Altered Serotonin 1B Receptor Binding After Escitalopram for Depression Is Correlated With Treatment Effect.

BACKGROUND: Major depressive disorder (MDD) is commonly treated with selective serotonin reuptake inhibitors (SSRIs). SSRIs inhibit the serotonin transporter (5-HTT), but the downstream antidepressant mechanism of action of these drugs is poorly understood. The serotonin 1B (5-HT1B) receptor is functionally linked to 5-HTT and 5-HT1B receptor binding and 5-HT1B receptor mRNA is reduced in the raphe nuclei after SSRI administration in primates and rodents, respectively. The effect of SSRI treatment on 5-HT1B receptor binding in patients with MDD has not been examined previously. This positron emission tomography (PET) study aimed to quantify brain 5-HT1B receptor binding changes in vivo after SSRI treatment for MDD in relation to treatment effect. METHODS: Eight unmedicated patients with moderate to severe MDD underwent PET with the 5-HT1B receptor radioligand [11C]AZ10419369 before and after 3 to 4 weeks of treatment with the SSRI escitalopram 10 mg daily. Depression severity was assessed at time of PET and after 6 to 7 weeks of treatment with the Montgomery-Åsberg Depression Rating Scale. RESULTS: We observed a significant reduction in [11C]AZ10419369 binding in a dorsal brainstem (DBS) region containing the median and dorsal raphe nuclei after escitalopram treatment (P = .036). Change in DBS [11C]AZ10419369 binding correlated with Montgomery-Åsberg Depression Rating Scale reduction after 3-4 (r = 0.78, P = .021) and 6-7 (r = 0.94, P < .001) weeks' treatment. CONCLUSIONS: Our findings align with the previously reported reduction of 5-HT1B receptor binding in the raphe nuclei after SSRI administration and support future studies testing change in DBS 5-HT1B receptor binding as an SSRI treatment response marker.

Beneficial effect of 5-HT1b/1d agonist on Parkinson's disease by modulating glutamate and reducing deposition of α-synuclein.

The given investigation examined the neuroprotection role of 5-HT1b/1d agonist in reserpine induced Parkinson's disease (PD) in male Wistar rats. PD was induced in rats by reserpine at 5 mg/kg ip for 3 days and thereafter the rats were provided with the following treatments for 4 days, zolmitriptan (ZLM) group (30 mg/kg ip); STD group (levodopa + carbidopa, 200 + 5 mg/kg ip); ZLM + GA group (zolmitriptan, 30 mg/kg ip and glutamic acid, 1.5 mg/kg); ZLM + DX group (zolmitriptan, 30 mg/kg ip and dextromethorphan, 20 mg/kg ip). All the groups were then assessed for cognitive and motor functions at the end of the protocol. Moreover, oxidative stress parameters and histopathological changes were observed in rats of all treatment groups. Deposition of α-synuclein in the brain tissue was observed by silver staining. Data of this investigation revealed that motor and cognitive functions were improved in the ZLM-treated group compared with the negative control group, which was observed to be reversed in ZLM + GA group. Treatment with ZLM ameliorated oxidative stress and histopathological changes in the brain tissue of PD rats. Further, ZLM reduced the deposition of α-synuclein in PD rats, which reversed in ZLM + GA-treated group. This study concludes by stating that 5-HT1b/1d agonist can prevent neurodegeneration and reduce oxidative stress in PD rats. The probable underlying mechanism of such an effect of 5-HT1b/1d agonist could be by regulating the deposition of α-synuclein and reducing the expression of NMDA receptor.

Electroacupuncture Alleviates Memory Deficits in APP/PS1 Mice by Targeting Serotonergic Neurons in Dorsal Raphe Nucleus.

OBJECTIVE: Alzheimer's disease (AD) has become a significant global concern, but effective drugs able to slow down AD progression is still lacked. Electroacupuncture (EA) has been demonstrated to ameliorate cognitive impairment in individuals with AD. However, the underlying mechanisms remains poorly understood. This study aimed at examining the neuroprotective properties of EA and its potential mechanism of action against AD. METHODS: APP/PS1 transgenic mice were employed to evaluate the protective effects of EA on Shenshu (BL 23) and Baihui (GV 20). Chemogenetic manipulation was used to activate or inhibit serotonergic neurons within the dorsal raphe nucleus (DRN). Learning and memory abilities were assessed by the novel object recognition and Morris water maze tests. Golgi staining, western blot, and immunostaining were utilized to determine EA-induced neuroprotection. RESULTS: EA at Shenshu (BL 23) and Baihui (GV 20) effectively ameliorated learning and memory impairments in APP/PS1 mice. EA attenuated dendritic spine loss, increased the expression levels of PSD95, synaptophysin, and brain-derived neurotrophic factor in hippocampus. Activation of serotonergic neurons within the DRN can ameliorate cognitive deficits in AD by activating glutamatergic neurons mediated by 5-HT1B. Chemogenetic inhibition of serotonergic neurons in the DRN reversed the effects of EA on synaptic plasticity and memory. CONCLUSION: EA can alleviate cognitive dysfunction in APP/PS1 mice by activating serotonergic neurons in the DRN. Further study is necessary to better understand how the serotonergic neurons-related neural circuits involves in EA-induced memory improvement in AD.

Lateral habenula 5-HT1B receptors are involved in regulation of anxiety-like behaviors in parkinsonian rats.

Although the output of the lateral habenula (LHb) controls the activity of midbrain dopaminergic and serotonergic systems, which are implicated in the pathophysiology of anxiety, it is not clear the role of LHb 5-HT1B receptors in regulation of anxiety-like behaviors, particularly in Parkinson's disease-related anxiety. In this study, unilateral 6-hydroxydopamine lesions of the substantia nigra pars compacta in rats induced anxiety-like behaviors, led to decreased normalized δ power and increased normalized θ power in the LHb, and decreased dopamine (DA) level in the prelimbic cortex (PrL) compared with sham rats. Down-regulation of LHb 5-HT1B receptors by RNA interference produced anxiety-like effects, decreased normalized δ power and increased normalized θ power in the LHb in both sham and lesioned rats. Further, intra-LHb injection of 5-HT1B receptor agonist CP93129 induced anxiolytic-like responses, increased normalized δ power and decreased normalized θ power in the LHb, and increased DA and serotonin (5-HT) release in the PrL; conversely, 5-HT1B receptor antagonist SB216641 produced anxiety-like effects, decreased normalized δ power and increased normalized θ power in the LHb, and decreased DA and 5-HT release in the PrL in sham and lesioned rats. Additionally, effects of CP93129 and SB216641 on the behaviors, normalized δ and θ power in the LHb, and DA and 5-HT release in the PrL were decreased in lesioned rats, which were consistent with down-regulation of LHb 5-HT1B receptors after DA depletion. Collectively, these findings suggest that 5-HT1B receptors in the LHb are involved in the regulation of anxiety-like behaviors.

The dorsal raphe-to-ventral hippocampal projection modulates reactive aggression through 5HT1B receptors.

Maladaptive impulsive aggression is a core symptom of neuropsychiatric disorders such as schizophrenia. While uncontrolled impulsive aggression dampens societal safety, there is a limited understanding of the neural regulation involved in impulsive aggression and its treatment. High levels of impulsivity and aggression have been linked to low serotonin (5-HT) levels. Additionally, post-weaning socially isolated (SI) mice exhibit outbursts of aggression following encountering acute stress, and hyperactivated ventral hippocampus (vHip) involves this stress-provoked escalated aggression. Here, we investigated the potential role of the raphe nucleus projecting to the vHip in modulating aggressive behavior. Chemogenetically activating the dorsal raphe nucleus (DRN) soma projecting the vHip or DRN nerve terminals in the vHip reduced impulsive aggression. The reduction of attack behavior was abolished by the pretreatment of 5HT1BR antagonist SB-224289. However, activating the median raphe nucleus (MRN)-to-vHip pathway ameliorated depression-like behavior but did not affect impulsive aggression. DRN→vHip activation suppressed the vHip downstream area, the ventromedial hypothalamus (VMH), which is a core aggression area. Intra-vHip infusion of 5HT1BR agonists (anpirtoline, CP-93129) suppressed impulsive aggression and decreased c-Fos levels in the vHip neurons projecting to the VMH, suggesting an inhibition mechanism. Our findings indicate that activating the DRN projecting to the vHip is sufficient to inhibit impulsive aggression in a 5HT1BR-dependent manner. Thus, targeting 5HT1BR could serve as a promising therapeutic approach to ameliorate symptoms of impulsive aggression.

SERT and OCT mediate 5-HT1B receptor regulation of immobility behavior and uptake of 5-HT and HIS.

5-HT clearance, commonly mediated by transporters in the uptake-1 and uptake-2 families, has been linked to 5-HT1B receptor's action on behaviors. Since no specific transporters identified yet, effects of serotonin transporter (SERT) and organic cation transporter (OCTs) on 5-HT1B-elicited immobility phenotype, and 5-HT and HIS uptake were then investigated. Intraperitoneal injections of SERT inhibitor fluoxetine (FLX) and/or OCTs inhibitor decynium (D22) were used prior to local perfusion of 5-HT1B agonist CP93129 into the ventral hippocampus to measure immobility times in the FST and TST, to measure 5-HT uptake efficiencies and HIS uptake efficiencies derived from linear regressions using the transient no-net-flux quantitative microdialysis in C57BL/6 mice. Exogenous 5-HT and HIS uptake were measured following incubation of FLX and/or D22 with CP93129 in the RBL-2H3 cells. Moreover, surface membrane levels of SERT and OCT were detected in response to CP93129. Local CP93129 prolonged immobility times, which were attenuated following pretreatment of either inhibitor. Local CP93129 lowered the slopes obtained from the lineal regressions for 5-HT and HIS (slope is reciprocal to uptake efficiency), which were then weakened following pretreatment of either inhibitor. Similar findings were obtained following CP93129 incubation, and co-incubation of CP93129 with either inhibitor in the RBL-2H3. Moreover, CP93129 dose-dependently moved SERT and OCT3 in the cytosol to the surface membrane. Both SERT and OCT are the target effectors mediating 5-HT1B regulation of immobility time and 5-HT uptake, OCT mediates 5-HT1B regulation of HIS uptake. Their underlying signal transductions need to be further explored.