Curves relating renal sympathetic nerve activity and mean arterial pressure were derived in conscious rabbits during ramp changes in mean arterial pressure, elicited by perivascular balloon inflation. The renal sympathetic nerve activity-mean arterial pressure relationship consisted of a high-gain sigmoidal region about resting, where renal sympathetic nerve activity rose or fell in response to moderate falls and rises of mean arterial pressure. With larger pressure rises, renal sympathetic nerve activity first fell to a lower plateau and then reversed at even higher mean arterial pressure. When mean arterial pressure was lowered below resting, renal sympathetic nerve activity rose to an upper plateau and then reversed abruptly toward resting at low mean arterial pressure. Both arterial and cardiac baroreceptors exerted substantial inhibitory influences on renal sympathetic nerve activity at all pressure levels. These effects appeared additive over the central high gain region of the curve, but beyond this region there were non-additive interactions. The latter were affected considerably by alfathesin anesthesia. In other experiments, we studied the effects of sustained alterations in resting mean arterial pressure induced by infusing nitroprusside and phenylephrine, which produced rapid resetting of the renal baroreflex. The latter could be accounted for, in part, by resetting of the threshold of the arterial baroreceptors and in part by contributions from other afferents, probably the cardiac receptors. During resetting associated with nitroprusside-induced falls in resting blood pressure, high-gain reflex adjustments in renal sympathetic nerve activity to moderate changes in mean arterial pressure were preserved, but during resetting associated with phenylephrine-induced rises in resting mean mean arterial pressure, the resting renal sympathetic nerve activity lay on the lower curve plateau, resulting in reduction in the apparent gain of the reflex renal sympathetic nerve activity response to moderate changes in mean arterial pressure.

Conscious instrumented rabbits were bled at a constant rate of congruent to 3% of the blood volume (BV) per minute. We determined the BV-response relationships for mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), mesenteric and hindlimb blood flows, and for the corresponding conductances. We studied the responses 1) under normal conditions; 2) after pretreatment with captopril, arginine vasopressin (AVP) antagonist, or both; 3) during total autonomic blockade (TAB); and 4) during neurohumoral blockade (NHB, i.e., TAB + captopril + AVP antagonist). We determined the direct local response component from the responses obtained during NHB. The local chronotropic effects congruent to 0, so that the reflex rise in HR was entirely autonomically mediated. The local vascular response consisted of vasodilatation and provided the base line for assessing the estimated constrictor component from the net response from control, with the former ranging from 2 to 16 times the conventional estimates based on the net responses. In normal rabbits, the phase of good maintenance of MAP was entirely governed by autonomic mechanisms, which minimized the fall in CO and offset the local vasodilator component. During the hypotensive phase immediately after hemorrhage, when congruent to 30-35% BV had been removed, the constrictor effects of AVP and angiotensin II (ANG II) became important, whereas the role of autonomic mechanisms diminished. During TAB, the constrictor effects of AVP and ANG II were prominent even with small BV losses.

1981. The effect of extra food and cover on declining populations of Microtus townsendii. Can. J . Zool. 59: 1593-1599. Microtus townsendii populations were supplied with extra food and extra cover during a spring decline in numbers in 1979.Compared with the control population, late-winter addition of food resulted in lower rates of decline of males and females. On the area with extra cover, the rate of decline was significantly lower in males, and females actually increased in number. Breeding was earlier in the population with extra cover, and four times as many females became pregnant during the spring. This resulted in twice as many young voles entering the population in early summer. Survival was higher in both experimental populations during the spring. Females with extra food and males with extra cover had the smallest home ranges for their sex group.The experiments were repeated in summer 1979, except that cover was reduced on one grid. Demography during the summer experiments was similar in all populations. This period coincided with a botfly (Cuterebra) larva infection which reduced survival of voles in all populations.The addition of cover reduced bird predation. If this was the only effect of added cover, the demography of the covered population suggests that predation may be important in the spring decline of M. townsendii. Further, we suggest that the severity of the spring decline, particularly in female voles, may determine when the population "cycles." TAITT, M. J., J. H. W. GIPPS, C. J. KREBS et Z. DUNDJERSKI. 198 1. The effect of extra food and cover on declining populations of Microtus townsendii. Can. J . Zool. 59: 1593-1599.Des populations de Microtus townsendii ont requ des soins particuliers (plus de nourriture, plus de couverture) durant un dkclin de leur abondance au printemps de 1979. L'addition de noumture h la fin de I'hiver rkduit les taux de diminution des miles et des femelles. Dans la rCgion 8 couverture additionnelle, le taux de diminution des males a baissC sensiblement et le nombre de femelles a meme augmentk. Chez la population 8 couverture additionnelle, la reproduction s'est faite plus t6t et quatre fois plus de femelles sont devenues enceintes au printemps, ce qui doubla le nombre de petits campagnols qui sont entrCs dans la population au debut de I'CtC. La survie s'est avkrke plus ClevCe chez les deux populations exp6rimentales au printemps. De toutes les femelles, ce sont celles qui ont requ de la noumture en plus, et de tous les males, ceux qui ont reGu une couverture additionnelle, qui avaient les plus petites aires vitales.Les exp6riences ont Ctk dp6tCes durant 1' 1% 1979, mais la couverture a kt6 rkduite dans l'une des aires expCrimentales. La dCmographie s'est avtrCe la meme chez toutes les populations en Ctk. Cette pCriode coincidait avec une infestation d'cestres (Cuterebra) qui a rkduit la survie des campagnols chez toutes les populations. L'addition de couverture rCduit la predation due aux oiseaux. S'il s'agit 18 du seul effet de la couverture additionnelle, la ...

With 2 figures in the text)The area and inter-trap distance of small mammal live trapping grids can seriously influence observed movement patterns and estimates of animal densities. This paper examines inter-trap movement (ITM) according to inter-trap distance, time of the year, weather and numbers captured for the wood mouse, Apodemus sylvaticus, and the bank vole, Clethrionornys glareolus, in an oak wood in southern England. The analysis is based on live trapping data collected in three studies over an eight-year period. Trap spacing affected inter-trap movement, including the statistic, 'Mean Distance Moved' between successive captures (MDM), of different species and sexes of rodents in different and predictable ways. No association was found in MDM between males and females of the same species, MDM and time of the year or MDM and weather. However, there was a weak negative association between MDM and numbers captured, particularly in mice. Using an independent method of assessing effective grid area, the usefulness of the MDM in correcting grid areas for the estimation of animal densities is discussed.