Pre-existing level of tone is an important determinant of cerebral artery autoregulatory responsiveness.

The objective of this study was to test the hypothesis that cerebral artery autoregulatory responses to increasing transmural pressure depend on the pre-existing level of vascular tone. Pial arteries were obtained from adult normotensive Wistar-Kyoto (WKY) rats, and were cannulated and studied under pressurized conditions using a video-assisted perfusion system. Myogenic tone developed spontaneously during equilibration, reducing the lumen diameter by 31% (n = 6). Each artery was then subjected to a series of step increases in transmural pressure of between 50 and 100 mmHg, a manoeuvre that produces autoregulatory constriction. Afterwards, serotonin was added to the perfusate to decrease lumen diameter by another 27% and the transmural pressure changes were repeated once more. The autoregulatory effectiveness in response to a change of 50----100 mmHg in transmural pressure was expressed as both the percentage change in diameter and the myogenic 'gain'. During the increased activation induced by serotonin, the autoregulatory responses to a change in transmural pressure were completely abolished; lumen diameter, which had previously decreased by 4.9 +/- 1.5%, increased by 10.5 +/- 4.5% (P less than 0.05). The nature of this change is further reflected in the myogenic gain, which was 0.39 +/- 0.14 in vessels with myogenic tone alone, and -1.14 +/- 0.56 for the same arteries at the higher level of activation (P less than 0.05). In additional experiments (n = 6), a comparable degree of constriction was induced with 0.5% ethanol, which increases calcium influx through receptor-independent mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary reaction to intravenously injected polymer beads.

The purpose of this study was to characterize the foreign body reaction in the mouse lung following embolization of intravenously injected divinylbenzene copolymer beads. In contrast to usual surgical implantation, this model dissociates the local foreign body reaction to the beads (in the lung) from inflammation and repair of tissue injury associated with implantation (peripheral site of injection). Quantitative determinations of pulmonary granuloma area using light microscopic morphometric measurements on tissue sections confirmed that the intensity of pulmonary inflammatory reaction increased rapidly to a maximum at 48 h following injection, with a volume exceeding 10 times that of the bead; at this time, the cellular exudate was 90% polymorphonuclear leukocytes. Thereafter, the inflammatory reaction decreased in intensity, and individual lesions became progressively richer in mononuclear cells (60% at 4 days and greater thereafter). Determination of intra- and interobserver variability indicated that maximal data precision was attained by measurement of the cross-sectional areas of as few as 10 granulomas in each of five animals for each set of specific experimental conditions. Collagen was undetectable in granulomas at 7 weeks and 6 months, suggesting that the usual fibrous capsule forming in response to surgically implanted biomaterials is largely caused by repair of surgical trauma. The volume of inflammatory exudate at 48 h was reduced 68-86% by the nonsteroidal antiinflammatory agents indomethacin, aspirin, and ibuprofen and the antiinflammatory steroid methylprednisolone. Thus, the pulmonary bead granuloma model is a quantitative, reliable, and economical approach to investigating some aspects of biomaterial/time interactions in the absence of super-imposed surgical trauma.

A field study of the fertility of transported equine semen.

A field trial of artificial insemination in horses with transproted, chilled semen was conducted using a specially designed container which permitted a controlled, slow initial rate of cooling (-0.3 degrees C/min) and maintenance of a final temperature of 4 degrees -6 degrees C for more than 36 hrs. Forty-six mares in 23 states were inseminated with semen from three German Warmblood stallions standing at stud in Hamilton, Massachusetts. A third-cycle conception rate of 91% was obtained.

Description and surgical removal of the cranial cervical ganglia in 3- to 5-day-old chicks.

The cranial cervical sympathetic ganglion (CCG) provides the primary innervation of the pineal gland in several gallinaceous species. The CCG is located at the base of the skull near the exoccipital bone, dorsal to the level of the vagus and glossopharyngeal nerves. It occupies a much larger volume and appears pinkish-gray, instead of white, when compared to the petrosal ganglion. To surgically remove the CCG, chicks were anesthetized with halothane vapor. Following a small skin incision, blunt dissection was used to expose the CCG lying adjacent to the internal carotid. The ganglion was grasped with small forceps and pinched free of its fine neural connections to adjacent nerves. The success of the surgery was confirmed visually and by complete adrenergic dennervation of the pineal gland. The entire surgical procedure required approximately 20 min per bird. Mortality was less than 20% overall.