Neuroendocrinology

Peripubertal Immune Challenges Attenuate Reproductive Development in Male Siberian Hamsters (Phodopus sungorus)

Abstract
Differential allocation of energy to reproduction versus host defense is assumed to drive the seasonal antiphase relation between peak reproductive function and immunocompetence; however, evidence supporting this assumption is only correlational. These experiments tested whether photoperiod affects immune responses to antigens in peripubertal Siberian hamsters, whether such activation of the immune system exacts energetic and reproductive costs, and whether such costs vary seasonally. Male Siberian hamsters were raised from birth in long (LD) or short days (SD), which respectively initiate or inhibit the onset of puberty. To elicit a specific immune response, hamsters were injected with a novel antigen (keyhole limpet hemocyanin; KLH) as juveniles. Reproductive development was delayed and body temperature was elevated in LD hamsters relative to saline-injected control animals. In contrast, KLH treatments affected neither thermoregulation nor reproductive development in photoinhibited SD-hamsters. In Experiment 2 juvenile male hamsters were challenged with bacterial lipopolysaccharide (LPS), in order to elicit an innate immune response. Febrile and anorexic responses to LPS were greater in reproductively-stimulated LD-hamsters relative to reproductively-inhibited SD-hamsters. LPS treatments attenuated somatic and testicular development in LD-hamsters, but did not significantly affect circulating testosterone concentrations. In contrast, LPS treatments were without effect on somatic and reproductive development in SD-hamsters. These experiments indicate that photoperiod affects antigen-specific antibody production, febrile responses to LPS, and sickness behaviors in juvenile Siberian hamsters, and that peripubertal activation of the immune system exacts energetic and metabolic costs which can diminish the magnitude of somatic and reproductive maturation in LD. The data also underscore the importance of seasonally-dependent life history factors in assessing physiological trade-offs.

Key words: Immunology • Neuroendocrinology • Developmental biology • Puberty • Testosterone

This article has been cited by other articles:

				S. R. Baillie and B. J. Prendergast Photoperiodic Regulation of Behavioral Responses to Bacterial and Viral Mimetics: A Test of the Winter Immunoenhancement Hypothesis J Biol Rhythms, February 1, 2008; 23(1): 81 - 90. [Abstract] [PDF]

				D. A. Freeman Multiple neuroendocrine pathways mediate seasonal immunity Am J Physiol Regulatory Integrative Comp Physiol, February 1, 2008; 294(2): R382 - R383. [Full Text] [PDF]

				L. B. Martin 2nd, K. J. Navara, Z. M. Weil, and R. J. Nelson Immunological memory is compromised by food restriction in deer mice Peromyscus maniculatus Am J Physiol Regulatory Integrative Comp Physiol, January 1, 2007; 292(1): R316 - R320. [Abstract] [Full Text] [PDF]

				L. B. Martin II, Z. M. Weil, and R. J. Nelson Refining approaches and diversifying directions in ecoimmunology Integr. Comp. Biol., December 1, 2006; 46(6): 1030 - 1039. [Abstract] [Full Text] [PDF]

				Z. M. Weil, L. M. Pyter, L. B. Martin II, and R. J. Nelson Perinatal photoperiod organizes adult immune responses in Siberian hamsters (Phodopus sungorus) Am J Physiol Regulatory Integrative Comp Physiol, June 1, 2006; 290(6): R1714 - R1719. [Abstract] [Full Text] [PDF]