Fluctuations and stimulus-induced changes in blood flow observed in individual capillaries in layers 2 through 4 of rat neocortex

Cortical blood flow at the level of individual capillaries and the coupling of neuronal activity to flow in capillaries are fundamental aspects of homeostasis in the normal and the diseased brain. To probe the dynamics of blood flow at this level, we used two-photon laser scanning microscopy to image the motion of red blood cells (RBCs) in individual capillaries that lie as far as 600 μm below the pia mater of primary somatosensory cortex in rat; this depth encompassed the cortical layers with the highest density of neurons and capillaries. We observed that the flow was quite variable and exhibited temporal fluctuations around 0.1 Hz, as well as prolonged stalls and occasional reversals of direction. On average, the speed and flux (cells per unit time) of RBCs covaried linearly at low values of flux, with a linear density of ≈70 cells per mm, followed by a tendency for the speed to plateau at high values of flux. Thus, both the average velocity and density of RBCs are greater at high values of flux than at low values. Time-locked changes in flow, localized to the appropriate anatomical region of somatosensory cortex, were observed in response to stimulation of either multiple vibrissae or the hindlimb. Although we were able to detect stimulus-induced changes in the flux and speed of RBCs in some single trials, the amplitude of the stimulus-evoked changes in flow were largely masked by basal fluctuations. On average, the flux and the speed of RBCs increased transiently on stimulation, although the linear density of RBCs decreased slightly. These findings are consistent with a stimulus-induced decrease in capillary resistance to flow.

Augustan art; an exhibition commemorating the bimillennium of the birth of Augustus, New York, January 4, 1939, through February 19.

"This handbook of the exhibition has been written by Gisela M.A. Richter ... except the chapter on Minor arts and painting, of which Christine Alexander ... is the writer."--Pref.

Symphony no. 9, choral, in D minor, op. 125. Piano four hands.

Mode of access: Internet.

Symphony no. 4 /

Arr. for piano.

A Look at the planets.

"PAM 107"--P. [4] of cover.

Iusti Lipsi De vesta et vestalibus syntagma.

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Iusti Lipsi De vesta et vestalibus syntagma.

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Liberti Fromondi ... Vesta, siue Antaristarchi vindex, adversus Jac Lansbergium ... : in quo decretum S. Congregationis S. R. E. Cardinalium anno MDCXVI et alterum anno MDCXXXIII adversus Copernicanos terrae motores editum, iterum defenditur

Mode of access: Internet.

Dialectica seu logica minor : tribus disputationibus circumscripta /

Mode of access: Internet.