Christophe Grundschober

Dimorphic effects of leptin on the circadian and hypocretinergic systems of mice.

The hormone leptin controls food intake and body weight through its receptor in the hypothalamus, and may modulate physiological functions such as reproduction, sleep or circadian timing. In the present study, the effects of leptin on the resetting of the circadian clock, the hypothalamic suprachiasmatic nucleus (SCN) and on the activity of the hypocretinergic system were examined in vivo, with comparative analysis between male and female mice. A single leptin injection (5u2003mg/kg) at both the onset and offset of the activity period did not alter locomotion of mice housed under a 12u2003:u200312u2003h light/dark cycle and did not shift the circadian behavioral rhythm of mice housed in constant darkness. By contrast, leptin potentiated the phase‐shifting effect of a 30‐min light‐pulse on behavioural rhythms during the late subjective night, although only in females. This was accompanied by a higher induction of the clock genes Per1 and Per2 in the SCN. A 2‐week chronic exposure to a physiological dose of leptin (100u2003μg/kg per day) decreased locomotor activity, expression of hypocretin receptor 1 and 2, as well as the number of hypocretin‐immunoreactive neurones only in female mice, whereas the number of c‐fos‐positive hypocretinergic neurones was reduced in both genders. These results highlight a dimorphic effect of leptin on the hypocretinergic system and on the response of the circadian clock to light. Leptin may thus modulate the sleep/wake cycle and circadian system beside its well‐established action on food intake and regulation of body weight.

Examining face and construct validity of a noninvasive model of panic disorder in Lister-hooded rats.

RationaleIncreasing evidence suggests that defensive escape behavior in Lister-hooded (LH) rats induced by ultrasound application may be an animal model of panic disorder.ObjectiveThe objectives of this study were to further explore the face and construct validity of ultrasound-induced escape behavior by characterizing the autonomic and neuroendocrine response to ultrasound, and to examine the underlying neuronal structures by comparing the effects of the anxiolytic with panicolytic properties, diazepam, with a preclinical anxiolytic without panicolytic-like activity, the NOP agonist Ro 64-6198.Materials and methodsLH rats were implanted with telemetry transmitters to monitor heart rate and core body temperature before, during, and after ultrasound application. Blood samples were taken after ultrasound application for corticosterone analysis. Ultrasound-induced c-Fos expression was measured in different periaqueductal gray (PAG) and amygdala subregions after treatment with diazepam or Ro 64-6198.ResultsUltrasound application increased heart rate and body temperature, but did not alter plasma corticosterone levels. Ultrasound application increased c-Fos expression in the dorsal and dorsolateral PAG (dPAG, dlPAG) and amygdaloid subregions. Diazepam, but not Ro 64-6198, reduced c-Fos expression in the dPAG/dlPAG, while Ro 64-6198, but not diazepam, reduced c-Fos expression in the central amygdala.ConclusionsSimilar to human panic attacks, ultrasound application to LH rats activated the autonomic, but not the neuroendocrine, stress system. Also, like in humans, the current data confirm and extend that the dPAG/dlPAG plays a key role in ultrasound-induced escape behavior. These observations suggest that ultrasound-induced escape behaviors in LH rats have face and construct validity for panic disorders.

Discovery of highly selective brain-penetrant vasopressin 1a antagonists for the potential treatment of autism via a chemogenomic and scaffold hopping approach.

From a micromolar high throughput screening hit 7, the successful complementary application of a chemogenomic approach and of a scaffold hopping exercise rapidly led to a low single digit nanomolar human vasopressin 1a (hV1a) receptor antagonist 38. Initial optimization of the mouse V1a activities delivered suitable tool compounds which demonstrated a V1a mediated central in vivo effect. This novel series was further optimized through parallel synthesis with a focus on balancing lipophilicity to achieve robust aqueous solubility while avoiding P-gp mediated efflux. These efforts led to the discovery of the highly potent and selective brain-penetrant hV1a antagonist RO5028442 (8) suitable for human clinical studies in people with autism.

Imaging trait anxiety in high anxiety F344 rats: Focus on the dorsomedial prefrontal cortex

Functional magnetic resonance imaging (fMRI) has become an important method in clinical psychiatry research whereas there are still only few comparable preclinical investigations. Herein, we report that fMRI in rats can provide key information regarding brain areas underlying anxiety behavior. Perfusion as surrogate for neuronal activity was measured by means of arterial spin labeling-based fMRI in various brain areas of high anxiety F344 rats and control Sprague-Dawley rats. In one of these areas, the dorsomedial prefrontal cortex (dmPFC), c-Fos labeling was compared between these two strains with immunolabeling. The effects of a neurotoxic ibotenic acid lesion of the dmPFC in F344 rats were examined in a social approach-avoidance anxiety procedure and fMRI. Regional brain activity of high anxiety F344 rats was different in selective cortical and subcortical areas as compared to that of low anxiety Sprague-Dawley rats; the largest difference (i.e. hyperactivity) was measured in the dmPFC. Independently, c-Fos labeling confirmed that F344 rats show increased dmPFC activity. The functional role was confirmed by neurotoxic lesion of the dmPFC that reversed the high anxiety-like behavior and partially normalized the brain activity pattern of F344 rats. The current findings may have translational value as increased activity is reported in an equivalent cortical area in patients with social anxiety, suggesting that pharmacological or functional inhibition of activity in this brain area should be explored to alleviate social anxiety in patients.

Building bridges for highly selective, potent and stable oxytocin and vasopressin analogs

Oxytocin (OT) is an exciting potential therapeutic agent, but it is highly sensitive to modification and suffers extensive degradation at elevated temperature and in vivo. Here we report studies towards OT analogs with favorable selectivity, affinity and potency towards the oxytocin receptor (OTR), in addition to improving stability of the peptide by bridging the disulfide region with substituted dibromo-xylene analogs. We found a sensitive structure-activity relationship in which meta-cyclized analogs (dOTmeta) gave highest affinity (50u202fnM Ki), selectivity (34-fold), and agonist potency (34u202fnM EC50, 87-fold selectivity) towards OTR. Surprisingly, ortho-cyclized analogs demonstrated OTR and vasopressin V1a receptor subtype affinity (220u202fnM and 69u202fnM, respectively) and pharmacological activity (294u202fnM and 35u202fnM, respectively). V1a binding and selectivity for ortho-cyclized peptides could be improved 6-fold by substituting a neutral residue at position 8 with a basic amino acid, providing potent antagonists (14u202fnM IC50) that displayed no activation of the OTR. Furthermore, xylene-bridged analogs demonstrated increased stability compared to OT at elevated temperature, demonstrating promising therapeutic potential for these analogs which warrants further study.