A Study Of The Effects Of Topiramate On The Mouse Sudomotor Function And The Potential Mechanism Involved In It

Topiramate,2,3:4,5-bis-O-(1-methyl-ethylidene-)-β-fructopyran -ose sulfamate , a novel antiepileptic drug, has been demonstrated to be effective in controlling a wide range of seizure types, including focal seizures, primary generalized tonic-clonic seizures and Lennox-Gastaut syndrome, among others. It possesses a broad-spectrum of anticonvulsant activity, mainly through the following mechanisms: attenuation of voltage-gated Na+ currents; enhancement of GABAA -mediated neurotransmission;negative modulatory effects on AMPA/KA subtype of glutamate receptors; inhibition of glutamate and aspartate release from the nerve terminal; inhibition of carbonic anhydrase isozymes, particularly, CA II and CA IV; modulatory effects on K+ channel currents and inhibition of neuronal L-type high voltage-activated Ca2+ channels.Heat intolerance with hypohidrosis or anhidrosis has been recently reported in children undergoing epilepsy treatment with TPM. This effect was reversible, and was disappeared with the cessation of TPM treatment. It was about 10-20% children developed hypohidrosis after TPM treatment.A pilot study found that more than fifty percents children have reduced sweat quantity on the pilocarpine iontophoresis sweat test following TPM reatment,although only some of them revealed symptoms related to heat intolerance. This means that hypohidrosis is a common phenomenon in children with TPM treatment.The mechanism underlying this effect on sweating has not been fully elucidated for that indistinct mechanism of sudomotor function. The hypohidrotic effects of TPM might be attributed to the inhibition of CA II and CA IV, which might alter primary sweat composition and reduce water formation leading to an impaired sweat rate. However, carbonic anhydrase inhibitors are not thought to be potent causes of exercise-related oligohidrosis, as the carbonic anhydrase mechanisms for water excretion cannot be rapidly regulated by the body.Immunohistochemical staining revealed a strong anti-AQP5 labeling of both apical and basolateral plasma membrane domains of secretory regions of mouse SGs. AQP5 may be important in several clinical sweat disorders.Contrarily, previous research provided direct evidence against functionally important involvement of AQP5 in sweat fluid secretion in mice.The sweat pathway originates in the preoptic area of the anterior hypothalamus and descends uncrossed through the medial portion of the lateral funiculus of the brain stem to synapse upon preganglionic neurons in the intermediolateral column of the spinal cord.and then synapse on sympathetic ganglia, which supplies sweat glands.The ability of humans to dissipate heat during exercise and in hot environments depends mainly on the evaporation of sweat secreted by eccrine sweat glands (SGs). Consequently, sweat production is essential for heat tolerance, preventing hyperthermia, and influences performance during physical activity. SGs are innervated by sympathetic postganglionic axons, which, in contrast to the ordinary sympathetic innervation, use acetylcholine as the principal neurotransmitter.Whether the TPM related hypohidrosis result from the effect of TPM on cholinergic system?In the current study, we investigated the effects of TMP on the responsiveness of mouse eccrine SGs to pilocarpine stimulation by utilizing silicone imprints, Additionally, We explored the sweat glands structure by HE staining and examined ultrastructure of sweat gland with electron microscope.Then immunolabelling was used to examine the effects of TMP on choline acetyltransferase (ChAT) in cholinergic sudomotor nerves, tyrosine hydroxylase (TH) in noradrenalinergic nerves, total innervation of sweat glands by PGP9.5 immunostaining as well as the expression of M3 molecular subtype of muscarinic receptor in mouse foot pad sweat gland. By immunohistochemical staining and western blotting,the expression of acetylcholine esterase was observed in the in mouse footpad sweat gland. Also the acetylcholine esterase Activity was determined by the method of Ellman with some modifications. the expressioin of GABA-ergic neuron in intermediolateral column of spinal cord ,and the the expressioin of GABA-ergic neuron in the hypothalamus following heat exposure were explored. Here are the results:(1) Young mice (two weeks old) were given topiramate (TPM) daily for one month, after that and one week later,the sudomotor function was evaluated utilizing impression mould techniques by pilocarpine stimulation. While a 17% decrease in the number of secreting SGs and a 40% decline in sweat output per gland were observed following TPM treatment,there were no distinct differences in mouse footpad ecrrine sweat gland structural and ultrastructure in both group mouse.(2) The expression of ChAT , TH and PGP in sweat gland and ChAT/TH in stellate ganglion, showed no significant change after TPM treatment, neither the M3 receptor and the size of the sweat gland secretory coil area.(3) There were no statistics difference of the optical density value of acetylcholine esterase immunostaining in mouse foot pad sweat gland in both group. Neither the protein expression of the acetylcholine esterase and the acetylcholine esterase activity in mouse footpad sweat gland.(4) The GABA-ergic maker GAD65 was co-expressed with cholinergic neuron in the intermediolateral column of spinal cord.So was GABA-ergic neuron with c-fos protein and TRPV with c-fos protein in the hypothalamus after heat exposure.Following points can be concluded from the results of the present studies. (1) The sudomotor function of mice can be lowered by long-time TPM treatment,and recovered after the discontinuation of TPM.(2) The hypohidrosis following TPM treatment was not induced by the effect of TPM on the eccrine coil area and structure change.(3) The depressed sudomotor function of mouse foot pad sweat gland related TPM have no association with the development and innervation of sympathetic nerve that supplies mouse sweat gland. Neither with the expression of M3 receptor, Nor the expression and activiety of AChE in sweat gland.(4) GABA-ergic neuron may involve in the modulation of acetylcholine releasing in spinal cord and in the thermoregulation in preoptic area and anterior hypothalamus,which may lead to the TPM related hypohidrosis.