Growth curve of the body weight, body length and tail length in the cotton rat (Sigmodon hispidus)

The body weight (BW), body length (BL) and tail length (TL) of 202 cotton rats, 102 males and 100 females. were measured. Significant sex differences in the BW were observed 3 weeks after birth. The BLs in one-day-old males and females were 8.33 = 0.36 cm and 7.82 +/- 0.69 cm respectively, while the TLs were 2.98 +/- 0.12 cm and 2.88 + 0.28 cm. Growth of the BL and TL was rapid until about 8th week of age, when a steady length was reached. The equations in males were BL (em) = 8.07 + 0.23 x BW (g) - 0.00068 x BW (g)2, TL (em) = 2.79 + 0.11 x BW (g) -0.00037 x BW (g)2 and TL (cm) = — 2.21 + 0.67 x BL (em) — 0.0068 >< BL (cm)2. Correlations among the BW, BL and TL in male and female cotton rats were all highly significant (r 20.98, P < 0.001)

Reference values for blood chemistry in the cotton rat (Sigmadon hispidus)

Fifteen blood chemistry values for cotton rat (Sig-modon hispidur) were measured in 17 females ranged from 122.0 and 170.0 g and 11 males ranged from 91.0 to 190.0 g in weight. Significant sex differences were found for creatinine and triclyccridc (P < 0.05). Six items (UA, TB, GPT, CK, HDLCHO, TG) in temales and 4 items (TB, GOT, GPT, CK) in males varied with coefficient of variation being over 40 %. The average values for TP, ALB, UA, TB in the cotton rat tended to be lower than those in the rat. On the contrary, the average values 0f GOT, GPT,  ALP, CK, LDH, GLU tended to be higher than those in the rat

Development of the Aortic Baroreflex in Microgravity

Baroreceptors sense pressure in blood vessels and send this information to the brain. The primary baroreceptors are located in the main blood vessel leaving the heart (the aorta) and in the arteries in the neck (the carotid arteries). The brain uses information from the baroreceptors to determine whether blood pressure should be raised or lowered. These reflex responses are called baroreflexes. Changing position within a gravity field (i.e., moving from lying to sitting or standing) powerfully stimulates the baroreflexes. In weightlessness, the amount of stimuli that the baroreflexes receive is dramatically reduced. If this reduction occurs when the pathways that control the baroreflexes are being formed, it is possible that either the structure or function of the baroreceptors may be permanently changed. To study the effect of microgravity on structural and functional development of the aortic baroreflex system, we studied young rats (eight days old at launch) that flew on the Space Shuttle Columbia for 16 days. Six rats were studied on landing day; another six were studied after re-adapting to Earth's gravity for 30 days. On both landing day and 30 days after landing, we tested the sensitivity of the rats' baroreflex response. While the rats were anaesthetized, we recorded their arterial pressure, heart rate, and aortic nerve activity. After the tissues were preserved with perfusion fixation, we also examined the baroreflex structures. On landing day, we found that, compared to the controls, the flight rats had: fewer unmyelinated nerve fibers in their aortic nerves lower baroreflex sensitivity significantly lower contraction ability and wall tension of the aorta a reduced number of smooth muscle cells in the aorta. In the 30-day recovery group, the sensitivity of the baroreflex showed no difference between the flight rats and the control groups, although the unmyelinated fibers of the aortic nerve remained reduced in the flight rats. The results show that spaceflight does affect the development of the aortic baroreflex. The sensitivity of the reflex may be suppressed; however, the function of the blood pressure control system can re-adapt to Earth's gravity if the rats return before maturation. The structural differences in the input pathway of the reflex (Le., the reduction in nerve fibers) may remain permanently

Spaceflight Affects Postnatal Development of the Aortic Wall in Rats

We investigated effect of microgravity environment during spaceflight on postnatal development of the rheological properties of the aorta in rats. The neonate rats were randomly divided at 7 days of age into the spaceflight, asynchronous ground control, and vivarium control groups (8 pups for one dam). The spaceflight group rats at 9 days of age were exposed to microgravity environment for 16 days. A longitudinal wall strip of the proximal descending thoracic aorta was subjected to stress-strain and stress-relaxation tests. Wall tensile force was significantly smaller in the spaceflight group than in the two control groups, whereas there were no significant differences in wall stress or incremental elastic modulus at each strain among the three groups. Wall thickness and number of smooth muscle fibers were significantly smaller in the spaceflight group than in the two control groups, but there were no significant differences in amounts of either the elastin or collagen fibers among the three groups. The decreased thickness was mainly caused by the decreased number of smooth muscle cells. Plastic deformation was observed only in the spaceflight group in the stress-strain test. A microgravity environment during spaceflight could affect postnatal development of the morphological and rheological properties of the aorta