Hampton W. Shirer

A Radiotelemetric Study of Spatial Relationships in Some Common Snakes

Radio transmitters embedded in silicone rubber in elongate, oval, smooth-surfaced packages 50 x 21 x 14 mm or a little larger, were forcefed to 67 snakes of eight species (a 68th snake had an abdominally implanted transmitter), which were then trailed on a day to day basis. Forty per cent of all snakes located had made no movement since the previous day. Average distances, in meters covered per day, were: 142, Pituophis melanoleucus; 51.3, Elaphe obsoleta; 44.7, Crotalus horridus; 28.5, Coluber constrictor; 10, Thamnophis sirtalis; 8, Agkistrodon contortrix; 7, Lampropeltis calligaster; 3.7, Natrix sipedon. Movements were irregular and erratic. For periods of 15-30 days the trailed snakes usually moved progressively farther from their starting points. Three displaced snakes exhibited no homing ability. One female N. sipedon made short, irregular movements typical of resident individuals. A displaced male A. contortrix made an unusually long movement the first night, then settled down to a pattern of short, irregular movements like those of residents. A displaced female C. horridus moved away from the release point but did not travel toward its place of origin approximately 10 km distant.

Comparison from Radiotracking of Movements and Denning Habits of the Raccoon, Striped Skunk, and Opossum in Northeastern Kansas

A comparative study of spatial relationships of the opossum ( Didelphis marsupialis ), raccoon ( Procyon lotor ), and striped skunk ( Mephitis mephitis ) was made on the University of Kansas Natural History Reservation, an area of deciduous woodland, brush and grassland. Thirty-nine animals, including 27 opossums, eight raccoons and four skunks, were each equipped with small radio transmitters and were trailed to their dens over periods ranging from 2 to 239 days. Each animal was found to use a series of dens and each well-situated den was used by many different individuals. Sometimes two or several different animals used a den simultaneously; on one occasion an opossum and a skunk were known to have used the same den simultaneously over a period of days. Whereas raccoons and skunks are somewhat social, opossums are generally solitary and instances of known co-occupancy could be attributed either to chance or to sexual attraction. Average occupancy of a den was 1.5 days for the raccoons and 2.2 days for both skunks and opossums. The average shift between successive dens was 1430 feet for the raccoon, 1359 feet for the skunk and 990 feet for the opossum. The most used dens were underground and were situated along a hilltop limestone outcrop. Raccoons often spent the day in trees, sometimes in cavities but more often in exposed situations such as on top of the platform of an old squirrel nest. Sign indicated that the underground dens used by all three species were chiefly the work of the striped skunk.

A Radiotelemetric Study of Spatial Relationships in the Opossum

Habits of 27 opossums were studied by attaching small radio transmitters and trailing them on the University of Kansas Natural History Reservation in 1966 and parts of 1965 and 1967. Activity is normally nocturnal and during the day each animal stays in a den. Most of the 88 dens located were in underground cavities of hilltop limestone outcrops; others were among tree roots in cutbanks of gullies; relatively few were in miscellaneous situations such as hollow trees, old buildings, or burrows away from rock outcrops. The average sojourn at a den is 2.2 days and each opossum uses many different dens but returns frequently to each of several favorite dens. An adult opossum forages from its den over an area with mean radius of 620 m but tends to stay much closer to its den. Extent of movement and frequency of shift were not closely correlated with season or temperature. A newly independent, young opossum tends to stay within a relatively small area at first, and to extend its range by gradual stages. Of nine young opossums that were trailed, three were preyed upon by the horned owl.

Cardiopulmonary responses to HCl infusion are mediated by thromboxane A2 but not by serotonin.

Intravenous infusion of HCl has been shown to elicit the release of thromboxane A2 (TxA2) which alters blood pressure and breathing independent of reductions in circulating blood pH. The present experiments were designed to determine if the release of serotonin (5-HT) in the anesthetized cat contributed to cardiorespiratory responses during acid infusion and, furthermore to define the source of TxA2, viz. blood or other tissues. To infuse HCl into the bloodstream without reducing circulating blood pH (= neutral acid-base infusion), an extracorporeal arteriovenous shunt (20 ml/min) between the femoral artery and femoral vein was installed. Into this loop, acid (0.25 M HCl), and approximately 10 cm downstream, base (0.25 M NaOH) could be infused whereby blood pH could be locally reduced in the blood within the loop. This procedure was performed in three groups of cats: one group which received no drugs, a second group that was pretreated with indomethacin (2.5 mg/kg) and a third group that received the 5-HT2 receptor antagonist, ketanserin (0.75 mg/kg), prior to the infusion. During neutral acid-base infusion in the nontreated animals, right ventricular blood pressure (PRV) increased and systemic arterial blood pressure (Pa) decreased. Respiratory frequency was increased, but total ventilation was not elevated because of a concomitant fall in tidal volume (VT). The response was transient and could not be evoked with repetitive infusions of HCl and NaOH. These responses were significantly attenuated in the indomethacin-treated animals, but persisted in the cats pretreated with ketanserin. In addition, TxB2, the stable degradation metabolite of TxA2, was elevated during the acid/base infusion, but there were no measurable changes in plasma 5-HT concentration. The source of TxA2 was likely to be the blood since TxB2 was increased in plasma when acid and base were added to blood in vitro. We conclude from these experiments that transient cardiorespiratory responses to HCl infusion are mediated by the release of TxA2 from the blood and do not involve serotonin.

Thromboxane A2 mimetic, U46,619, and slowly adapting stretch receptor activity in the rabbit

The effect of infusing the thromboxane A2 mimetic U46,619 on afferent activity from slowly adapting airway stretch receptors (SARs) in the anesthetized rabbit was examined in these experiments. SAR vagal afferent fibers (n = 29) were identified by their slow adaptation to a sustained (10-15 s duration) lung inflation in the closed-chest, mechanically ventilated animal (n = 16). Intravenous infusion of U46,619 increased the discharge frequency of the SAR, measured at the end of inspiration, in a dose-dependent manner: by 6.6% and 8.0% at doses of 0.1 and 0.5 microgram of U46,619/kg, respectively. This increase in SAR activity was correlated with increases in end-inspiratory tracheal airway pressure (6.4% at 0.1 micrograms/kg and 9.1% at 0.5 micrograms/kg). Higher doses of U46,619 could not be administered due to decreases in systemic arterial blood pressure. The increase in SAR activity and tracheal airway pressure was qualitatively comparable to the response to histamine (25 micrograms/kg), a known bronchoconstrictor. We conclude that intravenous infusion of U46,619 in the anesthetized rabbit at doses that elicit significant hemodynamic effects causes modest bronchoconstriction and comparable increases (less than 10%) in SAR afferent nerve activity. From these data, it appears that U46,619 has no direct effect on SARs, but rather increases SAR activity due to bronchoconstriction.

Cerebrovascular response to acute decreases in arterial PO2

The purpose of these studies was to examine the time course of the cerebrovascular response to acute hypoxia in unanesthetized ponies. An electromagnetic flow transducer chronically placed on the internal carotid artery of the pony allowed continuous recording of internal carotid artery blood flow (ICBF) which has been shown to be representative of cerebral blood flow (CBF). The ponies were subjected to three levels of acute isocapnic hypoxia (PaO2 = 62, 44, and 39 mm Hg for hypoxia level I, II, and III, respectively), and the temporal and steady-state cerebrovascular response was examined. ICBF increased significantly at all three hypoxia levels (8, 25, and 40% at hypoxia I, II, and III, respectively). This increase was rapid in the two most severe levels of hypoxia, beginning within 45 s, and was complete within 90 s. The increase lagged behind the reduction in PaO2 by 24–28 s. During the very mild level of hypoxia (I), no such rapid increase in flow was observed; rather, the increase occurred only after 5 min of hypoxia. Microsphere (15 μm diameter) measurements from six ponies during the most severe level of hypoxia (III) demonstrated that CBF increased 38%. Noncerebral tissues known to be vascularly connected to the circle of Willis, and thus capable of receiving blood flow via the internal carotid artery, either did not change or increased so slightly during hypoxia that their effect on ICBF was minimal. These data imply that mediators of the cerebrovascular response to hypoxia must be capable of sensing hypoxia and affecting cerebrovascular smooth muscle within seconds. The slower time course in mild hypoxia suggests other mechanisms may be involved when PaO2 is greater than 50 mm Hg.