NGFI-A gene expression induced in the rat suprachiasmatic nucleus by photic stimulation: spread into hypothalamic periventricular somatostatin neurons and GABA receptor involvement

Electroconvulsive Seizure Alters the Expression and Daily Oscillation of Circadian Genes in the Rat Frontal Cortex

OBJECTIVE

Electroconvulsive therapy (ECT) is the most effective treatment for mood disorders. Accumulating evidence has suggested the important role of circadian genes in mood disorders. However, the effects of ECT on circadian genes have not been systemically investigated.

METHODS

We examined the expression and daily oscillation of major circadian genes in the rat frontal cortex after electroconvulsive seizure (ECS).

RESULTS

Firstly, mRNA and protein level were investigated at 24 hr after single ECS (E1X) and repeated ECS treatements for 10 days (E10X), which showed more remarkable changes after E10X than E1X. mRNA expression of Rorα, Bmal1, Clock, Per1, and Cry1 was decreased, while Rev-erbα expression was increased at 24 hr after E10X compared to sham. The proteins showed similar pattern of changes. Next, the effects on oscillation and rhythm properties (mesor, amplitude, and acrophase) were examined, which also showed more prominent changes after E10X than E1X. After E10X, mesor of Rorα, Bmal1, and Cry1 was reduced, and that of Rev-erbα was increased. Five genes, Rev-erbα, Bmal1, Per1, Per2, and Cry2, showed earlier acrophase after E10X.

CONCLUSION

The findings suggest that repeated ECS induces reduced expression and phase advance of major circadian genes in the in vivo rat frontal cortex.

The development of day-night differences in sleep and wakefulness in norway rats and the effect of bilateral enucleation

The suprachiasmatic nucleus exhibits circadian rhythmicity in fetal and infant rats, but little is known about the consequences of this rhythmicity for infant behavior. Here, in experiment 1, the authors measured sleep and wakefulness in rats during the day and night in postnatal day (P)2, P8, P15, and P21 subjects. As early as P2, day-night differences in sleep-wake activity were detected. Nocturnal wakefulness began to emerge around P15 and was reliably expressed by P21. The authors hypothesized that the process of photic entrainment over the 1st postnatal week, which depends on the development of connectivity between the retinohypothalamic tract (RHT) and the SCN, influences the later emergence of nocturnal wakefulness. To test this hypothesis, in experiment 2 infant rats were enucleated bilaterally at P3 and P11, that is, before and after photic entrainment. Whereas pups enucleated at P11 and tested at P21 exhibited increased wakefulness at night, identical to sham controls, pups enucleated at P3 and tested at P21 exhibited the opposite pattern of increased wakefulness during the day. Pups tested at P28 and P35 exhibited this same pattern of increased daytime wakefulness. All together, these results suggest that prenatal and postnatal experience modulates the development of species-typical circadian sleep-wake patterns. Moreover, the authors suggest that visual system stimulation, via the RHT's connections with the SCN, exerts an organizational influence on the developing circadian system and, consequently, contributes to the emergence of nocturnality in this species.

Developmental expression and serotonergic regulation of relaxin 3/INSL7 in the nucleus incertus of rat brain

Relaxin 3 or insulin like peptide 7 has been identified as a new member of the insulin/relaxin superfamily. We recently reported that relaxin 3 was dominantly expressed in the brain, particularly in neurons of the nucleus incertus (NI) of the median dorsal tegmental pons and that it might act as a neurotransmitter. In the present study we investigated the developmental expression and serotonergic regulation of relaxin 3 gene in the rat brain. Relaxin 3 mRNA appeared at embryonic day 18 in the near region of the fourth ventricle, and was shown to have increased its density and the number of expressing neurons by in situ hybridization and RT-PCR examination. Relaxin 3 peptide was detected after birth by immunocytochemistry. Since the NI is located just caudal to the dorsal raphe nucleus where abundant serotonin (5-HT) neurons are present, we examined if 5-HT effects on the expression of relaxin 3. Relaxin 3 gene expression in the NI significantly increased after 5-HT depletion by p-chlorophenylalanine (PCPA) administration. We also observed the 5-HT1A receptor localization in relaxin 3 positive neurons of the NI. This result suggests that 5-HT negatively regulates the expression of relaxin 3 gene in the NI. The function of relaxin 3 neurons in the brain is influenced by the serotonergic activity.

Neurons expressing relaxin 3/INSL 7 in the nucleus incertus respond to stress

Relaxin 3/INSL 7 has recently been identified as a new member of the insulin/relaxin superfamily. Although it was reported to be dominantly expressed in the brain, its detailed distribution and function in the central nervous system are still obscure. In the present study we demonstrated that in the rat relaxin 3 was mainly expressed in neurons of the nucleus incertus (NI) of the median dorsal tegmental pons. Other relaxin 3-expressing neurons were scattered in the pontine raphe nucleus, the periaqueductal gray and dorsal area to the substantia nigra in the midbrain reticular formation. Relaxin 3-immunoreactive fibers projected particularly densely in the septum, hippocampus, lateral hypothalamus and intergeniculate leaflet of the thalamus. Ultrastructural examination revealed that relaxin 3 was localized in the dense-cored vesicles in the perikarya and was also observed in the synaptic terminals of axons. As almost all relaxin 3-containing neurons express corticotropin-releasing factor (CRF) type 1 receptor in the NI, we examined the response of relaxin 3 neurons to intracerebroventricular administration of CRF; 65% of relaxin 3 neurons expressed c-Fos 2 h after intracerebroventricular administration of 1 microg CRF. We then confirmed that c-Fos was induced in 60% of relaxin 3 neurons in the NI and the expression of relaxin 3 mRNA increased significantly in the NI after water-restraint stress. Collectively, these results suggest that relaxin 3 produced in the NI is released from nerve endings and is involved in the regulation of the stress response.

Circadian and light-induced transcription of clock gene Per1 depends on histone acetylation and deacetylation

Circadian clock genes are regulated through a transcriptional-translational feedback loop. Alterations of the chromatin structure by histone acetyltransferases and histone deacetylases (HDACs) are commonly implicated in the regulation of gene transcription. However, little is known about the transcriptional regulation of mammalian clock genes by chromatin modification. Here, we show that the state of acetylated histones fluctuated in parallel with the rhythm of mouse Per1 (mPer1) or mPer2 expression in fibroblast cells and liver. Mouse CRY1 (mCRY1) repressed transcription with HDACs and mSin3B, which was relieved by the HDAC inhibitor trichostatin A (TSA). In turn, TSA induced endogenous mPer1 expression as well as the acetylation of histones H3 and H4, which interacted with the mPer1 promoter region in fibroblast cells. Moreover, a light pulse stimulated rapid histone acetylation associated with the promoters of mPer1 or mPer2 in the suprachiasmatic nucleus (SCN) and the binding of phospho-CREB in the CRE of mPer1. We also showed that TSA administration into the lateral ventricle induced mPer1 and mPer2 expression in the SCN. Taken together, these data indicate that the rhythmic transcription and light induction of clock genes are regulated by histone acetylation and deacetylation.

Cloning and characterization of a novel GRP78-binding protein in the rat brain

The full-length cDNA clone of a novel GRP78-binding protein (GBP) was isolated from rat brain using PCR-selected cDNA subtraction. GBP was predominantly expressed in neuronal cells among various brain tissues. GBP mRNA was already detected in the E12 brain and then gradually increased to reach a peak within P0-2 weeks after birth. GBP expression in the brain decreased age-dependently to approximately 30% of the postnatal level at 12 months. GBP encoded 1021 amino acids and was predicted to have two transmembrane regions and glutamic acid- and proline-rich regions. Because the sequence of GBP offered few clues to the possible function, we performed a GST-tagged GBP pull-down assay in PC12 lysates and identified GRP78, one of the heat shock proteins, as a counterpart. Observation of COS7 cells expressing green fluorescent protein- or Myc-tagged GBP showed that GBP was localized in the endoplasmic reticulum-Golgi domain where BODIPY 558/568 (4,4-difluro-5-(2-thienyl)-4-bora-3alpha,4alpha-diaza-S-indacene)-labeled brefeldin A accumulated. To investigate a biological role for GBP, we established Neuro2a cells stably expressing Myc-tagged GBP. Overexpression of GBP did not affect cell growth or morphological features but attenuated the time-dependent decrease in cell viability caused by serum deprivation compared with control cells. After 48 h of serum starvation, Neuro2a cells overexpressing GBP were resistant to the cell death induced by serum withdrawal. These results suggest that GBP would have a relevant functional role in embryonic and postnatal development of the brain.

Local inflammation increases vanilloid receptor 1 expression within distinct subgroups of DRG neurons

Vanilloid receptor 1 (VR1) is essential to the development of inflammatory hyperalgesia. We investigated whether inflammation can increase in VR1 positive neuronal profiles in rat DRG neurons using histochemical methods. We also used size frequency analysis and double staining with several neuronal markers to investigate whether or not inflammation alters VR1 expression. Inflammation induced a 1.5-fold increase in percentage of VR1-like immunoreactivity (LI) positive profiles per total neuronal profiles, suggesting that the number of heat and pH sensitive neurons increase during inflammation. Area frequency histograms showed that VR1 expression increased in small and medium-sized neurons after inflammation. Double labeling of VR1 with NF200 showed that VR1 positive neurons with NF200 positive profiles significantly increased, indicating that the medium-sized VR1 positive neurons were neurons with myelinated A-fibers. Local inflammation thus increases in VR1 protein level within distinct subgroups of DRG neurons that may participate in the development and maintenance of inflammatory hyperalgesia.

Anatomical and temporal differences in the regulation of ZIF268 (NGFI-A) protein in the hamster and mouse suprachiasmatic nucleus

Several immediate-early genes have been shown to be induced in the rodent circadian pacemaker, the suprachiasmatic nucleus, by retinal illumination at night. We compared spontaneous and light-evoked levels of the immediate-early gene protein ZIF268 (NGFI-A) in the Syrian hamster and C57BL/6J mouse suprachiasmatic nucleus. Exposure of both hamsters and mice to light pulses early and late in the subjective night caused increased ZIF268 immunoreactivity in the region of the suprachiasmatic nucleus that receives retinal innervation. In contrast to hamsters, mice also showed spontaneous increases in ZIF268 at both subjective night phases at the lateral edges of the suprachiasmatic nucleus. Light also evoked a significant increase in ZIF268 levels during the subjective day in the lateral suprachiasmatic nucleus, with few labeled cells in the ventral and dorsal suprachiasmatic nucleus. These results demonstrate a novel circadian pattern and regional differentiation of ZIF268 immunoreactivity in the suprachiasmatic nucleus of mice that differ from those in other rodents. There are pronounced species differences in both spontaneous and light-evoked expression of ZIF268 immunoreactivity.

HPA-axis responses during experimental colitis in the rat

We investigated the responses of the hypothalamic-pituitary-adrenal (HPA) axis during experimental colitis induced by intracolonic administration of 2,4,6-trinitrobenzenesulfonic acid in the rat. On days 3 and 7 after induction of colitis, the corticotropin-releasing hormone (CRH) mRNA level in the parvocellular paraventricular nucleus (pPVN) of the hypothalamus was reduced, the plasma ACTH level remained at the basal level, and the plasma corticosterone (Cort) level was high. Induction of colitis on day 3 after adrenalectomy with Cort pellet replacement (ADX + Cort) resulted in a marked increase in CRH mRNA on day 7 after induction of colitis compared with noncolitic ADX + Cort animals. Pair feeding to match the food intake of the colitic animals resulted in no significant change in CRH mRNA in the pPVN, plasma ACTH, and Cort compared with healthy control animals. These findings indicated that CRH mRNA expression in the pPVN was inhibited by glucocorticoid feedback during this experimental colitis, and the decrease in food intake during colitis was not simply responsible for the expression of CRH mRNA. It is inferred that the HPA axis including the CRH level in the pPVN is altered in patients with inflammatory bowel disease.

Stimulus-specific induction of an Egr-1 transgene in rat brain

Regulated expression of Egr-1 (Zif268/NGFIA) in a variety of brain networks suggests a diversity of roles in neuronal plasticity. Here, we aimed to determine whether an egr-1 transgene would mediate transcriptional responses to different pharmacological and physiological stimuli in the brain of transgenic rats. Constitutive transgene expression was observed in the cortex, CA1 hippocampal area and pituitary, recapitulating expression of egr-1. Transgene induction was stimulus-specific. Metrazole induced widespread expression in the dentate gyrus, CA2 and CA3 areas, amygdala, and ventromedial nucleus. In contrast, induction following a light stimulus was restricted to the hypothalamic suprachiasmatic and periventricular nuclei. Our studies have provided novel insights into the differential regulation of egr-1, and facilitated approaches to the genetic manipulation of Egr-1-regulated neuronal systems.

Serotonin modulates expression of VIP and GRP mRNA via the 5-HT(1B) receptor in the suprachiasmatic nucleus of the rat

The expression of vasoactive intestinal peptide (VIP) and gastrin-releasing peptide (GRP) in the suprachiasmatic nucleus (SCN) changes depending on light. VIP mRNA increases and GRP mRNA decreases in the light phase, while they do not show change without light. In the present study we investigated the involvement of serotonin (5-HT) in the expression of VIP and GRP messenger RNA in the SCN of the rat. The decrease in VIP mRNA and the increase in GRP mRNA in the light phase were amplified by 5-HT depletion using 5,6-dihydroxytryptamine injected into the lateral ventricle. These enhancements due to 5-HT depletion were reversed to control levels by applying 5-HT(1B) agonists TFMPP and CGS12066A, but not a 5-HT(1A)/5-HT(7) agonist, 8-OH-DPAT. The 5-HT(1B) receptor is known to exist on the terminals of the retinohypothalamic tract (RHT). Therefore, next we investigated the morphological relationship of RHT and 5-HT terminals by double-labeling immunocytochemistry and demonstrated that 5-HT-immunoreactive fibers and cholera toxin B subunit-labeled RHT terminals were intermingled in the ventrolateral SCN, and 5-HT axon processes had close contact with RHT terminals. Collectively, these pharmacological and morphological results suggest that 5-HT afferents from raphe nuclei modulate VIP and GRP expression in neurons of the ventrolateral SCN by activating the 5-HT(1B) receptor in the RHT.

Genetic engineering of neural function in transgenic rodents: towards a comprehensive strategy?

As mammalian genome projects move towards completion, the attention of molecular neuroscientists is currently moving away from gene identification towards both cell-specific gene expression patterns (neuronal transcriptions) and protein expression/interactions (neuronal proteomics). In the long term, attention will increasingly be directed towards experimental interventions which are able to question neuronal function in a sophisticated manner that is cognisant of both transcriptomic and proteomic organization. Central to this effort will be the application of a new generation of transgenic approaches which are now evolving towards an appropriate level of molecular, temporal and spatial resolution. In this review, we summarize recent developments in transgenesis, and show how they have been applied in the principal model species for neuroscience, namely rats and mice. Current concepts of transgene design are also considered together with an overview of new genetically-encoded tools including both cellular indicators such as fluorescent activity reporters, and cellular regulators such as dominant negative signalling factors. Application of these tools in a whole animal context can be used to question both basic concepts of brain function, and also current concepts of underlying dysfuction in neurological diseases.

Gonadal regulation of PrRP mRNA expression in the nucleus tractus solitarius and ventral and lateral reticular nuclei of the rat

We investigated the prolactin-releasing peptide (PrRP) gene expression quantitatively in the rat brain and the involvement of estrogen and progesterone using in situ hybridization. The strongest signals were observed in the nucleus tractus solitarius (NTS), which showed approximately 70% of total PrRP mRNA in the brain. Moderate expression was observed in the ventral and lateral reticular nuclei (VLRN) of the medulla oblongata. PrRP mRNA signals in the hypothalamic ventromedial- and dorsomedial nuclei showed only 5% of total signals. The PrRP mRNA expression among female rats showing normal gonadal cycle and male rats showed that the highest levels were in female rats in proestrus. Administration of estrogen or progesterone after ovariectomy induced an increase in PrRP mRNA expression in the NTS. PrRP mRNA content in the NTS increased with the progress of the pregnancy and reached a peak on the 14th day, the mid-period of pregnancy, when plasma progesterone increases. We also observed the colocalization of PrRP and estrogen receptor alpha in the neurons distributed in the NTS by double labeling immunocytochemistry. These findings indicate that PrRP gene expression is regulated by gonadal steroid hormones in the medulla oblongata, and parts of PrRP synthesizing neurons are considered to be directly influenced by estrogen in the NTS.

New neuropeptides containing carboxy-terminal RFamide and their receptor in mammals

Only a few RFamide peptides have been identified in mammals, although they have been abundantly found in invertebrates. Here we report the identification of a human gene that encodes at least three RFamide-related peptides, hRFRP-1-3. Cells transfected with a seven-transmembrane-domain receptor, OT7T022, specifically respond to synthetic hRFRP-1 and hRFRP-3 but not to hRFRP-2. RFRP and OT7T022 mRNAs are expressed in particular regions of the rat hypothalamus, and intracerebroventricular administration of hRFRP-1 increases prolactin secretion in rats. Our results indicate that a variety of RFamide-related peptides may exist and function in mammals.