Molecular mechanisms of classical fear conditioning : GABAergic factors and their role in fear-related network activities

Magdeburg, Univ., Fak. für Naturwiss., Diss., 2010Jorge R. Bergado Acost

Human Stiff-Person Syndrome IgG Induces Anxious Behavior in Rats

Background: Anxiety is a heterogeneous behavioral domain playing a role in a variety of neuropsychiatric diseases. While anxiety is the cardinal symptom in disorders such as panic disorder, co-morbid anxious behavior can occur in a variety of diseases. Stiff person syndrome (SPS) is a CNS disorder characterized by increased muscle tone and prominent agoraphobia and anxiety. Most patients have high-titer antibodies against glutamate decarboxylase (GAD) 65. The pathogenic role of these autoantibodies is unclear. Methodology/Principal Findings: We re-investigated a 53 year old woman with SPS and profound anxiety for GABA-A receptor binding in the amygdala with (11)C-flumazenil PET scan and studied the potential pathogenic role of purified IgG from her plasma filtrates containing high-titer antibodies against GAD 65. We passively transferred the IgG fraction intrathecally into rats and analyzed the effects using behavioral and in vivo electrophysiological methods. In cell culture, we measured the effect of patient IgG on GABA release from hippocampal neurons. Repetitive intrathecal application of purified patient IgG in rats resulted in an anxious phenotype resembling the core symptoms of the patient. Patient IgG selectively bound to rat amygdala, hippocampus, and frontal cortical areas. In cultured rat hippocampal neurons, patient IgG inhibited GABA release. In line with these experimental results, the GABA-A receptor binding potential was reduced in the patient’s amygdala/hippocampus complex. No motor abnormalities were found in recipient rats. Conclusion/Significance: The observations in rats after passive transfer lead us to propose that anxiety-like behavior can be induced in rats by passive transfer of IgG from a SPS patient positive for anti-GAD 65 antibodies. Anxiety, in this case, thus may be an antibody-mediated phenomenon with consecutive disturbance of GABAergic signaling in the amygdala region

A dopaminergic switch for fear to safety transitions

Overcoming aversive emotional memories requires neural systems that detect when fear responses are no longer appropriate. The midbrain ventral tegmental area (VTA) dopamine system has been implicated in reward and more broadly in signalling when a better than expected outcome has occurred. This suggests that it may be important in guiding fear to safety transitions. We report that when an expected aversive outcome does not occur, activity in midbrain dopamine neurons is necessary to extinguish behavioral fear responses and engage molecular signalling events in extinction learning circuits. Furthermore, a specific dopamine projection to the nucleus accumbens medial shell is partially responsible for this effect. By contrast, a separate dopamine projection to the medial prefrontal cortex opposes extinction learning. This demonstrates a novel function for the canonical VTA-dopamine reward system and reveals opposing behavioural roles for different dopamine neuron projections in fear extinction learning

Efectos del Factor de Crecimiento Nervioso (NGF) sobre la conducta en un modelo experimental de corea de huntington en ratas

The Huntington disease is neurodegenerative pathology with affects the basal ganglia. The neutrotrophic factors have been suggested as a possible treatment of the disease. The aims of our study were to increase our knowledge about the behavioral characterization of the Huntington models induced by quinolinic acid (QA) and the effects of nerve growth factor (NGF). In our work we used rats with unilateral lesion of striatum induced by AQ (112mM, pH=7,4), which received NGF-treatment in different times in relation to the day of the lesion: NGF 2 day before the lesion (NGFQA), NGF simultaneously with QA (QA+NGF) and NGF 2 day after the lesion (QANGF). The intact and lesioned rats without treatment served as the control groups. The memory (Morris water maze) and motor activity (rotational behavior induced by amphetamine) were evaluated to study the effects of the lesion and treatment. Our results demonstrated that this early ap-plication of NGF has like preventives action in the neuroprotection of striatal population demostrated in behavioral results.La enfermedad de Huntington (EH) es un trastorno neurodegenerativo que afecta a los ganglios basales. El uso de factores neurotróficos ha sido propuesto como posible tratamiento de esta enfermedad. El objetivo de nuestro estudio fue el de evaluar los efectos del factor de crecimiento neural (NGF) en el modelo de Huntington inducido por la lesión estriatal de acido queinolínico (AQ). Para el estudio se utilizaron ratas las cuales fueron lesionadas con AQ (112mM, pH = 7,4) las cuales fueron tratadas con NG, en diferentes tiempos en relación al día de la lesión: NGF 2 días antes de la inducción de la lesión (NGFAQ), NGF simultaneo con la lesión (AQ+NGF) y NGF 2 días después de la lesión (AQNGF). Los animales intactos y lesionados sin tratamiento sirvieron como grupos controles. Se realizaron estudios conductuales para evaluar los efectos de la lesión y del tratamiento sobre la memoria y aprendizaje espacial (laberinto acuático de Morris) y la actividad motora (rotación inducida por anfetamina). Los resultados de nuestro experimento demostraron que el NGF parece actuar de forma preventiva en la neuroprotección de poblaciones neuronales en el estriado demostrado en los estudios conductuales

Efector del factor de crecimiento nervioso (NGF) sobre la conducta en un modelo experimental de Corea de Huntington en ratas.

Pág. 55-68La enfermedad de Huntington (EH) es un trastorno neurodegenerativo que afecta a los ganglios basales. El uso de factores neurotróficos ha sido propuesto como posible tratamiento de esta enfermedad. El objetivo de nuestro estudio fue el de evaluar los efectos del factor de crecimiento neural (NGF) en el modelo de Huntington inducido por la lesión estriatal de acido queinolínico (AQ). Para el estudio se utilizaron ratas las cuales fueron lesionadas con AQ (112mM, pH = 7,4) las cuales fueron tratadas con NG, en diferentes tiempos en relación al día de la lesión: NGF 2 días antes de la inducción de la lesión (NGFAQ), NGF simultaneo con la lesión (AQ+NGF) y NGF 2 días después de la lesión (AQNGF). Los animales intactos y lesionados sin tratamiento sirvieron como grupos controles. Se realizaron estudios conductuales para evaluar los efectos de la lesión y del tratamiento sobre la memoria y aprendizaje espacial (laberinto acuático de Morris) y la actividad motora (rotación inducida por anfetamina). Los resultados de nuestro experimento demostraron que el NGF parece actuar de forma preventiva en la neuroprotección de poblaciones neuronales en el estriado demostrado en los estudios conductuales.ABSTRACT The Huntington disease is neurodegenerative pathology with affects the basal ganglia. The neutrotrophic factors have been suggested as a possible treatment of the disease. The aims of our study were to increase our knowledge about the behavioral characterization of the Huntington models induced by quinolinic acid (QA) and the effects of nerve growth factor (NGF). In our work we used rats with unilateral lesion of striatum induced by AQ (112mM, pH=7,4), which received NGF-treatment in different times in relation to the day of the lesion: NGF 2 day before the lesion (NGFQA), NGF simultaneously with QA (QA+NGF) and NGF 2 day after the lesion (QANGF). The intact and lesioned rats without treatment served as the control groups. The memory (Morris water maze) and motor activity (rotational behavior induced by amphetamine) were evaluated to study the effects of the lesion and treatment. Our results demonstrated that this early application of NGF has like preventives action in the neuroprotection of striatal population demostrated in behavioral results

Deficiency of the 65 kDa isoform of glutamic acid decarboxylase impairs extinction of cued but not contextual fear memory

Extinction procedures are clinically relevant for reducing pathological fear, and the mechanisms of fear regulation are a subject of intense research. The amygdala, hippocampus, and prefrontal cortex (PFC) have all been suggested to be key brain areas in extinction of conditioned fear. GABA has particularly been implicated in extinction learning, and the 65 kDa isoform of glutamic acid decarboxylase (GAD65) may be important in elevating GABA levels in response to environmental signals. Extinction of conditioned fear was examined in Gad65−/− mice while recording local field potentials from the amygdala, hippocampus, and PFC simultaneously while monitoring behavior. Gad65−/− mice showed generalization of cued fear, as reported previously, and impaired extinction of cued fear, such that fear remained high across extinction training. This endurance in cued fear was associated with theta frequency synchronization between the amygdala and hippocampus. Extinction of contextual fear, however, was unaltered in Gad65−/− mice when compared with wild-type littermates. The data imply that GAD65 plays a critical role in regulating cued fear responses during extinction learning and that, during this process, GABAergic signaling is involved in modulating synchronized activity between the amygdala and hippocampus. In view of the more pronounced effect on cued versus contextual fear extinction, these influences may rely more on GABAergic mechanisms in the amygdala

Circadian modulation of anxiety: a role for somatostatin in the amygdala.

Pharmacological evidence suggests that the neuropeptide somatostatin (SST) exerts anxiolytic action via the amygdala, but findings concerning the putative role of endogenous SST in the regulation of emotional responses are contradictory. We hypothesized that an endogenous regulation of SST expression over the course of the day may determine its function and tested both SST gene expression and the behavior of SST knock out (SST⁻/⁻) mice in different aversive tests in relation to circadian rhythm. In an open field and a light/dark avoidance test, SST⁻/⁻ mice showed significant hyperactivity and anxiety-like behavior during the second, but not during the first half of the active phase, failing to show the circadian modulation of behavior that was evident in their wild type littermates. Behavioral differences occurred independently of changes of intrinsically motivated activity in the home cage. A circadian regulation of SST mRNA and protein expression that was evident in the basolateral complex of the amygdala of wild type mice may provide a neuronal substrate for the observed behavior. However, fear memory towards auditory cue or the conditioning context displayed neither a time- nor genotype-dependent modulation. Together this indicates that SST, in a circadian manner and putatively via its regulation of expression in the amygdala, modulates behavior responding to mildly aversive conditions in mice

Critical role of the 65-kDa isoform of glutamic acid decarboxylase in consolidation and generalization of Pavlovian fear memory

Evidence suggests that plasticity of the amygdalar and hippocampal GABAergic system is critical for fear memory formation. In this study we investigated in wild-type and genetically manipulated mice the role of the activity-dependent 65-kDa isozyme of glutamic acid decarboxylase (GAD65) in the consolidation and generalization of conditioned fear. First, we demonstrate a transient reduction of GAD65 gene expression in the dorsal hippocampus (6 h post training) and in the basolateral complex of the amygdala (24 h post training) during distinct phases of fear memory consolidation. Second, we show that targeted ablation of the GAD65 gene in Gad65−/− mice results in a pronounced context-independent, intramodal generalization of auditory fear memory during long-term (24 h or 14 d) but not short-term (30 min) memory retrieval. The temporal specificity of both gene regulation and memory deficits in Gad65 mutant mice suggests that GAD65-mediated GABA synthesis is critical for the consolidation of stimulus-specific fear memory. This function appears to involve a modulation of neural activity patterns in the amygdalo-hippocampal pathway as indicated by a reduction in theta frequency synchronization between the amygdala and hippocampus of Gad65−/− mice during the expression of generalized fear memory