Dual immunostaining procedure demonstrating neurotransmitter and neuropeptide codistribution in the same brain section

Enhanced cyclooxygenase-2 expression in olfactory-limbic forebrain following kainate-induced seizures

Cyclooxygenase-2 is expressed at low levels in a subset of neurons in CNS and is rapidly induced by a multiplicity of factors including seizure activity. A putative relationship exists between cyclooxygenase-2 induction and glutamatergic neurotransmission. Cyclooxygenase-1 is constitutively expressed in glial cells and has been specifically linked to microglia. In this study we evaluated cyclooxygenase-2 protein immunocytochemically and found markedly enhanced immunostaining primarily in olfactory-limbic regions at 2, 6 and 24 h following kainate-induced status epilepticus. Impressive enhanced cyclooxygenase-2 immunoreactivity was localized in anterior olfactory nucleus, tenia tecta, nucleus of the lateral olfactory tract, piriform cortex, lateral and basolateral amygdala, orbital frontal cortex, nucleus accumbens (shell) and associated areas of ventral striatum, entorhinal cortex, dentate gyrus granule cells and hilar neurons, hippocampal CA subfields and subiculum. Alternate sections were processed for dual immunocytochemical analysis utilizing c-Fos and cyclooxygenase-2 antiserum to examine the possibility that the neuronal induction of cyclooxygenase-2 was associated with seizure activity. Neurons that showed a timeline of cyclooxygenase-2 upregulation were found to possess c-Fos immunopositive nuclei. Additional results from all seizure groups showed cyclooxygenase-1 induction in microglia, which was confirmed by Western blot analysis of hippocampus. Western blot and real-time quantitative RT-PCR analysis showed significant upregulation of cyclooxygenase-2 expression, confirming its induction in neurons. These data indicate that cyclooxygenase-2 induction in a neuronal network can be a useful marker for pathways associated with seizure activity.

P2X7 receptor immunoreactive profile confined to resting and activated microglia in the epileptic brain

The purpose of this study was to identify the CNS cellular constituent immunoreactive for specific P2X7 receptor antiserum in the kainate-induced seizure and non-seizure rat brain. Analysis of P2X7 immunocytochemistry (ICC) revealed small immunoreactive cells with processes showing distinct morphological changes as seizures progressed in time. These morphological changes were reminiscent of reactive glia during CNS injury. In order to determine the identity of this non-neuronal cellular constituent, we employed dual ICC techniques using sequential antibody incubations and reacted the sections with contrasting chromagens. Specific glial markers tested in the series included Iba1 (microglia), COX-1 (microglia), and GFAP (astroglia). Results of this study revealed distinct colocalization when sections immunostained for P2X7 were dual immunostained with antisera specific for microglia (Iba1, COX-1). In contrast, no colocalization was evident when sections were dual immunostained with P2X7 and GFAP, an astrocytic marker. In the latter experiment, dual ICC revealed two distinct cell populations with contrasting color demonstrating a population of distinct GFAP immunopositive cells and a population of distinct P2X7 immunopositive cells. We conclude that P2X7 antiserum used in this study is specific for and identifies microglia in rat and that there exists a timeline of progressive changes in microglia morphology that can be demonstrated following kainate-induced seizures. In addition, the morphological changes in microglia following seizure induction that can be identified with P2X7 antisera or with antisera specific for microglia suggest a neuroinflammatory milieu in areas of CNS seizure activity.

Immunocytochemical detection of two nuclear proteins within the same neuron using light microscopy

We developed a method of double immunocytochemistry (ICC) that can be used with conventional light microscopy for localizing two different nuclear proteins. The procedure involves two sequential rounds of ICC that both employ the avidin and biotin conjugated enzyme (ABC) amplification method, separated by an Avidin D and biotin blocking step to reduce non-specific avidin-biotin reactions. Round one of ICC employs the use of avidin and biotin conjugated alkaline phosphatase (ABC-AP) and the Vector Red (VR) substrate, which produces a red colorimetric reaction product. The second round of ICC makes use of avidin and biotin conjugated peroxidase (ABC-HRP) and the Vector(R) SG substrate, which produces a gray colorimetric reaction product. Neuronal nuclei that are double-labeled for both proteins appear red with a gray core. This protocol allows the simultaneous detection of two proteins within the same subcellular compartment of a single neuron, without the need for epifluorescence or scanning confocal laser microscopy.

NF-kappa B transcription factor subunits in rat brain: colocalization of p65 and alpha-MSH

The subunit proteins p50 and p65 of the transcription factor NF-kappa B inhibitory protein were immunocytochemically identified and mapped in rat brain. The p65 subunit was localized to the cytoplasm of neurons in the lateral hypothalamus and colocalized with alpha-MSH in neurons identified as the alpha-2 component of the alpha-MSH system. The p50 subunit protein was distributed throughout the neocortex, basal ganglia, thalamic, and hypothalamic nuclei, and certain nuclei of the pons and medulla. The I-kappa B protein, which is necessary for the cytoplasmic sequestration of the NF-kappa B transcription factor complex, was identified specifically in regions of limbic, hypothalamic, and autonomic nuclei.

NADPH-diaphorase activity and Fos expression in brain nuclei following nitroglycerin administration

Organic nitrates are considered nitric oxide donors in that they have been shown to form nitric oxide in vitro and in vivo. Nitroglycerin is an organic nitrate which possesses peculiar activities mediated, to some extent, by the central nervous system via the noradrenergic system. Previous reports have shown that systemic nitroglycerin is able to induce Fos expression in brain nuclei which are known to contain nitric oxide synthesizing enzyme. Neuronal NADPH-diaphorase has been shown to be a nitric oxide synthase. Thus, in this study we used NADPH-diaphorase histochemistry to evaluate the distribution of Fos-immunoreactive cells within neurons which contain nitric oxide synthase. The data showed co-localization of Fos with NADPH-diaphorase activity in numerous neurons of the paraventricular and supraoptic nuclei of the hypothalamus. In the brainstem, a few neurons were doubly labeled for Fos and NADPH-diaphorase activity, but NADPH-diaphorase positive fibers and Fos-immunoreactive neurons were consistently co-distributed in the locus coeruleus, parabrachial nucleus, nucleus tractus solitarius and spinal trigeminal nucleus caudalis. These findings demonstrate that nitroglycerin administration activates a selective group of neurons which are a source of nitric oxide or which are in close proximity with neuronal processes containing nitric oxide synthase, and suggest that the nitric oxide synthase synthesizing pathway may be involved at various levels in the central effect of nitroglycerin.

Systemic nitroglycerin induces Fos immunoreactivity in brainstem and forebrain structures of the rat

Nitroglycerin is a vasodilator which induces vascular relaxation by releasing nitric oxide in the wall of blood vessels. It has been suggested that the cardiovascular inhibitory responses which are induced by this drug are mediated by central structures. In this study, we evaluated the distribution and intensity of Fos immunoreactivity in rat brain nuclei following the systemic administration of nitroglycerin. In the medulla, a significant number of Fos-immunoreactive neurons were observed in the nucleus tractus solitarius, ventrolateral medulla, area postrema and spinal trigeminal nucleus caudalis. A robust staining was seen in the parabrachial nucleus, locus coeruleus and ventrolateral periaqueductal grey. In the hypothalamus, Fos-positive cells were densely packed in the paraventricular and supraoptic nuclei. Other areas where significant staining was observed include the central nucleus of the amygdala and the subfornical organ. These findings demonstrate that the systemic administration of nitroglycerin is capable of activating a spectrum of functionally diverse brain regions. This spectrum includes areas involved in reflex adjustments to nitroglycerin-induced hypotension, areas involved in sensory nociceptive perception and areas associated with integrative regulation of autonomic, behavioral and neuroendocrine functions.

Noradrenergic innervation of vasopressin- and oxytocin-containing neurons in the hypothalamic paraventricular nucleus of the macaque monkey: quantitative analysis using double-label immunohistochemistry and confocal laser microscopy

Previous reports on the rat and monkey hypothalamus have revealed a dense noradrenergic innervation within the hypothalamic paraventricular nucleus as assessed by dopamine-beta-hydroxylase immunohistochemistry. These single-label analyses were unable to delineate the cellular structures which receive this catecholaminergic innervation. Double-label preparations in the rat hypothalamic paraventricular nucleus have demonstrated synaptic interactions between noradrenergic varicosities and magnocellular neurons. However, the density and distribution of varicosities contacting chemically identified magnocellular neurons have not been assessed at the light or electron microscopic level. In this report, single-label immunohistochemistry was used to assess the morphology and distribution of vasopressin- and oxytocin-immunoreactive neurons within the macaque hypothalamic paraventricular nucleus. In addition, double-label immunohistochemistry was combined with confocal laser scanning microscopy to quantify the number of dopamine-beta-hydroxylase-immunoreactive varicosities in apposition to magnocellular neurons expressing vasopressin or oxytocin immunoreactivity. The morphology of chemically identified neurons was also compared to magnocellular neurons in the monkey hypothalamic paraventricular nucleus which were filled with Lucifer Yellow in order to assess the somatodendritic labeling of the immunohistochemical preparation. Qualitative assessment of immunohistochemically identified magnocellular cells indicated that vasopressin- and oxytocin-containing neurons are observed throughout the rostrocaudal extent of the monkey hypothalamic paraventricular nucleus, demarcating this structure from the surrounding anterior hypothalamus. The distribution of the two nonapeptides is complementary, with vasopressin-immunoreactive neurons having a greater somal volume and located in a more medial aspect of the mid and caudal hypothalamic paraventricular nucleus relative to oxytocin-immunoreactive perikarya. For the double-label preparations, a series of confocal optical sections was assessed through the total somal volume of vasopressin- and oxytocin-immunoreactive neurons along with the corresponding dopamine-beta-hydroxylase-immunoreactive varicosities in the same volume of tissue, generating a varicosity-to-neuron ratio which was further characterized morphologically to assess afferent input to the soma and proximal dendrites. Quantitative analysis revealed that vasopressin-immunoreactive neurons received approximately two thirds of their dopamine-beta-hydroxylase-immunoreactive varicosities in apposition to the proximal dendrites and one third in apposition to the somata. Furthermore, vasopressin-immunoreactive neurons received a greater innervation density than oxytocin-immunoreactive neurons, which did not have a differential distribution of varicosities on the proximal dendrites and somata. The distribution of dopamine-beta-hydroxylase-immunoreactive afferents on magnocellular neurons in the hypothalamic paraventricular nucleus may reflect a physiological role of this circuit in terms of preferential release of vasopressin from magnocellular neurons upon noradrenergic stimulation.

Evidence for projections from medullary nuclei onto serotonergic and dopaminergic neurons in the midbrain dorsal raphe nucleus of the rat

The anterograde tracer Phaseolus vulgaris-leucoagglutinin was injected into the medial nucleus of the solitary tract and into the rostral dorsomedial medulla. A sequential two-color immunoperoxidase staining was accomplished in order to demonstrate the co-distribution of presumed terminal axons with chemically distinct neurons in the dorsal raphe nucleus of the midbrain central gray, i.e., B7 serotonergic and A10dc dopaminergic neurons. Black-stained efferent fibers from the medial nucleus of the solitary tract and the rostral dorsomedial medulla intermingled with brown-stained serotonergic (5-hydroxytryptamine-immunoreactive) or dopaminergic (tyrosine hydroxylase-immunoreactive) neurons. Light microscopy revealed that the black-stained efferent axons exhibited numerous en passant and terminal varicosities that were often found in close apposition to brown-stained serotonergic and dopaminergic somata, and to proximal and distal dendrites and dendritic processes. The close association of immunoreactive elements suggests the presence of axo-somatic and axo-dendritic synaptic contacts of medullary fibers with serotonergic and dopaminergic neurons in the dorsal raphe nucleus. These projections could be involved in the modulation of dorsal raphe neurons, depending on the autonomic status of an animal.

Arginine vasopressin-anti-idiotypic immunostaining of human brain cells

Abstract Polyclonal anti-idiotypic antibodies, generated against the IgG fraction of antisera to arginine vasopressin (AVP), were shown to recognize two proteins in rat brain and bovine pituitary associated with [(3) H]AVP binding. Immunochemical analyses with these antisera revealed reactivity in paraventricular and supraoptic nucleus neuronal elements and in terminals of the posterior pituitary in the human central nervous system. With the use of a dual immunocytochemical staining technique employing both the anti-idiotype and idiotype for AVP it was possible to demonstrate a pattern of AVP-anti-idiotypic-immunoreactivity on AVP neuronal elements which suggests the existence of autoreceptors.

Co-localization of putative vasopressin receptors and vasopressinergic neurons in rat hypothalamus

Vasopressin and oxytocin are synthesized by neurons in the paraventricular and supraoptic nuclei of hypothalamus. Dense concentrations of vasopressin binding sites have also been localized in these nuclei. Using a vasopressin anti-idiotypic antiserum, a dual immunocytochemical labeling procedure has been employed to elucidate the distribution of putative vasopressin receptors in anatomical relation to vasopressin and oxytocin immunoreactive cells in rat brain. Putative vasopressin receptors are observed in relation to magnocellular neurons in hypothalamus that are vasopressin immunoreactive. They do not appear to be associated with parvocellular vasopressinergic cells or oxytocin immunoreactive neurons. The presence of these presumed autoreceptors would support evidence that vasopressin may autoregulate the activity of magnocellular vasopressinergic neurons in hypothalamus.

Transmitter cosynthesis by corticopetal basal forebrain neurons

The objective was to determine if corticopetal basal forebrain neurons could co-synthesize different transmitters. Histochemical labeling of a molecular marker of connectivity (wheat germ agglutinin lectin-bound horseradish peroxidase [HRP]; axonal uptake and retrograde transport from neocortex) and immunohistochemical labeling of molecular markers of transmitter synthesis (glutamic acid decarboxylase [GAD]: choline acetyltransferase [ChAT]) were combined in adult cats and examined by light microscopy. Adjoining partial profiles of the same neurons in the basal forebrain co-localized GAD + HRP and ChAT + HRP in adjacent faces of serial tissue sections. GAD + ChAT were also co-localized within individual profiles of neurons in the basal forebrain from single tissue sections. The results indicate that infrequent corticopetal neurons in the basal forebrain can produce both gamma-aminobutyric acid and acetylcholine.

Correlative scanning-immunoelectromicroscopic analysis of neuropeptide localization and neuronal plasticity in the endocrine hypothalamus

Thirty-two Sprague-Dawley rats were divided into four groups, eight rats per group. Animals were hypophysectomized with removal of both the pars distalis and the neural lobe of the neurohypophysis. Groups of eight rats were euthanized 1, 2, 4 and 8 weeks following hypophysectomy and prepared for routine scanning electron microscopy (SEM) and correlative immunoelectron microscopy employing antisera against arginine vasopressin (AVP). Eight normal rats served as controls. In experimental rats that survived one to eight weeks posthypophysectomy, remarkable neuroanatomical alterations were notable in the median eminence and adjacent third cerebral ventricular lumen. In contrast to normal control rats, large numbers of neurites were observed with SEM to insinuate from the lateral recess into the cerebral ventricular lumen and as early as one week following hypophysectomy they overgrew the apical surfaces of ependymal cells that constitute the lining of the cerebral ventricle. Immunoelectron microscopy revealed that a significant proportion of these neurites were magnocellular in origin in that they harbored AVP-positive neurosecretory vesicles. In addition to large numbers of invading magnocellular neurites, neuronal perikayria with apparent axosomatic synapses were observed to emerge upon the thick feltwork of invading axons, the latter of which appeared to freely terminate within the ventricular lumen. AVP-positive axon profiles were, in addition, seen to terminate upon the basal lamina of portal perivascular spaces in the zona externa of the median eminence. These data are consistent with the idea that following hypophysectomy (to include high stalk section of the neurohypophyseal system), that there is rapid, and dynamic sprouting and regrowth of AVP-positive axons into the adjacent third cerebral ventricular lumen and to the contact zone of the median eminence as well. This phenomenon may represent a compensatory physiological response to injury of the neurohypophyseal system characterized by a highly plastic neuroanatomical reorganization of magnocellular elements which appear to utilize the CSF of the third cerebral ventricle as a functional terminus for the neurocisternal secretion of AVP which ultimately enters the systemic circulation.

Immunocytochemical localization of pro-opiomelanocortin neurons in human brain areas subserving stimulation analgesia

The distribution of pro-opiomelanocortin (beta-endorphin, adrenocorticotropic hormone, and 16-K) neurons and fiber projections was evaluated immunocytochemically in 50-mu thick cryostat sections of human diencephalon and midbrain. Specific attention was focused upon regions in which deep brain stimulation has been most effective in the relief of selected chronic pain syndromes. This study revealed a remarkable, nearly point-to-point correlation between clinically effective stimulation sites and the distribution of pro-opiomelanocortin fibers in the human brain. Of particular interest was the dense innervation of the periventricular stratum along the third ventricle, the parafascicular centromedian region of the thalamus, and the periaqueductal gray matter of the midbrain. This study provides anatomical support for the hypothesis that beta-endorphin-containing neuronal systems may contribute to stimulation analgesia in the human.

Staining of magnocellular neurons of the supraoptic and paraventricular nuclei with vasopressin anti-idiotype antibody: a potential method for receptor immunocytochemistry

A vasopressin anti-idiotype antibody was generated by immunization with a primary anti-vasopressin IgG. This antibody was capable of immunostaining vasopressinergic neurons in the supraoptic and paraventricular nuclei of the hypothalami of normal and Brattleboro rats. Staining was eliminated by preabsorption or coincubation of the antibody with a vasopressin binding protein prepared from rat neural membranes. The anti-idiotype also inhibited binding of [3H]vasopressin to this neural membrane protein in a dose-dependent manner. These experiments suggest that the anti-idiotype antibody recognizes a receptor associated with vasopressinergic neurons.

The distribution pattern of adrenocorticotropin-like immunoreactivity in the cat central nervous system

The distribution pattern of adrenocorticotropin-like immunoreactivity (ACTH-LI) in cats using the avidin-biotin modification of an immunocytochemical method shows cell bodies containing ACTH-LI in the medial basal hypothalamus, especially in the infundibular nucleus. The fibers from these neurons extended beyond the hypothalamus, into the paraventricular nucleus of the thalamus, rostral amygdala, periaqueductal gray, locus coeruleus, parabrachial nucleus and medial nucleus of the nucleus tractus solitarius. The distribution pattern of the cell bodies and fibers containing ACTH-LI bears several similarities to that seen in rats. The pattern differs from that of rats in the fact that the termination in the amygdala is more extensive and that ACTH-LI was not observed in cell bodies in any location other than the medial basal hypothalamus.

Co-existence of CRF and vasopressin immunoreactivity in parvocellular paraventricular neurons of rat hypothalamus

New dual immunocytochemical staining procedures were used in the same tissue section to elucidate the distribution and co-existence of CRF and vasopressin in parvocellular neuronal perikarya in the paraventricular nucleus (PVN) of rat hypothalamus. CRF immunostained cells were for the most part concentrated in the medial parvocellular component of PVN. Few vasopressin-immunoreactive (ir) neurons were seen in this area in the normal and colchicine-treated animals. Vasopressin-containing neurons predominated in the magnocellular component of PVN. In the adrenalectomized and adrenalectomized-colchicine-treated animals, a dense accumulation of vasopressin-ir cells were observed in the medial parvocellular area of PVN; this region is normally vasopressin-ir poor and CRF-ir rich. The vasopressin immunostained cells appeared to have an anatomical distribution similar to that seen for CRF-containing cell bodies. Results of this study unequivocally establish the co-existence of vasopressin and CRF in the same parvocellular perikarya of PVN following pertubation of the pituitary-adrenal axis.