Kevin H. McAllister

Translocator protein (18 kD) as target for anxiolytics without benzodiazepine-like side effects.

Keeping Calm Benzodiazepines are the most prescribed anxiolytics and are used by a broad population. However, benzodiazepines can cause unwanted side effects, including sedation, development of tolerance, and withdrawal symptoms after long-term administration. Rupprecht et al. (p. 490; published online 18 June) now find that a translocator protein (18-kD) ligand, XBD173, is a fast-acting anxiolytic agent, both in animals and humans, which lacks the unwanted side effects of benzodiazepines and provides a promising target for novel clinically effective anxiolytic drugs. Possible drug alternative for rapid treatment of anxiety disorders could replace benzodiazepines. Most antianxiety drugs (anxiolytics) work by modulating neurotransmitters in the brain. Benzodiazepines are fast and effective anxiolytic drugs; however, their long-term use is limited by the development of tolerance and withdrawal symptoms. Ligands of the translocator protein [18 kilodaltons (kD)] may promote the synthesis of endogenous neurosteroids, which also exert anxiolytic effects in animal models. Here, we found that the translocator protein (18 kD) ligand XBD173 enhanced γ-aminobutyric acid–mediated neurotransmission and counteracted induced panic attacks in rodents in the absence of sedation and tolerance development. XBD173 also exerted antipanic activity in humans and, in contrast to benzodiazepines, did not cause sedation or withdrawal symptoms. Thus, translocator protein (18 kD) ligands are promising candidates for fast-acting anxiolytic drugs with less severe side effects than benzodiazepines.

The selective nicotinic acetylcholine receptor α7 agonist JN403 is active in animal models of cognition, sensory gating, epilepsy and pain

Several lines of evidence suggest that the nicotinic acetylcholine receptor alpha7 (nAChR alpha7) is involved in central nervous system disorders like schizophrenia and Alzheimers disease as well as in inflammatory disorders like sepsis and pancreatitis. The present article describes the in vivo effects of JN403, a compound recently characterized to be a potent and selective partial nAChR alpha7 agonist. JN403 rapidly penetrates into the brain after i.v. and after p.o. administration in mice and rats. In the social recognition test in mice JN403 facilitates learning/memory performance over a broad dose range. JN403 shows anxiolytic-like properties in the social exploration model in rats and the effects are retained after a 6h pre-treatment period and after subchronic administration. The effect on sensory inhibition was investigated in DBA/2 mice, a strain with reduced sensory inhibition under standard experimental conditions. Systemic administration of JN403 restores sensory gating in DBA/2 mice, both in anaesthetized and awake animals. Furthermore, JN403 shows anticonvulsant potential in the audiogenic seizure paradigm in DBA/2 mice. In the two models of permanent pain tested, JN403 produces a significant reversal of mechanical hyperalgesia. The onset was fast and the duration lasted for about 6h. Altogether, the present set of data suggests that nAChR alpha7 agonists, like JN403 may be beneficial for improving learning/memory performance, restoring sensory gating deficits, and alleviating pain, epileptic seizures and conditions of anxiety.

mGluR7 facilitates extinction of aversive memories and controls amygdala plasticity

Formation and extinction of aversive memories in the mammalian brain are insufficiently understood at the cellular and molecular levels. Using the novel metabotropic glutamate receptor 7 (mGluR7) agonist AMN082, we demonstrate that mGluR7 activation facilitates the extinction of aversive memories in two different amygdala-dependent tasks. Conversely, mGluR7 knockdown using short interfering RNA attenuated the extinction of learned aversion. mGluR7 activation also blocked the acquisition of Pavlovian fear learning and its electrophysiological correlate long-term potentiation in the amygdala. The finding that mGluR7 critically regulates extinction, in addition to acquisition of aversive memories, demonstrates that this receptor may be relevant for the manifestation and treatment of anxiety disorders.

The rostral anterior cingulate cortex modulates the efficiency of amygdala-dependent fear learning.

BACKGROUND The rostral anterior cingulate cortex (rACC) and the amygdala consistently emerge from neuroimaging studies as brain regions crucially involved in normal and abnormal fear processing. To date, however, the role of the rACC specifically during the acquisition of auditory fear conditioning still remains unknown. The aim of this study is to investigate a possible top-down control of a specific rACC sub-region over amygdala activation during pavlovian fear acquisition. METHODS We performed excitotoxic lesions, temporal inactivation, and activation of a specific sub-region of the rACC that we identified by tracing studies as supporting most of the connectivity with the basolateral amygdala (r(Amy)-ACC). The effects of these manipulations over amygdala function were investigated with a classical tone-shock associative fear conditioning paradigm in the rat. RESULTS Excitotoxic lesions and transient inactivation of the r(Amy)-ACC pre-training selectively produced deficits in the acquisition of the tone-shock associative learning (but not context). This effect was specific for the acquisition phase. However, the deficit was found to be transient and could be overcome by overtraining. Conversely, pre-training transient activation of the r(Amy)-ACC facilitated associative learning and increased fear expression. CONCLUSIONS Our results suggest that a subregion of the rACC is key to gating the efficiency of amygdala-dependent auditory fear conditioning learning. Because r(Amy)-ACC inputs were confirmed to be glutamatergic, we propose that recruitment of this brain area might modulate overall basolateral amygdala excitatory tone during conditioned stimulus-unconditioned stimulus concomitant processing. In the light of clinical research, our results provide new insight on the effect of inappropriate rACC recruitment during emotional events.

MRI Analysis of the Changes in Apparent Water Diffusion Coefficient, T2 Relaxation Time, and Cerebral Blood Flow and Volume in the Temporal Evolution of Cerebral Infarction Following Permanent Middle Cerebral Artery Occlusion in Rats

Detailed knowledge of similarities and differences between animal models and human stroke is decisive for selecting clinically effective drugs based on efficacy data obtained preclinically. Differences in the temporal evolution of stroke pathologies between animal models and man have been reported. In view of the importance of this issue for the development of neuroprotective treatments, the temporal evolution of stroke pathologies in the rat permanent middle cerebral artery occlusion (pMCAO) model has been evaluated with magnetic resonance imaging modalities under experimental conditions matching as close as possible those used in humans. Changes in the ipsilateral and contralateral cortex and striatum of cerebral blood flow (CBF) and volume (CBV), apparent diffusion coefficient (ADC), and spin-spin relaxation time (T(2)), as well as total cortical and striatal infarct volumes, calculated from CBF, ADC, and T(2) maps, were determined starting 1 h up to 216 h post-pMCAO. The temporal evolution of the MRI parameters in this rat model was similar to that observed in humans. In particular, the ADC values were decreased for more than 3 days and returned back to baseline between 4 to 8 days, to increase by day 9 only. Thus the stroke pathology in this rat model develops at a similar pace as in stroke patients arguing against a fundamental difference in the mechanisms involved. The infarct volumes however develop differently in this rat model as they invariably increase over the first 48 h, while in humans the evolution of infarct volume is slower and more heterogeneous.

The rostral anterior cingulate cortex modulates depression but not anxiety-related behaviour in the rat

A growing body of functional imaging studies suggests that human depression and anxiety symptoms are associated with functional abnormalities in the circuitry formed by the rostral anterior cingulate cortex (rACC) and its direct limbic and paralimbic connections. In rodents however, the role of the rACC (rCG1/rCG2) remains unknown in depression-related behaviours and elusive in acute anxiety. In order to address this, we specifically lesioned the rat rCG1/rCG2, and assessed the behavioural outcome using a modified forced swim test (FST) and the elevated plus maze (EPM), tests for depression and anxiety related behaviours respectively. Lesions of the rostral anterior cingulate cortex significantly increased the time spent immobile in the FST without affecting climbing or swimming performances, suggesting a pro-depressant effect. On the contrary, none of the parameters measured in the EPM was affected by the lesion. These data point to an involvement of the rCG1/rCG2 in depression-related coping behaviours.

Fear-reducing effects of intra-amygdala neuropeptide Y infusion in animal models of conditioned fear: an NPY Y1 receptor independent effect

RationaleNeuropeptide Y (NPY) and its receptors are densely localized in brain regions involved in the mediation and modulation of fear, including the amygdala. Several studies showed that central NPY is involved in the modulation of fear and anxiety.ObjectivesIn the present study, we investigated (1) whether intra-amygdala injections of NPY affect the expression of conditioned fear and (2) whether NPY Y1 receptors (Y1R) mediates the effects of these intra-amygdaloid NPY injections.ResultsIntra-amygdala NPY injections robustly decreased the expression of conditioned fear measured by conditioned freezing and fear-potentiated startle. These NPY effects were not mimicked by intra-amygdala injections of the Y1R agonists Y-28 or Y-36, and co-infusion of the Y1R antagonist BIBO 3304 did not block the NPY effects. Furthermore, we tested Y1R-deficient mice in conditioned freezing and found no differences between wild type and mutant littermates. Finally, we injected NPY into the amygdala of Y1R-deficient mice. Y1R deficiency had no effect on the fear-reducing effects of intra-amygdala NPY.ConclusionsThese data show an important role of the transmitter NPY within the amygdala for the expression of conditioned fear. Y1R do not appear to be involved in the mediation of the observed intra-amygdala NPY effects suggesting that these effects are mediated via other NPY receptors.

Cytoprotection does not preserve brain functionality in rats during the acute post-stroke phase despite evidence of non-infarction provided by MRI.

In animal models of stroke the promise of a therapy is commonly judged from infarct size measurements, assuming that a reduction in infarct size results in reduction of the functional deficits. We have evaluated the validity of the concept that structural integrity translates into functional integrity during the acute post‐stroke period (24 h). Unilateral permanent middle cerebral artery occlusion (pMCAO) in Fischer F344 rats leads to infarcts comprising the ipsilateral striatum and cortical structures, including the somatosensory cortex. Infarct volumes were assessed using magnetic resonance imaging (MRI) methods (T2, diffusion, perfusion MRI). The functional integrity of the somatosensory cortex was assessed by functional MRI (fMRI) measuring changes in local cerebral blood volume, and by assessing the forelimb grip strength and the beam‐walking performance of the animals. Treatment with the calcium antagonist isradipine (2.5 mg/kg injected s.c. immediately after pMCAO) reduced the total infarct size by more than 40% compared to vehicle‐injected controls. In particular, the ipsilateral somatosensory cortex appeared normal in diffusion‐ and T2‐weighted MRI images. In sham‐operated rats simultaneous electrical stimulation of both forepaws led to similar activation of both somatosensory cortices, while in pMCAO animals given vehicle only the contralateral cortex showed an fMRI response. Similarly, in pMCAO rats treated with isradipine, functional activation following bilateral electrical stimulation was only detected in the contralateral somatosensory cortex despite the normal appearance of the ipsilateral cortex in MRI images. Furthermore, fMRI responses to pharmacological stimulation with bicuculline were virtually absent in the ipsilateral somatosensory cortices both in vehicle‐ and isradipine‐treated rats. Finally there was no significant difference between vehicle‐ and isradipine‐treated animals upon the performance of beam‐walking test or in forelimb grip strength. It is concluded that during the acute (24 h) post‐occlusion period, structural integrity in the somatosensory cortex revealed by MRI does not translate into preservation of function. Copyright

JN403, in vitro characterization of a novel nicotinic acetylcholine receptor α7 selective agonist

This report describes the in vitro features of a novel selective nicotinic acetylcholine receptor (nAChR) alpha7 agonist, JN403, (S)-(1-Aza-bicyclo[2.2.2]oct-3-yl)-carbamic acid (S)-1-(2-fluoro-phenyl)-ethyl ester. JN403 was evaluated in a number of in vitro systems of different species, at recombinant receptors using radioligand binding, signal transduction and electrophysiological studies. When using [(125)I] alpha-bungarotoxin (alpha-BTX) as a radioligand, JN403 has high affinity for human recombinant nAChR alpha7 (pK(D)=6.7). Functionally, JN403 is a partial and potent agonist at human nAChR alpha7. The compound stimulates calcium influx in GH3 cells recombinantly expressing the human nAChR with an pEC(50) of 7.0 and an E(max) of 85% (compared to the full agonist epibatidine). In Xenopus oocytes expressing human nAChR alpha7 JN403 induces inward currents with an pEC(50) of 5.7 and an E(max) of 55%. In both recombinant systems JN403 is a partial agonist and the agonistic effects are blocked after pre-administration of methyllycaconitine (MLA, 100nM), a nAChR alpha7 antagonist. In functional calcium influx assays, JN403 displays a significantly lower potency for other subtypes of human nAChRs like alpha4beta2, alpha3beta4, alpha1beta1gammadelta as well as 5HT(3) receptors when tested functionally as an antagonist (pIC(50)<4.8) and is devoid of agonistic activity (pEC(50)<4). Similarly, JN403 shows low binding activity at a wide panel of neurotransmitter receptors. Thus, JN403 is a potent and selective nAChR alpha7 agonist and will be a useful tool for the characterization of nAChR alpha7 mediated effects both in vitro and in vivo.

Intra-amygdala injections of neuropeptide S block fear-potentiated startle

Injections of neuropeptide S (NPS) into the lateral ventricle induce a strong hyperactivity. Since most behavioral paradigms are dependent of spontaneous locomotor activity, this makes it difficult to interpret the role of NPS in such paradigms. The aim of the present experiment was to investigate the effects of NPS in fear-potentiated startle, a behavioral fear paradigm which we believe is less sensitive to general changes in locomotor activity. Furthermore, NPS was directly injected into the amygdala, the central site of the neural fear circuitry. Our data shows that intra-amygdala NPS injections dose-dependently block the expression of conditioned fear and that this effect is independent of NPS effects on locomotor activity. This strongly supports a crucial role of amygdaloid NPS in conditioned fear.