Peptides in the Central Nervous System: Focus on Thyrotropin Releasing Hormone and Neurotensin

This chapter discusses the extensive data generated by study on the various peptides discovered. It discusses the findings in animals and on pharmaco-behavioral effects at the expense of peripheral and endocrine effects. A consideration of the actions and interactions of thyrotropin-releasing hormone (TRH) and neurotensin (NT) is done to provide with a beginning sense of an aspect of current central nervous sytem (CNS) peptide research. In peptides, various hypothalamic hypophysiotropic hormones, anterior pituitary peptides, posterior pituitary peptides, and other neuropeptides, their origin, composition, and actions have been discussed in the chapter. On TRH, their isolation, localization, synthesis, receptor binding, and central nervous system effects are mentioned in the chapter. Similarly the NT isolation, localization, interactions with barbiturates and ethanol, effects on thermoregulation, interactions with dopaminergic drugs, and antinociceptive effects are delved upon. The chapter describes that after they had demonstrated the analeptic properties of TRH, they examined a series of substances for activity in the pentobarbital-sedated mouse. Several substances, like TRH, shortened barbiturate-induced sleep but only one reliably extended it-NT. Dualism of central action between TRH and NT has been extended to a variety of parameters and this dualism, along with the quality of effects exerted by the two peptides, allows the broad hypothesis that TRH subserves the ergotropic functions of the organism, NT its trophotropic functions. The view is that dualism between the central effects of TRH and NT, whatever its best interpretation is, appears unusual among peptides. At present, NT must be regarded as unique among peptides in its ability to both stimulate and inhibit the activity of a neurochemical pathway, the mesolimbic dopamine system.