Antibiotic treatment during post-natal reverses behavioural and molecular alterations in experimental meningitis survivor rat model

The present study was aimed to examine the behavioural and molecular alterations in experimental meningitis survivor rat model. On postnatal day (PND)-2, animals were assigned to different groups: (i) Control (Ctrl), (ii) Positive Control [PCtrl: gavaged with Luria-Bertani (LB) broth on PND-2 and received antibiotics treatment (AbT) from PND-5 to 11], (iii) Cronobacter sakazakii (CS: received single dose of live bacterial culture on PND-2) infected. Later, a subset of CS group received antibiotics treatment (AbT) from PND-5 to 11 and assigned as group (iv) (CS + AbT/ survivor). On PND-35, animals were subjected to behavioural tasks [viz., elevated plus maze (EPM) test and step-through inhibitory retention], and sacrificed for molecular analyses. We found that CS infection induces anxiety-like behaviour, impaired short/long-term memory and differentially altered the expression of brain-derived neurotrophic factor (BDNF) splice variants (III, IV and VI), decreased expression of BDNF, Src family tyrosine kinase (FYN), focal adhesion kinase (FAK) and nerve growth factor (NGF). The observed behavioural phenotype and expression pattern of candidate genes fit in the correlation. In addition, NGF expression was reduced in dentate gyrus (DG) and CA1 regions of hippocampus. Notably, antibiotic treatment reduced the anxiety-like behaviour, improved step-through inhibitory retention and suppressed infection induced reduction in BDNF, FYN, FAK and NGF expressions in survivors, however, not comparable to the control group. Overall, our experimental meningitis survivor model demonstrate that antibiotic treatment minimize the C. sakazakii infection induced effect on behaviour and signaling molecules involving in neuronal development, survival, and synaptic plasticity, but the consequences are long-term.

Antidepressant amitriptyline-induced matrix metalloproteinase-9 activation is mediated by Src family tyrosine kinase, which leads to glial cell line-derived neurotrophic factor mRNA expression in rat astroglial cells

Background

Astrocytes have been implicated in the pathophysiology of mood disorders and in the mechanism of the pharmacological effects of antidepressant drugs by the production of neurotrophic/growth factors. Previous studies have identified astrocyte‐expressed Gα_i/o‐coupled lysophosphatidic acid receptor 1 (LPAR1), as being involved in antidepressant‐induced production of glial cell line‐derived neurotrophic factor (GDNF) and matrix metalloproteinase‐9 (MMP‐9) activation, an important step in the production of GNDF. However, the precise mechanism of MMP‐9 activation by antidepressants has yet to be identified, in particular the intracellular signaling pathway between LPAR1/Gα_i/o and MMP‐9.

Methods and Results

Treatment of rat C6 astroglial cells (C6 cells) with amitriptyline increased Src family tyrosine kinase phosphorylation in a time and concentration‐dependent manner. Amitriptyline‐induced GDNF mRNA expression was blocked by Src family tyrosine kinase inhibitors. In addition, inhibiting Src family tyrosine kinase blocked amitriptyline‐induced zymographic MMP‐9 activation in C6 cells. The amitriptyline‐induced zymographic MMP‐9 activity was completely blocked by selective inhibition of Gα_i/o protein and LPAR1. Furthermore, the amitriptyline‐induced Src family tyrosine kinase phosphorylation was blocked by LPAR1, but not MMP‐9 inhibition, indicating that Src family tyrosine kinase involvement is downstream of LPAR1.

Conclusions

The current findings suggest that the pharmacological effect of antidepressant such as amitriptyline is mediated through an intracellular signaling pathway via the LPAR1/Gα_i/o/Src family tyrosine kinase, which leads to MMP‐9 activation and GDNF production.

Treatment of rat C6 astroglial cells (C6 cells) with amitriptyline increased Src family tyrosine kinase phosphorylation in a time‐ and concentration‐dependent manner. The current findings suggest that the pharmacological effect of antidepressant such as amitriptyline is mediated through an intracellular signaling pathway via the LPAR1/Gαi/o/Src family tyrosine kinase, which leads to MMP‐9 activation and glial cell line‐derived neurotrophic factor production.

Chronic Ca2+ influx through voltage-dependent Ca2+ channels enhance delayed rectifier K+ currents via activating Src family tyrosine kinase in rat hippocampal neurons

Excessive influx and the subsequent rapid cytosolic elevation of Ca²⁺ in neurons is the major cause to induce hyperexcitability and irreversible cell damage although it is an essential ion for cellular signalings. Therefore, most neurons exhibit several cellular mechanisms to homeostatically regulate cytosolic Ca²⁺ level in normal as well as pathological conditions. Delayed rectifier K⁺ channels (I_DR channels) play a role to suppress membrane excitability by inducing K⁺ outflow in various conditions, indicating their potential role in preventing pathogenic conditions and cell damage under Ca²⁺-mediated excitotoxic conditions. In the present study, we electrophysiologically evaluated the response of I_DR channels to hyperexcitable conditions induced by high Ca²⁺ pretreatment (3.6 mM, for 24 hours) in cultured hippocampal neurons. In results, high Ca²⁺-treatment significantly increased the amplitude of I_DR without changes of gating kinetics. Nimodipine but not APV blocked Ca²⁺-induced I_DR enhancement, confirming that the change of I_DR might be targeted by Ca²⁺ influx through voltage-dependent Ca²⁺ channels (VDCCs) rather than NMDA receptors (NMDARs). The VDCC-mediated I_DR enhancement was not affected by either Ca²⁺-induced Ca²⁺ release (CICR) or small conductance Ca²⁺-activated K⁺ channels (SK channels). Furthermore, PP2 but not H89 completely abolished I_DR enhancement under high Ca²⁺ condition, indicating that the activation of Src family tyrosine kinases (SFKs) is required for Ca²⁺-mediated I_DR enhancement. Thus, SFKs may be sensitive to excessive Ca²⁺ influx through VDCCs and enhance I_DR to activate a neuroprotective mechanism against Ca²⁺-mediated hyperexcitability in neurons.