Response Calls Evoked by Playback of Natural 50-kHz Ultrasonic Vocalizations in Rats

Rats are highly social animals known to communicate with ultrasonic vocalizations (USV) of different frequencies. Calls around 50 kHz are thought to represent a positive affective state, whereas calls around 22 kHz are believed to serve as alarm or distress calls. During playback of natural 50-kHz USV, rats show a reliable and strong social approach response toward the sound source. While this response has been studied in great detail in numerous publications, little is known about the emission of USV in response to natural 50-kHz USV playback. To close this gap, we capitalized on three data sets previously obtained and analyzed USV evoked by natural 50-kHz USV playback in male juvenile rats. We compared different rat stocks, namely Wistar (WI) and Sprague-Dawley (SD) and investigated the pharmacological treatment with the dopaminergic D2 receptor antagonist haloperidol. These response calls were found to vary broadly inter-individually in numbers, mean peak frequencies, durations and frequency modulations. Despite the large variability, the results showed no major differences between experimental conditions regarding call likelihood or call parameters, representing a robust phenomenon. However, most response calls had clearly lower frequencies and were longer than typical 50-kHz calls, i.e., around 30 kHz and lasting generally around 0.3 s. These calls resemble aversive 22-kHz USV of adult rats but were of higher frequencies and shorter durations. Moreover, blockade of dopamine D2 receptors did not substantially affect the emission of response calls suggesting that they are not dependent on the D2 receptor function. Taken together, this study provides a detailed analysis of response calls toward playback of 50-kHz USV in juvenile WI and SD rats. This includes calls representing 50-kHz USV, but mostly calls with lower frequencies that are not clearly categorizable within the so far known two main groups of USV in adult rats. We discuss the possible functions of these response calls addressing their communicative functions like contact or appeasing calls, and whether they may reflect a state of frustration. In future studies, response calls might also serve as a new read-out in rat models for neuropsychiatric disorders, where acoustic communication is impaired, such as autism spectrum disorder.

An Original Approach to Measure Ligand/receptor Binding Affinity in Non-purified Samples

Several biochemical and biophysical methods are available to determine dissociation constants between a biological target and its ligands. Most of them require purification, labelling or surface immobilisation. However, these measurements remain challenging concerning membrane proteins because purification requires their extraction from the native lipid environment using different approaches, a process that may impact receptor conformation and functionality. We have developed a novel experimental procedure to determine binding affinities of a ligand to a membrane protein, the dopamine D2 receptor (D2R), directly from cell membrane fragments, using microscale thermophoresis (MST). Two main challenges had to be overcome: to determine the concentration of dopamine D2R in the crude sample; to find ways to minimize or account for non-specific binding of the ligand to cell fragments. Using MST, we were able to determine the D2R concentration in cell membrane fragments to be about 36.8 ± 2.6 pmol/mg. Then titration curves allowed the determination of a KD about 5.3 ± 1.7 nM, that is very close to the reported value. Important details of the experimental procedure are detailed to allow the transposition of this novel method to various membrane proteins.

Nonlinear computational models of dynamical coding patterns in depression and normal rats: from electrophysiology to energy consumption

Major depressive disorder (MDD) is one of the most serious neuropsychiatric disorders. Exploring the pathogenesis and dynamical coding patterns of MDD can provide new targets for clinical drug treatment and new ideas for the research of other neuropsychiatric and neurodegenerative diseases. We selected the medium spiny neuron (MSN) of nucleus accumbens (NAc) as the research objective. NAc is located in the dopaminergic pathway, regulating rewards, emotions and other behaviors. Abnormalities in these behaviors are considered as the main clinical symptoms of MDD. We simulated the different spike patterns of MSNs in MDD group and control group by dynamical Hodgkin–Huxley model. The simulated results can match the electrophysiological experiments, which occurred due to following reasons: (1) The external stimulus current of MDD group was amplified by the local neural microcircuit; (2) the selective permeability to sodium was abnormally decreased; and (3) the dopamine D2 receptor signaling pathway was abnormal in the MDD group. Furthermore, we proposed a dynamical energy model, and the energy results demonstrated that the energy cost in MDD group was lower, which led to persistent depression in patients with MDD. Simultaneously, the negative-to-total energy ratio of MSN in MDD group was higher than that in control group, and the delay time of the power peak and the potential peak in MDD group was shorter than that in the control group. The results showed that the abnormal firing patterns were the direct cause of abnormal behaviors of MDD and indicated that subthreshold activities of MDD group were more intense.

Herbs’ Disease-matched Pharmacological Mechanisms of HuanglianJiedu Decoction in Behavioral and Psychological Symptoms of Dementia in Alzheimer's Disease

Along with cognitive deficit, behavioral and psychological symptoms in dementia (BPSD) is another characteration of Alzheimer's disease that hamper clinical management and exacerbate burden for caregivers. However, therapeutic management of BPSD remains challenging. HuanglianJiedu decoction (HLJDD), a traditional Chinese prescription which contains Coptidis rhizome(Huang lian), Scutellariae radix (Huang-qin), Phellodendri chinrnsis cortex (Huang-bai) and Gardeniae fructus (Zhi-zi), is applied to treat BPSD. So elucidating the herbs’ disease-matched pharmacological mechanisms underlying HLJDD, further put forward each herbs’ disease-matched combination are critical to the application of HLJDD. In this study, network pharmacology was used to determine the targets and biological processes regulated by HLJDD in the treatment of BPSD. Moreover, molecular docking was utilized to evaluate the binding activity between the herbs' main active ingredients and neurotransmitter receptors. The results showed that the KEGG signaling pathway of HLJDD in treating BPSD mainly lies in TNF signaling pathway and AGE-RAGE signaling pathway in diabetic complications. Scutellariae radix and Phellodendri chinrnsis cortex exhibited better anti-BPSD effects when compared to Coptidis rhizoma and Gardeniae fructus. Scutellariae radix exhibited superior anti-neuroinflammation functions, with better blood vessel regulation effects. Phellodendri chinrnsis cortex showed a higher binding affinity to the dopamine D2 receptor (DRD2) and 5-hydroxytryptamine receptor 2A (HTR2A). Coptidis rhizoma and Gardeniae fructus were better in neuronal signaling. In conclusion, for treating BPSD, Scutellariae radix and Phellodendri chinrnsis cortex are the principal herbs while Coptidis rhizoma and Gardeniae fructus are the ancillary herbs. Beta-sitosterol, stigmasterol, chelerythrine, campesterol and berberine are the potential effective ingredients in treating BPSD.

Relief of neuropathic pain by cell-specific manipulation of nucleus accumbens dopamine D1- and D2-receptor-expressing neurons

Emerging evidence suggests that the mesolimbic dopaminergic network plays a role in the modulation of pain. As chronic pain conditions are associated with hypodopaminergic tone in the nucleus accumbens (NAc), we evaluated the effects of increasing signaling at dopamine D1/D2-expressing neurons in the NAc neurons in a model of neuropathic pain induced by partial ligation of sciatic nerve. Bilateral microinjection of either the selective D1-receptor (Gs-coupled) agonist Chloro-APB or the selective D2-receptor (Gi-coupled) agonist quinpirole into the NAc partially reversed nerve injury-induced thermal allodynia. Either optical stimulation of D1-receptor-expressing neurons or optical suppression of D2-receptor-expressing neurons in both the inner and outer substructures of the NAc also transiently, but significantly, restored nerve injury-induced allodynia. Under neuropathic pain-like condition, specific facilitation of terminals of D1-receptor-expressing NAc neurons projecting to the VTA revealed a feedforward-like antinociceptive circuit. Additionally, functional suppression of cholinergic interneurons that negatively and positively control the activity of D1- and D2-receptor-expressing neurons, respectively, also transiently elicited anti-allodynic effects in nerve injured animals. These findings suggest that comprehensive activation of D1-receptor-expressing neurons and integrated suppression of D2-receptor-expressing neurons in the NAc may lead to a significant relief of neuropathic pain.

Error-related Signaling in Nucleus Accumbens D2 Receptor-expressing Neurons Guides Avoidance-based Goal-directed Behavior

Learnt associations between environmental cues and the outcomes they predict (cue-outcome associations) play a major role in behavioral control, guiding not only which responses we should perform, but also which we should avoid, in order to achieve a specific goal. The encoding of such cue-outcome associations, as well as the performance of cue-guided goal-directed behavior, is thought to involve dopamine D1 and D2 receptor-expressing medium spiny neurons (D1-/D2-MSNs) of the nucleus accumbens (NAc). Here, using a visual discrimination task in mice, we assessed the role of NAc D1-/D2-MSNs in cue-guided goal-directed avoidance of inappropriate responding. Cell-type specific neuronal silencing and in-vivo imaging revealed NAc D2-MSNs to selectively contribute to cue-guided avoidance behavior, with activation of NAc D2-MSNs following response error playing an important role in optimizing future goal-directed behavior. Our findings indicate that error-signaling by NAc D2-MSNs underlies the ability to use environmental cues to avoid inappropriate behavior.

Impact of membrane lipid polyunsaturation on dopamine D2 receptor ligand binding and signaling

The heterogenous and dynamic constitution of the membrane fine-tunes signal transduction. In particular, the polyunsaturated fatty acid (PUFA) tails of phospholipids influence the biophysical properties of the membrane, production of second messengers, or membrane partitioning. Few evidence mostly originating from studies of rhodopsin suggest that PUFAs directly modulate the conformational dynamic of transmembrane proteins. However, whether such properties translate to other G protein-coupled receptors remains unclear. We focused on the dopamine D2 receptor (D2R), a main target of antipsychotics. Membrane enrichment in n-3, but not n-6, PUFAs potentiates ligand binding. Molecular dynamics simulations show that the D2R preferentially interacts with n-3 over n-6 PUFAs. Furthermore, even though this mildly affects signalling in heterologous systems, in vivo n-3 PUFA deficiency blunts the effects of D2R ligands. These results suggest that n-3 PUFAs act as allosteric modulators of the D2R and provide a putative mechanism for their potentiating effect on antipsychotic efficacy.