Nerve injury alters profile of receptor-mediated Ca2+ channel modulation in vagal afferent neurons of rat nodose ganglia

Exploring poisonous mechanism of honeybee, Apis mellifera ligustica Spinola, caused by pyrethroids

As the important intracellular secondary messengers, calcium channel is the target of many neurotoxic pesticides as calcium homeostasis in the neuroplasm play important role in neuronal functions and behavior in insects. This study investigated the effect of deltamethrin (DM) on calcium channel in the brain nerve cells of adult workers of Apis mellifera ligustica Spinola that were cultured in vitro. The results showed that the intracellular calcium concentration was significantly elevated even with a very low concentration of the DM (3.125×10^-2mg/L). Further testing revealed that T-type voltage-gated calcium channels (VGCCs), except for sodium channels, was one of the target of DM on toxicity of Apis mellifera, while DM has no significant effect on the L-type VGCCs, N-methyl-d-aspartate receptor-gated calcium channels and calcium store. These results suggesting that the DM may act on T-type VGCCs in brain cells of honeybees and result in behavioral abnormalities including swarming, feeding, learning, and acquisition.

Decreased excitability and voltage-gated sodium currents in aortic baroreceptor neurons contribute to the impairment of arterial baroreflex in cirrhotic rats

Cardiovascular autonomic dysfunction, which is manifested by an impairment of the arterial baroreflex, is prevalent irrespective of etiology and contributes to the increased morbidity and mortality in cirrhotic patients. However, the cellular mechanisms that underlie the cirrhosis-impaired arterial baroreflex remain unknown. In the present study, we examined whether the cirrhosis-impaired arterial baroreflex is attributable to the dysfunction of aortic baroreceptor (AB) neurons. Biliary and nonbiliary cirrhotic rats were generated via common bile duct ligation (CBDL) and intraperitoneal injections of thioacetamide (TAA), respectively. Histological and molecular biological examinations confirmed the development of fibrosis in the livers of both cirrhotic rat models. The heart rate changes during phenylephrine-induced baroreceptor activation indicated that baroreflex sensitivity was blunted in the CBDL and TAA rats. Under the current-clamp mode of the patch-clamp technique, cell excitability was recorded in DiI-labeled AB neurons. The number of action potential discharges in the A- and C-type AB neurons was significantly decreased because of the increased rheobase and threshold potential in the CBDL and TAA rats compared with sham-operated rats. Real-time PCR and Western blotting indicated that the NaV1.7, NaV1.8, and NaV1.9 transcripts and proteins were significantly downregulated in the nodose ganglion neurons from the CBDL and TAA rats compared with the sham-operated rats. Consistent with these molecular data, the tetrodotoxin-sensitive NaV currents and the tetrodotoxin-resistant NaV currents were significantly decreased in A- and C-type AB neurons, respectively, from the CBDL and TAA rats compared with the sham-operated rats. Taken together, these findings implicate a key cellular mechanism in the cirrhosis-impaired arterial baroreflex.

Bladder outlet obstruction causes up-regulation of nicotinic acetylcholine receptors in bladder-projecting pelvic ganglion neurons

Pelvic ganglion (PG) neurons relay sympathetic and parasympathetic signals to the lower urinary tract, comprising the urinary bladder and bladder outlet, and are thus essential for both storage and voiding reflexes. Autonomic transmission is mediated by activation of the nicotinic acetylcholine receptor (nAChR) in PG neurons. Previously, bladder outlet obstruction (BOO), secondary to benign prostatic hyperplasia, was found to increase soma sizes of bladder-projecting PG neurons. To date, however, it remains unknown whether these morphological changes are accompanied by functional plasticity in PG neurons. In the present study, we investigated whether BOO alters acetylcholine receptor (nAChR) transcript expression and current density in bladder PG neurons. Partial ligation of the rat urethra for six weeks induced detrusor overactivity (DO), as observed during cystometrical measurement. In rats exhibiting DO, membrane capacitance of parasympathetic bladder PG neurons was selectively increased. Real-time PCR analysis revealed that BOO enhanced the expression of the transcripts encoding the nAChR α3 and β4 subunits in PG neurons. Notably, BOO significantly increased ACh-evoked current density in parasympathetic bladder PG neurons, whereas no changes were observed in sympathetic bladder and parasympathetic penile PG neurons. In addition, other ligand-gated ionic currents were immune to BOO in bladder PG neurons. Taken together, these data suggest that BOO causes upregulation of nAChR in parasympathetic bladder PG neurons, which in turn may potentiate ganglionic transmission and contribute to the development of DO.

Neuregulin 1 up-regulates the expression of nicotinic acetylcholine receptors through the ErbB2/ErbB3-PI3K-MAPK signaling cascade in adult autonomic ganglion neurons

We investigated effects of Neuregulin 1 (NRG1) on the expression of nicotinic acetylcholine receptor (nAChR) in major pelvic ganglion (MPG) from adult rat. MPG neurons were found to express transcripts for type I and III NRG1s as well as α and β-type epidermal growth factor (EGF)-like domains. Of the four ErbB receptor isoforms, ErbB1, ErbB2, and ErbB3 were expressed in MPG neurons. Treating MPG with NRG1β significantly increased the transcript and protein level of the nAChR α3 and β4 subunits. Consistent with these molecular data, nicotinic currents (I(ACh) ) were significantly up-regulated in NRG1β-treated sympathetic and parasympathetic MPG neurons. In contrast, the type III NRG1 and the α form of the NRG1 failed to alter the I(ACh) . Inhibition of the ErbB2 tyrosine kinase completely abolished the effects of NRG1β on the I(ACh) . Stimulation of the ErbB receptors by NRG1β activated the phosphatidylinositol-3-kinase (PI3K) and mitogen-activated protein kinase (MAPK). Immunoblot analysis revealed that PI3K-mediated activation of Akt preceded Erk1/2 activation in NRG1β-treated MPG neurons. Furthermore, specific PI3K inhibitors abrogated the phosphorylation of Erk1/2, while inhibition of MEK did not prevent the phosphorylation of Akt. Taken together, these findings suggest that NRG1 up-regulates nAChR expression via the ErbB2/ErbB3-PI3K-MAPK signaling cascade and may be involved in maintaining the ACh-mediated synaptic transmission in adult autonomic ganglia.

Alteration of primary afferent activity following inferior alveolar nerve transection in rats

Background

In order to evaluate the neural mechanisms underlying the abnormal facial pain that may develop following regeneration of the injured inferior alveolar nerve (IAN), the properties of the IAN innervated in the mental region were analyzed.

Results

Fluorogold (FG) injection into the mental region 14 days after IAN transection showed massive labeling of trigeminal ganglion (TG). The escape threshold to mechanical stimulation of the mental skin was significantly lower (i.e. mechanical allodynia) at 11-14 days after IAN transection than before surgery. The background activity, mechanically evoked responses and afterdischarges of IAN Aδ-fibers were significantly higher in IAN-transected rats than naive. The small/medium diameter TG neurons showed an increase in both tetrodotoxin (TTX)-resistant (TTX-R) and -sensitive (TTX-S) sodium currents (I_Na) and decrease in total potassium current, transient current (I_A) and sustained current (I_K) in IAN-transected rats. The amplitude, overshoot amplitude and number of action potentials evoked by the depolarizing pulses after 1 μM TTX administration in TG neurons were significantly higher, whereas the threshold current to elicit spikes was smaller in IAN-transected rats than naive. Resting membrane potential was significantly smaller in IAN-transected rats than that of naive.

Conclusions

These data suggest that the increase in both TTX-S I_Na and TTX-R I_Na and the decrease in I_A and I_k in small/medium TG neurons in IAN-transected rats are involved in the activation of spike generation, resulting in hyperexcitability of Aδ-IAN fibers innervating the mental region after IAN transection.

Prostaglandin E2 depresses solitary tract-mediated synaptic transmission in the nucleus tractus solitarius

Prostaglandin E(2) (PGE(2)) is a prototypical inflammatory mediator that excites and sensitizes cell bodies [Kwong K, Lee LY (2002) PGE(2) sensitizes cultured pulmonary vagal sensory neurons to chemical and electrical stimuli. J Appl Physiol 93:1419-1428; Kwong K, Lee LY (2005) Prostaglandin E(2) potentiates a tetrodotoxin (TTX)-resistant sodium current in rat capsaicin-sensitive vagal pulmonary sensory neurons. J Physiol 56:437-450] and peripheral nerve terminals [Ho CY, Gu Q, Hong JL, Lee LY (2000) Prostaglandin E (2) enhances chemical and mechanical sensitivities of pulmonary C fibers in the rat. Am J Respir Crit Care Med 162:528-533] of primary vagal sensory neurons. Nearly all central nerve terminals of vagal afferents are in the nucleus tractus solitarius (NTS), where they operate with a high probability of release [Doyle MW, Andresen MC (2001) Reliability of monosynaptic sensory transmission in brain stem neurons in vitro. J Neurophysiol 85:2213-2223]. We studied the effect of PGE(2) on synaptic transmission between tractus solitarius afferent nerve terminals and the second-order NTS neurons in brain stem slices of Sprague-Dawley rats. Whole-cell patch recording in voltage clamp mode was used to study evoked excitatory postsynaptic glutamatergic currents (evEPSCs) from NTS neurons elicited by electrical stimulation of the solitary tract (ST). In 34 neurons, bath-applied PGE(2) (200 nM) decreased the evEPSC amplitude by 49+/-5%. In 22 neurons, however, PGE(2) had no effect. We also tested 15 NTS neurons for capsaicin sensitivity. Seven neurons generated evEPSCs that were equally unaffected by PGE(2) and capsaicin. Conversely, evEPSCs of the other eight neurons, which were PGE(2)-responsive, were abolished by 200 nM capsaicin. Furthermore, the PGE(2-)induced depression of evEPSCs was associated with an increase in the paired pulse ratio and a decrease in both the frequency and amplitude of the spontaneous excitatory postsynaptic currents (sEPSCs) and TTX-independent spontaneous miniature excitatory postsynaptic currents (mEPSCs). These results suggest that PGE(2) acts both presynaptically on nerve terminals and postsynaptically on NTS neurons to reduce glutamatergic responses.

Contralateral cytokine gene induction after peripheral nerve lesions: dependence on the mode of injury and NMDA receptor signaling

There is increasing evidence that unilateral nerve injury evokes contralateral responses, but the underlying mechanisms are largely unknown. In the present investigation, we analyzed cytokine and chemokine gene induction in contralateral, non-lesioned nerves after sciatic nerve crush and chronic constriction injury (CCI) by quantitative reverse transcriptase polymerase chain reaction in mice. After sciatic nerve crush, contralateral changes in cytokine gene expression were restricted to interleukin (IL)-1beta, which showed a monophasic peak at the first postoperative day. Following CCI, contralateral transcripts for IL-1beta, IL-10 and monocyte chemoattractant protein-1 (MCP-1) were significantly increased already at day 1 and upregulation persisted over the next 4 weeks. In contrast, tumor necrosis factor alpha (TNF-alpha) levels remained unchanged. Contralateral gene induction was restricted to the homonymous opposite sciatic nerve, but spared the femoral nerve. NMDA receptor blockade completely abolished contralateral cytokine expression after CCI on the mRNA level. In contralateral dorsal root ganglia, only IL-10 mRNA levels were modified after nerve injury. Sham operation significantly increased the cytokine and chemokine gene expression at the ipsilateral side, but could not mediate contralateral effects. Our study confirms that nerve injury evokes contralateral responses and identifies NMDA-mediated signaling as one underlying mechanism.

Fluoxetine-induced up-regulation of 14-3-3zeta and tryptophan hydroxylase levels in RBL-2H3 cells

The primary mechanisms of antidepressants are based on the monoamine depletion hypothesis. However, we do not yet know the full cascade of mechanisms responsible for the therapeutic effect of antidepressants. To identify the genes involved in the therapeutic mechanism of the selective serotonin reuptake inhibitor, fluoxetine, we used a cDNA microarray analysis with RBL-2H3 cells. We observed the transcriptional changes of several tens of genes containing the 14-3-3zeta gene in the fluoxetine-treated RBL-2H3 cells. Real-time RT-PCR and Western blotting confirmed changes in the expression of the gene and protein. The increase of 14-3-3zeta mRNA was observed at 72 h in the fluoxetine-treated RBL-2H3 cells. The increase of 14-3-3zeta protein was observed at 48 and 72 h. In this study, the expressions of the 14-3-3zeta gene and the protein were up-regulated at 72 h. In addition, the increase of TPH mRNA was observed at 12, 24 and 72 h in the fluoxetine-treated RBL-2H3 cells. We conclude that fluoxetine induces increases of 14-3-3zeta mRNA, 14-3-3zeta protein and TPH mRNA at 72 h in the RBL-2H3 cells. This suggests that the 14-3-3zeta and TPH genes may play a role in the molecular mechanism of fluoxetine. To date, no cases of 14-3-3zeta alterations by antidepressants and specifically by fluoxetine have been reported.