Immunocytochemistry of endothelial nitric oxide synthase in the rat brain: a light and electron microscopical study using the tyramide signal amplification technique

Fluorochromized tyramide-glucose oxidase as a multiplex fluorescent tyramide signal amplification system for histochemical analysis

Tyramide signal amplification (TSA) is a highly sensitive method for histochemical analysis. Previously, we reported a TSA system, biotinyl tyramine-glucose oxidase (BT-GO), for bright-filed imaging. Here, we develop fluorochromized tyramide-glucose oxidase (FT-GO) as a multiplex fluorescent TSA system. FT-GO involves peroxidase-catalyzed deposition of fluorochromized tyramide (FT) with hydrogen peroxide produced by enzymatic reaction between glucose and glucose oxidase. We showed that FT-GO enhanced immunofluorescence signals while maintaining low background signals. Compared with indirect immunofluorescence detections, FT-GO demonstrated a more widespread distribution of monoaminergic projection systems in mouse and marmoset brains. For multiplex labeling with FT-GO, we quenched antibody-conjugated peroxidase using sodium azide. We applied FT-GO to multiplex fluorescent in situ hybridization, and succeeded in labeling neocortical interneuron subtypes by coupling with immunofluorescence. FT-GO immunofluorescence further increased the detectability of an adeno-associated virus tracer. Given its simplicity and a staining with a high signal-to-noise ratio, FT-GO would provide a versatile platform for histochemical analysis.

An Advanced Method for the Immunohistochemical Detection of Nitric Oxide Synthase (NOS) in the Female Genital Tract

The expression of nitric oxide synthase (NOS) in male and female urogenital tissues has been investigated by using conventional light microscopical immunoperoxidase staining. We present an improved immunohistochemical method for the specific and simultaneous detection of endothelial and neuronal NOS (eNOS/nNOS) in vaginal tissue. Specific antibodies have been used in combination with the tyramide signal amplification method. We found a subepithelial meshwork of varicose nerve fibers. A subpopulation of fibers presented immunoreactivity specific for nNOS. Epithelial cells also showed cytoplasmatic labeling for nNOS. Arteries presenting signals for eNOS in their endothelial layer were found in close proximity to nNOS-positive nerve fibers.

Re-evaluation of the immunohistochemical distribution of isoforms of nitric oxide synthase in the human prostate: A light and electron microscopical study

Up until today, there are still uncertainties regarding the occurrence of isoforms of the nitric oxide synthase (eNOS, nNOS) in the human prostate. While nNOS was exclusively seen in slender nerve fibres branching within the transition zone, eNOS was reported in glandular structures and also in small vessels interspersing the tissue. This study aimed to re-evaluate by means of light and electron microscopy (LM, EM), the distribution of eNOS and nNOS in the transition zone of the human prostate. Tissue specimens were obtained from 16 patients who underwent surgery for pelvic malignancies. Using specific antibodies in conjunction with advanced fixation and staining procedures, the occurrence of eNOS and nNOS was investigated. nNOS was detected in nerve fibres interspersing the tissue and was also seen in glandular structures. EM revealed that in glandular epithelial cells immunoreaction for nNOS was limited to the cytoplasmic compartment. Vascular endothelial cells of small vessels transversing glandular structures significantly stained for eNOS, while epithelial layers of prostatic glandules appeared free of eNOS. The results implicate that, in the prostate, nNOS is a mediator of stromal and glandular tissue function, and counteract the assumption of eNOS activity in glandular epithelial cells as a source of NO synthesis.

The role of nitric oxide in stroke

Stroke is considered to be an acute cerebrovascular disease, including ischemic stroke and hemorrhagic stroke. The high incidence and poor prognosis of stroke suggest that it is a highly disabling and highly lethal disease which can pose a serious threat to human health. Nitric oxide (NO), a common gas in nature, which is often thought as a toxic gas, because of its intimate relationship with the pathological processes of many diseases, especially in the regulation of blood flow and cell inflammation. However, recent years have witnessed an increased interest that NO plays a significant and positive role in stroke as an essential gas signal molecule. In view of the fact that the neuroprotective effect of NO is closely related to its concentration, cell type and time, only in the appropriate circumstances can NO play a protective effect. The purpose of this review is to summarize the roles of NO in ischemic stroke and hemorrhagic stroke.

Nanomolar nitric oxide concentrations quickly and reversibly modulate astrocytic energy metabolism

Nitric oxide (NO) is an intercellular messenger involved in multiple bodily functions. Prolonged NO exposure irreversibly inhibits respiration by covalent modification of mitochondrial cytochrome oxidase, a phenomenon of pathological relevance. However, the speed and potency of NO's metabolic effects at physiological concentrations are incompletely characterized. To this end, we set out to investigate the metabolic effects of NO in cultured astrocytes from mice by taking advantage of the high spatiotemporal resolution afforded by genetically encoded Förster resonance energy transfer (FRET) nanosensors. NO exposure resulted in immediate and reversible intracellular glucose depletion and lactate accumulation. Consistent with cytochrome oxidase involvement, the glycolytic effect was enhanced at a low oxygen level and became irreversible at a high NO concentration or after prolonged exposure. Measurements of both glycolytic rate and mitochondrial pyruvate consumption revealed significant effects even at nanomolar NO concentrations. We conclude that NO can modulate astrocytic energy metabolism in the short term, reversibly, and at concentrations known to be released by endothelial cells under physiological conditions. These findings suggest that NO modulates the size of the astrocytic lactate reservoir involved in neuronal fueling and signaling.

Brain BDNF levels are dependent on cerebrovascular endothelium-derived nitric oxide

Scientific evidence continues to demonstrate a link between endothelial function and cognition. Besides, several studies have identified a complex interplay between nitric oxide (NO) and brain-derived neurotrophic factor (BDNF), a neurotrophin largely involved in cognition. Therefore, this study investigated the link between cerebral endothelium-derived NO and BDNF signaling. For this purpose, levels of BDNF and the phosphorylated form of endothelial NO synthase at serine 1177 (p-eNOS) were simultaneously measured in the cortex and hippocampus of rats subjected to either bilateral common carotid occlusion (n = 6), physical exercise (n = 6) or a combination of both (n = 6) as experimental approaches to modulate flow-induced NO production by the cerebrovasculature. Tropomyosin-related kinase type B (TrkB) receptors and its phosphorylated form at tyrosine 816 (p-TrkB) were also measured. Moreover, we investigated BDNF synthesis in brain slices exposed to the NO donor glyceryl trinitrate. Our results showed increased p-eNOS and BDNF levels after exercise and decreased levels after vascular occlusion as compared to corresponding controls, with a positive correlation between changes in p-eNOS and BDNF (r = 0.679). Exercise after vascular occlusion did not change levels of these proteins. Gyceryl trinitrate increased proBDNF and BDNF levels in brain slices, thus suggesting a possible causal relationship between NO and BDNF. Moreover, vascular occlusion, like exercise, resulted in increased TrkB and p-TrkB levels, whereas no change was observed with the combination of both. These results suggest that brain BDNF signaling may be dependent on cerebral endothelium-derived NO production.

The role of nitric oxide in spatial memory stages, hippocampal ERK and CaMKII phosphorylation

Nitric oxide (NO) is an important intercellular messenger in the control of physiologic functions. It is synthesized by 3 different nitric oxide synthase enzymes (NOS). Uses of non-selective NOS inhibitor (L-NAME) have shown that NO is involved in neuronal plasticity and memory. This study aimed to determine the differential role of NO in spatial memory formation steps. In addition, regarding the roles of ERK and CaMKII in hippocampal plasticity, the hippocampal ERK and CaMKII activities were assessed to identify the effect of L-NAME on those proteins during each phase of memory. Adult male Sprague-Dawely rats weighing 220-280 g were trained in a single session consisting of 8 trials. To evaluate the effect of L-NAME on acquisition, L-NAME (3 or 10 mg/kg/i.p.) was administered 30 min before training. To assess its effect on the consolidation phase, L-NAME (3 or 10 mg/kg/i.p.) was injected immediately after training and a probe test was carried out 24 h later to analyse memory retention. To determine its effect on memory retrieval L-NAME (3 or 10 mg/kg/i.p.) was injected 30 min before probe trial which was conducted 24 h after training. The hippocampi were isolated after behavioural studies and western blotting analysis on hippocampal lysates was performed to illustrate the levels of phosphorylated ERK and CaMKII. The results showed that pre-training administration of L-NAME in 10 mg/kg but not 3mg/kg deteriorates acquisition. Post-training and pre-probe administration of L-NAME in 10 mg/kg but not 3 mg/kg impaired animal's performance in probe test. Additionally L-NAME treatment decreased the amount of phosphorylated (activated) ERK and CaMKII in the hippocampus. This study showed that endogenous nitric oxide is involved not only in all stages of memory, but also in ERK and CaMKII activation in the hippocampus during all 3 stages of memory.

Endothelial nitric oxide: protector of a healthy mind

Endothelial nitric oxide (NO) is generated by constitutively active endothelial nitric oxide synthase (eNOS), an essential enzyme responsible for cardiovascular homeostasis. Historically, endothelial NO was first recognized as a major vasodilator involved in control of vasomotor function and local blood flow. In this review, our attention is focused on the emerging role of endothelial NO in linking cerebrovascular function with cognition. We will discuss the recognized ability of endothelial NO to modulate processing of amyloid precursor protein (APP), influence functional status of microglia, and affect cognitive function. Existing evidence suggests that the loss of NO in cultured human cerebrovascular endothelium causes increased expression of APP and β-site APP-cleaving enzyme 1 (BACE1) thereby resulting in increased secretion of amyloid β peptides (Aβ1-40 and Aβ1-42). Furthermore, increased expression of APP and BACE1 as well as increased production of Aβ peptides was detected in the cerebral microvasculature and brain tissue of eNOS-deficient mice. Since Aβ peptides are considered major cytotoxic molecules responsible for the pathogenesis of Alzheimer's disease, these observations support the concept that a loss of endothelial NO might significantly contribute to the initiation and progression of cognitive decline. In addition, genetic inactivation of eNOS causes activation of microglia and promotes a pro-inflammatory phenotype in the brain. Behavioural analysis revealed that eNOS-deficient mice exhibit impaired cognitive performance thereby indicating that selective loss of endothelial NO has a detrimental effect on the function of neuronal cells. Together with findings from prior studies demonstrating the ability of endothelial NO to affect synaptic plasticity, mitochondrial biogenesis, and function of neuronal progenitor cells, it is becoming apparent that the role of endothelial NO in the control of central nervous system function is very complex. We propose that endothelial NO represents the key molecule linking cerebrovascular and neuronal function.

Is there a role for nitric oxide in methamphetamine-induced dopamine terminal degeneration?

Methamphetamine (METH) abuse results in long-term damage to the dopaminergic system, manifesting as decreases in dopamine (DA) tissue content, DA transporter binding, as well as tyrosine hydroxylase and vesicular monoamine transporter immunostaining. However, the exact cascade of events that ultimately result in this damage has not been clearly elucidated. One factor that has been heavily implicated in METH-induced DA terminal degeneration is the production of nitric oxide (NO). Unfortunately, many of the studies attempting to clarify the role of NO in METH-induced neurotoxicity have been confounded by issues such as the disruption of METH-induced hyperthermia, preventing the formation of strong conclusions. As a result, there is a body of work suggesting that NO is sufficient for METH-induced neurotoxicity, while other studies suggest that NO does not play a role in METH-induced degeneration of DA nerve terminals. This review summarizes the existing studies investigating the role of NO in METH-induced neurotoxicity, and argues that while NO may be necessary for METH-induced neurotoxicity, it is not sufficient. Finally, important areas of future investigation are highlighted and discussed.

Nitric oxide donors as neuroprotective agents after an ischemic stroke-related inflammatory reaction

Cerebral ischemia initiates a cascade of detrimental events including glutamate-associated excitotoxicity, intracellular calcium accumulation, formation of Reactive oxygen species (ROS), membrane lipid degradation, and DNA damage, which lead to the disruption of cellular homeostasis and structural damage of ischemic brain tissue. Cerebral ischemia also triggers acute inflammation, which exacerbates primary brain damage. Therefore, reducing oxidative stress (OS) and downregulating the inflammatory response are options that merit consideration as potential therapeutic targets for ischemic stroke. Consequently, agents capable of modulating both elements will constitute promising therapeutic solutions because clinically effective neuroprotectants have not yet been discovered and no specific therapy for stroke is available to date. Because of their ability to modulate both oxidative stress and the inflammatory response, much attention has been focused on the role of nitric oxide donors (NOD) as neuroprotective agents in the pathophysiology of cerebral ischemia-reperfusion injury. Given their short therapeutic window, NOD appears to be appropriate for use during neurosurgical procedures involving transient arterial occlusions, or in very early treatment of acute ischemic stroke, and also possibly as complementary treatment for neurodegenerative diseases such as Parkinson or Alzheimer, where oxidative stress is an important promoter of damage. In the present paper, we focus on the role of NOD as possible neuroprotective therapeutic agents for ischemia/reperfusion treatment.

Nitric oxide as key mediator of neuron-to-neuron and endothelia-to-glia communication involved in the neuroendocrine control of reproduction

Nitric oxide (NO) is a peculiar chemical transmitter that freely diffuses through aqueous and lipid environments and plays a role in major aspects of brain function. Within the hypothalamus, NO exerts critical effects upon the gonadotropin-releasing hormone (GnRH) network to maintain fertility. Here, we review recent evidence that NO regulates major aspects of the GnRH neuron physiology. Far more active than once thought, NO powerfully controls GnRH neuronal activity, GnRH release and structural plasticity at the neurohemal junction. In the preoptic region, neuronal nitric oxide synthase (nNOS) activity is tightly regulated by estrogens and is found to be maximal at the proestrus stage. Natural fluctuations of estrogens control both the differential coupling of this Ca²+-activated enzyme to glutamate N-methyl-D-aspartic acid receptor channels and phosphorylation-mediated nNOS activation. Furthermore, NO endogenously produced by neurons expressing nNOS acutely and directly suppresses spontaneous firing in GnRH neurons, which suggests that neuronal NO may serve as a synchronizing switch within the preoptic region. At the median eminence, NO is spontaneously released from an endothelial source and follows a pulsatile and cyclic pattern of secretion. Importantly, GnRH release appears to be causally related to endothelial NO release. NO is also highly involved in mediating the dialogue set in motion between vascular endothelial cells and tanycytes that control the direct access of GnRH neurons to the pituitary portal blood during the estrous cycle. Altogether, these data raise the intriguing possibility that the neuroendocrine brain uses NO to coordinate both GnRH neuronal activity and GnRH release at key stages of reproductive physiology.

Alarin stimulates food intake in male rats and LH secretion in castrated male rats

Alarin is a newly identified member of the galanin family of neuropeptides that includes galanin-like peptide (GALP) and galanin. Alarin was discovered as an alternate transcript of the GALP gene in neuroblastoma cells, and subsequently alarin mRNA was detected in the brain of rodents. GALP and galanin are important central regulators of both feeding and reproductive behavior. We hypothesized, that, as a member of the galanin family of peptides, alarin would also have central effects on feeding and reproduction. To test this hypothesis, we treated male rats with alarin intracerebroventricularly (i.c.v.) and measured its effects on food intake and energy homeostasis as well as sexual behavior and luteinizing hormone (LH) secretion. We observed that i.c.v. injection of 1.0 nmol alarin significantly increased food intake (p<0.01) and body weight (p<0.05). Alarin did not affect sexual behavior in male rats; however, alarin did significantly (p<0.01) increase LH levels in castrated, but not intact, male rats. Alarin immunoreactive cell bodies were detected within the locus coeruleus and locus subcoeruleus of the midbrain, which is a brainstem nucleus involved in coordinating many physiological activities, including food intake and reproduction. Lastly, alarin stimulated Fos induction in hypothalamic nuclei, such as the paraventricular nucleus and the nucleus of the tractus solitarious. Our studies demonstrate that alarin, like other members of the galanin family, is a neuromediator of food intake and body weight.

Concepts of neural nitric oxide-mediated transmission

As a chemical transmitter in the mammalian central nervous system, nitric oxide (NO) is still thought a bit of an oddity, yet this role extends back to the beginnings of the evolution of the nervous system, predating many of the more familiar neurotransmitters. During the 20 years since it became known, evidence has accumulated for NO subserving an increasing number of functions in the mammalian central nervous system, as anticipated from the wide distribution of its synthetic and signal transduction machinery within it. This review attempts to probe beneath those functions and consider the cellular and molecular mechanisms through which NO evokes short- and long-term modifications in neural performance. With any transmitter, understanding its receptors is vital for decoding the language of communication. The receptor proteins specialised to detect NO are coupled to cGMP formation and provide an astonishing degree of amplification of even brief, low amplitude NO signals. Emphasis is given to the diverse ways in which NO receptor activation initiates changes in neuronal excitability and synaptic strength by acting at pre- and/or postsynaptic locations. Signalling to non-neuronal cells and an unexpected line of communication between endothelial cells and brain cells are also covered. Viewed from a mechanistic perspective, NO conforms to many of the rules governing more conventional neurotransmission, particularly of the metabotropic type, but stands out as being more economical and versatile, attributes that presumably account for its spectacular evolutionary success.

Involvement of nitric oxide in insulin induced memory improvement

Although brain was considered as an insulin-insensitive organ, recently it has appeared that insulin has some interesting effects on some brain regions like hippocampus. It has been known that intra-hippocampally administered insulin can improve learning and memory. Knowing that insulin can stimulate nitric oxide (NO) synthesis via eNOS activation and also that NO synthase (NOS) inhibitors can affect learning and memory, the aim of this study was to assess if NO is involved in insulin induced memory improvement. Wistar male rats were intra-CA1 cannulated and the effect of post-training and pre-probe trial intra-hippocampal administration of N-nitro-L-arginine methyl ester (L-NAME) (5, 10, 30 microg), insulin+L-NAME+/-L-arginine were assessed in a single-day testing version of Morris water maze (MWM) task. Our results show that, l-NAME can prevent insulin induced memory improvement. This drug had no effect on escape latency of a non-spatial visual discrimination task. Therefore, it seems that endogenous nitric oxide has a role in spatial learning and memory improvement caused by insulin.

NO/cGMP-dependent modulation of synaptic transmission

Nitric oxide (NO) is a multifunctional messenger in the CNS that can signal both in antero- and retrograde directions across synapses. Many effects of NO are mediated through its canonical receptor, the soluble guanylyl cyclase, and the second messenger cyclic guanosine-3',5'-monophosphate (cGMP). An increase of cGMP can also arise independently of NO via activation of membrane-bound particulate guanylyl cyclases by natriuretic peptides. The classical targets of cGMP are cGMP-dependent protein kinases (cGKs), cyclic nucleotide hydrolysing phosphodiesterases, and cyclic nucleotide-gated (CNG) cation channels. The NO/cGMP/cGK signalling cascade has been linked to the modulation of transmitter release and synaptic plasticity by numerous pharmacological and genetic studies. This review focuses on the role of NO as a retrograde messenger in long-term potentiation of transmitter release in the hippocampus. Presynaptic mechanisms of NO/cGMP/cGK signalling will be discussed with recently identified potential downstream components such as CaMKII, the vasodilator-stimulated phosphoprotein, and regulators of G protein signalling. NO has further been suggested to increase transmitter release through presynaptic clustering of a-synuclein. Alternative modes of NO/cGMP signalling resulting in inhibition of transmitter release and long-term depression of synaptic activity will also be addressed, as well as anterograde NO signalling in the cerebellum. Finally, emerging evidence for cGMP signalling through CNG channels and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels will be discussed.

Differences in inflammatory pain in nNOS-, iNOS- and eNOS-deficient mice

To assess the relative importance of the isoforms of nitric oxide synthase (NOS) in inflammatory pain, we directly compared pain behaviour and paw thickness after intraplantar injection of complete Freund's adjuvant (CFA) in wild-type (WT) mice and in mice lacking either inducible (iNOS), endothelial (eNOS) or neuronal NOS (nNOS). In mice deficient for nNOS, thermal hyperalgesia was reduced by approximately 50% compared to wild type mice at 4 and 8h after CFA injection, and mechanical hypersensitivity was absent. The only change in pain behaviour in iNOS and eNOS deficient mice compared to WT mice was a more rapid recovery from thermal hyperalgesia. A compensatory up-regulation of nNOS in dorsal root ganglia (DRG) and spinal cords of iNOS and eNOS knockout mice was excluded using RT-PCR. However, an increase of iNOS gene expression was found in spinal cords of eNOS and nNOS deficient mice. To study the downstream effects of nNOS deficiency on DRG neurones, we assessed their immunoreactivity for calcitonin gene-related peptide (CGRP) and cytokines. We found a significant reduction in the CFA induced increase in CGRP immunoreactive neurones as well as in CGRP gene expression in nNOS deficient mice, whereas the percentage of cells immunopositive for tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) was unchanged. These results support the proposed role of nNOS in sensitization of DRG neurones, and might indicate that CGRP is involved in this process.

Tonic and phasic nitric oxide signals in hippocampal long-term potentiation

Nitric oxide (NO) participates in long-term potentiation (LTP) and other forms of synaptic plasticity in many different brain areas but where it comes from and how it acts remain controversial. Using rat and mouse hippocampal slices, we tested the hypothesis that tonic and phasic NO signals are needed and that they derive from different NO synthase isoforms. NMDA increased NO production in a manner that was potently inhibited by three different neuronal NO synthase (nNOS) inhibitors. Tonic NO could be monitored after sensitizing guanylyl cyclase-coupled NO receptors, allowing the very low ambient NO concentrations to be detected by cGMP measurement. The levels were unaffected by inhibition of NMDA receptors, nNOS, or the inducible NO synthase (iNOS). iNOS was also undetectable in protein or activity assays. Tonic NO was susceptible to agents inhibiting endothelial NO synthase (eNOS) and was missing in eNOS knock-out mice. The eNOS knock-outs exhibited a deficiency in LTP resembling that seen in wild-types treated with a NO synthase inhibitor. LTP in the knock-outs could be fully restored by supplying a low level of NO exogenously. Inhibition of nNOS also caused a major loss of LTP, particularly of late-LTP. Again, exogenous NO could compensate, but higher concentrations were needed compared with those restoring LTP in the eNOS knock-outs. It is concluded that tonic and phasic NO signals are both required for hippocampal LTP and the two are generated, respectively, by eNOS and nNOS, the former in blood vessels and the latter in neurons.

Signaling from blood vessels to CNS axons through nitric oxide

Brain function is usually perceived as being performed by neurons with the support of glial cells, the network of blood vessels situated nearby serving simply to provide nutrient and to dispose of metabolic waste. Revising this view, we find from experiments on a rodent central white matter tract (the optic nerve) in vitro that microvascular endothelial cells signal persistently to axons using nitric oxide (NO) derived from the endothelial NO synthase (eNOS). The endogenous NO acts to stimulate guanylyl cyclase-coupled NO receptors in the axons, leading to a raised cGMP level which then causes membrane depolarization, apparently by directly engaging hyperpolarization-activated cyclic nucleotide-gated ion channels. The tonic depolarization and associated endogenous NO-dependent cGMP generation was absent in optic nerves from mice lacking eNOS, although such nerves responded to exogenous NO, with raised cGMP generation in the axons and associated depolarization. In addition to the tonic activity, exposure of optic nerves to bradykinin, a classical stimulator of eNOS in endothelial cells, elicited reversible NO- and cGMP-dependent depolarization through activation of bradykinin B2 receptors, to which eNOS is physically complexed. No contribution of other NO synthase isoforms to either the action of bradykinin or the continuous ambient NO level could be detected. The results suggest that microvascular endothelial cells participate in signal processing in the brain and can do so by generating both tonic and phasic NO signals.

Detection of angiotensin II mediated nitric oxide release within the nucleus of the solitary tract using electron-paramagnetic resonance (EPR) spectroscopy

We previously identified an action of nitric oxide (NO) within the nucleus tractus solitarii (NTS) that attenuates the cardiac component of the baroreceptor reflex. In the present study we have tested the hypothesis that angiotensin II (AngII), acting on angiotensin type 1 receptors (AT1R), can release NO within the NTS and that its actions are mediated by soluble guanylate cyclase (sGC). Utilising cryogenic electron paramagnetic resonance (EPR), we have detected NO release in brainstem samples following AngII, but not saline, microinjections into the NTS. In these experiments, we confirmed that both AngII and a NO donor (diethylamine NONOate) in the NTS both depressed the baroreflex bradycardia. In additional studies, we showed that the latter effects were both sensitive to blockade of sGC using 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ). To initiate studies to resolve the cellular source of NO released by angiotensin II in the NTS, we performed immunohistochemical/electron microscopy studies on the distribution of AT1R. We found AT1R located on NTS neurones and blood vessels. Since a rise in intracellular calcium [Ca]i levels is prerequisite for nNOS activation, we imaged responses in [Ca]i in NTS neurones during exposure to AngII in vitro using confocal microscopy. Our data indicate a paucity of neurones showing changes in [Ca]i when exposed to AngII (200 nM). We suggest that AngII-induced release of NO is from non-neuronal sites. With the presence of AT1R on blood vessel endothelial cells we propose that AngII released NO in the NTS is due to activation of endothelial nitric oxide synthase located within the endothelium. The present study supports the novel concept that AngII can trigger NO release in the NTS by a mechanism of vascular-neuronal signalling that affects central neuronal networks regulating cardiovascular function.

NOS isoenzyme content in brain nuclei as related to food intake in experimental cancer cachexia

Evidence implies that nitric oxide (NO) in the central nervous systems mediates anorexia in tumor-bearing hosts. We have therefore evaluated, by immunohistochemical image analyses, net alterations of nitric oxide synthases (nNOS, eNOS, iNOS) in brain nuclei [paraventricular hypothalamic nucleus (PVN), medial habenular nucleus (MHB), lateral habenular nucleus (LHB), paraventricular thalamic nucleus (PV), lateral hypothalamic area (LHA), ventromedial hypothalamic nucleus (VMH), nucleus of the solitary tract (NTS)] of tumor-bearing mice (TB) with prostanoid-related anorexia. Pair-fed (PF) and freely fed (FF) non-tumor-bearing mice were used as controls. c-fos was analyzed as indicator of neuronal activation. nNOS was significantly increased in VMH and PVN from TB mice, while eNOS was significantly increased in LHB and LHA. iNOS was significantly increased in LHA and PVN nuclei, but decreased in MHB, LHB and VMH from tumor-bearers. However, several of these alterations were similarly observed in brain nuclei from pair-fed controls. Provision of unspecific NOS-antagonists to TB mice increased nNOS, eNOS and iNOS in several brain nuclei (PVN, LHA, VMH), but left tumor-induced anorexia unchanged. c-fos was significantly increased in all brain nuclei in PF mice except for NTS, LHA and PVN compared to controls, while tumor-bearing mice had increased c-fos in LHA and PVN only compared to controls. Our results demonstrate a complex picture of NOS expression in brain areas of relevance for appetite in tumor-bearing hosts, where most changes seemed to be secondary to stress during negative energy balance. By contrast, NOS content in PVN and LHA nuclei remains candidate behind anorexia in tumor disease. However, nitric oxide does not seem to be a primary mediator behind tumor-induced anorexia. NO may rather secondarily support energy intake in conditions with negative energy balance.

Neuropeptide Y and its receptor analogs differentially modulate the immunoreactivity for neuronal or endothelial nitric oxide synthase in the rat brain following focal ischemia with reperfusion

An intracerebroventricular (i.c.v.) injection of neuropeptide Y (NPY) or [Leu31, Pro34]-NPY (non-Y2 receptor agonist) given during middle cerebral artery occlusion (MCAO) increases the infarct volume and nitric oxide (NO) overproduction in the rat brain. An i.c.v. injection of NPY3-36 (non-Y1 receptor agonist) has no effects, while BIBP3226 (selective Y1 receptor antagonist) reduces the infarct volume and NO overproduction. This study examined the effects of NPY or its receptor analog on the immunoreactivity (ir) for three isoforms of NO synthase (NOS) following 1 h of MCAO and 3 h of reperfusion. Focal ischemia/reperfusion led to increased ir for neuronal NOS (nNOS) within the ipsilateral caudate putamen and insular cortex. NPY or [Leu31, Pro34]-NPY enhanced but BIBP3226 suppressed such increase in the nNOS-ir. Focal ischemia/reperfusion also led to an ipsilateral increase in extent and/or intensity of the ir for endothelial NOS (eNOS) in the caudate putamen and/or parietal cortex. NPY or [Leu31, Pro34]-NPY suppressed but BIBP3226 enhanced such change in the eNOS-ir. NPY3-36 did not consistently influence the nNOS-ir or eNOS-ir following MCAO. Specific ir for inducible NOS was undetectable. These opposing effects of NPY-Y1 receptor activation or inhibition on nNOS and eNOS may lead to harmful or beneficial consequences following ischemia/reperfusion.

Hippocampal nitric oxide synthase and arginase and age-associated behavioral deficits

The present study investigated age-related changes in nitric oxide synthase (NOS) and arginase in the subregions of the hippocampus and their correlations with animals' performance in the open field, T-maze, and water maze tasks. Aged rats (24 months old) showed reduced exploratory activity and poorer spatial learning relative to the young adults (4 months old). Significant increases in total NOS activity were found in the aged dentate gyrus and a dramatic decrease in endothelial NOS expression was observed in the aged CA2/3. Activity or protein expression of inducible NOS was not detected in any subregion of the hippocampus. There were no age-related changes in total arginase activity or arginase I and arginase II protein expression. Correlation analysis revealed that animals' motor ability was associated with CA1 NOS and arginase, as well as hippocampal function. The present findings provide further support for the involvement of NOS/NO and arginase in the normal aging process. A strong positive correlation between CA1 eNOS protein expression and swimming speed in the water maze task may reflect a relationship between the local cerebral blood flow and neuronal activity.

Species, strain and developmental variations in hippocampal neuronal and endothelial nitric oxide synthase clarify discrepancies in nitric oxide-dependent synaptic plasticity

Nitric oxide (NO) has been implicated in long-term potentiation (LTP) in pyramidal neurons in cellular area 1 (CA1) of the hippocampus. However, considerable confusion exists about the exact role of NO, and the contribution of the endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) isoforms of NO synthase to NO-dependent LTP (NO-LTP), with results often varying, depending on the organism and experimental paradigm used. Using immunohistochemistry and in situ hybridization, we contrast NO synthase expression and activity in rat, mouse, and human hippocampus. nNOS is prominently expressed in all CA1 pyramidal cells of C57B6 mice and humans, while in rats and SV129 mice, its levels are much lower and restricted to the caudal hippocampus. By contrast, eNOS is restricted to endothelial cells. We observe N-methyl-D-aspartate-dependent citrulline production in pyramidal cells of mouse hippocampus, which is absent in nNOS(Delta/Delta) animals. Finally, we observe robust nNOS expression in human CA1 pyramidal cells.The considerable axial, developmental, strain and species-dependent variations in nNOS expression in CA1 pyramidal neurons can explain much of the variation observed in reports of NO-dependent LTP. Moreover, our data suggest that NO produced by eNOS in endothelial cells may play a paracrine role in modulating LTP.

Immunocytochemical distribution of nitric oxide synthase in the human seminal vesicle: a light and electron microscopical study

Although nitric oxide (NO) has been proven to be one of the most important non-adrenergic, non-cholinergic mediators in the control of human reproductive tract organs, to date information on the significance of NO-mediated signal transduction in the control of human seminal vesicle (SV) function is still sparse.()Recent investigations have underlined the significance of NO in the maintenance of sperm capacitation and viscosity of the seminal plasma as well as in the control of mammalian seminal vesicle smooth muscle tone. In order to further investigate the functional impact of NO on the regulation of normal SV function, we examined the distribution of NADPH-diaphorase (NADPH-d), endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) in the cellular anatomy of human SV by means of light and electron microscopical immunocytochemistry (LM, EM) in combination with the tyramide signal amplification technique. Human SV were obtained from 15 patients who had undergone surgery for pelvic malignancies (carcinoma of the prostate or urinary bladder). SV specimens were fixed, sectioned and examined by LM and EM for the presence of NAPDH-d, eNOS and nNOS using specific antibodies and advanced staining procedures. LM revealed a dense NADPH-d reaction in glandular epithelial structures, whereas no substantial labeling was detected in the fibromuscular stroma. EM showed that the NADPH-d reaction product was abundantly detectable attached to membranes of the endoplasmic reticulum, mitochondria and the nuclei of glandular epithelial cells. nNOS staining was found in nerve fibers branching within the SV tissue. eNOS staining was present in small vessels but was only observed to a minor degree in glandular and subglandular structures and the smooth muscle stroma. Our results support the hypothesis that human SV is a site of NO production. The distribution of NADPH-d may give rise to the speculation that NO is mainly involved in the regulation of SV secretory activity. The sparse correlation between NADPH-d-, eNOS- and nNOS-staining might hint at the existence of a previously unidentified NOS isoform in human SV.

Role of endothelin type B receptor in NO/cGMP signaling pathway in rat median eminence

We studied the effect of endothelins (ETs) on receptor-mediated NO/cGMP signaling in rat arcuate nucleus-median eminence (AN-ME) fragments, an hypothalamic structure known to contain a rich plexus of nitric oxide synthase (NOS)-containing neurons and fibers together with densely arranged ET(B)-receptor-like immunoreactive fibers. NOS activity was determined measuring the conversion of [3H] arginine to [3H] citrulline, as an index of NO produced. cGMP production was determined by radio immunoassay. ET-1, ET-3, and the selective ET(B) receptor agonist, IRL1620, significantly increased cGMP formation and NOS activity. Preincubation of AN-ME fragment with L-arginine analog, N-nitro-L-arginine (L-NAME), inhibited ET-1 or IRL1620-stimulated cGMP formation. The addition of theselective ET(B) receptor antagonist, BQ788, blocked ET-1-, ET-3-, or IRL1620-induced increase in NOS activity and cGMP generation, while BQ123, a selective ET(A) receptor antagonist, was ineffective. Our results demonstrate that in whole rat AN-ME fragments, ETs stimulate NO/cGMP signaling pathway through the interaction with the ET(B) receptor subtype, supporting the concept that ETs may represent an important regulator of reproductive and neuroendocrine function.

Nitric oxide and autonomic control of heart rate: a question of specificity

Despite its highly diffusible nature, the gaseous signalling molecule nitric oxide (NO) can exert specific effects within the CNS and PNS. To date, the specificity of the actions of NO remains an unsolved puzzle. There are several plausible mechanisms that might account for this specificity in the context of autonomic regulation of heart rate. NO acts at distinct levels within the autonomic nervous system to control cardiac rate, with opposing effects at different sites. We discuss factors that might contribute to this diversity of action, and conclude that the isoform of enzyme involved in producing NO, the spatial proximity of the NO source to the target, and differences in the intracellular coupling within the target cell are all crucial for encoding the functional action of NO.

Genetic and pharmacological dissection of pathways involved in the angiotensin II-mediated depression of baroreflex function

Heart failure and hypertension are associated with increases in angiotensin II (ANG II) activity. One brain area where ANG II effects may be particularly important in these situations is the nucleus of the solitary tract (NTS). Located in the dorsomedial medulla, the NTS is the termination site of baroreceptor afferents and is essential for mediating the baroreflex. In hypertensive animals the baroreflex is impaired; this may be reversed by antagonizing ANG II AT1 receptors in the NTS. Recently, we showed that the baroreflex depressant action of ANG II in the NTS is mediated by activation of endothelial nitric oxide synthase (eNOS) and enhanced release of GABA. Using conventional pharmacological tools and a range of adenoviral-mediated expression of dominant negative proteins, we have determined the intracellular pathway(s) in the NTS by which ANG II activates eNOS. Our data indicate that ANG II acting in the NTS depresses the baroreflex via a Gq protein-mediated activation of phospholipase C, which through 1,4,5-inositol triphosphate causes release of calcium from the IP3-sensitive intracellular stores and calcium-calmodulin formation. In contrast, multiple site disruption of a pathway leading to eNOS activation via the serine/threonine kinase Akt was ineffective

Unaltered radial maze performance and brain acetylcholine of the endothelial nitric oxide synthase knockout mouse

Proceeding from previous findings of a beneficial effect of endothelial nitric oxide synthase (eNOS) gene inactivation on negatively reinforced water maze performance, we asked whether this improvement in place learning capacities also holds for a positively reinforced radial maze task. Unlike its beneficial effects on the water maze task, eNOS gene inactivation did not facilitate radial maze performance. The acquisition performance over the days of place learning did not differ between eNOS knockout (eNOS-/-) and wild-type mice (eNOS+/+). eNOS-/- mice displayed a slight and eNOS+/+ mice a more severe working memory deficit in the place learning version of the radial maze compared to the genetic background C57BL/6 strain. Possible differential effects of eNOS inactivation, related to differences in reinforcement contingencies between the Morris water maze and radial maze tasks, behavioral strategy requirements, or to different emotional and physiological concomitants inherent in the two tasks are discussed. These task-unique characteristics might be differentially affected by the reported anxiogenic and hypertensional effects of eNOS gene inactivation. Post-mortem determination of acetylcholine concentrations in diverse brain structures revealed that acetylcholine and choline contents were not different between eNOS-/- and eNOS+/+ mice, but were increased in eNOS+/+ mice compared to C57BL/6 mice in the frontal cortex. Our findings demonstrate that phenotyping of learning and memory capacities should not rely on one learning task only, but should include tasks employing both negative and positive reinforcement contingencies in order to allow valid statements regarding differences in learning capacities between rodent strains.

A comparison of anti-biotin and biotinylated anti-avidin double-bridge and biotinylated tyramide immunohistochemical amplification

Often it is difficult to detect very small amounts of antigen with conventional immunohistochemical techniques. We evaluate three amplification techniques involving anti-biotin or anti-avidin double-bridges or biotinylated tyramide amplification to enhance the sensitivity of serotonin transporter immunohistochemistry. For the anti-biotin double-bridge, after the secondary antibody, the sections were incubated in anti-biotin antibody followed by a second incubation in the secondary antibody and then avidin-biotin-peroxidase complex (ABC). For the biotinylated anti-avidin technique, after the ABC, sections were incubated in biotinylated anti-avidin, followed by another incubation in ABC. For the biotinylated tyramide technique, after the ABC step, sections were incubated in biotinylated tyramide and hydrogen peroxide, followed by another incubation in ABC. The anti-biotin double-bridge also resulted in a large increase in the number of stained fibers and the intensity of labeling with no increase in background. A biotinylated anti-avidin double-bridge also produced significant signal amplification but significant background. The biotinylated tyramide technique resulted in an even larger increase in the number of labeled fibers and an intensity of their staining with a moderate amount of background staining. However, this advantage was not present at high dilutions of primary antibody. Thus, the anti-biotin double-bridge is likely to be useful in immunohistochemistry and immunofluorescence as well as other situations where increased sensitivity and low background from biotin markers is needed. The biotinylated tyramide technique may also be useful where some degree of background labeling is acceptable.

Lack of neuronal NOS has consequences for the expression of POMC and POMC-derived peptides in the mouse pituitary

The relevance of NO in neuroendocrine signalling has been investigated by analysis of cellular expression of pro-opiomelanocortin (POMC) and the POMC-derived peptides beta-endorphin, alpha-melanocyte stimulating hormone and adrenocorticotropin. Expression patterns were studied in the pituitary gland of 150-day old wild-type and neuronal-NOS (nNOS) knock-out mice by using immunohistochemistry, in situ hybridization and Northern blot analysis. Remaining NO-generating capacities in the knock-out mice were demonstrated by immunohistochemical localization of inducible, endothelial and neuronal NOS isoforms. Quantitative analysis revealed that cellular expression of POMC mRNA was drastically reduced in the pituitary of knock-out mice in comparison to controls. In situ hybridization studies demonstrated that this reduction was most pronounced in the intermediate lobe, while the anterior lobe was much less affected. Immunostaining for the proteolytic fragments of POMC was significantly reduced in the intermediate lobe cells of knock-out mice. A moderate reduction of immunostaining for these peptides was also observed in adenopituitary cells of nNOS knock-out mice. Our data demonstrate that the lack of nNOS substantially affects cellular levels of pituitary opioid peptides, which may have consequences for the response of these animals to stress and pain.

Amplification methods for the immunolocalization of rare molecules in cells and tissues

The needs to precisely assign macromolecules to specific locations and domains within tissues and cells and to reveal antigens which are present in low or even in trace amounts, led to the elaboration of a wide spectrum of immunocytochemical amplification procedures. These arise from the successive improvements of tissue preparation techniques, of antigen retrieval procedures and of immunological or non-immunological detection systems. Improvement of detection systems may be the most active in the development of amplification techniques. Since the early work of Coons, in which by the introduction of the indirect technique has started amplifying the signal, different systems have succeeded in increasing the sensitivity of antigens detection. Indeed, amplification techniques such as the multiple antibody layers, the multiple bridges, the enzyme complexes, the avidin-biotin, the silver intensification, and the numerous variations and combinations among these have increased the sensitivity for the detection of scarce tissue antigens. However, as shown by the recent progress carried out with new approaches such as the catalyzed reporter deposition (CARD) and the enhanced polymer one-step staining (EPOS), more efficient methods are still needed. In electron microscopy, few techniques have reached the resolution afforded by the post-embedding immunogold approach. In spite of this and in order to further increase its sensitivity, new probes and novel approaches are allowing combination of the gold marker with the amplification capacity of enzymes afforded by the CARD technique. Immunogold amplification strategies, such as the multiple incubations with the primary antibody and the use of an anti-protein A antibody have also led to enhanced signals displaying the advantages in terms of resolution and possibilities of quantification inherent to the colloidal gold marker.

Specific labeling of connexin43 in NRK cells using tyramide-based signal amplification and fluorescence photooxidation

Imaging of gap junction proteins, the connexins, has been performed in tissue culture cells both by labeling of connexins with immunocytochemical tags and by cloning and expressing chimeras of connexins and fluorescent proteins such as Green Fluorescent Protein. These two approaches have been used to gain information about protein localization or trafficking at light microscopic resolution. Electron microscopy provides higher resolution; however, analysis of electron micrographs of unlabeled connexins has been generally limited to recognition of gap junction structures. Immunolabeling of gap junction proteins in whole cells at the electron microscopic level has been difficult to achieve because of the fixation sensitivity of most gap junction antibodies. To obtain reasonable sensitivity, immunoperoxidase procedures are typically employed, and these suffer from relatively poor resolution. Here we describe the combination of tyramide signal amplification techniques and fluorescence photooxidation for higher resolution immunolocalization studies for correlative light and electron microscopic imaging. By using correlative microscopy, we can not only localize connexin pools or structures, but also discover what other cellular substructures interact with gap junction proteins. The use of tyramide signal amplification techniques is necessary to increase fluorescence levels that have decreased due to increased specimen fixation required to maintain cell ultrastructure. The fluorescence photooxidation technique provides a high-resolution method for staining of proteins in cells. Unlike colloidal gold-based methods, fluorescence photooxidation allows for three-dimensional localization using high-voltage electron microscopy.

Constitutively synthesized nitric oxide is a physiological negative regulator of mammalian angiogenesis mediated by basic fibroblast growth factor

We recently reported that the systemically administered nitric oxide synthase (NOS) inhibitor Nw-nitro-L-arginine methyl ester, L-NAME, administered before, during and after the angiogenic treatment stimulated angiogenesis induced by basic fibroblast growth factor, bFGF, in the rat. This suggests that suppression of constitutively expressed NOS, cNOS, plus inducible NOS, iNOS, and thus reduced production of nitric oxide, NO, was the stimulating factor. In those studies, the rat mesenteric-window angiogenesis assay was used. Moreover, the systemic administration of a NO releaser inhibited bFGF-mediated angiogenesis. Using the same experimental system, we have now studied whether the inhibition of cNOS alone in adult animals under physiological conditions, i.e. prior to the administration of the angiogenic stimulation with bFGF, affected the subsequent angiogenic response. cNOS constitute endothelial cell NOS (ecNOS) and neuronal NOS (nNOS). L-NAME or its inactive enantiomer Nw-nitro-D-arginine methyl ester, D-NAME, were given continuously in the drinking water (1.0 g/L) during 14 days prior to the start of the treatment with bFGF. The treatment with L-NAME significantly enhanced the subsequent angiogenic response. NO synthesized under physiological conditions by ecNOS in endothelial cells and platelets or nNOS in platelets may thus act as a first constitutional angiostatic factor in bFGF-mediated mammalian angiogenesis.

Median eminence nitric oxide signaling

It is becoming increasingly clear that nitric oxide (NO), an active free radical formed during the conversion of arginine to citrulline by the enzyme NO synthase (NOS), is a critical neurotransmitter and biological mediator of the neuroendocrine axis. Current evidence suggests that NO modulates the activity of both the hypothalamic-pituitary-gonadal axis and the hypothalamic-pituitary-adrenal axis. Supporting this hypothesis is the finding that the highest expression of neuronal NOS in the brain is found within the hypothalamus in areas where the cell bodies of the neurons from the different neuroendocrine systems are located. In this regard, the influence of neuronal NO on the regulation of the neuroendocrine neural cell body activity has been well-documented whereas little is known about NO signaling that directly modulates neurohormonal release into the pituitary portal vessels from the neuroendocrine terminals within the median eminence, the common termination field of the adenohypophysiotropic systems. Studies in rat suggest that NO is an important factor controlling both gonadotropin-releasing hormone (GnRH) and corticotropin-releasing hormone (CRH) release at the median eminence. The recent use of amperometric NO detection from median eminence fragments coupled to the use of selective NOS inhibitors demonstrated that a major source of NO at the median eminence might be endothelial in origin rather than neuronal. The present article reviews the recent progress in identifying the origin and the role of the NO produced at the median eminence in the control of neurohormonal release. We also discuss the potential implications of the putative involvement of the median eminence endothelial cells in a neurovascular regulatory process for hypothalamic neurohormonal signaling.

Superior water maze performance and increase in fear-related behavior in the endothelial nitric oxide synthase-deficient mouse together with monoamine changes in cerebellum and ventral striatum

Nitric oxide (NO) has been implicated in the control of emotion, learning, and memory. We have examined endothelial NO synthase-deficient mice (eNOS-/-) in terms of habituation to an open field, elevated plus-maze behavior, Morris water maze performance, and changes in cerebral monoamines. In the open field, eNOS-/- animals were less active than wild-type controls but showed unimpaired habituation. In the plus-maze, an anxiogenic effect was observed. Proceeding from previous findings of deficits in hippocampal and neocortical long-term potentiation (LTP) in our eNOS-/- mice, we investigated whether these animals also express deficits in learning tasks that have been linked to hippocampal function and LTP. Unexpectedly, eNOS gene disruption led to accelerated place learning in the water maze. Furthermore, during long-term retention and reversal learning, eNOS-/- mice showed improved performance. In a cued version of the water maze task, eNOS-/- and control mice did not differ, implying that the superior performance of eNOS-/- animals on the former tasks cannot be attributed solely to differences in sensorimotor capacities. The neurochemical evaluation of the eNOS-/- mice revealed increases in the concentrations of the serotonin metabolite 5-HIAA in the cerebellum, together with an accelerated serotonin turnover in the frontal cortex. Furthermore, eNOS-/- mice had a higher dopamine turnover in the ventral striatum. These findings are discussed in terms of possible concomitant effects on physiological parameters, such as a decreased reactivity of GABAergic neurotransmission or changes in vascular functions, and effects on behavioral processes related to reinforcement, learning, and emotion.

Nitric oxide regulates body temperature, neuronal activation and interleukin-1 beta gene expression in the hypothalamic paraventricular nucleus in response to immune stress

An immune challenge initiates a complex cascade of events in the body including important responses from the central nervous system. As nitric oxide (NO) has been implicated in the central regulation of neuroendocrine and autonomic responses, this study was performed to determine if NO regulates physiological responses, neuronal activation, and/or interleukin-1 beta (IL-1 beta) gene expression in the paraventricular nucleus of the rat hypothalamus (PVN) in response to intravenous endotoxin, lipopolysaccharide (LPS, 100 microg/kg). Intracerebroventricular injections of NO synthase (NOS) inhibitors (7-nitroindazole sodium salt for neuronal NOS, N(G)-nitro-L-arginine for neuronal NOS and endothelial NOS, and aminoguanidine for inducible NOS) in LPS-treated rats showed that inhibition of NOS eliminated the drop in body temperature and led to increased neuronal activation in the PVN as assessed by immunohistochemistry for Fos-like immunoreactivity. Activation of NO-producing PVN neurons was also increased in these rats suggesting that NO influences neuronal NOS activity in PVN neurons. Finally, increased IL-1 beta gene expression in the PVN of LPS-treated rats receiving N(G)-nitro-L-arginine showed that NO regulates brain IL-1 beta gene expression. The results obtained with the NOS inhibitors support the hypothesis that NO produced from eNOS in the brain participates in temperature regulation, and inhibits PVN neuronal activity and IL-1 beta gene expression during immune stress.

Maternal aggression in endothelial nitric oxide synthase-deficient mice

Lactating female rodents protect their pups by expressing fierce aggression, termed maternal aggression, toward intruders. Mice lacking the neuronal nitric oxide synthase gene (nNOS-/-) exhibit significantly impaired maternal aggression, but increased male aggression, suggesting that nitric oxide (NO) produced by nNOS has opposite actions in maternal and male aggression. In contrast, mice lacking the endothelial nitric oxide synthase gene (eNOS-/-) exhibit almost no male aggression, suggesting that NO produced by eNOS facilitates male aggression. In the present study, maternal aggression in eNOS-/- mice was examined and found to be normal relative to wild-type (WT) mice in terms of the percentage displaying aggression, the average number of attacks against a male intruder, and the total amount of time spent attacking the male intruder. The eNOS-/- females also displayed normal pup retrieval behavior. Because a significant elevation of citrulline, an indirect marker of NO synthesis, occurs in neurons of the hypothalamus of lactating WT mice in association with maternal aggression, we examined the brains of eNOS-/- females for citrulline immunoreactivity following an aggressive encounter. The aggressive eNOS-/- females exhibited a significant elevation of citrulline in the medial preoptic nucleus and the subparaventricular zone of the hypothalamus relative to unstimulated lactating eNOS-/- females. Taken together, these results suggest that NO produced by eNOS neither facilitates nor inhibits maternal aggression and that NO produced by eNOS has a different role in maternal and male aggression.

Immunoelectron microscopy in the age of molecular pathology

The introduction of molecular biology-based diagnostic procedures in pathology has created substantial expectations in regard to screening, characterization, monitoring, and detection of predisposition to a variety of diseases, most notably malignant neoplasms. It should be emphasized, however, that molecular studies are only one component of the diagnostic process and that more traditional methods are still required in the evaluation of tumors and management of patients. The data obtained from the molecular biology-based studies must be always interpreted in conjunction with the clinical history, immunomorphologic findings, and other pertinent ancillary data. Routine evaluation of tissues using traditional light microscopy remains the backbone of pathologic evaluation. The additive role of molecular diagnostics often depends on how accurate the initial evaluation has been. Ancillary techniques such as immunohistochemistry and electron microscopy remain essential in properly characterizing diseased tissues and in speciation of tumors. Ultrastructural immunolabeling capitalizes on combining these two techniques and providing exquisite immunomorphologic evaluation. The extra time and effort required are more than compensated by the degree of sophistication that can be achieved when this diagnostic technique is utilized and the added expense is rather reasonable. The value of molecular biology-based diagnostics is potentially questionable if the tissue samples are not initially accurately characterized. The question that molecular diagnostics may be trying to answer may be the wrong one or the answer obtained may be interpreted incorrectly if the context of the clinicopathologic situation has not been clearly defined using traditional diagnostic techniques.

Novel application of tyramide signal amplification (TSA): ultrastructural visualization of double-labeled immunofluorescent axonal profiles

Fluorescent immunocytochemistry (FICC) allows multiple labeling approaches when enzyme-based techniques are difficult to combine, such as in double-labeling experiments targeting small-caliber axonal segments. Nevertheless, the conversion of FICC to a product visible at the electron microscopic (EM) level requires labor-intensive procedures, thus justifying the development of more user-friendly conversion methods. This study was initiated to simplify the conversion of FICC to EM by employing the unique properties of tyramide signal amplification (TSA), which allowed the simultaneous targeting of a fluorescent tag and biotin label to the same antigenic site. Briefly, one of two antigenic sites typically co-localized in damaged axonal segments was visualized by the application of a fluorescent secondary antibody, with the other tagged via a biotinylated antibody. Next, an ABC kit was used, followed by the simultaneous application of fluorophore-tyramide and biotin-tyramide. After temporary mounting for fluorescent digital photomicroscopy, sections were incubated in ABC and reacted with diaminobenzidine before EM analysis. Double-labeling fluorescent immunocytochemistry with TSA clearly delineated damaged axonal segments. In addition, these same axonal segments yielded high-quality EM images with discrete electron-dense reaction products, thereby providing a simple and reproducible means for following fluorescent analysis with EM.