Vascular and hemodynamic effects of behavioral stress in borderline hypertensive and Wistar-Kyoto rats.

In borderline hypertensive rats (BHR), behavioral stress produces hypertension, which has been attributed to increases in sympathetic nervous system activity and peripheral changes in vascular structure. However, the mechanisms mediating development of stress-induced hypertension have not been well defined. Experiments were designed to determine hemodynamic effects and changes in small mesenteric artery (approximately 300 microns) vascular reactivity in response to 10 days of air-jet stress (2 h/day) in BHR and in Wistar-Kyoto (WKY) rats. The acute stress-induced increase in mean arterial pressure (AP) was impaired in WKY rats compared with BHR on day 1, and habituation developed to the increase in AP in BHR, but not WKY rats. Conversely, WKY rats adapted to the stress-induced tachycardia to a larger extent than BHR. The mechanisms mediating endothelium-dependent relaxation to acetylcholine (ACh) were altered in small mesenteric arteries isolated from WKY rats and BHR after 10 days of air-jet stress. Inhibition of nitric oxide synthase activity had a significantly larger inhibitory effect on ACh-induced relaxation in vessels from stressed compared with control BHR. Also, cyclooxygenase products contributed to ACh-induced relaxation of small mesenteric arteries from stressed WKY rats, but not control WKY rats. Endothelium-independent relaxation to nitroprusside was impaired in vessels from stressed WKY rats, but not stressed BHR. Finally, contraction to phenylephrine was impaired in vessels from stressed BHR, but not WKY rats. In conclusion, changes in vascular reactivity induced by air-jet stress appear to correlate with, and may contribute to, the differential hemodynamic adaptations to stress observed in WKY rats and BHR.

Diurnal temperature patterns of early lactating cows with milking parlor cooling.

Ten cows in early stages of lactation (less than 100 days postpartum) were used to test the effect of sprinkler/fan cooling on vaginal temperature patterns. Cows were assigned to two groups matched according to milk production. The trial was divided into three periods: period 1, when one group was treated and the other group was not, period 2, when neither group was treated, and period 3, when treatment was switched from period 1 between groups. Treatment consisted of forced air misting in a premilking holding pen, fan cooling during milking, and forced air-sprinkling in a postmilking holding area. Weather conditions were measured by dry bulb, wet bulb, and black globe temperatures. Black globe temperatures in pre- and postmilking holding areas were used to estimate treatment magnitude. All measures were obtained through radiotelemetry at 15-min intervals for 31 days. Animals were milked twice a day. Animals spent an average of 140 min in treatment at each milking. In both morning and afternoon milking, treatment caused a transient increase of body temperature. However, this was followed in the afternoon by low vaginal temperatures for 1 to 2 h beyond treatment with lower temperatures throughout the day.

Non-simultaneous auditory masking in the goldfish, Carassius auratus.

Auditory thresholds were determined for 500 HZ pure tone pulses of 15, 25 and 50 ms duration presented leading, following or simultaneously with noise pulses of 50 or 250 ms duration. Masking by the noise decreased: (i) with an increase in tone pulse duration; (ii) with a shortening of the noise pulse duration; and (iii) as the interval between tone and noise pulses was increased from 0 to 350 ms. The effect of the noise was independent of whether the noise led or followed the pure tone. It is suggested that the most significant factor affecting masking was the duration of the interval between tone and noise, and that the site for the interactions between signals is central to the inner ear.

Laser light-scattering investigations of the teleost swimbladder response to acoustic stimuli.

When a laser pencil is directed through the teleost swimbladder fringe patterns can be seen in the far-field that are (a) highly sensitive to the orientation and position of the swimbladder with respect to the incident pencil and (b) a representation of contributions from each membrane through which the light passes. The fringe pattern fluctuates in intensity, and to some extent in position, in response to driving forces that distort the swimbladder. The spectrum of these very small distortions can be measured by standard light scattering techniques. This method was used to study the response of in situ swimbladders to imposed acoustic fields and evidence for a sharp roll-off of the response at frequencies above 1,000 Hz was found. Models for these effects are discussed.