The roles of oxidative stress and structural alterations in the cerebrovascular dysfunctions associated with Alzheimer's disease (AD) were investigated in transgenic mice overexpressing amyloid precusor protein (APP ϩ ) or transforming growth factor-␤1 (TGF ϩ ). Age-related impairments and their in vitro reversibility were evaluated, and underlying pathogenic mechanisms were assessed and compared with those seen in AD brains. Vasoconstrictions to 5-HT and endothelin-1 were preserved, except in the oldest (18 -21 months of age) TGF ϩ mice. Despite unaltered relaxations to sodium nitroprusside, acetylcholine (ACh) and calcitonin gene-related peptide-mediated dilatations were impaired, and there was an age-related deficit in the basal availability of nitric oxide (NO) that progressed more gradually in TGF ϩ mice. The expression and progression of these deficits were unrelated to the onset or extent of thioflavin-S-positive vessels. Manganese superoxide dismutase (SOD2) was upregulated in pial vessels and around brain microvessels of APP ϩ mice, pointing to a role of superoxide in the dysfunctions elicited by amyloidosis. In contrast, vascular wall remodeling associated with decreased levels of endothelial NO synthase and cyclooxygenase-2 and increased contents of vascular endothelial growth factor and collagen-I and -IV characterized TGF ϩ mice. Exogenous SOD or catalase normalized ACh dilatations and NO availability in vessels from aged APP ϩ mice but had no effect in those of TGF ϩ mice. Increased perivascular oxidative stress was not evidenced in AD brains, but vascular wall alterations compared well with those seen in TGF ϩ mice. We conclude that brain vessel remodeling and associated alterations in levels of vasoactive signaling molecules are key contributors to AD cerebrovascular dysfunctions.

The whisker-to-barrel cortex is widely used to study neurovascular coupling, but the cellular basis that underlies the perfusion changes is still largely unknown. Here, we identified neurons recruited by whisker stimulation in the rat somatosensory cortex using double immunohistochemistry for c-Fos and markers of glutamatergic and GABAergic neurons, and investigated in vivo their contribution along with that of astrocytes in the evoked perfusion response. Whisker stimulation elicited cerebral blood flow (CBF) increases concomitantly with c-Fos upregulation in pyramidal cells that coexpressed cyclooxygenase-2 (COX-2) and GABA interneurons that coexpressed vasoactive intestinal polypeptide and/or choline acetyltransferase, but not somatostatin or parvalbumin. The evoked CBF response was decreased by blockade of NMDA (MK-801, Ϫ37%), group I metabotropic glutamate (MPEPϩLY367385, Ϫ40%), and GABA-A (picrotoxin, Ϫ31%) receptors, but not by GABA-B, VIP, or muscarinic receptor antagonism. Picrotoxin decreased stimulus-induced somatosensory evoked potentials and CBF responses. Combined blockade of GABA-A and NMDA receptors yielded an additive decreasing effect (Ϫ61%) of the evoked CBF compared with each antagonist alone, demonstrating cooperation of both excitatory and inhibitory systems in the hyperemic response. Blockade of prostanoid synthesis by inhibiting COX-2 (indomethacin, NS-398), expressed by ϳ40% of pyramidal cells but not by astrocytes, impaired the CBF response (Ϫ50%). The hyperemic response was also reduced (Ϫ40%) after inhibition of astroglial oxidative metabolism or epoxyeicosatrienoic acids synthesis. These results demonstrate that changes in pyramidal cell activity, sculpted by specific types of inhibitory GABA interneurons, drive the CBF response to whisker stimulation and, further, that metabolically active astrocytes are also required.

Neurovascular coupling, or the tight coupling between neuronal activity and regional cerebral blood flow (CBF), seems largely driven by the local processing of incoming afferent signals within the activated area. To test if cortical c-aminobutyric acid (GABA) interneurons-the local integrators of cortical activity-are involved in this coupling, we stimulated the basalocortical pathway in vivo, monitored cortical CBF, and identified the activated interneurons (c-Fos-immunopositive) and the neuromediators involved in this response. Basal forebrain (BF) stimulation induced ipsilateral increases in CBF and selective activation of layers II to VI somatostatin-and/or neuropeptide Ycontaining, as well as layer I GABA interneurons. Nitric oxide synthase interneurons displayed weak bilateral activation, whereas vasoactive intestinal polypeptide-or acetylcholine (ACh)-containing GABA interneurons were not activated. Selective cholinergic deafferentation indicated that ACh released from stimulated BF afferents triggered the CBF response, but the latter was mediated, in part, by the local release of GABA from cholinoceptive cortical interneurons, and through GABA-A receptor-mediated transmission. These data show that activation of specific subsets of GABA interneurons and their GABA-A-mediated effects on neuronal, vascular, and/or astroglial targets are necessary for the full expression of the hemodynamic response to BF stimulation. Further, these findings highlight the importance of understanding the cellular networks and circuitry that underlie hemodynamic signals, as only specific subsets of neurons may be activated by a given stimulus, depending on the afferent inputs they receive and integrate.