bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of PlasticityIn VivoandIn Vitroin the Developing Visual Cortex of Normal and Protein Kinase A RIβ-Deficient Mice
Authors: Hensch Takao K. , Gordon Joshua A. , Brandon Eugene P. , McKnight G. Stanley , Idzerda Rejean L. , Stryker Michael P.
Published: April 2018

Developing sensory systems are sculpted by an activity-dependent strengthening and weakening of connections. Long-term potentiation (LTP) and depression (LTD)in vitrohave been proposed to model this experience-dependent circuit refinement. We directly compared LTP and LTD inductionin vitrowith plasticityin vivoin the developing visual cortex of a mouse mutant of protein kinase A (PKA), a key enzyme implicated in the plasticity of a diverse array of systems.

In mice lacking the RIβ regulatory subunit of PKA, we observed three abnormalities of synaptic plasticity in layer II/III of visual cortexin vitro. These included an absence of (1) extracellularly recorded LTP, (2) depotentiation or LTD, and (3) paired-pulse facilitation. Potentiation was induced, however, by pairing low-frequency stimulation with direct depolarization of individual mutant pyramidal cells. Together these findings suggest that the LTP defect in slices lacking PKA RIβ lies in the transmission of sufficient net excitation through the cortical circuit.

Nonetheless, functional development and plasticity of visual cortical responsesin vivoafter monocular deprivation did not differ from normal. Moreover, the loss of all responsiveness to stimulation of the originally deprived eye in most cortical cells could be restored by reverse suture of eyelids during the critical period in both wild-type and mutant mice. Such an activity-dependent increase in response would seem to require a mechanism like potentiationin vivo. Thus, the RIβ isoform of PKA is not essential for ocular dominance plasticity, which can proceed despite defects in several commonin vitromodels of neural plasticity.
Temporal Cortex Activation in Humans Viewing Eye and Mouth Movements
Authors: Puce Aina , Allison Truett , Bentin Shlomo , Gore John C. , McCarthy Gregory
Published: April 2018

We sought to determine whether regions of extrastriate visual cortex could be activated in subjects viewing eye and mouth movements that occurred within a stationary face. Eleven subjects participated in three to five functional magnetic resonance imaging sessions in which they viewed moving eyes, moving mouths, or movements of check patterns that occurred in the same spatial location as the eyes or mouth. In each task, the stimuli were superimposed on a radial background pattern that continually moved inward to control for the effect of movement per se. Activation evoked by the radial background was assessed in a separate control task. Moving eyes and mouths activated a bilateral region centered in the posterior superior temporal sulcus (STS). The moving check patterns did not appreciably activate the STS or surrounding regions. The activation by moving eyes and mouths was distinct from that elicited by the moving radial background, which primarily activated the posterior-temporal-occipital fossa and the lateral occipital sulcus—a region corresponding to area MT/V5. Area MT/V5 was also strongly activated by moving eyes and to a lesser extent by other moving stimuli. These results suggest that a superior temporal region centered in the STS is preferentially involved in the perception of gaze direction and mouth movements. This region of the STS may be functionally related to nearby superior temporal regions thought to be involved in lip-reading and in the perception of hand and body movement.
Neuromodulatory Inputs Maintain Expression of a Lobster Motor Pattern-Generating Network in a Modulation-Dependent State: Evidence from Long-Term DecentralizationIn Vitro
Authors: Thoby-Brisson Muriel , Simmers John
Published: April 2018

Neuromodulatory inputs play a critical role in governing the expression of rhythmic motor output by the pyloric network in the crustacean stomatogastric ganglion (STG). When these inputs are removed by cutting the primarily afferent stomatogastric nerve (stn) to the STG, pyloric neurons rapidly lose their ability to burst spontaneously, and the network falls silent. By using extracellular motor nerve recordings from long-term organotypic preparations of the stomatogastric nervous system of the lobsterJasus lalandii, we are investigating whether modulatory inputs exert long-term regulatory influences on the pyloric network operation in addition to relatively short-term neuromodulation. When decentralized (stn cut), quiescent STGs are maintained in organ culture, pyloric rhythmicity gradually returns within 3–5 d and is similar to, albeit slower than, the triphasic motor pattern expressed when the stn is intact. This recovery of network activity still occurred after photoinactivation of axotomized input terminals in the isolated STG after migration of Lucifer yellow. The recovery does not depend on action potential generation, because it also occurred in STGs maintained in TTX-containing saline after decentralization. Resumption of rhythmicity was also not activity-dependent, because recovery still occurred in STGs that were chronically depolarized with elevated K+saline or were maintained continuously active with the muscarinic agonist oxotremorine after decentralization. We conclude that the prolonged absence of extraganglionic modulatory inputs to the pyloric network allows expression of an inherent rhythmogenic capability that is normally maintained in a strictly conditional state when these extrinsic influences are present.
Genetic Dissection of Functional Contributions of Specific Potassium Channel Subunits in Habituation of an Escape Circuit inDrosophila
Authors: Engel Jeff E. , Wu Chun-Fang
Published: April 2018

Potassium channels have been implicated in central roles in activity-dependent neural plasticity. The giant fiber escape pathway ofDrosophilahas been established as a model for analyzing habituation and its modification by memory mutations in an identified circuit. Several genes inDrosophilaencoding K+channel subunits have been characterized, permitting examination of the contributions of specific channel subunits to simple conditioning in an identified circuit that is amenable to genetic analysis. Our results show that mutations altering each of four K+channel subunits (Sh,slo,eag, andHk) have distinct effects on habituation at least as strong as those ofdunceandrutabaga, memory mutants with defective cAMP metabolism (Engel and Wu, 1996). Habituation, spontaneous recovery, and dishabituation of the electrically stimulated long-latency giant fiber pathway response were shown in each mutant type. Mutations ofSh(voltage-gated) andslo(Ca2+-gated) subunits enhanced and slowed habituation, respectively. However, mutations ofeagandHksubunits, which confer K+-current modulation, had even more extreme phenotypes, again enhancing and slowing habituation, respectively. In double mutants,Shmutations moderated the strong phenotypes ofeagandHk, suggesting that their modulatory functions are best expressed in the presence of intactShsubunits. Nonactivity-dependent responses (refractory period and latency) at two stages of the circuit were altered only in some mutants and do not account for modifications of habituation. Furthermore, failures of the long-latency response during habituation, which normally occur in labile connections in the brain, could be induced in the thoracic circuit stage inHkmutants. Our work indicates that different K+channel subunits play distinct roles in activity-dependent neural plasticity and thus can be incorporated along with second messenger “memory” loci to enrich the genetic analysis of learning and memory.
N- and P/Q-Type Ca2+Channels Mediate Transmitter Release with a Similar Cooperativity at Rat Hippocampal Autapses
Authors: Reid Christopher A. , Bekkers John M. , Clements John D.
Published: April 2018

The relationship between extracellular Ca2+concentration and EPSC amplitude was investigated at excitatory autapses on cultured hippocampal neurons. This relationship was steeply nonlinear, implicating the cooperative involvement of several Ca2+ions in the release of each vesicle of transmitter. The cooperativity was estimated to be 3.1 using a power function fit and 3.3 using a Hill equation fit. However, simulations suggest that these values underestimate the true cooperativity. The role of different Ca2+channel subtypes in shaping the Ca2+dose–response relationship was studied using the selective Ca2+channel blockers ω-agatoxin GIVA (ω-Aga), which blocks P/Q-type channels, and ω-conotoxin GVIA (ω-CTx), which blocks N-type channels. Both blockers broadened the dose–response relationship, and the Hill coefficient was reduced to 2.5 by ω-Aga and to 2.6 by ω-CTx. This broadening is consistent with a nonuniform distribution of Ca2+channel subtypes across presynaptic terminals. The similar Hill coefficients in ω-Aga or ω-CTx suggest that there was no difference in the degree of cooperativity for transmitter release mediated via N- or P/Q-type Ca2+channels. A model of the role of calcium in transmitter release is developed. It is based on a modified Dodge–Rahamimoff equation that includes a nonlinear relationship between extracellular and intracellular Ca2+concentration, has a cooperativity of 4, and incorporates a nonuniform distribution of Ca2+channel subtypes across presynaptic terminals. The model predictions are consistent with all of the results reported in this study.
Contributions of the Optic Tectum and the Retina as Sources of Brain-Derived Neurotrophic Factor for Retinal Ganglion Cells in the Chick Embryo
Authors: Herzog Karl-Heinz , von Bartheld Christopher S.
Published: April 2018

Retinal ganglion cells (RGC) are supported by brain-derived neurotrophic factor (BDNF), but it is not known if BDNF acts as a target-derived factor or as an afferent or autocrine trophic factor. Here we demonstrate that BDNF mRNA is expressed in the retinorecipient layer of the chick optic tectum as well as in the inner nuclear layer and ganglion cell layer of the retina. Amacrine cells rather than RGC were the main source of BDNF mRNA in the ganglion cell layer, as determined byin situhybridization that was combined with retrograde labeling of RGC and destruction of RGC by optic stalk transection, followed by quantitative RT-PCR. Cells in the ganglion cell layer as well as the retinorecipient layers of the optic tectum were BDNF-immunolabeled. After injections into the tectum, radio-iodinated BDNF was transported to the retina where autoradiographic label accumulated in the inner plexiform and ganglion cell layers. After intraocular injection, iodinated BDNF accumulated in these same retinal layers and correlated with the distribution of p75 neurotrophin receptor protein. The majority of cross-linked receptor-bound BDNF in the retina immunoprecipitated with p75 antibodies. No difference in the intensity of BDNF immunolabel was observed in the experimental retina or tectum after optic stalk transection, indicating that most of the BDNF in the RGC was not derived from the optic tectum. These data indicate that a substantial fraction of the BDNF in the ganglion cell layer is derived from local sources, afferents within the retina, rather than from the optic tectum via retrograde transport.
Evidence for a Tetrameric Structure of Recombinant NMDA Receptors
Authors: Laube Bodo , Kuhse Jochen , Betz Heinrich
Published: April 2018

The amino acidsl-glutamate and glycine are essential agonists of the excitatory NMDA receptor, a subtype of the ionotropic glutamate receptor family. The native NMDA receptor is composed of two types of homologous membrane-spanning subunits, NR1 and NR2. Here, the numbers of glycine-binding NR1 and glutamate-binding NR2 subunits in the NMDA receptor hetero-oligomer were determined by coexpressing the wild-type (wt) NR1 with the low-affinity mutant NR1Q387K, and the wt NR2B with the low-affinity mutant NR2BE387A, subunits inXenopusoocytes. In both cases, analysis of the resulting dose–response curves revealed three independent components of glycine and glutamate sensitivity. These correspond to the respective wild-type and mutant affinities and an additional intermediate hybrid affinity, indicating the existence of three discrete receptor populations. Binomial analysis of these data indicates the presence of two glycine and two glutamate binding subunits in the functional receptor. In addition, we analyzed the inhibitory effects of the negative dominant NR1R505Kand NR2BR493Kmutants on maximal inducible whole-cell currents of wt NR1/NR2B receptors. The inhibition profiles obtained on expression of increasing amounts of these mutant proteins again were fitted best by assuming an incorporation of two NR1 and two NR2 subunits into the receptor hetero-oligomer. Our data are consistent with NMDA receptors being tetrameric proteins that are composed of four homologous subunits.
Phase Shifting of Circadian Rhythms and Depression of Neuronal Activity in the Rat Suprachiasmatic Nucleus by Neuropeptide Y: Mediation by Different Receptor Subtypes
Authors: Gribkoff Valentin K. , Pieschl Rick L. , Wisialowski Todd A. , van den Pol Anthony N. , Yocca Frank D.
Published: April 2018

Neuropeptide Y (NPY) has been implicated in the phase shifting of circadian rhythms in the hypothalamic suprachiasmatic nucleus (SCN). Using long-term, multiple-neuron recordings, we examined the direct effects and phase-shifting properties of NPY application in rat SCN slicesin vitro(n= 453). Application of NPY and peptide YY to SCN slices at circadian time (CT) 7.5–8.5 produced concentration-dependent, reversible inhibition of cell firing and a subsequent significant phase advance. Several lines of evidence indicated that these two effects of NPY were mediated by different receptors. NPY-induced inhibition and phase shifting had different concentration–response relationships and very different phase–response relationships. NPY-induced phase advances, but not inhibition, were blocked by the GABAAantagonist bicuculline, suggesting that NPY-mediated modulation of GABA may be an underlying mechanism whereby NPY phase shifts the circadian clock. Application of the Y2 receptor agonists NPY 13–36 and (Cys2,8-aminooctanoic acid5,24,d-Cys27)-NPY advanced the peak of the circadian rhythm but did not inhibit cell firing. The Y1 and Y5 agonist [Leu31,Pro34]-NPY evoked a substantial inhibition of discharge but did not generate a phase shift. NPY-induced inhibition was not blocked by the specific Y1 antagonist BIBP-3226; the antagonist also had no effect on the timing of the peak of the circadian rhythm. Application of the Y5 agonist [d-Trp32]-NPY produced only direct neuronal inhibition. These are the first data to indicate that at least two functional populations of NPY receptors exist in the SCN, distinguishable on the basis of pharmacology, each mediating a different physiological response to NPY application.
Localization of Genes Mediating Acute and Sensitized Locomotor Responses to Cocaine in BXD/Ty Recombinant Inbred Mice
Authors: Phillips Tamara J. , Huson Mary G. , McKinnon Carrie S.
Published: April 2018

Sensitization to the psychostimulant effects of cocaine has received widespread attention because concomitant changes occur in neurochemical pathways that are part of the brain reward pathway. The current study was undertaken with the purpose of mapping genes determining sensitivity to the acute stimulant and sensitizing effects of cocaine. Sensitivity and sensitization to cocaine (5, 10, and 40 mg/kg) were measured in 25 BXD/Ty recombinant inbred (BXD RI) strains and the progenitor C57BL/6J (B6) and DBA/2J (D2) strains. Quantitative trait locus (QTL) mapping provisionally localized cocaine sensitivity genes to regions on all chromosomes except 6, 11, 17, and X; sensitization QTLs were localized to chromosomes 1–10, 13, 15, 18, 19, and X. Provisional QTLs for locomotion after saline injection in a novel setting were mapped to chromosomes 1, 3–6, 9, 12, 13, 18, and 19 and in a familiar setting to chromosomes 4–7, 9, 13, and 19. There were both common and unique QTL regions across the phenotypes. Evidence for a genetic association between magnitude of acute cocaine response and sensitization was obtained for only the 10 mg/kg dose. Some common QTL regions for cocaine, ethanol, and methamphetamine responses suggest the possibility that these drugs induce stimulant effects or sensitization through some common mechanisms. However, independent mechanisms were also indicated. Many candidate genes reside near the provisional QTLs mapped for cocaine responses, including genes coding a variety of neurotransmitter and hormone receptors. These data, once confirmed, should prove useful for directing investigations of acute and chronic cocaine effects down already suspected and novel avenues.
Vagotomy-Induced Enhancement of Mechanical Hyperalgesia in the Rat Is Sympathoadrenal-Mediated
Authors: Khasar Sachia G. , Miao Frederick J.-P. , Jänig Wilfrid , Levine Jon D.
Published: April 2018

We have recently shown that subdiaphragmatic vagotomy enhances bradykinin-induced hyperalgesic behavior and decreases baseline paw withdrawal threshold to mechanical stimulation of the hindpaw skin in rats by a peripheral mechanism. To elucidate the underlying mechanism, we studied whether lesions of efferent neuroendocrine pathways could prevent or reverse the potentiating effect of vagotomy. In groups of sham-vagotomized or vagotomized rats, we surgically removed or denervated the adrenal medulla. Bradykinin was injected intradermally into the skin of the dorsal surface of the rat hindpaw. Threshold of paw withdrawal to mechanical stimulation of the skin was measured.

Vagotomy induced a decrease in mechanical baseline paw withdrawal threshold and enhancement of bradykinin-induced mechanical hyperalgesic behavior, both of which were maintained over the 5 week testing period. Adrenal enucleation or denervation of the adrenal gland by suprarenal ganglionectomy prevented vagotomy-induced decrease in baseline paw withdrawal threshold and enhancement of bradykinin-induced hyperalgesia. In animals that had a demonstrated decrease in baseline paw withdrawal threshold and enhancement of bradykinin-induced hyperalgesia 2 weeks after vagotomy, additional denervation of the adrenal medulla significantly reversed these effects over a 3 week period.

These results imply that both the decrease in baseline paw withdrawal threshold and enhancement of bradykinin-induced hyperalgesic behavior after vagotomy are dependent on a hormonal signal released from the adrenal medulla and suggest a novel mechanism of sensitization of cutaneous nociceptors.
Rats with Fimbria–Fornix Lesions Are Impaired in Path Integration: A Role for the Hippocampus in “Sense of Direction”
Authors: Whishaw Ian Q. , Maaswinkel Hans
Published: April 2018

Animals can locate their present position in relation to a starting point and return to that starting point using cues generated by self-movement, a navigation strategy called dead-reckoning. Because contemporary research on spatial navigation suggests that some aspects of spatial navigation depend on the integrity of the hippocampal formation, whereas others do not, the present study examined whether dead-reckoning is hippocampally dependent. The task capitalized on the proclivity of foraging rats to carry large food pellets to a shelter for eating. Control rats and rats with fimbria–fornix (FF) lesions left a hidden burrow to search for one piece of food located somewhere on a circular table. The accuracy with which they returned to the burrow with the food was measured. In three experiments, rats received probe trials in which they (1) started from novel locations, (2) wore blindfolds to obscure visual cues, and (3) foraged under a condition in which surface cues, e.g., odors left by their outward searches, were displaced. Both sighted control and FF rats preferentially used visual cues for guidance when foraging from a familiar location. Control rats were accurate and FF rats were impaired in returning to novel starting locations (1) when sighted, (2) when blindfolded, and (3) when blindfolded in tests in which surface cues were displaced. These results, as well as detailed observations on the behavior of the animals, are consistent with the hypothesis that rats can use dead-reckoning to solve spatial problems, and this ability depends on the integrity of the hippocampal formation.
Comparison of Mesocorticolimbic Neuronal Responses During Cocaine and Heroin Self-Administration in Freely Moving Rats
Authors: Chang Jing-Yu , Janak Patricia H. , Woodward Donald J.
Published: April 2018

To compare neuronal activity within the mesocorticolimbic circuit during the self-administration of cocaine and heroin, multiple-channel single-unit recordings of spike activity within the rat medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) were obtained during the consecutive self-administration of cocaine and heroin within the same session. The variety of neuronal responses observed before the lever press are termed anticipatory responses, and those observed after the lever press are called post-drug infusion responses. For the total of the 110 mPFC and 111 NAc neurons recorded, 30–50% of neurons, depending on the individual sessions, had no alteration in spike activity in relation to either cocaine or heroin self-administration. Among the neurons exhibiting significant neuronal responses during a self-administration session, only a small portion (16–25%) of neurons responded similarly under both reinforcement conditions; the majority of neurons (75–84%) responded differently to cocaine and heroin self-administration as revealed by variations in both anticipatory and/or post-drug infusion responses. A detailed video analysis of specific movements to obtain the self-administration of both drugs provided evidence against the possibility that locomotive differences contributed to the observed differences in anticipatory responses. The overall mean activity of neurons recorded in mPFC and NAc measured across the duration of the session segment for either cocaine or heroin self-administration also was different for some neurons under the two reinforcement conditions. This study provides direct evidence that, in mPFC and NAc, heterogeneous neuronal circuits mediate cocaine and heroin self-administration and that distinct, but overlapping, subpopulations of neurons in these areas become active during operant responding for different reinforcers.
Calcium-Dependent Regulation of Rab3 in Short-Term Plasticity
Authors: Doussau Frédéric , Clabecq Aude , Henry Jean-Pierre , Darchen François , Poulain Bernard
Published: April 2018

The Rab3 proteins are monomeric GTP-binding proteins associated with secretory vesicles. In their active GTP-bound state, Rab3 proteins are involved in the regulation of hormone secretion and neurotransmitter release. This action is thought to involve specific effectors, including two Ca2+-binding proteins, Rabphilin and Rim. Rab3 acts late in the exocytotic process, in a cell domain in which the intracellular Ca2+concentration is susceptible to rapid changes. Therefore, we examined the possible Ca2+-dependency of the regulatory action of GTP-bound Rab3 and wild-type Rab3 on neuroexocytosis at identified cholinergic synapses inAplysia californica. The effects of recombinant GTPase-deficientAplysia-Rab3 (apRab3-Q80L) or wild-type apRab3 were studied on evoked acetylcholine release. Intraneuronal application of apRab3-Q80L in identified neurons of the buccal ganglion ofAplysialed to inhibition of neurotransmission; wild-type apRab3 was less effective. Intracellular chelation of Ca2+ions by EGTA greatly potentiated the inhibitory action of apRab3-Q80L. Train and paired-pulse facilitation, two Ca2+-dependent forms of short-term plasticity induced by a rise in intraterminal Ca2+concentration, were increased after injection of apRab3-Q80L. This result suggests that the inhibition exerted by GTP-bound Rab3 on neuroexocytosis is reduced during transient augmentations of intracellular Ca2+concentration. Therefore, a Ca2+-dependent modulation of GTP-bound Rab3 function may contribute to short-term plasticity.
Type I Adenylyl Cyclase Mutant Mice Have Impaired Mossy Fiber Long-Term Potentiation
Authors: Villacres Enrique C. , Wong Scott T. , Chavkin Charles , Storm Daniel R.
Published: April 2018

Long-term potentiation (LTP) at the mossy fiber→CA3 pyramidal cell synapse in the hippocampus is an NMDA-independent form of LTP that requires cAMP-dependent protein kinase (PKA) activity and can be induced by forskolin, a general activator of adenylyl cyclases. Presynaptic Ca2+influx and elevated cAMP may be obligatory for mossy fiber LTP. Because the Ca2+-stimulated type 1 adenylyl cyclase (AC1) is expressed in the dentate gyrus and CA3 pyramidal cells, it is hypothesized that AC1 may be critical for mossy fiber LTP. To test this hypothesis, we examined several forms of hippocampal LTP in wild-type and AC1 mutant mice. Wild-type and AC1 mutant mice exhibited comparable perforant path LTP recorded in the dentate gyrus as well as decremental LTP at the Schaffer collateral→CA1 pyramidal cell synapse. Although the mutant mice exhibited normal paired pulse facilitation, mossy fiber LTP was impaired significantly in AC1 mutants. High concentrations of forskolin induced mossy fiber LTP to comparable levels in wild-type and AC1 mutant mice, indicating that signaling components downstream from the adenylyl cyclase, including PKA, ion channels, and secretory machinery, were not affected by disruption of the AC1 gene. These data indicate that coupling of Ca2+to activation of AC1 is crucial for mossy fiber LTP, most likely via activation of PKA and enhancement of excitatory amino acid secretion.
Experience-Induced Neurogenesis in the Senescent Dentate Gyrus
Authors: Kempermann Gerd , Kuhn H. Georg , Gage Fred H.
Published: April 2018

We demonstrate here that under physiological conditions neurogenesis continues to occur in the dentate gyrus of senescent mice and can be stimulated by living in an enriched environment. Neurogenesis was investigated by confocal microscopy of three-channel immunofluorescent staining for the proliferation marker bromodeoxyuridine (BrdU) and neuronal and glial markers. Quantification was performed with unbiased stereological counting techniques. Neurogenesis decreased with increasing age. Stimulation of adult and aged mice by switching from standard housing to an enriched environment with opportunities for social interaction, exploration, and physical activity for 68 d resulted in an increased survival of labeled cells. Phenotypic analysis revealed that, in enriched living animals, relatively more cells differentiated into neurons, resulting in a threefold net increase of BrdU-labeled neurons in 20-month-old mice (105 vs 32 cells) and a more than twofold increase in 8-month-old mice (684 vs 285 cells) compared with littermates living under standard laboratory conditions. Corresponding absolute numbers of BrdU-positive astrocytes and BrdU-positive cells that did not show colabeling for neuronal or glial markers were not influenced. The effect on the relative distribution of phenotypes can be interpreted as a survival-promoting effect that is selective for neurons. Proliferation of progenitor cells appeared unaffected by environmental stimulation.
Stable Complexes Involving Acetylcholinesterase and Amyloid-β Peptide Change the Biochemical Properties of the Enzyme and Increase the Neurotoxicity of Alzheimer’s Fibrils
Authors: Alvarez Alejandra , Alarcón Rodrigo , Opazo Carlos , Campos Eliseo O. , Muñoz Francisco José , Calderón Frances H. , Dajas Federico , Gentry Mary K. , Doctor Bhupendra P. , De Mello Fernando G. , Inestrosa Nibaldo C.
Published: April 2018

Brain acetylcholinesterase (AChE) forms stable complexes with amyloid-β peptide (Aβ) during its assembly into filaments, in agreement with its colocalization with the Aβ deposits of Alzheimer’s brain. The association of the enzyme with nascent Aβ aggregates occurs as early as after 30 min of incubation. Analysis of the catalytic activity of the AChE incorporated into these complexes shows an anomalous behavior reminiscent of the AChE associated with senile plaques, which includes a resistance to low pH, high substrate concentrations, and lower sensitivity to AChE inhibitors. Furthermore, the toxicity of the AChE–amyloid complexes is higher than that of the Aβ aggregates alone. Thus, in addition to its possible role as a heterogeneous nucleator during amyloid formation, AChE, by forming such stable complexes, may increase the neurotoxicity of Aβ fibrils and thus may determine the selective neuronal loss observed in Alzheimer’s brain.
Development of Bone Morphogenetic Protein Receptors in the Nervous System and Possible Roles in Regulating trkC Expression
Authors: Zhang Damin , Mehler Mark F. , Song Qingbin , Kessler John A.
Published: April 2018

Characterization of bone morphogenetic protein receptor (BMPR) expression during development is necessary for understanding the role of these factors during neural maturation. In this study,in situhybridization analyses demonstrate that BMP-specific type I (BMPR-IA and BMPR-IB) and type II (BMPR-II) receptor mRNAs are expressed at significant levels in multiple regions of the CNS, cranial ganglia, and peripheral sensory and autonomic ganglia during the embryonic and neonatal periods. All three BMP receptor subunits are expressed within periventricular generative zones. BMPR-IA is more abundant than the other receptor subtypes, with widespread expression in the brain, cranial ganglia, and peripheral ganglia. By contrast, BMPR-IB mRNA displays significant expression within more restricted regions, including the anterior olfactory nuclei. BMPR-II mRNA exhibits peak expression within the cerebellar Purkinje cell layer and the hippocampus, as well as within cranial ganglia. The distribution of BMP receptors within large neurons in adult dorsal root ganglia suggested a possible role in regulating expression of the neurotrophin receptor trkC. This hypothesis was tested in explant cultures of embryonic day 15 (E15) and postnatal day 1 (P1) sympathetic superior cervical ganglia (SCG). Treatment of the E15 or the P1 SCG with BMP-2 induced expression of trkC mRNA and responsiveness of sympathetic neurons to NT3 as measured by neurite outgrowth. The pattern of expression of BMP receptors in embryonic brain suggests several potentially novel areas for further developmental analysis and supports numerous recent studies that indicate that BMPs have a broad range of cellular functions during neural development and in adult life.
Muscle Response to Changing Neuronal Input in the Lobster(Panulirus Interruptus)Stomatogastric System: Slow Muscle Properties Can Transform Rhythmic Input into Tonic Output
Authors: Morris Lee G. , Hooper Scott L.
Published: April 2018

Slow, non-twitch muscles are widespread in lower vertebrates and invertebrates and are often assumed to be primarily involved in posture or slow motor patterns. However, in several preparations, including some well known invertebrate “model” preparations, slow muscles are driven by rapid, rhythmic inputs. The response of slow muscles to such inputs is little understood. We are investigating this issue with a slow stomatogastric muscle (cpv1b) driven by a relatively rapid, rhythmic neural pattern. A simple model suggests that as cycle period decreases, slow muscle contractions show increasing intercontraction temporal summation and at steady state consist of phasic contractions overlying a tonic contracture. We identify five components of these contractions: total, average, tonic, and phasic amplitudes, and percent phasic (phasic amplitude divided by total amplitude).

cpv1b muscle contractions induced by spontaneous rhythmic neural inputin vitroconsist of phasic and tonic components. Nerve stimulation at varying cycle periods and constant duty cycle shows that a tonic component is always present, and at short periods the muscle transforms rhythmic input into almost completely tonic output. Varying spike frequency, spike number, and cycle period show that frequency codes total, average, and tonic amplitudes, number codes phasic amplitude, and period codes percent phasic.

These data suggest that tonic contraction may be a property of slow muscles driven by rapid, rhythmic input, and in these cases it is necessary to identify the various contraction components and their neural coding. Furthermore, the parameters that code these components are interdependent, and control of slow muscle contraction is thus likely complex.
Extrasynaptic Vesicular Transmitter Release from the Somata of Substantia Nigra Neurons in Rat Midbrain Slices
Authors: Jaffe Erica H. , Marty Alain , Schulte Albert , Chow Robert H.
Published: April 2018

Substantia nigra neurons release dopamine from their somatodendritic regions. A long-unresolved question is whether this release occurs by exocytosis or by a nonvesicular mechanism. We used carbon fiber microelectrodes in a brainstem slice to assay secretion from single cell bodies that had been cleared of connective tissue. Amperometry at the carbon fiber microelectrodes revealed unitary events in ∼90% of cells in resting conditions. These events had charge integrals ranging from a few femtocoulombs to several hundred femtocoulombs (fC). Local glutamate application enhanced the event frequency by 3.5-fold on average and up to 10-fold in highly responsive cells, although the mean charge integral was not modified. Local application of a high K+-containing saline had effects similar to those of glutamate. The frequency of resting and stimulated amperometric events was much lower at 21–22°C than at 32–35°C. The addition of Cd2+(50 μm), a blocker of voltage-dependent Ca2+channels, to the bath solution blocked the stimulatory effects of glutamate. These results suggest that dopamine is released from the somata of substantia nigra neurons by exocytosis and that this mechanism is regulated by neuronal electrical activity. More generally, this study demonstrates the applicability of carbon fiber microelectrodes to the measurement of quantal monoamine secretion in brain slices.
Activation and Cleavage of Caspase-3 in Apoptosis Induced by Experimental Cerebral Ischemia
Authors: Namura Shobu , Zhu Jinmin , Fink Klaus , Endres Matthias , Srinivasan Anu , Tomaselli Kevin J. , Yuan Junying , Moskowitz Michael A.
Published: April 2018

We examined the expression, activation, and cellular localization of caspase-3 (CPP32) using immunohistochemistry, immunoblots, and cleavage of the fluorogenic substrateN-benzyloxycarbonyl-Asp-Glu-Val-Asp-7-amino-4-trifluoromethyl coumarin (zDEVD-afc) in adult mouse brain after temporary (2 hr) middle cerebral artery occlusion produced by filament insertion into the carotid artery. Immunoreactive caspase-3p32 but not its cleavage product caspase-3p20 was constitutively expressed in neurons throughout brain and was most prominent in neuronal perikarya within piriform cortex. Caspase-like enzyme activity was elevated in brain homogenate 0–3 hr after reperfusion and reached a peak within 30 to 60 min. Caspase-3p20 immunoreactivity became prominent in neuronal perikarya within the middle cerebral artery territory at the time of reperfusion and on immunoblots 1–12 hr later. DNA laddering (agarose gels) and terminal deoxynucleotidyl transferase-mediated dUTP—biotin nick-end labeling (TUNEL)-stained cells were detected 6–24 hr after reperfusion. At 12–24 hr, immunoreactive p20 was visualized in TUNEL-positive cells, a finding also observed in apoptotic mouse cerebellar granule cells on postnatal day 5. Together, these observations suggest the existence of a time-dependent evolution of ischemic injury characterized by the close correspondence between caspase-like enzyme activation and an associated increase in immunoreactive product (caspase-3p20) beginning at or before reperfusion and followed several hours later by morphological and biochemical features of apoptosis.
Carbachol Stimulates [35S]Guanylyl 5′-(γ-Thio)-Triphosphate Binding in Rapid Eye Movement Sleep-Related Brainstem Nuclei of Rat
Authors: Capece M. Luisa , Baghdoyan Helen A. , Lydic Ralph
Published: April 2018

Carbachol enhances rapid eye movement (REM) sleep when microinjected into the pontine reticular formation of the cat and rat. Carbachol elicits this REM sleep-like state via activation of postsynaptic muscarinic cholinergic receptors (mAChRs). The present study usedin vitroautoradiography of carbachol-stimulated [35S]guanylyl-5′-O-(γ-thio)-triphosphate ([35S]GTPγS) binding to test the hypothesis that carbachol activates mAChRs to induce stimulation of G-proteins in brainstem nuclei contributing to REM sleep generation. The results demonstrate a heterogeneous increase in carbachol-stimulated G-protein activation across rat brainstem. Binding of [35S]GTPγS in the presence of carbachol, compared with basal binding, was significantly increased in the laterodorsal tegmental nucleus (75.7%), caudal pontine reticular nucleus (68.9%), oral pontine reticular nucleus (64.5%), pedunculopontine tegmental nucleus (55.7%), and dorsal raphe nucleus (54.0%) but not in the nucleus locus coeruleus. The activation of G-proteins by carbachol was concentration-dependent and antagonized by atropine, demonstrating that G-proteins were activated via mAChR stimulation. The results provide the first direct measures of mAChR-activated G-proteins in brainstem nuclei known to contribute to REM sleep generation.
Nerve Gas-Induced Seizures: Role of Acetylcholine in the Rapid Induction of Fos and Glial Fibrillary Acidic Protein in Piriform Cortex
Authors: Zimmer Lee A. , Ennis Matthew , Wiley Ronald G. , Shipley Michael T.
Published: April 2018

Soman (pinacolymethylphosphonofluoridate), a highly potent irreversible inhibitor of acetylcholinesterase (AChE), causes seizures and rapidly increases Fos and glial fibrillary acidic protein (GFAP) staining in piriform cortex (PC). This suggests that the inhibition of AChE by soman leads to increased acetylcholine (ACh) and neuronal excitability in PC. The sole source of cholinergic input to PC is from the nucleus of the diagonal band (NDB). To investigate the role of ACh in soman-induced seizures, we lesioned cholinergic neurons in NDB unilaterally with192-IgG-saporin. By 10 d, saporin eliminated staining for choline acetyltransferase (ChAT), the synthetic enzyme for ACh, in NDB ipsilateral to the lesion. Staining for AChE, the degradative enzyme for ACh, was eliminated in PC ipsilateral to the lesioned NDB. By 45–60 min after soman, increased Fos and GFAP staining in PC was evident only ipsilateral to the unlesioned NDB. By 90–120 min after soman, Fos and GFAP staining increased bilaterally in PC.

In a second experiment, electrical stimulation electrodes were implanted unilaterally in the NDB to activate focally the projections to PC in unanesthetized rats. Within 5 min of NDB stimulation, there were clear behavioral and EEG signs of convulsions. After 45–60 min of NDB stimulation, there was increased Fos and GFAP staining in layer II of PC ipsilateral to the stimulation site. Pretreatment with the selective muscarinic receptor antagonist scopolamine blocked the convulsions and prevented increased Fos and GFAP staining in PC. These results suggest that ACh release in PC triggers the initiation of seizures and gliosis after soman administration, predominantly by the activation of muscarinic receptors.
Presynaptic Recording of Quanta from Midbrain Dopamine Neurons and Modulation of the Quantal Size
Authors: Pothos Emmanuel N. , Davila Viviana , Sulzer David
Published: April 2018

The observation of quantal release from central catecholamine neurons has proven elusive because of the absence of evoked rapid postsynaptic currents. We adapted amperometric methods to observe quantal release directly from axonal varicosities of midbrain dopamine neurons that predominantly contain small synaptic vesicles. Quantal events were elicited by high K+or α-latrotoxin, required extracellular Ca2+, and were abolished by reserpine. The events indicated the release of 3000 molecules over 200 μsec, much smaller and faster events than quanta associated with large dense-core vesicles previously recorded in vertebrate preparations. The number of dopamine molecules per quantum increased as a population to 380% of controls after glial-derived neurotrophic factor (GDNF) exposure and to 350% of controls after exposure to the dopamine precursorl-dihydroxyphenylalanine (l-DOPA). These results introduce a means to measure directly the number of transmitter molecules released from small synaptic vesicles of CNS neurons. Moreover, quantal size was not an invariant parameter in CNS neurons but could be modulated by neurotrophic factors and altered neurotransmitter synthesis.
Modulation of Rat Rotational Behavior by Direct Gene Transfer of Constitutively Active Protein Kinase C into Nigrostriatal Neurons
Authors: Song Song , Wang Yaming , Bak Sun-Yung , During Matthew J. , Bryan John , Ashe Oliver , Ullrey Donna B. , Trask Laura E. , Grant Frederick D. , O’Malley Karen L. , Riedel Heimo , Goldstein David S. , Neve Kim A. , LaHoste Gerald J. , Marshall John F. , Haycock John W. , Neve Rachael L. , Geller Alfred I.
Published: April 2018

The modulation of motor behavior by protein kinase C (PKC) signaling pathways in nigrostriatal neurons was examined by using a genetic intervention approach. Herpes simplex virus type 1 (HSV-1) vectors that encode a catalytic domain of rat PKCβII (PkcΔ) were developed. PkcΔ exhibited a constitutively active protein kinase activity with a substrate specificity similar to that of rat brain PKC. As demonstrated in cultured sympathetic neurons, PkcΔ caused a long-lasting, activation-dependent increase in neurotransmitter release. In the rat brain, microinjection of HSV-1 vectors that contain the tyrosine hydroxylase promoter targeted expression to dopaminergic nigrostriatal neurons. Expression of pkcΔ in a small percentage of nigrostriatal neurons (∼0.1–2%) was sufficient to produce a long-term (≥1 month) change in apomorphine-induced rotational behavior. Nigrostriatal neurons were the only catecholaminergic neurons that contained PkcΔ, and the amount of rotational behavior was correlated with the number of affected nigrostriatal neurons. The change in apomorphine-induced rotational behavior was blocked by a dopamine receptor antagonist (fluphenazine). D2-like dopamine receptor density was increased in those regions of the striatum innervated by the affected nigrostriatal neurons. Therefore, this strategy enabled the demonstration that a PKC pathway or PKC pathways in nigrostriatal neurons modulate apomorphine-induced rotational behavior, and altered dopaminergic transmission from nigrostriatal neurons appears to be the affected neuronal physiology responsible for the change in rotational behavior.
Hippocampal Synaptic Plasticity in Mice Overexpressing an Embryonic Subunit of the NMDA Receptor
Authors: Okabe Shigeo , Collin Carlos , Auerbach Jonathan M. , Meiri Noam , Bengzon Johan , Kennedy Mary B. , Segal Menahem , McKay Ronald D. G.
Published: April 2018

The effects of changing NMDA receptor subunit composition on synaptic plasticity in the hippocampus were analyzed by creating transgenic mice overexpressing NR2D, a predominantly embryonic NMDA receptor subunit. NMDA-evoked currents in the transgenic mice had smaller amplitudes and slower kinetics. The transgenics also displayed age-dependent deficits in synaptic plasticity in area CA1 of the hippocampus. Long-term depression was selectively impaired in juvenile mice when NR2D overexpression was moderate. In mature mice, overexpression of NR2D was associated with a reduction of both NR2B and Ca2+-independent activity of Ca2+- and calmodulin-dependent protein kinase II. These biochemical changes were correlated with a marked impairment of NMDA-dependent long-term potentiation, but spatial behavior was normal in these mice. These results show that the developmental regulation of NMDA receptor subunit composition alters the frequency at which modification of synaptic responses occur after afferent stimulation.
Differentially Interconnected Networks of GABAergic Interneurons in the Visual Cortex of the Cat
Authors: Tamás Gábor , Somogyi Peter , Buhl Eberhard H.
Published: April 2018

Networks of GABAergic neurons have been implicated in neuronal population synchronization. To define the extent of cellular interconnections, we determined the effect, number, and subcellular distribution of synapses between putative GABAergic neurons in layers II–IV of the cat visual cortex using paired intracellular recordingsin vitrofollowed by correlated light and electron microscopy. All neurons having interneuronal electrophysiological properties were classified by their postsynaptic target profile and were identified as basket (BC;n= 6), dendrite-targeting (DTC;n= 1), and double bouquet (DBC;n= 2) cells. In four out of five anatomically fully recovered and reconstructed cell pairs, synaptic connections were found to be reciprocal. Generally BCs established synaptic junctions closer (21 ± 20 μm) to postsynaptic somata than did DBCs (43 ± 19 μm;p< 0.01). The unitary number of synapses (nvalues, 10, 7, and 20) in each of three BC-to-BC pairs was higher than that in three BC-to-DBC (nvalues, 1, 2, and 2) and three DBC-to-BC (nvalues, 1, 4, and 4) connections (p< 0.05). A BC innervated a DTC through two synaptic junctions. Unitary postsynaptic effects mediated by five BCs could be recorded in two BCs, two DBCs, and a DTC. The BCs elicited short-duration fast IPSPs, similar to those mediated by GABAAreceptors. At a membrane potential of −55.0 ± 6.4 mV, unitary IPSPs (n= 5) had a mean amplitude of 919 ± 863 μV. Postsynaptic response failures were absent when an IPSP was mediated by several release sites. Thus, distinct GABAergic interneurons form reciprocally interconnected networks. The strength of innervation and the proximal placement of synapses suggest a prominent role for BCs in governing the activity of intracortical GABAergic networks in layers II–IV.
Expression of Integrin-Associated Protein Gene Associated with Memory Formation in Rats
Authors: Huang A-Min , Wang Hai Long , Tang Yu Ping , Lee Eminy H. Y.
Published: April 2018

The present study has adopted the PCR differential display method to identify cDNA clones associated with memory formation in rats. The one-way inhibitory avoidance learning task was used as the behavioral paradigm. Total RNA isolated from the hippocampus of poor-memory (<80 sec) and good-memory (600 sec) rats 3 hr after training was used for comparison. Three cDNA fragments corresponding to different spliced forms of integrin-associated protein (IAP) mRNA were found to be differentially expressed in the hippocampus of good-memory rats. Quantitative reverse transcription-PCR revealed approximately four fold higher of IAP mRNA level in good-memory rats. This result was confirmed further byin situhybridization analysis, and the major difference was in the dentate gyrus. It has been demonstrated that this difference in IAP mRNA expression is not attributable to different sensitivities of individual rats to electric shock. Rapid amplification of cDNA ends obtained the full-length IAP cDNA, which is 1192 bp in length excluding the poly(A+) tail. The IAP mRNA expression was significantly upregulated by NMDA and amphetamine injections to the dentate gyrus of the hippocampus. On the other hand, injection of antisense oligonucleotide complementary to the IAP transcript markedly impaired memory retention in rats and decreased the amplitude and slope of EPSP in thein vivolong-term potentiation paradigm. These results together suggest that IAP gene expression plays an important role in memory formation and synaptic plasticity in rat hippocampus.