The Use of Push-Pull Perfusion and in Vivo Microdialysis to Assess Changing Patterns of Hypothalamic Releasing Hormone Output in Aging Animals

Abstract

A thorough understanding of the nature of age-related changes at the hypothalamic level would be greatly enhanced by the ability to directly measure neuropeptide release. In vivo measurement of neurosecretion is a demanding undertaking in young animals and increases in difficulty in aging animals due to additional considerations that must be acknowledged. Push-pull perfusion and in vivo microdialysis are two methods currently being used to directly measure neuropeptide output. The advantages and disadvantages of each are discussed. Moreover, special concerns regarding their use in aging animals are addressed, including the potential for: (1) differences in the response of the aging brain to insult; (2)age-related differences in levels of degradative enzymes; and (3) confounding effects of age-related differences in the stress response. Push-pull perfusion was used to compare the pattern of luteinizing hormone-releasing hormone output in middle-aged and young female rats during a steroid-induced LH surge. The data revealed age-related differences in the overall pattern and the mean levels of LHRH output. When used with the proper precautions, these in vivo protocols enable characterization of the patterns of release of neuroactive substances in a single animal over time. They eliminate the need to sacrifice large numbers of animals to obtain measurements for a single time point, a feature particularly important for aging studies due to the heterogeneity of the population and the expense of the animals. Moreover, use of these methods is essential if alterations in the patterns of neuropeptide release play an important role in the changes that accompany aging.