Pinealocyte

About: Pinealocyte is a research topic. Over the lifetime, 1605 publications have been published within this topic receiving 55609 citations.

Genetic targeting: the serotonin N-acetyltransferase promoter imparts circadian expression selectively in the pineal gland and retina of transgenic rats.

Abstract: The arylalkylamine N-acetyltransferase (AA-NAT) gene is strongly expressed in the rat primarily in the pineal gland; low levels of expression are also found in the retina. AA-NAT catalyzes the key regulatory step controlling rhythmic melatonin output: the acetylation of serotonin. In the rat, the AA-NAT gene is expressed at night. This is controlled partly by cyclic AMP (cAMP) acting through a composite cAMP-responsive element-CCAAT site located upstream of the transcription start point. In the present study, we have extended our previous in vitro findings and found that additional elements in the 5' flanking region and first intron play an important role in the regulation of the AA-NAT gene. This led us to test the influence of an AA-NAT 5' flanking segment on the expression of the bacterial chloramphenicol acetyltransferase gene in a rat transgenic model. The results of this study clearly demonstrate that the segment of the AA-NAT gene that encompasses the minimal promoter and the first intron is able to confer the highly specific pineal/ retinal and time-of-day patterns of AA-NAT gene expression. This advance also provides a tool that selectively targets genetic expression to pinealocytes and retinal photoreceptors, providing new experimental opportunities to probe aene exoression in these tissues.

Transcription factor dynamics and neuroendocrine signalling in the mouse pineal gland: a comparative analysis of melatonin-deficient C57BL mice and melatonin-proficient C3H mice

Abstract: In rodents, the nocturnal rise and fall of arylalkylamine N-acetyltransferase (AANAT) activity controls the rhythmic synthesis of melatonin, the hormone of the pineal gland. This rhythm involves the transcriptional regulation of the AANAT by two norepinephrine (NE)-inducible transcription factors, e.g. the activator pCREB (phosphorylated Ca2+/cAMP-response element binding protein) and the inhibitor ICER (inducible cAMP early repressor). Most inbred mouse strains do not produce melatonin under standard laboratory light/dark conditions. As melatonin-deficient mice are often the founders for transgenic animals used for chronobiological experimentations, molecular components of neuroendocrine signalling in the pineal gland as an integral part of clock entrainment mechanisms have to be deciphered. We therefore compared calcium signalling, transcriptional events and melatonin synthesis in the melatonin-deficient C57BL mouse and the melatonin-proficient C3H mouse. Pineal glands and primary pinealocytes were cultured and stimulated with NE or were collected at various times of the light/dark (LD) cycle. Changes in intracellular calcium concentrations, the phosphorylation of CREB, and ICER protein levels follow similar dynamics in the pineal glands of both mouse strains. pCREB levels are high during the early night and ICER protein shows elevated levels during the late night. In the C57BL pineal gland, a low but significant increase in melatonin synthesis could be observed upon NE stimulation, and, notably, also when animals were exposed to long nights. We conclude that the commonly used C57BL mouse is not completely melatonin-deficient and that this melatonin-deficiency does not affect molecular details involved in regulating transcriptional events of melatonin synthesis.

Circadian regulation of ion channels and their functions

Abstract: Ion channels are the gatekeepers to neuronal excitability. Retinal neurons of vertebrates and invertebrates, neurons of the suprachiasmatic nucleus (SCN) of vertebrates, and pinealocytes of non-mammalian vertebrates display daily rhythms in their activities. The interlocking transcription-translation feedback loops with specific post-translational modulations within individual cells form the molecular clock, the basic mechanism that maintains the autonomic approximately 24-h rhythm. The molecular clock regulates downstream output signaling pathways that further modulate activities of various ion channels. Ultimately, it is the circadian regulation of ion channel properties that govern excitability and behavior output of these neurons. In this review, we focus on the recent development of research in circadian neurobiology mainly from 1980 forward. We will emphasize the circadian regulation of various ion channels, including cGMP-gated cation channels, various voltage-gated calcium and potassium channels, Na(+)/K(+)-ATPase, and a long-opening cation channel. The cellular mechanisms underlying the circadian regulation of these ion channels and their functions in various tissues and organisms will also be discussed. Despite the magnitude of chronobiological studies in recent years, the circadian regulation of ion channels still remains largely unexplored. Through more investigation and understanding of the circadian regulation of ion channels, the future development of therapeutic strategies for the treatment of sleep disorders, cardiovascular diseases, and other illnesses linked to circadian misalignment will benefit.

Circadian rhythm in the serotonin content of the rat pineal gland: regulating factors.

Abstract: There is a marked circadian rhythm in the serotonin content of the rat pineal gland. The rhythm can be inverted 180° by reversal of the lighting regimen. Phase inversion is complete in 6 days. The activities of 5-hydroxytryptophan decarboxylase and monoamine oxidase in the pineal gland do not exhibit a circadian variation. The absolute increase in pineal gland serotonin produced by tryptophan or 5-hydroxytryptophan injection is much greater than in other tissues but does not vary at different times of day and night. Treatment with β-phenylisopropyhlmydrazine, a monoamine oxidase inhibitor, prevents the nocturnal decline of pineal serotonin but does not alter daytime levels. Treatment with actinomycin D partially inhibits time daytime increase in pineal serotonin.