Chorioamnionitis induced by intraamniotic lipopolysaccharide resulted in an interval-dependent increase in central nervous system injury in the fetal sheep

OBJECTIVE

We quantified the impact of chorioamnionitis on both the white and gray matter structures of the preterm ovine central nervous system (CNS).

STUDY DESIGN

The CNS was studied at 125 days of gestation, either 2 or 14 days after the intraamniotic administration of 10 mg of lipopolysaccharide (LPS) (Escherichia coli) or saline. Apoptotic cells and cell types were analyzed in the brain, cerebellum, and spinal cord using flow cytometry.

RESULTS

Apoptosis and microglial activation increased in all regions with prolonged exposure to LPS-induced chorioamnionitis. Astrocytes were increased in the brain and cerebellum of LPS-exposed fetuses but not in the spinal cord. Mature oligodendrocytes decreased in the cerebral and cerebellar white matter, the cerebral cortex, caudate putamen, and hippocampus 14 days after LPS. Neurons in the cerebral cortex, hippocampus, and substantia nigra were reduced 14 days after LPS.

CONCLUSION

Fetal inflammation globally but differentially affected the CNS depending on the maturational stage of the brain region.

Effect of buspirone on the behavioral regulation of rats in low versus high anxiety conditions

INTRODUCTION

Buspirone (CAS 33386-08-2) is reported to have anxiolytic effects in humans and is mostly described for mild anxiety. To further explore the effects of buspirone on different levels of anxiety, the effect of buspirone was evaluated in two different conditions of the open field which were distinguished as low and high anxiety (enclosed and exposed open field, respectively).

MATERIALS AND METHODS

Twenty-eight albino Wistar rats (350-400 g) were tested in two different arena settings, an enclosed and an exposed open field. Fourteen animals were initially injected with 1 ml saline while the others (n = 14) received buspirone 3 mg/kg.

RESULTS

The data showed clear differences in the two open-field settings, suggesting a higher anxiety level in the exposed open field. In addition, correlation analysis showed that the two anxiety tests measure different aspects of anxiety. Buspirone treatment reduced the behavioral activity in both the enclosed and exposed open-field, which is generally interpreted as an anxiogenic effect. However, buspirone increased the time in the center areas and decreased the frequencies in the outer regions. These behavioral changes are generally seen as an anxiolytic effect. Correlation analysis showed that buspirone treatment disrupted the relation between indices of anxiety.

CONCLUSION

These results showed that in an open-field setting buspirone appears to have a dual effect. The reduced activity and increase in time spent in the center areas are indicative of both an anxiogenic and an anxiolytic effect, respectively. This was found in both open-field settings, suggesting that the effects of buspirone are independent of the anxiety level.

High-frequency stimulation of the dorsolateral periaqueductal gray and ventromedial hypothalamus fails to inhibit panic-like behaviour

Electrical stimulation of the dorsolateral periaqueductal gray (dlPAG) and one of its target structures, the ventromedial hypothalamus (VMH), produces a typical behaviour in rats consisting of vigorous running and jumping which is known as "escape behaviour". Escape behaviour in rodents closely mimics panic attacks in humans. Since electrical stimulation at higher frequencies generally inhibits the stimulated region, we tested in this study the hypothesis that deep brain stimulation (DBS) of the dlPAG and VMH at higher frequencies (> 100 Hz) would not induce escape behaviour. More specifically, we evaluated whether experimental DBS could be used to inhibit panic-like behaviour. Rats underwent implantation of DBS-electrodes at the level of the dlPAG and VMH and the effects of various stimulation parameters were assessed. In addition, we studied the neural activation pattern resulting from DBS of the dlPAG and VMH using c-Fos immunohistochemistry. We found that stimulation amplitude is the most important stimulation parameter in the induction of escape behaviour. Remarkably, stimulation frequency (1-300 Hz) had no effect on stimulation-induced escape behaviour and therefore it was not possible to prevent the induction of escape behaviour with higher frequencies. The neuronal activation pattern resulting from dlPAG and VMH DBS was similar. These findings suggest that DBS of the dlPAG and VMH induces panic-related behaviours even at higher frequencies.

Kynurenine pathway in major depression: evidence of impaired neuroprotection

The neurodegeneration hypothesis proposed major depression as a consequence of the imbalance between neuroprotective and neurodegenerative metabolites in the kynurenine pathway. To test the hypothesis, plasma tryptophan and kynurenine pathway metabolites were studied in 58 patients with major depression and 189 normal controls. The mean tryptophan breakdown index was higher (p=0.036), and mean kynurenic acid concentration and mean neuroprotective ratios were lower, in depressed patients (p=0.003 and 0.003, respectively). In receiver operating characteristic analysis, the kynurenic acid concentrations and the neuroprotective ratio showed clear discrimination between depressed patients and controls with area under the curve 79% and 76.3% respectively. The neuroprotective ratio did not change after treatment in those with repeated episodes of depression but it increased significantly (p=0.044) in those with first episodes. The results suggested that the reduction in neuroprotective markers, which indicated an impaired neuroprotection, might play an important role in pathophysiology of major depression.

Gestational stress leads to depressive-like behavioural and immunological changes in the rat

Stress during pregnancy, gestational stress, can increase the chance of developing postpartum depression, which is estimated to occur in 10% of women. Since major depression is accompanied by an activation of the inflammatory response system, the aim of this study was to investigate if stress during pregnancy induces postpartum depressive-like behaviour, and if so, is it accompanied by activation of the inflammatory response system in female Fisher rats. We investigated the effect of gestational stress on the production of depressive-like behaviour in the rats. The pregnant dams underwent daily restraint stress (for 1 week, 3 times/day) or were left undisturbed (control). On postpartum day 22, the rats were introduced to the forced swim test (pre-test). On postpartum days 23 and 24 (test days), the immobility time was measured. Gestational stress significantly elevated immobility scores by 35-40% above the control values on both test days, which suggests that the stressed group displayed postpartum depressive-like behaviour. The concentrations of the pro-inflammatory cytokines interleukin-1beta, tumour necrosis factor-alpha and the anti-inflammatory cytokine interleukin-10 in stimulated whole-blood culture were also analysed. The stressed group showed higher levels of all three cytokines. No significant differences in the cytokine concentrations were detected in the hypothalamus, hippocampus or pre-frontal cortex.

The negative immunoregulatory effects of fluoxetine in relation to the cAMP-dependent PKA pathway

Recently, we have shown that various types of antidepressants, including selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine, have negative immunoregulatory effects. These antidepressants suppress the interferon-gamma (IFN-gamma)/interleukin-10 (IL-10) production ratio, which is of critical importance for the determination of the capacity of immunocytes to inhibit or activate monocytic/lymphocytic functions. Since cyclic adenosine monophosphate (cAMP) production is stimulated by some antidepressants, and since cAMP inhibits IFN-gamma and stimulates IL-10 production, we postulate that the negative immunoregulatory effects of antidepressants result from their effects on the cAMP-dependent protein kinase A (PKA) pathway. The aim of the present study was to determine whether the negative immunoregulatory effects of fluoxetine may be blocked by antagonists of the cAMP-dependent PKA pathway, such as, e.g., SQ 22536, an adenylate cyclase inhibitor, and Rp-8-Br-cAMPs (Rp-isomer of 8-bromo-adenosine-3',5'-monophosphorothioate), a PKA antagonist. To this end, diluted whole blood collected from 17 normal volunteers was incubated with fluoxetine (10(-6) and 10(-5) M), with or without SQ 22536 (10(-6) and 10(-4) M) and Rp-8-Br-cAMPs (10(-6) and 10(-4) M), afterwards, IFN-gamma, IL-10 and the tumor necrosis factor alpha (TNF-alpha) were determined. Fluoxetine, 10(-6) and 10(-5) M, significantly reduced the production of IFN-gamma and TNF-alpha, and significantly decreased the IFN-gamma/IL-10 production ratio. SQ 22536 and Rp-8-Br-cAMPs were unable to block the suppressant effects of fluoxetine on the IFN-gamma/IL-10 ratio. Rp-8-Br-cAMPs, 10(-4), but not 10(-6) M, normalized the fluoxetine-induced suppression of TNF-alpha production. It is concluded that the suppressant effect of fluoxetine on the IFN-gamma/IL-10 production ratio is probably not related to the induction of the cAMP-dependent PKA pathway, whereas the suppressant effect on TNF-alpha may be related to the induction of PKA. The obtained results suggest that increased activation of the PKA-dependent pathway may constitute an important molecular basis for some (suppression of TNF-alpha production), but not all (suppression of IFN-gamma production), negative immunoregulatory effects of fluoxetine.

Efavirenz induces depressive-like behaviour, increased stress response and changes in the immune response in rats

Efavirenz is a non-nucleoside reverse transcriptase inhibitor that is used in the treatment of the HIV-1 variant. Adverse central nervous system side effects such as headache, dizziness, insomnia, fatigue, severe depression and suicidal ideation are noted in patients receiving efavirenz. In this study, the effects of efavirenz on changes in behaviour and on some pro- and anti-inflammatory cytokines in Wistar rats were studied to assess whether efavirenz causes depressive symptoms via the cytokine network and, if so, whether antidepressant therapy known to attenuate the effects of pro-inflammatory cytokines could prevent these changes. The efavirenz-treated rats displayed spatial memory deficits in the Morris water maze. These rats also appeared to be more susceptible to stress than the other groups as seen by an increase in the latency to emerge in the home cage emergence test following the stress of the Morris water maze. The concentrations of pro-inflammatory cytokines interleukin-1 beta and tumour necrosis factor-alpha were also significantly higher in the efavirenz group. The antidepressant paroxetine reduced the susceptibility to stress and prevented such an increase in pro-inflammatory cytokines. It is concluded that efavirenz induces depressive-like behaviour in the rat and a susceptibility to stress, which are accompanied by an increase in pro-inflammatory cytokines. These symptoms are partially alleviated by chronic treatment with paroxetine.

Dual effect of diazepam on cGMP levels in rat brain slices

The effect of diazepam on NO-mediated cGMP synthesis was studied in rat brain slices. It was found that diazepam dose-dependently decreased cGMP synthesis in cerebellar slices, with an inhibition of 90% at 1 mM diazepam. cGMP levels in the presence of diazepam were not restored to control levels by the addition of 0.1 mM sodium nitroprusside, whereas the decrease in cerebellar cGMP levels induced by 0.1 mM L-NAME was restored by the simultaneous application of NO-donors. In addition to the decrease of cGMP levels in neuronal structures induced by 1 mM diazepam, we observed increased cGMP immunoreactivity in glial cells in the cerebellum, the hippocampus, and the cerebral cortex. The significance of this observation is discussed.

Decreased levels of cGMP in vitreous and subretinal fluid from eyes with retinal detachment

BACKGROUND

Cyclic guanosine monophosphate (cGMP) is produced in different retinal cells, including photoreceptor cells, wherein cGMP mediates photo-transduction. CGMP is degraded by phosphodiesterases (PDE). The aim was to investigate whether retinal detachment alters intraocular cGMP levels in human eyes.

METHODS

cGMP and PDE were determined in vitreous fluid from 50 eyes with a retinal detachment (group I) and in 20 control samples (group II) of vitreous fluid from eyes without retinal detachment. Group III consisted of subretinal fluid samples from 70 eyes with retinal detachment.

RESULTS

cGMP in vitreous fluid from eyes with retinal detachment (6.5 (SD 1.7) nM) was decreased compared to controls (67.1 (10.0) nM) (p<0.0001). In subretinal fluid, the mean level of cGMP was 2.4 (0.2) nM. No PDE could be detected in any of the intraocular fluid samples of patients nor controls. A decrease in the mean level of cGMP in subretinal fluid of eyes with retinal detachment correlated with a longer duration of detachment (r = -0.45, p = 0.007).

CONCLUSIONS

Retinal detachment was found to be associated with a decrease in vitreous cGMP concentration. In subretinal fluid, a low cGMP level correlated inversely with the duration of the detachment.

Influence of antidepressants on intracellular levels of cyclic adenosine monophosphate in human peripheral blood mononuclear cells

This study examines the effects of paroxetine and imipramine on intracellular concentrations of cyclic adenosine monophosphate (cAMP) in human peripheral blood mononuclear cells. It was found that imipramine and paroxetine had no effect on basal cAMP-levels. Stimulation with lipopolysaccharides and phytohaemagglutinin increased intracellular cAMP concentrations. However, pre-incubation with imipramine or paroxetine, did not influence this increase. These data do not support the hypothesis that cAMP may be related to the in vitro anti-inflammatory effects of antidepressants.

Stability of interleukin 6, soluble interleukin 6 receptor, interleukin 10 and CC16 in human serum

The stability of interleukin 6 (IL-6), its soluble receptor (sIL-6R), IL-10 and CC16 or uteroglobin (an endogenous cytokine inhibitor) in human serum was examined using an accelerated stability testing protocol according to the Arrhenius equation. Further, the effect of time delay between blood sampling and sample processing, clotting temperature and repeated freeze-thaw cycles on serum levels of these proteins were determined. Paired serum samples were stored at 4 degrees C, 20 degrees C, 30 degrees C and 40 degrees C for 1 to 21 days. We found that IL-6 and CC16 concentrations did not change at 4 degrees C, 20 degrees C and 30 degrees C. Interleukin-6 concentrations significantly declined after 11 days at 40 degrees C. The concentrations of sIL-6R and IL-10 did not change at 4 degrees C but significantly decreased at 20 degrees C (after 21 and 14 days respectively), 30 degrees C and 40 degrees C (after 1 day at both temperatures for both cytokines). Arrhenius-plots indicated that sIL-6R and IL-10 are stable for at least several years at -20 degrees C and -70 degrees C, respectively. Since their relative stability, no Arrhenius-plot could be calculated for IL-6 and CC16. The concentrations of the proteins examined were not significantly altered by repeated freeze-thaw cycles, nor by extended clotting times at 4 degrees C or 20 degrees C. We conclude that serum samples for the determination of IL-6, sIL-6R and CC16 can be stored at -20 degrees C for several years, but for IL-10 determinations, storage at -70 degrees C is recommended.

Basic fibroblast growth factor, glutamine synthetase, and interleukin-6 in vitreous fluid from eyes with retinal detachment complicated by proliferative vitreoretinopathy

PURPOSE

To investigate the presence of basic fibroblast growth factor (bFGF), glutamine synthetase (GS), and interleukin-6 (IL-6) in vitreous fluid from eyes with retinal detachment complicated by proliferative vitreoretinopathy (PVR).

DESIGN

Comparative case series; experimental study.

METHODS

In a prospective study, we measured bFGF, GS, IL-6, and total protein in vitreous fluid samples from 53 eyes from 53 consecutive patients with PVR operated on in our hospital. As controls, vitreous fluid samples from eyes with a macular hole (n = 9) or pucker (n = 11) were used.

MAIN OUTCOME MEASURES

Laboratory data of the patient group were compared with the control group and correlated with various clinical data, especially with visual recovery and redetachment.

RESULTS

For IL-6, bFGF, and total protein we found significantly higher levels in PVR patients' eyes than in control eyes (P =.03, P =.046, and P <.0001, respectively). Within the PVR group, no significant correlation was found for IL-6, bFGF, GS, or total protein with the various tested clinical variables.

CONCLUSIONS

We found increased levels of IL-6, bFGF, and total protein in vitreous fluid from patients' eyes with PVR. Whether the increased levels of IL-6, bFGF, and total protein are the result of an injury-induced upregulation of these proteins as part of a self-protective mechanism of the retina to minimize photoreceptor damage after the mechanical injury induced by retinal detachment is, at present, not known.

Levels of basic fibroblast growth factor, glutamine synthetase, and interleukin-6 in subretinal fluid from patients with retinal detachment

PURPOSE

To investigate the presence of basic fibroblast growth factor, glutamine synthetase activity, and interleukin-6 in subretinal fluid from patients with retinal detachment.

METHODS

In a prospective study we measured basic fibroblast growth factor, glutamine synthetase activity, interleukin-6, and total protein in subretinal fluid samples from 96 eyes from 94 consecutive patients with a retinal detachment corrected by a conventional scleral buckling operation in our clinical practice. As controls, vitreous fluid samples from eyes with a macular hole (n = 6) or pucker (n = 11) were used. Laboratory data of the patient group were compared with the control group and correlated with various clinical data.

RESULTS

Levels (median, range) of basic fibroblast growth factor, glutamine synthetase activity, interleukin-6, and total protein were significantly higher in patients than in controls (P <.0001). An increased level of glutamine synthetase and total protein correlated with a longer duration of the retinal detachment (r =.4, P =.002, and r =.34, P =.001, respectively). Interleukin-6 and basic fibroblast growth factor levels did not correlate with the duration of the detachment. After multivariate logistic regression analysis, no significant relation was found between any of the tested subretinal proteins and a low visual outcome or redetachment.

CONCLUSIONS

We found increased levels of basic fibroblast growth factor and glutamine synthetase in subretinal fluid from patients with retinal detachment. Basic fibroblast growth factor and glutamine synthetase may play a role in the pathogenesis and recovery after retinal detachment. The questions of whether the increased levels of basic fibroblast growth factor and glutamine synthetase result from leakage of dying glia cells (including Müller cells) and neurons and if basic fibroblast growth factor is actively produced to protect the photoreceptor cells need further research.

Nitric oxide synthase does not mediate neurotoxicity after an i.c.v. injection of streptozotocin in the rat

In the present study we evaluated the possible role of nitric oxide (NO) in mediating neuronal damage in middle-aged rats after an i.c.v. injection of streptozotocin (STREP). An i.c.v. injection of STREP has been reported to decrease the central metabolism of glucose. This inhibition of the energy metabolism after STREP treatment might induce an excitotoxic mechanism, which may lead to the stimulation of NO synthase and, consequently to the synthesis of NO. On the other hand, STREP might induce oxidative stress directly by liberation of NO from its nitroso moiety. To investigate whether NO synthase is involved in a possible excitotoxic mechanism after STREP treatment, some of the rats treated with STREP (1.25 mg/ kg in 4 microl, bilaterally 2 microl/injection site) were also treated with the NO synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME, 20 mg/kg i.p. 10 min, 6, 24 and 96 h after STREP injection). To investigate whether NO liberated from STREP may be responsible for neurotoxic effects, one additional group of control rats received an i.c.v. injection of the NO donor sodium nitroprusside (SNP, 10 microg in 4 microl). We found that STREP affected the behavioral performances in the open field and two-way active avoidance task. In addition, immunostaining for glial fibrillary acidic protein, an indicator of reactive astroglial changes to neuronal damage, showed that this was mainly located in peri- and paraventricular regions of the third and lateral ventricles, like for instance in the septum, caudate putamen and hippocampus. L-NAME treatment had no protective effect on the behavioral impairments and neuronal damage of STREP-treated rats. This suggests that the neuronal damage of STREP may still be a result of the decrease in the central energy metabolism, but without the involvement of NO synthase. This was supported by measuring, using immunostaining, the NO-mediated cyclic GMP production by the enzyme soluble guanylyl cyclase in cortical slices, i.e. L-NAME did not prevent NO production after STREP administration in vitro. In addition, it was found that SNP liberated NO in vitro, whereas in vivo SNP administration did not lead to any behavioral and neuronal deficits at all. However, the present study cannot exclude the involvement of NO liberated from STREP in neuronal damage.

Specificity of Chicken (IgY) versus Rabbit (IgG) Antibodies Raised against Cholecystokinin Octapeptide (CCK-8)

Antibodies produced in chickens (egg yolk Antibody-IgY) and rabbits against CCK-8 TyrSE (a C-terminal extended CCK-version) were compared with respect to their specificity against several modified CCK-sequences by means of radioimmunoassay and spot blot assay. The content of neuronal CCK was determined by using both an "avian" and a "mammalian" RIA. The IC50 values obtained indicate differences between the binding capacity of rabbit and chicken Antibody, respectively. Supported by the data from spot blot assay, it appears, that the avian Antibody binding activity was directed primarily towards short CCK-sequences whereas the longer sequences are less well recognised in contrast to the mammalian antibody. Probably, these differences may be due to characteristics regarding the shape of the molecules (caused also by fixation processes necessary for blotting procedures) as well as to structural differences between avian and mammalian antibodies itself (both antibodies originate from quite different immune systems). By comparing the quantitative CCK data (avian versus mammalian RIA) a significant correlation could be observed. Immunohistochemical studies using avian antibodies revealed a neuronal CCK pattern different from those using rabbit antibodies. These results are discussed on the basis of the specificity studies.

Presence of soluble and particulate guanylyl cyclase in the same hippocampal astrocytes

The localisation of particulate and soluble guanylyl cyclase was studied in hippocampal astrocytes. Counting the colocalisation of cGMP immunoreactivity with the astrocytic marker glial fibrillary acidic protein after stimulation of brain slices with sodium nitroprusside (0.1 mM) or atrial natriuretic peptide (100 nM), we were able to show that at least 67% of the hippocampal astrocytes contained both guanylyl cyclase isoforms. In addition, it was shown that a large number of atrial natriuretic peptide, brain-derived natriuretic peptide or sodium nitroprusside responsive cells contain the beta1-subunit of the soluble guanylyl cyclase. The results show that, in at least a subset of hippocampal astrocytes, soluble and particulate guanylyl cyclases are simultaneously present in the same cells.

Localization and age-related changes of nitric oxide- and ANP-mediated cyclic-GMP synthesis in rat cervical spinal cord: an immunocytochemical study

An immunocytochemical technique was used to study the localization and developmental aspects of cyclic GMP (cGMP)-synthesizing structures in the cervical spinal cord of 2-week and 3-month-old Lewis rats in response to the nitric oxide (NO) donor sodium nitroprusside (SNP) and/or atrial natriuretic peptide (ANP). By using cell-specific markers, the cell structures involved were investigated. To visualize cGMP, a combined technique of low- and high-power magnification, using a confocal laser scanning microscope was used. NOS-mediated cGMP synthesis was observed in the cervical spinal cord in laminae I, II and III in 14-day-old rats, which activity was mainly absent at the age of 3 months. The involvement of NO in the NMDA-mediated increase in cGMP immunostaining (cGMP-IS) was demonstrated by the absence of cGMP-IS in slices incubated in the presence of NMDA together with the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). This NO-mediated effect of NMDA on cGMP-IS was completely absent in the 3-month-old rats. ANP-mediated cGMP synthesis resulted in an increase in cGMP in laminae I and II, which was generally similar at both ages. Astrocytes in both white and gray matter were found to be cGMP-IS in the basal, NO- and ANP-stimulated conditions. Using confocal laser microscopy, NO-mediated cGMP synthesis was observed in large cholinergic terminals nearby motor neurons in the ventral horn. An extensive colocalization between NO-stimulated cGMP synthesis and parvalbumin-positive (GABAergic) neurons and fibers was observed in all laminae. In the ANP-stimulated condition, a colocalization with parvalbumin structures was found in laminae II and III. No NO- or ANP-mediated cGMP synthesis was found in fibers immunopositive for the presynaptic glutamate transporter, serotonin, or tyrosine hydroxylase.

Down-regulation of ACTH and glucocorticoid receptor immunoreactivity in hypothalamic arcuate neurons after adrenalectomy in the rat

The expression of glucocorticoid receptor (GR) in rat adrenocorticotropin (ACTH)-containing neurons in rat brain was immunohistochemically investigated. ACTH-containing cell bodies were found mainly in the arcuate nucleus. Most of these neurons exhibited GR immunoreactivities in their nuclei. ACTH-containing nerve fibers were distributed in the bed nucleus of the stria terminalis, periventricular nucleus, retrochiasmatic nucleus, parvocellular part of paraventricular nucleus and dorsomedial hypothalamic nucleus. After adrenalectomy there was a marked decrease of ACTH immunoreactivity, as well as GR immunoreactivity, in neurons of the arcuate nucleus, but ACTH immunoreactivity in the fibers was not affected. These results indicate that glucocorticoids up-regulate ACTH and GR production in hypothalamic arcuate neurons, but that glucocorticoid-induced changes could be delayed in the fibers derived from these neurons.

Local inhibition of hippocampal nitric oxide synthase does not impair place learning in the Morris water escape task in rats

Recent studies have provided evidence that nitric oxide (NO) has a role in certain forms of memory formation. Spatial learning is one of the cognitive abilities that has been found to be impaired after systemic administration of an NO-synthase inhibitor. As the hippocampus has a pivotal role in spatial orientation, the present study examined the role of hippocampal NO in spatial learning and reversal learning in a Morris task in adult rats. It was found that N omega-nitro-L-arginine infusions into the dorsal hippocampus affected the manner in which the rats were searching the submerged platform during training, but did not affect the efficiency to find the spatial location of the escape platform. Hippocampal NO-synthase inhibition did not affect the learning of a new platform position in the same water tank (i.e. reversal learning). Moreover, no treatment effects were observed in the probe trials (i.e. after acquisition and after reversal learning), indicating that the rats treated with N omega-nitro-L-arginine had learned the spatial location of the platform. These findings were obtained under conditions where the NO synthesis in the dorsal hippocampus was completely inhibited. On the basis of the present data it was concluded that hippocampal NO is not critically involved in place learning in rats.

Effect of peripheral nerve injury on cGMP and nitric oxide synthase levels in rat dorsal root ganglia: time course and coexistence

Using the indirect immunofluorescence method, the distribution of cyclic GMP (cGMP) and nitric oxide synthase (NOS) was investigated in lumbar 5 dorsal root ganglia (DRGs) of untreated rats 1, 3 and 7 days following sciatic nerve section (axotomy). Untreated and axotomized (7 days) rats were also studied after perfusion with the NO donor sodium nitroprusside (SNP). Moreover, rats were injected with carrageenan lambda into the unilateral hindpaw and studied after 6 h, 1 day or 2 days. An increase in the number of cGMP-positive satellite cell profiles was found in axotomized DRGs at 3 days with lower numbers after 7 days. In contrast, no change in cGMP-like immunoreactivity (LI) in satellite cell profiles was detected 1 day after axotomy or 6h, 1 day or 2 days after inflammation, as compared to controls. Axotomy induced a marked increase in the percentage of NOS-immunoreactive (IR) neuron profiles in the ipsilateral DRGs as follows: 3.0% at 1 day, 15% at 3 days and 25% at 7 days, whereas no significant change was found in the expression of NOS-LI in the inflamed DRGs as compared to untreated DRGs. Between 15 and 20% of all NOS-positive neuron profiles were surrounded by, or in partial contact with, cGMP-IR satellite cells in controls 1 and 3 days after axotomy, whereas the corresponding figure was around 5% after 7 days. After SNP perfusion 60-70% of all DRG neuron profiles were partly or totally associated with cGMP-positive satellite cell profiles, with no significant difference between untreated and axotomized ganglia. The nerve injury-induced, parallel upregulation of NOS in DRG neurons and cGMP in satellite cells in the initial phase after axotomy suggests an involvement of NO as a signalling molecule between neurons and satellite cells in DRGs, especially after peripheral nerve injury, perhaps exerting a survival effect as recently proposed by Thippeswamy and Morris (1997).

The NO-cGMP pathway in the rat locus coeruleus: electrophysiological, immunohistochemical and in situ hybridization studies

The effect of two nitric oxide (NO) donors, SIN-1 and DEA/NO, as well as of the inactive SIN-1 derivative molsidomin, was studied on locus coeruleus (LC) neurons in a slice preparation using intracellular recordings. In addition, the effect of the guanylate cyclase inhibitor ODQ was analysed. Furthermore, the effect of NO donors on cyclic guanosine monophosphate (GMP) levels in the LC was studied using the indirect immunofluorescence technique, and the expression of soluble guanylyl cyclase with in situ hybridization. In 36 of 66 LC neurons extracellular application of SIN-1 and DEA/NO caused a hyperpolarization and a decrease in apparent input resistance. In almost 20% of neurons SIN-1 increased the firing rate. No effect could be recorded with the brain-inactive SIN-1 derivative molsidomin. The membrane permeable cGMP analogue 8-bromo-cGMP imitated the action of SIN-1. The hyperpolarizing effect of SIN-1 and DEA/NO was attenuated by preincubation with the guanylyl cyclase inhibitor ODQ. The immunohistochemical analysis revealed lack of cGMP immunostaining in non-stimulated slices, whereas SIN-1 dramatically increased this staining in about 40% of the LC neurons, and these neurons were all tyrosine hydroxylase positive, that is noradrenergic. A large proportion of the LC neurons expressed soluble guanylyl cyclase mRNA. The present and previous results suggest that NO, released from a small number of non-noradrenergic neurons in the LC, mainly has an inhibitory influence on many noradrenergic neurons, by upregulating cGMP levels via stimulation of soluble guanylyl cyclase. As nitric oxide synthase is present only in a small number of non-noradrenergic neurons (Xu et al., 1994), a few neurons may influence a large population of noradrenergic LC neurons, which in turn may control activity in many regions of the central nervous system.