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S. W. McDonald and J. Halliday

Summary. This study investigated the development of a cell-mediated immune response after vasectomy in Swiss Albino rats, by comparing the development of the thymus-dependent lymphoid tissue of the regional testicular lymph node and the spleen in vasectomized and in sham-operated control animals. Frozen sections were used and thymus-dependent regions were stained by immunocytochemistry. After vasectomy, the areas occupied by the paracortex in the lymph node sections showed a significant increase in size; the thymus-dependent regions of the spleen, in contrast, showed no change. The regional lymph node, rather than the spleen, seems to be important in cell-mediated and humoral immune responses to vasectomy.

Keywords: lymph node; spleen; cell-mediated immunity, T-areas; rat

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J. J. Cowley, R. Pewtress and S. McDonald

Summary. Newly born TO strain female mice were exposed daily to the urine from male albino mice of the same and CFLP strains, from feral mice carrying Robertsonian translocation chromosomes and to water as a control condition. At 21 days of age, when exposure was discontinued, there were differences in body weight between treatments which were not present when adult. Exposure to urine from mice with Robertsonian translocations did not accelerate puberty and the interval between vaginal opening and first oestrus was longer (4·2 days) than in mice exposed to the urine from the albino strains (1·8 days). Mice exposed to the urine from the Robertsonian stock were in dioestrus more often than those exposed to the urine from laboratory strains. The Robertsonian mice also differed in their behaviour in an open arena in that they passed fewer faecal pellets than those exposed to the urine from the albino mice. The water control mice defecated the least frequently. The mice exposed to the Robertsonian urine were less active than the laboratory strains but the differences did not reach an acceptable level (P < 0·06) of significance.

Keywords: pheromones; mice; translocation chromosomes; sexual development

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Z. Z. Xu, M. F. McDonald, S. N. McCutcheon and H. T. Blair

Summary. In castrated rams (Romney and Poll Dorset, n = 8 for each breed), inhibition by testosterone treatment (administered via Silastic capsules) of luteinizing hormone (LH) pulse frequency, basal and mean LH concentrations, mean folliclestimulating hormone (FSH) concentration, and the peak and total LH responses to exogenous gonadotrophin-releasing hormone (GnRH) were significantly (P < 0·01) greater during the nonbreeding than during the breeding season. Poll Dorset rams were less sensitive to testosterone treatment than Romney rams. In rams not receiving testosterone treatment, LH pulse frequency was significantly (P < 0·05) lower during the nonbreeding season than during the breeding season in the Romneys (15·8 ± 0·9 versus 12·0 ± 0·4 pulses in 8 h), but not in the Poll Dorsets (13·6 ± 1·2 versus 12·8 ± 0·8 pulses in 8 h). It is concluded that, in rams, season influences gonadotrophin secretion through a steroid-independent effect (directly on hypothalamic GnRH secretion) and a steroid-dependent effect (indirectly on the sensitivity of the hypothalamo–pituitary axis to the negative feedback of testosterone). The magnitude of these effects appears to be related to the seasonality of the breed.

Keywords: season; testosterone feedback; FSH; LH; breed effect; Romney; Poll Dorset; sheep