Biomedical Engineering Reference
In-Depth Information
The problem arose because the “rapid” negativities could be fully
blocked by intraglomerular NBQX or TTX without affecting vas-
cular responses. This meant that under physiological conditions
where several spatially distinct neuronal populations are activated,
i.e. several glomeruli, local blow flow could be independent of the
glomerular activity recorded locally with a single electrode. This
problem will be particularly important when the distribution of
the activated brain loci is unknown or when the spatial resolution
of the imaging technique used to measure CBF includes several
activated loci.
A very recent study confirmed our results that local intra-
glomerular blockade of glutamate ionotropic antagonists did not
blocked odor-evoked vascular responses and even increased them
by decreasing presynaptic inhibition. More importantly, it also
showed that local activation of astrocytic metabotropic glutamate
receptors and glutamate transporters can trigger functional hyper-
emia independently of neuronal activation
(64)
. How can these
results be reconciled with the fact that, as in cerebellum, topi-
cal application of NBQX and D-AP5 decreased (rat) or blocked
(mice) odor-evoked functional hyperemia? One possibility is that
the experimental conditions required to achieve topical applica-
tions alter some mechanisms of neurovascular coupling. A second
one is that we used higher odor concentrations, inducing postsy-
naptic responses that trigger additional regulatory mechanisms of
vascular responses
(65)
? To conclude, in the bulb as in other brain
regions, several pathways most probably participate to functional
hyperemia.
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