Stimulation Of Amygdala Research Articles

Genome-Wide microRNA Profiling of Rat Hippocampus after Status Epilepticus Induced by Amygdala Stimulation Identifies Modulators of Neuronal Apoptosis

MicroRNAs (miRNAs) are small and endogenously expressed non-coding RNAs that negatively regulate the expression of protein-coding genes at the translational level. Emerging evidence suggests that miRNAs play critical roles in central nervous system under physiological and pathological conditions. However, their expression and functions in status epilepticus (SE) have not been well characterized thus far. Here, by using high-throughput sequencing, we characterized miRNA expression profile in rat hippocampus at 24 hours following SE induced by amygdala stimulation. After confirmation by qRT-PCR, six miRNAs were found to be differentially expressed in brain after SE. Subsequent Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that most of the predicted target genes for these six miRNAs were related to neuronal apoptosis. We then investigated the dynamic changes of these six miRNAs at different time-point (4 hours, 24 hours, 1 week and 3 weeks) after SE. Meanwhile, neuronal survival and apoptosis in the hippocampus after SE were evaluated by Nissl staining and terminal deoxynucleotidyl transferase-mediated dUTP end-labeling assay. We found that the expression of miR-874-3p, miR-20a-5p, miR-345-3p, miR-365-5p, and miR-764-3p were significantly increased from 24 hours to 1 week, whereas miR-99b-3p level was markedly decreased from 24 hours to 3 weeks after SE. Further analysis revealed that the levels of miR-365-5p and miR-99b-3p were significantly correlated with neuronal apoptosis after SE. Taken together, our data suggest that miRNAs are important modulators of SE-induced neuronal apoptosis. These findings also open new avenues for future studies aimed at developing strategies against neuronal apoptosis after SE.

Alterations in miRNA Levels in the Dentate Gyrus in Epileptic Rats

The aim of this study was to characterize changes in miRNA expression in the epileptic dentate gyrus. Status epilepticus evoked by amygdala stimulation was used to induce epilepsy in rats. The dentate gyri were isolated at 7 d, 14 d, 30 d and 90 d after stimulation (n=5). Sham-operated time-matched controls were prepared for each time point (n=5). The miRNA expression was evaluated using Exiqon microarrays. Additionally, mRNA from the same animals was profiled using Affymetrix microarrays. We detected miRNA expression signatures that differentiate between control and epileptic animals. Significant changes in miRNA expression between stimulated and sham operated animals were observed at 7 and 30 d following stimulation. Moreover, we found that there are ensembles of miRNAs that change expression levels over time. Analysis of the mRNA expression from the same animals revealed that the expression of several mRNAs that are potential targets for miRNA with altered expression level is regulated in the expected direction. The functional characterization of miRNAs and their potential mRNA targets indicate that miRNA can participate in several molecular events that occur in epileptic tissue, including immune response and neuronal plasticity. This is the first report on changes in the expression of miRNA and the potential functional impact of these changes in the dentate gyrus of epileptic animals. Complex changes in the expression of miRNAs suggest an important role for miRNA in the molecular mechanisms of epilepsy.

Differential effects of electrical stimulation of the central amygdala and lateral hypothalamus on fos-immunoreactive neurons in the gustatory brainstem and taste reactivity behaviors in conscious rats.

Projections from the central amygdala (CeA) and lateral hypothalamus (LH) modulate the activity of gustatory brainstem neurons, however, the role of these projections in gustatory behaviors is unclear. The goal of the current study was to determine the effects of electrical stimulation of the CeA or LH on unconditioned taste reactivity (TR) behaviors in response to intra-oral infusion of tastants. In conscious rats, electrical stimulation of the CeA or LH was delivered with and without simultaneous intra-oral infusion of taste solutions via an intra-oral cannula. Immunohistochemistry for the Fos protein was used to identify neurons in the gustatory brainstem activated by the electrical and/or intra-oral stimulation. In the absence of intra-oral infusion of a tastant, electrical stimulation of either the CeA or the LH increased the number of ingestive, but not aversive, TR behaviors performed. During intra-oral infusions of taste solutions, CeA stimulation tended to increase aversive behaviors whereas LH stimulation dramatically reduced the number of aversive responses to quinine hydrochloride (QHCl). These data indicate that projections from the CeA and LH alter TR behaviors. A few of the behavioral effects were accompanied by changes in the number of Fos-immunoreactive neurons in the gustatory brainstem, suggesting a possible anatomical substrate for these effects.

Emergence of GABAergic-dependent regulation of input-specific plasticity in the adult rat prefrontal cortex during adolescence

The prefrontal cortex (PFC) receives multiple cortical and subcortical afferents that regulate higher order cognitive functions, many of which emerge late in adolescence. However, it remains unclear how these afferents influence PFC processing, especially in light of the protracted, late adolescent maturation of prefrontal GABAergic function. Here we investigated the role of PFC GABAergic transmission in regulating plasticity elicited from the ventral hippocampus and basolateral amygdala, and how such modulation undergoes functional changes during adolescence in rats. In vivo local field potential recordings, combined with prefrontal microinfusion of the GABA-A receptor antagonist picrotoxin, were employed to study the impact of ventral hippocampal and basolateral amygdala high-frequency stimulation on PFC plasticity. Ventral hippocampal-induced PFC plasticity begins to appear only by postnatal days (P) 45-55 with a transient suppression of the evoked response. A switch from transient to long-lasting depression (LTD) of the PFC response emerges after P55 and throughout adulthood (P65-120). Recordings conducted in the presence of picrotoxin revealed that PFC GABAergic transmission is critical for the expression of LTD. In contrast, basolateral amygdala stimulation resulted in PFC long-term potentiation, a form of plasticity that is already enabled by P30 and is insensitive to picrotoxin. The development of ventral hippocampal-dependent PFC LTD is contingent upon the recruitment of local prefrontal GABAergic transmission during adolescence whereas plasticity elicited from the basolateral amygdala is not. Thus, different mechanisms contribute to the refinement of prefrontal plasticity during adolescence as inputs from these two regions are critical for shaping PFC functions.

Status Epilepticus Induces Long Lasting Increase in S100A6 Expression in Astrocytes

In the present work we examined expression and localization of the S100A6 protein in rat brain in a model of epilepsy induced by Status Epilepticus evoked by amygdala stimulation. We demonstrate, through the use of the reverse transcriptase-polymerase chain reaction technique, that mRNA level of S100A6 was increased in cortex while, as found by immunoblotting, the level of the S100A6 protein was significantly higher in the cortex and in the CA1 area of the hippocampus at day 14 after stimulation. Immunohistochemical studies performed on rat brain slices indicated that S100A6 immunoreactivity was elevated in GFAP-positive astrocytes in the hippocampus and cortex starting from day 1, and further increased at day 4 and 14 after stimulation. Interestingly, in a subpopulation of astrocytes, up-regulation of S100A6 was associated with an increased level of β-catenin, a protein involved in regulation of S100A6 expression. Altogether, our data show a widespread and prolonged up-regulation of S100A6 in the epileptic brain and indicate that an increase in S100A6 immunoreactivity is related to astrogliosis.

A Transient Upregulation of Glutamine Synthetase in the Dentate Gyrus Is Involved in Epileptogenesis Induced by Amygdala Kindling in the Rat.

Reduction of glutamine synthetase (GS) function is closely related to established epilepsy, but little is known regarding its role in epileptogenesis. The present study aimed to elucidate the functional changes of GS in the brain and its involvement in epileptogenesis using the amygdala kindling model of epilepsy induced by daily electrical stimulation of basolateral amygdala in rats. Both expression and activity of GS in the ipsilateral dentate gyrus (DG) were upregulated when kindled seizures progressed to stage 4. A single dose of L-methionine sulfoximine (MSO, in 2 µl), a selective GS inhibitor, was administered into the ipsilateral DG on the third day following the first stage 3 seizure (just before GS was upregulated). It was found that low doses of MSO (5 or 10 µg) significantly and dose-dependently reduced the severity of and susceptibility to evoked seizures, whereas MSO at a high dose (20 µg) aggravated kindled seizures. In animals that seizure acquisition had been successfully suppressed with 10 µg MSO, GS upregulation reoccurred when seizures re-progressed to stage 4 and re-administration of 10 µg MSO consistently reduced the seizures. GLN at a dose of 1.5 µg abolished the alleviative effect of 10 µg MSO and deleterious effect of 20 µg MSO on kindled seizures. Moreover, appropriate artificial microRNA interference (1 and 1.5×106 TU/2 µl) of GS expression in the ipsilateral DG also inhibited seizure progression. In addition, a transient increase of GS expression and activity in the cortex was also observed during epileptogenesis evoked by pentylenetetrazole kindling. These results strongly suggest that a transient and region-specific upregulation of GS function occurs when epilepsy develops into a certain stage and eventually promotes the process of epileptogenesis. Inhibition of GS to an adequate degree and at an appropriate timing may be a potential therapeutic approach to interrupting epileptogenesis.

Anticonvulsant effect of dexmedetomidine in a rat model of self-sustaining status epilepticus with prolonged amygdala stimulation

Status epilepticus (SE), leading to 27 percent mortality in adult patients, becomes refractory to firstline intravenous diazepam, with prolonged seizure duration. The mechanism could be attributed to the declined inhibitory action of GABA; therefore, alternative medications acting on other targets are necessary. The aim of the present study was to examine whether DEX, a highly specific central α2-adrenoreceptor agonist, could show the anticonvulsant effect on self-sustaining SE (SSSE), and to explore the involved mechanisms. Five minutes after SSSE, which was induced in adult Wistar rats by constant amygdala stimulation for 25min, DEX was injected intraperitoneally at two dosages (50/100μg/kg). The number and cumulative time of repeated seizures were recorded; the levels of Glu/GABA and glutathione/malondialdehyde (GSH/MDA) in hippocampus tissue were detected. The results showed that DEX effectively decreased the number and cumulative time of repeated seizures, alleviated the levels of Glu and GSH/MDA in hippocampus tissue, but no effect was detected on the level of GABA, suggesting that DEX could be a potential agent for the treatment of SSSE, the possible mechanisms were antioxidation and inhibition of the Glu release.

Priming stimulation of basal but not lateral amygdala affects long-term potentiation in the rat dentate gyrus in vivo

The amygdaloid complex, or amygdala, has been implicated in assigning emotional significance to sensory information and producing appropriate behavioral responses to external stimuli. The lateral and basal nuclei (lateral and basal amygdala), which are termed together as basolateral amygdala, play a critical role in emotional and motivational learning and memory. It has been established that the basolateral amygdala activation by behavioral manipulations or direct electrical stimulation can modulate hippocampal long-term potentiation (LTP), a putative cellular mechanism of memory. However, the specific functional role of each subnucleus in the modulation of hippocampal LTP has not been studied yet, even though studies have shown cytoarchitectural differences between the basal and lateral amygdala and differences in the connections of each one of them to other brain areas. In this study we have tested the effects of lateral or basal amygdala pre-stimulation on hippocampal dentate gyrus LTP, induced by theta burst stimulation of the perforant path, in anesthetized rats. We found that while priming stimulation of the lateral amygdala did not affect LTP of the dentate gyrus, priming stimulation of the basal amygdala enhanced the LTP response when the priming stimulation was relatively weak, but impaired it when it was relatively strong. These results show that the basal and lateral nuclei of the amygdala, which have been already shown to differ in their anatomy and connectivity, may also have different functional roles. These findings raise the possibility that the lateral and basal amygdala differentially modulate memory processes in the hippocampus under emotional and motivational situations.

The Endogenous Opioids Related with Antinociceptive Effects Induced by Electrical Stimulation into the Amygdala

Pain relief is necessary and essential for dental treatments. Recently, the relationships of pain and emotion were studied, and electrical stimulation applied to the amygdala depressed the nociceptive response in the anterior cingulate cortex (ACC). Thus, the antinociceptive effects of the amygdala are elucidated, but its mechanism is not yet clarified. The present study was performed to investigate whether endogenous opioid system is related to the depression, and the quantitative changes of endogenous opioids induced by electrical stimulation to the amygdala. We investigated immunohistologically c-Fos expression to confirm the activated neurons, as well as the distribution and the amount of endogenous opioids (β-endorphin, enkephalin and dynorphin A) in the brain using male Wistar rats, when electrical stimulation was applied to the central nucleus of the amygdala (CeA) or noxious stimulation was delivered to the peripheral tissue. c-Fos expression in the ipsilateral ACC was increased by electrical stimulation to the CeA. However, only a small amount of endogenous opioids was observed in the ACC when noxious stimulation or electrical stimulation was applied. In contrast, the amount of dynorphin A in the periaqueductal gray (PAG) was increased by electrical stimulation to the CeA, and the amount of β-endorphin in the PAG was increased by noxious stimulation to the peripheral tissue. The results suggest that dynorphin A in the PAG induced by electrical stimulation to the CeA activate the descending antinociceptive system, and suggest that the nociceptive response in the ACC is depressed indirectly.

Hippocampal neurotrophins after stimulation of the basolateral amygdala, and memory improvement in lesioned rats

To investigate a possible role of neurotrophins in the memory improving effect of stimulating the basolateral amygdala. The BDNF and NGF levels were measured in the hippocampus of fimbria-fornix lesioned male rats after four days of training in the water maze and stimulation of the basolateral amygdala. The behavioral results confirm that daily post-training stimulation of the amygdala improves the learning abilities of the lesioned animals. BDNF increased in lesioned and trained animals, but stimulating the basolateral amygdala induces a significantly greater increase. NGF showed a slight (but significant) increase in fimbria-fornix lesioned and trained animals, but stimulating the amygdala does not produce a further increase. In separate groups of animals we measured the levels of both neurotrophins in acute experiments, after 2 and 24 hours of stimulating the amygdala. BDNF was significantly increased at both times, while NGF showed again only slight increases (significant at 24 h). These results suggest that the BDNF response to amygdala stimulation might be of functional importance in the observed learning improvement. The changes in NGF are most likely due to the accumulation of this protein after removal of the septal axons.

Amniotic Fluid or Its Fatty Acids Produce Actions Similar to Diazepam on Lateral Septal Neurons Firing Rate

Human amniotic fluid (AF) contains eight fatty acids (FATs), and both produce anxiolytic-like effects in adult rats and appetitive responses in human newborns. The medial amygdala and lateral septal nucleus function are related to social behavior, but the action of AF or its FATs in this circuit is known. We obtained 267 single-unit extracellular recordings in Wistar rats treated with vehicle (1 mL, s.c.; n = 12), human AF (1 mL, s.c.; n = 12), a FAT mixture (1 mL, s.c.; n = 13), diazepam (1 mg/kg, i.p.; n = 11), and fluoxetine (1 mg/kg, p.o.; n = 12). Compared with the vehicle group, the spontaneous septal firing rate in the AF, FAT mixture, and diazepam groups was the lowest and in the fluoxetine group the highest. Cumulative peristimulus histograms indicated that the significant change in septal firing occurred only in the AF and FAT mixture groups and exclusively in those neurons that increased their firing rate during amygdala stimulation. We conclude that human AF and its FATs produce actions comparable to anxiolytic drugs and are able to modify the responsivity of a circuit involved in social behavior, suggesting facilitation of social recognition processes by maternal-fetal fluids.

How repeated and unpredictable experiences turn into fear-memories

FRONTIERS COMMENTARY article Front. Neurosci., 21 February 2013 Volume 7 - 2013 | https://doi.org/10.3389/fnins.2013.00017

Electrical Low Frequency Stimulation of the Kindling Site Preserves the Electrophysiological Properties of the Rat Hippocampal CA1 Pyramidal Neurons From the Destructive Effects of Amygdala Kindling: The Basis for a Possible Promising Epilepsy Therapy

BackgroundDeep brain stimulation (DBS) has emerged as a potential therapeutic strategy in the treatment of neurological disorders including epilepsy. However, the cellular mechanism responsible for the effects of DBS remains largely undefined. Therefore, using electrophysiological approach, we aimed to determine the antiepileptic effects and restorative potential of low frequency stimulation (LFS) on amygdala kindling-induced changes in electrophysiological properties of rat hippocampal CA1 pyramidal neurons. MethodsAnimals were kindled by electrical stimulation of amygdala in a rapid kindling manner (12 times per day). In one group of animals, immediately after termination of daily 12 rapid kindling stimulations, the kindling site was subjected to 4 packages of LFS at intervals of 5 min (each package contained 200 monophasic square-wave pulses, 0.1 ms pulse duration at 1 Hz). Whole cell patch clamp recording under current clamp conditions was performed on visually identified pyramidal neurons in hippocampal slice preparations obtained from amygdala-kindled rats and the rats receiving LFS. ResultsKindling of the right basolateral amygdala profoundly affected spontaneous firing behavior and repetitive discharge characteristics of pyramidal neuronal electrophysiological properties. Application of LFS at the kindling site almost completely prevented the development of epilepsy and the disruptive effects of kindling on neuronal electrical activity through restoration of the normal electrophysiological characteristics. ConclusionsThe results of this study implied that application of LFS during kindling acquisition prevents the kindling induced changes in functional electrical properties of CA1 pyramidal neurons, suggesting that this action may be involved in the antiepileptogenic mechanism of LFS.

Morphology, PKCδ expression, and synaptic responsiveness of different types of rat central lateral amygdala neurons

Recent findings implicate the central lateral amygdala (CeL) in conditioned fear. Indeed, CeL contains neurons exhibiting positive (CeL-On) or negative (CeL-Off) responses to fear-inducing conditioned stimuli (CSs). In mice, these cells differ in their expression of protein kinase Cδ (PKCδ) and physiological properties. CeL-Off cells are PKCδ(+) and late firing (LF), whereas CeL-On cells are PKCδ(-) and express a regular-spiking (RS) or low-threshold bursting (LTB) phenotype. However, the scarcity of LF cells in rats raises questions about the correspondence between the organization of CeL in mice and rats. Therefore, we studied the PKCδ expression, morphological properties, synaptic responsiveness, and fear conditioning-induced plasticity of rat CeL neurons. No PKCδ(+) LF cells were encountered, but ≈20-25% of RS and LTB neurons were PKCδ(+). Compared with RS neurons, a higher proportion of LTB cells projected to central medial amygdala (CeM) and they had fewer primary dendritic branches, yet the amplitude of excitatory postsynaptic potentials (EPSPs) evoked by lateral amygdala (LA) stimulation was similar in RS and LTB cells. In contrast, LA-evoked inhibitory postsynaptic potentials (IPSPs) had a higher amplitude in LTB than RS neurons. Finally, fear conditioning did not induce plasticity at LA inputs to RS or LTB neurons. These findings point to major species differences in the organization of CeL. Since rat LTB cells are subjected to stronger feedforward inhibition, they are more likely to exhibit inhibitory CS responses than RS cells. This is expected to cause a disinhibition of CeM fear output neurons and therefore an increase in fear expression.

Amygdalar Stimulation Produces Alterations on Firing Properties of Hippocampal Place Cells

Stress is a biologically ubiquitous factor that, when perceived uncontrollable by humans and animals, can have lingering adverse effects on brain and cognitive functions. We have previously reported that rats that experienced inescapable-unpredictable stress subsequently exhibited decreased stability of firing rates of place cells in the CA1 hippocampus, accompanied by impairments in CA1 long-term synaptic potentiation and spatial memory consolidation. Because the elevated level of glucocorticoid hormones and the heightened amygdalar activity have been implicated in the emergence of stress effects on the hippocampus, we investigated whether administration of corticosterone and electrical stimulation of the amygdala can produce stress-like alterations on hippocampal place cells. To do so, male Long-Evans rats chronically implanted with tetrodes in the hippocampus and stimulating electrodes in the amygdala were placed on a novel arena to forage for randomly dispersed food pellets while CA1 place cells were monitored across two recording sessions. Between sessions, animals received either corticosterone injection or amygdalar stimulation. We found that amygdalar stimulation reliably evoked distress behaviors and subsequently reduced the pixel-by-pixel correlation of place maps across sessions, while corticosterone administration did not. Also, the firing rates of place cells between preamygdalar and postamygdalar stimulation recording sessions were pronouncedly different, whereas those between precorticosterone and postcorticosterone injection recording sessions were not. These results suggest that the heightened amygdalar activity, but not the elevated level of corticosterone per se, reduces the stability of spatial representation in the hippocampus by altering the firing rates of place cells in a manner similar to behavioral stress.

Measurement validity of tests for implicit negative bias

The study by Terbeck et al. (2012) that was published in Psychopharmacology, Online First concluded that propranolol reduces implicit negative racial bias. However, this conclusion is not supported by the study because the implicit association test (IAT) (Greenwald et al. 2009) has not been sufficiently validated and because the claim for clinical treatment due to amygdala suppression is unsupported. The classic race IAT compares whether one is quicker to link European–Americans with words associated with the concept “good” and African–Americans with words related to “bad” or vice versa. Gladwell (2005) summarizes it in the following way: The IAT measures a person’s attitude on an unconscious level or the immediate and automatic associations that occur even before a person has time to think. Is it possible to reliably measure “unconscious attitude” without using presumptions or indirect measures that rely on subjective notions? Blanton et al. (2007) also question the arbitrary nature of the cutoffs for mild, moderate, and strong preferences when no research shows where these limits should be. There is no research to support differences in individuals above or below the cutoffs. The IAT essentially attempts to measure the immeasurable and has been used prematurely in research without sufficient methodological validation. The measurement reliability of the IAT, as determined by test–retest methods, shows negligible consistency. The study only used data from blocks containing less than 15 % errors, but does not state how many of these blocks were discounted, which could be substantial. Moreover, it is mentioned that one participant was excluded due to high errors on both trials, and three participants had onlymain trials analyzed due to extreme errors in the practice session. These breakdowns in measurement quality are further compounded on the IAT developer's website (Greenwald et al. 2012) which states that “besides normal variation in the reliability of assessment, the IAT is also known to be malleable based on differences in the social setting and recent experience. These factors will influence the consistency of measurement across occasions.” The IATcould not have high measurement quality of attitude if so many extraneous factors have such influence. Lastly, the conclusion that the minimal effect seen in response latencies is the result of direct inhibition of amygdala stimulation is not supported. The limitations of previous studies that correlated the participant's IATscore with the extent of amygdala activation are noted, but the same limitations are not applied to the present study. For example, contradictory findings are referenced: “Phelps et al. (2003) found that a patient with bilateral amygdala damage exhibited an intact IATeffect, leading the authors to suggest that the amygdala may not be a critical structure for the manifestation of implicit bias.” In addition, the study concluded that more research needs to be conducted in order to determine whether propranolol acts peripherally or centrally. This means that propranolol may not even directly affect the brain, let alone a specific anatomic structure such as the amygdala. As a last possibility, an explanation that cannot be excluded is that propranolol simply equalizes mental reflex latencies, regardless of task. The study has many strengths, including an excellent review of previous studies, the use of visual analog scales, the use of a control group and two different post-intervention time points, excellent statistical analysis, well-constructed data tables, and most of all, an important topic. However, due to important T. S. Burchett : L. L. Glenn College of Nursing and Institute for Quantitative Biology, East Tennessee State University, P.O. Box 70658, Johnson City, TN 37604, USA

P.1.018 Modulation of glutamatergic synaptic transmission in prefrontal cortex by 5-HT2A receptors

glucocorticoids and b-adrenergic receptor activation could modulate amygdalar LTP. Experimental design: The effects of acute stress on BLA synaptic plasticity was studied in undisturbed control or restraint stressed mice. Next, the contribution of (i) corticosterone acting via the mineralocorticoid or glucocorticoid receptor (MR or GR) and (ii) b-adrenergic actions via the b2-adrenoceptor was investigated. Hereto, animals were pretreated intraperitoneally with the specific antagonists spironolactone (50mg/kg), mifepristone (10mg/kg) and propranolol (10mg/kg) respectively, or their vehicles. Thirty minutes later, animals were exposed to 20 min restraint stress or left undisturbed, subsequently decapitated after which brain slices were prepared for in vitro electrophysiological recordings. BLA field potentials were evoked 1−4 hours after stress via lateral amygdala stimulation. Subsequently, LTP was induced by applying high-frequency stimulation (100Hz, 1s) and recorded for 1 hr post-tetanus. Results: Compared to slices from non-stressed control mice, restraint stress effectively enhanced in vitro BLA LTP (response relative to pre-LTP baseline = 100%, mean±SEM: 142.1±5.9% vs 163.2±6.5%, p< 0.001), indicating increased synaptic strengthening after an acute emotional stressor. Next, we investigated the role of MR, GR and the b2-adrenoceptor in LTP formation of these mice. In undisturbed controls, mifepristone and propranolol did not influence LTP compared to vehicle. However, while initial responses remained unchanged, spironolactone gradually attenuated LTP (last 10 min, control: 135.4±2.6% vs spironolactone: 120.2±5.0%, p< 0.05), suggesting unstable LTP formation when MR is blocked. While initially reaching stressed control levels, similar attenuation with spironolactone was observed in stressed animals. Pretreatment with mifepristone resulted in very little LTP (stress/vehicle: 143.3±4.4% vs stress/mifepristone:117.2±4.0%, p< 0.05), suggesting that GR blockade not only prevented the stress-induced enhancement of LTP but attenuated LTP even beyond control levels. Propranolol decreased the initial stressinduced enhancement to control levels but also affected long-term LTP resulting in highly unstable synaptic strengthening. Conclusions: The present study shows that the BLA is highly sensitive to acute emotional stress, a situation that quickly and effectively increases LTP. Furthermore, the stress-induced strengthening in amygdalar plasticity seems to require both elevated central b-adrenergic signalling as well as corticosteroid actions. Although these systems affect LTP differently, they both seem to be critical in the formation of long-term stable emotional memory, even hours after the initial stress exposure. Reference(s)

Which cue to ‘want’? Opioid stimulation of central amygdala makes goal-trackers show stronger goal-tracking, just as sign-trackers show stronger sign-tracking

Pavlovian cues that have been paired with reward can gain incentive salience. Drug addicts find drug cues motivationally attractive and binge eaters are attracted by food cues. But the level of incentive salience elicited by a cue re-encounter still varies across time and brain states. In an animal model, cues become attractive and ‘wanted’ in an ‘autoshaping’ paradigm, where different targets of incentive salience emerge for different individuals. Some individuals (sign-trackers) find a predictive discrete cue attractive while others find a reward contiguous goal cue more attractive (location where reward arrives: goal-trackers). Here we assessed whether central amygdala mu opioid receptor stimulation enhances the phasic incentive salience of the goal-cue for goal-trackers during moments of predictive cue presence (expressed in both approach and consummatory behaviors to goal cue), just as it enhances the attractiveness of the predictive cue target for sign-trackers. Using detailed video analysis we measured the approaches, nibbles, sniffs, and bites directed at their preferred target for both sign-trackers and goal-trackers. We report that DAMGO microinjections in central amygdala made goal-trackers, like sign-trackers, show phasic increases in appetitive nibbles and sniffs directed at the goal-cue expressed selectively whenever the predictive cue was present. This indicates enhancement of incentive salience attributed by both goal trackers and sign-trackers, but attributed in different directions: each to their own target cue. For both phenotypes, amygdala opioid stimulation makes the individual's prepotent cue into a stronger motivational magnet at phasic moments triggered by a CS that predicts the reward UCS.

Post-treatment with rapamycin does not prevent epileptogenesis in the amygdala stimulation model of temporal lobe epilepsy

Approximately 30% of all epilepsy cases are acquired. At present there is no effective strategy to stop epilepsy development after the precipitating insult. Recent data from experimental models pointed to the mTOR pathway, which can be potently inhibited by rapamycin. However, data on the antiepileptic and antiepileptogenic properties of rapamycin are conflicting. Therefore, we tested whether rapamycin post-treatment influences epileptogenesis in the amygdala stimulation model of temporal lobe epilepsy in rats. Animals were treated with rapamycin (6mg/kg) or vehicle daily for 2 wks, beginning 24h after stimulation. Sham-operated animals were treated with rapamycin or vehicle but were not stimulated. Animals were video-EEG monitored to detect spontaneous seizures. Animals were sacrificed 4 wks later and brains were collected for Timm staining. There were no significant differences in the number of stimulated rats developing epilepsy; latency to first spontaneous seizure; number of seizures, or seizure frequency in epileptic animals. The area occupied by mossy fibers was significantly increased in stimulated vs. sham-operated animals but was not different in animals treated with rapamycin vs. vehicle. Collectively, our data suggest that the antiepileptic or antiepileptogenic action of rapamycin is not a universal phenomenon and might be limited to certain experimental models or experimental conditions.

Inter-individual variation in the anticonvulsant effect of phenobarbital in the pilocarpine rat model of temporal lobe epilepsy

Despite a large therapeutic arsenal of old and new antiepileptic drugs (AEDs), there remains a substantial unmet need for the patients with refractory (AED-resistant) epilepsy. Animal models of refractory epilepsy are needed for at least two goals; (1) better understanding of the mechanisms underlying resistance to AEDs, and (2) development of more efficacious AEDs for patients with refractory seizures. It is only incompletely understood why two patients with seemingly identical types of epilepsy and seizures may respond differently to the same AED. Prompted by this well-known clinical phenomenon, we tested whether epileptic rats from the same epilepsy model respond differently to AEDs and previously discovered phenobarbital (PB) responsive and resistant animals in groups of rats in which epilepsy had been induced by sustained electrical stimulation of the basolateral amygdala (BLA). In the present study, we used the same approach for the widely used pilocarpine model of temporal lobe epilepsy. Epileptic rats from this model were continuously video/EEG monitored over seven consecutive weeks, starting with a predrug control period of two weeks, then two weeks of daily treatment with PB at maximum tolerated doses, and finally a postdrug control period of three weeks. In those rats that were included in response selection, 50% did not adequately respond to PB, whereas PB significantly decreased seizure frequency and severity in another 50% of the animals. Responders and nonresponders did not differ in predrug seizure frequency, PB plasma levels or hippocampal neurodegeneration, but behavioral differences were observed in anxiety models. These findings demonstrate that in the pilocarpine model, similar to epilepsy patients, epileptic rats differ in their response to an AED, which is most likely due to as yet unknown genetic factors.