The aim of this study was to set up a statistical measure for determine the total cumulative noise exposure of Finnish conscripts (n = 1,054) as a result of leisure-time noise activities. All of the conscripts underwent hearing screening. The conscripts' time in noisy activities and their rating of the loudness and estimated noise levels of the activities were used as the predictors in the risk analysis. Self-reported hearing symptoms (i.e., tinnitus, pain in the ear) and hearing loss due to noise exposure were also inquired about. Twenty-seven percent of the conscripts had weekly noise exposure to > 85 dBA. Approximately 20% of the conscripts had >20 dB hearing loss in either ear in the frequency range of 0.5 to 8 kHz. The incidence of hearing symptoms seemed to correlate with an increased noise dose.
This study presents an evaluation of the total cumulative noise exposure of Finnish conscripts (N = 416) during military service. All of the conscripts underwent a hearing screening and filled out a noise exposure questionnaire at the beginning and end of their military service. Eighty-nine percent of the conscripts were exposed weekly to military noise of over 85 dBA during the service. Eighteen percent of the conscripts had already reached at the end of their military service a cumulative noise dose corresponding to noise exposure of 85 dB for 40 years. During military service, permanent hearing loss of > 20 dB in the frequency range of 0.5 to 8 kHz increased from 19 to 27% among the conscripts.
The effects of central 5-hydroxytryptamine (5-HT) infusions on the cold-stimulated thyrotropin (TSH) levels were studied in male rats. Stainless-steel cannulas were implanted stereotaxically into the anterior or the posterior third ventricle or just lateral to the hypothalamic paraventricular nuclei bilaterally 7 days before experiments. Infusion of 5-HT(4.5 and 9 µg/rat) into the posterior third ventricle attenuated significantly the cold-stimulated TSH levels. Inversely, infusion of 5-HT (9 µg/rat) into the anterior third ventricle augmented significantly the TSH cold response. Bilateral 5-HT infusions into the vicinity of the hypothalamic paraventricular nuclei did not affect the TSH cold response. Serum prolactin levels increased significantly after 5-HTadministration into the anterior and the posterior third ventricle, but no consistent effect on growth hormone (GH) levels could be detected. Infusion of 5-HT into the anterior and the posterior third ventricle decreased body temperature irrespective of the observed hormonal response to 5-HT. The results are in favor of a dual and possibly site-dependent role for 5-HTin the regulation of the cold-stimulated TSH secretion in the rat. The opposite effects of 5-HT on the TSH cold response may result from the predominant inhibition of either the thyrotropin-releasing hormone or the somatostatin-secreting cell groups.
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