Fluoxetine ameliorates cognitive impairments induced by chronic cerebral hypoperfusion via down-regulation of HCN2 surface expression in the hippocampal CA1 area in rats

Serotonergic neuromodulation of synaptic plasticity

Synaptic plasticity constitutes a fundamental process in the reorganization of neural networks that underlie memory, cognition, emotional responses, and behavioral planning. At the core of this phenomenon lie Hebbian mechanisms, wherein frequent synaptic stimulation induces long-term potentiation (LTP), while less activation leads to long-term depression (LTD). The synaptic reorganization of neuronal networks is regulated by serotonin (5-HT), a neuromodulator capable of modify synaptic plasticity to appropriately respond to mental and behavioral states, such as alertness, attention, concentration, motivation, and mood. Lately, understanding the serotonergic Neuromodulation of synaptic plasticity has become imperative for unraveling its impact on cognitive, emotional, and behavioral functions. Through a comparative analysis across three main forebrain structures-the hippocampus, amygdala, and prefrontal cortex, this review discusses the actions of 5-HT on synaptic plasticity, offering insights into its role as a neuromodulator involved in emotional and cognitive functions. By distinguishing between plastic and metaplastic effects, we provide a comprehensive overview about the mechanisms of 5-HT neuromodulation of synaptic plasticity and associated functions across different brain regions.

Multiple Exposures to Sevoflurane General Anesthesia During Pregnancy Inhibit CaMKII/CREB Axis by Downregulating HCN2 to Induce an Autism-Like Phenotype in Offspring Mice

The objective of this investigation was to examine the impact of multiple exposures to general anesthesia (GA) with sevoflurane on the offspring of pregnant mice, as well as to elucidate the underlying mechanism. Neurodevelopmental assessments, including various reflexes and behavioral tests, were conducted on the offspring in the GA group to evaluate neuronal cell development. Furthermore, neonatal mouse neuronal cells were isolated and transfected with a high-expression CREB vector (pcDNA3.1-CREB), followed by treatment with sevoflurane (0.72 mol/L), ZD7288 (50 μmol/L), and KN-62 (10 μmol/L), or a combination of these compounds. The expression of relevant genes was then analyzed using qRT-PCR and western blot techniques. In comparison to the sham group, neonatal mice in the GA group exhibited significantly prolonged latencies in surface righting reflex, geotaxis test, and air righting reflex. Furthermore, there was a notable deceleration in the development of body weight and tail in the GA group. These mice also displayed impairments in social ability, reduced reciprocal social interaction behaviors, diminished learning capacity, and heightened levels of anxious behaviors. Additionally, synaptic trigger malfunction was observed, along with decreased production of c-Fos and neurotrophic factors. Sevoflurane was found to notably decrease cellular c-Fos and neurotrophic factor production, as well as the expression of HCN2 and CaMKII/CREB-related proteins. The inhibitory effects of sevoflurane on HCN2 or CaMKII channels were similar to those observed with ZD7288 or KN-62 inhibition. However, overexpression of CREB mitigated the impact of sevoflurane on neuronal cells. Repetitive exposure to sevoflurane general anesthesia while pregnant suppresses the CaMKII/CREB pathway, leading to the development of autism-like characteristics in offspring mice through the reduction of HCN2 expression.

Chronic but not acute nicotine treatment ameliorates acute inflammation-induced working memory impairment by increasing CRTC1 and HCN2 in adult male mice

BACKGROUND

Systemic inflammation in which lipopolysaccharide (LPS) is released into circulation can cause cognitive dysfunction and we have previously shown that LPS impaired working memory (WM) which refers to the ability to guide incoming behavior by retrieving recently acquired information. However, the mechanism is not very clear, and currently, there is no approved strategy to improve inflammation-induced WM deficit. Notably, epidemiological studies have demonstrated a lower occurrence rate of inflammatory-related diseases in smoking patients, suggesting that inflammation-induced WM impairment may be improved by nicotine treatment. Here, our object is to investigate the effect and potential mechanisms of acute and chronic nicotine treatment on LPS-produced WM deficiency.

METHODS

Delayed alternation T-maze task (DAT) was applied for evaluating WM which includes both the short-term information storage and the ability to correct errors in adult male mice. Immunofluorescence staining and immunoblotting were used for assessing the levels and distribution of CREB-regulated transcription coactivator 1 (CRTC1) and hyperpolarization-activated cation channels 2 (HCN2) in the medial prefrontal cortex (mPFC) and hippocampus. Quantitative PCR and ELISA were employed for analyzing the mRNA and protein levels of TNF-α and IL-1β.

RESULTS

Our results revealed that administration of LPS (i.p.) at a dose of 0.5 mg/kg significantly produced WM impairment in the DAT task accompanied by an increase in IL-1β and TNF-α expression in the mPFC. Moreover, intra-mPFC infusion of IL-1Ra, an IL-1 antagonist, markedly alleviated LPS-induced WM deficiency. More important, chronic (2 weeks) but not acute nicotine (0.2 mg/kg, subcutaneous) treatment significantly alleviated LPS-induced WM deficiency by upregulating CRTC1 and HCN2. Of note, intra-mPFC infusion of HCN blocker ZD7288 produced significant WM deficiency.

CONCLUSIONS

In summary, in this study, we show that chronic nicotine treatment ameliorates acute inflammation-induced working memory deficiency by increasing CRTC1 and HCN2 in adult male mice.

Antidepressants and risk of dementia in migraine patients: A population-based case-control study

To ascertain the relationship between receipt of antidepressant agents and the risk of subsequent dementia in migraine patients. A population-based case-control analysis, using the Taiwan National Health Insurance Research Database. We identified 1774 patients with dementia and 1774 matched nondementia controls from migraine patients enrolled in the Taiwan National Health Insurance program between 2005 and 2011. The proportional distributions of exposure to three classes of antidepressant were compared between dementia and nondementia groups. Univariable and multivariable logistic regression analyses were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the risk of dementia based on antidepressant exposure. The proportions of subjects taking tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), and new-generation antidepressants (NGAs) in dementia versus nondementia groups are 52.3 vs 51.2%, 25.5 vs 30.7%, and 18.8 vs 6.26%, respectively. The adjusted ORs of dementia were 1.02 (95% CI=0.89, 1.17; P=0.56) for TCAs, 0.58 (95% CI=0.50, 0.69; P<0.001) for SSRIs, and 4.23 (95% CI=3.34, 5.37; P<0.001) for NGAs. Treatment with SSRIs was associated with a decreased risk of dementia in migraine patients. TCAs showed no association with dementia risk, and NGAs showed increased risk. Given the possibility of confounding by indication, additional prospective trials and basic research are needed before drawing conclusions about the population-level risks for dementia onset conferred by antidepressant medications.

Effect of Selective 5-HT6R Agonist on Expression of 5-HT Receptor and Neurotransmitter in Vascular Dementia Rats

Background

5-HT6 receptor (5-HT6R) has pluripotent roles regulating secretion of neurotransmitters. However, whether 5-HT6R is involved in the development of vascular dementia (VD) remains unclear. To evaluate the role and mechanism of 5-HT6R in VD, this study established a rat VD model to evaluate the effect of selective 5-HT6R agonist on the expression of 5-HT6R mRNA and neurotransmitter.

Material/Methods

Eighty healthy male SD rats (7 weeks old) were randomly assigned to sham, model, 5-HT6R agonist, and placebo groups (N=20 each). A rat VD model was generated by permeant bilateral ligation of the common carotid artery. 5-HT6R agonist, placebo, or saline were given intraperitoneally for 4 weeks. The Morris water maze was utilized to test learning and memory function. Brains were extracted to separate the cortex and hippocampal tissues, in which glutamate and γ-aminobutyric acid (GABA) levels were analyzed. mRNA and protein levels of 5-HT6R were determined by RT-PCR and immunohistochemistry (IHC), respectively.

Results

Model rats had longer escape latency and fewer crossing platform times. Contents of DA, Glu, GABA, and Ach were lowered in cortical and hippocampal tissues, and 5-HT6R expression was suppressed (p<0.05). The application of 5-HT6R agonist shortened escape latency and increased the number of passing through the platform. It also improved hippocampal CA1 neuronal damage and elevated DA, Glu, GABA, and Ach contents and expression of 5-HT6R. Expression of 5-HT6R was not different from the placebo group.

Conclusions

Selective 5-HT6R agonist can alleviate learning deficit of VD rats, possibly via improving neurotransmitter levels in brain regions.

Baclofen ameliorates spatial working memory impairments induced by chronic cerebral hypoperfusion via up-regulation of HCN2 expression in the PFC in rats

Chronic cerebral hypoperfusion (CCH) causes memory deficits and increases the risk of vascular dementia (VD) through several biologically plausible pathways. However, whether CCH causes prefrontal cortex (PFC)-dependent spatial working memory impairments and Baclofen, a GABAB receptor agonist, could ameliorate the impairments is still not clear especially the mechanisms underlying the process. In this study, rats were subjected to permanent bilateral occlusion of the common carotid arteries (two-vessel occlusion, 2VO) to induce CCH. Two weeks later, rats were treated with 25mg/kg Baclofen (intraperitioneal injection, i.p.) for 3 weeks. Spatial working memory was evaluated in a Morris water maze using a modified delayed matching-to-place (DMP) procedure. Western blotting and immunohistochemistry were used to quantify the protein levels and protein localization. Our results showed that 2VO caused striking spatial working memory impairments, accompanied with a decreased HCN2 expression in PFC, but the protein levels of protein gene product 9.5 (PGP9.5, a neuron specific protein), glial fibrillary acidic protein (GFAP), synaptophysin (SYP), brain-derived neurotrophic factor (BDNF), parvalbumin (PV) and HCN1 were not distinguishably changed as compared with sham-operated rats. Baclofen treatment significantly improved the spatial working memory impairments caused by 2VO, accompanied with a reversion of 2VO-induced down-regulation of HCN2. Furthermore, there was a co-localization of HCN2 subunits and parvalbumin-positive neurons in PFC. Therefore, HCN2 may target inhibitory interneurons that is implicated in working memory processes, which may be a possible mechanism of the up-regulation of HCN2 by Baclofen treatment that reliefs spatial working memory deficits in rats with CCH.