Effects of Voluntary Locomotion and Calcitonin Gene-Related Peptide on the Dynamics of Single Dural Vessels in Awake Mice

Abstract

The dura mater is a vascularized membrane surrounding the brain and is heavily innervated by sensory nerves. Our knowledge of the dural vasculature has been limited to pathological conditions, such as headaches, but little is known about the dural blood flow regulation during behavior. To better understand the dynamics of dural vessels during behavior, we used two-photon laser scanning microscopy (2PLSM) to measure the diameter changes of single dural and pial vessels in the awake mouse during voluntary locomotion. Surprisingly, we found that voluntary locomotion drove the constriction of dural vessels, and the dynamics of these constrictions could be captured with a linear convolution model. Dural vessel constrictions did not mirror the large increases in intracranial pressure (ICP) during locomotion, indicating that dural vessel constriction was not caused passively by compression. To study how behaviorally driven dynamics of dural vessels might be altered in pathological states, we injected the vasodilator calcitonin gene-related peptide (CGRP), which induces headache in humans. CGRP dilated dural, but not pial, vessels and significantly reduced spontaneous locomotion but did not block locomotion-induced constrictions in dural vessels. Sumatriptan, a drug commonly used to treat headaches, blocked the vascular and behavioral the effects of CGRP. These findings suggest that, in the awake animal, the diameters of dural vessels are regulated dynamically during behavior and during drug-induced pathological states.

Anti-CGRP antibodies block CGRP-induced diarrhea in mice

“…Our finding that administration of CGRP leads to diarrhea in mice is fully consistent with prior reports (Bhargava et al, 2013; Gao and Drew, 2016; Keates et al, 1998; Yoshikawa et al, 2011), as well as the ability of CGRP to affect intestinal motility (Fargeas et al, 1985; Holzer et al, 1989; Rasmussen and Olesen, 1992) and water secretion (Rolston et al, 1989). In this regard, it is important to reiterate that diarrhea following icv CGRP was not due to central actions, but rather was a consequence of peripheral leakage during the injection procedure.…”

Time to wake up: Studying neurovascular coupling and brain-wide circuit function in the un-anesthetized animal

“…3) showed a 20% dilation in the arteries in awake animals, will cause a 100% increase in flow, while in anesthetized animals an 8% dilation was observed, which will cause a 36% increase in flow. The dilation of arteries is accompanied by a slow distention of veins, which can build to levels of 10% or more for prolonged stimuli (Drew et al, 2011; Huo et al, 2015a; Gao and Drew, 2016). Voluntary locomotion drives nearly identical dynamics and amplitudes of arterial and venous dilations as those evoked by passive stimulation (Huo et al, 2015a), suggesting that this pattern of arterial and venous dilation is an invariant feature of cerebral hemodynamics found across different behavioral and cardiovascular states when the animal is awake.…”

“…Because the extracellular space exchanges ions with active neurons, changes in the volume of this extracellular space should impact neural excitability (Somjen, 2002) and cerebrospinal fluid flow (Iliff et al, 2013). Besides brain temperature and extracellular space, intracranial pressure (ICP) is another important physiological variable that can be altered by various anesthetics (Artru, 1984; Gao and Drew, 2016). Elevating ICP alters heart beat and respiratory rhythm (Matsuura et al, 1984), decreases CBF in the cortex (Sadoshima et al, 1981), and changes neural activity (Seigo Nagao et al, 2009), all of which could impact neurovascular coupling.…”

“…8). We typically habituate mice to being on the treadmill or head-fixing in a tube by acclimating them over two to five days (Drew et al, 2010a; Drew et al, 2011; Huo et al, 2015a; Gao and Drew, 2016) in several 15-min to ½-h sessions. Mice are briefly (< 1 min) anesthetized with isoflurane before being head fixed to minimize handling stress.…”

“…With a stable preparation, the noise in the intrinsic signal due to animal motion is negligible, as it is several orders of magnitude below the amplitude of the sensory-evoked response (Huo et al, 2014; 2015a; 2015b). Two-photon microscopy is sensitive to animal movement, but movement during voluntary locomotion are typically small enough to be corrected using motion correction software (Dombeck et al, 2007; Gao and Drew, 2016). Head-fixation and optical imaging can be longitudinally done on very young animals, starting as early at postnatal day 3 (P3) (Letourneur et al, 2014).…”