The ACTH-immunoreactive system in the brain of the white-crowned sparrow, Zonotrichia leucophrys gambelii (Passeriformes, Emberizidae)

The transcription factor nuclear factor interleukin 6 mediates pro- and anti-inflammatory responses during LPS-induced systemic inflammation in mice

The transcription factor nuclear factor interleukin 6 (NF-IL6) plays a pivotal role in neuroinflammation and, as we previously suggested, hypothalamus-pituitary-adrenal-axis-activation. Here, we investigated its contribution to immune-to-brain communication and brain controlled sickness symptoms during lipopolysaccharide (LPS)-induced (50 or 2500 μg/kg i.p.) systemic inflammation in NF-IL6-deficient (KO) or wildtype mice (WT). In WT LPS induced a dose-dependent febrile response and reduction of locomotor activity. While KO developed a normal fever after low-dose LPS-injection the febrile response was almost abolished 3-7 h after a high LPS-dose. High-dose LPS-stimulation was accompanied by decreased (8 h) followed by enhanced (24 h) inflammation in KO compared to WT e.g. hypothalamic mRNA-expression including microsomal prostaglandin E synthase, inducible nitric oxide synthase and further inflammatory mediators, neutrophil recruitment to the brain as well as plasma levels of inflammatory markers such as IL-6 and IL-10. Interestingly, KO showed reduced locomotor activity even under basal conditions, but enhanced locomotor activity to novel environment stress. Hypothalamic-pituitary-adrenal-axis-activity of KO was intact, but tryptophan-metabolizing enzymes were shifted to enhanced serotonin production and reuptake. Overall, we showed for the first time that NF-IL6 plays a dual role for sickness response and immune-to-brain communication: acting pro-inflammatory at 8h but anti-inflammatory at 24 h after onset of the inflammatory response reflecting active natural programming of inflammation. Moreover, reduced locomotor activity observed in KO might be due to altered tryptophan metabolism and serotonin reuptake suggesting some role for NF-IL6 as therapeutic target for depressive disorders.

Activation of the inflammatory transcription factor nuclear factor interleukin-6 during inflammatory and psychological stress in the brain

BACKGROUND

The transcription factor nuclear factor interleukin 6 (NF-IL6) is known to be activated by various inflammatory stimuli in the brain. Interestingly, we recently detected NF-IL6-activation within the hypothalamus-pituitary-adrenal (HPA)-axis of rats after systemic lipopolysaccharide (LPS)-injection. Thus, the aim of the present study was to investigate whether NF-IL6 is activated during either, inflammatory, or psychological stress in the rat brain.

METHODS

Rats were challenged with either the inflammatory stimulus LPS (100 μg/kg, i.p.) or exposed to a novel environment. Core body temperature (Tb) and motor activity were monitored using telemetry, animals were killed at different time points, brains and blood removed, and primary cell cultures of the anterior pituitary lobe (AL) were investigated. Analyses were performed using immunohistochemistry, RT-PCR, and cytokine-specific bioassays.

RESULTS

Stress stimulation by a novel environment increased NF-IL6-immunoreactivity (IR) in the pituitary's perivascular macrophages and hypothalamic paraventricular cells and a rise in Tb lasting approximately 2 h. LPS stimulation lead to NF-IL6-IR in several additional cell types including ACTH-IR-positive corticotrope cells in vivo and in vitro. Two other proinflammatory transcription factors, namely signal transducer and activator of transcription (STAT)3 and NFκB, were significantly activated and partially colocalized with NF-IL6-IR in cells of the AL only after LPS-stimulation, but not following psychological stress. In vitro NF-IL6-activation was associated with induction and secretion of TNFα in folliculostellate cells, which could be antagonized by the JAK-STAT-inhibitor AG490.

CONCLUSIONS

We revealed, for the first time, that NF-IL6 activation occurs not only during inflammatory LPS stimulation, but also during psychological stress, that is, a novel environment. Both stressors were associated with time-dependent activation of NF-IL6 in different cell types of the brain and the pituitary. Moreover, while NF-IL6-IR was partially linked to STAT3 and NFκB activation, TNFα production, and ACTH-IR after LPS stimulation; this was not the case after exposure to a novel environment, suggesting distinct underlying signaling pathways. Overall, NF-IL6 can be used as a broad activation marker in the brain and might be of interest for therapeutic approaches not only during inflammatory but also psychological stress.

Characteristics of the proopiomelanocortin system in the outdoor-bred domestic gander. I. ACTH and beta-endorphin levels in the brain, pituitary, and plasma

Immunoreactive (ir-) adrenocorticotropic hormone (ACTH) and beta-endorphin (beta E) levels were determined in seven brain regions, in the three pituitary lobes, and in the plasma of the domestic gander by specific radioimmunoassays. In the brain regions studied the relative concentrations of ir-ACTH and ir-beta E were the highest in the mediobasal hypothalamus and in the paraventricular nucleus. There were lower levels of these peptides in the supraoptic nucleus, in the septum, and in the dorsal thalamus. Very low ir-ACTH and -beta E contents were found in the archistriatum and in the lobus parolfactorius. In the pars distalis of the pituitary gland the cephalic lobe contained about 10 times more ir-ACTH (3596 pmol/lobe) and 4 times more ir-beta E (867 pmol/ lobe) than the caudal lobe (383 pmol/lobe and 189 pmol/lobe, respectively). Sephadex G-50 chromatography of pooled cephalic and caudal lobe extracts resulted in two distinct ir-beta E peaks, with elution volumes corresponding to the mammalian beta-lipotropin and beta E, and three ir-ACTH peaks, the second one coeluting with mammalian ACTH. In the neural lobe the ir-ACTH/-beta E concentrations were similar to those in the hypothalamus. Resting plasma ir-ACTH (12.8 +/- 1.47 pmol/ml) but not ir-beta E (31.4 +/- 1.22 pmol/ml) levels were significantly increased following castration (to 41.4 +/- 1.11 pmol/ml). Serial blood sampling indicated pulsatile ir-beta E secretion (mean, coefficients of variation, and minimum-maximum range: 17.5, 62.78, and 2.9-49.7, respectively, for gander 1 and 23.3, 62.85, and 5.00-61.5, respectively, for gander 2).

Comparative localization of corticotropin and corticotropin releasing factor-like peptides in the brain and hypophysis of a primitive vertebrate, the sturgeon Acipenser ruthenus L

The sturgeon is a primitive actinopterigian fish that, unlike modern teleosts, possess a portal vascular system that connects a true median eminence with the anterior pituitary as in mammals. The occurrence and localization of corticotropin and corticotropin releasing factor-like immunoreactivies were examined in the brain of the sturgeon (Acipenser ruthenus L.) by immunocytochemistry with antisera raised against synthetic non-conjugated human corticotropin, and rat/human corticotropin releasing factor. In the hypothalamus, corticotropin-immunoreactive parvicellular perikarya were found in the infundibular nucleus and in dendritic projections to the infundibular recess. In addition, ependymofugal corticotropin-immunoreactive fibres were found to terminate in the ventral hypothalamus. Corticotropin releasing factor-immunoreactive neurons were found in the rostral portion of the ventral hypothalamus (tuberal nucleus), and in the vicinity of the rostral aspect of the lateral recess. These cells projected to the dorsal hypothalamus, the ventral hypothalamus, the median eminence, the anterior and posterior telencephalon, the tegmentum mesencephali, and the pars nervosa of the pituitary. An affinity-purified UI antiserum failed to stain the sturgeon hypothalamus. Corticotrophs in the rostral pars distalis of the pituitary were also corticotropin-immunoreactive. In the neurointermediate lobe, only about 50% of cells of the pars intermedia appeared to be corticotropin-positive, the rest appeared unstained. These results suggest that the presence of corticotropin-like and corticotropin releasing factor-like peptides in the brain is a relatively early event in vertebrate evolution, already occurring in Chondrostean/Actinopterigian fishes, as exemplified by A. ruthenus. The close spatial relationship between corticotropin releasing factor immunoreactivity and corticotropin immunoreactivity in the ventral hypothalamus of A. ruthenus supports a possible interaction between the two systems in that area of the sturgeon brain. The pars intermedia might be an important site for corticotropin synthesis, even though the possibility cannot be excluded that the antiserum was recognizing the proopiomelanocortin molecule. The occurrence of corticotropin releasing factor immunoreactivity in the region of median eminence/pars intermedia of the sturgeon suggests that the sturgeon corticotropin releasing factor might regulate the adenohypophyseal release of proopiomelanocortin products in the same manner as in other vertebrates. The presence of extrahypothalamic corticotropin releasing factor-immunoreactive projections suggests further neuromodulatory functions for this peptide in A. ruthenus.

Peptides for calling? An immunohistochemical study of the avian n. intercollicularis

We used two phylogenetically distant avian species (dark-eyed junco, hyemalis, Passeriformes; domestic pigeon, Columba livia, Columbiformes) to determine the immunocytochemical distribution of opioid (leucine-enkephalin, dynorphin B) and non-opioid (adrenocorticotropic hormone) peptides in the n. intercollicularis (ICo), a midbrain region which plays a central role in the control of vocalizations. We found that, in both species, the peptides under study are present as fibers and terminal-like structures, and are similarly distributed. The n. dorsomedialis intercollicularis division contains much less immunoreactivity than the rest of the ICo. Based on this and previous studies, we propose that opioid peptides, possibly transported from the preoptic and hypothalamic regions of the diencephalon to the ICo, regulate vocal behavior by altering respiratory function rather than syringeal mechanisms.

Corticotropin-like immunoreactivity in the brain of intact, hypophysectomized, cortisol- and metopirone-treated eels. Comparison with changes in pituitary corticotropes and brain corticotropin-releasing factor

An ACTH-like peptidergic system was demonstrated in the brain of three teleost species by immunocytochemistry. In order to investigate the origin of brain ACTH and factors modulating its synthesis, similar techniques were applied to the brain of eels (1) submitted to hypophysectomy in order to suppress pituitary ACTH and plasma cortisol, (2) injected with cortisol to inhibit pituitary ACTH synthesis and release, and (3) injected with metopirone to block cortisol synthesis and stimulate ACTH synthesis and release. Hypophysectomized eels showed a normal distribution of immunoreactive perikarya in the ventral hypothalamus and fibers in the brain, suggesting that brain ACTH does not arise from the pituitary. In cortisol-treated eels immunostaining was markedly reduced in brain perikarya and pituitary corticotropes, suggesting a reduced synthesis. In metopirone-injected eels, one third of the animals showed an increased immunostaining in perikarya and a dense network of immunoreactive fibers, suggesting that ACTH synthesis was increased. Brain ACTH was not affected in other animals. Pituitary corticotropes were rapidly degranulated. Responses of ACTH in the brain and pituitary occur independently when cortisol synthesis is inhibited. These responses are compared to those of the corticotropin-releasing factor system in the same eels.

Distribution of glucocorticoid receptor-like immunoreactivity in the brain, and its relation to CRF and ACTH immunoreactivity in the hypothalamus of the japanese quail, Coturnix coturnix japonica

Monoclonal antibody (MAb49) against the rat liver glucocorticoid receptor was used to evaluate glucocorticoid receptor (GR) immunoreactive structures in the brain of the japanese quail, Coturnix coturnix japonica. Using the avidin-biotin technique, the immunoreaction was present in the nerve cell nuclei in intact male birds. High density of glucocorticoid receptor-like immunoreactivity was found in the tubero-infundibular area, nucleus paraventricularis, posteromedialis and lateralis hypothalami, lateral septum and in some brainstem nuclei. Cerebellar cortex was also immunopositive. In contrast to mammals, no immunoreactive cell nuclei were found in the hippocampal region. The glucocorticoid receptors were colocalized with adrenocorticotropin (ACTH) immunoreactivity in the tubero-infundibular region, while corticotropin releasing factor (CRF) positive cells in the paraventricular nucleus did not contain glucocorticoid receptor-like immunoreactivity in their cell nuclei.