phorbol-12-13-didecanoate and Nerve-Degeneration

To examine the mechanisms involved in hypotension induced by transient receptor potential vanilloid 4 (TRPV4) activation.. Wistar rats were given 50 mg/kg capsaicin subcutaneously 1-2 days postnatally to cause degeneration of capsaicin-sensitive sensory nerves. Vehicle was given to the corresponding newborn rats that formed the control group. After being weaned, male rats were picked for further investigation. At the age of 8 weeks, mean arterial pressure and its response to 4alpha-phorbol 12,13-didecanoate [4alpha-PDD, a selective TRPV4 activator, 2.5 mg/kg, intravenous(ly) or i.v.] with or without CGRP8-37 (1 mg/kg per min, i.v.), an antagonist of calcitonin gene-related peptide (CGRP, a potent vasodilator released from sensory nerves), in vehicle or capsaicin-pretreated rats anesthetized with sodium pentobarbital [50 mg/kg, intraperitoneal(ly)] were monitored to observe the contributions of neuropeptides released from sensory nerves to the 4alpha-PDD-induced hypotension. To detect the roles of various vasodilating factors released by vascular endothelium in the hypotensive effect induced by TRPV4 activation, the corresponding inhibitors/blockers, including indomethacin (a cyclooxygenase inhibitor, 10 mg/kg, i.v.), Nomega-nitro-L-arginine (L-NA, a nitric oxide synthase inhibitor, 20 mg/kg, i.v.), apamin [a blocker of small conductance Ca2+-activated K+ (MaxiK) channels, 50 microg/kg, i.v.] combined with charybdotoxin (a blocker of intermediate and large conductance MaxiK channels, 50 microg/kg, i.v.), were used at various time before 4alpha-PDD injection. Plasma CGRP and substance P levels of rats before or after administration were measured using the corresponding radioimmunoassays. At last, immunohistochemistry stainings were performed to observe expression of TRPV4/CGRP/MaxiK in mesenteric resistance arteries and sensory neurons/nerve fibers.. Intravenous administration of 4alpha-PDD produced remarkable hypotension in vehicle-pretreated rats. The depressor effect was attenuated by degeneration of capsaicin-sensitive sensory nerves (P < 0.05) or administration of CGRP8-37 (P < 0.05). In both vehicle and capsaicin-pretreated rats, the combined administration of apamin and charybdotoxin markedly reduced the 4alpha-PDD-induced hypotensive effect (P < 0.05), but i.v. administration of indomethacin and Nomega-nitro-L-arginine did not produce the similar effect. Intravenous administration of 4alpha PDD increased plasma CGRP but not substance P levels in vehicle-pretreated rats only (P < 0.05), which was not affected by indomethacin, Nomega-nitro-L-arginine, or apamin and charybdotoxin. Immunohistochemistry staining showed that TRPV4 colocalized with MaxiK channels in endothelium of mesenteric resistance arteries and with CGRP in sensory neurons/nerve fibers.. Our data show that the hypotensive effect induced by TRPV4 activation attributes to, at least in part, activation of MaxiK channels and CGRP receptors upon CGRP release from sensory nerves.

Topics: Animals; Animals, Newborn; Apamin; Blood Pressure; Calcitonin Gene-Related Peptide; Capsaicin; Charybdotoxin; Drug Combinations; Drug Therapy, Combination; Endothelium, Vascular; Hypotension; Injections, Subcutaneous; Male; Mesenteric Arteries; Nerve Degeneration; Neurons, Afferent; Peptide Fragments; Phorbol Esters; Potassium Channels, Calcium-Activated; Rats; Rats, Wistar; Sensory System Agents; Substance P; TRPV Cation Channels; Vasodilator Agents

Roles of protein kinases in mediating adaptive neuronal responses to activation of signal transduction pathways are well known. Recent findings suggest that kinases may also be involved in pathological processes in the nervous system. The present study employed cultured human cerebral cortical neurons to test the hypothesis that overactivation of protein kinase C (PKC) can result in neurodegeneration. Phorbol 12-myristate 13-acetate (PMA), an activator of PKC, caused the degeneration of neurons over a period of 3-24 h. The PKC inhibitor H-7 prevented the neurodegeneration normally caused by PMA, and an inactive phorbol (4 alpha-phorbol 12,13-didecanoate; PDD) did not cause neurodegeneration. The neurodegeneration caused by PMA was independent of calcium influx. Immunoreactivity toward antibodies that recognize the microtubule-associated protein tau in Alzheimer neurofibrillary tangles (Alz-50 and 5E2) was greatly increased in neurons exposed to PMA. The antigenic changes were prevented by H-7. These findings indicate that high levels of activation of PKC can cause neurodegeneration and are consistent with the possibility that altered cellular signaling contributes to pathological neuronal degeneration in the intact nervous system.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Cell Survival; Cells, Cultured; Cerebral Cortex; Fetus; Humans; Isoquinolines; Kinetics; Nerve Degeneration; Neurons; Phorbol Esters; Piperazines; Protein Kinase C; Signal Transduction; Tetradecanoylphorbol Acetate