bluuebunny/crossref_metadata_2025 huggingface dataset:
The impact of basal forebrain lesions on the ability of rats to perform a sensory discrimination task involving barrel cortex
Authors: Jacobs SE , Juliano SL
Published: April 2018

Depletion of cortical acetylcholine (ACh) correlates with reduced stimulus-evoked 2-deoxyglucose (2-DG) uptake in rodent somatosensory cortex. We examined the effect of unilateral basal forebrain lesions and subsequent cortical ACh depletion on (1) the ability of rats to detect a passively applied deflection of the whiskers, and (2) whisker- evoked 2-DG uptake. Normal adult rats were trained on a T-maze to respond by turning in one direction if the whiskers were displaced and in the opposite direction on presentation of a sham stimulus; only the left set of whiskers was stimulated. When the animal performed at the 80% correct level for three consecutive sessions (criterion), it was randomly assigned to a group receiving either a saline injection (sham lesion) or an ibotenic acid injection (excitotoxic lesion) into the right basal forebrain. Behavioral testing continued until the animal returned to the prelesion criterion, at which time a terminal 2-DG experiment was conducted. None of the sham-lesioned rats experienced disruption of their ability to perform the task. All excitotoxic basal forebrain-lesioned rats were impaired in task performance, but eventually returned to prelesion performance levels. The length of time required to return to criterion was positively correlated with the amount of cortical ACh depletion. Despite the behavioral recovery of the ACh-depleted rats, 2-DG uptake in response to whisker stimulation continued to be reduced in the somatosensory cortex ipsilateral to the basal forebrain lesion. These findings suggest that ACh depletion, which results in a long-lasting decrease in neuronal responses to evoked stimuli, transiently impairs an animal's ability to perceive and appropriately respond to sensory information; the duration of impairment is related to the degree of depletion.
Apoptosis in cerebellar granule cells is blocked by high KCl, forskolin, and IGF-1 through distinct mechanisms of action: the involvement of intracellular calcium and RNA synthesis
Authors: Galli C , Meucci O , Scorziello A , Werge TM , Calissano P , Schettini G
Published: April 2018

Cerebellar granule cells deprived of depolarizing concentration of extracellular potassium, [K+]o, undergo apoptosis. We here report that this apoptotic process is associated with an immediate and permanent decrease in the levels of free intracellular calcium, [Ca2+]i. Although forskolin and IGF-1 are both able to prevent apoptosis, only forskolin is able to counteract the instantaneous decrease of [Ca2+]i. However, the early effect of forskolin on [Ca2+]i is lost after longer incubation in low [K+]o. The calcium antagonist nifedipine is able to inhibit the survival effect of high [K+]o, while not affecting forskolin and IGF-1 promoted survival, as assessed by viability and genomic DNA analysis. Accordingly, the L-type calcium channels agonist Bay K8644 significantly enhanced the survival of low KCl treated neurons. To temporally characterize the signal transduction events and the essential transcriptional step in cerebellar granule cells apoptosis, we determined the time course of the rescue capacity of high [K+]o, forskolin, IGF-1, and actinomycin D. Addition of high KCl, forskolin, or IGF-1 6 hr after the initial KCl deprivation saves 50% of cells. Remarkably, 50% of neurons loss the potential to be rescued by actinomycin D after only 1 hr in low [K+]o. Finally, we show that the survival promoting activities of high [K+]o, forskolin, and IGF-1 do not require RNA synthesis. We conclude that [Ca2+]i is involved in the survival promoting activity exerted by high [K+]o but not in those of forskolin and IGF-1, and that all three agents, although rescuing neurons from apoptosis through distinct mechanisms of action, do not necessitate RNA transcription.
Enhanced survival and neuronal differentiation of adrenal chromaffin cells cografted into the striatum with NGF-producing fibroblasts
Authors: Niijima K , Chalmers GR , Peterson DA , Fisher LJ , Patterson PH , Gage FH
Published: April 2018

Although adrenal medullary chromaffin cells have been used extensively for intracerebral grafting, their survival has generally been poor. Improved survival of the implanted cells has been achieved by exposing the chromaffin cells to NGF in vivo. Culture studies have shown, however, that chromaffin cells are converted into sympathetic neurons when NGF is included in the medium. The degree to which such a transdifferentiation may occur in vivo has not been determined. We assessed the effects of cografting chromaffin cells with primary fibroblasts genetically engineered to express NGF. Chromaffin cells from 10 d old rats were implanted with NGF-producing or beta- galactosidase-producing primary fibroblasts (control fibroblasts) into the striatum of 6-hydroxydopamine treated adult rats of the same strain. Eight weeks postgrafting, chromaffin cells cografted with NGF- producing fibroblasts displayed many of the features of mature sympathetic neurons such as large somata, long processes, transmitter vesicles similar to those found in neurons, and positive immunolabeling for the neuronal markers neurofilament, MAP2 and SCG10. Chromaffin- derived neuron number was also significantly enhanced in the presence of NGF-producing fibroblasts. While control fibroblasts were also found to increase chromaffin cell number above that of chromaffin cells grafted alone, the control fibroblasts did not induce neuronal transdifferentiation. These results demonstrate that chromaffin cells cografted with NGF-producing fibroblasts undergo transdifferentiation in vivo and express many characteristics of mature sympathetic neurons. The consequences of this transdifferentiation on the long term survival and function of the transplanted cells in vivo remain to be clarified.
Identification and characterization of antidepressant-sensitive serotonin transporter proteins using site-specific antibodies
Authors: Qian Y , Melikian HE , Rye DB , Levey AI , Blakely RD
Published: April 2018

Serotonin (5HT) transporters (SERTs) are responsible for clearance of synaptic and plasma 5HT and are molecular targets for multiple therapeutic and addictive compounds. Recently brain and peripheral SERT cDNAs have been cloned and characterized functionally in transfected cells. Antipeptide (S365) and anti-fusion protein (CT-2) antibodies, directed at epitopes poorly conserved among other Na+/Cl- cotransporters, have been prepared to facilitate the identification and characterization of SERT proteins in native and transfected cells. Immunoprecipitations and immunoblots of rat/human SERT-transfected HeLa cells reveal specific SERT-immunoreactive glycoproteins absent from extracts of vector-transfected cells and absent when incubations were conducted using peptide- or fusion protein-absorbed antibody. In SDS- PAGE of membranes prepared from rat midbrain and cortex, SERTs migrate as single 76 kDa polypeptides with a relative abundance consistent with the known distribution of 5HT neurons and axonal projections. SERT- immunoreactive proteins are also detectable in platelet and pulmonary membranes, sites of peripheral 5HT uptake, but not in liver. Our studies also indicate that brain and platelet SERTs are formed from identical polypeptides differing significantly in their extent of N- linked glycosylation. Immunocytochemistry performed on rat brain sections with CT-2 antibody revealed SERT expression associated with brainstem raphe nuclei in a pattern virtually identical to that obtained by labeling adjacent sections with 5HT antisera. SERT- immunoreactive fibers were found to be widely distributed throughout the rodent brain, with highest density in forebrain regions known to receive a dense serotonergic innervation. In a similar manner, CT-2 antibody also detects endogenous expression of human SERT proteins, providing an opportunity for future studies on the modulation of transporter protein expression in neurologic and psychiatric disorders.
Postsynaptic modifications in long-term facilitation in Aplysia: upregulation of excitatory amino acid receptors
Authors: Trudeau LE , Castellucci VF
Published: April 2018

Long-term sensitization of the gill and siphon withdrawal in Aplysia is accompanied by facilitation of sensorimotor synaptic connections that depends on new protein synthesis. This phenomenon has been previously shown to involve presynaptic growth. At the postsynaptic level, a reorganization should occur to parallel the formation of new synaptic contacts. We show here that 24 hr following an application of 5-HT, which produces long-term synaptic facilitation (LTF), the response of the motoneuron to an excitatory amino acid agonist of the synaptic receptors is increased. General inhibition of protein synthesis with anisomycin blocks this enhancement. Inhibiton of protein synthesis limited to the postsynaptic neuron by intracellular injection of gelonin, a ribosome-inactivating toxin, also blocks the increase in the response to the agonist but fails to block 24 hr LTF. These results are compatible with a model of LTF that involves coordinate pre- and postsynaptic changes. The latter may include an upregulation of functional postsynaptic receptors. These may not be initially required for LTF measured at a 24 hr time point, but could become necessary for later stages of LTF. An increase in the number of functional postsynaptic receptors in a reserve pool may also prime the postsynaptic neuron for subsequent learning-associated plasticity.
Synaptic interactions between primary afferent terminals and GABA and nitric oxide-synthesizing neurons in superficial laminae of the rat spinal cord
Authors: Bernardi PS , Valtschanoff JG , Weinberg RJ , Schmidt HH , Rustioni A
Published: April 2018

The superficial laminae (I and II) of the spinal dorsal horn receive small caliber primary afferent fibers responsive to noxious stimulation, and contain local circuit neurons that modulate afferent input. Many of these neurons are GABAergic; about a third of these also synthesize nitric oxide. We identified three main morphological types of primary afferent terminals in superficial laminae after injections of a tracer selective for small caliber afferents into the sciatic nerve of rats. The relative densities of the three types varied through the dorsoventral extent of laminae I and II. Synaptic contacts of each type with GABA- and nitric oxide synthase (NOS)-containing dendrites and axon terminals were determined by preembedding and postembedding immunocytochemistry. Nonglomerular primary afferent terminals, likely to originate from peptidergic unmyelinated fibers, were not seen in synaptic contact with either GABA- or NOS-containing neurons. Primary afferent terminals at the center of type 1 glomeruli (C1) and at the center of type 2 glomeruli (C2) are likely to originate from unmyelinated and small myelinated fibers, respectively. GABAergic terminals contacted more C2 than C1 terminals, suggesting more effective presynaptic inhibition of C2 terminals. Many GABAergic terminals were also positive for NOS, but all GABAergic terminals presynaptic to primary afferent terminals were negative for NOS. Only C2 terminals established frequent synapses with NOS-positive dendrites. (ABSTRACT TRUNCATED AT 250 WORDS)
Differential modulation by sulfhydryl redox agents and glutathione of GABA- and glycine-evoked currents in rat retinal ganglion cells
Authors: Pan ZH , Bahring R , Grantyn R , Lipton SA
Published: April 2018

Some areas of the mammalian CNS, such as the retina, contain not one but two fast inhibitory neurotransmitter systems whose actions are mediated by GABA and glycine. Each inhibitory receptor system is encoded by a separate gene family and has a unique set of agonists and antagonists. Therefore, in rat retinal ganglion cells we were surprised to find that a single agent, extracellular glutathione, was capable of modulating currents activated by either GABAA or glycine receptor stimulation. Both oxidized and reduced glutathione influence inhibitory neurotransmission in a manner similar to that of the sulfhydryl redox agents dithiothreitol (DTT) and 5,5′-dithio-bis-(2-nitrobenzoic acid) (DTNB). Remarkably, the actions of glutathione are diametrically opposed on the GABAA and glycine systems. In whole-cell recordings of single retinal ganglion cells with patch pipettes, reduced glutathione enhances GABA-evoked currents but decreases glycine-evoked currents. These findings suggest that endogenous redox agents, such as glutathione, may constitute a novel modulatory system for the differential regulation of inhibitory neurotransmission in the mammalian retina.
Acetylcholine-induced retraction of an identified axon in the developing leech embryo
Authors: Elsas SM , Kwak EM , Stent GS
Published: April 2018

At early stages of embryonic development of the glossiphoniid leech, Theromyzon rude, a branch, termed MAC, of the axon of the segmentally iterated Retzius neuron extends into the anterior interganglionic connective nerve. At later stages, this branch disappears again in about 30% of the Retzius neurons in the standard midbody segments and in about 75% of the Retzius neurons in the two reproductive midbody segments. The frequency of disappearance of the MAC branch increases to about 85% in all Retzius neurons upon exposure of the embryos to culture media containing 1 mM acetylcholine (ACh) and 10 microM physostigmine during a sensitive period of axon outgrowth. This disappearance represents a retraction of the MAC branch to its point of origin, while other axon branches of the Retzius neuron remained unaffected. In later development, the retracted (medial) MAC branch was replaced by a new (lateral) branch termed LAC. The observations were made using confocal microscopy of fixed embryos stained with anti-5-HT antibody and confirmed by Lucifer yellow injection of individual Retzius neurons. The specific retraction of a single axon branch might be attributable to the local presence of extracellular matrix molecules in the ganglionic neuropil, which is contacted only by the MAC axon branch and could render this branch susceptible to growth-regulating signals. Since Retzius axon morphology in standard segments of ACh- treated embryos resembled that of reproductive segments in untreated embryos, it appears possible that ACh treatment may have simulated a process that contributes to the segmental differentiation of the Retzius neuron.
Decreased monosynaptic sensory input to an identified motoneuron is associated with steroid-mediated dendritic regression during metamorphosis in Manduca sexta
Authors: Streichert LC , Weeks JC
Published: April 2018

The proleg withdrawal reflex of Manduca sexta larvae is mediated by mono- and polysynaptic connections from afferents innervating mechanosensory planta hairs (PHs) to ipsilateral proleg retractor motoneurons. During the larval-pupal transformation, a rise in ecdysteroids causes the dendrites of proleg motoneurons to regress and, concurrently, the proleg withdrawal reflex is lost. The objective of this study was to identify synaptic correlates of dendritic regression that contributed to this behavioral change. The accessory planta retractor (APR) motoneuron regresses during the larval-pupal transformation and dies in a segment-specific pattern after pupation. The compound excitatory postsynaptic potential (cEPSP) evoked in APR by electrically stimulating the proleg sensory nerve decreased in amplitude during the larval-pupal transformation. The developmental decrease in cEPSP amplitude, the extent of APR's regression, and several of APR's intrinsic electrical properties were similar in segments in which the motoneuron was fated to live or die. In heterochronic mosaic pupae bearing retained larval PH afferents, APR's dendritic regression was associated with decreases in both the mean amplitude of monosynaptic EPSPs produced by PH afferents and the proportion of PH afferents that produced detectable EPSPs. These changes appeared due to a developmental decrease in the size of the synaptic currents produced by PH afferents. Evidence was also obtained suggesting that PH afferents do not regress at pupation. These findings support the hypothesis that the ecdysteroid-mediated regression of proleg motoneuron dendrites disconnects them from sensory inputs and, thereby, contributes to the elimination of the proleg withdrawal reflex.
Interactions during a critical period inhibit bilateral projections in embryonic neurons
Authors: Wolszon LR , Passani MB , Macagno ER
Published: April 2018

The anterior pagoda (AP) neurons in the CNS of the medicinal leech are found as homologous pairs in 20 of the 21 midbody ganglia. Each AP is the mirror image of its mate, extending its main axon across the midline of the CNS and eventually into the contralateral body wall, thereby attaining a unilateral pattern of innervation. Certain features of the adult AP morphology are known to arise through interactions among homologs early in development (Gao and Macagno, 1987b), but it is not known whether the contralateral nature of the projection pattern is due to intrinsic “one-sidedness” or rather to cell-cell interactions that inhibit the formation of a second, ipsilateral projection. In the experiments described in this report, we tested the possibility that an AP's contralateral homolog itself inhibits the formation of bilateral projections. One AP was photoablated in the intact embryo early in development and then the response of the remaining AP was examined. We found that an AP can extend bilaterally symmetrical projections when its homolog is missing, but only during a critical period that, interestingly, begins when an AP's interactions with other specific neurons come to an end. To determine whether synaptic communication between AP homologs could be responsible for the timing of this critical period, we recorded electrophysiologically from pairs of embryonic AP neurons. Although no detectable chemical signaling was observed, AP cells were electrically coupled throughout the entire critical period. Further, the junctions between these neurons were permeated by 5-HT, whereas larger molecules such as carboxyfluorescein were impermeant. This dye coupling decreased with age even while electrical coupling persisted, suggesting but not proving that the properties of the gap junctions between AP neurons may also change with time. We conclude that unilateral AP cells possess the intrinsic ability to project bilaterally, but are inhibited from doing so by age- dependent interactions with homologous neurons, possibly mediated by gap-junctional communication.
NMDA-receptor antagonists disrupt the formation of the auditory space map in the mammalian superior colliculus
Authors: Schnupp JW , King AJ , Smith AL , Thompson ID
Published: April 2018

In the ferret (Mustela putorius) the map of auditory space in the deeper layers of the superior colliculus (SC) matures over a period of several postnatal weeks, a process known to be guided by both visual and auditory experience. The auditory responses are initially very broadly tuned, and gradually become more selective for specific sound locations that coincide with the visual receptive fields recorded in the same region of the SC. To investigate the possible involvement of NMDA-type glutamate receptors in the postnatal development of this auditory representation, we have reared ferrets in which 400 microns thick sheets of the slow-release polymer Elvax, containing the NMDA receptor antagonists MK801 or APV, were placed on the dorsal surface of the SC. The Elvax was implanted on postnatal day (P) 25–27, just before the onset of hearing, and removed 5–6 weeks later, just prior to recording from the SC on around P61–70. In vitro measurements with Elvax containing 3H-MK801 revealed that the amount of drug released declined sharply over the first 10 d and then stabilized at a fairly constant rate for the following 5 weeks. These in vitro data were found to parallel the in vivo release of MK801 from implanted Elvax slices. Diffusion of MK801 from the implant was measured and significant levels were found within 800 microns of the SC surface, suggesting that the action of MK801 was restricted to the superficial and intermediate layers of the nucleus. Extracellular recordings were made from visual and auditory units in the SC in response to free-field stimulation. The visual responses of units recorded in the superficial layers appeared to be unaffected by either of the drug treatments, and formed a normal, adult-like map of visual azimuth along the rostrocaudal axis of the SC in all animals. Most of the auditory single-unit responses recorded at this age in normal, unoperated controls were spatially tuned and topographically organized, although the map of sound azimuth was less precise than that in adult ferrets. Data from age-matched control animals that had been reared with drug-free Elvax implants were not statistically different from the unoperated juvenile ferrets. However, in animals reared with APV or MK801 Elvax implants, there was an increase in the relative numbers of auditory units that were ambiguously tuned to two or more locations.(ABSTRACT TRUNCATED AT 400 WORDS)
Cellular and molecular characterization of a brain-enriched protein tyrosine phosphatase
Authors: Boulanger LM , Lombroso PJ , Raghunathan A , During MJ , Wahle P , Naegele JR
Published: April 2018

Regional variations in the expression of a striatal enriched protein tyrosine phosphatase called STEP were studied in the adult rat brain by a combination of immunocytochemistry, lesion studies, Western blotting, and in situ hybridization. Monoclonal antibodies generated against STEP identified multiple polypeptides of M(r) 46, 37, 33 and a doublet of M(r) 64–66 kDa on Western blots. Although the three STEP immunoreactive bands with lower molecular weights were enriched in cytosolic fractions, the 64–66 kDa doublet was enriched in membrane fractions. All of the immunoreactive forms were abundant in the caudate-putamen and were present in lower amounts or were undetectable in other brain regions. In substantia nigra, the M(r) 64–66 kDa doublet was not detected but bands with M(r) 46, 37, and 33 kDa were present. Immunocytochemical and lesion experiments demonstrated that the cytosolic STEP isoforms present in the substantia nigra are in presynaptic axons originating from the projection neurons of the caudate putamen, which innervate this structure. Additional in situ hybridization studies showed that STEP mRNA expression patterns correlate with the patterns of immunocytochemical staining. These findings indicate that there are multiple polypeptide isoforms of STEP enriched in the basal ganglia and related structures which differ in terms of their intracellular locations and functional roles.
Functional identification of central afferent projections conveying information of acute "stress" to the hypothalamic paraventricular nucleus
Authors: Larsen PJ , Mikkelsen JD
Published: April 2018

Intraperitoneal administration of hypertonic saline is a potent stimulus to the “stress” responsive hypophysiotrophic parvicellular neurons of the hypothalamic paraventricular nucleus (PVN), as well as to magnocellular neurons of the hypothalamo-neurohypophysial system. Precise identification of the pathways gating information about the “stress” of intraperitoneal hypertonic saline to the PVN has not been ascertained earlier. In this study we demonstrate that intraperitoneal injection of hypertonic saline induces increased expression of c-fos immunoreactivity within neurons of the medial parvicellular division of the PVN, within the circumventricular organs surrounding the anteroventral tip of the third ventricle, and within the magnocellular neurons of the PVN and supraoptic nucleus. Also, neurons involved in conveying visceral information to the PVN, including the parabrachial nucleus, the nucleus of the solitary tract and the ventrolateral medulla responded with increased c-fos expression to the “stress” paradigm. Combined c-fos immunocytochemistry and retrograde tracing experiments with cholera toxin B (ChB) was used to identify neurons projecting to the PVN activated by the applied “stressor.” Neither the mere intracerebral presence of ChB nor intraperitoneal administration of isotonic saline influenced the number of c-fos immunoreactive nuclei in the brain. Dual immunocytochemistry revealed that intraperitoneal administration of hypertonic saline induced expression of c-fos immunoreactive nuclei in approximately half of the retrogradely labeled neurons projecting to the PVN from the anteroventral tip of the third ventricle (AV3v), including the subfornical organ (SFO) and the organum vasculosum laminae terminalis (OVLT). In the brainstem, the “stressor” induced expression of c-fos-IR nuclei in almost all of the retrogradely labeled cells of the ventrolateral part of the medulla oblongata (A1 and C1), while only about 25% of the ChB-labeled cells of the caudal part of the nucleus of the solitary tract (A2) were concomitantly immunoreactive to c-fos. Within the parabrachial nucleus, only 20% of the ChB-labeled cells were also immunoreactive for c-fos. The present results provide evidence that information about the “stress” of intraperitoneal hypertonic saline is conveyed to both magnocellular neurons projecting to the neurohypophysis and hypophysiotrophic parvicellular neurons the PVN via afferent projections from a variety of neurons in the osmosensitive anteroventral tip of the third ventricle and visceromotor neurons of the parabrachial nucleus, the ventrolateral medulla and the nucleus of the solitary tract.
Neurotrophin-4/5 (NT-4/5) and brain-derived neurotrophic factor (BDNF) act at later stages of cerebellar granule cell differentiation
Authors: Gao WQ , Zheng JL , Karihaloo M
Published: April 2018

The developing cerebellum expresses genes which encode for both neurotrophins and their receptors. The present study was designed to determine at what stages during cerebellar granule cell neurogenesis neurotrophin family molecules may act. We report here that in purified, well-characterized granule cell cultures (Gao et al., 1991; 1992), none of the neurotrophins stimulated proliferation of granule cell precursors or rescued phenotypic defect of mutant weaver granule cell precursors in the initiation of neuronal differentiation. However, neurotrophin-4/5 (NT-4/5) and BDNF, but not neurotrophin-3 (NT-3) or NGF, promoted neurite extension and survival of differentiated cerebellar granule cells. Both of these effects were blocked by the specific inhibitor for Trk tyrosine kinases, K-252a. NT-4/5 and BDNF also enhanced neurite extension by weaver granule cells which were rescued by wild-type granule cells during differentiation. Moreover, TrkB immunohistochemistry performed on sections of the developing wildtype and weaver cerebella revealed that only differentiated granule cells, but not the precursor cells, make high levels of TrkB receptor. These findings together suggest that NT-4/5 and BDNF promote the maturation and maintenance of differentiated granule cells, effects which are downstream to the weaver gene. Since no additive effects were seen with the combination of NT-4/5 and BDNF, it seems likely that the two neurotrophins activate the same receptor trkB for signal transduction.
Multiple GABA receptor subtypes mediate inhibition of calcium influx at rat retinal bipolar cell terminals
Authors: Pan ZH , Lipton SA
Published: April 2018

Inhibitory effects of GABA on K(+)-evoked Ca2+ influx into rat retinal bipolar cell terminals were studied using calcium imaging methods. Application of high K+ evokes a sustained, reversible increase in [Ca2+]i at bipolar cell terminals, which occurs mainly via dihydropyridine-sensitive (L-type) Ca2+ channels. There are at least two GABA receptor subtypes coexisting at bipolar cell terminals: a conventional GABAA receptor and a bicuculline/baclofen-insensitive GABA receptor. Activation of either GABA receptor inhibited the K(+)-evoked Ca2+ response. However, these two GABA receptor subtypes have distinct properties. GABAA receptors suppress the Ca2+ response only at relatively high concentrations of agonist, and with fas kinetics and a narrow dynamic range. In contrast, the bicuculline/baclofen-insensitive GABA receptors produce inhibition on the Ca2+ response at a much lower concentration of agonist, and with slow onset and a wider dynamic range. The pharmacologic profile of the bicuculline/baclofen- insensitive GABA receptor at bipolar cell terminals is most similar to the GABAC receptor reported by Feigenspan et al. (1993). Unlike the GABAC receptors described in other species, it is extremely insensitive to picrotoxin. Therefore, it may be appropriate to refer to this receptor as a picrotoxin-insensitive GABAc receptor. 3- Aminopropyl(methyl)phosphinic acid (3-APMPA) and 3- aminopropylphosphonic (3-APA), two phosphate analogs of GABA, selectively antagonize the picrotoxin-insensitive GABAc receptors but not the GABAA receptors in this system. These results imply a functional role for multiple GABA receptors in regulating synaptic transmission at bipolar cell terminals.
Immune challenge and immobilization stress induce transcription of the gene encoding the CRF receptor in selective nuclei of the rat hypothalamus
Authors: Rivest S , Laflamme N , Nappi RE
Published: April 2018

The present study investigated the effect of intraperitoneal (i.p.) administration of endotoxin lipopolysaccharide (LPS) and immobilization stress on the genetic expression of corticotropin-releasing factor receptor (CRF-R) in the brains of conscious male Sprague-Dawley rats. One group of rats was killed at 1, 3, 6, 9, and 12 hr after a single intraperitoneal injection of either the LPS (250 micrograms/100 gm of body weight) or the vehicle solution; the other group was killed before, immediately after, 1.5, 3, 6, and 12 hr after a 90 min acute session of immobilization stress. Rats were deeply anesthetized and rapidly perfused with a solution of 4% paraformaldehyde-borax. Frozen brains were mounted on a microtome and cut from the olfactory bulb to the medulla in 30 microns coronal sections. mRNA encoding the rat CRF-R was assayed by in situ hybridization histochemistry using a 35S-labeled riboprobe, and CRF-R localization within CRF-immunoreactive neurons in the PVN was determined using a combination of immunocytochemistry and in situ hybridization techniques. Strong basal levels of CRF-R transcripts were observed in several regions of the brain (piriform cortex, medial and basolateral nuclei of the amygdala, red nucleus, pontine gray, cerebellum, laterodorsal tegmental nucleus, caudal division of the zona incerta, nucleus incertus, spinal and principal sensory nuclei of the trigeminal nerve, and various layers of the cortex). A low to moderate signal was also detected in multiple sites (medial septal nucleus, nucleus of the diagonal band, supraoptic nucleus, arcuate nucleus of the hypothalamus, interpeduncular nucleus, and nucleus prepositus). Whereas vehicle-treated and control rats displayed hardly detectable signals of CRF-R mRNA in the paraventricular nucleus (PVN), CRF-R gene transcription was highly stimulated by LPS administration and immobilization stress in this hypothalamic structure. Indeed, the CRF-R mRNA signal was positive in the dorsomedial parvocellular PVN 3 hr after LPS injection, strong and maximum in both parvo- and magno-PVN at 6 hr postinjection, and declined 9 and 12 hr after treatment. Similarly, 90 min and 3 hr after the immobilization session, mRNA encoding the CRF-R was highly expressed in the parvo-PVN and totally vanished 12 hr after the stress. A lower but significant increase in the CRF-R transcript signal was also observed in the supraoptic nucleus 6 hr after the LPS treatment.
Distribution of the excitatory amino acid receptor subunits GluR2(4) in monkey hippocampus and colocalization with subunits GluR5-7 and NMDAR1
Authors: Siegel SJ , Janssen WG , Tullai JW , Rogers SW , Moran T , Heinemann SF , Morrison JH
Published: April 2018

Ionotropic excitatory amino acid (EAA) receptors are divided pharmacologically into three categories termed NMDA, AMPA/kainate, and high affinity kainate receptors. Each of these receptor subtypes is composed of a specific subset of subunits termed GluR1–4 (AMPA/kainate), GluR5–7, KA1–2 (high affinity kainate), and NMDAR1, 2 A- D (NMDA). Although colocalization of NMDA and non-NMDA receptors has been previously demonstrated electrophysiologically in rat, comprehensive analyses of subunit specific colocalization patterns have not been possible until the advent of appropriate antibodies. The present study investigates such immunocytochemical colocalization of several EAA receptor subunits within individual cells as well as dendritic spines in the monkey hippocampus. Double-label immunohistochemical experiments using antibodies which are specific for GluR2(4), GluR5–7, and NMDAR1 demonstrated that virtually all projection neurons in each subfield of the hippocampus contain subunits from the AMPA/kainate, kainate, and NMDA receptor families. In addition, confocal microscopy has demonstrated that individual spines may contain subunits representative of multiple EAA receptor families. Furthermore, detailed regional, cellular, and ultrastructural distribution patterns of the EAA receptor subunits GluR2 and GluR4 in monkey hippocampus are presented based on the use of a monoclonal antibody (mAb), 3A11, which was generated against the putative extracellular N-terminal domain of GluR2. Since this antibody recognizes only GluR2 in Western blots, and GluR2 as well as GluR4 in fixed transiently transfected cells, it has been designated anti- GluR2(4). Immunocytochemical labeling with mAb 3A11 revealed pyramidal cell somata and dendrites in each field of the hippocampus, as well as granule cells and polymorphic hilar cells in the dentate gyrus. Small cells with the morphologic characteristics of astroglia were also immunolabeled for GluR2(4) within the alveus and fimbria. Immunoreactivity at the ultrastructural level was localized to postsynaptic densities on dendritic spines and shafts and within the somatodendritic cytoplasm in all major hippocampal regions, as well as in a subset of dentate granule cell axons within the mossy fiber projection.
Complementary distribution of receptors for neurotensin and NPY in small neurons in rat lumbar DRGs and regulation of the receptors and peptides after peripheral axotomy
Authors: Zhang X , Xu ZQ , Bao L , Dagerlind A , Hokfelt T
Published: April 2018

Neurotensin (NT) has been reported to have antinociceptive effects at the spinal level. In situ hybridization, electrophysiology, immunohistochemistry, and electronmicroscopy were used to investigate the distribution of NT receptors, possible effects of NT on primary sensory neurons, and the effect of nerve injury on the expression of NT receptors and NT. NT receptor (R) mRNA was observed in more than 25% of the small dorsal root ganglion (DRG) neurons, which lacked neuropeptide Y NPY-R mRNA and essentially other neuropeptide mRNAs. Intracellular recording using voltage-clamp mode showed that NT evokes an outward current in NPY-insensitive small neurons, and NPY an outward current in NT-insensitive small neurons. Both peptides lacked effect on several small DRG neurons. In the superficial dorsal horn NT immunoreactive (IR) terminals directly contacted primary afferent terminals without synaptic specializations. This new category (> 25%) of the small DRG neurons expressing NT-R mRNA was complementary to the around 60% of small neurons expressing NPY-R mRNA (and also substance P and calcitonin gene-related peptide mRNAs) and to the rest exhibiting somatostatin mRNA expression. The electrophysiological results support this classification, showing that NT and NPY have inhibitory effects on separate subpopulations of small DRG neurons. After sciatic nerve transection, a marked decrease was observed in (1) the number of NT-R mRNA-positive neurons in DRGs, (2) NT mRNA-positive neurons in the dorsal horn, and (3) NT-IR cell bodies and fibers in laminae I-II. Thus, axotomy causes downregulation of several NT systems at the spinal level, suggesting that the possible effects of NT on primary sensory neurons is attenuated after peripheral axotomy.
Magnetic and electric brain activity evoked by the processing of tone and vowel stimuli
Authors: Eulitz C , Diesch E , Pantev C , Hampson S , Elbert T
Published: April 2018

Sustained magnetic and electric brain waves may reflect linguistic processing when elicited by auditory speech stimuli. In the present study, only in the latency interval subsequent to the N1m/N1 has a sensitivity of brain responses to features of speech been demonstrated. We conclude this from studying the auditory-evoked magnetic field (AEF) and the corresponding evoked potential (AEP) in response to vowels and a tone. Brain activity was recorded from the left and the right hemisphere of 11 subjects. Three aspects of transient activity were examined: (1) the amplitudes and source characteristics of the N1m component of the AEF; (2) the amplitudes and source characteristics of the sustained field (SF), and (3) the corresponding amplitude characteristics of the AEP. Sustained potential amplitudes and SF root mean square amplitudes, as well as the dipole strength of the SF source, were found to be larger for vowel-evoked signals than for signals elicited by the tone stimulus. The amplitude and dipole strength effects had an interaction with hemisphere, with larger interhemispheric differences for the vowel condition, as well as larger tone-vowel differences of these parameters in the speech-dominant left hemisphere. No statistically significant hemisphere-by-stimulus-type interactions were found in N1/N1m amplitudes and N1m source parameters.
Increased collateral sprouting of primary afferents in the myelin-free spinal cord
Authors: Schwegler G , Schwab ME , Kapfhammer JP
Published: April 2018

After partial lesions, uninjured nerve fibers have been shown to sprout and expand their connections within the CNS of adult mammals. The extent of this anatomical plasticity in adults is rather limited in comparison to embryonic or neonatal animals. Factors that might limit sprouting of nerve fibers and suppress anatomical plasticity in the CNS include myelin-associated neurite growth inhibitory molecules present in the CNS of adult mammals. To examine further the role of these neurite growth inhibitors, we have studied the ability of primary afferent fibers to sprout in the absence of myelin within a partially deafferented spinal cord. Myelination was suppressed in the lower thoracic and lumbar spinal cord of rats using neonatal x-irradiation. Dorsal roots of lumbar segments L2-L4 were cut in myelin-free and normal spinal cords of 8- or 15-d-old rats. Sprouting of primary afferents was measured after 20 d using thiamine monophosphatase (TMP) histochemistry. TMP is a specific marker enzyme for small-diameter primary afferents that terminate in the substantia gelatinosa (lamina II) of the spinal cord. When compared to the control groups, collateral sprouting of TMP-positive afferents was significantly enhanced in the myelin-free spinal cords: in animals deafferented at postnatal day P8, the average volume occupied by sprouting fibers in the upper dorsal horn was 0.103 mm3 +/- 0.008 (mean +/- SEM) in myelin-free spinal cords and 0.044 mm3 +/- 0.011 in control spinal cords. In spinal cords deafferented at P15, this difference was even larger, with 0.106 mm3 +/- 0.010 in the absence of myelin and 0.031 mm3 +/- 0.010 in controls. Our results indicate that myelin and its associated neurite growth inhibitors restrict collateral sprouting. These data provide further evidence that CNS myelin and its associated neurite growth inhibitors are involved in the regulation of anatomical plasticity in the normal CNS.
A critical band filter in touch
Authors: Makous JC , Friedman RM , Vierck CJ
Published: April 2018

Separate mechanoreceptor systems in humans were isolated by varying the spectra of vibrotactile stimuli. First, the function relating threshold to frequency of a sinusoid was obtained on the fingertip for each of four subjects, and it was found to comprise two limbs: a Pacinian and a non-Pacinian limb. The peak sensitivity within the Pacinian limb (mediated by Pacinian corpuscles) was around 250 Hz and spanned the region from 65 to 400 Hz. The non-Pacinian limb showed no detectable change in sensitivity in the region between 10 and 65 Hz. These two limbs were then treated as psychophysical channels in experiments in which narrow band noise and individual sinusoids were used to excite one or both channels. In the second and third experiments, the noise stimuli varied in bandwidth from 8 to 70 Hz and varied in center frequency from 25 to 218 Hz. Masking functions were obtained for ON- frequency conditions (the sinusoidal test and noise masker occupied the same frequency region) and for OFF-frequency conditions (the test and masker occupied different frequency regions). The ON-frequency experiments were used to estimate the signal-to-noise ratio (S/N) of the Pacinian channel at threshold. The OFF-frequency masking experiments were used to infer the shape of the Pacinian channel at frequencies below 65 Hz, where thresholds for Pacinian activation were above detection threshold. The results of these three experiments predicted the findings of a fourth masking experiment with a parameter free model that treated the Pacinian channel as a filter that integrates stimulus power. The results show that the Pacinian channel is analogous to a critical band in the auditory system.
N-acetylcysteine (D- and L-stereoisomers) prevents apoptotic death of neuronal cells
Authors: Ferrari G , Yan CY , Greene LA
Published: April 2018

In the present study we tested whether N-acetyl-L-cysteine (LNAC) affects apoptotic death of neuronal cells caused by trophic factor deprivation. LNAC, an antioxidant, elevates intracellular levels of glutathione. We used serum-deprived PC12 cells, neuronally differentiated PC12 cells deprived of serum and NGF, and NGF-deprived neonatal sympathetic neurons. In each case LNAC prevents apoptotic DNA fragmentation and maintains long-term survival in the absence of other trophic support. Unlike NGF, LNAC does not induce or maintain neurite outgrowth or somatic hypertrophy. To rule out actions of LNAC metabolic derivatives, we assessed N-acetyl-D-cysteine (DNAC). DNAC also prevents death of PC12 cells and sympathetic neurons. However, other antioxidants were ineffective in this regard. Since it has been hypothesized that trophic factors prevent neuronal death by either preventing or coordinating cell cycle progression, we tested whether LNAC or DNAC treatment can affect cell cycle. We found that both (but not other antioxidants) suppress proliferation and DNA synthesis by PC12 cells and do so at concentrations similar to those at which they prevent apoptotic death. Although the abilities of LNAC and DNAC to rescue cells from apoptosis triggered by trophic factor deprivation could derive from their direct influences on cellular responsiveness to oxidative stress, our observations raise the possibility of a mechanism involving cell cycle regulation.
Cellular localization of thrombin receptor mRNA in rat brain: expression by mesencephalic dopaminergic neurons and codistribution with prothrombin mRNA
Authors: Weinstein JR , Gold SJ , Cunningham DD , Gall CM
Published: April 2018

Cell culture studies demonstrating that the serine protease thrombin can induce neuronal and glial process retraction, glial proliferation, and changes in gene expression suggest a role for thrombin in CNS development, plasticity, and response to injury. Most cellular responses to thrombin are mediated by proteolytic activation of the cloned thrombin receptor (TR), a member of the seven transmembrane domain, G-protein-coupled receptor superfamily. As a step toward understanding the role of thrombin and its receptor in the CNS, Northern blot, in situ hybridization, and immunohistochemical techniques were used to analyze the cellular localization of TR mRNA in weanling-age rat brain. TR mRNA was broadly distributed across the neuraxis, although expression was very focal and often anatomically limited within specific neural structures. The greatest hybridization was associated with individual neurons in neocortex, cingulate/retrosplenial cortex, and subiculum, subsets of nuclei in hypothalamus, thalamus, pretectum, and ventral mesencephalon, and discrete cell layers in the hippocampus, cerebellum, and olfactory bulb. Patterns of hybridization included neuronal, glial, and ependymal cells, although white matter was uniformly negative, as were most cerebrovascular endothelial cells. Expression of TR mRNA by astroglia and dopaminergic neurons was confirmed by colocalization with immunoreactivity for glial fibrillary acidic protein (GFAP) in hippocampus and tyrosine hydroxylase in the substantia nigra. Comparison between TR and prothrombin (thrombin's precursor) cRNA hybridization demonstrated distinct but overlapping brain distributions of these transcripts, most clearly evident in postnatally developing, laminated structures. These results suggest widespread utilization of, and multiple physiologic, and possibly pathophysiologic, functions for, the thrombin/TR cell signaling system in the CNS.
Effect of bacterial endotoxin and interleukin-1 beta on hippocampal serotonergic neurotransmission, behavioral activity, and free corticosterone levels: an in vivo microdialysis study
Authors: Linthorst AC , Flachskamm C , Muller-Preuss P , Holsboer F , Reul JM
Published: April 2018

In this study the effect of immune system stimulation and intracerebroventricular (i.c.v.) administration of interleukin-1 beta (IL-1 beta) on hippocampal serotonergic neurotransmission, behavioral activity, and the hypothalamic-pituitary-adrenocortical (HPA) axis is described. An in vivo microdialysis method was used to measure hippocampal extracellular concentrations of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in conscious, freely moving rats. In addition, we established a method to continuously monitor free corticosterone levels in dialysates. Behavioral activity was scored by measuring the time during which rats were active (locomotion, grooming, eating, drinking). We found a significant, positive relationship between behavioral activity and hippocampal extracellular concentrations of 5-HT. Intraperitoneal (i.p.) administration of the bacterial endotoxin lipopolysaccharide (LPS; 30, 100, and 300 micrograms/kg body weight) produced an increase in the extracellular concentrations of 5-HT and 5-HIAA in the hippocampus, which was paralleled by a significant decline in behavioral activity and a marked increase in extracellular corticosterone levels. Thus, the close correlation between hippocampal extracellular 5-HT levels and behavioral activity observed in control rats was disrupted in the LPS- treated animals. The effects of i.p. LPS could be mimicked by i.c.v. application of recombinant human IL-1 beta (hIL-1 beta; 100 ng). i.c.v. pretreatment with the IL-1 receptor antagonist (IL-1ra; 10 micrograms) antagonized the hIL-1 beta-induced effects. IL-1ra showed no intrinsic effects. Furthermore, it was found that i.c.v. pretreatment with IL-1ra (10 micrograms) significantly attenuated the i.p. LPS-induced (100 micrograms/kg body weight) rise in hippocampal extracellular 5-HT levels.