Cell organization of the rat pars tuberalis. Evidence for open communication between pars tuberalis cells, cerebrospinal fluid and tanycytes

Abstract

The pars tuberalis (PT) is the only pituitary region in close contact with the medial-basal hypothalamus and bathed by cerebrospinal fluid (CSF). Although PT has long been recognized as an endocrine gland, certain aspects of its structure remain obscure. The present investigation has been designed to gain information concerning (1) the cellular organization of PT, (2) the PT/median eminence spatial relationship and (3) the exposure of various cell compartments of PT to CSF. Non-endocrine cells (S100-reactive) appear as the organizer of the PT architecture. The apical poles of these cells line large cistern-like cavities and the processes of these cells establish a close spatial relationship with PT-specific secretory cells, portal capillaries and tanycytes. The cisterns are also endowed with clusters of ciliated cells and with a highly electron-dense and PAS-reactive content. The unique spatial organization of endocrine and non-endocrine cells of the PT supports a functional relationship between both cell populations. PT endocrine cells display a hallmark of PT-specific cells, namely, the paranuclear spot, which is a complex structure involving the Golgi apparatus, a large pool of immature secretory granules and a centriole from which originates a single 9+0 cilium projecting to the intercellular channels. Horseradish peroxidase (HRP) injected into the CSF readily reaches the intercellular channels of PT and the inner channel of the single cilium and is incorporated by the endocytic machinery of the secretory cells. The PT endocrine cells, through their single 9+0 cilium, may act as sensors of the CSF. HRP also reaches the lumen of the cisterns, indicating that this PT compartment is also exposed to CSF. PT endocrine cells establish direct cell-to-cell contacts with hypothalamic beta(1) tanycytes, suggesting a second means of brain-PT communication.

Encoding and Decoding Photoperiod in the Mammalian Pars Tuberalis

“…Recent studies in the rat have characterised up to five different secretory cell types [25]. In the same studies, the authors described the follicular cells as cistern-like structures making close contact with the PT-specific cells, portal capillaries and tanycytes; this complex cellular network highly supports a central role for the PT in processing information to and from the brain and periphery.…”

Photoperiod-dependent effect of inflammation on nocturnal gene expression of proinflammatory cytokines and their receptors in <i>pars tuberalis</i> of ewe

“…Obtained results suggest that the PT may be one of the gateways for immune-endocrine interactions and these interactions may be affected by the photoperiod. stalk and is the exclusive pituitary structure in close anatomical contact with the medial-basal hypothalamus, ME and the third ventricle (Guerra et al, 2010). The PT is bathed in the cerebrospinal fluid (Guerra et al, 2010;Yasuo and Korf, 2011) and possessed by intercellular channels needed for direct communication with the subarachnoid space (Morgan and Williams, 1996;Lafarque et al, 2004;Dupré, 2011).…”

“…stalk and is the exclusive pituitary structure in close anatomical contact with the medial-basal hypothalamus, ME and the third ventricle (Guerra et al, 2010). The PT is bathed in the cerebrospinal fluid (Guerra et al, 2010;Yasuo and Korf, 2011) and possessed by intercellular channels needed for direct communication with the subarachnoid space (Morgan and Williams, 1996;Lafarque et al, 2004;Dupré, 2011). The PT is composed of the follicular cells -small cells without secretory features, PT-specific secretory cells and PD-like cells (Dupré, 2011).…”

Dual signal transduction pathways activated by TSH receptors in rat primary tanycyte cultures

“…Ventrally, tanycyte processes are localised in the median eminence, where they appose peptidergic terminals and portal capillaries (Rodriguez et al 2005). Tanycytes sense biologically active hormones and metabolites from the ventricle and portal blood vessels, and they connect the ventricle and neighbouring pars tuberalis via networks of cisterna (Guerra et al 2010, Frayling et al 2011, Bolborea & Dale 2013, Balland et al 2014. They express receptors and/or transport proteins for a wide variety of known and unknown biologically active compounds (Graham et al 2003, Rodriguez et al 2005, Barrett et al 2007, Coppola et al 2007, Cottrell et al 2009, Nilaweera et al 2011, Shearer et al 2012, Dardente et al 2014.…”