Exposure of adult male golden hamsters to short days (< 12.5 h light/day) leads to suppression of gonadal function which is secondary to reductions in gonadotropin and prolactin (PRL) secretion. Short-day (SD) exposure also leads to a reduction in hypothalamic norepinephrine (NE) and dopamine (DA) metabolism and an increase in hypothalamic LHRH content which appears to be related to a decrease in LHRH release. To determine whether SD-induced changes in NE and DA metabolism are dependent or independent of changes in circulating testosterone (T) levels and thus possible mediators of photoperiod effects on gonadotropin secretion, the effects of castration and steroid replacement on hypothalamic amine metabolism were studied in male hamsters maintained under long or short photoperiod conditions. The presence of Silastic® T-implants resulted in a greater suppression of LH and FSH in SD than in long-day (LD) hamster, but increased median eminence (ME) LHRH content in both groups. Exposure of castrate hamsters to short days led to a reduction of NE turnover in the ME and medial preoptic-suprachiasmatic area (MPOA) and a decrease in serum FSH levels. LH levels tended to be lower, but not significantly so. The decrease in ME NE turnover was potentiated by T replacement, but in the MPOA-SCN, T-implants reversed the effects of short days. NE turnover in the MBH was reduced by T in both LD and SD animals, but the effect was much greater in the SD animals. SD exposure also caused a decrease in ME DA metabolism that was reversed by T replacement. From these data, we suggest that many of the effects of photoperiod on hypothalamic LHRH and neurotransmitter metabolism are independent of its effects on serum T levels, which supports the hypothesis that SD-induced changes in gonadotropin secretion are secondary to changes in neurotransmitter metabolism.

This content is only available via PDF.
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.