Cortical spreading depression (SD) has not been shown in the human neo
cortex by direct cortical recordings. However, animal studies suggest
that cortical injury, such as that occurring during neurosurgical proc
edures, should result in the initiation of SD. It is possible that inh
ibition of SD by volatile anesthetic agents may partially explain the
failure to observe SD in the human neocortex during surgery. This stud
y examines the effect of the anesthetic agents alpha-chloralose, halot
hane, nitrous oxide and isoflurane on the initiation of cortical SD in
the cat neocortex. SD was seen in 100% of cats anesthetized with alph
a-chloralose (n=15), in 3 of 7 (42%) animals anesthetized with isoflur
ane (p<0.05, chi(2) with Yates correction) and none of the animals (n=
4, 6 hemispheric preparations) anesthetized with halothane (p<0.005, c
hi(2) with Yates correction, halothane vs ct-chloralose group). In all
cases this inhibitory effect was reversible. In four animals the admi
nistration of nitrous oxide (66%) reduced the inspired concentration o
f isoflurane required to inhibit SD by 0.75%. This study suggests that
halothane, and to a lesser extent isoflurane and nitrous oxide, prote
ct against the initiation of cortical SD. This observation may partial
ly explain why SD has not been demonstrated in human neocortex during
surgery. Further studies are needed to determine if SD may occur under
pathological conditions, such as during migraine with aura, where the
cortex may be predisposed to SD.