Synaptic and vascular associations of neurons containing cyclooxygenase-2 and nitric oxide synthase in rat somatosensory cortex

Cyclooxygenase-2 (COX-2) is a rate-limiting enzyme for prostanoid synthesis that is present in cortical pyramidal neurons and highly implicated in control of cerebral blood flow during neural activity.We examined the electron microscopic localization of COX-2 and neur-onal nitric oxide synthase (nNOS), a functionally related enzyme, in the somatosensory cortex of rat brain to determine the relevant functional sites. COX-2 immunoreactivity was detected in signifi-cantly more somatodendritic than axonal profiles, while nNOS was more often seen in axon terminals. The dendritic COX-2was localized to endomembranes near synaptic inputs from axon terminals, some of which contained nNOS. Conversely, COX-2 terminals formed asym-metric, excitatory-type synapses with dendrites containing nNOS. The dendritic and axonal profiles containing COX-2 as well as those containing nNOS were minimally separated from penetrating arterio-les and capillaries by filamentous glial processes. The perivascular COX-2 labeled terminals were among those that also formed axo-dendritic synapses, suggesting that the release of prostanoids and/or excitatory transmitters from a single terminal may simultaneously affect neuronal activity and cerebral blood flow. Thus, COX-2 has a compartmental distribution in somatosensory cortical neurons consistent with the local neuronal synthesis of prostanoids that are involved in neurovascular coupling andwhose actions are modulated by nitric oxide