Sustained pharmacological inhibition of nitric oxide synthase does not affect the survival of intrastriatal rat fetal mesencephalic transplants

The objective of the present study was to investigate the potential role of the free radical nitric oxide (NO) in the development of fetal rat mesencephalic neurons grafted in a 6-hydroxydopamine (6-OHDA) lesioned rat model of Parkinson's disease. First, using nitric oxide synthase (NOS)-immunocytochemistry and reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry, we investigated the presence of the neuronal isoform of NOS (nNOS) in intrastriatal mesencephalic grafts. During the course of the experiment (16 weeks) an increase in the staining intensity and the number of nNOS/NADPH-d positive cells within the grafts was observed, as well as a gradual maturation of dopaminergic neurons. In addition, within both the host striatal and grafted mesencephalic tissue, a NO-dependent accumulation of cyclic guanosine monophosphate (cGMP) was detected, indicating the presence of guanylate cyclase, i.e., the target-enzyme for NO. Secondly, to determine the impact of NO on the survival of grafted dopaminergic neurons, 6-OHDA lesioned rats received mesencephalic grafts and were subsequently treated with the competitive NOS-inhibitor Nomega-nitro-l-arginine methylester (l-NAME). After chronic treatment for 4 weeks, tyrosine hydroxylase immunocytochemistry revealed no apparent differences between the survival of grafted dopaminergic neurons in control- or l-NAME treated animals, respectively. As the maturation of grafted dopaminergic neurons coincides with a gradual increase in the expression of nNOS within the graft and since dopaminergic cell numbers are not changed upon administration of l-NAME, it is concluded that endogenously produced and potentially toxic NO does not affect the survival of grafted fetal dopaminergic neurons.

Hypothermia during or after severe perinatal asphyxia prevents increase in cyclic GMP-related nitric oxide levels in the newborn rat striatum

The striatum is rich in nitric oxide synthase (NOS). It is present in a dense fiber network and in a few medium-sized non-spiny interneurons. Previous work showed chronic overexpression of NOS in the rat striatum after a severe perinatal asphyctic (SPA) insult. This was prevented by hypothermia. We investigated whether the overexpression of NOS was accompanied by increased NOS activity. As nitric oxide (NO) is a potent activator of the soluble isoform of guanylyl cyclase, we measured striatal 3',5'-cyclic monophosphate (cyclic GMP) synthesis in 10-day-old (P10) rat pups that were subjected to SPA during normothermia or hypothermia during or after the insult. Cyclic GMP levels in striatal tissue from control pups were approximately 25.8 pmol/mg protein and in the SPA group approximately 38.1 pmol/mg protein (p<0.01). Hypothermia, during as well as after insult, prevented this increase of cyclic GMP. Nomega-nitro-L-arginine (L-NAME) (0.1 mM) decreased cyclic GMP levels in control, SPA and hypothermia treated pups to similar low levels (approximately 8% of level without L-NAME). Sodium nitroprusside (SNP) stimulated cyclic GMP showed no differences between the four groups. This indicates that high cyclic GMP levels in the striatum of rats subjected to SPA are caused by increased NOS activity. Hypothermia after an asphyctic insult could be a promising treatment.

Nitric oxide-mediated cGMP production in the islands of Calleja in the rat

cGMP-immunostaining in the islands of Calleja (ICj) in slices incubated in vitro partially co-localized with nitric oxide synthase (NOS) inside the ICj. No cGMP-immunostaining was found outside the ICj in unstimulated slices, whereas the NO-donor sodium nitroprusside (SNP) stimulated cGMP in cells and fibers bordering on the ICj. These findings show an ongoing NO synthesis in in vitro slices and suggest a relatively restricted diffusion range for endogenously synthesized NO.

Facilitation of learning after lesions of the tuberomammillary nucleus region in adult and aged rats

The tuberomammillary nucleus (TM) located in the posterior part of the hypothalamus is the main source of neuronal histamine in the central nervous system. Recent work from our laboratories has indicated an involvement of the TM region in neuronal plasticity and reinforcement processes. In the present study, we investigated the effects of TM lesions on the performance of adult and aged Wistar rats in a set of learning tasks, which differed in terms of complexity and reward contingencies (habituation learning, inhibitory avoidance, discrimination learning, Morris water maze). An improvement was found in every test applied, indicating that TM lesions seem to generally enhance learning and memory capacities independent of the special demands of a given task. Age-related learning deficits were strongly diminished. Immunohistochemistry revealed that the excitotoxic lesions used to destroy the TM region led to a marked decrease in the number of histamine-positive neurons in the vicinity of the injection site, indicating an involvement of the brain histaminergic system in the observed behavioral changes.

Possible role of nitric oxide-cyclic GMP pathway in object recognition memory: effects of 7-nitroindazole and zaprinast

The effects of 7-nitroindazole, a putative selective inhibitor of neuronal nitric oxide (NO) synthase and zaprinast, a cGMP-selective phosphodiesterase inhibitor, were evaluated on recognition memory of rats in the object recognition test. This test is based on the differential exploration of a new and a familiar object. Two doses of 7-nitroindazole (10 and 30 mg/kg) and zaprinast (3 and 10 mg/kg) were used. The substances were administered i.p. immediately after the exposure to two identical objects, i.e., at the start of the delay interval. After a delay interval of 1 h, control rats spent more time exploring the new object which demonstrates that they recognized the familiar one. Both doses of 7-nitroindazole impaired the discrimination between the two objects after the 1 h interval. After a 4 h interval, control rats did not discriminate between the objects. The highest dose of zaprinast facilitated object recognition after the 4 h interval. In addition, this dose of zaprinast (10 mg/kg) reversed the recognition memory deficit induced by 7-nitroindazole (10 mg/kg) at the 1 h interval. The highest dose of 7-nitroindazole slightly increased mean arterial blood pressure 1 h after its administration. 4 h after administration of zaprinast (10 mg/kg), mean arterial blood pressure was also slightly increased, but not after 1 h after zaprinast administration. However, these effects on blood pressure do not explain the differential effects on object recognition memory. These results therefore suggest that NO-cGMP signal transduction is involved in object recognition memory independently of its cardiovascular role. Finally, since 7-nitroindazole affected mean arterial blood pressure it can not be regarded as a selective inhibitor of neuronal NO synthase.

Region-specific developmental patterns of atrial natriuretic factor- and nitric oxide-activated guanylyl cyclases in the postnatal frontal rat brain

In the rat central nervous system, cyclic GMP can be produced by two isoforms of guanylyl cyclase: a cytosolic isoform, which is activated by nitric oxide, and a membrane-bound isoform, activated by atrial natriuretic factor. We studied the development of guanylyl cyclase activity upon maturation of the rat forebrain from postnatal days 4 to 24, using a combined immunocytochemical and biochemical approach. Atrial natriuretic factor-activated particulate guanylyl cyclase activity was found to decrease in the frontal cortex, in the lateral septum and in the piriform cortex upon maturation. A transient expression of atrial natriuretic factor-sensitive guanylyl cyclase activity was observed at postnatal day 8 in the caudate putamen complex, whereas an increase was observed in the lateral olfactory tract from postnatal days 8 to 24. Biochemical and immunocytochemical studies using the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester, or the inhibitor of soluble guanylyl cyclase 1H-[1,2,4]oxadiazolo[4,3-a]quinaloxin-1-one, indicated high levels of endogenous nitric oxide release at postnatal days 4 and 8. This activity decreased strongly in all brain areas examined. From postnatal day 8 onwards, atrial natriuretic factor-responsive cyclic GMP-immunoreactive cells could be characterized as astrocytes, with the exception of those in the the lateral olfactory tract, where the myelinated fibers became cyclic GMP producing. Furthermore, our results on activation of both guanylyl cyclases at postnatal day 8 leads to the suggestion that both isoforms might be found in the same cells. This study shows that there are pronounced differences between various frontal brain areas in the development of the responsiveness of both the particulate and soluble isoforms of guanylyl cyclase, and lends further support to the hypothesis that natriuretic peptides have a role in neuronal growth and plasticity of the rat brain.

Nitric oxide-mediated cGMP synthesis in oligodendrocytes in the developing rat brain

We investigated the nature of cGMP-synthesizing cells in the developing rat forebrain using cGMP-immunocytochemistry in combination with in vitro incubation of brain slices. When brain slices of immature rats, aged between 1 and 4 weeks, were incubated with sodium nitroprusside (SNP), a nitric oxide (NO) donor compound, in the presence of the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX), small round cells with a few processes in and around the corpus callosum were visualized with the cGMP-antibody. The morphology and the distribution of the cGMP-positive cells were consistent with the criteria for oligodendrocytes. Furthermore, the cGMP-positive cells expressed 2'3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) and gelsolin, which are marker proteins for oligodendrocytes. Therefore, we concluded that the cGMP-positive cells were oligodendrocytes. A subpopulation of the oligodendrocyte was found to be cGMP-immunoreactive also when slices were incubated in the absence of SNP. Furthermore, incubation of the slice in the presence of L-NAME, an inhibitor of NO synthase, but in the absence of SNP abolished cGMP immunostaining. In addition, some populations of neurons and astrocytes in restricted brain areas produced cGMP in response to the incubation with SNP as previously reported, whereas both ameboid and ramified microglial cells did not respond to the treatment. Atrial natriuretic peptide, a stimulator of particulate guanylyl cyclase, enhanced cGMP synthesis in astrocytes in some brain regions but not in oligodendrocytes. These findings indicate that oligodendrocytes in the immature rat brain express soluble guanylyl cyclase. No cGMP-positive oligodendrocytes were found in the mature rat brain, suggesting that cGMP may mediate signals related to myelinogenesis in the rat brain.

Nitric oxide synthase and cGMP in the anterior pituitary gland: effect of a GnRH antagonist and nitric oxide donors

Using immunohistochemistry and in situ hybridization, it has been previously shown that gonadotropes and folliculo-stellate cells in the rat anterior pituitary gland express nitric oxide (NO) synthase (NOS), and that NOS expression is increased by gonadectomy. Using the indirect immunofluorescence technique in conjunction with antibodies raised to conjugated cGMP, we have attempted to establish the target cells for NO in the anterior pituitary and to define the mediator of NO regulation. After incubation of pituitary slices with several NO donors, numerous endocrine cells, but no folliculo-stellate cells, expressed cGMP. Most of these cells stained for LH, that is they were gonadotropes. However, there were apparently cGMP-positive, LH-negative and LH-positive, cGMP-negative endocrine cells. The increase in cGMP could be virtually completely blocked by a guanylyl cyclase inhibitor. cGMP was not expressed in corticotropes, but cGMP-positive cells often contained NOS-like immunostaining. Incubation with GnRH did not result in detectable levels of cGMP. However, when castrated rats were pretreated with a potent longlasting GnRH antagonist, antide, the castration-induced increase in NOS was completely blocked. This suggests that GnRH is involved in the in vivo upregulation of NOS after castration, but that GnRH cannot induce cGMP accumulation in normal pituitary slices in vitro. Taken together, the present results give further evidence for a role of NO in the control of, in particular, LH secretion from the anterior pituitary gland in the rat.

Nitric oxide synthase, cGMP, and NO-mediated cGMP production in the olfactory bulb of the rat

High levels of nitric oxide synthase and cyclic 3',5'-guanosine monophosphate (cGMP) in the olfactory bulb suggest that nitric oxide, acting as a diffusible intercellular messenger molecule inducing increased synthesis of cGMP, plays an important role in olfaction. The localization of cGMP after sodium nitroprusside stimulation of in vitro slices of rat olfactory bulb was compared with the distribution of nicotinamide adenine dinucleotide phosphatediaphorase, nitric oxide synthase, and glial fibrillary acidic protein. cGMP was detected immunohistochemically in cryostat sections. In the presence of the phosphodiesterase blocker isobutyl methylxanthine, cGMP was present in neurons in the glomerular layer, axons in the external and internal plexiform layers, and in a few somata and axons of the granule cell layer. This staining was blocked by NG-nitro-L-arginine methylester hydrochloride or hemoglobin. After sodium nitroprusside stimulation, the olfactory nerve layer was intensely stained, as were the glomeruli and periglomerular cells. In the external plexiform layer, axonal staining was increased substantially, and there were occasional multipolar cGMP-positive neurons. In the internal plexiform and granule cell layers, axonal staining was greatly increased. Many granule cells were also cGMP positive after sodium nitroprusside stimulation. cGMP and nitric oxide synthase-positive neuronal elements overlapped in the glomerular and granule cell layers, but staining was not colocalized, cGMP was not found in astrocytes. The glutamatergic antagonists D-2-amino-5-phosphonovalerate and 6-cyano-7-nitroquinoxaline caused differential inhibition of cGMP accumulation in layers of the olfactory bulb. These findings support the hypothesis that nitric oxide is an intercellular messenger in the olfactory bulb (Breer and Shepherd [1993] Trends Neurosci. 16:5-9).

Dopaminergic transmission in the rat retina: evidence for volume transmission

The study was designed to determine whether dopaminergic neurotransmission in the retina can operate via volume transmission. In double immunolabelling experiments, a mismatch as well as a match was demonstrated in the rat retina between tyrosine hydroxylase (TH) and dopamine (DA) immunoreactive (ir) terminals and cell bodies and dopamine D2 receptor-like ir cell bodies and processes. The match regions were located in the inner nuclear and plexiform layers (D2 ir cell bodies plus processes). The mismatch regions were located in the ganglion cell layer, the outer plexiform layer, and the outer segment of the photoreceptor layer, where very few TH ir terminals can be found in relation to the D2 like ir processes. In similar experiments analyzing D1 receptor like ir processes versus TH ir nerve terminals, mainly a mismatch in their distribution could be demonstrated, with the D1 like ir processes present in the outer plexiform layer and the outer segment where a mismatch in D2 like receptors also exists. The demonstration of a mismatch between the localization of the TH terminal plexus and the dopamine D2 and D1 receptor subtypes in the outer plexiform layer, the outer segment and the ganglion cell layer (only D2 immunoreactivity (IR)) suggests that dopamine, mainly from the inner plexiform layer, may reach the D2 and D1 mismatch receptors via diffusion in the extracellular space. After injecting dopamine into the corpus vitreum, dopamine diffuses through the retina, and strong catecholamine (CA) fluorescence appears in the entire inner plexiform layer and the entire outer plexiform layer, representing the match and mismatch DA receptor areas, respectively. The DA is probably bound to D1 and D2 receptors in both plexiform layers, since the DA receptor antagonist chlorpromazine fully blocks the appearance of the DA fluorescence, while only a partial blockade is found after haloperidol treatment which mainly blocks D2 receptors. These results indicate that the amacrine and/or interplexiform DA cells, with sparse branches in the outer plexiform layer, can operate via volume transmission in the rat retina to influence the outer plexiform layer and the outer segment, as well as other layers of the rat retina such as the ganglion cell layer.

Effects of unilateral vagotomy on nitric oxide synthase and histamine H3 receptors in the rat dorsal vagal complex

Nitric oxide synthase (NOS) and histamine H3 receptors are both markedly increased by neuronal injuries. To examine whether peripheral axotomy produced differential changes in NOS and H3 receptors, both NOS and H3 receptors were measured in the dorsal vagal complex after unilateral vagotomy. The presence of NOS-positive neurons was examined using both NADPH-diaphorase histochemistry and neuronal NOS-immunohistochemistry in rats vagotomized at the mid-cervical level. NADPH-diaphorase activity and NOS-immunoreactivity were markedly enhanced on the dorsal motor nucleus of the vagus (DMX) and in the ambiguous nucleus at the denervated side. Intraperitoneal injection of NOS inhibitors, N omega-nitro-L-arginine (10 mg/kg) or dexamethasone (0.5 mg/kg) attenuated the increase in NADPH-diaphorase activity. Glial fibrillary acidic protein (GFAP) was similarly induced 2 weeks after vagotomy in the vagal complex and surrounding area. Histamine H3 receptors in the vagal complex were visualized with [3H]N alpha-methylhistamine. The ligand-labeled H3 receptors were mainly located at the nucleus of the solitary tract (NST). The densities of H3 receptors did not change in the NST after unilateral vagotomy. These results suggest that peripheral axotomy such as mid-cervical vagotomy preferentially induces NOS in damaged neurons without affecting the level of H3 receptors.

Gradual inhibition of inducible nitric oxide synthase but not of interleukin-1 beta production in rat microglial cells of endotoxin-treated mixed glial cell cultures

In cultures of purified microglial cells and astrocytes from newborn rats, the immunocytochemical localization of interleukin-1 beta (IL-1 beta) and inducible nitric oxide synthase (iNOS) using recently developed antibodies, as well as the release of IL-1 beta and nitric oxide (NO), was studied following exposure of the cells to endotoxin [lipopolysaccharide (LPS)]. In the absence of LPS, IL-1 beta- and iNOS-immunoreactive microglial cells and IL-1 beta or NO release were not observed, whereas in the presence of the endotoxin, the production of NO and IL-1 beta by microglial cells dramatically exceeded their synthesis and release by astrocytes. Interestingly, microglial cells cultured for 4-8 days in the presence of astrocytes appeared to lose their ability to produce iNOS, whereas the release of IL-1 beta remained unaltered. Moreover, endotoxin-stimulated microglial cells appeared to regain their ability to synthesize iNOS following their separation from astrocytes. These data show that microglia are primarily responsible for NO and IL-1 beta production in mixed glial cell cultures upon endotoxin stimulation. Moreover, in the presence of astrocytes the induction of iNOS, but not that of IL-1 beta in microglial cells is gradually inhibited.

Effects of the 3',5'-phosphodiesterase inhibitors isobutylmethylxanthine and zaprinast on NO-mediated cGMP accumulation in the hippocampus slice preparation: an immunocytochemical study

The effect of inhibition of 3',5'-phosphodiesterase (PDE) activity on the cGMP accumulation was studied in control and nitric oxide (NO) stimulated hippocampal slices incubated in vitro using immunohistochemical visualisation of cGMP. Isobutylmethylxanthine (IBMX) was used as a non-selective PDE inhibitor and zaprinast was used as a selective inhibitor of cGMP-specific PDE activity. In the absence of PDE inhibitors cGMP-immunoreactivity (cGMP-IR) was found in blood vessel walls only. After incubation with the NO-donor sodium nitroprusside (SNP) cGMP-IR was found in a few isolated varicose fibres which were distributed throughout the slice. Incubation in the presence of either 1 mM IBMX or 10 microM zaprinast resulted in cGMP-IR in small numbers of varicose fibres distributed throughout the hippocampal slice. SNP in combination with IBMX resulted in cGMP-IR in small numbers multitude of varicose fibres throughout the slice; occasionally cell somata were observed. After incubation with SNP and zaprinast cGMP-IR was found in varicose fibres, although with a more restricted distribution and less numerous than in the presence of IBMX. In the latter combination, varicose fibres were observed predominantly in the CA2/CA3 region and in the stratum lacunosum molecular of the hippocampus, and cell somata were occasionally observed throughout the hippocampus. The differential distribution of cGMP-IR in the presence of different PDE inhibitors is consistent with the notion that there are regional differences in the localization of cGMP hydrolyzing enzymes in the hippocampus.

Developmental pattern of NADPH-diaphorase activity and nitric oxide-stimulated cGMP immunoreactivity in the frontal rat cortex and its role in functional recovery from aspiration lesions

The present study was undertaken to (1) explore the cortical nitric oxide (NO)-system during postnatal development and (2) to see whether or not the NO-system reacts differentially after neonatal and adult lesions of the medial prefrontal cortex. Three aspects of the NO-system were studied, i.e., NADPH-diaphorase (NADPH-d) activity, sodium nitroprusside (SNP)- and N-methyl-D-aspartate (NMDA)-stimulated cGMP-immunoreactivity (cGMP-IR). It was shown that: (1) the development of NADPH-d activity containing cells is continued in the period from P6 until P21; (2) during the same period, large developmental changes take place in basal, and SNP- or NMDA-stimulated cGMP-IR in the cortex. These changes are regionally specific and follow the general cortical developmental pattern; and (3) aspiration lesions do not induce major changes in the distribution of NADPH-d activity or cGMP-IR, either basal, SNP- or NMDA-stimulated.

Reinnervation after destruction of the dopaminergic system in the rat nucleus accumbens: a quantitative immunohistochemical analysis

The recurrence of dopamine-immunoreactive (DAi) fibers and the effect of the adrenocorticotrophic hormone (ACTH)-(4-9) analog ORG 2766 on this process were investigated 1, 4, 12 and 24 weeks after a unilateral 6-hydroxydopamine (6-OHDA) lesion in the nucleus accumbens (NAc). DAi fibers were almost completely absent 1 week after the lesion. A gradual increase in DAi fibers throughout the NAc was observed, with subnormal values at 24 weeks. Treatment with ORG 2766 during the first week after the lesion resulted in more DAi fibers 4 weeks after the lesion as compared to placebo treatment, but not 12 and 24 weeks after the lesion. After 6-OHDA lesioning reinnervation of the NAc takes place and this process is transiently facilitated by ORG 2766.

Repeated administration of a selective dopamine D2 receptor agonist to 6-OHDA-lesioned rats does not affect the survival and outgrowth of intrastriatal fetal mesencephalic grafts

The objective of the present study was to investigate the effects of chronic activation of dopamine D2 receptors on the development of grafted fetal rat mesencephalic dopaminergic neurons. Therefore, unilaterally 6-hydroxydopamine - lesioned rats received intrastriatal mesencephalic cell suspension grafts and were subsequently chronically treated with the selective dopamine D2 receptor agonist LY 171555 (Quinpirole). After treatment for 6 consecutive weeks, the rats were processed for tyrosine-hydroxylase immunocytochemistry to assess the survival and outgrowth from grafted dopaminergic neurons. morphological analysis revealed that, like the volume and morphology of the graft, neither the number nor the cell area of grafted dopaminergic neurons was significantly different between vehicle- and LY 171555-treated animals. To obtain a quantitative estimate of the graft-derived dopaminergic reinnervation, a computerized image analysis system was used. Using this procedure, which was based on the densitometric measurement of tyrosine hydroxylase immunoreactivity in the area adjacent to the grafted tissue, it was found that the extent of graft-derived outgrowth also appeared to be unaffected upon chronic treatment with LY 171555. It is concluded that long-term concurrent administration of a dopamine D2 receptor agonist for 6 consecutive weeks does not impair the survival and outgrowth of grafted rat fetal mesencephalic dopaminergic neurons.

Characterization of the binding of the first selective radiolabelled histamine H3-receptor antagonist, [125I]-iodophenpropit, to rat brain

1. The binding of the first selective radiolabelled histamine H3-receptor antagonist [125I]-iodophenpropit to rat cerebral cortex membranes was characterized. 2. [125I]-iodophenpropit, radiolabelled to a high specific activity of 1900 Ci mmol-1, saturably bound to a single class of sites with a KD of 0.57 +/- 0.16 nM (n = 4) and Bmax of 268 +/- 119 fmol mg-1 protein. 3. Specific binding at a concentration below 1 nM represented 50 to 60% of total binding. 4. Binding of [125I]-iodophenpropit to rat cerebral cortex membranes was readily displaced by histamine H3-agonists and antagonists. In contrast, the inhibitory potencies of selective histamine H1- and H2-receptor ligands were very low. 5. [125I]-iodophenpropit was biphasically displaced by the histamine H3-receptor antagonists, burimamide and dimaprit, which may indicate the existence of histamine H3-receptor subtypes. Other histamine H3-receptor antagonists showed a monophasic displacement. 6. Competition binding curves of H3-agonists were biphasic and showed a rightward shift upon the addition of the nonhydrolysable GTP analogue, guanosine 5'-o-(3-thio) triphosphate (GTP gamma S; 100 microM) which implicates the interaction of histamine H3-receptors with G-proteins. The affinities of the H3-receptor antagonists iodophenpropit, thioperamide and burimamide were not altered by GTP gamma S. 7. Histamine competition binding curves were shifted to the right by different nucleotides (100 microM) with a rank order of potency GTP gamma S > Gpp(NH)p, GTP. 8 In vitro autoradiographic studies revealed a heterogeneous distribution of [125I]-iodophenpropitbinding sites in rat brain, with highest densities observed in specific cerebral cortical areas and layers,the caudate-putamen complex, the olfactory tubercles, the hippocampal formation, the amygdala complex, the hypothalamic area and the mammillary bodies.9 It is concluded that the histamine H3-receptor antagonist, [125I]-iodophenpropit, meets the criteria fo ra suitable radioligand for histamine H3-receptor binding studies in rat brain.

An ultrastructural study of dopamine-immunoreactive nerve fibres in milky spots of the human greater omentum

An ultrastructural study was performed to examine the presence and distribution of dopamine-immunoreactive nerve fibres in milky spots of the human greater omentum. Non-myelinated nerve fibres were located perivascularly as well as throughout the milky spots. Dopamine immunoreactivity was demonstrated in the nerve fibres and in a portion of the macrophage population. These results demonstrate a discrepancy between human and non-human milky spots.

Dopamine D-2 autoreceptors regulating the release of dopamine from cultured rat fetal dopaminergic neurons do not desensitize upon sustained activation: implications for the combined pharmaco- and grafting therapy in parkinsonian patients

Cultured rat fetal mesencephalic dopaminergic neurons exhibit specific high-affinity uptake for [3H]dopamine (DA) and express DA D-2 autoreceptors, functionally coupled to the inhibition of depolarization evoked [3H]DA release. In this study, we examined the effect of short- and long-term sustained agonist exposure on the responsiveness of these DAD-2 receptors, expressed on cultured fetal mesencephalic dopaminergic neurons. Therefore, cultures were incubated in the absence or presence of the selective D-2 receptor agonist LY 171555 (Quinpirole, 1 microM) before the DA D-2 receptor-mediated inhibition of depolarization-induced [3H]DA release was determined. Short-term preincubation of cultures for 4 h did not lead to any change in the K(+)-evoked [3H]DA release nor to a change in the efficacy of LY 171555 (1 microM) to inhibit this release. Similar results were obtained after long-term agonist exposure for 6 days. Only after exposure for 12 consecutive days was a small reduction of the LY 171555 mediated inhibitory effect on DA release observed, while the IC50 value was slightly shifted to the right as compared to control cultures. Additionally, in pretreated cultures, a statistically significant increase was observed in the depolarization-induced release of [3H]DA in the absence of drugs. In the same model, activation of muscarinic acetylcholine (M-ACh) receptors was shown to potentiate the depolarization-induced release of [3H]DA. Preincubation for 4 h with the muscarinic agonist carbachol (100 microM) induced a strong reduction in the M-ACh receptor-mediated effect on [3H]DA release, indicative of a rapid desensitization of M-ACh receptors. It is concluded that, while no functional desensitization of DA D-2 autoreceptors is apparent, the depolarization-induced release of DA from cultured fetal dopaminergic neurons is enhanced upon long-term sustained activation of DA D-2 receptors.

Distribution of dopamine-immunoreactive neurons and their relationships to transmitter and hypothalamic hormone-immunoreactive neuronal systems in the rat mediobasal hypothalamus. A morphometric and microdensitometric analysis

A morphometric and microdensitometric characterization of the dopamine neurons of the mediobasal hypothalamus and their relationships with several other chemically identified systems, including putative tyrosine hydroxylase-positive/dopamine-negative neurons, was carried out after visualization of dopamine content by both immunocytochemistry and the Falck-Hillarp technique. Quantitative assessment of co-existence demonstrated that more than 95% of dopamine-immunoreactive neurons also contained tyrosine hydroxylase immunoreactivity and more than 90% of growth hormone-releasing factor-immunoreactive neurons also contained tyrosine hydroxylase immunoreactivity. Morphometric and densitometric analysis of dopamine, tyrosine hydroxylase and growth hormone-releasing factor-immunoreactive neurons in the arcuate nucleus showed that dopamine/tyrosine hydroxylase-containing and growth hormone-releasing factor/tyrosine hydroxylase-containing neuronal populations are two largely segregated cell groups with specific localization in the arcuate region, rostrocaudal extension and tyrosine hydroxylase-immunoreactivity content. Morphometric characteristics of dopamine-immunoreactive neurons were shown to be equivalent to those of catecholamine fluorescent cell bodies in the arcuate region. In addition, a cell group lacking detectable catecholamine fluorescence in normal animals but accumulating L-DOPA after peripheral loading was identified and characterized from a morphometric standpoint in the ventral premammillary nucleus. Quantitative analysis of nerve terminal co-distribution in the median eminence revealed significant correlations between dopamine and other transmitter or neurohormone systems, such as gamma-aminobutyric acid, galanin, luteinizing hormone-releasing hormone, in specific subregions of the palissade zone. These data point to discrete subregions of the median eminence, which have been called 'medianosomes', as main sites of interactions between transmitter-identified nerve terminal systems in the control of hypothalamic hormone release.

Morphological and behavioral drawbacks of fetal dopaminergic grafts, prelabeled with Phaseolus vulgaris leucoagglutinin

The anterograde tracer Phaseolus vulgaris Leucoagglutinin (Pha-L) was tested as a fetal cell marker in short-term labeling of a fetal dopaminergic cell suspension and in long-term surviving grafts in vivo. As a model we used the grafting of fetal dopaminergic cells into the denervated caudate putamen of the rat. Short-term labeling revealed that the viability of the fetal cells was not affected by the Pha-L incubation within the 4 h of the test period. Yet, a subtle difference was noticed in the morphological development of the fetal neurons. Whereas many dopaminergic cells in the control suspension developed from an initially round soma to a more triangular or bipolar one, Pha-L-incubated cells maintained their round appearance. Moreover, cells with developing neurites were commonly noted in the control suspension, but were absent after incubation with Pha-L. Long-term effects of Pha-L were studied in three groups of unilaterally 6-hydroxydopamine-lesioned rats, which all received an injection of a fetal dopaminergic cell suspension in the denervated caudate putamen. The first group (T-Pha-L) received dopaminergic cells, prelabeled with Pha-L. The second group (T-saline) received cells incubated with vehicle (saline). The third group (T) received only dissociated cells. Eight weeks after the implantation the morphological analysis showed a minor Pha-L-immunoreactivity inside the labeled grafts. We detected Pha-L-positive fiber particles as well as weakly Pha-L-positive spots, presumably cell bodies. Pha-L-labeled grafts were significantly decreased in graft volume and contained markedly less dopamine-immunoreactive (DAi) cells than the control grafts of groups T-saline and T. The ratio DAi cell type I (cell with < or = 3 processes)/DAi cell type II (cell with > or = 4 processes) was approximately 8 in the control groups and 3 in group T-Pha-L. This suggests primarily a toxic effect of Pha-L and DAi cell type I neurons. Our behavioral data revealed that the Pha-L-labeled grafts did not cause a recovery from lesion-induced motor asymmetries.(ABSTRACT TRUNCATED AT 400 WORDS)

Development, characterization and application of an antibody against 5-fluoro-2'deoxyuridine-5'monophosphate, the active metabolite of 5-fluorouracil

5-Fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP) is the active metabolite of the anticancer agent 5-fluorouracil (5FU). Antibodies against a conjugate of thyroglobulin with acetylated FdUMP were raised in 4 rabbits. The maximal titer was reached after 3-5 boosters. Subsequently, the antisera were collected and partially purified. In a competition assay a 100-fold excess of the natural nucleotide dUMP could displace tritiated FdUMP (20 pmol per assay) by about 50% in all antisera. However, tritiated dUMP itself did not bind to the antibody. No cross-reactivity was observed with the FdUMP precursor 5FU and with the natural nucleoside uridine and the nucleotides dTMP, dTTP and UTP. A considerable cross-reactivity was observed with the monophosphate of bromodeoxyuridine (Br-dUMP). Radio-immuno assays for FdUMP and dUMP were developed, for which a 100-fold dilution could be used. The FdUMP assay was linear in a range of 0.1 to 5 pmol FdUMP in aqueous solutions. Tumour samples contained a non-identified interfering factor; a similar interference was observed in an enzyme based assay for FdUMP. The dUMP assay was performed by competition of unlabeled dUMP with tritiated FdUMP and was linear from 50 to 2000 pmol dUMP per assay. The antibody recognized FdUMP bound in a ternary complex synthesized in a cell-free system between FdUMP, its target enzyme thymidylate synthase and the folate co-factor. Immunohistochemical staining for demonstration of the ternary complex in 5FU treated cells and tumours from patients and animals was not yet successful, neither with peroxidase nor with immunofluorescence staining. Possibly the amount of bound FdUMP is below the detection limit or FdUMP bound to TS is masked. The antibody may prove to be useful in studies on modulation of FdUMP and dUMP after treatment with thymidylate synthase inhibitors.

A new approach to the immunocytochemistry of cAMP. Initial characterization of antibodies against acrolein-fixed cAMP

A method is described to couple cyclic adenosine 3',5' monophosphate (cAMP) to a carrier protein by means of acrolein. Antibodies against this conjugate were raised in mice. These antibodies proved to be highly specific for acrolein-fixed cAMP in a gelatin model system. Slices (300 microns in thickness) from rat cerebral cortex were incubated in vitro and the dopaminergic control of adenylate cyclase activity was drug-manipulated. This manipulation was visualized by application of the cAMP-antisera on cryostat sections of the acrolein fixed slices.