neurokinin-a and Seizures

Excitotoxic damage appears to be a critical factor in the formation of perinatal brain lesions associated with cerebral palsy (CP). When injected into newborn mice, the glutamatergic analogue, ibotenate, produces cortical lesions and white matter cysts that mimic human perinatal brain lesions. Neuropeptides are neuronal activity modulators and could therefore modulate glutamate-induced lesions. However, neuropeptides are rapidly degraded by peptidases. Racecadotril, which is rapidly metabolized to its active metabolite thiorphan, is a neutral endopeptidase (NEP) inhibitor used in clinical practice for diarrhoea with a remarkable safety profile. This study aimed to test the original hypothesis that thiorphan could be neuroprotective against ibotenate-induced lesions in newborn mice. Intraperitoneal administration of thiorphan reduced ibotenate-induced cortical lesions by up to 57% and cortical caspase-3 cleavage by up to 59%. This neuroprotective effect was long-lasting and was still observed when thiorphan was administered 12 h after the insult, showing a remarkable window for therapeutic intervention. Further supporting the neuroprotective effect of pharmacological blockade of NEP, mouse pups with a genetic deletion of NEP displayed a significantly reduced size of the ibotenate-induced cortical grey matter lesion when compared with wild-type animals. Thiorphan effects were mimicked by substance P (SP) and, in a less potent manner, by neurokinin A. Thiorphan effects were inhibited by blockers of NK1 and NK2 receptors. Real-time reverse transcription-polymerase chain reaction, autoradiography and immunohistochemistry confirmed the expression of NK1 and NK2 receptors in the neonatal murine neocortex. These data demonstrate that thiorphan prevents neonatal excitotoxic cortical damage, an effect largely mediated by SP. Thiorphan could represent a promising drug for the prevention of CP, which remains a challenging disease. In a broader context, these results also raise potential implications for the prevention of neurodegenerative diseases involving glutamate-mediated excitotoxic neuronal death.

Topics: Animals; Animals, Newborn; Caspase 3; Cell Death; Cells, Cultured; Cerebral Cortex; Cerebral Palsy; Excitatory Amino Acid Agonists; Female; Ibotenic Acid; Immunohistochemistry; Injections, Intraperitoneal; Male; Mice; Mice, Inbred C57BL; Neprilysin; Neurokinin A; Neurokinin-1 Receptor Antagonists; Neurons; Neuroprotective Agents; Neurotransmitter Agents; Protease Inhibitors; Receptors, Neurokinin-2; Seizures; Substance P; Thiorphan

We studied the effects of modification of duration of seizures induced by electroconvulsive stimuli (ECS) on the changes in concentration of neuropeptide Y (NPY), neurokinin A (NKA), substance P (SP) and neurotensin (NT)-like immunoreactivity (-LI) in specific rat brain regions. Rats were divided into groups pretreated with saline, indomethacin, flurbiprofen or diazepam prior to either six sham ECSs or six ECSs. After sacrifice by focused microwave irradiation, brains were dissected into frontal cortex, occipital cortex, striatum, hippocampus, pituitary and hypothalamic sections. Peptides were extracted and measured in extract aliquots by specific radioimmunoassays. Repeated ECS increased NPY-LI and NKA-LI in the hippocampus and the occipital cortex. No effect on SP-LI or NT-LI was found. Indomethacin and flurbiprofen had no effect on the tonic seizure time following ECS, and they did not affect the ECS-induced alterations of the brain peptides. Diazepam pretreatment decreased the tonic seizure time following ECS in a dose-dependent manner. However, diazepam did not modify the ECS-induced increase in NPY-LI and NKA-LI concentrations. The results firmly establish that ECS leads to specific peptide increases in discrete rat brain regions and raise the possibility that such changes may not entirely be a consequence of seizures per se.

Topics: Animals; Brain; Diazepam; Eicosanoids; Electroshock; Male; Neurokinin A; Neuropeptide Y; Neuropeptides; Neurotensin; Rats; Rats, Sprague-Dawley; Seizures; Substance P; Time Factors; Tissue Distribution