Ontogeny of Fos protein-like immunoreactivity in the suprachiasmatic nucleus

Regional Fos expression induced by morphine withdrawal in the 7-day-old rat

Human infants are often exposed to opiates chronically but the mechanisms by which opiates induce dependence in the infant are not well studied. In the adult the brain regions involved in the physical signs of opiate withdrawal include the periaqueductal gray area, the locus coeruleus, amygdala, ventral tegmental area, nucleus accumbens, hypothalamus, and spinal cord. Microinjection studies show that many of these brain regions are involved in opiate withdrawal in the infant rat. Our goal here was to determine if these regions become metabolically active during physical withdrawal from morphine in the infant rat as they do in the adult. Following chronic morphine or saline treatment, withdrawal was precipitated in 7-day-old pups with the opiate antagonist naltrexone. Cells positive for Fos-like immunoreactivity were quantified within select brain regions. Increased Fos-like labeled cells were found in the periaqueductal gray, nucleus accumbens, locus coeruleus, and spinal cord. These are consistent with other studies showing that the neural circuits underlying the physical signs of opiate withdrawal are similar in the infant and adult.

A putative transcription factor with seven zinc-finger motifs identified in the developing suprachiasmatic nucleus by the differential display PCR method

The suprachiasmatic nucleus (SCN) is a mammalian central circadian pacemaker. This nucleus develops in the last stage of fetal life and matures to make strong synaptic connections within 2 weeks of postnatal life to establish strong oscillation characteristics. To identify factors that initiate the circadian oscillation, we applied a differential display PCR method to developing SCN, and isolated a gene with seven zinc-finger motifs, Lot1, which encodes a gene that appeared at a very high level in the SCN during the early postnatal days. Lot1 mRNA first appeared at postnatal day 1 (P1) at a very high level, and the signal in the SCN continued to be very high until P10 and thereafter rapidly decreased until P20 and was expressed at a very faint level during adulthood. Lot1 mRNA expression was observed only in neurons of the dorsomedial SCN throughout the course of development. During the developmental stage, Lot1 mRNA expression shows a circadian rhythm with a peak in the day time and a trough at night time in both light-dark and constant dark conditions. These observations imply that Lot1 is the first identified putative transcription factor expressed only in the period of active synaptogenesis in the SCN, where Lot1 might play a role in establishing autonomous oscillation.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Synchronizing circadian rhythms in early infancy

Entrainment to the 24-hour light-dark cycle is of adaptive significance to mammals. Human infants are no exception, but some postnatal care habits prevalent in developed countries can interfere with the physiological mechanisms underlying circadian synchronization. We describe the physiological mechanisms of entrainment to the light-dark cycle in fetuses and newborns, and some common parental care behaviors which subject the developing circadian system of the newborn to conflicting temporal cues. Improvements in parental care are proposed which may improve the circadian synchronization of newborns, and their parents or caregivers.