bluuebunny/crossref_metadata_2025 huggingface dataset:
Visual responses in the lateral geniculate nucleus of dichromatic and trichromatic marmosets (Callithrix jacchus)
Authors: Yeh T , Lee BB , Kremers J , Cowing JA , Hunt DM , Martin PR , Troy JB
Published: April 2018

New-world primates such as the marmoset (Callithrix jacchus) show polymorphism for the middle- to long-wavelength sensitive cone pigments. Each X-chromosome carries a gene for only one of three possible pigments. All males are thus dichromats, but some females will be trichromats. We have investigated the responses of cells of the parvocellular (PC) and magnocellular (MC) systems within animals from a single marmoset family. The middle- to long-wavelength pigment of dichromats was identified physiologically. Trichromats could readily be distinguished from dichromats by the presence of a high proportion of red-green opponent PC-cells. The physiological classification of phenotypes was confirmed with genetic analysis. The pattern of inheritance was consistent with current genetic models. In trichromatic females, the properties of cells resembled in detail those of cells from the PC- and MC-pathways of the macaque. In dichromats, cell responses resembled those of trichromats (except for the lack of opponency in PC-cells); PC-cells showed sustained and MC-cells transient responses, with a lower contrast gain for the former type. One difference was that a proportion of PC-cells in dichromats showed strong rod input even at high levels of retinal illuminance. Thus, in trichromatic marmosets the presence of two middle- to long-wave pigments appears to permit the elaboration of all the physiological properties associated with trichromacy.
Cellular processing of temporal information in medial vestibular nucleus neurons
Authors: du Lac S , Lisberger SG
Published: April 2018

Quantitative descriptions of the cellular transformations from behaviorally relevant inputs into temporal patterns of firing are crucial for understanding information processing in systems of neurons and for incorporating biological properties of neurons into models of the neural control of behavior. To understand how neurons that mediate vestibulo-ocular behavior transform their inputs into temporal patterns of firing, we examined responses of medial vestibular nucleus (MVN) neurons to current injected intracellularly. MVN neurons recorded from avian brain slices fired spontaneously. Sinusoidal modulation of input current produced precisely sinusoidal modulation of firing rate. The transformation between input current and firing rate was remarkably linear: firing rate scaled linearly as a function of current amplitude, and the responses to steps of input current were predicted accurately from the linear superposition of responses to sinusoidal modulation of input current. Over the physiological range of head movement frequencies, from 0.1 to 10 Hz, peak-to-peak modulation of firing rate was relatively constant or increased slightly in most neurons. In contrast, when hyperpolarizing current was used to keep neurons below threshold for action potentials, the frequency response of the membrane potential behaved like a low-pass filter. These results imply that the membrane conductances that are active when MVN neurons fire compensate for the low-pass characteristics of the membrane to allow faithful transmission of high frequency head movement signals.
Facilitation of olfactory learning by a modulator of AMPA receptors
Authors: Larson J , Lieu T , Petchpradub V , LeDuc B , Ngo H , Rogers GA , Lynch G
Published: April 2018

The effects of a benzoyl-piperidine drug (BDP) that facilitates AMPA receptor-mediated synaptic responses were tested on the acquisition and retention of long-term memory at dosages that had no detectable effects on a variety of performance measures. BDP-12 produced a dose-dependent suppression of exploratory activity in rats with statistically reliable effects occurring at 50 mg/kg (i.p.). The drug had no effects on balance beam performance at 30 mg/kg but at 45 mg/kg reduced the number of crossings made within a session; it did not, however, affect the time required to perform a traversal. The performance of well-trained rats presented with a familiar pair of odors (correct and incorrect) was not not detectably altered by BDP-12 at 30 mg/kg; however, the number of correct responses made in a five-trial test was reduced at 45 mg/kg. These results indicate that the AMPA receptor modulator at 30 mg/kg has little influence on arousal, motivation, sensori-motor processing, and attention; higher dosages cause a depression of learned and unlearned prepotent responses. The effects of the lower concentration were tested on two-odor discrimination learning in rats that had extensive training on the task. The animals (n = 20) were given three or five acquisition trials with novel odor pairs immediately after an injection of drug or vehicle and then tested 1–3 d later for retention in five unrewarded probe trials. Retention performance was not significantly better than chance 52.6 +/- 4.5% correct) for odors learned on vehicle injection days but was well above chance for odors learned on drug injection days (70.6 +/- 4.2% correct). Within-subject comparisons confirmed the memory enhancing effect of BDP-12 (p < 0.01). Analyses of performance during five training trials indicated that the rats made more correct responses on days on which they were given the drug than on days on which they were injected with vehicle (p < 0.02). Within-subject differences in acquisition were correlated with differences in retention (r = 0.70). There were no evident effects of the drug on response latencies during acquisition. These results suggest that AMPA receptor modulators reduce the amount of training needed for the formation of long-term memory and do so at dosages which have little effect on variables that secondarily influence acquisition. Possible reasons for this selectivity are discussed.
Opioid and adenosine peripheral antinociception are subject to tolerance and withdrawal
Authors: Aley KO , Green PG , Levine JD
Published: April 2018

The selective mu-opioid agonist, D-Ala2,N-Me-Phe4,Gly5-ol-enkephalin (DAMGO), or the selective A1-adenosine agonist N6-cyclopentyladenosine (CPA), when coinjected intradermally with prostaglandin E2 (PGE2), dose- dependently inhibited PGE2-induced mechanical hyperalgesia in the rat hindpaw, as determined by the Randall-Selitto paw-withdrawal test. Repeated (hourly x 3) intradermal injections of DAMGO or CPA produced tolerance to the antinociceptive effect of a fourth injection 1 hr later. Furthermore, repeated (hourly x 3) intradermal injections of DAMGO produced cross-tolerance to the antinociceptive effect of CPA, and repeated (hourly x 3) intradermal injection of CPA produced cross- tolerance to the antinociceptive effect of DAMGO. The demonstration of the bidirectional cross-tolerance between the peripheral antinociceptive effects of DAMGO and CPA supports the hypothesis that both these agents produced antinociception by acting on the same cell, presumably the primary afferent nociceptor, and that the development of tolerance involves changes downstream to activation of mu-opioid and A1- adenosine receptors. The opioid antagonist naloxone, which had no effect on paw-withdrawal threshold in normal paws, produced withdrawal threshold in normal paws, produced withdrawal hyperalgesia in DAMGO- tolerant paws. Furthermore, naloxone elicited a cross-withdrawal hyperalgesia response in CPA-tolerant paws. Similarly, the A1-adenosine antagonist 1,3-dipropyl-8-(2-amino-4- chlorophenyl)-xanthine (PACPX), which had no effect on paw-withdrawal threshold in normal paws, elicited a withdrawal hyperalgesia response in CPA-tolerant paws and cross-withdrawal hyperalgesia responses in DAMGO-tolerant paws. These cross-dependence and cross-withdrawal responses suggest that the development of dependence to mu-opioid and A1-adenosine agonists involves changes in the same second messenger system downstream to both mu-opioid and A1-adenosine receptor activation.
Synchronized oscillations in hippocampal CA3 neurons induced by metabotropic glutamate receptor activation
Authors: Taylor GW , Merlin LR , Wong RK
Published: April 2018

The metabotropic glutamate receptor agonist (1S,3R)-1-aminocyclopentane- 1,3 dicarboxylic acid (ACPD) at concentrations above 60 microM produced stereotypic oscillatory activity in CA3 pyramidal cells of rat hippocampal slices. This oscillatory activity consisted of trains of depolarizations with overriding action potentials. On average, individual trains lasted 7 sec and recurred at intervals of 24 sec. During each train, the constituent depolarizations achieved a maximum frequency of 27 Hz, then slowed to 8 Hz toward the end of the train. Extracellular and dual intracellular recordings suggested that this ACPD-induced oscillatory activity occurred synchronously in the CA3 population. The oscillations persisted in the presence of GABAA, GABAB, and NMDA receptor antagonists. In contrast, the oscillations were blocked by the AMPA/kainate receptor antagonist 6-cyano-7- nitroquinoxaline-2,3-dione (CNQX; 10–30 microM). Likewise, the oscillations were blocked by the metabotropic glutamate receptor antagonists (+)-alpha-methyl-4-carboxyphenylglycine [(+)-MCPG; 1 mM], (S)-4-carboxy-3-hydroxyphenylglycine [(S)-4C3HPG; 1mM] and (S)-4- carboxyphenylglycine [(S)-4CPG; 1 mM]. The results suggest that activation of metabotropic glutamate receptors can result in a permissive state that allows AMPA/kainate receptor-mediated conductances to mediate synchronized activity among hippocampal CA3 neurons.
Large-scale reorganization at multiple levels of the somatosensory pathway follows therapeutic amputation of the hand in monkeys
Authors: Florence SL , Kaas JH
Published: April 2018

Reorganization of somatosensory cortex after peripheral nerve damage typically has been attributed to cortical plasticity. Here we provide evidence that much of the large-scale cortical reorganization that occurs after a major loss of peripheral inputs reflects the sprouting or expansion of afferents from the remaining forelimb into deprived territories of the spinal cord and brainstem. We examined sensory afferent terminations in the spinal cord and brainstem, and determined the somatotopic organization of cortical area 3b in three adult monkeys with previous hand or forearm amputation, as veterinary treatment of forelimb injuries. In each monkey, the distribution of labeled sensory afferent terminations from the remaining parts of the fore-limb was much more extensive than the normal distribution of inputs from the forelimb, and extended into portions of the dorsal horn of the spinal cord and the cuneate nucleus of the brainstem related to the amputated hand. In the same animals, tactile stimulation of the forelimb activated much of the deprived hand representation in area 3b of cortex; the lateral portion of the deprived region in area 3B appeared to be reactivated by inputs from the face. These data provide important new evidence that one of the mechanisms subserving large scale reorganization in cortex is a relay of topographic changes that occur subcortically. Presumably, the expanded primary sensory inputs activate postsynaptic neurons that are normally driven by inputs from the hand so that the neurons now have receptive fields on the forearm. Since the topographic representation of the body is greatly magnified in the relay to cortex, the subcortical changes can result in dramatic cortical map changes.
Role of neural activity during synaptogenesis in Drosophila
Authors: Jarecki J , Keshishian H
Published: April 2018

This article reveals a novel aspect in the regulation of synaptic connectivity in Drosophila. Reducing neural activity genetically or pharmacologically disrupts the normally precise embryonic and larval neuromuscular connections. In third instar larvae with mutations that affect sodium channel function or expression such as no action potential, temperature-induced paralysis E, or seizure1, foreign neuromuscular synapses, arising from inappropriate nerve sources, are observed on muscle fibers throughout the abdominal body wall. Their frequencies increase as neural activity is further reduced in double mutant combinations. These foreign connections are first observed during late embryogenesis as filopodial-like contacts, but critical period analysis suggests that neural activity must be reduced during both late embryogenesis and the first larval instar to promote the differentiation of these embryonic contacts into foreign motor synapses. In addition, the loss of electrical activity in the motoneuron, as opposed to the loss of postsynaptic potentials in the muscle fibers, appears to be responsible for these changes in connectivity. Our experiments suggest that neural activity may function during development by preventing inappropriate connections and thereby maintaining the precise connectivity achieved during nerve outgrowth and target selection.
The central nucleus of the amygdala contributes to the production of morphine antinociception in the rat tail-flick test
Authors: Manning BH , Mayer DJ
Published: April 2018

Current models of endogenous pain control circuitry emphasize neural substrates within the brainstem and spinal cord. We have recently shown, however, that the central nucleus of the amygdala (Ce) contributes to morphine-induced suppression of formalin-induced nociceptive behaviors. In the four experiments reported here, we investigated the possibility that the Ce also contributes to morphine- induced suppression of simple, spinally mediated nociceptive reflexes. Bilateral N-methyl-D-aspartate (NMDA)-induced lesions of the rat Ce, but not bilateral lesions centered on either the basolateral or medial amygdaloid nucleus, abolished the antinociception produced by 2.5 mg/kg morphine sulfate in the noxious heat-evoked tail-flick test. Bilateral Ce lesions also abolished the antinociception produced by 2 or 4 mg/kg morphine sulfate, but a relatively large dose of morphine sulfate (10 mg/kg, s.c.) resulted in partial reinstatement of antinociception. It is unlikely that these effects were due to secondary, seizure-induced damage following NMDA injection (e.g., to areas outside the amygdala) since bilateral inactivation of the Ce with the local anesthetic lidocaine also reliably attenuated morphine antinociception. It is also unlikely that these effects were artifacts of lesion-induced hyperalgesia, since Ce lesions failed to result in reliable thermal hyperalgesia, even at baseline tail-flick latencies of 10–12 sec. These data are the first to provide direct evidence that systemically administered morphine requires the integrity of a forebrain area in order to suppress spinally mediated nociceptive reflexes. It is argued that the present results, together with recent evidence linking the Ce to the production of several forms of conditioned and unconditioned environmentally induced antinociception, warrant incorporation of the Ce into current models of endogenous pain control circuitry.
Inflammatory leukocytic recruitment and diffuse neuronal degeneration are separate pathological processes resulting from traumatic brain injury
Authors: Soares HD , Hicks RR , Smith D , McIntosh TK
Published: April 2018

The present study characterized whether inflammatory leukocytic infiltration is temporally and regionally correlated with neuronal degeneration and/or blood brain barrier (BBB) breakdown resulting from traumatic brain injury. Adult rats were sacrificed at 5 min, 2, 4, 12, 24, and 72 hr after lateral fluid percussion brain injury. BBB breakdown, neuronal degeneration and leukocyte infiltration were assessed using immunocytochemistry, silver impregnation and toluidine blue and eosin staining. BBB breakdown and neuronal degeneration occurred concomitantly in injured cortex, hippocampus, and along the dorsolateral quadrant of the diencephalon. However, neuronal degeneration within deep diencephalic structures transpired in the absence of IgG extravasation. Neutrophils were observed only in regions exhibiting BBB damage and were first apparent in injured cortex and hippocampus between 2–12 hr posttrauma lining the vasculature and filling subarachnoid/subdural spaces. Neutrophils then migrated from damaged vasculature into traumatized cortical and hippocampal parenchyma by 24 hr after lateral fluid percussion injury. Macrophages were also observed within cortical parenchyma at 24 hr and completely filled the cortical lesion site by 72 hr after injury. Macrophages were not as abundant throughout hippocampal parenchyma and were found only in hippocampal regions exhibiting focal hemorrhage at 72 hr. Finally, neutrophils did not migrate to deep diencephalic structures that showed no BBB damage despite extensive neuronal degeneration. Indeed, lateral fluid percussion elicits inflammatory leukocytic recruitment only in regions experiencing concomitant BBB damage and neuronal degeneration. In summary, inflammatory leukocytic recruitment and diffuse neuronal degeneration are separate pathological processes resulting from traumatic brain injury.
Selective alterations in gene expression for NMDA receptor subunits in prefrontal cortex of schizophrenics
Authors: Akbarian S , Sucher NJ , Bradley D , Tafazzoli A , Trinh D , Hetrick WP , Potkin SG , Sandman CA , Bunney WE , Jones EG
Published: April 2018

NMDA receptor antagonists can induce a schizophrenia-like psychosis, but the role of NMDA receptors in the pathophysiology of schizophrenia remains unclear. Expression patterns of mRNAs for five NMDA receptor subunits (NR1/NR2A-D) were determined by in situ hybridization in prefrontal, parieto-temporal, and cerebellar cortex of brains from schizophrenics and from neuroleptic-treated and nonmedicated controls. In the cerebral cortex of both schizophrenics and controls, mRNAs for NR1, NR2A, NR2B, and NR2D subunits were preferentially expressed in layers II/III, Va, and VIa, with much higher levels in the prefrontal than in the parieto-temporal cortex. Levels of mRNA for the NR2C subunit were very low overall. By contrast, the cerebellar cortex of both schizophrenics and controls contained very high levels of NR2C subunit mRNA, whereas levels for the other subunit mRNAs were very low, except NR1, for which levels were moderate. Significant alterations in the schizophrenic cohort were confined to the prefrontal cortex. Here there was a shift in the relative proportions of mRNAs for the NR2 subunit family, with a 53% relative increase in expression of the NR2D subunit mRNA. No comparable changes were found in neuroleptic-treated or untreated controls. These findings indicate regional heterogeneity of NMDA receptor subunit expression in human cerebral and cerebellar cortex. In schizophrenics, the alterations in expression of NR2 subunit mRNA in prefrontal cortex are potential indicators of deficits in NMDA receptor-mediated neurotransmission accompanying functional hypoactivity of the frontal lobes.
11 beta-Hydroxysteroid dehydrogenase in cultured hippocampal cells reactivates inert 11-dehydrocorticosterone, potentiating neurotoxicity
Authors: Rajan V , Edwards CR , Seckl JR
Published: April 2018

11 beta-Hydroxysteroid dehydrogenase (11 beta-HSD) catalyzes the conversion of the glucocorticoid corticosterone (cortisol in humans) to inert 11-dehydrocorticosterone (cortisone). 11 beta-HSD activity is present in the hippocampus, where it is induced by glucocorticoids and stress in vivo, prompting suggestions that the enzyme may attenuate the deleterious effects of chronic glucocorticoid excess on neuronal function and survival. Two isoforms exist: 11 beta-HSD1, a bidirectional NADPH-dependent enzyme, and 11 beta-HSD2, an NAD(+)- dependent exclusive 11 beta-dehydrogenase (corticosterone-inactivating enzyme). In this study, 11 beta-HSD1 activity and mRNA synthesis were demonstrated in primary fetal hippocampal cell cultures. Unexpectedly, the reaction direction in intact hippocampal cells was 11 beta- reduction (reactivation of inert 11-dehydrocorticosterone), although homogenization revealed that the enzyme was capable of 11 beta- dehydrogenation when removed from its normal cellular context. Dexamethasone (10(-7) M) increased 11 beta-HSD activity in homogenates of hippocampal cultures (102% increase). In intact hippocampal cells, dexamethasone induced 11 beta reductase, not dehydrogenase. To determine the functional relevance of hippocampal 11 beta-reductase, glucocorticoid potentiation of kainic acid neurotoxicity was examined. Pretreatment of hippocampal cells with corticosterone reduced survival on kainate exposure. Hippocampal cell 11 beta-HSD activity was potently inhibited by carbenoxolone. Carbenoxolone had no effect on cell survival after kainate alone and did not alter the effect of corticosterone. 11-Dehydrocorticosterone also potentiated kainate neurotoxicity; this effect was lost, however, if 11 beta-HSD was inhibited with carbenoxolone. Thus, hippocampal 11 beta-HSD seems to be a functional 11 beta-reductase in intact cells. Measures to attenuate hippocampal 11 beta-reductase may reduce neuronal vulnerability to glucocorticoid toxicity.
Taurine induces a long-lasting increase of synaptic efficacy and axon excitability in the hippocampus
Authors: Galarreta M , Bustamante J , Martin del Rio R , Solis JM
Published: April 2018

The physiological role of taurine, one of the most abundant free amino acids in the mammalian brain, is still poorly understood. We have found that bath application of the amino acid taurine induces two opposite actions on field excitatory synaptic potentials (fEPSP) recorded in the CA1 area of hippocampal slices: a decrease in fEPSP slope prevented by GABAA antagonists, and a long-lasting potentiation of fEPSP independent of GABAA or NMDA receptor activation. Two long-lasting processes account for this taurine-induced potentiation: (1) an increase in synaptic efficacy that is accompanied neither by modifications in the basic postsynaptic membrane electrical properties nor by those presynaptic changes involved in fEPSP paired-pulse facilitation; and (2) an increase in the axon excitability revealed by a reduction on the threshold for antidromic action potential activation. In addition, taurine perfusion also induces a long-lasting increase in intracellularly recorded EPSPs and monosynaptically activated IPSPs. A number of experimental observations such as temperature dependence, extracellular Na+ concentration dependence, and saturation studies, although they are not unequivocally conclusive, suggest that the taurine uptake system is required for the taurine-induced fEPSP potentiation. Our data describe a new taurine action defined as a potentiation of synaptic transmission due in part to an increment in presynaptic axon excitability and in synaptic efficacy.
Downregulation of Cu/Zn superoxide dismutase leads to cell death via the nitric oxide-peroxynitrite pathway
Authors: Troy CM , Derossi D , Prochiantz A , Greene LA , Shelanski ML
Published: April 2018

We previously showed that the downregulation of Cu/Zn superoxide dismutase (SOD1) activity in PC12 cells by exposure to an appropriate antisense oligonucleotide causes their apoptotic death. In this report, we used this model to examine the pathways by which SOD1 downregulation leads to death and to compare these pathways with those responsible for death caused by withdrawal of trophic support. To improve delivery of the SOD1 antisense oligonucleotide, we coupled it to a carrier “vector” peptide homologous to the third helix of the Drosophila Antennapedia homeodomain. This caused not only efficient cellular uptake even in the presence of serum, but also inhibition of SOD1 activity and promotion of apoptosis at 100-fold lower concentrations of oligonucleotide. Death induced by SOD1 downregulation appeared to require the reaction of superoxide with nitric oxide (NO) to form peroxynitrite. In support of this, inhibitors of NO synthase, the enzyme responsible for NO synthesis, blocked death in our experiments, whereas NO generators and donors accelerated cell death. N-Acetylcysteine and chlorophenylthiol cAMP, which rescue PC12 cells and neurons from the withdrawal of nerve growth factor and other forms of trophic support, did not protect PC12 cells from SOD1 downregulation. In contrast, overexpression of bcl-2, which also rescues these cells form loss of trophic support, was equally effective in saving the cells in the SOD1 downregulation paradigm. Taken together with past findings, such observations suggest that SOD1 downregulation and withdrawal of trophic support trigger apoptosis via distinct initial mechanisms but may utilize a common final pathway to bring about death. Our findings may be relevant to the causes and potential amelioration of neuronal degenerative disorders caused by impaired regulation of cellular levels of NO and superoxide.
Sequence of stress-induced alterations in indices of synaptic and transcriptional activation in parvocellular neurosecretory neurons
Authors: Kovacs KJ , Sawchenko PE
Published: April 2018

Immediate-early genes (IEGs) are widely used to mark endocrine hypothalamic neurons that are activated in response to stress, yet their relationship to the transcriptional control of relevant effector molecule expression is unclear. Acute ether stress provokes increased adrenocorticotropic hormone (ACTH) and corticosterone secretion that peaks at 5 and 30 min, respectively, after the challenge. Using probes complementary to intronic sequences of genes encoding ACTH secretagogues in parvocellular neurosecretory neurons of the paraventricular nucleus, we found these events to be accompanied by rapid and transient increases in corticotropin-releasing factor heteronuclear RNA (CRF hnRNA; peak at 5 min) and by a delayed upregulation of arginine vasopressin (AVP) hnRNA (120 min). To identify candidate mechanisms regulating peptide expression, we followed the timing of ether effects on representatives of three transcription factor classes: IEGs [c-fos and nerve growth factor I-B (NGFI-B)], a POU-domain factor (Brn-2), and the cAMP response element-binding protein (CREB), using antisera specific to its transcriptionally active, phosphorylated form (pCREB). After ether exposure, c-fos and NGFI-B mRNA induction were maximal at 30--60 min, whereas Fos protein peaked at 60--120 min. Brn-2 mRNA was expressed constitutively in the PVH and was unresponsive to stress. By contrast, pCREB was induced in parvocellular neurons with a time course parallel to that of CRF hnRNA expression. Stress-induced transcriptional activation of the CRF and AVP genes in hypophysiotropic neurons follows distinct time courses that are compatible with control mechanisms involving phosphorylation events and de novo protein synthesis, respectively.
Drugs of abuse and stress increase the expression of GluR1 and NMDAR1 glutamate receptor subunits in the rat ventral tegmental area: common adaptations among cross-sensitizing agents
Authors: Fitzgerald LW , Ortiz J , Hamedani AG , Nestler EJ
Published: April 2018

Behavioral and electrophysiological evidence suggests that glutamatergic neurotransmission plays an important role in some of the long-term effects of cocaine and other drugs of abuse on brain function. We therefore examined the effect of repeated cocaine treatment on glutamate receptor subunit expression in central dopamine (DA) pathways implicated in many of cocaine's behavioral actions. By immunoblotting procedures using subunit-specific antibodies, we found that repeated, but not acute, cocaine treatment increased the levels of immunoreactivity of GluR1 (an AMPA receptor subunit) and NMDAR1 (an NMDA receptor subunit) in the ventral tegmental area (VTA), a nucleus containing mesolimbic DA neurons. In contrast, chronic cocaine treatment did not alter levels of GluR2 (an AMPA receptor subunit), NMDA2A/B (NMDA receptor subunits), or GluR6/7 (kainate receptor subunits) in this brain region. Moreover, GluR1 and NMDAR1 levels were not regulated in other regions of the mesolimbic or nigrostriatal DA pathways, including the substantia nigra. Because several drugs of abuse and stress can elicit common and cross-sensitizing effects on mesolimbic DA function, we next examined whether repeated morphine and stress treatments would regulate these proteins similarly in the VTA. Although morphine delivered by subcutaneous pellet implantation had no significant effect on subunit levels, morphine delivered intermittently by subcutaneous injections of escalating doses elevated GluR1 levels in the VTA. Repeated restraint stress also paradigm (2 stressors/d under variable conditions) increased both GluR1 and NMDAR1 levels in this brain region. Unlike cocaine, morphine, and stress, repeated treatment with other psychotropic drugs (haloperidol, raclopride, sertraline, and desipramine) that lack reinforcing or sensitizing properties did not regulate GluR1 or NMDAR1 subunit levels in the VTA. Increased glutamate receptor subunit expression in the VTA may represent an important molecular mechanism by which drugs of abuse and stress exert common, long-term effects on mesolimbic DA function.
High-speed optical imaging of afferent flow through rat olfactory bulb slices: voltage-sensitive dye signals reveal periglomerular cell activity
Authors: Senseman DM
Published: April 2018

Fast, multiple-site optical recording and video imaging techniques were combined to visualize the olfactory processing stream as it flowed through rat olfactory bulb slices stained with the voltage-sensitive dye RH155. A 464 element photodiode detector array was used to record the voltage-sensitive dye signals. Focal electrical stimulation of the olfactory nerve layer evoked relatively large optical responses in the olfactory nerve and glomerular layers but only small responses within the external plexiform layer. With paired-pulse stimulation, glomerular attenuation was evident in signals recorded from the glomerular and external plexiform layers but not from the olfactory nerve layer. At very high recording speeds ( < 0.2 msec/frame), the presynaptic component of the olfactory processing stream could be followed as it flowed through the olfactory nerve layer and into the glomerular layer, where its amplitude rapidly declined. This decline was followed by a reciprocal rise in a postsynaptic depolarization that was largely restricted to the glomerular layer. Spatiotemporal interactions between overlapping afferent streams within the glomerular layer were observed and partially characterized. The optically recorded glomerular layer response was largely resistant to bath application of GABAA receptor antagonists but was sensitive to manipulations of external chloride concentration and to bath application of a stilbene derivative, 4- acetamido-4′isothiocyanatostilbene-2,2′-disulfonic acid known to block Cl- conductances. It is suggested the the voltage-sensitive dye signals recorded from the glomerular layer reflect activity in periglomerular cells and that Cl- efflux through non-GABAA chloride channels contributes to the postsynaptic depolarization of these cells after olfactory nerve stimulation.
The effect of efferent stimulation on basilar membrane displacement in the basal turn of the guinea pig cochlea
Authors: Murugasu E , Russell IJ
Published: April 2018

Tone-evoked basilar membrane (BM) displacements were measured with a laser diode interferometer from the basal turn of the guinea pig cochlea. The olivocochlear bundle (OCB) was electrically stimulated for 60--80 msec periods at rates of < 200 sec-1 via electrodes placed at the point at which the OCB crosses the floor of the fourth ventricle. For tones close to the best or characteristic frequency (CF), OCB stimulation tended to linearize the highly compressive displacement- level functions and to displace the steep, low-level region toward higher intensities along the intensity axis by < 27 dB sound pressure levels. This shift resulted in a desensitization of the tip of the BM displacement tuning curve that was associated sometimes with downward shifts in the tuning curve CF of < 500 Hz. OCB-induced suppression of the BM response was not associated with a consistent broadening of the tuning curve or with major changes in the phase of the BM response. At frequencies in the low-frequency tail of the tuning curve, OCB stimulation had no observable effect on the motion of the BM. The effect of OCB stimulation on the BM response was blocked by perfusing the scala tympani with 1 microM strychnine. Thus, the effect of OCB stimulation on the frequency tuning of the BM is very similar to the effect of OCB stimulation on the sensitivity and frequency tuning of afferent fibers and inner hair cells. The results indicate that the postsynaptic action of the OCB may cause a change in gain of the voltage-dependent outer hair cell motility without observable changes in the stiffness of the cochlear partition or the position of the BM.
Medial preoptic area afferents to periaqueductal gray medullo-output neurons: a combined Fos and tract tracing study
Authors: Rizvi TA , Murphy AZ , Ennis M , Behbehani MM , Shipley MT
Published: April 2018

We have shown recently that the medial preoptic area (MPO) robustly innervates discrete columns along the rostrocaudal axis of the midbrain periaqueductal gray (PAG). However, the location of PAG neurons responsive to MPO activation is not known. Anterograde tract tracing was used in combination with Fos immunohistochemistry to characterize the MPO --> PAG pathway anatomically and functionally within the same animal. Focal electrical or chemical stimulation of MPO in anesthetized rats induced extensive Fos expression within the PAG compared with sham controls. Fos-positive neurons were organized as 2–3 longitudinal columns. The organization and location of these columns overlapped remarkably well with the distribution of fibers and terminals in PAG labeled by Phaseolus vulgaris leucoagglutinin (PHA-L) injected into the same MPO stimulation site. This indicates that MPO inputs may terminate on the soma or proximal dendrites of neurons exhibiting elevated Fos. A second series of experiments investigated whether MPO stimulation excited PAG neurons with descending projections to the medulla. Retrograde labelling of PAG neurons projecting to the medial and lateral regions of the rostroventral medulla (RVM) was combined with MPO-induced Fos expression. The results showed that a substantial population (37–53%) of Fos-positive PAG neurons projected to the ventral medulla. This indicates that MPO stimulation engages PAG- medullary output neurons. Taken together, these results suggest that the MPO --> Pag --> RVM projection constitutes a functional pathway. This circuit may coordinately regulate neuroendocrine, motor, and autonomic adjustments necessary for the elaboration of sexual behaviors.
NMDA receptor antagonists impair prefrontal cortex function as assessed via spatial delayed alternation performance in rats: modulation by dopamine
Authors: Verma A , Moghaddam B
Published: April 2018

The present study was performed to assess the role of excitatory amino acid and dopamine receptors on associative functions of the prefrontal cortex (PFC) of the rat. Spatial delayed alternation was used as a PFC- sensitive cognitive task. In addition, in vivo microdialysis was used to assess the release of dopamine in the PFC. The noncompetitive NMDA antagonists ketamine (10–30 mg/kg) and MK-801 (0.1 and 0.5 mg/kg) dose- dependently impaired the spatial delayed alternation performance compared with the saline-treated control group. Administration of the dopamine antagonists raclopride (0.1 and 0.5 mg/kg), SCH-23390 (0.1 mg/kg), or haloperidol (0.1 mg/kg) was without a significant effect. However, haloperidol and raclopride (but not SCH-23390) reversed the disruptive effect of 30 mg/kg ketamine on spatial delayed alternation performance. Microdialysis studies revealed that this dose of ketamine preferentially increased the release of dopamine in the PFC compared with the striatum. These findings indicate that attenuation of glutamatergic neurotransmission at the NMDA receptor impairs PFC- dependent cognitive functions. Furthermore, activation of dopamine neurotransmission contributes, at least in part, to this impairment.
Fibroblast growth factor-2 protects entorhinal layer II glutamatergic neurons from axotomy-induced death
Authors: Peterson DA , Lucidi-Phillipi CA , Murphy DP , Ray J , Gage FH
Published: April 2018

The entorhinal cortex is a major relay between the hippocampus and other cortical and subcortical regions. Glutamatergic axons from layer II neurons form the entorhinal cortical projection to the hippocampus via the perforant pathway. We have demonstrated previously that lesion of the perforant pathway causes the death of approximately 30% of entorhinal layer II (ECL2) neurons. To elucidate mechanisms contributing to neuronal death and to investigate strategies preventing it, we identified the phenotype of the vulnerable neuronal population. Sections were immunolabeled with antibodies to the neuronal markers NeuN, glutamate, and calbindin-D28k, and to receptors for fibroblast growth factor-2 (FGFR1) and NMDA (NMDAR1) and were examined using confocal microscopy. Calbindin immunoreactivity was strikingly lamina- specific to ECL2, where one-third of all ECL2 neurons were calbindin- positive. Localization of glutamate revealed that half of the glutamatergic ECL2 neurons coexpressed calbindin. Quantification using unbiased stereology at 9 weeks after lesion of the perforant pathway revealed that the only ECL2 neuronal population that experienced a significant (70%) loss (20% of the total) was the population of glutamatergic ECL2 neurons that did not coexpress calbindin. All ECL2 neurons expressed FGFR1; therefore, we tested the role of FGF-2 in the survival of glutamatergic ECL2 neurons. We grafted fibroblasts genetically engineered to express nerve growth factor or FGF-2 and found that only FGF-2 grafts prevented loss of the vulnerable glutamatergic/calbindin-negative neurons. We present a hypothesis for the selective vulnerability of these glutamatergic/calbindin-negative ECL2 neurons and address the role of FGF-2 in neuronal rescue.
Sensory transduction in vomeronasal neurons: evidence for G alpha o, G alpha i2, and adenylyl cyclase II as major components of a pheromone signaling cascade
Authors: Berghard A , Buck LB
Published: April 2018

The mammalian vomeronasal organ (VNO) is an accessory olfactory structure implicated in the sensing of pheromones. Although virtually nothing is known about sensory transduction in the mammalian VNO, recent findings have raised the possibility that it proceeds via a G- protein-coupled mechanism and involves a cyclic nucleotide-gated ion channel as in the nasal olfactory epithelium. To investigate this possibility, we cloned G-protein alpha subunits, adenylyl cyclases, and guanylyl cyclases that are expressed in the VNO and examined their patterns of expression. Of seven G alpha subunits identified as being expressed in the VNO, we found that mRNAs encoding only two, G alpha o and G alpha i2, are highly expressed in VNO neurons. Moreover, G alpha o and G alpha i2 are highly expressed by separate subsets of neurons that are located in different regions of the VNO neuroepithelium. Immunohistochemical studies show that both G alpha o and G alpha i2 are enriched in VNO microvilli, suggesting that G-proteins containing both of these alpha subunits may be involved in VNO sensory transduction. Of the adenylyl and guanylyl cyclases that we cloned, we found that only one, adenylyl cyclase type II, is highly expressed in VNO neurons; furthermore, it is expressed by both G alpha o+ and G alpha i2+ subsets. Our findings suggest that spatially segregated subsets of VNO neurons may use different, but related, sensory transduction pathways in which G-proteins and an adenylyl cyclase play major roles.
Colocalization of GABA, glycine, and their receptors at synapses in the rat spinal cord
Authors: Todd AJ , Watt C , Spike RC , Sieghart W
Published: April 2018

To determine whether GABA and glycine can act as cotransmitters at synapses in the rat spinal cord, we have compared the ultrastructural distribution of GABAA-receptor beta 3 subunit with that of the glycine receptor-associated protein gephyrin and combined this with postembedding detection of GABA and glycine. We also used a dual- immunofluorescence method to confirm that gephyrin was associated with the glycine-receptor alpha 1 subunit throughout the cord. GABAA beta 3- subunit immunoreactivity was restricted primarily to synapses, and at a majority of these synapses the presynaptic axon was GABA- immunoreactive. Many synapses showed both GABAA beta 3 and gephyrin immunoreactivity, and at most of these synapses GABA and glycine were enriched in the presynaptic axon. These results strongly support the idea that cotransmission by GABA and glycine occurs in the spinal cord.
Activity-dependent short-term enhancement of intercellular coupling
Authors: Pereda AE , Faber DS
Published: April 2018

It was reported previously that repeated brief tetanization of the posterior eight nerve can produce long-term homosynaptic potentiations of the electrotonic and chemical components of the mixed EPSP evoked in the Mauthner cell lateral dendrite by a single stimulus to the nerve. We show here that the same stimulus paradigm can lead, alternatively, to short-term enhancements of both excitatory responses. These transient modifications last for approximately 3 min, with a time course similar to post-tetanic potentiation at chemical synapses. However, a different stimulus pattern that transiently increases the presynaptic calcium concentration, paired-nerve stimuli, does not have any significant effect on electrotonic transmission, whereas it facilitates the chemically mediated EPSP. On the other hand, induction of the short-lasting potentiation of coupling, which depended on the discontinuous or burst-like property of the tetanizing paradigm, required NMDA-receptor activation and was blocked by postsynaptic intradendritic injections of the calcium chelator bis(2- aminophenoxy)ethane-N,N,N′,N′-tetra-acetic acid. The ineffectiveness of presynaptic calcium in potentiating electrotonic coupling likely reflects the involvement of a calcium-dependent regulatory protein in the postsynaptic cell and suggests that hemichannels on the two sides of a gap junction plaque can be modified independently. NMDA-mediated modulation of gap junctions could be widespread, because both types of channels coexist during development and in several mammalian adult central nervous system structures such as hippocampus.
In vitro analysis of optimal stimuli for phase-locking and time-delayed modulation of firing in avian nucleus laminaris neurons
Authors: Reyes AD , Rubel EW , Spain WJ
Published: April 2018

Neurons of the avian nucleus laminaris (NL) provide a neural substrate for azimuthal sound localization. We examined the optimal stimuli for NL neurons to maintain high discharge rates, reliable phase-locking, and sensitivity to time-delayed stimuli. Whole-cell recordings were performed in chick [embryonic days 19–21 (E19-E21)] NL neurons using an in vitro slice preparation. Variation of membrane properties along the tonotopic axis was examined. Computer-controlled intracellular current injection was used to mimic postsynaptic currents or conductances (PSCs) generated in NL neurons by the firing of nucleus magnocellularis (NM) neurons during acoustic stimulation. At various stimulus frequencies, the effects of varying the number of NM cells and PSC amplitudes on firing rate and phase-locking were examined. During high- frequency stimulation, the greatest firing rate and phase-locking occurred when the protocol contained few NM cells that generated large PSCs. Because the stimulus-evoked unitary PSCs are small, we propose that NM cells fire in synchrony to generate large PSCs. To mimic the arrival of PSCs during binaural stimulation, two stimulus trains were summed at different delays before injection. The firing rate of NL neurons was greatest with zero delay. A delay of half the stimulus period evoked firing that was less than that evoked with a single train. Neurons lacking strong outward rectification exhibited neither reliable phase-locking during high-frequency stimulation nor sensitivity to stimulus delays. These findings suggest that the firing responses of NL neurons are determined primarily by their membrane properties.
Inhibition of the Kv4 (Shal) family of transient K+ currents by arachidonic acid
Authors: Villarroel A , Schwarz TL
Published: April 2018

We have found that transient A-type currents expressed in Xenopus oocytes from members of the Kv4 family are suppressed by arachidonic acid. Currents from members of the Kv1, Kv2, and Kv3 families showed little or no inhibition by fatty acids in this expression system, although Shaker currents showed a modest increase in peak amplitude. The inhibition of Kv4 channels was not prevented by cyclo-oxygenase, lipoxygenase, or cytochrome P-450 inhibitors and was mimicked by 5,8,11,14-eicosatetraynoic acid, an arachidonic acid analog that is not metabolized by these pathways. Other unsaturated cis fatty acids with more than two double bonds produced a similar effect. In inside-out macropatches, the current was reversibly reduced > 50% by 2 mM arachidonic acid, and the inhibition developed in < 40 sec. These results suggest that, at concentrations that are likely to be physiologically relevant, arachidonic acid interacts directly with the channel or with a closely associated component. Preliminary mutagenesis of Kv4.2 channels indicates that the N terminal is not required for arachidonic acid action but that the S4-S5 loop may influence the effect.
Synapse formation and establishment of neuronal polarity by P19 embryonic carcinoma cells and embryonic stem cells
Authors: Finley MF , Kulkarni N , Huettner JE
Published: April 2018

A number of different cell lines that exhibit a partial neuronal phenotype have been identified, but in many cases the full extent of their neuronal differentiation has not been directly addressed by functional studies. We have used electrophysiology and immunofluorescence to examine the formation of synapses and the development of neuronal polarity by murine embryonic stem (ES) cells and the mouse P19 embryonic carcinoma cell line. Within 2–3 weeks after induction by retinoic acid, subsets of P19 and ES cells formed excitatory synapses, mediated by glutamate receptors, or inhibitory synapses, mediated by receptors for GABA or glycine. In ES-cell cultures, both NMDA and non-NMDA receptors contributed to the excitatory postsynaptic response. Staining with antibodies to growth- associated protein-43 and microtubule-associated protein-2 revealed segregation of immunoreactivity into separate axonal and somato- dendritic compartments, respectively. Consistent with our physiological evidence for synapse formation, intense punctate staining was observed with antibodies to the synaptic vesicle proteins synapsin, SV2, and synaptophysin. These results demonstrate the in vitro acquisition by pluri-potent cell lines of neuronal polarity and functional synaptic transmission that is characteristic of CNS neurons.