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Distribution and Characteristics of Brain Dopamine
Published in Nira Ben-Jonathan, Dopamine, 2020
Many mammals have a distinct IL that is interposed between the AL and NL. In humans, however, the IL is well developed in the fetus but undergoes involution to colloid-filled cysts that mingle with the neural lobe in the adult. Neither the role of the IL in fetal human development nor the reasons for its involution are known. Unless otherwise specified below, when presenting evidence obtained from animal studies, the term posterior pituitary refers to a combined neural and IL. Another small region, the pars tuberalis, extends upward from the pars distalis and joins the infundibular stalk arising from the posterior lobe (pars nervosa). The function of the pars tuberalis is poorly understood.
Summation of Basic Endocrine Data
Published in George H. Gass, Harold M. Kaplan, Handbook of Endocrinology, 2020
The pituitary gland is divided into three parts: (1) anterior lobe, (2) posterior lobe, and (3) infundibulum. The anterior lobe is in turn divided into the pars distalis and pars tuberalis. These two sections plus a pars intermedia are usually termed the adenohypophysis. In the human infant, the pars intermedia can be seen between the pars distalis and the pars nervosa (neurohypophysis), but in adults fusion occurs between the greater lobes and the intermediate lobe becomes obscure.
Neuroendocrine Morphology
Published in Paul V. Malven, Mammalian Neuroendocrinology, 2019
Pars Tuberalis. The vasculature of the pars tuberalis is not well understood, but there may be diffusion of secretory products and nutrients to and from the adjacent neural tissue of the pars eminens of the median eminence and hypophysial stalk. Although there are fewer cell types, pars tuberalis cytology is similar in some ways to that of the pars anterior. Relatively few stainable secretory vesicles are seen with light microscopy, but ultrastructural analysis does reveal the presence of secretory vesicles. Pars tuberalis cells that contain stainable luteinizing hormone (LH) and thyrotropin (TSH) have been observed in several species. There is even some evidence for secretion of these hormones from the pars tuberalis into blood. Many cells of the pars tuberalis do not stain for any known adenohypophysial hormones. Recent evidence that almost all cells of the pars tuberalis cells contain receptors for the pineal gland secretory product, melatonin, has raised the possibility of some unique function for the pars tuberalis in relation to pineal-mediated processes (de Reviers et al., 1989). It has been suggested that melatonin regulation of LH secretion by the pars tuberalis modulates release of LHRH in the adjacent pars eminens by diffusion (short feedback) of LH produced by pars tuberalis (Nadazawa et al., 1991). In this regard, it should be noted that almost all cells of the ovine pars tuberalis contain mRNA encoding the synthesis of LH, whereas only a fraction of the cells contain stainable quantities of LH (Pelletier et al., 1992).
Photoperiod regulates the daily profiles of tryptophan hydroxylase-2 gene expression the raphe nuclei of rats
Published in International Journal of Neuroscience, 2021
Zeina S. Malek, Louay M. Labban
On the other hand, melatonin secretion is a seasonal output of the SCN known to drive photoperiodic message. Indeed, the duration of the nocturnal melatonin secretion is proportional to the length of darkness, providing an internal signal for seasonal changes [17, 18]. A primary target tissue of this seasonal signal in mammals is the hypophyseal pars tuberalis in which melatonin is a key regulator of clock genes expression [27–30]. Melatonin could also be involved, as a seasonal signal, in the photoperiodic changes of TPH2 mRNA daily rhythm reported in the present study. Although melatonin receptors have not been identified in the raphe neurons [31,32], this hormone has been shown to modulate 5-HT synthesis in the SCN [33]. It can be suggested that melatonin would act indirectly upon the serotonergic neurons via melatonin-sensitive brain areas. Despite the fact that the expression patterns for both melatonin and TPH2mRNA are not similar, the physiological effect of the hormone could be mediated by other photoperiod actors under melatonin control, and that would explain the observed shift between both profiles. To further investigate the melatonin hypothesis, the present photoperiodic profiles must be studied after removing the pineal gland.
Melatonin mends adverse temporal effects of bright light at night partially independent of its effect on stress responses in captive birds
Published in Chronobiology International, 2020
Although ALAN has been studied extensively in birds, the exact physiological mechanism of action underlying the altered behavioral responses is not well-known. There is evidence that the ALAN signal is transduced by the avian photoperiodic system of the birds (Dominoni 2015). In mammals, nonvisual light signals are restricted to intrinsically photosensitive retinal ganglion cells (ipRGCs) that express the photopigment melanopsin (Hannibal et al. 2017). In contrast, birds have a wide array of extraretinal photoreceptors expressed by variant neural tissues, including the pineal gland and deep brain photoreceptors (DBPs; Yoshimura 2010). The DBPs are suggested to play a pivotal role in regulating photoperiodic responses by modulating the secretion of thyroid-stimulating hormones elicited by the pars tuberalis in the pituitary gland (Tamai and Yoshimura 2017). Nonetheless, the ipRGCs and the pineal gland can also modulate circadian responses in physiology and behavior by the rhythmic release of melatonin in several bird species (Surbhi and Kumar 2015).
Annual changes in the copulatory behavior of male rats maintained under constant laboratory conditions
Published in Chronobiology International, 2020
Mayra Liliana Ramírez-Rentería, Enrique Hernández-Arteaga, Marisela Hernández González, Manuel Alejandro Cruz-Aguilar, Trilce María Fernanda Ortega-Hernández, Carolina Sotelo-Tapia, Miguel Angel Guevara
It has been proposed that species which lack photoperiodic regulation have an internal mechanism that functions as a double switch for the EYA3 and CHGA transcriptional factors in specific thyrotropic cells of the Pars tuberalis (Freeman and Zucker 2001; Lincoln et al. 2005; Malpaux et al. 1998; Woodfill et al. 1994). These cells have the ability to stimulate the expression of genes involved in thyroid-stimulating hormone metabolism in its T3 form, which drives hypothalamic and pituitary endocrine circuits and, therefore, regulates the release of gonadotropins to produce a rhythm-like effect in the regulation of gonadotropin release. This is similar to species with seasonal activity regulated by the photoperiod (Sáenz de Miera et al. 2004; Wood et al. 2015).