Regulation of CREB Phosphorylation in Nucleus Accumbens after Relief Conditioning.

Relief learning is the association of environmental cues with the cessation of aversive events. While there is increasing knowledge about the neural circuitry mediating relief learning, the respective molecular pathways are not known. Therefore, the aim of the present study was to examine different putative molecular pathways underlying relief learning. To this purpose, male rats were subjected either to relief conditioning or to a pseudo conditioning procedure. Forty-five minutes or 6 h after conditioning, samples of five different brain regions, namely the prefrontal cortex, nucleus accumbens (NAC), dorsal striatum, dorsal hippocampus, and amygdala, were collected. Using quantitative Western blots, the expression level of CREB, pCREB, ERK1/2, pERK1/2, CaMKIIα, MAP2K, PKA, pPKA, Akt, pAkt, DARPP-32, pDARPP-32, 14-3-3, and neuroligin2 were studied. Our analyses revealed that relief conditioned rats had higher CREB phosphorylation in NAC 6 h after conditioning than pseudo conditioned rats. The data further revealed that this CREB phosphorylation was mainly induced by dopamine D1 receptor-mediated activation of PKA, however, other kinases, downstream of the NMDA receptor, may also contribute. Taken together, the present study suggests that CREB phosphorylation, induced by a combination of different molecular pathways downstream of dopamine D1 and NMDA receptors, is essential for the acquisition and consolidation of relief learning.

Angiotensin II-induced drinking behavior as a method to verify cannula placement into the cerebral ventricles of mice: An evaluation of its accuracy.

BACKGROUND: Intracerebroventricular (icv) injections are frequently used in neuroscience research. In addition to histological verification of the injection sites, administration of angiotensin II (ANG II) is often used to verify the injection placements. ANG II is a peptide hormone exerting dipsogenic effects, i.e., it increases drinking, when administered into the cerebral ventricles. This study investigated the accuracy of ANG II-induced drinking as a method to verify icv cannula placements. METHODS: Male C57BL/6J mice were implanted with cannulas in the lateral ventricle. Then, icv injections of ANG II were performed and drinking behavior of the mice was recorded. After the behavioral experiment, we histologically verified the cannula placements using dye injections. Based on this, mice were grouped in "icv" and "misplaced". The effects of icv and misplaced ANG II injections on drinking behavior were used to evaluate the accuracy of ANG II-induced drinking as a method to verify icv cannula placements. RESULTS: In general, ANG II injections in mice with histologically verified icv cannula placements induced robust drinking responses, while misplaced injections did not. However, there were exceptions in both groups. In about one third of the mice, icv ANG II did not induce drinking or misplaced ANG II injections induced drinking, respectively. CONCLUSION: These data demonstrated that ANG II-induced drinking is not a perfectly accurate method to verify icv cannula placements in mice. Therefore, we recommend to not base the decision of in- or excluding experimental subjects solely on this method, but also to histologically verify cannula placements.

Role of the mesolimbic dopamine system in relief learning.

The relief from an aversive event is rewarding. Since organisms are able to learn which environmental cues can cease an aversive event, relief learning helps to better cope with future aversive events. Literature data suggest that relief learning is affected in various psychopathological conditions, such as anxiety disorders. Here, we investigated the role of the mesolimbic dopamine system in relief learning. Using a relief learning procedure in Sprague Dawley rats, we applied a combination of behavioral experiments with anatomical tracing, c-Fos immunohistochemistry, and local chemogenetic and pharmacological interventions to broadly characterize the role of the mesolimbic dopamine system. The present study shows that a specific part of the mesolimbic dopamine system, the projection from the posterior medial ventral tegmental area (pmVTA) to the nucleus accumbens shell (AcbSh), is activated by aversive electric stimuli. 6-OHDA lesions of the pmVTA blocked relief learning but fear learning and safety learning were not affected. Chemogenetic silencing of the pmVTA-AcbSh projection using the DREADD approach, as well as intra-AcbSh injections of the dopamine D2/3 receptor antagonist raclopride inhibited relief learning. Taken together, the present data demonstrate that the dopaminergic pmVTA-AcbSh projection is critical for relief learning but not for similar learning phenomena. This novel finding may have clinical implications since the processing of signals predicting relief and safety is often impaired in patients suffering from anxiety disorders. Furthermore, it may help to better understand psychological conditions like non-suicidal self-injury, which are associated with pain offset relief.

Piperidyl amides as novel, potent and orally active mGlu5 receptor antagonists with anxiolytic-like activity.

High throughput screening led to the identification of nicotinamide derivative 2 as a structurally novel mGluR5 antagonist. Optimization of the modular scaffold led to the discovery of 16m, a compound with high affinity for mGluR5 and excellent selectivity over other glutamate receptors. Compound 16m exhibits a favorable PK profile in rats, robust anxiolytic-like effects in three different animal models of fear and anxiety, as well as a good PK/PD correlation.

TMT-induced autonomic and behavioral changes and the neural basis of its processing.

One of the main interests in the field of neuroscience is the investigation of the neural basis of fear. During recent years, an increasing number of studies have used trimethylthiazoline (TMT), a component of red fox feces, as a stimulus to induce fear in predator naive rats, mice, and voles. The aim of the present review is to summarize these studies. We present an overview to the autonomic and behavioral changes that are induced by TMT exposure. Then, we summarize the small number of studies that have examined the neural processing of the TMT stimulus. Finally, we compare these studies with those using a natural predator or predator odor to induce fear and discuss the possible use of TMT exposure in rodents as an animal model of unconditioned fear in humans.

Dopamine D1 receptors and adenosine A1 receptors in the rat nucleus accumbens regulate motor activity but not prepulse inhibition.

Locomotor activity and sensorimotor gating (measured as prepulse inhibition of startle) are regulated by mesoaccumbal dopamine. Recent evidence indicated antagonistic interactions between adenosine A(1) receptors and dopamine D(1) receptors, as well as between adenosine A(2) receptors and dopamine D(2) receptors in the nucleus accumbens. Therefore, it is conceivable that accumbal dopamine and adenosine are both involved in the regulation of prepulse inhibition and locomotion. We tested whether accumbal adenosine A(1) and dopamine D(1) receptors control locomotor activity and prepulse inhibition using the following four treatments. (1) Injections of the selective adenosine A(1) receptor agonist N(6)-cyclopentanyladenosine (CPA 1.5 and 3 microg/microl per side) into the nucleus accumbens. (2) Stimulation of the ventral tegmental area by local infusion of the GABA(A) receptor antagonist picrotoxin (25-100 ng/0.5 microl bilaterally). (3) Picrotoxin injections into the ventral tegmental area (100 ng/0.5 microl) and simultaneous bilateral injections of CPA (3 microg/microl per side) into the nucleus accumbens. (4) Injections of the selective dopamine D(1) receptor antagonist SCH 23390 (3 microg/0.5 microl per side) into the nucleus accumbens and ventral tegmental area stimulation by picrotoxin. Intra-accumbal CPA infusion reduced locomotor activity but had no effect on prepulse inhibition. Picrotoxin stimulation of the ventral tegmental area increased locomotor activity which was antagonized by co-administration of CPA or SCH 23390 into the nucleus accumbens. An enhancement of prepulse inhibition was observed after stimulation of the ventral tegmental area and co-administration of SCH 23390 into the nucleus accumbens. These findings demonstrate that adenosine A(1) and dopamine D(1) receptors are involved in the regulation of locomotor activity mediated by the mesoaccumbal dopamine system. The finding that locomotor effects induced by stimulation of the mesoaccumbal dopamine system were not accompanied by a prepulse inhibition-deficit suggests a dissociation of the neuronal substrates involved in the control of locomotion and the regulation of sensorimotor gating.