Interestingly, Trouche et al. (2013) also observed a subset of neurons that were not silenced after extinction, and these cells exhibited higher densities of perisomatic cannabinoid receptor 1 (CB1R) labeling. Because CB1Rs limit GABA release, these receptors suggest a mechanism for sustained activity in neurons that were not silenced by the extinction procedure. this website Altogether, the data reveal that extinction learning remodels inhibitory synaptic input onto BA neurons to limit the expression of fear. The reorganization of inhibitory synaptic input onto the specific network of neurons encoding the

fear memory is a novel, selective, and direct mechanism for limiting conditioned fear responses after extinction. Although the cellular

mechanisms underlying these synaptic changes are not yet understood, a large number of studies suggest that NMDA receptors may be involved (Falls et al., 1992 and Zimmerman and Maren, 2010). How NMDA receptors mediate both long-term potentiation of excitatory synapses onto BA neurons encoding fear conditioning and the remodeling of perisomatic inhibition onto these neurons after extinction is a fascinating question. Whatever the mechanism, these data are consistent with the idea that extinction involves new learning that suppresses learned fear responses, rather than erasing the fear memory itself. Of course, a critically important question concerns how these and GBA3 other inhibitory mechanisms are themselves silenced during fear relapse. That is, GSK1210151A manufacturer how does fear in response to an extinguished CS renew, for example, when the CS is presented outside the extinction context? One possibility is that the activity of inhibitory interneurons in the BA is context dependent; the activity of these neurons may be elevated in the extinction context but dampened in a dangerous context. Another possibility is that fear relapse is mediated by BA neurons that remain active after extinction. Clearly, further work is

required to understand how target-specific silencing of BA neurons is modulated to allow for the context-dependent expression of fear. It is becoming clear that hippocampal and medial prefrontal cortical projections to basal and lateral amygdala neurons are involved in fear relapse after extinction (Herry et al., 2008, Knapska et al., 2012 and Orsini et al., 2011). Whether these circuits ultimately suppress inhibitory activity in the amygdala or drive activity in BA neurons during fear relapse (or both) remains to be examined. Clearly, the use of activity-dependent neuronal tags to track neuronal populations engaged during encoding and retrieval processes is a promising strategy to answer these questions.

57, p < 0.05), and P7 (fold change = 2.86, p < 0.01) IP-astrocyte inserts (Figures 5G and 5H). Thus, IP-astrocytes are as capable of inducing structural synapses in RGC cultures as MD astrocytes are. Structural synapses are not indicative of functional synapses, thus we analyzed synaptic activity of the RGCs in the presence of a feeder layer of astrocytes. Previous studies have shown that the number of functional synapses increases significantly with an MD-astrocyte feeder layer (Ullian et al., 2001). Bortezomib in vivo We found that

both the frequency and amplitude of miniature excitatory postsynaptic currents (mEPSCs) increased significantly and to a comparable degree with feeder layers of IP-astrocytes P1 or P7, to that observed with an MD-astrocyte feeder layer (Figures 5I–5L). Taken together, these results show that IP-astrocytes MDV3100 cell line retain functional properties characteristic of astrocytes. Intracellular calcium oscillations have been observed in astrocytes in vivo and are considered an important functional property of astrocytes and may aid in regulation of

blood flow or neural activity (Nimmerjahn et al., 2009). Several stimuli have been implicated in initiating calcium waves in MD-astrocytes. We used calcium imaging with Fluo-4 to investigate if IP-astrocytes exhibit calcium rises in response to glutamate, adenosine, potassium chloride (KCl), and ATP and if the nature of their response was similar to MD astrocytes (Cornell-Bell et al., 1990, Jensen and Chiu, 1991, Kimelberg et al., 1997 and Pilitsis and Kimelberg, 1998). Few calcium oscillations were observed at rest in IP-astrocytes, contrary to MD-astrocytes. A single cell in confluent cultures of P7 IP-astrocytes would respond independently of its neighbors. Such isolated and spontaneous firing of astrocytes has previously been observed in brain slices (Nett et al., 2002 and Parri and Crunelli, 2003).

In contrast, rhythmic calcium activity and regular spontaneous activity were observed in MD-astrocytes grown in the same media as cultured IP-astrocytes P7 (Figures 6A and 6C). Both MD-astrocytes and IP-astrocytes responded to 10 μM of adenosine (100% of MD-astrocytes, 89.6% ± 5.5% of IP-astrocytes; Figures S2C and S2D), 50 μM of glutamate (100% of MD-astrocytes, 88.1% ± 7.9% of IP-astrocytes; Figures S2E and Ketanserin S2F), and 100 μM of ATP (94.4% ± 5.5% of MD-astrocytes, 92.5% ± 1.5% of IP-astrocytes; Figures 6A and 6B) with increased frequency of calcium oscillations and/or amplitude of calcium oscillations. Both have several P2X and P2Y receptors and adora1 and adora2b receptors and thus can respond to these stimuli. Both MD and IP-astrocytes express mRNA for ionotropic glutamate receptors, but only the latter have metabotropic receptors (accession record number, GSE26066). Thus, the second phase calcium response observed with glutamate in IP-astrocytes after a period of quiescence, could be a metabotropic response. This was not observed in MD-astrocytes.

The association of Kv3 channels with fast spiking interneurons (Lien and Jonas, 2003 and Rudy and McBain, 2001) does not preclude expression in CA3 pyramidal neurons, as is clear from in situ hybridization studies (Allen Brain Atlas; Supplemental Panobinostat price Experimental Procedures) and PCR experiments showing that Kv3.1/3.2/3.3 mRNA is present in CA3 pyramidal neurons (Perney et al., 1992 and Weiser et al., 1994), as confirmed by our PCR and immunohistochemistry data (Figure 4).

Kv2.1 is a prominent delayed rectifier of cortex and hippocampus (Du et al., 2000, Guan et al., 2007 and Murakoshi and Trimmer, 1999); Kv2.2 shows lower expression levels in cortical regions but is highly expressed in certain auditory nuclei (Johnston et al., 2008). Interestingly, both Kv2.1 and Kv2.2 show localization to the initial segment in native neurons ( Johnston et al., 2008 and Sarmiere

et al., 2008), suggesting a common role in regulating excitability; although clustering at INCB024360 ic50 cholinergic synapses and cell bodies is also important for other roles ( Misonou et al., 2004 and Muennich and Fyffe, 2004). CA3 pyramidal neurons in vivo show a majority of single spiking responses in awake animals (Tropp Sneider et al., 2006), with only 20% of events giving a burst firing response. Spontaneous firing rates are in the range of 0.2 Hz in urethane anesthetized mice (Hahn et al., 2007), but spike trains from freely moving rodents can range between 4 and 62 Hz (Fenton and Muller, 1998 and Klyachko and Stevens, 2006). As we demonstrate, potentiation of Kv2 favors single spiking (see Figure 2)

in the hippocampus and would contribute to activity-dependent suppression of after-depolarizing potentials observed in vitro (Brown and Randall, 2009). Indeed, the mediation of Kv2 potentiation by NMDAR/nitrergic signaling seen here suggests that the commissural associative pathways (DCG-IV insensitive EPSCs activated under our conditions, L-NAME HCl Figure S1C), which express high levels of NMDAR (Fukushima et al., 2009 and Rajji et al., 2006), may have a direct role in switching between CA3 pyramidal neuron single spiking and burst firing. This is consistent with increased CA3 pyramidal neuron excitability following genetic ablation of NMDAR (Fukushima et al., 2009) in the CA3 region. The dominant subunit of the MNTB Kv3 channel is Kv3.1b (Macica et al., 2003), which is basally phosphorylated (Song et al., 2005) and following moderate periods of activity, becomes dephosphorylated and active. Our observations extend the concept of activity-dependent regulation of K+ currents over longer time periods, to when Kv3 is inactivated and Kv2 channels dominate MNTB excitability.

Accordingly, most theories have tended to ascribe to dACC selleck chemicals llc a role in either task selection (identity specification) or modulation of control (intensity specification). The EVC model integrates these accounts, proposing that they refer to different dimensions of the same function. Accordingly, dACC should be responsive to circumstances that engage either or both. In the two sections that follow, we review the literature concerning the association of dACC with each of these two

dimensions of control specification. Among the earliest theories of dACC function were ones that proposed a role in action selection (Devinsky et al., 1995, Matsumoto et al., 2003, Rangel and Hare, 2010, Rushworth et al., 2007 and Rushworth et al., 2004). More recent theories have elaborated this idea to include task selection (Holroyd and Yeung, 2012, Kouneiher et al., 2009 and O’Reilly, 2010). These are commensurate with the role of dACC in the specification of control signal identity proposed by the EVC model. Some evidence for this comes from studies showing dACC selectivity

for different control signal identities, including rules and task sets. However, the EVC model also requires selleck compound that control signals be specified based on their expected value. This predicts that the dACC should exhibit responses that are both selective for a particular line of behavior and sensitive to the value of outcomes associated with that behavior. This prediction is consistent with the findings of several recent studies. For example, when monkeys were required to choose between targets in a visual saccade task, overlapping populations of dACC neurons were found to encode the value and direction of the saccade chosen on a given trial (Cai and Padoa-Schioppa, 2012 and Hayden and Platt, 2010). Kaping and colleagues (2011) demonstrated similar effects in a task involving

covert shifts of visual attention, rather than explicit eye movements. In their study, a colored fixation cue at the start of each trial indicated which of two subsequently presented colored visual stimuli should be attended. The monkeys were then rewarded if they correctly reported whether the stimulus with the corresponding color rotated clockwise Cediranib (AZD2171) or counterclockwise. The amount of reward earned by a correct response was signaled by the color of the initial fixation cue. As in previous studies, overlapping neuronal populations in rostral dACC were found to encode the target of the attentional shifts and the value of those targets, independently of any overt saccade used to report movement direction. These findings are consistent with a role for dACC in specifying control signal identity based on its expected value. However, an alternative interpretation is possible: they could instead reflect the state and/or outcome monitoring functions of dACC without reflecting a role in specification.

5 Hz; Figure S5J). Together, these data demonstrate that a circuit intrinsic to the OT can generate and maintain persistent gamma oscillations. If the generator of these oscillations is indeed located in the OT, then the pharmacological manipulations that

altered the structure of the oscillations in the intact slice (Figure 3) should alter them in the same way when applied specifically to the OT. First, we tested the effects of the NMDA-R blocker APV on induced gamma oscillations in the isolated OT. In transected slices, bath application of APV substantially reduced the duration (11.1% of control, p < 0.001, n = 8; Figures 7, S6A, S6B, and S6C) and power AG-014699 ic50 (49.3% of control, p < 0.001, Friedman test, n = 8) of activity in the i/dOT. Moreover,

increasing the strength of afferent stimulation by 3–4× in the presence of APV did not increase the duration of the oscillations (Figure S6D), suggesting that the effect of APV was not merely to reduce the general excitability of the OT circuitry. In sum, these data suggested that NMDA-R mediated glutamatergic transmission in the i/dOT was essential for the persistence of the oscillations. Next, we tested the effects of focal application of the GABA-R blocker PTX to the OT in intact slices. Recall that PTX, when bath-applied to intact slices, eliminated gamma periodicity (Figure 3A). We puffed PTX focally onto either the OT or the lpc with a micropipette while recording activity in the sOT in intact midbrain slices. Both the OT and the Ipc are innervated by GABAergic circuits, as indicated by the presence of parvalbumin immunoreactivity in both structures HDAC inhibitor Ketanserin (Figure 8A). When applied to the OT, puffs of PTX transiently changed gamma oscillations into episodes of high-frequency spiking, mimicking the results of bath application

(Figures 8B, 8C, and S7A; duration: 33% of control, p > 0.5; power: 31% of control, p < 0.001, Friedman test, n = 7). In contrast, puffs of PTX applied to the Ipc in the same slice did not alter the periodic structure of gamma oscillations in the sOT (Figures 8D, 8E, and S7B; duration: 88% of control, p > 0.3; power: 74% of control, p > 0.5, n = 7). These results demonstrate conclusively that inhibition in the OT regulates the gamma periodicity of the midbrain oscillator. This study demonstrates that gamma oscillations can be induced in an in vitro slice preparation of the avian midbrain network and that these oscillations strongly resemble those induced by salient sensory stimuli in vivo. The synaptic mechanisms that regulate the frequency, power, and duration of the oscillations are similar to those that regulate gamma oscillations in mammalian forebrain structures. The source of the midbrain oscillations is the i/dOT. Rhythmic output from the i/dOT entrains periodic burst firing in the cholinergic nucleus Ipc, and the Ipc broadcasts the oscillations to the sOT.

, 2007 and Lee et al., 2007). Studies of the role of PKC in PTP have been limited by the lack of selectivity and ineffectiveness of pharmacological tools available to inhibit and activate PKC (e.g., Lee et al., 2008; for review see Brose and Rosenmund, 2002). Phorbol esters activate other synaptic proteins, including Munc13 (Lou et al., 2008, Rhee et al., 2002 and Wierda et al., 2007). PKC inhibitors have highly variable effects on PTP: at the same synapse, different PKC inhibitors disrupt PTP to very different extents (Lee et al., 2008; D.F. and W.G.R., unpublished data);

at some EPZ-6438 ic50 synapses, PKC inhibitors do not affect PTP (Eliot et al., 1994, Lee et al., 2008, Reymann et al., 1988a and Reymann et al., 1988b); and in some cases PKC inhibitors and their inactive analogs have similar effects on PTP (Lee et al., 2008). In addition, other proteins have been implicated in PTP, including

Munc13 (Junge et al., 2004 and Shin et al., 2010), calmodulin and CamKII (Chapman et al., 1995, Fiumara et al., 2007, Junge et al., 2004, Khoutorsky and Spira, 2009, Reymann et al., 1988a and Wang and Maler, 1998) and myosin light chain kinase (Lee et al., 2008). These findings have cast doubt on the involvement of PKC in PTP. If PKC is involved in PTP, identifying which PKC isoform mediates PTP is of fundamental importance. Is it a classical, selleck chemicals llc calcium-sensitive PKC isoform such as PKCα, PKCβ, or PKCγ, or one of the eight calcium-insensitive isoforms? The involvement of calcium-sensitive PKCs would be compatible with PKC being a sensor of calcium according to the residual calcium hypothesis, whereas if calcium-insensitive PKC isoforms regulate PTP, tetanic stimulation would have to elevate presynaptic DAG or act through some

unidentified pathway, and another presynaptic calcium sensor would need to respond to residual calcium. At the calyx of Held, calcium-insensitive PKCs have been implicated (Saitoh et al., 2001). These results suggest that if PKC plays a role in PTP, it does not serve as a calcium sensor. Here we use knockout animals to examine the roles of PKCα and PKCβ Tryptophan synthase in tetanus-induced enhancement of evoked and spontaneous transmission, and phorbol-ester-mediated enhancement at the calyx of Held synapse, where these forms of plasticity have been thoroughly characterized in wild-type animals (Habets and Borst, 2005, Habets and Borst, 2006, Habets and Borst, 2007, He et al., 2009, Hori et al., 1999, Korogod et al., 2005, Korogod et al., 2007, Lee et al., 2008, Lou et al., 2005, Lou et al., 2008 and Wu and Wu, 2001). We find that PKCα and PKCβ are both present at the calyx of Held. In PKCα/β double knockout animals, the calyx of Held is devoid of all calcium-dependent PKCs, as PKCγ is not present at this synapse (Saitoh et al., 2001). In PKCα/β double knockouts, basal properties of synaptic transmission are normal but 80% of PTP is eliminated.

This would then lead to the ability of the fear memory to be weakened, rendering it easier to extinguish. Finally, the effects of FGF2 on fear conditioning exhibit site-specificity. When it was administered into the basolateral amygdala, FGF2 enhanced extinction and reduced renewal and reinstatement similar to the peripheral injection findings in adult rats. In summary, FGF2 plays a role in fear conditioning, FXR agonist extinction, and reinstatement, as well as reacquisition and re-extinction. Moreover, FGF2 has both developmental and long-term effects on the memory of fearful events. Glutamate receptors in the amygdala may

also play an important role in the functions of FGF2. Thus, the ability of FGF2 to modulate affective behavior includes both spontaneous anxiety as well as conditioned emotional responses, all of which may contribute to long-lasting negative affect as seen in mood disorders. This body of work underscores the role of FGF2 at the interface of affect, learning, and memory. The FGF system plays a role in the cellular Selleck MDV3100 and behavioral neuroadaptations to stress. As will be discussed below, these adaptations take place across a wide range of developmental time points ranging from embryonic to adulthood. Moreover, the impact of stress on FGF expression appears to be dynamic within a given developmental window. In general, neuroprotective

molecules such as FGF2 are induced by short-term stress or exposure to glucocorticoids, and these FGFs may play an important role in coping with acute stress. Their Calpain induction may also buffer against the potential negative impact of high steroid levels (Molteni et al., 2001). However, with repeated or sustained stress, this induction is not sustained, and the expression

of the protective FGF molecules and receptors is in fact reduced relative to control levels, likely contributing to the long-term negative sequelae of chronic stress. Early animal work by the Fuxe laboratory demonstrated that acute and subchronic corticosterone administration can increase FGF2 protein levels in the substantia nigra (Chadi et al., 1993). This induction is indeed consistent with a neuroprotective response, as FGF2 can protect neurons from excitotoxic, metabolic, and oxidative insults (Mark et al., 1997). Similarly, FGF9 can protect dopaminergic neurons from MPTP-induced cell death (Huang et al., 2009). In contrast to its induction by acute glucocorticoids in adulthood, FGF2 is typically reduced by early life stress, and this effect is manifested into adulthood. Embryonic stress has been reported to decrease FGF2 expression in the adult hippocampus (Molteni et al., 2001). This manipulation also changed the response of the adult brain to subsequent stress or to corticosterone administration. Furthermore, perinatal anoxia decreased basal levels of FGF2 in the ventral tegmental area in adulthood while simultaneously enhancing the response of FGF2 to an acute stressor (Flores et al., 2002).

After 250 ms, however, the majority of cells (n = 40, 85%) accurately reflected the response values predicted by the steady-state gain fields (Figure 4C, two-saccade cells). The remainder of the cells (n = 7, 15%) did so by 350 ms (Figure 4D,

two-saccade cells). The median values of the gain field indices had a similar time course (Figure 4E). We also calculated the time point of transition from nonveridical to veridical eye position information (see Experimental Afatinib Procedures; Figure 4F). 43 of the 47 cells (91%) reported the steady-state values in the same stimulus interval for saccades in both directions. We recorded 13 cells that had no eye-position modulation of visual responses to test if the spatial inaccuracy Panobinostat molecular weight of immediate postsaccadic visual responses were simply the result of flashing stimuli around the time of a saccade. For these cells, responses to visual probes were not statistically different (p > 0.05 by KS test) regardless of the probe delay and the direction of the first saccade (Figure S2). Although the gain fields among the population of neurons reflect eye position inaccurately immediately after the first saccade in the two-saccade task, there is a potential shortcoming to using

this task to assess the monkey’s behavioral performance during this period. In the two-saccade task, the retinal location of the second target and the vector of the saccade necessary to acquire it are coincident. Therefore, it could be argued that the task does not depend on the accuracy

of the gain fields since it can be solved without employing a supraretinal 4-Aminobutyrate aminotransferase mechanism. The double-step task has been used to show that the oculomotor system can compensate for an intervening saccade and accurately acquire a target even when there is a dissonance between the retinal location of a target and the vector of the saccade necessary to acquire it (Hallett and Lightstone, 1976). If the brain used a gain-field mechanism to solve the double-step task, the position of targets flashed immediately after a saccade would be calculated as if the eyes had not moved. We used the three-saccade task (Figure 5A), which cannot be solved without employing a supraretinal mechanism, to test if the inaccuracy of the gain fields immediately after a conditioning saccade was reflected in the monkeys’ behavior. In this task, the monkey performed a traditional double-step task following a conditioning saccade in the high-to-low or low-to-high gain field direction. Two targets, one blue and one red (the probe), appeared simultaneously 50, 550, or 1,050 ms after the end of the first saccade. The red probe flashed in the cell’s receptive field for 75 ms and disappeared.

These recordings confirmed that glutamate receptor antagonists blocked synaptic input to the cortex driven by electrical stimulation of the contralateral forelimb. Glutamate receptor antagonists did not block direct activation of ChR2, but they did cause a decrease in

delayed, presumably synaptic, components (Figure 7A). ABT-199 This effect was evident at all depths recorded (Figure 7B), but may have been primarily due to inactivation of the upper cortical layers, where drug concentrations are expected to be highest after topical application. Because optogenetic stimulation of ChR2-expressing neurons does not require synaptic activation, corticofugal neurons could still propagate their action potentials beyond the influence of the cortically applied glutamate receptor antagonists to evoke movements. The fact that cortical application of glutamate receptor antagonists does not abolish movement topography (Figure 6) or prevent direct activation of corticofugal ChR2-expressing neurons (Figure 7) suggests that cortical output circuits may differentiate the Mab and Mad subregions. To test this hypothesis, we injected the deep cortical layers of Mab and Mad with adeno-associated virus containing fluorescent marker constructs to label axonal projections throughout the brain (Figure 8A). In addition to reciprocal intracortical projections

between find more these regions and trans-callosal projections to homotopic sensorimotor cortex, we observed adjacent, nonoverlapping projections in the striatum and internal capsule Astemizole (Figures 8B and 8C), with fibers originating in Mab occupying positions medial to those from Mad (2.0 ± 0.1 versus 2.5 ± 0.07 mm from midline in the dorsolateral striatum, p = 0.03, n = 7, paired t test; Figure 8D). This observation further supports the hypothesis that movement map topography is a product of the pattern of corticofugal projections, whereas the generation of complex movements by prolonged stimulation requires input from recurrent intracortical circuits and/or loops with subcortical structures. We have applied

light-based motor mapping to reveal that the mouse forelimb motor cortex is subdivided into distinct movement representations. Prolonged stimulation of these regions drives movements with similar speed profiles, but which terminate at different positions in space. Although complex movements evoked by prolonged stimulation were sensitive to perturbations of intracortical synaptic transmission, the topography of movement direction was not abolished by blockade of either excitatory or inhibitory synaptic transmission. The persistence of movement topography in spite of disrupted intracortical synaptic transmission may be due to the presence of segregated corticofugal pathways from the two movement representations. Functional differences between movement representations are likely the product of both their intracortical circuits (Jacobs and Donoghue, 1991 and Rouiller et al.

, 2002). In contrast,

our physiological and behavioral data indicate that CGRPα DRG neurons are required to sense noxious heat but are not required to detect innocuous or noxious mechanical stimuli. However, our data do not exclude a redundant role for CGRPα DRG neurons in mechanosensation or for sensing forms of mechanical stimuli that we did not test, such as pleasurable touch or pressure. This discrepancy between Lawson’s study and our present study suggests that physiology alone may not be sufficient to define the function of somatosensory neurons. Indeed, using a different physiological preparation, Rau and colleagues found that Mrgprd-expressing sensory neurons were polymodal and could be activated by noxious heat and check details mechanical stimuli ( Rau et al., 2009); however, when these neurons were ablated, only mechanosensory behaviors were impaired Alectinib supplier ( Cavanaugh

et al., 2009). We previously found that <10% of all CGRPα-expressing DRG neurons (defined by expression of a knocked in GFP reporter) were IB4+ (McCoy et al., 2012). However, in our present study, the number of IB4+ neurons was reduced by 36% after CGRPα DRG neuron ablation (from 25.8% to 16.3%; Figure 1H). This suggests that there may be greater overlap between IB4 and CGRPα than our previous histochemical studies indicated. Alternatively, quantification of markers relative to NeuN (in representative sections as done in this study) may not estimate how many cells were lost after ablation as accurately as counting the total number of marker-positive neurons in a specific ganglia (such as L4). Although these potential discrepancies in IB4 and CGRPα overlap should be noted, based on the maintenance of an independent additional marker for nonpeptidergic neurons (PAP) and the ablation

of the majority of CGRPα-expressing neurons (Figure 1H), our conclusions related to the function of CGRPα DRG neurons remain well founded. Unexpectedly, we found that behavioral responses to cold temperatures and cold mimetics were enhanced when CGRPα DRG neurons were ablated. This enhancement in cold sensitivity was not due to an increase in the number of TRPM8+ DRG neurons, an increase in the number STK38 of cold-receptive fields, or to a change in C-fiber cold threshold (which also excluded peripheral sensitization of C-fibers to low temperature). Furthermore, since physiological responses to cold were not altered peripherally after ablating CGRPα DRG neurons, it is unlikely that any other cold-sensing channel, including TRPA1 (Story et al., 2003), was more active peripherally. Since cold signals were processed normally in the periphery in DTX-treated mice, this suggested that enhanced cold sensitivity might instead be due to alterations in central processing of cold signals.