As shown in Figure 1, thymic hormones also modulate the production of hypothalamus pituitary hormones and neuropeptides. Initial experiments revealed that neonatal thymectomy promotes a decrease in the number of secretory granules in acidophic cells of the adenopituitary . In the same vein, athymic nude mice display low levels of various pituitary hormones, such as PRL, GH, LH and FSH . With regard to thymic peptides, thymosin beta-4, when perfused intraventricularly, stimulates LH and LHRH secretion . Similar results were obtained with another thymic peptide, thymulin, in perfused or fragmented pituitary preparations . The administration of thymopoietin (another chemically-defined thymic hormone) in children with Hodgkin’s disease increased GH and cortisol serum levels . Moreover, thymopentin (the synthetic biologically active peptide of thymopoietin) enhances in vitro the production of ACTH and beta-endorphin . In addition, thymulin exhibits an in vitro stimulatory effect on perfused rat pituitaries, enhancing PRL, GH, TSH and LH release . Using short-term cultures of pituitary fragments, an increase in ACTH secretion occurs after in vitro thymulin addition, with no changes in GH levels and significant reductions in PRL release . A further thymosin peptide was recently isolated with the task in stimulating IL-6 release from rat glioma cells . By contrast, thymosin alpha-1 is apparently able to down regulate TSH, ACTH and PRL secretion in vivo with no modifications on GH levels . These inhibitory effects seem to occur through hypothalamic pathways. Indeed, the production of the corresponding releasing hormones by hypothalamic neurones decreased after in vitro addition of thymosin alpha-1 in medial basal hypothalamic fragments .
The peripheral actions of oxytocin mainly reflect secretion from the pituitary gland. The behavioral effects of oxytocin are thought to reflect release from centrally projecting oxytocin neurons, different from those that project to the pituitary gland, or that are collaterals from them. Oxytocin receptors are expressed by neurons in many parts of the brain and spinal cord, including the amygdala, ventromedial hypothalamus, septum, nucleus accumbens, and brainstem.
Horvath, G. A., Stockler-Ipsiroglu, S. G., Salvarinova-Zivkovic, R., Lillquist, Y. P., Connolly, M., Hyland, K., Blau, N., Rupar, T., and Waters, P. J. Autosomal recessive GTP cyclohydrolase I deficiency without hyperphenylalaninemia: evidence of a phenotypic continuum between dominant and recessive forms. Mol.Genet.Metab 2008;94:127-131. View abstract.
An estimated 1.4 million people sustain traumatic brain injury (TBI) each year in the United States, and more than 5 million people are coping with disabilities from TBI at an annual cost of more than $56 billion.1 There are no commercially-available pharmacological treatment options available for TBI because all clinical trial strategies have failed.2,3 The disappointing clinical trial results may be due to variability in treatment approaches and heterogeneity of the population of TBI patients.4-9 Another important aspect is that most clinical trial strategies have used drugs that target a single pathophysiological mechanism, although many mechanisms are involved in secondary injury after TBI.4 Neuroprotection approaches have historically been dominated by targeting neuron-based injury mechanisms as the primary or even exclusive focus of the neuroprotective strategy.3 In the vast majority of preclinical studies, the treatment compounds are administered early and, frequently, even before TBI.10,11 Clinically, the administration of a compound early may be problematic because of the difficulty in obtaining informed consent.12
When combined with antidepressants of the MAOI or SSRI class, very high parenteral doses of 5-HTP can cause acute serotonin syndrome in rats. It is unclear if such findings have clinical relevance, as most drugs will cause serious adverse events or death in rodents at very high doses. In humans 5-HTP has never been clinically associated with serotonin syndrome, although 5-HTP can precipitate mania when added to an MAOI.