PubMed · 15392037
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A JENTZER, MILLETTI. 1949. About current anesthesia problems.. https://pubmed.ncbi.nlm.nih.gov/15392037/
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Since the launch in 1998 of the anti-impotence drug sildenafil (viagra), the American food and drug administration has identified 50 cases of drug-related blindness, the so-called nonarteritic anterior ischemic optic neuropathy. This, very serious, side effect frequently leads to sudden, mostly irreversible loss of vision, and there is no proven effective treatment to cure patients or to prevent recurrence. The mechanism of ischemic optic neuropathy is not clear, but it could be related to the fact that the ophthalmic and central retinal arteries have an autoregulation of their own blood flow without any autonomic nerve supply; vasoreactivity could be lower albeit efficient, and therefore more vulnerable to systemic modifications of the circulation. But decreased visual acuity and loss of visual ability also are, although uncommon, anesthesiological and surgical complications. These data are consistent with the hypothesis that sildenafil, surgery and anesthesia, taken together, could be a potentially dangerous cocktail of risk factors for sudden irreversible loss of vision. To reduce the risk, sildenafil use should be avoided at least one week before surgical operations, since the reported cases of blindness developed 36h after drug ingestion.
Extracellular recordings were made from output neurons in the dorsal half of the periaqueductal gray matter (dPAG) in urethane-anesthetized female Wistar rats. All the neurons were quiescent. A basal level of firing was therefore induced by continuous iontophoretic application of D,L-homocysteic acid (DLH). In the presence of the GABA(A) receptor antagonist bicuculline methiodide (BIC 0-30 nA) the DLH-induced firing increased further, revealing the presence of ongoing GABAergic inhibitory tone on the recorded neurons. The BIC-induced increase in firing rate was significantly greater in neurons recorded during estrus (Est) and late diestrus (LD) compared with proestrus (Pro) and early diestrus (ED) suggesting that GABAergic tone was lower in Est and LD. I.v. injection of the panicogenic cholecystokinin (CCK)(B) receptor agonist pentagastrin (PG, 40 microg kg(-1)) produced an increase in firing rate in 12/17 (70%) of neurons tested in the dPAG. Iontophoretic application of PG (10-30 nA) also produced a current-related increase in firing rate in 73.6% of the neurons tested. The excitatory response was reduced during application of the selective CCK(B) receptor antagonist beta-[2-([2-(8-azaspiro[4.5]dec-8-ylcarbonyl)-4,6-dimethylphenyl]amino)-2-oxoethyl]-(R)-napthalenepropanoic acid (CR2945) (60 nA, n=6). The PG-evoked increase in firing rate was significantly greater in neurons recorded during Est and LD compared with during Pro and ED. Juxtacellular labeling with neurobiotin in eight neurons revealed multipolar cells 12-44 microm diameter with up to six primary dendrites. In three of eight neurons, a filled axon was present and coursed without branching toward the perimeter of the periaqueductal gray matter (PAG). The estrous cycle-related change in responsiveness to BIC and PG suggests that the panic circuitry in the PAG may become more responsive to panicogenic agents during estrus and late diestrus as a consequence of a decrease in the intrinsic level of inhibitory GABAergic tone. The findings may have implications for understanding the neural processes that underlie the development of premenstrual dysphorias in women.
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