The Effect of Light Exposure at Night (LAN) on Carcinogenesis via Decreased Nocturnal Melatonin Synthesis

In mammals, a master clock is located within the suprachiasmatic nucleus (SCN) of the hypothalamus, a region that receives input from the retina that is transmitted by the retinohypothalamic tract. The SCN controls the nocturnal synthesis of melatonin by the pineal gland that can influence the activity of the clock's genes and be involved in the inhibition of cancer development. On the other hand, in the literature, some papers highlight that artificial light exposure at night (LAN)-induced circadian disruptions promote cancer. In the present review, we summarize the potential mechanisms by which LAN-evoked disruption of the nocturnal increase in melatonin synthesis counteracts its preventive action on human cancer development and progression. In detail, we discuss: (i) the Warburg effect related to tumor metabolism modification; (ii) genomic instability associated with L1 activity; and (iii) regulation of immunity, including regulatory T cell (Treg) regulation and activity. A better understanding of these processes could significantly contribute to new treatment and prevention strategies against hormone-related cancer types.

Circadian responses to endotoxin treatment in mice

We tested the ability of Escherichia coli lipopolysaccharide (LPS) to phase-shift the activity circadian rhythm in C57Bl/6J mice. Intraperitoneal administration of 25 microg/kg LPS induced photic-like phase delays (-43+/-10 min) during the early subjective night. These delays were non-additive to those induced by light at CT 15, and were reduced by the previous administration of sulfasalazine, a NF-kappaB activation inhibitor. At CT 15, LPS induced c-Fos expression in the dorsal area of the suprachiasmatic nuclei (SCN). Our results suggest that the activation of the immune system should be considered an entraining signal for the murine circadian clock.

Infiltration of T-lymphocytes in the brain after anterior chamber inoculation of a neurovirulent and neuroinvasive strain of HSV-1

Following anterior chamber (AC) inoculation of BALB/c mice with the KOS strain of herpes simplex virus type 1 (HSV-1), or with H129, a neuroinvasive and neurovirulent strain of HSV-1, both strains of virus spread from the injected eye through the brain to cause retinitis. However, KOS-infected mice develop retinitis in the uninoculated eye only, whereas H129-infected mice develop bilateral retinitis. Previous studies have shown that infiltrating T-cells in the suprachiasmatic nuclei (SCN) of the hypothalamus of KOS-infected mice concomitant with or before virus protect KOS-infected mice from ipsilateral retinitis. To determine the timing of T cell infiltration and cytokine production in the brain of H129-infected mice, adjacent, frozen sections of the brain were immunostained for virus, T-cells, IL-2, TNF-alpha or IFN-gamma. T-cells infiltrated the brains of H129-infected mice and cytokines were produced in infected tissues. However, virus spread to the optic nerve and retina of both the inoculated and uninoculated eye before T-cells and cytokines were detected in the SCN of H129-infected mice. These results suggest that infiltrating T-cells in the SCN of H129-infected mice may arrive too late to prevent the spread of virus into the optic nerves and retinas and thus prevent development of bilateral retinitis in infected mice.

Light-dependent regulation and postnatal development of the interferon-gamma receptor in the rat suprachiasmatic nuclei

The interferon-gamma receptor gene was detected in the rat hypothalamic suprachiasmatic nuclei (SCN), the main pacemaker for circadian rhythms, and the molecular identity of the transcript was confirmed by sequencing. The expression of the receptor protein showed a daily rhythm that was dependent on light. It reached its adult pattern in the SCN between postnatal day 11 and 20, i.e., at a time when capacity for photic entrainment of the pacemaker is established.

Pseudorabies virus-induced leukocyte trafficking into the rat central nervous system

When the swine alphaherpesvirus pseudorabies virus (PRV) infects the rat retina, it replicates in retinal ganglion cells and invades the central nervous system (CNS) via anterograde transynaptic spread through axons in the optic nerve. Virus can also spread to the CNS via retrograde transport through the oculomotor nucleus that innervates extraocular muscles of the eye. Since retrograde infection of the CNS precedes anterograde transynaptic infection, the temporal sequence of infection of the CNS depends on the route of invasion. Thus, motor neurons are infected first (retrograde infection), followed by CNS neurons innervated by the optic nerve (anterograde transynaptic infection). This temporal separation in the appearance of virus in separate groups of neurons enabled us to compare the immune responses to different stages of CNS infection in the same animal. The data revealed focal trafficking of peripheral immune cells into areas of the CNS infected by retrograde or anterograde transport after PRV Becker was injected into the vitreous body of the eye. Cells expressing the leukocyte common antigen, CD45(+), entered the area of infection from local capillaries prior to any overt expression of neuropathology, and quantitative analysis demonstrated that the number of cells increased in proportion to the number of infected neurons within a given region. Recruitment of cells of monocyte/macrophage lineage began prior to the appearance of CD8(+) cytotoxic lymphocytes, which were, in turn, followed by CD4(+) lymphocytes. These data demonstrate that PRV replication in CNS neurons stimulates the focal infiltration of specific classes of CD45(+) cells in a time-dependent, temporally organized fashion that is correlated directly with the number of infected neurons and the time that a given region has been infected.

Spread of HSV-1 to the suprachiasmatic nuclei and retina in T cell depleted BALB/c mice

Following uniocular anterior chamber inoculation of the KOS strain of HSV-1 in euthymic BALB/c mice, virus spreads from the injected eye to the brain, and from the brain to the optic nerve and retina of the uninjected eye by day 7 post inoculation (p.i.), but the optic nerve and retina of the injected eye are not infected with virus. Infection of the optic nerve and retina of the injected eye is observed only in athymic mice or in mice depleted of both CD4+ and CD8+ T cells. To determine the role of T cells in virus spread, adult female BALB/c mice were thymectomized and T cell depleted. Mice were co-injected with the KOS strain of HSV-1 and RH116, a thymidine kinase-negative mutant of KOS containing the Escherichia coli lac Z gene. Animals were sacrificed on days 3-7 p.i., and the eyes and brains were examined for blue-stained, virus-infected cells. A difference in the timing of virus infection was observed in the area of the suprachiasmatic nuclei only in mice depleted of both CD4+ and CD8+ T cells, and in this group, the contralateral suprachiasmatic nucleus was infected two days earlier. Since one route by which virus could infect the retina of the injected eye is via connections of the contralateral suprachiasmatic nucleus to the ipsilateral optic nerve, these findings suggest that (a) retinitis observed in the injected eyes of mice depleted of both CD4+ and CD8+ T cells results from virus infection of the contralateral suprachiasmatic nucleus followed by spread of virus to the ipsilateral optic nerve and retina and (b) early HSV-1 infection of the contralateral suprachiasmatic nucleus is prevented by a T cell dependent mechanism.

Time course of neuronal sensitivity to light in the circadian timing system of the golden hamster

The mammalian suprachiasmatic nuclei of the hypothalamus (SCN) have been identified as containing the pacemaker for circadian rhythms. Photic stimulation is known to induce the expression of the immediate early gene c-fos in the SCN of rodents during the subjective night. In order to determine the exact time course of the light sensitivity in the different cell subgroups of the SCN, we have investigated the effect of a light pulse every hour of the subjective night in golden hamsters kept in constant darkness for 3 days. Three neuronal populations inside and outside the SCN have been identified as sensitive to light at different times of the subjective night. These findings indicate (1) that there are neurons outside the SCN that are activated by light which might be part of the pacemaker system, and (2) that the switch from light-induced phase delays to phase advances as illustrated by phase-response curves is linked to the appearance of sensitivity to light in the three cell populations defined here.

Ontogeny of Fos protein-like immunoreactivity in the suprachiasmatic nucleus

This study examined the normal development of neuronal activity in the suprachiasmatic nuclei (SCN) of rats between age 3-60 days, using Fos protein-like immunoreactivity (Fos-LI) as a marker. At age 3 days, Fos-positive nuclei are sparsely distributed throughout the SCN. Between age 3-10 days, the density of labeled nuclei increases significantly. Fos-LI labeling is maximal at 10 days. Between age 10-14 days, the number of labeled nuclei decreases and remains relatively constant thereafter, although the intensity of the reaction product diminishes as the animal matures. By age 60 days, the number of Fos-LI labeled nuclei in the SCN is substantially decreased and is essentially the same as in the 3-day-old rat. The appearance of Fos-LI nuclei in the SCN during development appears to reflect the development of visual system afferents to the nucleus as well as the development of intrinsic SCN synaptology.

Seasonal variation in NPY immunoreactivity in the suprachiasmatic nucleus of the jerboa (Jaculus orientalis), a desert hibernator

Using immunocytochemical techniques the seasonal variation in NPY immunoreactive fibers was investigated in the suprachiasmatic nucleus of both male and female jerboas. During the period of sexual quiescence (autumn), the amount of NPY immunoreactive fibers in the suprachiasmatic nucleus of both male and female jerboas was higher than in the period of sexual activity (spring-middle of summer). Compared with the respective control groups, castration during the period of sexual activity and testosterone or estrogen supplementation in sexually inactive animals did not affect NPY immunolabeling. These results indicate that the seasonal variation observed in NPY immunoreactivity in the suprachiasmatic nucleus of the jerboa is independent of circulating levels of steroid hormones. The possible influence of another hormonal system or a direct influence of an external factor such as photoperiod on NPY content in the suprachiasmatic nucleus remains to be determined.

T lymphocyte infiltration in the brain following anterior chamber inoculation of HSV-1

Following inoculation of the KOS strain of herpes simplex virus type 1 (HSV-1) into one anterior chamber of euthymic BALB/c mice, virus spreads from the injected eye to the central nervous system and from the central nervous system to the optic nerve and retina of only the uninoculated eye. In contrast, in athymic BALB/c mice or mice depleted of both CD4+ and CD8+ T cells, virus spreads to the optic nerve and retina of both the injected eye and the uninjected eye. To determine the location in the central nervous system where spread of virus to the optic nerve and retina of the injected eye is prevented, euthymic BALB/c mice were injected with a mixture of KOS and RH116, a mutant of KOS that contains the Escherichia coli beta-galactosidase (beta-gal) gene. Several animals were sacrificed each day; serial frozen sections of the brain were prepared and sequential sections were stained for beta-gal or for T cells. At all sites except the suprachiasmatic nuclei, virus and T cells arrived at approximately the same time. However, at day 5 post inoculation (PI), T cells were present in both the ipsilateral and the contralateral suprachiasmatic nuclei, but only the ipsilateral suprachiasmatic nucleus was virus-positive. Since virus spreads from the ipsilateral suprachiasmatic nucleus to the contralateral optic nerve, these results suggest that T cells infiltrating the area of the contralateral suprachiasmatic nucleus prior to the arrival of virus at this site prevent virus spread into the optic nerve of the inoculated eye.

Differential effects on substance P immunoreactivity in rat suprachiasmatic and olivary pretectal nuclei

We examined the effects of constant dark or constant light on substance P (SP) and/or neuropeptide Y (NPY) immunoreactive fibres in the rat suprachiasmatic nucleus (SCN) and olivary pretectal nucleus (OPT) by immunohistochemistry. After constant dark, SP immunoreactive fibres and terminals decreased slightly in the SCN, while they increased markedly in the OPT. After constant light, they increased markedly in the SCN, but were little changed in the OPT. NPY immunoreactive fibres and terminals in the SCN decreased slightly after after constant light, but there were no effects on these fibres after constant dark. These findings suggest that SP immunoreactive fibres are involved in mediating illumination discrimination in the SCN and/or OPT.

Distribution of substance P-immunoreactive elements in the preoptic area and the hypothalamus of the rat

The localization and morphology of neurons, processes, and neuronal groups in the rat preoptic area and hypothalamus containing substance P-like immunoreactivity were studied with a highly selective antiserum raised against synthetic substance P. The antiserum was thoroughly characterized by immunoblotting; only substance P was recognized by the antiserum. Absorption of the antiserum with synthetic substance P abolished immunostaining while addition of other hypothalamic neuropeptides had no effect on the immunostaining. The specificity of the observed immunohistochemical staining pattern was further confirmed with a monoclonal substance P antiserum. The distribution of substance P immunoreactive perikarya was investigated in colchicine-treated animals, whereas the distribution of immunoreactive nerve fibers and terminals was described in brains from untreated animals. In colchicine-treated rats, immunoreactive cells were reliably detected throughout the preoptic area and the hypothalamus. In the preoptic region, labeled cells were found in the anteroventral periventricular and the anteroventral preoptic nuclei and the medial and lateral preoptic areas. Within the hypothalamus, immunoreactive cells were found in the suprachiasmatic, paraventricular, supraoptic, ventromedial, dorsomedial, supramammillary, and premammillary nuclei, the retrochiasmatic, medial hypothalamic, and lateral hypothalamic areas, and the tuber cinereum. The immunoreactive cell groups were usually continuous with adjacent cell groups. Because of the highly variable effect of the colchicine treatment, it was not possible to determine the actual number of immunoreactive cells. Mean soma size varied considerably from one cell group to another. Cells in the magnocellular subnuclei of the paraventricular and supraoptic nuclei were among the largest, with a diameter of about 25 microns, while cells in the supramammillary and suprachiasmatic nuclei were among the smallest, with a diameter of about 12 microns. Immunoreactive nerve fibers were found in all areas of the preoptic area and the hypothalamus. The morphology, size, density, and number of terminals varied considerably from region to region. Thus, some areas contained single immunoreactive fibers, while others were innervated with such a density that individual nerve fibers were hardly discernible. During the last decade, knowledge about neural organization of rodent hypothalamic areas and mammalian tachykinin biochemistry has increased substantially. In the light of these new insights, the present study gives comprehensive morphological evidence that substance P may be centrally involved in a wide variety of hypothalamic functions. Among these could be sexual behavior, pituitary hormone release, and water homeostasis.

Localization of vasopressin-, vasoactive intestinal polypeptide-, peptide histidine isoleucine- and somatostatin-mRNA in rat suprachiasmatic nucleus

Messenger RNAs (mRNA) coding for vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI), somatostatin and vasopressin were localized in the suprachiasmatic nucleus (SCN) of the rat hypothalamus using in situ hybridization histochemistry. Specific mRNA coding for each of these peptides was distributed in areas coextensive with the immunohistochemical localization of the appropriate peptide. The autoradiographic signal produced with probes to VIP and PHI created dense concentrations of silver grains over neuronal perikarya in the ventrolateral SCN, and the coextensive distribution of both VIP- and PHI-mRNAs suggests that both peptides are synthesized within the same neurons. The distribution of somatostatin-mRNA was distinct from the of VIP and PHI. Labeled neurons are observed at the interface of the two SCN subdivisions and the distribution of these neurons is identical to those shown to contain somatostatin immunoreactivity. Vasopressin-mRNA is also differentially concentrated within neurons in the dorsomedial subdivision of the SCN in an area that is coextensive with vasopressin-immunoreactive perikarya. The discrete pattern of hybridization for each of these mRNAs indicates that each of these peptides are synthesized in SCN neurons and reaffirms the differential distribution of each of these chemically defined cell populations within cytoarchitecturally distinct subdivisions of the nucleus.

Identification of neuropeptide Y immunoreactivity in the suprachiasmatic nucleus and the lateral geniculate nucleus of some mammals

The distribution of neuropeptide Y (NPY) immunoreactivity in the suprachiasmatic nucleus (SCN) and the lateral geniculate nucleus (LGN) of 5 kinds of mammals was studied using the peroxidase-anti-peroxidase method. In the SCN of the rat, hamster, chipmunk and cat, NPY-immunoreactive fibers were detected, particularly in the ventral part. In the 3 rodents and the cat, the somata and fibers of NPY-immunoreactive neurons were observed in the LGN. However, immunoreactive structures were not found in the SCN or LGN of the monkey. These results indicate that NPY immunoreactivity in the monkey LGN-SCN tract is absent.