TY - JOUR

T1 - 3-Dimensional Ultrastructural Analysis of the Rat Pinealocyte

T2 - Presence of Secretory Bulbous Projections Delineated from the Cell Body by Junctional Complexes

AU - Møller, Morten

AU - Midtgaard, Jens

AU - Qvortrup, Klaus

AU - Rath, Martin Fredensborg

PY - 2024

Y1 - 2024

N2 - Introduction: The superficial pineal gland of the Sprague Dawley rat is a neuroendocrine structure secreting the hormone melatonin. By use of block face scanning electron microscopy, our aim here was to identify the 3-dimensional ultrastructure of the gland. Methods: A series of 2,731 block face images of the rat pineal tissue, 30 nm in thickness, was obtained in a Teneo volume scanning electron microscope and used for 3-dimensional reconstruction by use of the TrakEM2-plugin in the ImageJ software. Thin sections of the tissue were cut for transmission electron microscopy. Results: Our analyses revealed cellular bulbous processes, containing 50–100 nm clear vesicles, that emerged from a neck-like area at the cell body of the pinealocyte. These bulbous processes extend into small canaliculi located in the center of parenchymal folliculi of the gland as well as into the perivascular spaces. Junctional complexes, comprising both gap and tight junctions, connected the lateral cellular membranes of the pinealocytes, where the bulbous processes emerged from the cell bodies. The canaliculi were, via the extracellular space, connected to the perivascular spaces. Discussion: The junctional complexes reported here would prevent a substance, released from the vesicles in the bulbous processes, from targeting the cell body from which they emerge. In line with previous combined morphological and biochemical demonstrations of glutamate located in clear vesicles of bulbous processes in the rat pineal gland, our data ultrastructurally support the concept that bulbous processes could participate in a paracrine glutamatergic inhibition of the melatonin secretion in the pineal gland. Conclusion: Bulbous secretory projections separated from the cell body by a junctional complex represents a new feature of neuroendocrine cells.

AB - Introduction: The superficial pineal gland of the Sprague Dawley rat is a neuroendocrine structure secreting the hormone melatonin. By use of block face scanning electron microscopy, our aim here was to identify the 3-dimensional ultrastructure of the gland. Methods: A series of 2,731 block face images of the rat pineal tissue, 30 nm in thickness, was obtained in a Teneo volume scanning electron microscope and used for 3-dimensional reconstruction by use of the TrakEM2-plugin in the ImageJ software. Thin sections of the tissue were cut for transmission electron microscopy. Results: Our analyses revealed cellular bulbous processes, containing 50–100 nm clear vesicles, that emerged from a neck-like area at the cell body of the pinealocyte. These bulbous processes extend into small canaliculi located in the center of parenchymal folliculi of the gland as well as into the perivascular spaces. Junctional complexes, comprising both gap and tight junctions, connected the lateral cellular membranes of the pinealocytes, where the bulbous processes emerged from the cell bodies. The canaliculi were, via the extracellular space, connected to the perivascular spaces. Discussion: The junctional complexes reported here would prevent a substance, released from the vesicles in the bulbous processes, from targeting the cell body from which they emerge. In line with previous combined morphological and biochemical demonstrations of glutamate located in clear vesicles of bulbous processes in the rat pineal gland, our data ultrastructurally support the concept that bulbous processes could participate in a paracrine glutamatergic inhibition of the melatonin secretion in the pineal gland. Conclusion: Bulbous secretory projections separated from the cell body by a junctional complex represents a new feature of neuroendocrine cells.

KW - 3-D ultrastructure

KW - Paracrine regulation

KW - Rat pineal

U2 - 10.1159/000535567

DO - 10.1159/000535567

M3 - Journal article

C2 - 38029731

AN - SCOPUS:85186743662

VL - 114

SP - 291

EP - 301

JO - Neuroendocrinology

JF - Neuroendocrinology

SN - 0028-3835

IS - 3

ER -