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Subject: search.filters.subject.Neuroendocrinology

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    Studies in neuro-endocrinology : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physiology at Massey University
    (Massey University, 1983) Kettle, Anthony
    Gonadectomy is the commonest surgical procedure carried out in the cat, mainly for fertility control. However, the effect of gonadectomy on body weight in the cat has received little study although this subject is well researched in other species, such as the rat. Part I of the present study involved gonadectomy at 20 weeks. The cats were housed in outdoor colony cages and given food ad libidum, adjusted to leave daily residues. Body weight was measured weekly and transformed to log10. For statistical analysis, differences in body weight of each cat were tested by one-way analysis of variance and serial covariance using the previous week's body weight as the covariate. Differences between groups were investigated with 't' tests and growth rates were studied by regression. Up to 32 weeks of age there was no statistically significant difference between the growth rates of entire versus the castrates in either sex. However, when extended to 55 weeks of age prepubertal gonadectomy in the female cat caused significantly increased growth. This was not observed for the male cat. Little information is available on the anatomy of the brain of the Australasian possum (Trichosurus vulpecula). Part II of the present study aims at presenting a simple description of the possum hypothalamus viewed in three planes of section and concentrating on some of the fibre tracts which are clearly visible. The main findings were that the mammillothalamic tract appears in a similar position to that as seen in other mammals such as the rat, cat, and sheep, while the fornix appears much steeper in its descent into the anterior hypothalumus. In addition, there is described a fibre tract emanating from the optic chiasma and passing to the caudal part of the paraventricular nucleus. This tract has not been described in other mammals, such as the rat, cat, and sheep.
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    Effects of cranial cervical ganglionectomy and castration on endocrine and morphological characteristics of male lambs : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physiology at Massey University
    (Massey University, 1978) Fisher, Mark Warren
    In a study of the effects of the pineal gland on reproductive development and hormone secretion, male lambs were incorporated into an overall 2 x 2 factorial design in which the experimental factors were: (1) cranial cervical ganglionectomized or non-ganglionectomized, and (2) castrated or entire. The first experiment described was a longitudinal study of endocrine and morphological parameters recorded from these animals between 7 and 37 weeks of age. Plasma LH levels in entire lambs usually were very low throughout the experiment, although non-ganglionectomized entires did display a small elevation in levels between 8 and 13 weeks of age, which was not evident in ganglionectomized entires. At all ages plasma LH levels were elevated significantly in castrated animals. Neither ganglionectomy nor its interaction with castration had any significant effect on LH levels. In entire lambs plasma testosterone concentrations increased from 7 weeks to highest concentrations between 31 and 37 weeks of age. Overall, ganglionectomy reduced testosterone secretion, but this probably was due to the lower body and testicular weights recorded from that group. The normal photoperiod-induced seasonal pattern of prolactin secretion in non-ganglionectomized lambs, with high levels during the summer months and low during winter, was markedly disrupted by ganglionectomy. Castration had no effect on prolactin levels and the interaction of castration and ganglionectomy also was non-significant. Bodyweight was reduced significantly by ganglionectomy and this effect was accentuated in the ganglionectomized castrates. At autopsy, testicular weights and epididymal weights as well as epididymal sperm reserves were reduced, but not significantly, by ganglionectomy; these results probably reflected the bodyweight of those animals. Neither ganglionectomy nor castration had any significant effect on pineal weights, however the interaction of these two factors was significant due to the very large pineal of one of the non-ganglionectomized castrates. A second experiment involved measurement of LH, prolactin and testosterone profiles in plasma obtained during hourly blood samplings which were conducted for 24 hours when lambs were both approximately 100 and 300 days of age. At both ages pulsatile secretion of LH and testosterone was confirmed, but no circadian rhythms of LH, testosterone or prolactin secretion were detected. Castration elevated LH levels significantly at both ages. Ganglionectomy and its interaction with castration had no effect on LH secretion at 100 days, but at 300 days these factors were significant largely due to elevated levels being recorded from ganglionectomized castrates. Ganglionectomy did not affect testosterone levels in entire animals at either age while castrates had no detectable testosterone. Ganglionectomy reduced prolactin concentrations at 100 days of age (summer) and prevented the normal winter decline at 300 days of age. Castration and the interaction of castration with ganglionectomy had no significant influence on plasma prolactin levels at either age. Pituitary LH and gonadal testosterone responses to 10 μg synthetic GnRH were tested at 100 days and 300 days of age in a third experiment. In all animals, GnRH elevated LH levels and in entires this in turn resulted in increased testosterone levels. Castration significantly increased basal and peak LH levels together with total LH output. At both ages the LH and testosterone responses to GnRH were not influenced significantly by ganglionectomy, nor did the interaction of castration and ganglionectomy have any significant effect on LH secretory responses. These studies confirm the concept that the pineal gland can influence the secretion of prolactin, and probably also LH and testosterone, and thus may be involved in the regulation of pubertal development in ram lambs.
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    Studies of neuroendocrine mechanisms influencing seasonal variations in semen production and plasma hormone levels in rams : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 1976) Barrell, Graham Keith
    Many workers have shown that sheep are seasonal breeders with peak reproductive activity occurring during the autumn months. The initial experiment in this thesis was designed to define the seasonality of reproduction in rams of the N.Z. Romney breed as determined by repeated measurements of semen characteristics and of plasma hormone levels. These parameters were studied for 16 months in six N.Z. Romney rams on pasture, with five Merino and four Polled Dorset rams included for comparison. Semen from all three breeds showed relatively regular seasonal changes in ejaculate volumes and seminal fructose levels with peak values being recorded during March. Likewise, monthly hormone levels varied in a regular manner with plasma LH, testosterone and prolactin concentration being elevated during the summer months. Many of the other semen parameters measured showed little tendency for seasonal variations, however a change in semen collection technique, from predominantly artificial vagina to entirely electro-ejaculation, may have masked some seasonal changes. All three breeds showed similar seasonal changes in the parameters studied although semen from the Polled Dorsets did not exhibit regular seasonal variations in fructose levels. Further experiments were carried out to define the neuroendocrine mechanisms which regulate the seasonal reproductive changes in N.Z. Romney rams. Three olfactory bulbectomized rams, three cranial cervical ganglionectomized rams and four rams which had undergone both of these surgical modifications, were grazed together with the rams mentioned above. These surgical treatments disrupted the regular seasonal changes in plasma levels of LH and prolactin, but not, of testosterone. Spermatozoal concentrations in ejaculates from operated rams were higher than those from unoperated controls, whereas mean fructose concentrations were lower; however the pattern of seasonal changes in seminal fructose levels was similar in all groups of rams. Cranial cervical ganglionectomy reduced hydroxyindole-O-methyl transferase activity and cell volumes in the pineal glands, so it was concluded that disrupted seasonal patterns of changes in plasma LH and prolactin levels, plus the altered semen production in the surgically treated rams, resulted from modified pineal gland and/or olfactory system activity. A preliminary investigation into the role of changes in daily photoperiod as the stimulus for seasonality of reproduction, was carried out by placing rams in light-controlled rooms at the time of the March equinox. Over the following nine months rams exposed to a phase-reversed annual lighting cycle showed earlier elevations of seminal fructose and plasma testosterone levels than rams on either the normal annual or a constant equinoctial lighting regime. In all three groups plasma prolactin levels were directly related to the length of daily photoperiod. The findings of the above experiments were extended by a final study in which both pinealectomized and sham-operated rams were exposed to normal or reversed annual lighting cycles. Effects of lighting on plasma testosterone and prolactin levels, and on seminal fructose levels, were diminished by pinealectomy. Autopsy data related to gonadal and accessory sex gland function showed significant operations x lighting regimes interactions, which supported the conclusion that in rams pineal gland function mediates endocrine and gonadal responses to changes in daily photoperiod. Three short-term investigations of hormonal secretion profiles conducted during the latter experiment, showed that major fluctuations in the release of LH, testosterone, prolactin and cortisol occurred irregularly during the day. A nocturnal elevation of plasma prolactin levels was abolished by pinealectomy. These acute studies tended to confirm the findings of the latter experiment, but in particular they highlighted the pulsatile nature of hormonal secretion.