Evidence for the modulation of nociception in mice by central mast cells

BACKGROUND

Hyperalgesia that develops following nerve ligation corresponds temporally and in magnitude with the number of thalamic mast cells located contralateral to the ligature. We tested the possibility that mast cells modulate nociception centrally, similar to their role in the periphery.

METHODS

We examined the central effect of two hyperalgesic compounds that induce mast cell degranulation and of stabilized mast cells using cromolyn.

RESULTS

Thermal hyperalgesia (tail flick) induced by nerve growth factor (NGF, a neurotrophic compound) and mechanical hyperalgesia (von Frey) induced by dynorphin A (1-17) (opioid compound) each correlated with the per cent of thalamic mast cells that were degranulated. Degranulation of these mast cells by the central injection of compound 48/80, devoid of neurotrophic or opioid activity, was sufficient to recapitulate thermal hyperalgesia. Stabilization of mast cells by central injections of cromolyn produced no analgesic effect on baseline tail flick or von Frey fibre sensitivity, but inhibited thermal hyperalgesia produced by compound 48/80 and tactile hyperalgesia induced by dynorphin and by Freund's complete adjuvant. Finally, chemical nociception produced by the direct activation of nociceptors by formalin (phase I) was not inhibited by centrally injected cromolyn whereas chemical nociception dependent on central sensitization (formalin-phase II and acetic acid-induced abdominal stretches) was.

CONCLUSIONS

These convergent lines of evidence suggest that degranulation of centrally located mast cells sensitizes central nociceptive pathways leading to hyperalgesia and tonic chemical sensitivity.

SIGNIFICANCE

Hyperalgesia induced by spinal nerve ligation corresponds temporally and in magnitude with degranulation of thalamic mast cells. Here, we provide evidence that hyperalgesia induced by NGF, formalin and dynorphin also may depend on mast cell degranulation in the CNS whereas cromolyn, a mast cell stabilizer, blocks these effects in mice.

Intrathecal urocortin I in the spinal cord as a murine model of stress hormone-induced musculoskeletal and tactile hyperalgesia

Stress is antinociceptive in some models of pain, but enhances musculoskeletal nociceptive responses in mice and muscle pain in patients with fibromyalgia syndrome. To test the hypothesis that urocortins are stress hormones that are sufficient to enhance tactile and musculoskeletal hyperalgesia, von Frey fibre sensitivity and grip force after injection of corticotropin-releasing factor (CRF), urocortin I and urocortin II were measured in mice. Urocortin I (a CRF1 and CRF2 receptor ligand) produced hyperalgesia in both assays when injected intrathecally (i.t.) but not intracerebroventricularly, and only at a large dose when injected peripherally, suggesting a spinal action. Morphine inhibited urocortin I-induced changes in nociceptive responses in a dose-related fashion, confirming that changes in behaviour reflect hyperalgesia rather than weakness. No tolerance developed to the effect of urocortin I (i.t.) when injected repeatedly, consistent with a potential to enhance pain chronically. Tactile hyperalgesia was inhibited by NBI-35965, a CRF1 receptor antagonist, but not astressin 2B, a CRF2 receptor antagonist. However, while urocortin I-induced decreases in grip force were not observed when co-administered i.t. with either NBI-35965 or astressin 2B, they were even more sensitive to inhibition by astressin, a non-selective CRF receptor antagonist. Together these data indicate that urocortin I acts at CRF receptors in the mouse spinal cord to elicit a reproducible and persistent tactile (von Frey) and musculoskeletal (grip force) hyperalgesia. Urocortin I-induced hyperalgesia may serve as a screen for drugs that alleviate painful conditions that are exacerbated by stress.

After a cold conditioning swim, UCP2-deficient mice are more able to defend against the cold than wild type mice

Uncoupling protein 2 (UCP2) is widely distributed throughout the body including the brain, adipose tissue and skeletal muscles. In contrast to UCP1, UCP2 does not influence resting body temperature and UCP2-deficient (-/-) mice have normal thermoregulatory responses to a single exposure to cold ambient temperatures. Instead, UCP2-deficient mice are more anxious, exhibit anhedonia and have higher circulating corticosterone than wild type mice. To test the possible role of UCP2 in depressive behavior we exposed UCP2-deficient and wild type mice to a cold (26°C) forced swim and simultaneously measured rectal temperatures during and after the swim. The time that UCP2-deficient mice spent immobile did not differ from wild type mice and all mice floated more on day 2. However, UCP2-deficient mice were more able to defend against the decrease in body temperature during a second daily swim at 26°C than wild type mice (area under the curve for wild type mice: 247.0±6.4; for UCP2-deficient mice: 284.4±3.8, P<0.0001, Student's t test). The improved thermoregulation of wild type mice during a second swim at 26°C correlated with their greater immobility whereas defense against the warmth during a swim at 41°C correlated better with greater immobility of UCP2-deficient mice. Together these data indicate that while the lack of UCP2 has no acute effect on body temperature, UCP2 may inhibit rapid improvements in defense against cold, in contrast to UCP1, whose main function is to promote thermogenesis.

Cell sorting in a Petri dish controlled by computer vision

Fluorescence-activated cell sorting (FACS) applying flow cytometry to separate cells on a molecular basis is a widespread method. We demonstrate that both fluorescent and unlabeled live cells in a Petri dish observed with a microscope can be automatically recognized by computer vision and picked up by a computer-controlled micropipette. This method can be routinely applied as a FACS down to the single cell level with a very high selectivity. Sorting resolution, i.e., the minimum distance between two cells from which one could be selectively removed was 50–70 micrometers. Survival rate with a low number of 3T3 mouse fibroblasts and NE-4C neuroectodermal mouse stem cells was 66±12% and 88±16%, respectively. Purity of sorted cultures and rate of survival using NE-4C/NE-GFP-4C co-cultures were 95±2% and 62±7%, respectively. Hydrodynamic simulations confirmed the experimental sorting efficiency and a cell damage risk similar to that of normal FACS.

Spontaneous locomotor activity correlates with the degranulation of mast cells in the meninges rather than in the thalamus: disruptive effect of cocaine

Mast cells are located in the central nervous system (CNS) of many mammals and stress induces their degranulation. We postulated that mast cells are associated with wakefulness and stimulatory tone in the CNS, as reflected by spontaneous motor activity. Because stress also precipitates drug-seeking behavior in cocaine addicts, we also postulated that cocaine manifests its effects through this relationship. We investigated the influence of single and repeated injections of cocaine on circulating corticosterone, motor activity and degranulation of mast cells in both the thalamus and meninges of mice. Mice were subjected to 5 consecutive days of cocaine or saline followed by a single injection of cocaine or saline 11 days later. Spontaneous locomotor activity was measure for 1h after the final injection before death. Neither a single injection nor prior treatment with cocaine increased motor activity compared to saline-injected controls, however, repeated administration of cocaine induced a significant sensitization to its behavioral effect when delivered 11 days later. In mice that received only saline, motor activity correlated positively with mast cell degranulation in the meninges but not in the thalamus. Cocaine, regardless of the treatment schedule, disrupted this correlation. The concentration of corticosterone did not differ amongst groups and did not correlate with either behavior or mast cell parameters in any group. The correlation between behavioral activity and the mast cell degranulation in the meninges suggests that these parameters are linked. The disruptive effect of cocaine on this relationship indicates a role downstream from mast cells in the regulation of motor activity.

Direct inhibitory effect of glucocorticoids on corticotrophin-releasing hormone gene expression in neurones of the paraventricular nucleus in rat hypothalamic organotypic cultures

Corticotrophin-releasing hormone (CRH) in the parvocellular neurosecretory neurones of hypothalamic paraventricular nucleus governs neuroendocrine stress cascade and is the major target of the negative feedback effect of corticosteroids. To assess whether glucocorticoids exert their inhibitory effect on CRH expression directly on parvocellular neurones or indirectly through a complex neuronal circuit, we examined the effect of corticosterone (CORT) and dexamethasone (DEX) on CRH mRNA levels in slice explant cultures of the rat hypothalamus. Organotypic slice cultures were prepared from 6 days old rat pups and maintained in vitro for 14 days. CRH mRNA expression was measured by in situ hybridisation histochemistry. Under basal conditions, CRH mRNA expressing cells were exclusively revealed in the paraventricular region along the third ventricle. Inhibition of action potential spike activity by tetrodotoxin (TTX, 1 microm) reduced CRH mRNA signal in the organotypic cultures. CORT (500 nm) or DEX (50 nm) treatment for 24 h significantly inhibited CRH expression in the parvocellular neurones and this effect of corticosteroids was not affected following blockade of voltage dependent sodium channels by TTX. Forskolin-stimulated CRH mRNA levels in the paraventricular nucleus were also inhibited by CORT or DEX in the presence and in the absence of TTX. These studies identify paraventricular CRH neurones as direct target of corticosteroid feedback. Type II corticosteroid receptor agonists act directly on paraventricular neurones to inhibit basal and forskolin-induced CRH mRNA expression in explant cultures of the rat hypothalamus.

Measurement of immediate-early gene activation- c-fos and beyond

Immediate-early genes (IEG) are powerful tools for identifying activated neurosecretory neurones and extended circuits that affect neuroendocrine functions. The generally acknowledged scenario is when cells became activated, IEGs expressed and IEG-encoded transcription factors affect target gene expression. However, there are several examples in which: (i) neuronal activation occurs without induction of IEGs; (ii) IEG induction is not related to challenge-induced neuropeptide expression; and (iii) markers of neuronal activation are not expressed in chronically activated neurones. In spite of these limitations, the use of c-Fos and other regulatory- or effector transcription factors as markers of neuronal activation will continue to be an extremely powerful technique. Recently-developed models, including transgenic mice expressing different marker genes under the regulation of IEG promoters, will help to monitor neuronal activity in vivo or ex vivo and to reveal connection between activated neurones. Furthermore, combinations between novel imaging techniques, such as magnetic resonance and IEG-based mapping strategies, will open new means with which to study functional activity in the neurosecretory systems.

Movement-evoked hyperalgesia induced by lipopolysaccharides is not suppressed by glucocorticoids

Systemic exposure to lipopolysaccharides (LPS) produces a variety of effects, including movement-evoked hyperalgesia that can be measured using the grip force assay in mice. Because both lethality and enhanced sensitivity to cutaneous pain following exposure to endotoxins have each been attributed to inflammatory mediators, we explored the possibility that LPS-induced movement-evoked hyperalgesia is also sensitive to manipulations of glucocorticoids that regulate these other LPS responses. We found that the hyperalgesic effect of LPS (5mg/kg s.c.) in mice that were adrenalectomized did not differ from that in control mice that were sham operated, even though mortality after LPS was potentiated by adrenalectomy. The development of tolerance to the movement-evoked hyperalgesic effect of LPS also did not differ between adrenalectomized and sham-operated control mice. In addition, mifepristone (25mg/kg s.c.), a glucocorticoid antagonist, did not attenuate the hyperalgesic effect of LPS (2mg/kg s.c.), yet this dose of mifepristone was sufficient to enhance the incidence of lethality induced by LPS. Enhancement of glucocorticoid activity by two injections of dexamethasone (1mg/kg s.c.) had no effect on the degree of hyperalgesia in mice injected with LPS (5mg/kg s.c.), yet this dose of dexamethasone was sufficient to attenuate the incidence of mortality induced by LPS in adrenalectomized mice. Finally, morphine (10mg/kg i.p.) reversed the decrease in grip force caused by LPS (5mg/kg i.p.), supporting the interpretation that decreases in grip force produced by LPS reflect muscle hyperalgesia that is not sensitive to glucocorticoids.

Mast cells accumulate in the anogenital region of somatosensory thalamic nuclei during estrus in female mice

Mast cells are located in the mammalian thalamus where their numbers are sensitive to reproductive hormones. To evaluate whether differences between sexes and over the estrus cycle influence the nuclear distribution of mast cells in mice, we mounted a comprehensive analysis of their distribution in males compared to females and in females over the estrus cycle. Compared to males, mast cells were more numerous in the lateral intralaminar and posterior nuclei of females during estrus and in the ventral posterolateral (VPL) and medial geniculate nuclei during proestrus. During estrus, mast cells were especially concentrated in those regions within the VPL and posterior thalamic nuclei that receive somatosensory information from the anogenital region. Treatment of ovariectomized mice with estrogen increased the number and the percent of mast cells that were degranulated compared to that after ovariectomy alone, an effect that was most apparent in the lateral intralaminar, VPL and posterior nuclei. In estrogen-primed, ovariectomized females, progesterone delivered 5 h before tissue collection counteracted the effects of estrogen. Cromolyn, a mast cell stabilizer, injected centrally 1 h prior to and 24 h after estrogen in ovariectomized mice, prevented the increase in number of mast cells in the whole thalamus and in the intralaminar, VPL and posterior nuclei. This suggests that estrogen induces hyperplasia by a mechanism that involves mast cell degranulation. Based on the discrete anatomical location of mast cells in areas of somatosensory nuclei that receive anogenital input together with the temporal correspondence of these cells with estrus, mast cells are well situated to influence sensory input in females during mating.

Central autonomic control of the bone marrow: multisynaptic tract tracing by recombinant pseudorabies virus

Bone marrow is the primary place of hematopoiesis, where the development, survival and release of multipotent stem cells, progenitors, precursors and mature cells are under continuous humoral and neural control. Dense network of nerve fibers, containing various neurotransmitters is found in the bone marrow, however, the central neuronal circuit that regulates the activities of the bone marrow through these fibers remained unexplored. Transsynaptically connected neurons were mapped by virus-based transneuronal tracing technique using two isogenic, genetically engineered pseudorabies viruses, Bartha-DupGreen and Ba-DupLac expressing green fluorescent protein and beta-galactosidase, respectively. Bartha-DupGreen was injected into the femoral bone marrow of male rats and the progression of infection was followed 4-7 days post-inoculation. Virus-labeled cells were revealed in ganglia of the paravertebral chain and in the intermediolateral cell column of the lower thoracic spinal cord. Neurons were retrogradely labeled in the C1, A5, A7 catecholaminergic cell groups and several other nuclei of the ventrolateral and ventromedial medulla, the periaqueductal gray matter, the paraventricular and other hypothalamic nuclei, and in the insular and piriform cortex. Nerve transections and double-virus tracing from the bone marrow and the surrounding muscles were used to confirm the specific spreading of the virus. These results provide anatomical evidence for the CNS control of the bone marrow and identify putative brain areas, which are involved in autonomic regulation of the hematopoiesis, the release of progenitor cells, the blood supply and the immune cell function in the bone marrow.

Chronic daily intrathecal injections of a large volume of fluid increase mast cells in the thalamus of mice

Mast cells are found in the central nervous system (CNS) as well as in the periphery. In the brain of mice, they are localized primarily in the thalamus and meninges. Although their numbers increase in response to stress, the mediator of their recruitment is not known. During studies in which drugs were delivered intrathecally in a volume sufficiently large to distribute to the brain, we discovered that repeated daily injections of this large volume increased the number of mast cells in the thalamus. The increase was not due to changes in electrolyte composition of the cerebrospinal fluid (CSF) as chronically administered artificial CSF produced similar effects. Repeated injections of even small volumes (2 mul) increased mast cells in the medial intralaminar (Med), ventral posterior (VP) and posterior (Po) nuclei. Increasing the volume injected daily to 20 mul increased mast cells in the lateral intralaminar (Lat), laterodorsal (LD), ventrolateral (VL) and lateral geniculate (LG) nuclei and further increased those in the lateral extension of the Po nucleus. Thus, small and large volumes augment distinct populations of mast cells. While stem cell factor (SCF) is abundant in the CNS and is chemotactic to mast cells in the periphery, thalamic mast cells in the rodent do not express c-kit, the SCF receptor, suggesting that this factor may not be responsible for the effect. Consistent with this, centrally injected SCF was incapable of increasing thalamic mast cell populations after either single or chronic (21 days) daily injections compared to the effect of saline alone. Although the mechanism is not known, repeated injections of a large volume of fluid dramatically increase mast cells in the CNS, a phenomenon that may be relevant to clinical conditions of increased CSF pressure or volume.

Unilateral spinal nerve ligation leads to an asymmetrical distribution of mast cells in the thalamus of female but not male mice

Mast cells are restricted to the leptomeninges and thalamus of healthy mice. These populations are increased by stress and highly sensitive to reproductive hormones. To examine the influence of nociception, a form of stress, on thalamic mast cells, we ligated the left fifth lumbar spinal nerve of male and female mice to induce hyperalgesia. Two, 7 and 14 days later, mice were killed and thalami examined histologically using toluidine blue stain. The total number of thalamic mast cells was not influenced by ligation of the spinal nerve compared to sham-operation in either female or male mice. However, in females, the percent of thalamic mast cells located on the side of the thalamus contralateral to the ligation was greater on days 2 and 7, coincident with mechanical hyperalgesia. At these times, areas in which mast cells were most dense contralateral to nerve-injury included the posterior (Po) and lateral geniculate (LG) nuclei compared to their symmetrical distribution in sham-operated mice. These data suggest that local nociceptive signals to each side of the thalamus rather than stress hormones influence the location of mast cells during the development of allodynia and hyperalgesia. In addition, both hyperalgesia and mast cell distribution induced by nerve-ligation differ in females compared to males, reflecting a novel neuroimmune response to pain within the CNS.

Tolerance develops to the effect of lipopolysaccharides on movement-evoked hyperalgesia when administered chronically by a systemic but not an intrathecal route

Single exposures to lipopolysaccharides (LPS) produce deep tissue pain in humans and cutaneous hyperalgesia in rodents. While tolerance develops to many effects of LPS, sensitization to hyperalgesia is documented after a single injection. To determine the effect of long-term exposure to LPS, we explored the chronic effect of LPS on movement-evoked pain using a new assay based on grip force in mice. We found that a single systemic injection of LPS (i.p. or s.c.) induced a dose-related decrease in forelimb grip force responses beginning 6-8 h after injection and peaking between 9 and 24 h. The consequence of LPS is likely hyperalgesia rather than weakness as these decreases were rapidly attenuated by either 10 mg/kg of morphine i.p. or 10 microg of morphine injected intrathecally (i.t.). Complete tolerance to this hyperalgesia developed after repeated injections of LPS at doses of 0.9 mg/kg i.p. or 5 mg/kg s.c. Tolerance began after a single injection and was fully developed after as few as four injections of 5 mg/kg of LPS delivered s.c. The concentration of circulating LPS 5 h after a single parenteral injection was less in LPS-tolerant mice than naïve controls, suggesting that tolerance may result from a more efficient clearance of LPS from the circulation. Injected i.t., LPS also induced hyperalgesia, however, tolerance did not develop to multiple injections by this route. There was no cross-tolerance between s.c. and i.t. injections of LPS. These data indicate that decreases in grip force are a sensitive measure of LPS-induced movement-evoked hyperalgesia and that tolerance develops to parenteral but not central hyperalgesic effects of LPS.

GABAergic mechanisms constraining the activity of the hypothalamo-pituitary-adrenocortical axis

There are two major inhibitory mechanisms that constrain the activity of the hypothalamo-pituitary-adrenocortical axis: the hormonal negative feedback and the neural inhibition including that posed by the GABAergic neurons. This chapter summarizes our recent morphologic and functional findings on the role of gamma-aminobutyric acid (GABA) in the transcriptional regulation of hypophyseotropic neuropeptide genes in the parvocellular neurosecretory cells of the hypothalamic paraventricular nucleus (PVH). We used organotypic hypothalamic slice cultures and in vivo microinjection protocols in combination with in situ histologic and ultrastructural procedures to address the role of local interneurons in the regulation of hypothalamic effector neurons. Under basal conditions, an intrinsic GABAergic mechanism in the PVH microenvironment was revealed that by itself, without limbic contribution, impinged a tonic inhibitory influence on the parvocellular corticotropin-releasing hormone (CRH) neurons in vitro. In vivo, remote inputs were superimposed on the local circuit, allowing differential transcriptional regulation of CRH and arginine vasopressin (AVP) genes in the hypophyseotropic neurons. During stress, GABAergic cells that are known to project to the PVH become activated and are involved in restraining the cellular, transcriptional, and hormonal responses to stress.

Naloxone-induced morphine withdrawal increases the number and degranulation of mast cells in the thalamus of the mouse

Naloxone-induced jumping in morphine-dependent mice is inhibited by cromolyn, a mast cell stabilizer, suggesting that this characteristic withdrawal behavior results from degranulation of mast cells. Because withdrawal is considered as a central phenomenon, degranulation of mast cells located within the CNS may influence aspects of opioid withdrawal. The present study evaluates histologically whether naloxone, injected into opioid dependent mice, induces degranulation of mast cells. Seventy-two hours after the s.c. implantation of a 75 mg morphine pellet, the number and degranulation of thalamic mast cells did not differ from those in placebo-implanted controls. However, two injections of 50 mg/kg of naloxone, 30 and 60 min before tissue collection, increased the number of degranulated mast cells compared to those in mice injected with saline. Analysis throughout the entire thalamus (90 40-micro sections) revealed increases in the total number of mast cells as well as the number that were degranulated, especially in sections 52-60, corresponding to Bregma -2.18 to 2.54. Here, mast cells were clustered in the IGL and VPL/VPM nuclei, and redistributed from the ventromedial to the dorsolateral aspects of the Po and PF nuclei during withdrawal. Degranulation was also greater throughout the LD, LP nuclei during withdrawal. These data reveal a novel neuroimmune reaction to opioid withdrawal in the CNS.

Functional heterogeneity of the responses of histaminergic neuron subpopulations to various stress challenges

In rats, the cell bodies of the histaminergic neuronal system are clustered in five distinct cell groups (E1-E5) within the posterior hypothalamus. On the basis of tract tracing studies, these histaminergic subgroups have been regarded as one functional unit. In addition to its well-characterized role in arousal, locomotor activity, metabolism, feeding, drinking and behaviour, as well as in coordination of autonomic functions, histamine has been implicated in regulation of the hypothalamo-pituitary-adrenocortical axis during stress. To address the capacity of different histaminergic subgroups to respond to various challenges, we revealed c-Fos, the immediate early gene marker of activated neurons, in histamine synthesizing neurons by combining c-Fos immunocytochemistry with in situ hybridization of histidine decarboxylase (HDC) mRNA. Compared to the negligible colocalization of these markers in control rats, restraint, insulin-induced hypoglycaemia and foot shock resulted in specific activation of histamine synthesizing neurons of the E4 and E5 subgroup in the tuberomammillary region. Up to 36% of HDC mRNA-expressing cells show c-Fos immunoreactivity in the E5 region. In addition, some neurons of the E1, E2 and E3 histaminergic groups were activated after restraint stress. Many less c-Fos-positive histaminergic neurons were detected after immobilization and dehydration. Ether stress, acute hyperosmotic stimulus or injection of bacterial lipopolysaccharide did not activate hypothalamic HDC-positive neurons. These results suggest, for the first time, the functional heterogeneity of histaminergic neuron population, the components of which are recruited in a stressor- and subgroup-specific manner.

Role of hypothalamic inputs in maintaining pituitary-adrenal responsiveness in repeated restraint

The role of hypothalamic structures in the regulation of chronic stress responses was studied by lesioning the mediobasal hypothalamus or the paraventricular nucleus of hypothalamus (PVH). Rats were acutely (60 min) and/or repeatedly (for 7 days) restrained. In controls, a single restraint elevated the plasma adrenocorticotropin (ACTH), corticosterone, and prolactin levels. Repeated restraint produced all signs of chronic stress, including decreased body and thymus weights, increased adrenal weight, basal corticosterone levels, and proopiomelanocortin (POMC) mRNA expression in the anterior pituitary. Some adaptation to repeated restraint of the ACTH response, but not of other hormonal responses, was seen. Lesioning of the mediobasal hypothalamus abolished the hormonal response and POMC mRNA activation to acute and/or repeated restraint, suggesting that the hypothalamo-pituitary-adrenal axis activation during repeated restraint is centrally driven. PVH lesion inhibited the ACTH and corticosterone rise to the first restraint by approximately 50%. In repeatedly restrained rats with PVH lesion, the ACTH response to the last restraint was reduced almost to basal control levels, and the elevation of POMC mRNA level was prevented. PVH seems to be important for the repeated restraint-induced ACTH and POMC mRNA stimulation, but it appears to partially mediate other restraint-induced hormonal changes.

Thrombin inhibits NMDA-mediated nociceptive activity in the mouse: possible mediation by endothelin

The CNS expresses many components of an extracellular protease signalling system, including the protease-activated receptor-1 (PAR-1) whose tethered ligand is generated by thrombin. Activation of PAR-1 potentiates NMDA receptor activity in hippocampal neurons. Because NMDA activity mediates hyperalgesia, we tested the hypothesis that PAR-1 receptors also regulate pain processing. In contrast to the potentiating effect of thrombin in the hippocampus, NMDA-induced behaviours and the transient mechanical hyperalgesia (von Frey fibres) induced by intrathecally injected NMDA in mice were inhibited by thrombin in a dose-related fashion. This anti-hyperalgesic effect was mimicked by SFLLRN, the natural ligand at PAR-1 binding sites, but not SLIGRL-amide, a PAR-2 agonist. The effects of SFLLRN were less potent and shorter in duration than that of thrombin, consistent with its more transient effect on PAR-1 sites. Both thrombin and SFLLRN inhibited acetic acid-induced abdominal stretch (writhing) behaviours, which were also sensitive to NMDA antagonism, but not hot plate or tail flick latencies, which were insensitive to NMDA antagonists. TFLLR-amide, a selective ligand for PAR-1 sites, mimicked the effects of thrombin while RLLFT-amide, an inactive, reverse peptide sequence, did not. In addition, the effect of TFLLR-amide was prevented by RWJ-56110, a PAR-1 antagonist. Thrombin and TFLLR-amide produced no oedema (Evans Blue extravasation) in the spinal cord that would account for these effects. Based on the reported ability of thrombin to mobilize endothelin-1 from astrocytes, we tested the role of this compound in thrombin's activity. BQ123, an endothelin A receptor antagonist, prevented thrombin's inhibition of writhing and NMDA-induced behaviours while BQ788, an endothelin B receptor antagonist, did not. Thus, activation of PAR-1 sites by thrombin in the CNS appears to inhibit NMDA-mediated nociception by a pathway involving endothelin type A receptors.

Upregulation of neurokinin-1 receptor expression in rat spinal cord by an N-terminal metabolite of substance P

Chronic inflammatory conditions are associated with an upregulation of both substance P (SP) and neurokinin-1 (NK-1) receptors in the dorsal spinal cord. These receptors have been implicated in hyperalgesia as well as stress-induced analgesia. On the basis of the release of SP during chronic pain, and its rapid metabolism, we tested the hypothesis that SP metabolites regulate the synthesis of either SP or NK-1 receptors in the spinal cord. We measured expression of preprotachykinin mRNA and NK-1 receptor mRNA following intrathecally administered substance P(1-7) (SP1-7), the major metabolite of SP in rat, and following capsaicin, a compound known to induce release of endogenous SP. SP(1-7) and capsaicin each increased NK-1 receptor mRNA in the spinal cord (6 h) followed by an increase in NK-1 receptor-immunoreactivity (24 h and 1 week). D-SP(1-7), a D-isomer and antagonist of SP(1-7), did not mimic the effect of SP(1-7), indicating stereoselectivity. Instead, D-SP(1-7) prevented the upregulation of NK-1 receptor immunoreactivity that was induced by capsaicin injected intrathecally, suggesting that the effect of capsaicin is also mediated by SP N-terminal metabolites. In contrast, the decrease in SP synthesis produced by capsaicin was not dependent on SP metabolites as SP(1-7) failed to decrease either preprotachykinin mRNA content in dorsal root ganglia (6 h) or SP immunoreactivity in the lumbar spinal cord (24 h and 1 week). In addition, the effects of capsaicin on SP synthesis were not prevented by D-SP(1-7). Thus, SP metabolites, at times and doses that are antinociceptive, appear to enhance SP-mediated signal transduction by upregulating NK-1 receptor expression without affecting SP synthesis.

GABAergic innervation of corticotropin-releasing hormone (CRH)-secreting parvocellular neurons and its plasticity as demonstrated by quantitative immunoelectron microscopy

GABA has been identified as an important neurotransmitter in stress-related circuitry mediating inhibitory effects on neurosecretory neurons that comprise the central limb of the hypothalamo-pituitary-adrenocortical axis. Using combinations of pre-embedding immunostaining and postembedding immunogold methods at the ultrastructural level, direct synaptic contacts were revealed between GABA-containing terminals and neurosecretory cells that were immunoreactive for corticotropin-releasing hormone (CRH) in the hypothalamic paraventricular nucleus (PVN). The vast majority of axo-dendritic GABA synapses was symmetric (inhibitory) type, and 46% of all synaptic boutons in the medial parvocellular subdivision of the PVN were immunoreactive to GABA. Using the disector method, an unbiased stereological method on serial ultrathin sections, the total calculated number of synaptic contacts within the medial parvocellular subdivision of the PVN was 55.4 x 10(6)/mm(3). On CRH-positive profiles 20.1 x 10(6) GABAergic synaptic boutons were detected per mm(3) in control, colchicine-treated rats. In the medial parvocellular subdivision, 79% of GABAergic boutons terminated on CRH neurons. Following adrenalectomy, which increases the synthetic and secretory activities of CRH neurons, the number of GABAergic synapses that terminate on CRH-positive profiles was increased by 55%. GABA-containing boutons appeared to be swollen, while the contact surfaces of cellular membranes between GABAergic boutons and CRH-positive profiles were shorter in adrenalectomized animals than in controls. Our data provide ultrastructural evidence for direct inhibitory GABAergic control of stress-related CRH neurons and suggest a pivotal role of GABA-containing inputs in the functional plasticity of parvocellular neurosecretory neurons seen in response to adrenalectomy.

Nociceptive aspects of fibromyalgia

Although characterized by a variety of symptoms, chronic widespread pain is the primary complaint bringing most patients with fibromyalgia syndrome (FMS) into the clinic. The etiology of this painful condition is unknown, and any possible relationship between pain and the many other symptoms of FMS is unclear. This article focuses on the unique characteristics of nociception in patients with FMS. The intent is to present criteria that should be considered in the search for biological events that contribute to FMS pain. Based on this approach, examples are proposed of factors that fulfill some criteria and may, therefore, deserve further study for their possible role in pain associated with FMS.

Double activity imaging reveals distinct cellular targets of haloperidol, clozapine and dopamine D(3) receptor selective RGH-1756

Acute administration of typical (haloperidol) and atypical (clozapine) antipsychotics results in distinct and overlapping regions of immediate-early gene expression in the rat brain. RGH-1756 is a recently developed atypical antipsychotic with high affinity to dopamine D(3) receptors that results in a unique pattern of c-Fos induction. A single injection of either antipsychotic results in c-fos mRNA expression that peaks around 30 min after drug administration, while the maximum of c-Fos protein induction is seen 2 h after challenge. The transient and distinct temporal inducibility of c-fos mRNA and c-Fos protein was exploited to reveal and compare cellular targets of different antipsychotic drugs by concomitant localization of c-fos mRNA and c-Fos immunoreactivity in brain sections of rats that were timely challenged with two different antipsychotics. Double activity imaging revealed that haloperidol, clozapine and RGH-1756 share cellular targets in the nucleus accumbens, where 40% of all labeled neurons displayed both c-fos mRNA and c-Fos protein. Haloperidol activates cells in the caudate putamen, while clozapine-responsive, single labeled neurons were dominant in the prefrontal cortex and major island of Calleja. RGH-1756 targets haloperidol-sensitive cells in the caudate putamen, but cells that are activated by clozapine and RGH-1756 in the major island of Calleja are different.

Intrathecal Zn2+ attenuates morphine antinociception and the development of acute tolerance

Vesicular Zn2+, released in the brain and from small dorsal root ganglion neurons, interacts with opioid as well as N-methyl-D-aspartate (NMDA) receptors. We investigated the effect of Zn2+ on morphine antinociception in mice (tail flick assay), as well as acute tolerance and dependence, phenomena associated with NMDA activity. Administered intrathecally (i.t.), Zn2+ inhibited morphine antinociception in a dose-related fashion. Zn2+ also inhibited acute tolerance to morphine antinociception (5 h after 100 mg/kg of morphine). Injection i.t. of di-sodium calcium ethylenediamine tetra acetic acid (Na+Ca2+ EDTA), a chelator of divalent cations, had no effect on analgesia, acute tolerance or acute dependence. However, withdrawal jumps produced by naloxone (1 mg/kg s.c.) in morphine-pellet implanted mice (3 days) were potentiated by injections twice daily of 10 nmol of Na+Ca2+ EDTA, suggesting that endogenous Zn2+ tends to inhibit long-term development of withdrawal. These data suggest that the availability of Zn2+ is an important factor in opioid activity.

Photostimulation affects gonadotropin-releasing hormone immunoreactivity and activates a distinct neuron population in the hypothalamus of the mallard

To reveal central mechanisms that transduce photic stimuli to sexually related neuroendocrine changes, Fra-2-ir, an inducible immediate-early gene marker of neuronal activation has been consecutively localized with that of GnRH-I in the brain of mallards that were triggered by artificial light at the photosensitive phase of the reproductive cycle. Strong neuronal activation was found in the POM and PVN in response to 1x or 4x 20 h light exposure that was accompanied with an increase of GnRH-ir in the hypothalamus and a dramatic depletion of GnRH-ir from terminals in the median eminence. The Fra-2 and GnRH-ir profiles, however, were not co-localized in any region at any phase of photostimulation. These results demonstrate profound changes of GnRH-ir in the hypothalamus and reveal a distinct, photoresponsive cell population in the anterior hypothalamic area of the mallard.

Postnatal handling alters the activation of stress-related neuronal circuitries

Postnatal handling, as a crucial early life experience, plays an essential role in the development of hypothalamo-pituitary-adrenal axis responses to stress. The impact of postnatal handling on the reactivity of stress-related neuronal circuitries was investigated in animals that were handled for the first 21 days of life and as adults they were exposed to physical (ether) or emotional (restraint) challenge. To assess neuronal activation we relied on the induction of immediate-early gene product c-Fos and analysed its spatial and temporal distribution at various time intervals after stress. Ether and restraint commonly activated parvocellular neurons in the hypothalamic paraventricular nucleus, and resulted in activation of brain areas providing stress-related information to the hypothalamic effector neurons and/or in regions governing autonomic and behavioural responses to stress. Beyond these areas, the strength and timing of c-Fos induction showed stressor specificity in olfactory and septal region, basal ganglia, hypothalamus, hippocampal formation, amygdala and brainstem. Handled rats displayed a lower number of c-Fos-positive cell nuclei and weaker staining intensity than non-handled controls in the hypothalamic paraventricular nucleus, bed nucleus of stria terminalis, central nucleus of amygdala, hippocampus, piriform cortex and posterior division of the cingulum. Significant differences were revealed in timing of c-Fos induction as a function of stressor and early life experience. Together, these data provide functional anatomical evidence that environmental enrichment in the early postnatal period attenuates the reactivity of stress-related neuronal circuitries in the adult rat brain.

Anaphylactoid reactions activate hypothalamo-pituitary-adrenocortical axis: comparison with endotoxic reactions

Infectious and allergic diseases represent distinct aspects of immune response that can be experimentally modeled as endotoxic reactions following bacterial lipopolysaccharide (LPS) administration and anaphylactoid reactions following systemic injection of foreign proteins, respectively. Although it is well established that LPS stimulates the activity of the hypothalamo-pituitary-adrenocortical (HPA) axis, such effects of anaphylactoid reactions are completely unknown. To evaluate the impact of anaphylactoid reactions on HPA regulation, secretion of adrenocorticotropin hormone (ACTH) was followed and the pattern of c-Fos induction in the hypothalamic paraventricular nucleus (PVN) was revealed in rats that were challenged with egg white or compound 48/80. Male rats were intravenously injected with 0.1 ml/100g b.wt. 1:1 diluted egg white or 50 microg/100 g b.wt. compound 48/80, blood samples were taken before and various time intervals between 15-240 min after challenge for plasma ACTH measurement. Anaphylactoid reactions resulted in a rapid, significant activation of ACTH secretion and induced c-Fos immunoreactivity in the corticotropin-releasing hormone (CRH)-secreting subset of the parvocellular neurosecretory neurons. In addition, magnocellular neurosecretory neurons and autonomic-related projection neurons in the PVN became also c-Fos positive upon challenge. Changes in these parameters are compared to those seen in rats challenged with bacterial endotoxin, LPS.

Glucocorticoid negative feedback selectively targets vasopressin transcription in parvocellular neurosecretory neurons

To identify molecular targets of corticosteroid negative feedback effects on neurosecretory neurons comprising the central limb of the hypothalamo-pituitary-adrenal (HPA) axis, we monitored ether stress effects on corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) heteronuclear RNA (hnRNA) expression in rats that were intact or adrenalectomized (ADX) and replaced with corticosterone (B) at constant levels ranging from nil to peak stress concentrations. Under basal conditions, relative levels of both primary transcripts varied inversely as a function of plasma B titers. In response to stress, the kinetics of CRF hnRNA responses of intact and ADX rats replaced with low B were similar, peaking at 5 min after stress. By contrast, intact rats showed a delayed AVP hnRNA response (peak at 2 hr), the timing of which was markedly advanced in ADX/low B-replaced animals (peak at 5-30 min). Transcription factors implicated in these responses responded similarly. Manipulation of B status did not affect the early (5-15 min) phosphorylation of transcription factor cAMP-response element-binding protein (CREB) but accelerated maximal Fos induction from 2 hr after stress (intact) to 1 hr (ADX). Assays of binding by proteins in hypothalamic extracts of similarly manipulated rats toward consensus CRE and AP-1 response elements supported a role for the stress-induced plasma B increment in antagonizing AP-1, but not CRE, binding. These findings suggest that glucocorticoid negative feedback at the transcriptional levels is exerted selectively on AVP gene expression through a mechanism that likely involves glucocorticoid receptor interactions with immediate-early gene products.

Functional neuroanatomy of the parvocellular vasopressinergic system: transcriptional responses to stress and glucocorticoid feedback

This chapter summarizes the regulation of vasopressin (VP) transcription within the parvocellular neurosecretory cells of the hypothalamic paraventricular nucleus in vivo, with special reference to stress-response and glucocorticoid feedback. VP is commonly held as the first and the most potent among the co-secretagogues that act synergistically with corticotropin-releasing factor (CRF-41) to induce adrenocorticotropin (ACTH) from the anterior pituitary in response to various internal and external stimuli. Cellular levels of the primary transcripts of VP and CRF genes, revealed by in situ hybridization histochemistry using probes complementary to intronic sequences, are increased after acute challenges with different time courses. In contrast to the rapid stress-induced upregulation of CRF gene expression, VP transcription shows a delayed increase suggesting different regulatory mechanisms governing the two main ACTH releasing neuropeptides in the parvocellular neurosecretory neurons. With respect of transcription factors that may mediate these effects, besides rapid phosphorylation of the cAMP-response element-binding protein (CREB), VP activation in the parvocellular neurons requires additional newly synthesized factors such as those encoded by immediate-early genes, like c-fos. In addition, it has recently been revealed that glucocorticoid negative feedback during stress, selectively targets vasopressin transcription in the parvocellular neurons that is likely mediated by interaction of glucocorticoid receptors and immediate-early gene products. These data speak for the emerging consensus that VP is the principal factor that imparts situation-specific drive and represents the regulated variable governing hypothalamo-pituitary-adrenocortical axis during stress.

c-Fos as a transcription factor: a stressful (re)view from a functional map

This article summarizes the achievements that have been accumulated about the role of c-Fos as a transcription factor and as a functional marker of activated neurons. Since its discovery, more than a decade ago, as an inducible immediate-early gene encoding a transcription factor, or third messenger, involved in stimulus-transcription coupling and mediation of extracellular signals to long-term changes in cellular phenotype, c-fos became the most widely used powerful tool to delineate individual neurons as well as extended circuitries that are responsive to wide variety of external stimuli. There still remain uncertainties as to how general is the c-fos induction in the central neurons, and whether the threshold of c-fos induction is comparable along a certain neuronal circuit. The major limitation of this technology is that c-fos does not mark cells with a net inhibitory synaptic or transcriptional drive, and c-fos induction, as a generic marker of trans-synaptic activation, does not provide evidence for transcriptional activation of specific target genes in a certain cell type of interest. The first part of the review focuses on recent functional data on c-fos as transcription factor, while the second part discusses c-fos as a cellular marker of transcriptional activity in the stress-related circuitry.

Corticosterone peak is responsible for stress-induced elevation of glutamate in the hippocampus

Effect of ether stress on dialysate concentration of extracellular amino acids in the hippocampus was studied by microdialysis in freely moving rats that have been either sham operated (SHAM) or adrenalectomized and supplemented with subcutaneous steroid pellets (ADX+CORT) providing constant corticosterone (CORT) plasma levels. In SHAM rats, ether stress resulted in a peak of glutamate and taurine 30 min after stress, while extracellular aspartate concentration was increased 120 min after challenge. These changes in amino acid levels as well as in glutamate/glutamine ratio were paralleled by stress-induced rise of plasma CORT. No significant alterations were detected in the concentration of hippocampal arginine, alanine, glycine, glutamine, threonine or serine. In contrast to SHAM animals, ether stress failed to have an effect on dialysate concentration of amino acid transmitters in the hippocampus of adrenalectomized rats supplemented with 50 mg CORT-pellets. Our results demonstrate that ether stress alters aspartate, glutamate, glutamate/glutamine ratio and taurine concentration in the hippocampus and indicate that stress-induced CORT release in plasma may be responsible for these amino acid alterations. These changes may also contribute to negative feedback effect of CORT on hypothalamo-pituitary-adrenocortical (HPA) axis via the hippocampus during stress.

Up-regulation of [3H]DTG but not [3H](+)-pentazocine labeled sigma sites in mouse spinal cord by chronic morphine treatment

To monitor the possible effect of morphine on sigma sites, binding characteristics of [3H](+)-pentazocine and [3H]1,3-di-(2-tolyl)guanidine (DTG) to brain and spinal cord membranes of morphine-treated and control mice were compared. For morphine treatment, a single injection (100 mg/kg, s.c.) of morphine was followed 4 h later by pellet implantation (75 mg morphine free base). Animals were sacrificed 24, 72 h or 7 days later. The equilibrium dissociation value (Kd) and the density (Bmax) of [3H](+)-pentazocine binding remained unaffected by morphine treatment. Also, no change was found in Kd and Bmax values of [3H]DTG labeled sigma2 subtypes after any morphine treatment schedule when measured in the presence of 100 nM (+)-pentazocine. However, the Bmax of [3H]DTG binding in the spinal cord in the absence of 100 nM (+)-pentazocine, was significantly elevated 72 h after implantation of the morphine pellet and recovered by 7 days, a time when the antinociceptive effect produced by the morphine pellet had dissipated. These data suggest that one population of sigma sites, that has a high affinity for [3H]DTG, but is not equivalent with the [3H](+)-pentozocine labeled sigma1 subtype or the [3H]DTG labeled sigma2 subtype, is upregulated by morphine and, therefore, may play a role in the development of tolerance to or dependence on the effects of morphine.

Lesioning of the hypothalamic paraventricular nucleus inhibits ether-induced ACTH but not prolactin release

Stress mediators, CRF-41 and vasopressin known to be synthesized in, and released from the parvocellular neurosecretory neurons of the hypothalamic paraventricular nucleus (PVN) are essential to release adrenocorticotropin (ACTH) in response to stress. In addition, suckling-induced prolactin (PRL) release also depends on the integrity of the PVN. In the present study, ether stress-induced adrenocorticotrop hormone (ACTH) and prolactin (PRL) release was studied 2, 5 and 42 days after placing lesions in the hypothalamic paraventricular nucleus (PVN) of male rats. Ether-induced ACTH secretion was strongly inhibited 2 and 5 days after lesions whereas 6 weeks later the lesion induced inhibition was fading. In contrast, PVN lesion failed to inhibit ether-induced PRL release at any time studied. The results suggest that contrary to previous suggestions the peptidergic neurons essential for stress-induced PRL release are outside the PVN.

Protein synthesis blockade differentially affects the stress-induced transcriptional activation of neuropeptide genes in parvocellular neurosecretory neurons

Corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) are synergistically interacting ACTH secretagogues that are co-expressed by parvocellular neurosecretory neurons of the hypothalamic paraventricular nucleus (PVH). To shed light on the mechanisms that mediate the stress-induced transcriptional activation of these neuropeptide genes, quantitative hybridization histochemical methods were used to assess the effects of systemic treatment with the protein synthesis inhibitor, cycloheximide, on the ether stress-induced upregulation of primary CRF and AVP transcripts, in vivo. Pretreatment with cycloheximide prevented the induction of FOS, but not CREB phosphorylation, normally seen in response to acute ether exposure, and significantly attenuated the stress-induced rise in AVP, but not CRF, heteronuclear RNA expression in the parvocellular division of the PVH. These results support the view that distinct molecular mechanisms govern the expression of the two principal corticotropin-releasing factors, in vivo.

Zn2+ inhibition of [3H]MK-801 binding is different in mouse brain and spinal cord: effect of glycine and glutamate

Zn2+ inhibits NMDA-type excitatory amino acid activity by a non-competitive action. Based on regional differences in the central nervous system (CNS) in binding characteristics of [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne maleate ([3H]MK-801) and other non-competitive antagonists of NMDA used to label open channels in the receptor complex, we compared the inhibitory influence of Zn2+ on [3H]MK-801 binding in whole mouse brain and spinal cord membranes. Radioligand binding techniques were used in the presence and absence of maximally effective concentrations of glycine and glutamate. Using extensively washed membranes without exogenous glycine and glutamate, Zn2+ was found to be a weaker inhibitor of the [3H]MK-801-labeled site in the spinal cord than in the whole brain. In contrast, exogenous glycine and glutamate decreased the inhibitory effect of Zn2+ in the brain but dramatically increased the inhibitory effect of Zn2+ in the spinal cord. Thus the inhibitory effect of Zn2+ in the spinal cord appears to be magnified by glutamatergic and glycinergic activity while that in the brain is not. The different actions of Zn2+ may be attributable to the differential distribution of NMDA receptor subunits in the mouse brain and spinal cord.

Effect of intrahippocampal dexamethasone on the levels of amino acid transmitters and neuronal excitability

Direct effect of type-II corticosteroid receptor agonist dexamethasone on extracellular amino acid levels and neuronal excitability in the hippocampus was studied by simultaneous application of in vivo microdialysis and recording hippocampal evoked responses in freely moving male rats. Microdialysis probes and hippocampal recording electrodes were implanted to the CA1-CA3 regions of dorsal hippocampus. Local dexamethasone infusion via microdialysis resulted in a transient increase in glutamate level at 30 min, while glutamine decreased by 30-40% throughout the 180-min sampling period. Taurine increased by 50% and remained elevated up to 180 min. No significant changes were detected in extracellular concentration of asparagine, arginine, glycine, threonine, alanine and serine. In contrast, dexamethasone infusion to the striatum had no effect on the extracellular levels of amino acid transmitters. Effect of dexamethasone injected via microdialysis on the neural activity elicited by perforant path stimulation was a decrease in population spikes after 60 min starting dexamethasone infusion. Steroid effect on neural excitability was reversible. Our data indicate that local infusion of type-II receptor agonist dexamethasone has a complex effect in the hippocampus, starts with a change in extracellular glutamate and glutamine concentration and followed by a reduced synaptic excitability.

Regulation of stress-induced transcriptional changes in the hypothalamic neurosecretory neurons

Transcriptional changes in corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) gene expression were studied by in situ hybridization histochemistry using cRNA probes directed against intronic sequences. Acute ether stress resulted in a rapid induction of CRF and a delayed activation of vasopressin heteronuclear (hn)RNA in the parvocellular neurosecretory neurons within the paraventricular nucleus (PVN) of the hypothalamus. To explore possible molecular mechanisms regulating stress-related neuropeptide expression in vivo, the time-courses of stress-induced activation of different transcription factor classes were compared to that of changes in neuropeptide transcription. The peak of CRF transcription was parallel to that of cAMP response-element binding protein (CREB) phosphorylation but preceded the induction of c-fos and NGFI-B mRNAs and Fos protein. In contrast, AVP expression occurred in step with immediate-early gene (IEG) responses, suggesting involvement of different mechanisms underlying stress-induced neuropeptide responses. The interference of glucocorticoid hormones with stress-induced neuropeptide and transcription-factor responses has also been revealed in rats acutely or chronically pretreated with glucocorticoids. Acute dexamethasone injection did not prevent neuropeptide and transcription factor responses to either inhalation, whereas chronic corticosterone administration completely blocked IEG and neuropeptide induction in the stress-related neurosecretory neurons.

C-kit ligand (Stem Cell Factor) affects neuronal activity, stimulates pituitary-adrenal axis and prolactin secretion in rats

Stem Cell Factor (SCF) is a potent growth factor affecting proliferation, differentiation and migration as well as secretory functions of various cells of different origin and function. The effect of SCF on neuronal activity and on neuroendocrine regulation has been studied by injecting SCF i.v. into conscious male rats. Administration of SCF elevated adrenocorticotropin (ACTH), corticosterone and prolactin (PRL) plasma levels in a dose-dependent manner. Adrenocorticotropin and corticosterone secretions were maximal after injecting 10 micrograms SCF, while prolactin secretion only reached a maximum at a dose of 20 micrograms. Hormone secretions were maximal at 15 min (ACTH and PRL) or at 30 min (CORT) and declined to the baseline between 90 and 180 min. The functional anatomical approach, using immediate-early gene product c-Fos as a marker of activated neurones, revealed that systemic administration of SCF activated neurosecretory neurones of the hypothalamus in a time-dependent manner. Somatosensory afferent pathways and extrahypothalamic areas--which are involved in the regulation of hypothalamic neurosecretory cells--including various parts of the lamina terminalis, bed nucleus of stria terminalis, central amygdala, locus coeruleus, parabrachial nucleus, nucleus of the solitary tract and ventrolateral medulla also became Fos-positive. As SCF-induced mediators have been suggested to be involved in brain pathophysiology, and as SCF might have been of potential therapeutic use in certain anaemias and leukaemias, the complex interaction between SCF-induced cell-specific actions and its effect on the neuroendocrine system should also be considered.

Sequence of stress-induced alterations in indices of synaptic and transcriptional activation in parvocellular neurosecretory neurons

Immediate-early genes (IEGs) are widely used to mark endocrine hypothalamic neurons that are activated in response to stress, yet their relationship to the transcriptional control of relevant effector molecule expression is unclear. Acute ether stress provokes increased adrenocorticotropic hormone (ACTH) and corticosterone secretion that peaks at 5 and 30 min, respectively, after the challenge. Using probes complementary to intronic sequences of genes encoding ACTH secretagogues in parvocellular neurosecretory neurons of the paraventricular nucleus, we found these events to be accompanied by rapid and transient increases in corticotropin-releasing factor heteronuclear RNA (CRF hnRNA; peak at 5 min) and by a delayed upregulation of arginine vasopressin (AVP) hnRNA (120 min). To identify candidate mechanisms regulating peptide expression, we followed the timing of ether effects on representatives of three transcription factor classes: IEGs [c-fos and nerve growth factor I-B (NGFI-B)], a POU-domain factor (Brn-2), and the cAMP response element-binding protein (CREB), using antisera specific to its transcriptionally active, phosphorylated form (pCREB). After ether exposure, c-fos and NGFI-B mRNA induction were maximal at 30--60 min, whereas Fos protein peaked at 60--120 min. Brn-2 mRNA was expressed constitutively in the PVH and was unresponsive to stress. By contrast, pCREB was induced in parvocellular neurons with a time course parallel to that of CRF hnRNA expression. Stress-induced transcriptional activation of the CRF and AVP genes in hypophysiotropic neurons follows distinct time courses that are compatible with control mechanisms involving phosphorylation events and de novo protein synthesis, respectively.

Discrepancies in characterization of sigma sites in the mouse central nervous system

The characteristics of [3H](+)-pentazocine and [3H]1,3-di(2-tolyl) guanidine (DTG) binding to mouse whole brain, cortex, cerebellum and spinal cord membranes were investigated in radioreceptor assays. [3H](+)-Pentazocine bound to a single, high affinity site (Kd = 1.2-1.6 nM) with increasing density along the neuraxis from the cortex (Bmax = 543 fmol/mg protein) to the spinal cord (Bmax = 886 fmol/mg protein). Hot saturation studies resolved the presence of one binding site for [3H]DTG showing no tissue variations in terms of density (Bmax = 1075-1264 fmol/mg protein) or affinity (Kd = 16.6-22.3 nM). Incubation with 100 nM (+)-pentazocine revealed two classes of high affinity [3H]DTG labeled binding sites corresponding to sigma 1 and sigma 2 subtypes. A preponderance of sigma 2 sites was revealed in all investigated tissues. Different pharmacological profiles were demonstrated for the sigma 2 sites in mouse whole bain compared to mouse spinal cord. However, competition studies indicated that the whole brain and spinal [3H](+)-pentazocine labeled sigma 1 binding sites exhibited similar pharmacological properties. The density of [3H](+)-pentazocine labeled sigma 1 population was found not to match that of [3H]DTG labeled sigma 1 site throughout the mouse central nervous system. The presence of low affinity [3H]DTG labeled sites was demonstrated in cold saturation experiments. Equilibrium binding data for the low affinity [3H]DTG binding site resulted in an increasing density (Bmax = 1973-11,369 fmol/mg protein) with a decreasing affinity (Kd = 242-943 nM) in mouse cortex through the spinal cord.

Modulation of lipopolysaccharide-induced tumor necrosis factor-alpha production by selective alpha- and beta-adrenergic drugs in mice

In a previous study we demonstrated that mice pretreated with the highly selective alpha 2-adrenoceptor antagonist CH-38083 showed blunting of the tumor necrosis factor-alpha (TNF-alpha) response induced by bacterial lipopolysaccharide (LPS). In the present study, the effect of a selective block of alpha 2-adrenoreceptors and the role of the sympathetic nervous system (SNS) in the regulation of LPS-induced TNF-alpha production was explored further using different selective adrenoceptor antagonists and agonists. While adrenalectomy did not prevent the effect of CH-38083, the block of the sympathetic transmission by chlorisondamine fully abolished the inhibitory effect of CH-38083 on LPS-induced TNF-alpha production, suggesting that the effect of the alpha 2-adrenoceptor blocking agent is corticosteroid-independent, but it requires intact sympathetic activity. Since the selective block of alpha 2-adrenoceptors results in an increased sympathetic activity and an increase of the release of noradrenaline (NA) in both the central and the peripheral nervous systems, and in our experiments propranolol, a non-selective beta-adrenoceptor antagonist, and atenolol, a selective antagonist of beta 1-adrenoceptors, prevented the effect of alpha 2-adrenoceptor blockade by CH-38083 of the TNF-alpha response induced by LPS, it seems likely that the excessive stimulation by NA of beta 1-adrenoceptors is responsible for this action. The role of beta-adrenoceptors and endogenous catecholamines is further substantiated by the finding that pretreatment of animals with propranolol alone resulted in a dose-dependent increase of the TNF-alpha response induced by LPS, and that isoproterenol, a non-selective beta-adrenoceptor agonist, decreased it.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential dependence of ACTH secretion induced by various cytokines on the integrity of the paraventricular nucleus

Effect of different cytokines, human recombinant interleukin-1 alpha and beta (IL-1 alpha, IL-1 beta), interleukin-6 and tumor necrosis factor-alpha (TNF) on adrenocorticotropin (ACTH) secretion was compared in sham-operated rats and those with lesions of the hypothalamic paraventricular nucleus. IL-1 alpha was less active than IL-1 beta in stimulating ACTH in sham-operated rats. Intravenous injection of IL-1 beta in sham-operated animals resulted in a rapid elevation of ACTH secretion. Five days after surgical lesion of the paraventricular nucleus, the main hypothalamic source of hypophysiotropic corticotropin-releasing factor-41, the response to IL-1 beta was attenuated but not abolished. This suggests involvement of extra-paraventricular releasing factors in mediation of ACTH-releasing activity of IL-1 beta, altered responsiveness of pituitary to CRFs, and/or direct action of IL-1 beta on the corticotrope cells. TNF resulted in a biphasic stimulation of ACTH concentration, with peaks at 15 min and 90 min. In paraventricular-lesioned, TNF injected rats both of these ACTH peaks disappeared, suggesting that CRFs from the paraventricular origin mediates ACTH-inducing activity of TNF. IL-6 elevated ACTH secretion much later than the other intravenously injected cytokines, the peak was at 1 h in sham-lesioned rats. Paraventricular lesion completely prevented the increase of ACTH plasma levels after IL-6 injection. These data suggest that: (1) Effect of TNF and IL-6 on hypothalamo-pituitary-adrenal axis is mediated through the hypothalamic paraventricular nucleus and (2) IL-1 beta is able to release ACTH even in the absence of hypothalamic drive.

Density of NMDA-coupled and uncoupled 1-[1-(2-[3H]thienyl) cyclohexyl]piperidine recognition sites in the brain and spinal cord: differential effects of NMDA agonists and antagonists

Binding of 1-[1-(2-[3H]thienyl)cyclohexyl]piperidine ([3H]TCP) to mouse brain and spinal cord membranes was studied using compounds selective for the NMDA-coupled 1-(1-phenylcyclohexyl)piperidine (PCP) and/or sigma recognition sites. In both tissues, [3H]TCP labeled two populations of binding sites. Density of the low-affinity sites was approximately the same in both tissues, but the population of the high-affinity [3H]TCP sites was three times bigger in the brain than in the spinal cord. Self- and cross-displacement studies showed that the high-affinity [3H]TCP binding sites could be identical with NMDA receptor-coupled PCP sites, whereas the low-affinity [3H]TCP sites may be associated with sigma binding sites in both tissues. The NMDA-coupled PCP sites labeled in the presence of 6.25 nM [3H]TCP constituted a much higher percentage of the total binding in the brain (75%) than in the spinal cord (44%). Consistent with this, reintroduction of glycine and glutamate significantly increased, but DA antagonists significantly inhibited [3H]TCP binding in the brain but not in the spinal cord. Together, these data suggest that a large component of [3H]TCP-labeled binding sites in the spinal cord may be associated with sigma but not the NMDA receptor-coupled PCP sites.

A functional anatomical analysis of central pathways subserving the effects of interleukin-1 on stress-related neuroendocrine neurons

Systemic administration of the cytokine interleukin-1 (IL-1) results in increased secretion of ACTH and corticosterone in rats. The available evidence suggests that the acute effects of IL-1 are exerted ultimately at the level of the hypothalamus to increase corticotropin-releasing factor (CRF) secretion into the hypophyseal portal circulation, and hence the central drive on the pituitary-adrenal system. However, the route(s) and mechanism(s) by which circulating IL-1 gains access to central mechanisms governing pituitary-adrenal output remain poorly understood. In this study, we show that intravenous injection of IL-1 beta provokes time- and dose-dependent increases in the expression of the immediate-early gene c-fos, in identified CRF and oxytocin-producing cells of the paraventricular nucleus of the hypothalamus (PVH). Several cell groups known to be involved in central visceromotor regulation also displayed comparable time- and dose-related activation to systemic IL-1, including the bed nucleus of the stria terminalis, the central nucleus of the amygdala, the lateral parabrachial nucleus, and cell groups of the dorsomedial and ventrolateral medulla. Activation of circumventricular organs, which have been hypothesized to serve as central monitors of circulating IL-1, required doses roughly an order of magnitude above those required to activate CRF neurons in the PVH. Combined immunohistochemical and retrograde tracing experiments revealed many IL-1-responsive cells in the nucleus of the solitary tract and the ventrolateral medulla to be catecholaminergic and to project to the region of the PVH. Discrete and unilateral interruption of ascending catecholaminergic projections from the medulla attenuated IL-1-stimulated increases in Fos immunoreactivity and CRF mRNA in the PVH on the ipsilateral side. Disruption of descending projections from circumventricular structures associated with the lamina terminalis did not affect IL-1-mediated Fos induction in the PVH. We conclude that medullary catecholaminergic projections to the PVH play either a mediating or a permissive role in the IL-1-induced activation of the central limb of the hypothalamo-pituitary-adrenal axis.

A comparison of two immediate-early genes, c-fos and NGFI-B, as markers for functional activation in stress-related neuroendocrine circuitry

The promoter regions of the rat corticotropin-releasing factor (CRF), oxytocin (OT), and vasopressin (AVP) genes contain sequences similar to the cis-acting response element identified for NGFI-B, an immediate-early gene structurally related to the steroid hormone receptor superfamily. Combined immuno- and hybridization histochemical approaches were used to determine whether challenges that influence the synthesis and secretion of CRF, OT, and/or AVP result in altered expression in neurosecretory neurons of NGFI-B and another immediate-early gene, c-fos, which is widely used as a marker for functionally activated neurons. NGFI-B mRNA was found to be expressed at constitutively high levels in the telencephalon, but not in the endocrine hypothalamus, of unperturbed controls; basal levels of c-fos expression were uniformly low throughout the CNS. NGFI-B and c-fos mRNAs, and Fos protein, were induced with a similar time course and in similar neuroendocrine cell types in response to acute hypotensive hemorrhage (15% reduction in blood volume), intravenous injection of interleukin-1 beta (IL-1 beta; 1.87 micrograms/kg), chronic salt loading (7 d maintenance on 2% saline), and acute bilateral adrenalectomy. c-fos mRNA and Fos protein were readily demonstrable in afferent pathways that have been implicated as mediating the neuroendocrine responses in the three stress paradigms; these include medullary catecholaminergic cell groups in response to IL-1 beta and hemorrhage, and cell groups lining the lamina terminalis in response to salt loading. Challenge-specific induction of NGFI-B expression was detectable in these extrahypothalamic cell groups, though with a lesser sensitivity than that required to reveal NGFI-B induction in the hypothalamus, or c-fos expression in these related afferents. These results establish NGFI-B as a useful adjunct to c-fos, for revealing synaptic and/or transcriptional activation in the magno- and parvocellular neurosecretory systems. Differences in the sensitivity of the two markers in revealing functionally related activation in extrahypothalamic regions speak to general issues concerning the use of immediate-early genes in mapping functional circuitry in the CNS.

Mediation of osmoregulatory influences on neuroendocrine corticotropin-releasing factor expression by the ventral lamina terminalis

Chronic exposure to a hyperosmolar challenge invokes coordinate, differential, and ostensibly adaptive alterations in the expression of mRNA encoding corticotropin-releasing factor (CRF) in the endocrine hypothalamus. Rats maintained on 2% (wt/vol) saline for 7 days displayed the expected reduction in CRF mRNA levels in the parvocellular neurosecretory compartment of the paraventricular nucleus, as well as a concomitant increase in CRF transcripts in oxytocin-containing magnocellular neurosecretory neurons. Also detected in salt-loaded animals was a prominent induction of the immediate-early gene product Fos in magnocellular neurosecretory cell groups and in several brain regions that are known to provide major projections to the endocrine hypothalamus. These included a triad of cell groups making up the lamina terminalis of the third ventricle, and, to a lesser extent, catecholaminergic cell groups in the caudal brain stem. Discrete transections of descending projections from structures associated with the lamina terminals, as well as excitotoxin lesions centered in one lamina terminalis-associated structure, the organum vasculosum, abolished the effects of salt loading in both the magno- and parvocellular neurosecretory systems. Knife cuts in the lamina terminalis complex that spared only projections from the organum vasculosum region or cuts that disrupted ascending catecholaminergic projections failed to modify either effect of salt loading. The results suggest the existence of a simple circuit through which osmotic influences on gene expression in the magnocellular and parvocellular neurosecretory systems are effected.

Factors from the paraventricular nucleus mediate inhibitory effect of alpha-2-adrenergic drugs on ACTH secretion

The controversy about putative stimulatory and inhibitory functions of catecholamines in regulation of ACTH secretion has been recently shifted towards a consensus that during stress catecholamines stimulate corticotropin-releasing factor (CRF-41) containing neurons through alpha 1-adrenoreceptors, while inhibiting their own secretion acting on presynaptic alpha 2-receptors. In this study the effect of the alpha 2-agonist clonidine and the antagonist CH-38083 was studied on exogenous CRF-41/AVP-induced ACTH secretion in rats with/without paraventricular nucleus lesion. Clonidine (30 micrograms/kg) attenuated CRF-41/AVP (1 pmol/10 pmol)-induced ACTH secretion in sham-operated rats, but was ineffective in reducing CRF-41/AVP-induced ACTH secretion in rats with paraventricular nucleus lesion. In sham-operated rats, alpha 2-receptor antagonist CH-38083 slightly elevated the basal, and significantly potentiated the CRF-41/AVP-induced ACTH secretion, while it had no effect on the hypophyseotropic cocktail-induced ACTH response in paraventricular-lesioned rats. Neither the agonist nor the antagonist affected CRF-41/AVP-induced ACTH release from pituitary fragments in vitro. These results suggest that in response to activation of alpha 2-adrenoreceptors a corticotropin release-inhibiting substance is released from the paraventricular nucleus.

Plasma adrenocorticotropin in domestic geese: effects of ether stress and endocrine manipulations

A direct radioimmunoassay for the determination of avian adrenocorticotropin (ACTH) in a small volume of plasma was developed using an antiserum specific for N-terminal region of the ACTH molecule. The sensitivity of the two stage assay is 0.1 fmol ACTH/tube. The specificity of the antiserum was tested by its cross reactions with synthetic ACTH fragments and by comparing curves obtained by dilution of different plasma specimens to that of ACTH reference standard. Adrenocorticotropin responses of chronically cannulated geese to ether stress were evaluated and compared to changes of plasma corticosterone (B) concentration over a 2-hr period. ACTH showed a maximum between 5 and 10 min after ether exposure, while B peak appeared 10-15 min later. Thirty minutes after ether inhalation plasma ACTH returned to the baseline, while B response was longer-lasting and decreased to the resting level between 60 and 120 min. Basal and stress-induced ACTH plasma levels were also investigated in male and female gonadectomized and thyroidectomized geese. Castration increased, while thyroidectomy decreased the basal ACTH concentration. These endocrine manipulations did not, however, markedly affect the stress-induced ACTH hypersecretion except in thyroidectomized ganders, where the increment of plasma ACTH 10 min after ether inhalation was significantly lower than in sham operated control geese.