Koen G.C. Westphal

Transcriptional and behavioral interaction between 22q11.2 orthologs modulates schizophrenia-related phenotypes in mice

Microdeletions of 22q11.2 represent one of the highest known genetic risk factors for schizophrenia. It is likely that more than one gene contributes to the marked risk associated with this locus. Two of the candidate risk genes encode the enzymes proline dehydrogenase (PRODH) and catechol-O-methyltransferase (COMT), which modulate the levels of a putative neuromodulator (L-proline) and the neurotransmitter dopamine, respectively. Mice that model the state of PRODH deficiency observed in humans with schizophrenia show increased neurotransmitter release at glutamatergic synapses as well as deficits in associative learning and response to psychomimetic drugs. Transcriptional profiling and pharmacological manipulations identified a transcriptional and behavioral interaction between the Prodh and Comt genes that is likely to represent a homeostatic response to enhanced dopaminergic signaling in the frontal cortex. This interaction modulates a number of schizophrenia-related phenotypes, providing a framework for understanding the high disease risk associated with this locus, the expression of the phenotype, or both.

Akt1 deficiency affects neuronal morphology and predisposes to abnormalities in prefrontal cortex functioning

There is accumulating evidence that AKT signaling plays a role in the pathogenesis of schizophrenia. We asked whether Akt1 deficiency in mice results in structural and functional abnormalities in prefrontal cortex (PFC). Exploratory transcriptional profiling revealed concerted alterations in the expression of PFC genes controlling synaptic function, neuronal development, myelination, and actin polymerization, and follow-up ultrastructural analysis identified consistent changes in the dendritic architecture of pyramidal neurons. Behavioral analysis indicated that Akt1-mutant mice have normal acquisition of a PFC-dependent cognitive task but abnormal working memory retention under neurochemical challenge of three distinct neurotransmitter systems. Thus, Akt1 deficiency creates a context permissive for gene–gene and gene–environment interactions that modulate PFC functioning and contribute to the disease risk associated with this locus, the severity of the clinical syndrome, or both.

Mouse strain differences in autonomic responses to stress

In humans, anxiety disorders are often accompanied by an overactive autonomic nervous system, reflected in increased body temperature (BT) and heart rate (HR). In rodents, comparable effects are found after exposure to stress. These autonomic parameters can give important information on stress and anxiety responses in mice. In the present experiments, stress reactivity of three frequently used mouse strains [129 Sv/Ev, Swiss Webster (SW) and C57 BL/6] was assessed using their autonomic stress responses. BT, HR and activity were telemetrically measured. Undisturbed circadian rhythms already showed clear differences between the mouse strains. Hereafter, autonomic responses to stressors with increasing intensity were measured. Strain differences were found in magnitude and duration of the stress responses, especially after high‐intensity stressors. Generally, C57BL/6 mice showed the largest autonomic response, SW the lowest and the 129Sv/Ev the intermediate response. Interestingly, the observed ranking in autonomic stress response does not match the behavioral stress responsivity of these strains. Finally, sensitivity to the anxiolytic diazepam (0, 1, 2, 4 and 8 mg/kg) was tested using the stress‐induced hyperthermia paradigm. Pharmacological sensitivity to diazepam differed between the strains with the 129Sv/Ev being most sensitive. These studies show that simultaneous measurement of behavioral and autonomic parameters under stressful conditions contributes considerably to a better interpretation of anxiety and stress levels in mice.

Reversal of startle gating deficits in transgenic mice overexpressing corticotropin-releasing factor by antipsychotic drugs.

Chronically elevated levels of corticotropin-releasing factor (CRF) in transgenic mice overexpressing CRF in the brain (CRF-OE) appear to be associated with alterations commonly associated with major depressive disorder, as well as with sensorimotor gating deficits commonly associated with schizophrenia. In the present study, we tested the hypothesis that antipsychotics may be effective in normalizing prepulse inhibition (PPI) of acoustic startle in CRF-OE mice, which display impaired sensorimotor gating compared to wild-type (WT) mice. The typical antipsychotic haloperidol and atypical antipsychotic risperidone improved PPI in the CRF-OE mice, but were ineffective in WT mice. The atypical antipsychotic clozapine did not influence PPI in CRF-OE mice, but reduced gating in WT mice. This effect of clozapine in the CRF-OE mice may thus be regarded as a relative improvement, consistent with the observed effect of haloperidol and risperidone. As expected, the anxiolytic, nonantipsychotic chlordiazepoxide was devoid of any effect. All four compounds dose-dependently reduced the acoustic startle response irrespective of genotype. These results indicate that antipsychotic drugs are effective in improving startle gating deficits in the CRF-OE mice. Hence, the CRF-OE mouse model may represent an animal model for certain aspects of psychotic depression, and could be a valuable tool for research addressing the impact of chronically elevated levels of CRF on information processing.

Stress―induced hyperthermia and infection―induced fever: Two of a kind?

Stress exposure activates the autonomic nervous system and leads to a body temperature increase (stress-induced hyperthermia, SIH). On the other hand, an activation of the immune system in response to an infection leads to fever. Both processes increase body temperature, and the relation between SIH and infection-induced fever has been subject to debate. It is not clear whether SIH is a form of fever, or whether both processes are more or less distinct. We therefore examined the relation between SIH and infection-induced fever by looking at the effects of a GABA(A) receptor agonist (diazepam) and a prostaglandin-synthesis blocking drug (acetylsalicylic acid, aspirin) on both the SIH response and fever in rats and mice. The present study shows that the benzodiazepine diazepam but not the prostaglandin-synthesis blocking drug aspirin dose-dependently attenuated the SIH response in both rats and mice. In contrast, aspirin reduced both LPS- and IL-1beta induced fever, whereas diazepam had little effect on these fever states. Altogether, our findings support the hypothesis that stress-induced hyperthermia and infection-induced fever are two distinct processes mediated largely by different neurobiological mechanisms.

Olfactory bulbectomy induces rapid and stable changes in basal and stress-induced locomotor activity, heart rate and body temperature responses in the home cage.

BACKGROUND Olfactory bulbectomy (OBX) in rats causes several behavioral and neurochemical changes. However, the extent and onset of physiological and behavioral changes induced after bulbectomy have been little examined. METHODS Male Sprague-Dawley rats received telemetric implants. Before and immediately after OBX surgery, basal and stress-induced heart rate, body temperature, and locomotor activity were measured in the home cage in sham (n=9) and OBX animals (n=11). Stress was induced using novel cage stress or witness stress. RESULTS Bulbectomized animals differed physiologically and behaviorally from shams. Nocturnally, OBX animals were significantly more active compared with shams, had a higher core body temperature and displayed a decreased heart rate variability. During the light period, OBX animals had a significantly lower basal heart rate and a reduced heart rate variability. These effects became apparent 2-3 days after OBX surgery, and were stable over time. After witness stress, OBX animals showed smaller autonomic (body temperature and heart rate) responses compared with shams, but showed no difference in locomotor responses. In contrast, novel cage stress led to increased locomotor responses in OBX rats compared with sham rats, while no differences were found in autonomic responses. CONCLUSION Removal of the olfactory bulbs results in rapid, stable and persistent changes in basal locomotor activity, body temperature, heart rate and heart rate variability. Although the sleep-wake cycle of these parameters is not altered, increases in circadian amplitude are apparent within 3 days after surgery. This indicates that physiological changes in the OBX rat are the immediate result of olfactory bulb removal. Further, stress responsivity in OBX rats depends on stressor intensity. Bulbectomized rats display smaller temperature and heart rate responses to less intense witness stress compared with sham rats. Increased locomotor responses to more intense novel cage stress are present in the home cage as well as the open field. The present study shows that olfactory bulbectomy has rapid and persistent influence on basal and stress-induced physiological parameters.

Lipopolysaccharide-induced anhedonia is abolished in male serotonin transporter knockout rats: an intracranial self-stimulation study.

A growing body of evidence suggests that pro-inflammatory cytokines contribute to the pathogenesis of depression. Previously, it has been shown that cytokines (e.g. interferon-α therapy) induce major depression in humans. In addition, administration of the cytokine-inducer lipopolysaccharide (LPS) provokes anhedonia (i.e. the inability to experience pleasure) in rodents. Furthermore, serum pro-inflammatory cytokine levels are increased in depressed patients. Nevertheless, the etiology of cytokine-induced depression is largely unknown. Previously, it has been shown that selective serotonin re-uptake inhibitors decrease serum pro-inflammatory cytokine levels and that pro-inflammatory cytokines increase activity of the serotonin transporter (SERT). The purpose of this study was to explore the effect of partial and complete lack of the SERT in LPS-induced anhedonia assessed in the intracranial self-stimulation (ICSS) paradigm. A single intraperitoneal injection of LPS was used to induce a pro-inflammatory immune response in male serotonin transporter wild type (SERT(+/+)), heterozygous (SERT(+/-)) and knockout (SERT(-/-)) rats. Body weight and ICSS thresholds were measured daily. Although LPS reduced body weight in all genotypes, loss of body weight was less pronounced in SERT(-/-) compared to SERT(+/+) rats. Remarkably, LPS-induced anhedonia was totally abolished in SERT(-/-) rats and as expected was still present in SERT(+/+) and to a lesser extent in SERT(+/-) rats. Therefore, it is concluded that an intact SERT function is needed for pro-inflammatory cytokine-induced anhedonia and weight loss in rats.

Local repeated corticotropin-releasing factor infusion exacerbates anxiety- and fear-related behavior: differential involvement of the basolateral amygdala and medial prefrontal cortex.

Increased central corticotropin-releasing factor (CRF) signaling has been associated with various psychiatric symptoms, including anxiety, depression and psychosis. CRF signaling in both the basolateral amygdala (BLA) and medial prefrontal cortex (mPFC) has been implicated in anxiety-like behavior. In addition, repeated activation of CRF receptors within the BLA induces a chronic anxious state. Here we studied the effects of local repeated CRF infusion in the BLA and mPFC on different forms of anxiety, as assessed during light-enhanced startle (LES, general anxiety) and acquisition of fear-potentiated startle (FPS, cue-conditioned fear). In addition, as CRF has been implicated in sensorimotor gating, prepulse inhibition (PPI) was assessed to determine if local CRF infusion within the BLA or mPFC would interfere with the processing of sensory information. To this end, canulas were placed bilaterally in either the BLA or mPFC of Wistar rats. After recovery, animals were infused with h/rCRF (200 ng/side) or vehicle for five consecutive days. Long term effects of local CRF infusion on LES and acquisition of FPS were measured 4 and 10 days post-treatment, respectively. In addition, the acute (day 1), sub-chronic (day 5) and long-term (7 days post treatment) effects on PPI were measured in the same animals. A clear regional differentiation was found on the long lasting effect of CRF on anxiety-like behavior: infusion into the BLA only enhanced acquisition of FPS, whereas infusion into the mPFC only enhanced LES. Sub-chronic CRF infusion into the BLA, but not the mPFC, disrupted PPI. This disturbed PPI was normalized 7 days post-treatment. Together, the current study shows that local repeated CRF receptor activation in the BLA and mPFC is differentially involved in anxiety- and fear-related behavior. In addition, the BLA may be involved in CRF-induced sensorimotor gating deficits. The absence of a long-term effect on these PPI deficits suggests that lasting activation of CRF receptors is a prerequisite for CRF-mediated effects on sensorimotor gating. The long-term effects of repeated CRF infusion on LES and acquisition of FPS on the other hand, show that in case of anxiety-related processes repeated CRF infusion may have lasting effects.

Systemic tumor necrosis factor-alpha decreases brain stimulation reward and increases metabolites of serotonin and dopamine in the nucleus accumbens of mice.

Many patients with chronic inflammatory disorders have an abnormal high prevalence of major depression accompanied by elevated levels of tumor necrosis factor-α (TNF-α). We hypothesize that systemic TNF-α increases brain monoamine metabolism, which might induce anhedonia (i.e. a core symptom of major depression). The effect of an intraperitoneal TNF-α injection on extracellular monoamine and metabolite concentrations was investigated by in vivo microdialysis in the nucleus accumbens (NAc) of C57BL/6 mice. In another group, the effects of TNF-α on body weight and intracranial self-stimulation (ICSS) thresholds were measured. TNF-α reduced body weight and increased ICSS thresholds, suggesting a state of anhedonia. TNF-α did not affect serotonin levels, but increased its metabolite 5-HIAA in the NAc. Remarkably, TNF-α also increased the dopamine metabolite HVA, without affecting dopamine levels itself. These data concur with earlier findings that pro-inflammatory cytokines enhance serotonin transporter activity, and possibly also dopamine transporter activity in the brain. However, more research is needed to understand the precise molecular mechanisms by which TNF-α increases transporter activity and anhedonia.

Memantine partly rescues behavioral and cognitive deficits in an animal model of neurodegeneration.

Memantine, a non-competitive NMDA receptor antagonist, is used for the treatment of Alzheimers disease (AD) and off-label as an anti-depressant. Here we investigated possible anti-depressant, cognitive enhancing and neuroprotective effects of memantine in the olfactory bulbectomized (OBX) rat. OBX is used as a screening model for antidepressants and shows cognitive disturbances. In Experiment I, memantine treatment started 14 days after OBX surgery (this setup is similar to what we use for screening of potential antidepressants) and 2 days before surgery in experiment II. In both experiments, memantine (20 mg/kg, p.o) was administered once daily for 28 days. Animals were tested in the open field (locomotor activity), passive avoidance (fear learning and memory), and holeboard (spatial acquisition and memory) before and after the bulbectomy. Memantine, when administered before surgery, prevented OBX-induced hyperactivity and partly fear memory loss. These behavioral effects were present for at least 3 weeks after cessation of treatment. Memantine, however did not improve spatial memory. When administered 2 weeks after OBX surgery, memantine was ineffective in normalizing open field hyperactivity and improving cognitive deficits. Interestingly, after the animals were retrained in passive avoidance, memantine- treated OBX rats (both in experiment I and II) showed improved fear learning and memory. Our findings suggest that memantine has both neuroprotective and cognitive enhancing effects without antidepressant-like properties in the OBX rat. Based on our results, we propose that memantine may be more beneficial to AD patients when administered early in the disease process.