Involvement of serotonin 2A receptor activation in modulating medial prefrontal cortex and amygdala neuronal activation during novelty-exposure

Effects of Chronic Combined Treatment with Ketanserin and Fluoxetine in B6.CBA-D13Mit76C Recombinant Mice with Abnormal 5-HT1A Receptor Functional Activity

The recombinant B6.CBA-D13Mit76C mouse strain is characterized by an altered sensitivity of 5-HT1A receptors and upregulated 5-HT1A gene transcription. Recently, we found that in B6.CBA-D13Mit76C mice, chronic fluoxetine treatment produced the pro-depressive effect in a forced swim test. Since 5-HT2A receptor blockade may be beneficial in treatment-resistant depression, we investigated the influence of chronic treatment (14 days, intraperitoneally) with selective 5-HT2A antagonist ketanserin (0.5 mg/kg), fluoxetine (20 mg/kg), or fluoxetine + ketanserin on the behavior, functional activity of 5-HT1A and 5-HT2A receptors, serotonin turnover, and transcription of principal genes of the serotonin system in the brain of B6.CBA-D13Mit76C mice. Ketanserin did not reverse the pro-depressive effect of fluoxetine, while fluoxetine, ketanserin, and fluoxetine + ketanserin decreased the functional activity of 5-HT1A receptors and Htr1a gene transcription in the midbrain and hippocampus. All tested drug regimens decreased the mRNA levels of Slc6a4 and Maoa in the midbrain. These changes were not accompanied by a significant shift in the levels of serotonin and its metabolite 5-HIAA. Notably, ketanserin upregulated enzymatic activity of tryptophan hydroxylase 2 (TPH2). Thus, despite some benefits (reduced Htr1a, Slc6a4, and Maoa transcription and increased TPH2 activity), prolonged blockade of 5-HT2A receptors failed to ameliorate the adverse effect of fluoxetine in the case of abnormal functioning of 5-HT1A receptors.

A spatiotemporal increase of neuronal activity accompanies the motivational effect of wheel running in mice

Spatiotemporal patterns of neuronal activity underlying the motivational effect of rotating running wheels (RWs) in rodents remain largely undetermined. Here, we investigated changes of neuronal activity among brain regions associated with motivation across different intensities of motivation for RWs in mice. Daily exposure to RWs gradually increased rotation number, then became stable after approximately 3 weeks. Immunohistochemical analyses revealed that the number of c-Fos (a neuronal activity marker)-positive cells increased in the medial prefrontal cortex (mPFC), core and shell of the nucleus accumbens (NAc), dorsal striatum (Str), and lateral septum (LS) at day 1, day 9, and days 20-24, in a time-dependent manner. Additionally, despite exposure to locked RWs for over 7 days after establishing stable rotation with 3-week RW access, increased c-Fos expression was still observed in most of these brain areas. Furthermore, daily overnight RW access developed stable rotation by day 6, with high and low rotation numbers at the start and end of the overnight session, respectively. The number of c-Fos-positive cells at the start of RW rotation was significantly higher than at the end of RW rotation in most brain regions. Furthermore, after establishing stable rotation, the number of c-Fos-positive cells increased in the mPFC and shell of the NAc of mice that only observed RWs. These findings suggest that the subareas of the mPFC and NAc may be critically involved in the motivational effects of RW rotations.

Altered Structural and Functional Connectivity Contribute to Rapid Ejaculation: Insights from a Multimodal Neuroimaging Study

Little is known about how the aberrant structural and functional connectivity relates to the rapid ejaculation. Data of diffusion tensor imaging and resting state functional magnetic resonance imaging were acquired from 32 PE patients and 38 healthy controls (HCs). Firstly, we investigated the structural connectivity (SC) disruptions of PE patients using the method of graph theoretical analysis. Brain regions with impaired nodal strength were then defined as regions of interest (ROI). Secondly, the corresponding functional connectivity (FC) changes were explored. Finally, the correlation analyses were performed between brain areas with abnormal connectivity and clinical characteristics. Structural analysis revealed that PE patients had increased nodal strength in the right superior frontal gyrus (dorsolateral), left middle frontal gyrus, right superior frontal gyrus (medial), right superior frontal gyrus (medial orbital) and decreased nodal strength in the left amygdala. FC analysis revealed that PE patients had decreased FC values in the default mode network, visual recognition network and subcortical network, as well as increased FC values in the attention network. Moreover, correlation analysis revealed that the nodal strength of right superior frontal gyrus (dorsolateral) was negatively associated with the intra-vaginal ejaculation latency, while FC values between the left middle frontal gyrus and middle occipital gyrus were positively related to the total scores of the premature ejaculation diagnostic tool (PEDT). Our results indicated that PE might be associated with the abnormal SC of areas in the prefrontal-amygdala pathway and aberrant FC in certain functional brain networks, especially in default mode network.

Remediation of chronic immobilization stress-induced negative affective behaviors and altered metabolism of monoamines in the prefrontal cortex by inactivation of basolateral amygdala

Exposure to chronic stress precipitates depression and anxiety. Stress-induced responses are differentially regulated by the prefrontal cortex (PFC) and basolateral amygdala (BLA). For instance, repeated stress leads to hypertrophy of BLA, resulting in the emergence of affective symptoms. Chronic stress-induced changes in the metabolism of monoamines are central in the manifestation of affective symptoms. Interestingly, BLA via its reciprocal connections modulates prefrontal cortical monoaminergic responses to acute stress. However, the effects of BLA inactivation on chronic stress-induced affective behaviors and monoaminergic changes in the PFC are relatively unknown. Thus, we hypothesized that inactivation of BLA might prevent chronic immobilization stress (CIS)-induced depressive-, anxiety-like behaviors, and associated monoaminergic alterations in the prelimbic (PrL) and anterior cingulate cortex (ACC) subregions of PFC. We used two different BLA silencing strategies, namely ibotenic acid lesion and reversible temporary inactivation using lidocaine. We found that CIS precipitates depressive- and anxiety-like behaviors. Further, CIS-induced negative affective behaviors were associated with decreased levels of 5-HT, DA, and NE, and increased 5-HIAA/5-HT, DOPAC + HVA/DA, and MHPG/NE ratio in the PrL and ACC, suggesting enhanced metabolism. Interestingly, BLA lesion prior to CIS blocked the emergence of depressive- and anxiety-like behaviors. Moreover, the lesion of BLA prior to CIS was sufficient to prevent alterations in levels of monoamines and their metabolites in the PrL and ACC. Thereafter, we evaluated whether the effects of BLA lesion could be mirrored by temporary inactivation of BLA, specifically during stress. Remarkably, temporary inactivation of BLA during stress recapitulated the effects of lesion. Our results have implications for understanding the role of BLA in chronic stress-induced metabolic alterations in prefrontal cortical monoaminergic systems, and associated mood and anxiety disorders. The current study supports the hypothesis that combating amygdalar hyperactivity might be a viable strategy for the management of stress and associated affective disorders.

Inhibitory Control of Basolateral Amygdalar Transmission to the Prefrontal Cortex by Local Corticotrophin Type 2 Receptor

BACKGROUND

Basolateral amygdalar projections to the prefrontal cortex play a key role in modulating behavioral responses to stress stimuli. Among the different neuromodulators known to impact basolateral amygdalar-prefrontal cortex transmission, the corticotrophin releasing factor (CRF) is of particular interest because of its role in modulating anxiety and stress-associated behaviors. While CRF type 1 receptor (CRFR1) has been involved in prefrontal cortex functioning, the participation of CRF type 2 receptor (CRFR2) in basolateral amygdalar-prefrontal cortex synaptic transmission remains unclear.

METHODS

Immunofluorescence anatomical studies using rat prefrontal cortex synaptosomes devoid of postsynaptic elements were performed in rats with intra basolateral amygdalar injection of biotinylated dextran amine. In vivo microdialysis and local field potential recordings were used to measure glutamate extracellular levels and changes in long-term potentiation in prefrontal cortex induced by basolateral amygdalar stimulation in the absence or presence of CRF receptor antagonists.

RESULTS

We found evidence for the presynaptic expression of CRFR2 protein and mRNA in prefrontal cortex synaptic terminals originated from basolateral amygdalar. By means of microdialysis and electrophysiological recordings in combination with an intra-prefrontal cortex infusion of the CRFR2 antagonist antisauvagine-30, we were able to determine that CRFR2 is functionally positioned to limit the strength of basolateral amygdalar transmission to the prefrontal cortex through presynaptic inhibition of glutamate release.

CONCLUSIONS

Our study shows for the first time to our knowledge that CRFR2 is expressed in basolateral amygdalar afferents projecting to the prefrontal cortex and exerts an inhibitory control of prefrontal cortex responses to basolateral amygdalar inputs. Thus, changes in CRFR2 signaling are likely to disrupt the functional connectivity of the basolateral amygdalar-prefrontal cortex pathway and associated behavioral responses.

16p11.2 deletion syndrome mice perseverate with active coping response to acute stress - rescue by blocking 5-HT2A receptors

In humans a chromosomal hemideletion of the 16p11.2 region results in variable neurodevelopmental deficits including developmental delay, intellectual disability, and features of autism spectrum disorder (ASD). Serotonin is implicated in ASD but its role remains enigmatic. In this study we sought to determine if and how abnormalities in serotonin neurotransmission could contribute to the behavioral phenotype of the 16p11.2 deletion syndrome in a mouse model (Del mouse). As ASD is frequently associated with altered response to acute stress and stress may exacerbate repetitive behavior in ASD, we studied the Del mouse behavior in the context of an acute stress using the forced swim test, a paradigm well characterized with respect to serotonin. Del mice perseverated with active coping (swimming) in the forced swim test and failed to adopt passive coping strategies with time as did their wild-type littermates. Analysis of monoamine content by HPLC provided evidence for altered endogenous serotonin neurotransmission in Del mice while there was no effect of genotype on any other monoamine. Moreover, we found that Del mice were highly sensitive to the 5-HT2A antagonists M100907, which at a dose of 0.1 mg/kg normalized their level of active coping and restored the gradual shift to passive coping in the forced swim test. Supporting evidence for altered endogenous serotonin signaling was provided by observations of additional ligand effects including altered forebrain Fos expression. Taken together, these observations indicate notable changes in endogenous serotonin signaling in 16p11.2 deletion mice and support the therapeutic utility of 5-HT2A receptor antagonists.