining the immunohistochemical localization of laminin, in conjunction with Dil labeling of the ciliary nerve projection, we have determined that the pathway taken by these neurons is rich in laminin expression. Therefore, laminins are good candidate molecules for mediating outgrowth of these neurons in vivo. In vitro, the ability of CG neurons to extend neurites on laminin-1 (EHS laminin, alpha 1 beta 1 gamma 1) is maximal up to E8, then declines dramatically. CG neuron outgrowth on laminin-1 requires the activity of beta 1-class integrins. We have used subunit-specific antibodies to determine which of the five beta 1- containing heterodimers known to be laminin receptors (alpha 1 beta 1, alpha 2 beta 1, alpha 6 beta 1, alpha 7 beta 1) are expressed, and which mediate neurite outgrowth. While we could not detect expression of alpha 2 or alpha 7, we have found that alpha 1, alpha 3 beta 1, and alpha 6 beta 1 are expressed on the surface of ciliary ganglion neuron cell bodies and axons, both in vitro and in vivo. Furthermore, antibodies against alpha 3 and alpha 6, but not alpha 1, interfered with CG neurite outgrowth on laminin-1 in vitro. Taken together, these data suggest that interactions of cell surface alpha 3 beta 1 and alpha 6 beta 1 integrins with laminin-1 are likely to mediate growth of CG neurons during pathfinding in vivo.
Different forms of synaptic plasticity in somatosensory and motor areas of the neocortex
Authors: Castro-Alamancos MA , Donoghue JP , Connors BW
Published: April 2018

We have studied vertical synaptic pathways in two cytoarchitectonically distinct areas of rat neocortex--the granular primary somatosensory (SI) area and the agranular primary motor (MI) area--and tested their propensity to generate long-term potentiation (LTP), long-term depression (LTD), and related forms of synaptic plasticity. Extracellular and intracellular responses were recorded in layer II/III of slices in vitro while stimulating in middle cortical layers (in or around layer IV). Under control conditions, 5 Hz theta-burst stimulation produced LTP in the granular area, but not in the agranular area. Agranular cortex did generate short-term potentiation that decayed within 20 min. Varying the inter-burst frequency from 2 Hz to 10 Hz reliably yielded LTP of 21–34% above control levels in granular cortex, but no lasting changes were induced in agranular cortex. However, the agranular cortex was capable of generating LTP if a GABAA receptor antagonist was applied locally at the recording site during the induction phase. In contrast to LTP, an identical form of homosynaptic LTD could be induced in both granular and agranular areas by applying low frequency stimulation (1 Hz for 15 min) to the middle layers. Under control conditions, both LTP and LTD were synapse- specific; theta-burst or low-frequency stimulation in the vertical pathway did not induce changes in responses to stimulation of a layer II/III horizontal pathway. Application of the NMDA receptor antagonist D-2-amino-5-phosphonovaleric acid (AP5) blocked the induction of both LTP and LTD in granular and agranular cortex. In the presence of AP5, low-frequency conditioning stimuli yielded a short-term depression in both areas that decayed within 10–15 min. Nifedipine, which blocks L- type, voltage-sensitive calcium channels, slightly depressed the magnitudes of LTP and LTD but did not abolish them. Synaptic responses evoked during theta-burst stimulation were strikingly different in granular and agranular areas. Responses in granular cortex were progressively facilitated during each sequence of 10 theta-bursts, and from sequence-to-sequence; in contrast, responses in agranular cortex were stable during an entire theta-burst tetanus. The results suggest that vertical pathways in primary somatosensory cortex and primary motor cortex express several forms of synaptic plasticity. They were equally capable of generating LTD, but the pathways in somatosensory cortex much more reliably generated LTP, unless inhibition was reduced. LTP may be more easily produced in sensory cortex because of the pronounced synaptic facilitation that occurs there during repetitive stimulation of the induction phase.
Response of serotonergic caudal raphe neurons in relation to specific motor activities in freely moving cats
Authors: Veasey SC , Fornal CA , Metzler CW , Jacobs BL
Published: April 2018

Serotonergic neuronal responses during three specific motor activities were studied in nuclei raphe obscurus (NRO) and raphe pallidus (NRP) of freely moving cats by means of extracellular single-unit recordings. Responses to treadmill-induced locomotion were primarily excitatory, with 21 of 24 neurons displaying increased firing rates, directly related to treadmill speed. Individual regression analyses determined three response patterns: maximal activation at low speed (0.25 m/sec), augmentation of neuronal activity only at high treadmill speed (0.77 m/sec), and a linear increase. A smaller fraction of NRO and NRP serotonergic neurons (6 of 27) also responded to hypercarbic ventilatory challenge with increased firing rates. The magnitude of neuronal response was dependent upon the fraction of inspired CO2 and was related to ventilatory motor output, specifically, inspiratory amplitude. A subgroup of neurons responsive to hypercarbia in wakefulness demonstrated significant reductions in neuronal response to hypercarbia in slow-wave sleep. Finally, unit activity for 12 of 29 cells increased in response to spontaneous feeding, displaying two distinct patterns of neuronal response in relation to onset and termination of feeding: rapid activation and deactivation versus a gradual increase and decrease. More than half of the cells studied under all three conditions were responsive to more than one motor task. These results indicate that serotonergic caudal raphe neurons are responsive to specific motor system challenges, with many neurons responsive to multiple motor tasks, and that the responsiveness of serotonergic neurons to at least one motor task, hypercarbic ventilatory challenge, is state dependent.
Association and colocalization of K+ channel alpha- and beta-subunit polypeptides in rat brain
Authors: Rhodes KJ , Keilbaugh SA , Barrezueta NX , Lopez KL , Trimmer JS
Published: April 2018

Recent cloning of auxiliary subunits associated with voltage-gated ion channels and their subsequent coexpression with the channel forming alpha-subunits has revealed that the expression level, gating and conductance properties of the expressed channels can be profoundly affected by the presence of an auxiliary subunit polypeptide. In the present study, we raised antibodies against the beta-subunit associated with the bovine dendrotoxin sensitive K(+)-channel complex and used these antibodies to characterize the related beta-subunit polypeptides in rat brain. The anti-beta-subunit antibodies displayed a specific reaction on immunoblots of rat brain membranes with a major 38 kDa polypeptide, and a minor 41 kDa polypeptide, which correspond closely to the predicted sizes of the Kv beta 2 and Kv beta 1 beta-subunit polypeptides, respectively, recently cloned from rat brain. Reciprocal coimmunoprecipitation experiments revealed that the beta-subunit polypeptides are associated with Kv1.2 and Kv1.4, but not Kv2.1, alpha- subunits. Immunohistochemical staining revealed that the beta-subunit polypeptides were widely distributed in adult rat brain. Moreover, the cellular distribution of beta-subunit immunoreactivity corresponded closely with immunoreactivity for Kv1.2, and to a lesser extent Kv1.4, but not with Kv2.1. These results suggest that neuronal mechanisms may exist to direct the selective interaction of K+ channel alpha- and beta- subunit polypeptides, and that the properties of K+ channels in specific subcellular domains may be regulated by the formation of heteromultimeric K+ channel complexes containing specific combinations of alpha- and beta-subunits.
Elevated body swing test: a new behavioral parameter for rats with 6- hydroxydopamine-induced hemiparkinsonism
Authors: Borlongan CV , Sanberg PR
Published: April 2018

Parkinson's disease is characterized by a depletion of dopamine (DA) neurons in the nigrostriatal pathway. Stereotaxic injections of 6- hydroxydopamine (6-OHDA), a selective neurotoxin, into either the medial forebrain bundle or the substantia nigra result in a massive DA denervation of the nigrostriatal pathway. Following unilateral nigrostriatal DA depletion, hemiparkinsonian animals develop a stereotypical rotational behavior when challenged with DA agonists such as apomorphine. The drug-induced rotational behavior has been widely used as the behavioral index of hemiparkinsonian animals, but it has some limitations. Although asymmetries in the rotational behavior may indicate an imbalance of DA contents and release capacity in the bilateral nigrostriatal pathway, the behavior is a pharmacological reaction. Accordingly, the drug-induced rotation test is subject to sensitization effects. The present study proposes the elevated body swing test (EBST) as a measure of asymmetrical motor behavior of hemiparkinsonian animals in a drug-free state. The EBST simply involves elevating the animal by handling its tail and recording the frequency and direction of the swing behavior. Unilateral nigral 6-OHDA-lesioned rats exhibited significant biased swing activity with the direction contralateral to the lesioned side, corresponding to the direction of apomorphine-induced rotations. A 30 sec EBST was noted as the peak time for biased swing activity. At 7 d postlesion (the start of testing), and every week thereafter for a period of 2 months, a fairly stable biased swing activity level was observed. At 1 and 2 months postlesion, the same animals were also challenged with apomorphine.
D1 receptors modulate glutamate transmission in the ventral tegmental area
Authors: Kalivas PW , Duffy P
Published: April 2018

Perfusion of the D1 agonist, SKF-82958, through a microdialysis probe implanted in the ventral tegmental area produced a dose-dependent increase in extracellular glutamate and GABA. The increase in extracellular glutamate occurred at approximately 30x lower dose than the elevation in GABA. The increase in extracellular glutamate by SKF- 82958 was blocked by coperfusion of the D1 antagonist, SCH-23390, and was not mimicked by perfusion of the D2/3 agonist, quinpirole, into the ventral tegmental area. In contrast, the elevation in extracellular GABA was insensitive to blockade by SCH-23390. Systemic administration of cocaine (15 mg/kg, i.p.) produced a rapid elevation in extracellular glutamate lasting for 20 min that was prevented by pretreating the ventral tegmental area with SCH-23390. In contrast, acute cocaine produced a reduction in extracellular GABA content in the ventral tegmental area that was not affected by SCH-23390. These data indicate that the stimulation of D1 receptors in the ventral tegmental area increases the release of glutamate and that increasing extracellular levels of somatodendritic dopamine by systemic cocaine can mimic this effect.
Thrombin receptor activation protects neurons and astrocytes from cell death produced by environmental insults
Authors: Vaughan PJ , Pike CJ , Cotman CW , Cunningham DD
Published: April 2018

Thrombin is a multifunctional serine protease that is rapidly produced from prothrombin at sites of tissue injury and catalyzes the final steps in blood coagulation. Thrombin also regulates gene expression and process outgrowth in neurons and astrocytes and stimulates proliferation of astrocytes. Since thrombin is produced immediately upon breakdown of the blood-brain barrier we examined its effects on astrocytes and neurons cultured under conditions which resemble those found in vivo following cerebrovascular injury. These studies showed that thrombin markedly protected rat primary astrocytes from cell death induced by hypoglycemia or oxidative stress. Thrombin also protected rat primary hippocampal neurons from cell death produced by hypoglycemia or growth supplement deprivation. Synthetic peptides which directly activate the thrombin receptor also protected astrocytes and neurons from these environmental insults, demonstrating that the thrombin effects were mediated through the thrombin receptor. In contrast to these results with stressed cells, high concentrations of thrombin killed both astrocytes and neurons cultured under normal conditions. All of the effects of thrombin on astrocytes and neurons were blocked by the brain thrombin inhibitor, protease nexin-1 (PN-1). This shows that the effects required the proteolytic activity of thrombin and is consistent with the known proteolytic mechanism by which thrombin activates its receptor. These results indicate that thrombin and PN-1 may regulate the viability of both astrocytes and neurons in early moments following trauma to the CNS or other conditions that alter the blood-brain barrier.
Induction and reversal of long-term potentiation by low- and high- intensity theta pattern stimulation
Authors: Barr DS , Lambert NA , Hoyt KL , Moore SD , Wilson WA
Published: April 2018

Reversal of long-term potentiation by low-frequency stimulation is often referred to as depotentiation. However, it is not clear whether depotentiation induced by low-frequency stimulation and long-term depression (LTD) induced by similar stimuli are distinct phenomena. We have performed a series of experiments in area CA1 of rat hippocampal slices in which a single pattern of theta-burst (TB) stimulation (Larson, et al., 1986; Staubli and Lynch, 1987) was found to produce either LTP or reversal of LTP depending on the intensity of the stimulation. TB stimulation (10 trains consisting of 4 pulses at 100 Hz, 200 msec apart) delivered at test pulse-intensity induced LTP. However, the same stimulation delivered at a higher intensity (10 times that of the test pulse, evoking a maximal response) did not induce LTP or depression of control responses, but produced lasting depression of previously potentiated responses. This reversal of LTP (TB depotentiation) was observed when the stimulus was delivered between 0.5 and 110 min after induction of LTP. TB depotentiation was reversible, cumulative and saturable when high-intensity TB trains were delivered in succession. TB depotentiation was also blocked by antagonists at NMDA receptors. Low-frequency (1 Hz) stimulation induced LTD, indicating that responses were not already maximally depressed. In addition, high-intensity TB stimulation did not reverse LTD. These results suggest that depotentiation induced by maximal TB stimulation and LTD induced by low-frequency stimulation are distinct phenomena, yet share some characteristics common to forms synaptic plasticity mediated by NMDA receptor activation.
Synergy between growth factors and transmitters required for catecholamine differentiation in brain neurons
Authors: Du X , Iacovitti L
Published: April 2018

The phenotypically plastic neurons of the embryonic mouse striatum were used to explore mechanisms of catecholamine differentiation in culture. De novo transcription and translation of the CA biosynthetic enzyme, tyrosine hydroxylase (TH), was induced in striatal neurons exposed, simultaneously or sequentially, to the growth factor, acidic fibroblast growth factor (aFGF) and a catecholamine. Although dopamine was the most potent aFGF partner (ED50 = 4 microM), a number of substances, including dopamine (D1) receptor agonists, beta-adrenoceptor agonists, and dopamine uptake inhibitors also trigger TH induction when accompanied by aFGF. However, since none of the receptor antagonists nor transport blockers tested could inhibit dopamine's action, the mechanism remains obscure. Structure-activity analysis suggests that effective aFGF partners all contain an amine group separated from a catechol nucleus by two carbons. Thus, TH expression can be novelly induced by the synergistic interaction of aFGF, and to a lesser extent basic FGF, and a variety of CA-containing partner molecules. We speculate that a similar association between growth factor and transmitter may be required in development for the differentiation of a CA phenotype in brain neurons.
Adhesive properties of proteolipid protein are responsible for the compaction of CNS myelin sheaths
Authors: Boison D , Bussow H , D'Urso D , Muller HW , Stoffel W
Published: April 2018

We have studied the molecular function of proteolipid protein (PLP), the main integral membrane protein of CNS myelin, by generating mice lacking PLP expression. Here, we demonstrate that these PLP-minus mice show no pleiotropism as mice carrying point mutations within the PLP gene. The expression of other myelin genes (myelin basic protein, MBP; myelin associated glycoprotein, MAG; UDP-galactose-ceramide galactosyl transferase, CGT) is unimpaired on the RNA level. Protein level immunofluorescence analysis by confocal microscopy reveals that in PLP- minus mice there is a complete absence of PLP, a scattered appearance of MBP, and MAG expressed more widely in regions lacking MBP staining, which may be a compensatory mechanism. In electron microscopy the myelin lamellae of the ensheathed CNS axons are loosely wrapped with wide extracellular spaces between turning loops. Intraperiod dense lines are missing. The lateral loops of the paranode form regular axoglial junctions. In PLP-minus mice axons form regular axoglial junctions. In PLP-minus mice axons with large diameters are loosely myelinated, whereas small axons remain unmyelinated. Functionally, the mutant mice show deficits in their locomotor activity. We propose that adhesion properties of the extracellular domains of PLP are responsible for the tight apposition of the plasma membrane processes of oligodendrocytes wrapping axons to form the compact myelin sheath.
Adrenergic calcium signaling in astrocyte networks within the hippocampal slice
Authors: Duffy S , MacVicar BA
Published: April 2018

Norepinephrine (NE) and glutamate (Glu) initiate intracellular calcium ([Ca2+]i) transients, oscillations, and intracellular [Ca2+]i waves in cultured astrocytes. To further elucidate the significance of NE- and Glu-evoked astrocytic [Ca2+]i signaling to neuron-astrocyte communication in the mature CNS, [Ca2+]i of astrocyte networks within hippocampal slices (P21–42) was measured during bath application of NE and Glu receptor agonists. Astrocytes in stratum radiatum were identified by highly negative membrane potentials (75 +/- 3 mV), absence of action potentials, and dye coupling following intracellular injection of the [Ca2+]-sensitive dye calcium orange. NE (2–100 microM) evoked [Ca2+]i increases (7 of 8 slices, 24 of 24 cells in responding slices) characterized by an initial rise, 20–50 sec to peak, followed by a slower return to baseline (over approximately 8 min). The alpha 1- agonist phenylephrine (PE) (10–100 microM) evoked complex [Ca2+]i signals (22 of 26 slices, 90 of 90 cells in responding slices) composed of both a prolonged component (5.1 +/- 1.8 min), synchronized in neighboring cells, and multiple, mainly asynchronous [Ca2+]i spikes (25.0 +/- 11.6 sec). PE responses were completely blocked by the alpha 1-antagonist prazosin (200 nM, n = 4 slices), but not by the alpha 2- antagonist yohimbine (n = 3 slices). The alpha 2-agonist clonidine (10- 100 microM) did not increase [Ca2+]i (n = 4 slices). alpha 1-mediated [Ca2+]i transients were observed after removal of extracellular [Ca2+]o (n = 8 of 9 slices), indicating PE-induced Ca2+ release from intracellular stores. Adrenergic responses were mediated by alpha 1- receptors localized to astrocytes because PE and NE increased [Ca2+]i of acutely isolated hippocampal astrocytes. Glu (0.75–2.0 mM) did not increase astrocytic [Ca2+]i in slices (0 of 7), even in the presence of the Glu uptake inhibitor L-trans-pyrrollidine-2,4-dicarboxylic acid (PDC) (0 of 5 slices), or in acutely isolated astrocytes (0 of 7 cells). The metabotropic agonist t-ACPD (30 or 50 microM) did not increase astrocytic [Ca2+]i in hippocampal slices (0 of 5), while kainate (200 microM or 1 mM) induced brief (1–2 min) [Ca2+]i increases only rarely (2 of 8 applications in 6 slices). These results support a primary role of NE release and alpha 1-adrenoceptor stimulation in neuron-astrocyte communication in the mature CNS.
The D2 antagonist spiperone mimics the effects of olfactory deprivation on mitral/tufted cell odor response patterns
Authors: Wilson DA , Sullivan RM
Published: April 2018

Wistar rats had a single nare occluded on postnatal day 30, depriving the ipsilateral olfactory bulb of odor stimulation. The deprivation lasted for either 1–2 months (short-term) or 12 months (long-term). As previously reported, deprivation greatly reduced tyrosine hydroxylase immunoreactivity (the rate limiting enzyme for dopamine synthesis) in the glomerular layer of the ipsilateral olfactory bulb. The nare was then reopened and odor response patterns of mitral/tufted cells were examined. The proportion of mitral/tufted cell single-units responding to a single odor was enhanced by deprivation. Furthermore, the proportion of mitral/tufted cells responding to more than one odor was increased by deprivation, suggesting a decrease in discrimination. Finally, in undeprived bulbs, the dopamine D2 receptor antagonist spiperone mimicked the effects of deprivation on mitral/tufted cell odor response patterns. The results are interpreted as an activity- dependent dopamine modulation of lateral and feedback inhibition in the olfactory bulb, and are compared with similar events in the dark- adapted retina.
Visual motion detection circuits in flies: peripheral motion computation by identified small-field retinotopic neurons
Authors: Douglass JK , Strausfeld NJ
Published: April 2018

Giant motion-sensitive tangential neurons in the lobula plate are thought to be cardinal elements in the oculomotor pathways of flies. However, these large neurons do not themselves compute motion, and elementary motion detectors have been proposed only from theory. Here we identify the forms, projections, and responses of small-field retinotopic neurons that comprise a well known pathway from the retina to the lobula plate. Already at the level of the second and third synapses beneath the photoreceptor layer, certain of these small elements show responses that distinguish motion from flicker. At a level equivalent to the vertebrate inner plexiform layer (the fly's outer medulla) at least one retinotopic element is directionally selective. At the inner medulla, small retinotopic neurons with bushy dendrites extending through a few neighboring columns leave the inner medulla and supply inputs onto lobula plate tangentials. These medulla relays have directionally selective responses that are indistinguishable from those of large-field tangentials except for their amplitude and modulation with contrast frequency. Centrifugal neurons leading back from the inner medulla out to the lamina also show orientation-selective responses to motion. The results suggest that specific cell types between the lamina and inner medulla correspond to stages of the Hassenstein-Reichardt correlation model of motion detection.
Neuropeptides phase shift the mammalian circadian pacemaker
Authors: Piggins HD , Antle MC , Rusak B
Published: April 2018

We studied the influence on circadian rhythms of peptides that have been reported to be colocalized in suprachiasmatic nucleus (SCN) neurons. Gastrin-releasing peptide (GRP1–27), peptide histidine isoleucine (PHI), and vasoactive intestinal polypeptide (VIP) were microinjected into the suprachiasmatic nucleus (SCN) region of Syrian hamsters free running under three different constant lighting conditions. All peptide injections caused phase-dependent phase shifts of hamster locomotor activity rhythms which were unaffected by constant lighting conditions. GRP1–27 (150 pmol) caused large phase delays when injected at circadian times (CT) 12–16, modest phase advances when administered at CT20–24, and few shifts during the subjective day. Injections of saline vehicle at any of these phases caused only very small phase shifts. Phase delays induced by GRP1–27 at CT12–14 were dose dependent, unrelated to injection volume (at a constant dose), and attenuated by pretreatment with the BN/GRP-preferring receptor antagonist BIM 26226. VIP (150 pmol) caused moderate phase delays at CT12–14 and moderate phase advances at CT20–24. PHI (150 pmol) caused moderate phase delays at CT12–14 only. Coadministration of 150 pmol of GRP1–27, PHI, and VIP in an equimolar neuropeptide cocktail (50 pmol of each peptide) caused phase delays at CT12–14 and phase advances at CT20- 24 which did not differ from those induced by 150 pmol of GRP1–27 alone at these phases. The shifts induced by 150 pmol of the peptide cocktail were smaller than the sum of the shifts induced by 50 pmol doses of each peptide administered separately at those phases. Since the phase- delaying effects of the cocktail were weaker than the summed effects of the component 50 pmol doses of the peptides, these data demonstrate a lack of synergism among the effects of these peptides. Since GRP1–27 (150 pmol) evoked shifts similar in magnitude to those of the cocktail, there is no evidence that these apparently colocalized neuropeptides must interact to exert maximal effects on the circadian pacemaker.
Proprioceptive sensory neurons of a locust leg receive rhythmic presynpatic inhibition during walking
Authors: Wolf H , Burrows M
Published: April 2018

Mechanosensory neurons from a proprioceptor (the femoral chordotonal organ) signal the movements and positions of the femorotibial joint of a locust leg. Intracellular recordings from these neurons during walking show that their spikes are superimposed on a depolarizing synaptic input generated near their output terminals in the CNS. The depolarization consists of a rhythmic synaptic input at each step, and a sustained input that begins before walking commences. In different sensory neurons, which signal particular features of the movement, the rhythmic depolarization occurs at distinct times during either the swing or stance phases of the step cycle. The depolarizing input is timed to coincide with the greatest spike response of a sensory neuron. The input is associated with a conductance change, appears to reverse just above resting potential, and thus has similar properties to the presynaptic inhibition in these same neurons during imposed joint movements (Burrows and Laurent, 1993; Burrows and Matheson, 1994). Three sources could contribute to these inputs: (1) interactions between sensory neurons of the same receptor signaling the same movement, (2) signals from different receptors in the same leg and other legs, and (3) outputs of central neurons involved in generating walking. When the leg, whose movements the sensory neurons signal is removed, both the sustained and rhythmic synaptic inputs persist. Sensory neurons in isolated ganglia treated with pilocarpine are also depolarized in phase with a rhythmic pattern expressed in leg motor neurons, indicating that central neurons must contribute. The maintained synaptic input to the terminals means that the overall effectiveness of the sensory spikes in evoking EPSPs in postsynaptic neurons will be reduced during walking, and the rhythmic component means that the spikes from particular sensory neurons will be further reduced at particular phases of the step cycle that they signal best.
Temperature compensation and temperature entrainment of the chick pineal cell circadian clock
Authors: Barrett RK , Takahashi JS
Published: April 2018

We have used an in vitro model system of the circadian clock, dispersed chick pineal cells, to examine the effects of temperature on the circadian clock of a homeotherm. This preparation enabled us to isolate a circadian clock from in vivo homeostatic temperature regulation and expose cells to both constant temperatures and abrupt temperature changes. By manipulating the temperature of the pineal cells, we have demonstrated that (1) the circadian clock compensates its period for temperature changes over the range of 34–40 degrees C; Q10 = 0.83, a value within the range of Q10 values measured for poikilothermic circadian clocks; (2) temperature pulses (42 degrees C, 6 hr duration) shift the phase (advance and delay) of the circadian rhythm in a phase- dependent manner; and (3) a temperature cycle (18 hr at 37 degrees C, 6 hr at 42 degrees C) will entrain the circadian clock in vitro. This is the first demonstration of temperature entrainment of the circadian clock of a homeotherm in vitro. In addition we have found that temperature directly influences the synthesis and release of melatonin, the primary hormonal product of the pineal gland. The biosynthesis of melatonin is strongly temperature dependent with a Q10 > 11 when melatonin release is measured at ambient temperatures between 31 degrees C and 40 degrees C. In contrast, 6 hr 42 degrees C temperatures pulses acutely inhibit melatonin release in a manner similar to that seen previously with light pulses. These results demonstrate that a circadian clock from a homeothermic vertebrate is temperature compensated, yet temperature cycles can entrain the circadian melatonin rhythm. Thus, the chick pineal circadian oscillator has retained all the fundamental properties of circadian rhythms.
Expression of mef2 genes in the mouse central nervous system suggests a role in neuronal maturation
Authors: Lyons GE , Micales BK , Schwarz J , Martin JF , Olson EN
Published: April 2018

Members of the myocyte enhancer factor 2 (MEF2) gene family are expressed in a dynamic pattern during development of the CNS of pre- and postnatal mice. The four MEF2 genes, Mef2A, -B, -C, -D, encode transcription factors belonging to the MADS (MCM1-agamous-deficiens- serum response factor) superfamily of DNA binding proteins. MEF2 factors have previously been shown to be positive regulators of gene expression in terminally differentiated muscle cells. To begin to determine the role of MEF2 factors in CNS development, we used in situ hybridization with gene-specific cRNA probes to define the expression patterns of each of the four Mef2 mRNAs in the developing and mature mouse CNS. Mef2C mRNA was first detected in a ventral portion of the telencephalon at 11.5 d postcoitum (p.c.). By 13.5 d p.c., each of the four Mef2 genes were expressed in overlapping yet distinct patterns in regions of the frontal cortex, midbrain, thalamus, hippocampus, and hindbrain. Temporal and spatial patterns of embryonic Mef2 gene expression appeared to follow gradients of neuron maturation and suggested that the onset of Mef2 gene expression coincides with withdrawal from the cell cycle and initiation of neuronal differentiation. This correlation is particularly striking for Purkinje cells in the cerebellum. Since the molecular mechanisms that regulate neuron differentiation are unknown, we propose that the MEF2 factors are likely to play an important role in this process.
Regional expression and cellular localization of the Na(+)-dependent inorganic phosphate cotransporter of rat brain
Authors: Ni B , Wu X , Yan GM , Wang J , Paul SM
Published: April 2018

We have recently isolated and identified a brain specific Na(+)- dependent inorganic phosphate (Pi) cotransporter cDNA (rBNPI) from a rat brain cDNA library (Ni, et al., 1994). We now report the regional and developmental expression, as well as the cellular localization, of rBNPI mRNA in the rat brain. In situ hybridization histochemistry reveals that rBNPI mRNA is selectively expressed in neuron-enriched regions of the adult rat brain, such as the cerebral cortex, hippocampus, and cerebellum. Cellular localization of rBNPI transcripts reveals expression in both pyramidal and granule neurons in these regions. By contrast, little to no hybridization signal was observed in white matter-enriched areas such as the corpus callosum. The expression of rBNPI mRNA was determined during pre- and postnatal development of the rat CNS. From embryonic day 17 to early postnatal day 10 (PND 10), there is a rather widespread but diffuse pattern of rBNPI expression in brain. During late postnatal development, however, the expression of rBNPI mRNA becomes confined to discrete populations of neurons in the cerebral cortex, hippocampus, and cerebellum. Thus, rBNPI expression is developmentally regulated and abundant levels of mRNA are found in rather discrete populations of neurons in the adult rat brain. The latter suggests that rBNPI may serve to selectively regulate intracellular Pi transport in certain neurons for either metabolic and (or) signaling events.
Seizures and failures in the giant fiber pathway of Drosophila bang- sensitive paralytic mutants
Authors: Pavlidis P , Tanouye MA
Published: April 2018

Drosophila bang-sensitive paralytic mutants suffer from hyperactivity and paralysis following a mechanical shock; after recovery from paralysis, they cannot be paralyzed for a refractory period lasting up to 1 hr. Previously, we have shown that in easily shocked (eas), a typical bang-sensitive mutant, electrical shocks delivered to the brain cause seizure-like activity in the dorsal longitudinal flight motor neurons (DLMmns), and failure of giant fiber (GF) stimulation to evoke DLM potentials via the escape response pathway (Pavlidis et al., 1994). Here, we show that seizure and failure in the GF pathway with a refractory period is common to all six members of the bang-sensitive class. This syndrome was not found in any of eight other excitability mutants, including those affecting voltage-gated sodium or potassium- channel function. We show that failure occurs at the synapse between a peripherally synapsing interneuron (PSI) and the DLMmns, while the DLMmn-DLM neuromuscular junctions remain functional. Additionally, failure occurs in all other GF pathway-activated muscles. Failures occurred without seizures in the tergotrochanteral jump muscle (TTM), as was also found in approximately 10% of DLM tests, suggesting that seizures and failures may be independent events. This hypothesis is supported by the finding that, in double mutant combination with mlenapts, which suppresses behavioral bang sensitivity, DLM failures, but not seizures, were reduced.
Long-term potentiation disrupts auditory gating in the rat hippocampus
Authors: Miller CL , Bickford PC , Wiser AK , Rose GM
Published: April 2018

The consequence of long-term potentiation (LTP) of hippocampal commissural inputs was investigated in an auditory gating paradigm. Auditory evoked potentials (AEPs) were recorded in the CA3b region of the hippocampus of rats anesthesitized with chloral hydrate. Two tones were delivered 0.5 sec apart; in this paradigm, the second AEP is diminished compared to the first. Electrical stimulation was applied to hippocampal commissural fibers to generate field potentials and population spikes which were recorded at the same site as the AEPs. LTP of the commissural input (initiated by three trains of 250 Hz/1 sec stimulation) was associated with changes in the AEPs: on average, the response to the first tone decreased and the response to the second tone increased, resulting in the disruption of auditory gating. When high-frequency stimulation of the commissural input failed to result in LTP, no effect on the AEPs was seen. If 3-(2-carboxypiperazin-4-yl)- propyl-L-phosphonic acid (CPP; 6 mg/kg, i.p.), an antagonist to the NMDA subclass of glutamate receptors, was administered prior to high- frequency stimulation, LTP induction was blocked and AEPs were not affected. Finally, reversal of LTP, achieved by high-frequency stimulation of CA3 input that was heterosynaptic to the particular commissural fibers at which the LTP was originally generated, caused disrupted auditory gating to return to normal. A model of reciprocal LTP and heterosynaptic depression of commissural and auditory input pathways is proposed to explain these findings.
Neuroligand-evoked calcium-dependent release of excitatory amino acids from Schwann cells
Authors: Parpura V , Liu F , Jeftinija KV , Haydon PG , Jeftinija SD
Published: April 2018

Bradykinin caused a receptor-mediated increase in release of the excitatory amino acids (EAAs) glutamate and aspartate from Schwann cell cultures obtained from dorsal root ganglia (DRG) together with an increase in the cytoplasmic level of free calcium. Perturbations which inhibited brady-kinin-induced calcium mobilization prevented the release of EAAs from glia. The addition of ionomycin caused a calcium- dependent release of EAAs. Therefore, bradykinin causes calcium dependent-release of EAAs from DRG Schwann cells. Bradykinin did not cause cell swelling and p-chloromercuriphenylsulfonic acid, an inhibitor of the electrogenic glutamate transporter, did not reduce bradykinin-induced EAA release. Therefore, bradykinin stimulates EAA release from Schwann cells through a mechanism that is neither the previously described volume regulated release mechanism nor due to the reversal of the glutamate transporter.