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Biomedical subjects

M M Knight

Publications and source records attributed to M M Knight.

At least 37 records · Page 2Linked to original sources
PubMed1998

The influence of elaborated pericellular matrix on the deformation of isolated articular chondrocytes cultured in agarose.

This study investigates the mechanical influence of pericellular matrix on the deformation of isolated articular chondrocytes compressed within 3% agarose specimens. After 1 day in culture, the cells were associated with minimal amounts of sulphated glycosaminoglycan (GAG) and hydroxyproline and exhibited substantial deformation from a spherical to an oblate ellipsoid morphology when subjected to 20% gross compressive strain. However, over the 6 day culture period, there was a reduction in cell deformation associated with an increase in matrix content. Treatment with testicular hyaluronidase at days 3 and 6 reduced sulphated GAG content to levels observed in untreated specimens at day 1. At day 3, the resulting cell deformation during 20% compression was equivalent to that in specimens compressed at day 1. However, at day 6 cell deformation was only partially restored, suggesting the presence of additional structural matrix components, other than sulphated GAG, which were not present at day 3. Dual scanning confocal microscopy indicated that the elaborated matrix formed a pericellular shell which did not deform during compression and was therefore stiffer than the 3% agarose substrate. Therefore, the elaboration of a mechanically functional pericellular matrix within 6 days, effectively limits the potential involvement of cell deformation in mechanotransduction within cell seeded systems such as those employed for cartilage repair.

Animals↗
PubMed1998

Response of chondrocyte subpopulations cultured within unloaded and loaded agarose.

Although it is well known that the metabolism of chondrocytes can be altered by the application of mechanical strain, it is unclear whether chondrocytes from the superficial and deep zones of cartilage respond in a similar manner. In this study, chondrocytes from the uppermost 15-20% (superficial cells) and the remaining tissue (deep cells) from bovine articular cartilage were isolated separately and cultured in agarose constructs. Cell deformation on application of a 15% static compressive strain was identical for both subpopulations after 24 and 72 hours in culture. The constructs were incubated under static and dynamic (0.3, 1, and 3 Hz) strains of 15% amplitude. Glycosaminoglycan synthesis by deep cells was unaffected by static strain or 3 Hz dynamic strain, whereas 0.3 Hz produced a significant reduction and 1 Hz induced a highly significant 50% stimulation of glycosaminoglycan synthesis (p < 0.001). Superficial cells exhibited a general inhibition of glycosaminoglycan synthesis. By contrast, proliferation of superficial cells was stimulated by dynamic strain whereas deep cells were not influenced. It has been suggested previously that mechanotransduction-induced controls of glycosaminoglycan synthesis and proliferation in chondrocytes embedded in agarose are uncoupled. Data presented in this study demonstrate that the two processes do, in fact, occur in different subpopulations of chondrocytes within the full-depth cell isolate.

Animals↗
PubMed1991

Parasites of domestic and wild animals in South Africa. XXVIII. Helminth and arthropod parasites of Angora goats and kids in Valley Bushveld.

Two adult Angora goats were slaughtered each month for 24 consecutive months on a farm in Valley Bushveld in the eastern Cape Province. On the same farm 2 Angora goat kids were slaughtered each month for 2 consecutive years from the time they were 1 week old until they reached 12 months of age. All these goats were processed for the recovery of helminth and arthropod parasites. Fourteen nematode species, 2 nematode genera and 1 cestode species were recovered. Worm burdens were generally low in the adult goats. Nematode burdens increased erratically in the kids reaching the greatest numbers when they were 1 year old. The tapeworm, Moniezia expansa, was present in kids at 3 or 4 months of age and had usually disappeared by the time they reached 7 months of age.

Animals↗
PubMed1991

Parasites of South African wildlife. IX. Helminths of kudu, Tragelaphus strepsiceros, in the eastern Cape Province.

The helminths of 25 kudu, Tragelaphus strepsiceros, from 3 localities in the eastern Cape Province were collected, counted and identified. The majority of kudu harboured no worms, and the burdens of those infected were small. A race of Cooperia rotundispiculum, a Dictyocaulus sp., a Haemonchus sp., Nematodirus helvetianus and Ostertagia ostertagi were recovered. Two parasites, Nematodirus helvetianus and Ostertagia ostertagi can be added to the list of helminth parasites of kudu in South Africa.

Animals↗
PubMed1988

The treatment of ticks on tortoises using amitraz.

Amitraz at a concentration of 2 ml litre-1 of water successfully induced detachment of Amblyomma marmoreum and Amblyomma hebraeum ticks from the mountain tortoise, Geochelone pardalis. Detached ticks died without reattaching. At the strength used, amitraz had no apparent adverse effects on the tortoises.

Animals↗
PubMed1986

A comparison of the tick burdens of wild animals in a nature reserve and on an adjacent farm where tick control is practised.

Acaricidal treatment of cattle, sheep and goats on a farm in Valley Bushveld in the Grahamstown district resulted in a reduction in the numbers of certain tick species on kudu (Tragelaphus strepsiceros), scrub hares (Lepus saxatilis) and crowned guinea fowl (Numida meleagris) on the same farm. The tick species most severely affected was Amblyomma hebraeum, while Haemaphysalis silacea, Hyalomma marginatum rufipes and Rhipicephalus appendiculatus were affected to a lesser extent. Rhipicephalus glabroscutatum and Rhipicephalus oculatus appeared to be unaffected.

Agriculture↗
PubMed1986

Parasites of domestic and wild animals in South Africa. XX. Arthropod parasites of the Cape mountain zebra (Equus zebra zebra).

The arthropod parasite burdens of 14 Cape mountain zebra (Equus zebra zebra), shot for survey purposes in the Mountain Zebra National Park in the eastern Cape Province, were determined. Three species of Gasterophilus larvae and 9 ixodid tick species were recovered. Larvae of Gasterophilus pecorum were the most numerous of the fly larvae recovered and Margaropus winthemi was the most abundant tick. Two horses examined in the park were infested with 3 species of Gasterophilus larvae and 7 species of ixodid ticks.

Animals↗
PubMed1986

Parasites of domestic and wild animals in South Africa. XXI. Arthropod parasites of vaal ribbok, bontebok and scrub hares in the western Cape Province.

Vaal ribbok (Pelea capreolus), bontebok (Damaliscus dorcas dorcas) and scrub hares (Lepus saxatilis) were slaughtered in the Bontebok National Park at regular intervals and examined for arthropod parasites. Twelve species of ixodid ticks were recovered; the antelope each harboured 9 species and the hares 11. Rhipicephalus nitens was the most prevalent and most abundant tick. The vaal ribbok also harboured large numbers of Ixodes pilosus and the bontebok fairly large numbers of Rhipicephalus glabroscutatum. The vaal ribbok were infested with 2 lice species and the larvae of 3 oestrid fly species. The bontebok harboured 2 lice species and the larvae of 2 oestrid flies, and the scrub hares were infested with a louse species and a flea species. The host preference and seasonal abundance of some of the parasites were determined.

Animals↗
PubMed1981

Life cycle in the laboratory and seasonal activity of the tick Rhipicephalus glabroscutatum (Acarina: Ixodidae).

The life cycle of Rhipicephalus glabroscutatum Du Toit was studied under laboratory conditions at 26 C +/- 1C. The preoviposition period was 6.0 +/- 0.12 days. The mean number of eggs was 2,044 +/- 186 (maximum 3,053, minimum 748), and the greatest production was recorded on day 3 (234 eggs/female). The incubation period was 37.4 +/- 0.32 days (maximum 41, minimum 35). The feeding time of larvae and nymphs of this two-host tick was 20.2 +/- 0.33 days (16-28). Nymphs producing males weighed less (4.09 +/- 0.07 mg) than those producing females (6.62 +/- 0.08 mg). The combined larval-nymphal feeding time of the former was shorter (19.3 +/- 0.90 days) than that of the latter (20.4 +/- 0.90 days). The molting period of nymphs to adults of both sexes was similar. Engorged females weighed (mean +/- SE) 204.0 +/- 10.75 mg and the feeding time was 7.9 +/- 0.34 days. Spermatogenesis was completed on day 5 after the commencement of feeding, and pairing between males and females and mating occurred subsequently. The adult ticks were active during early summer and were much more prevalent on kudu than on angora goats and cattle. Immature stages were not found during this study.

Animals↗
PubMed1978

The life cycle of the tick Hyalomma marginatum rufipes Koch (Acarina: Ixodidae) under laboratory conditions.

The life cycle of Hyalomma marginatum rufipes Koch was studied under laboratory conditions at 26 +/- 1 C. The preoviposition period was 7.1 +/- 0.23 days. The mean (+/- SE) number of eggs was 6,867 +/- 2,609 (max. 13,180, min. 3,184). The greatest egg production was recorded on day 3 (avg 1,170 egg/female). The incubation period was 29.3 +/- 2.96 days. The feeding time of larvae and nymphs of this 2-host tick was 22.8 +/- 0.13 days. Nymphs producing males weighed less (23.1 +/- 0.748 mg) than those producing females (26.8 +/- 1.19 mg); the combined larval-nymphal feeding time of the former was shorter (21.9 +/- 0.1 days) than that of the latter (22.9 +/- 1.12 days). The premolting period of nymphs to adults of both sexes was similar.

Animals↗
PubMed1977

Estrogen regulation of follicle stimulating hormone in cell cultures of sheep pituitaries.

Cell cultures of ovine pituitaries were maintained for up to 3 weeks. A specific double antibody radioimmunoassay was used to measure FSH in the media and cells. The rate of FSH synthesis increased in the cultures during the first 4-6 days to a level of approximately 50 ng/day/106 cells, generally remained constant for 2 weeks and then decreased. The FSH produced in vitro migrated similarly to highly purified ovine FSH on P-60 polyacrylamide gel filtration columns and had a biological potency essentially identical to that of the highly purified FSH standard. Addition of 17beta-estradiol (E2) at 10-9M on days 2 or 6 incubation decreased FSH synthesis greater than 95% within 30 h. Time-course analysis revealed that the effect of E2 can be observed as early as 6 h after treatment. FSH synthesis resumed after removal of E2 and reached control levels within 6 days. The lowest effective dose of E2 was 10-11M; E2 at 5 X 10-11M maintained FSH production at approximately 50% of the control levels. Diethylstilbestrol was as active estriol was 1/10th as active and 17alpha-estradiol was 1/100th as active as E2. Progesterone (P), 5alpha-pregnane-3,20-dione (5alphaDHP), 20alpha-hydroxy-pregn-4-en-3-one(20alpha-OHP), testosterone, 5alpha-dihydrotestosterone and corticosterone had no effect on FSH levels. These findings suggest that estrogen is capable of playing a major role in FSH synthesis and release by action directly at the pituitary level.

Animals↗
PubMed1977

Estrogen action in vitro: regulation of thyroid stimulating and other pituitary hormones in cell cultures.

Primary cell cultures of ovine pituitaries can maintain production of thyroid stimulating hormone (TSH) for as long as 24 days. These cultures responded in a normal fashion to thyroxine by decreasing TSH secretion. Addition of thyrotropin releasing hormone increased TSH secretion. Physiologic levels of estradiol-17 beta (10(-11)-10(-9)M) produced a five-fold increase in secretion of TSH and a two-fold increase in intracellular TSH concentration in cell cultures. Common estrogens, but not common progestins, androgens and glucocorticoids affected TSH production. Markedly different effects of estrogen in the pituitary on follicle stimulating, luteinizing and thyroid stimulating hormones and prolactin are discussed in terms of current models of estrogen action.

Animals↗
PubMed1977

Life cycle of the tick Rhipicephalus evertsi evertsi neumann (acarina: ixodidae) under laboratory conditions.

The preoviposition period of the tick Rhipicephalus evertsi Neumann maintained under laboratory conditions at 26 C was 6.1 +/- 0.38 days. The average number of eggs produced during the oviposition period was 10,400 +/- 397 (max. 13.307, min. 7,558). The greatest daily egg production was recorded on the 3rd day (1.107 eggs/female). The incubation period of eggs at 26 C was 24.8 +/- 1.37 and the feeding time of the larvae and nymphs (a two-host tick) was 17.2 +/- 0.14 days at 26 C. This tick represents the two-host type of cycle and the percentage of larvae, pharate nymphs, and nymphs on the host at various intervals after attachment was recorded. The changes in the weight of the immature stages during the feeding period was examined daily. Nymphs which produce males were lighter in weight (10.3 +/- 0.28 mg), than those which produce females (15.6 +/- 0.33) and males emerge (13.7 +/- 0.10 days of premolting period) before females (14.1 +/- 0.11 days).

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