The subunit expression of AMPARs and NMDARs in crucian carp brain tissue
was strikingly well preserved during such a drastic insult as one week of anoxia. Thus,
the anoxic crucian carp appears to keep its glutamatergic system in a steady-state,
retaining its functionality. This tentative conclusion goes well with the suggestion that
crucian carp needs to retain its brain tissue ion conductance to be able to survive anoxia
in an active state (Nilsson, 2001). Thus, after finding no effects of anoxia on K+ and Ca2+
permeability in crucian carp brain slices it was postulated that channel arrest is not an
important component of the anoxic survival strategy utilized by the crucian carp (Nilsson,
2001). Having said this, based on the current knowledge it is not possible to fully exclude
channel-arrest as a mean of lowering neuronal energy expenditure in anoxic crucian carp
brain. There are at least two reasons for this. Firstly, proteins such as AMPARs and
NMDARs may be altered at the post-translational level rather than at the transcriptional
level (e.g. by controlling the state of phosphorylation). Such post-translational changes
have been shown to occur in NMDARs of anoxic turtle brain tissue (Bickler et al., 2000).
Secondly, electric activity and the formation of action potentials are influenced by
numerous factors other than properties of AMPARs and NMDARs. Major sites for ion
fluxes in brain are sodium channels, and how they are influenced by anoxia has so far has
not been examined in crucian carp brain.