Mechanism of neuromuscular blockade induced by phenthonium, a quaternary derivative of (-)-hyoscyamine, in skeletal muscles

Effects of Huperzin-A on the Beta-amyloid accumulation in the brain and skeletal muscle cells of a rat model for Alzheimer's disease

AIMS

Alzheimer's Disease (AD) is characterized by a loss of cognitive function and also the accumulation of β-amyloid peptide (βAP) in the brain parenchyma, which plays an important role in this disease. However, it is often also associated with the non-cognitive symptoms such as loss of muscle function (Inclusion-Body Myositis-IBM).

MAIN METHODS

Sprague-Dawley rats (13 weeks-n=68) were randomly assigned into five groups: Group C: Control; Group D: d-galactose; Group O+D: Bilateral oophorectomy+d-galactose; Group O: Bilateral oophorectomy; Group O+D+H: Bilateral oophorectomy+d-galactose+Hup-A. Tissue fixation was performed with the perfusion method. The Compound Muscle Action Potential (CMAP) and mechanical muscle activity were recorded using the standard electro-biophysical techniques. Immune staining was performed with specific antibodies, and the pathological changes were examined. RNA was obtained from brain tissue samples with the Trizol Method. Then, the expression data of mature-miRNAs (rno-miR-9-5p, rno-miR-29a-3p, rno-miR-106a-5p, rno-miR-107 and rno-miR-125a-3p), which may be effective in AD, were taken with Real-Time PCR.

KEY FINDINGS

Impairments occurred in behavioral tests of the rats in the O+D group. βAP accumulation and AChE activity increased significantly in the forebrain in the O+D group compared to the C group. It was seen that Huperzine-A (Hup-A) reduced AChE activity and destructed βAP accumulation. There was a significant decrease in the maximum contractile force at different frequencies in the O+D group and in the O group compared to the C group.

SIGNIFICANCE

It was found that Hup-A contributed to the healing process in rats for damage occurring both in the brain and in the neuro-muscular system.

Allosteric interaction of the anticholinergic drug [N-(4-phenyl)-phenacyl-l-hyoscyamine] (Phenthonium) with nicotinic receptors of post-ganglionic sympathetic neurons of the rat vas deferens

Phenthonium (Phen), a quaternary analog of hyoscyamine, is a blocker of muscarinic activity and an allosteric blocker of alpha(1)2betagammaepsilon nicotinic receptors. Specifically, Phenthonium increases the spontaneous release of acetylcholine at the motor endplate without depolarizing the muscle or inhibiting cholinesterase activity. This paper compares Phenthonium's effects on sympathetic transmission and on ganglionic nicotinic receptor activation. Neurotransmitter release and twitch of the rat vas deferens were induced either by electrical stimulation or by 1,1-dimethyl-4-phenylpiperazine (DMPP) activation of nicotinic receptors. Contractions independent of transmitter release were induced by noradrenaline and adenosine 5'-triphosphate (ATP). Phenthonium inhibited transmitter release and depressed twitch without changing the responsiveness to noradrenaline or ATP. Twitch depression did not occur after K(+)-channel blockade with 4-aminopyridine (4-AP) or charybdotoxin. DMPP had a similar effect, but high concentrations induced contraction of non-stimulated organs. Incubation of Phenthonium inhibited further DMPP twitch depression and non-competitively depressed the contractile responses elicited by DMPP. Furthermore, mecamylamine, but neither methyllycaconitine nor atropine, blocked the contraction elicited by DMPP. Phenthonium and DMPP are K(+)-channel openers that primarily inhibit sympathetic transmission. Contraction induced by DMPP was probably mediated by neuronal nicotinic receptor other than the alpha7 subtype. The blockade of DMPP contractile response was unrelated to Phenthonium's antimuscarinic or K(+)-channel opening activities. Since Phenthonium's quaternary chemical structure limits its membrane diffusion, the non-competitive inhibition of DMPP excitatory responses should be linked to allosteric interaction with neuronal nicotinic receptors that putatively qualify Phenthonium as a novel modulator of cholinergic synapses.