Existence Of VGLuT2-like Immunoreactive Substances In Rat Anterior Pituitary Prolactin Cells

L-Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system and plays important roles in many neuronal processes such as fast synaptic transmission and neuronal plasticity. To use L-glutamate as an intercellular signaling molecule, neuronal cells develop glutamatergic systems comprising the storage of glutamate in synaptic vesicles and its exocytosis (signal output), glutamate receptors (signal input), and glutamate reuptake systems (signal termination). The storage of glutamate in synaptic vesicles is via VGLuTs(vesicular glutamate transporters). VGLuTs are located at the vesicle membranes and provide the vesicles with relatively high concentration of glutamate. Three types of VGLuTs have been discovered, namely VGLuT1, VGLuT2 and VGLuT3. They have similar pharmacological characters. The distribution of VGLuTs has mainly been studied in the nervous system. They are specifically located in the axon terminals.Recent evidence indicates that VGLuT2 exists in the mammalian pinealocytes and pancreatic a cells, playing its primary role in the storage ofL-glutamate in endocrine cells through the transport of L-glutamate at the expense of an electrochemical gradient of protons that is established by vacuolar H+-ATPase. These endocrine cells also develop glutamatergic systems. For instance, mammalian pinealocytes, endocrine cells for melatonin, secrete L-glutamate through Ca~2+-dependent regulated exocytosis and use it as a paracrine- or autocrine-like chemical transmitter to inhibit melatonin synthesis. Mammalian anterior pituitary is the most important endocrine organ, but there are not many researches about the function of glutamate in the anterior pituitary. Some evidence shows that glutamate induces apoptosis of lactotropes and somatotropes through group â…¡ mGluR activation, probably by decreasing cAMP synthesis. Other results show that L-glutamate has a differential direct effect on PRL release: it exerts a stimulatory action via iGluRs and an inhibitory effect via mGluRs. It is therefore interesting to see if the mammalian anterior pituitary also develop a glutamatergic system. To answer these questions, we first tried to make clear if the gland cells of mammalian anterior pituitary exist VGLuT2.By light and electron microscopy, we found that VGLuT2-like immunoreactive substances existed in the lactotrophs of the rat anterior pituitary. Two following steps were designed in the research. First, DAB immunocytochemistry and fluorenscence. VGLuT2 like immunoreactive substances were visible in the normal rat anterior pituitary. They were found in gland cells. Positive cells were normally distributed in clusters. Second, nanogold-silver enhancement immunoelectron microscropy. The nanogold-silver products were found at the membrane of the secretory vesicles of lactotrophs.This is the first evidence for the presence of VGLuT2 at the secretory...