Morphology

Hamster cheek pouches are bilateral invaginations of the oral mucosa and can be everted from the anesthetized hamster with their blood flow intact. They are therefore well suited for intravital microscopy. The cheek pouch tissue is transparent and the anatomical elements of the microcirculation, arterioles, capillaries and venules can be easily identified (Figure 1). Cheek pouches, as prepared for intravital microscopy, have been used for studies of inflammation, tumor growth, vascular smooth muscle function, blood flow regulation, and leukocyte behavior—rolling and adhesion— at the microcirculatory level. The hamster cheek pouch preparation (HCP) was described for the first time as a "natural window" for microscopic observation and motion picture recording of blood flow, vessel wall caliber, and intravascular behavior of blood cells by Fulton, Jackson, and Lutz in 1946. The early observation that the cheek pouch of an anesthetized hamster can be brought out and applied on a stage for intravital microscopy with minimal interference with their blood flow resulted in its application for physiological studies of arterioles, capillaries, and venules. The cheek pouch can also be studied in situ by introducing a light rod through the mouth into the pouch and applying an acrylic chamber on top of the light rod after a skin incision. It appears that these two methods of preparing the HCP for intravital microscopy give equivalent results. The way to prepare the HCP for physiological studies of the microcirculation was developed and refined by Duling in 1973 using the everted cheek pouch. Ever since dextrans labeled with fluorescein isothiocyanate—FITC dextrans— became available as intravital markers of vascular permeability in 1970, the HCP has been used in numerous studies of inflammation as induced by a large number of different inflammatory mediators or procedures, such as bradykinin, histamine, adenosine diphosphate (ADP), serotonin, prostaglandins, or leukotrienes; by temporary ischemia of the pouch (IR); or by application of live parasites (Trypanosoma cruzi, Leishmania donovani) (Table I).

Detailed descriptions of the morphology of the cheek pouch have been given by Priddy and Brodie in 1948 and by Handler and Shepro in 1968. Briefly, the cheek pouches of the golden hamster are invaginations of the oral mucosa, extending beneath the subcutaneous tissue down to the shoulder region, and they can be characterized histologi-cally as skinlike. The length of the distended cheek pouch is approximately 2.5 to 5.5 cm, and the width is about 1 cm. All parts except the distal portion of the pouch have longitudi-

Figure 1 Fluorescent micrograph of the hamster cheek pouch after IV injection of FITC-dextran. Same area before (A), 5 minutes after (B), and 30 minutes after (C) topical application of bradykinin (4 x 10-7 M). More than 25 leakage sites at postcapillary venules are shown by extravasation of FITC-dextran at postcapillary venules. (see color insert)

Figure 1 Fluorescent micrograph of the hamster cheek pouch after IV injection of FITC-dextran. Same area before (A), 5 minutes after (B), and 30 minutes after (C) topical application of bradykinin (4 x 10-7 M). More than 25 leakage sites at postcapillary venules are shown by extravasation of FITC-dextran at postcapillary venules. (see color insert)

Table I Mediators or Procedures That Have Been Shown to Increase FITC-Dextran Leakage in Postcapillary Venules.

Mediator or procedure

Effective concentration

Histamine, serotonin

Bradykinin, substance P

ADP, adenosine, inosine

Prostaglandins Ej, E2 and E2a

Leukotrienes C4, D4, E4, B4

Complement C3a, C5a

Platelet activating factor (PAF) Fibrin-derived peptides

VEGF (vascular endothelial growth factor)

Polyarginine, polylysine, major basic protein (MaBP) oxLDL, apolipoprotein B derived peptides Ischemia/Reperfusion (I/R) ROS (reactive oxygen species) Oxidant injury (tertiary-butyl-hydroperoxide, TBOOH) Immune aggregates (ovalbumin [OA] immunized hamsters) Phorbol ester (PDBu) Smokeless tobacco extract Endotoxin

Trypsin, cruzipain, gingipain

Live parasites—Trypanosoma cruzi, Leishmania donovani

10-6M

10-7M

10-5M

1 mg/ml

<10-9M <5 10-9 M 0, 1 mg/ml 30 min ischemia 10-4M

107/ml nal muscle fibers. The pouch is provided with a long retractor muscle and a sphincter-like arrangement around its aperture. There are no specific regional lymph nodes, and the nonmuscular part of cheek pouch lacks lymphatic drainage and has been characterized as an immunologically privileged site. Three layers are distinguishable in the pouch membrane. The epithelium is devoid of hair follicles and glands. The pouch is attached to the subcutaneous tissue by loose areolar connective tissue. The cheek pouch vascula-ture is mainly supplied by branches of the external carotid artery, via three saccular arteries. Blood is also supplied via the arteries of the retractor muscle. Terminal arterioles supply capillaries, which drain into postcapillary venules, which in turn empty into collecting venules. Arteriole-to-arteriole and venule-to-venule anastomoses are often seen, but there are no arteriole-to-venule anastomoses. The arterioles and, to a lesser extent, the venules are surrounded by numerous mast cells that appear to promote the oriented migration of leukocytes from the venules into the extravas-cular space.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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