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  • 1
    Electronic Resource
    Electronic Resource
    The Influence of Photoperiod on the Hypothalamic Content of Beta-Endorphin and the Luteinizing Hormone Responses to Naloxone and to Steroid Withdrawal in the Male Syrian Hamster (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neuroendocrinology 3 (1991), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The aim of this study was to investigate the influence of inhibitory photoperiods upon opioidergic function, as determined by changes in the hypothalamic content of β-endorphin and the luteinizing hormone response to opioidergic receptor blockade, in the male Syrian hamster over the course of gonadal involution and spontaneous gonadal recrudescence. Animals exposed to an 8 h light: 16 h dark cycle (8L: 16D) for 14 weeks underwent gonadal regression. Regression was also observed in animals held for 7 weeks on one of a range of short daylengths of between 11.5 h and 13.5 h, the degree of atrophy being greatest in those animals on the shortest daylength. The tissue concentration of β-endorphin within the mediobasal hypothalamus was significantly higher in animals exposed to 8L: 16D for 14 weeks than in gonadally active controls held on long days (16L: 8D). Exposure to photoperiods of less than 13.5 h for 7 weeks also caused a significant increase in the β-endorphin content of the mediobasal hypothalamus and there was a positive correlation between the concentration of β-endorphin, the degree of gonadal atrophy and the shortness of the photoperiod. Endorphin levels within the preoptic area were not affected by photoperiodic treatments.Exposure of intact animals to 8L: 16D for 12 weeks caused gonadal atrophy and an associated loss of the luteinizing hormone responses to both naloxone and castration. Castrated animals receiving testosterone replacement (cast + T) also exhibited photoinhibition, in the form of reduced serum levels of luteinizing hormone, and this was similarly accompanied by a loss of sensitivity to naloxone and to withdrawal of steroid. Prolonged exposure to 8L:16D led to spontaneous reactivation of the gonadotrophic axis as a consequence of the development of scotorefractoriness. In both gondally intact animals and in cast + T groups, this was associated with a restoration, in parallel, of the luteinizing hormone responses to naloxone and to castration/ steroid withdrawal. The time-course of the restoration of the response to steroid withdrawal in castrates was not significantly different to that observed in intact animals. The luteinizing hormone response to naloxone took significantly longer to redevelop in cast + T groups than it did in gonadally intact animals.The data demonstrate that central opioid systems are sensitive to photoperiod and are consistent with the hypothesis that opioids are involved in the neuroendocrine regulation of reproductive responses to daylength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2826.1991.tb00304.x
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  • 2
    Electronic Resource
    Electronic Resource
    The effects of nerve growth factor and anti-nerve growth factor antibody on the neuroendocrine reproductive system in the European starling Sturnus vulgaris (1997)
    Springer
    Journal of comparative physiology 181 (1997), S. 133-141 
    Details
    ISSN: 1432-1351
    Keywords: Key words Nerve growth factor ; Photorefractoriness ; Seasonality ; Starlings ; Thyroidectomy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Thyroidectomy of starlings causes them to remain in breeding condition indefinitely; deactivation of gonadotrophin-releasing hormone neurons that is characteristic of photorefractoriness does not occur. We hypothesise that a neurotrophin, whose presence or ability to function is dependent upon thyroid hormones, is somehow involved in this termination of gonadotrophin-releasing hormone release. Nerve growth factor is one such candidate. Mouse 7S-nerve growth factor dissolved in artificial cerebro-spinal fluid was therefore infused into the lateral ventricle of thyroidectomised male starlings held on long days four times daily for 21 days and 31 days, in separate experiments, to see if photorefractoriness would occur. The result was significant gonadal regression in the treatment groups during the infusion period, with no change in testicular volume in the control groups. Testicular recrudescence occurred after the end of the treatment period. To see if this was a non-specific effect, or progression towards photorefractoriness per se, we used castrated, photorefractory starlings held on long days. Anti-nerve growth factor antibody was infused into the lateral ventricle at increasing concentrations and frequency. There was a significant rise in circulating luteinising hormone levels in the treatment groups as compared to controls, increasing with antibody dosage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003590050100
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  • 3
    Electronic Resource
    Electronic Resource
    Prolonged electrical stimulation of the nipples evokes intermittent milk ejection in the anaesthetised lactating rat (1987)
    Springer
    Experimental brain research 66 (1987), S. 29-34 
    Details
    ISSN: 1432-1106
    Keywords: Milk-ejection ; Nipple ; Stimulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Intermittent and continuous electrical stimulation of the nipples elicited milk-ejection responses in the lactating rat. The responses occurred intermittently, with similar amplitudes and periodicity as those seen in suckled rats. The responses were always associated with synchronization of the electroencephalogram (EEG), but some rats with synchronized EEG activity did not milk eject during stimulation. Since continuous stimulation also resulted in intermittent milk ejection it seems unlikely that the periodicity of the reflex in suckled rats depends upon changes in the intensity of sensory stimulation. The techniques of nipple stimulation may be a useful method with which to study neural pathways and other phenomena such as gating involved in oxytocin release and milk ejection. The success of the technique depends on a variety of factors such as parameters of the stimulation and state of anaesthesia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00236198
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