Developmental changes in functional cerebral perfusion of rodent somatosensory cortex

Previous reports have indicated that functional cerebral perfusion may vary throughout development. The purpose of this study was to characterize and quantify developmental changes in the neurovascular response to peripheral stimulation. We used optical imaging of intrinsic signals (OIS) to record changes in functional perfusion because this modality offers the high spatial (μm) and temporal resolution(ms) necessary to identify the changes which occur with age. OIS is a functional neuroimaging technique which measures changes in cortical reflectance that are related to neuronal and vascular activity. Previous studies have shown that these intrinsic signals are closely related to increases in cerebral blood volume. Experiments were performed on groups of animals varying in age from 14 to 42 days after birth (four to five animals per group). Animals were anesthetized initially using halothane and maintained using enflurane. Animals were stabilized by stereotaxic frame and skulls were thinned over the somatosensory cortex. Optical signals were recorded in response to 10 Hz whisker deflection. Stimulus durations varied from 2s to 10s. We calculated spatial extent and response magnitudes for each group of animals. Previous reports have demonstrated and characterized neurovascular responses in adult rodents: signals appear within 750 ms, peak between 3 and 4 s, and return to baseline within 7s. The same general response pattern was observed in all age groups (14-42 days). While the spatial extent of the optical signals generally increased with age, the response magnitudes increased until about 21 days and subsequently decreased, reaching the adult magnitude at approximately 42 days of age. These results present evidence for a changing relationship between neurovascular responses and neuronal activity, suggesting that factors other than neuronal activity may influence the neurovascular response. Specifically, developmental events, such as synaptogenesis and synaptic pruning, myelination, and postnatal brain growth may influence the characteristics of observed responses.