Combined in situ hybridization and immunocytochemistry in the assay of pharmacological effects on tyrosine hydroxylase mRNA concentration

Blood-brain barrier disruption highly induces aquaporin-4 mRNA and protein in perivascular and parenchymal astrocytes: Protective effect by estradiol treatment in ovariectomized animals

Strong evidence involves aquaporin-4 (AQP4) in the physiopathology of brain edema. Two major points remain unsolved: (1) the capacity of perivascular glial cells to regulate AQP4 in response to disruption of the blood-brain barrier (BBB); and (2) the potential beneficial role of AQP4 in the clearance of brain edema. We used intraparenchymal injection of lipopolysaccharide (LPS) as an efficient model to induce BBB disruption. This was monitored by IgG extravasation and AQP4 was studied at the mRNA and protein level. The first signs of BBB disruption coincided with strong induction of AQP4 mRNA in perivascular glial cells. At the early phase, estradiol treatment highly prevented the LPS-induced disruption of the BBB and the induction of AQP4. Efficient clearance of vasogenic edema is supposed to occur once BBB is restored. This phase coincided with high induction of AQP4 mRNA in parenchymal reactive astrocytes and perivascular glial processes. High levels of AQP4 mRNA may be beneficial under these conditions. Our data may clarify why estradiol treatment reduces mortality in conditions typically associated with edema formation, like stroke.

Differential regulation of glutamic acid decarboxylase mRNA and tyrosine hydroxylase mRNA expression in the aged manganese-treated rats

Recent studies have implicated chronic elevated exposures to environmental agents, such as metals (e.g. manganese, Mn) and pesticides, as contributors to neurological disease. Eighteen-month-old rats received intraperitoneal injections of manganese chloride (6 mg Mn/kg/day) or equal volume of saline for 30 days in order to study the effect of manganese on the dopamine- and GABA-neurons. The structures studied were substantia nigra, striatum, ventral tegmental area, nucleus accumbens and globus pallidus. First, we studied the enzymatic activity of mitochondrial complex II succinate dehydrogenase (SDH). We found an overall decrease of SDH in the different brain areas analyzed. We then studied the mRNA levels for tyrosine hydroxylase (TH) and the dopamine transporter (DAT) by in situ hybridization. TH mRNA but not DAT mRNA was significantly induced in substantia nigra and ventral tegmental area following Mn treatment. Correspondingly, TH immunoreactivity was increased in substantia nigra and ventral tegmental area. Manganese treatment significantly decreased GAD mRNA levels in individual GABAergic neurons in globus pallidus but not in striatum. We also quantified the density of glial fibrillary acidic protein (GFAP)-labeled astrocytes and OX-42 positive cells. Reactive gliosis in response to Mn treatment occurred only in striatum and substantia nigra and the morphology of the astrocytes was different than in control animals. These results suggest that the nigrostriatal system could be specifically damaged by manganese toxicity. Thus, changes produced by manganese treatment on 18-month-old rats could play a role in the etiology of Parkinson's disease.

A simplified method for combined immunohistochemistry and in-situ hybridization in fresh-frozen, cryocut mouse brain sections

A method is described to perform combined immunohistochemistry and in situ hybridization in mouse brain sections. The protocol is specific to sections mounted on glass slides. In contrast to earlier methods that require either paraffin embedding or perfusion of the brain with paraformaldehyde, this protocol can be carried out on fresh-frozen, cryostat cut post-fixed sections. This simple and concise protocol increases the applicability of the technique as the RNAse-free immunodetection of antigen is useful by itself for immunologically identifying specific cells of interest and then examining gene expression in those cells using techniques such as real-time PCR and microarray analysis. The use of fresh-frozen, cryocut sections enables reliable detection of easily perturbable post-translational modifications such as phosphorylation and improves the quality of results obtained in subsequent in situ hybridization by reducing the background signal and interference from lower cell layers. Inducible transgenic mice that express either a dominant negative mutant form of the cAMP response element binding protein (mCREB) or CREB, in discrete brain regions, were used in this study. The combined immunohistochemistry and in situ hybridization protocol was used to examine colocalization of enkephalin or dynorphin mRNA, both downstream targets of CREB-mediated gene expression, in cells expressing transgenic mCREB or CREB.

Prenatal nicotine affects catecholamine gene expression in newborn rat carotid body and petrosal ganglion

Nicotine exposure modifies the expression of catecholamine and opioid neurotransmitter systems involved in attenuation of hypoxic chemosensitivity. We used in situ hybridization histochemistry to determine the effect of prenatal and early postnatal nicotine exposure on tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DbetaH), preproenkephalin (PPE), and D2-dopamine receptor mRNA levels in the rat carotid body and petrosal ganglion during postnatal development. In the carotid body, nicotine increased TH mRNA expression in animals at 0 and 3 postnatal days (both, P < 0.05 vs. control) without affecting TH mRNA levels at 6 and 15 days. At 15 postnatal days, DbetaH mRNA levels were increased in the carotid body of nicotine-exposed animals. Dopamine D2-receptor mRNA levels in the carotid body increased with postnatal age but were unaffected by nicotine exposure. PPE was not expressed in the carotid body at any of the ages studied in control or treated animals. In the petrosal ganglion, nicotine increased the number of ganglion cells expressing TH mRNA in animals at 3 days (P < 0.01 vs. control). DbetaH mRNA expression was not induced nor was PPE mRNA expression increased in the petrosal ganglion in treated animals. Prenatal nicotine exposure upregulates mRNAs involved in the synthesis of two inhibitory neuromodulators, dopamine and norepinephrine, in peripheral arterial chemoreceptors, which may contribute to abnormalities in cardiorespiratory control observed in nicotine exposed animals.

Decreased messenger RNA expression of key markers of the nigrostriatal dopaminergic system following vitamin E deficiency in the rat

We have evaluated the effect of a vitamin E-deficient diet on the rat nigrostriatal dopaminergic system. After 15 days of deficient diet, the amount and activity of striatal and nigral tyrosine hydroxylase increased, which contrasted with a decreased messenger RNA expression for tyrosine hydroxylase and the dopamine transporter in the ventral mesencephalon. When we prolonged the deficiency of vitamin E for 30 days, dopamine levels did not differ in both areas. In contrast, messenger RNA levels for tyrosine hydroxylase and the dopamine transporter were markedly reduced in 30-day deficient rats. In addition, the number of oxidatively modified proteins significantly increased in the striatal and nigral areas studied. Overall, we propose that these changes suggest an important role of vitamin E in maintaining the normal equilibrium of the dopaminergic nigrostriatal system.

Differential expression of a(2a), A(1)-adenosine and D(2)-dopamine receptor genes in rat peripheral arterial chemoreceptors during postnatal development

The sensitivity of peripheral arterial chemoreceptors in the carotid body to hypoxia increases with postnatal maturation. Carotid sinus nerve activity is augmented by adenosine binding to A(2a)-adenosine receptors and attenuated by dopamine binding to D(2)-dopamine receptors. In this study, we used in situ hybridization histochemistry to determine the change in the levels of mRNA expression for A(2a) and A(1)-adenosine receptors and D(2)-dopamine receptors in the rat carotid body. We also investigated the cellular distribution and possible colocalization of these receptor mRNAs and tyrosine hydroxylase (TH) mRNAs during the first 2 weeks of postnatal development. By using immunohistocytochemistry, we detected A(2a)-adenosine receptor protein in the carotid body and petrosal ganglion. We found that A(2a)-adenosine receptor mRNA and protein are expressed in the carotid body in animals at 0, 3, 6 and 14 postnatal days. The level of A(2a)-adenosine receptor mRNA expression significantly decreased by 14 postnatal days (P<0.02 vs. day 0) while D(2)-dopamine receptor mRNA levels significantly increased by day 3 and remained greater than D(2)-dopamine receptor mRNA levels at day 0 (P<0.001 all ages vs. day 0). TH mRNA was colocalized in cells in the carotid body with A(2a) adenosine receptor and D(2)-dopamine receptor mRNAs. A(1)-adenosine receptor mRNA was not expressed in the carotid body at any of the ages examined. In the petrosal ganglion, A(1)-adenosine receptor mRNA was abundantly expressed in numerous cells, A(2a)-adenosine receptor mRNA was expressed in a moderate number of cells while D(2)-dopamine receptor mRNA was seen in a few cells in the rostral petrosal ganglion. In conclusion, using in situ hybridization histochemistry, we have shown that mRNA for both the excitatory, A(2a)-adenosine receptor, and the inhibitory, D(2)-dopamine receptor, is developmentally regulated in presumably type I cells in the carotid body which may contribute to the maturation of hypoxic chemosensitivity. Furthermore, the presence A(1)-adenosine receptor mRNAs in cell bodies of the petrosal ganglion suggests that adenosine might also have an inhibitory role in hypoxic chemotransmission.

Lack of induction of substance P gene expression by hypoxia and absence of neurokinin 1-receptor mRNAs in the rat carotid body

Peripheral chemoreceptors are commonly thought to respond to hypoxia by releasing neurotransmitters from the type 1 cells of the carotid body; these molecules then bind to post-synaptic receptors on the carotid sinus nerve. The tachykinin substance P (SP) may act as an important neurotransmitter/neuromodulator in hypoxic chemotransmission in peripheral arterial chemoreceptors. In order to elucidate the role of SP in modulating hypoxic chemotransmission, we have used quantitative in situ hybridization histochemistry, to determine the effect of hypoxia on SP gene induction, and the localization of neurokinin 1 (NK-1) receptor mRNA in the carotid body and petrosal ganglia complex in rats at 21 days post-natal age. For comparison, we also determined: (1) the effect of hypoxia on tyrosine hydroxylase (TH) gene induction and (2) the localization of the mRNA encoding the D2-dopamine receptor. SP mRNA was not detected in the rat carotid body during normoxia and its expression was not induced after a 1 h of exposure to hypoxia (10% O2/90% N2), a stimulus that was sufficient to cause a significant increase (P < 0.01) in TH mRNA levels in the carotid body. Both SP and TH mRNAs were abundantly expressed in multiple cells in the petrosal and the jugular ganglia. However, these mRNAs were not co-localized and SP and TH mRNA levels were not affected by hypoxia in these ganglia. Although D2-dopamine receptor mRNA was abundantly expressed in the rat carotid body, we found no evidence of NK-1 receptor mRNA in the carotid body. In contrast, both NK-1 receptor mRNA and D2-dopamine receptor mRNA were present in petrosal ganglion cells. In the rat, SP does not appear to modulate hypoxic chemotransmission by being made in and released from type 1 cells in the carotid body, and neither does SP modulate the activity of type 1 cells by binding to NK-1 receptors on these cells.

Regionally specific induction of BDNF and truncated trkB.T1 receptors in the hippocampal formation after intraseptal injection of kainic acid

The septo-hippocampal cholinergic and GABAergic systems were lesioned with single unilateral injections of kainic acid (KA) into the septum to further characterize the role of these afferents in the regulation of hippocampal brain-derived neurotrophic factor (BDNF) expression. Nearly all cells expressing choline acetyltransferase, trkA or glutamic acid decarboxylase mRNA disappeared in the medial septum 7 days after the neurotoxin administration. The lesion resulted in a complete loss of CA3 pyramidal cells, and robust increases in BDNF mRNA levels in hippocampal granular dentate cells and in the amygdala. There were rapid transient increases of BDNF mRNA levels in the hippocampal formation and cortex. In addition, we found a strong induction of truncated trkB.T1 mRNA receptors in the stratum radiatum and stratum oriens of the CA3 subfield. The prolonged induction of BDNF mRNA levels suggests an important role of this neurotrophin, possibly mediated by truncated trkB receptors, in the regulation of hippocampal plasticity following injury.

Deprenyl induces the tyrosine hydroxylase enzyme in the rat dopaminergic nigrostriatal system

Chronic treatment of aged rats with deprenyl prevents age-induced protein oxidation in substantia nigra and protects tyrosine hydroxylase (TH) enzyme against inactivation [11]. With these precedents, we treated adult rats with deprenyl for 3 weeks in order to get further insight in the mechanism by which deprenyl exerts such actions. After completing the treatment, dopamine (DA) levels markedly increased in both striatum and substantia nigra while levels of the acid DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), decreased in the two brain areas, thus proving MAO-inhibiting properties of the treatment. We then studied the cellular expression of TH mRNA by in situ hybridization. Following treatment with deprenyl, levels of TH mRNA were significantly higher in individual dopaminergic nigral cell bodies than in those of control rats (+74%). Western blotting analysis of TH enzyme amount revealed a positive effect of the treatment in both the terminal field (+44%) and the cell body region (+31%). This correlation between TH mRNA and amount was also extended to TH enzyme activity in the two brain areas studied, which significantly increased in striatum (+57%) and substantia nigra (+35%) following deprenyl treatment. Taken together, our results clearly suggest a TH-inducing effect of deprenyl in the dopaminergic nigrostriatal system, which seems to be independent of its protective action against oxidative stress described previously. These results expand our knowledge about the beneficial effect of deprenyl in the therapy of Parkinson's disease.

L-Deprenyl and MDL72974 do not improve the recovery of dopaminergic cells following systemic administration of MPTP in mouse

L-Deprenyl, a monoamine oxidase B (MAO-B) inhibitor, administered prior to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) protects dopaminergic neurons against degeneration in several animal species including mice. L-Deprenyl inhibits MPP+ formation, the mediator of MPTP toxicity. In addition, L-deprenyl, administered 72 h following MPTP, improves the recovery of tyrosine hydroxylase (TH) immunopositive neurons in the substantia nigra (SN) of mice. This observation lead to the proposal that L-deprenyl exerts a 'neurorescue' effect. However, clinical trials failed to demonstrate that L-deprenyl can effectively 'rescues' degenerating dopaminergic neurons in early untreated Parkinson's disease (PD) patients. These observations prompted us to reevaluate the long-term impact of L-deprenyl on MPTP-induced dopaminergic cell loss in mice. In addition, we made use of another MAO-B inhibitor, MDL72974, to assess MAO-B participation in this paradigm. Our results suggest that L-deprenyl does not improve the recovery of TH immunopositive neurons in MPTP-treated mice. An apparent reduction in TH+ neurons is observed in the SN of MDL72974 and L-deprenyl/MPTP-treated mice at 30 days post-treatment. The possible implication of these findings in relation to the used of MAO-B inhibitors in PD is discussed.

Use of quantitative ultrastructural immunoperoxidase labeling for analysis of catecholamine neurotoxicity and plasticity

Levels of catecholamines and the synthesizing enzyme, tyrosine hydroxylase (TH) are markedly decreased in the dorsal striatum, caudate-putamen nuclei, following neurotoxic lesions with 6-hydroxy-dopamine (6-OHDA). We examined whether pre-embedding immunoperoxidase labeling of TH could be standardized for quantitatively examining the density and ultrastructure of spared dopaminergic terminals in the striatum of lesioned rats. The peroxidase-antiperoxidase (PAP) method was used to localize rabbit antiserum against TH in caudate-putamen nuclei of adult rats given unilateral nigral injections of either vehicle or 6-hydroxydopamine in the early postnatal period. Experimental differences in fixation and immunocytochemical labeling were minimized by limiting comparisons of immunoreactivity to co-processed sections from the same litters of animals. Imaging software and a Phillips CM-10 electron microscope were used to quantitatively examine immunoreactive profiles in a narrow zone of tissue in contact with the embedding resin. Under these conditions variables attributed to differences in penetration were minimized. There were no significant differences in numbers or mean-cross sectional diameter of immunoreactive terminals in striatum ipsilateral versus contralateral to vehicle injections. Ipsilateral to the 6-OHDA injections, the density (numbers/area) of striatal TH-immunoreactive terminals was reduced by 50-90% in the majority of animals. In the most extensively lesioned rats, the cross-sectional areas of the remaining immunoreactive axons were significantly larger than in the contralateral striatum of the same animal or either hemisphere of vehicle injected controls. These results confirm and extend earlier findings on the plasticity of residual dopaminergic terminals in adult animals after neurotoxic damage. They also establish a quantitative method for ultrastructural analysis of the density of immunoreactivity in thick sections of tissue labeled prior to plastic embedding. The method has broad applicability to quantitative studies of neurotoxicity and plasticity in brain.

Selective expression of clusterin (SGP-2) and complement C1qB and C4 during responses to neurotoxins in vivo and in vitro

This study concerns expression of the genes encoding three multifunctional proteins: clusterin and two complement cascade components, C1q and C4. Previous work from this and other laboratories has established that clusterin, Clq and C4 messenger RNAs are elevated during Alzheimer's disease, and in response to deafferenting and excitotoxic brain lesion. This study addresses hippocampal clusterin, ClqB and C4 expression in response to neurotoxins that caused selective neuron death. Kainate, which preferentially kills hippocampal CA3 pyramidal neurons but not dentate gyrus granule neurons induced clusterin immunoreactivity in CA1 and CA3 pyramidal neurons and adjacent astrocytes, but not in dentate gyrus granule neurons. In contrast, colchicine, which preferentially kills the dentate gyrus granule neurons, induced clusterin immunoreactivity in the local neuropil as punctate deposits, but not in the surviving or degenerating dentate gyrus granule neurons. Clusterin messenger RNA was increased in astrocytes. ClqB and C4 messenger RNAs increased within 48 h after kainate injections, particularly in the CA3 pyramidal layer, less in the dentate gyrus-CA4, and less in CA1. Clq immunoreactivity was detected in CA1 pyramidal neurons and also as small punctate deposits in the CA1 region at eight and 14 days after kainate. The increase of both clusterin and ClqB messenger RNAs after kainate injections was blocked by barbiturates that prevented seizures and neurodegeneration. In primary hippocampal neuronal cultures treated with glutamate, a subpopulation of cultured neurons that survived glutamate toxicity also had parallel elevations of clusterin and ClqB messenger RNA. In conclusion, cytotoxins that target selective hippocampal neurons increase the expression of both clusterin and ClqB in vivo and in vitro. These results show that elevations of clusterin messenger RNA or protein can be dissociated from each other and from cell death. These increased messenger RNAs were associated with immunoreactive deposits that differed by cell type and intra- versus extracellular locations. These results suggest that the complement system is involved in brain responses to injury.

Intrastriatal infusion of nerve growth factor after quinolinic acid prevents reduction of cellular expression of choline acetyltransferase messenger RNA and trkA messenger RNA, but not glutamate decarboxylase messenger RNA

Excitotoxic striatal lesions induced by quinolinic acid, a model for Huntington's disease, were used to test for neuroprotective actions of nerve growth factor on striatal cholinergic and GABAergic neurons. Expressions of the trkA receptor for nerve growth factor, choline acetyltransferase and glutamate decarboxylase were analysed by messenger RNA in situ hybridization in adult rats following quinolinic acid lesion (150 nmol) and daily striatal administration of nerve growth factor (1 microgram) or control protein (cytochrome C) for one week. One week after toxin administration, the numbers of cells expressing trkA or choline acetyltransferase messenger RNAs were decreased when compared with unlesioned animals. Moreover, the surviving cells showed a strong down-regulation of these messenger RNAs as deduced from grain count analysis of sections processed for emulsion autoradiography. Daily intrastriatal nerve growth factor administration for one week completely prevented the reduction in the number of cells expressing either of the two markers. Nerve growth factor treatment increased the cellular expression of choline acetyltransferase messenger RNA three times above control levels and restored the levels of trk A messenger RNA expression to control levels. In contrast to the protective effects on cholinergic cells, nerve growth factor treatment failed to attenuate the quinolinic acid-induced decrease in glutamate decarboxylase messenger RNA levels. Optical density measurements of the entire striatum on autoradiographs of brain sections from quinolinic acid-lesioned animals revealed a reduction of the glutamate decarboxylase messenger RNA-specific hybridization signal, which was unaltered by infusion of nerve growth factor or control protein. Our findings strongly suggest that in both the intact and the quinolinic acid-lesioned adult rat striatum, nerve growth factor action is confined to trk A-expressing cholinergic neurons. Striatal glutamate decarboxylase messenger RNA-expressing GABAergic neurons which degenerate in Huntington's disease are not responsive to nerve growth factor.

Expression of neurotrophin and trk receptor genes in adult rats with fimbria transections: effect of intraventricular nerve growth factor and brain-derived neurotrophic factor administration

The expression of the specific trk receptors for nerve growth factor and brain-derived neurotrophic factor (trkA and trkB) has been assayed by messenger RNA in situ hybridization in adult rats with partial fimbrial transections along with intraventricular treatment of nerve growth factor or brain-derived neurotrophic factor. In the forebrain, specific hybridization labeling for trkA messenger RNA showed an identical pattern to that of choline acetyltransferase messenger RNA, supporting the view that trkA expression is confined to the cholinergic population in the basal forebrain and the cholinergic interneurons in the striatum. After partial unilateral transections of the fimbria there was a progressive loss of choline acetyltransferase and trkA messenger RNA expression in the septal region ipsilateral to the lesion. Daily intraventricular administration of brain-derived neurotrophic factor or nerve growth factor partially prevented the lesion-induced decrease in the levels of both messengers, the latter being more effective than the former. Grain count analysis of individual cells was used to test whether the two factors upregulated choline acetyltransferase or trkA expression in individual cells surviving the lesion. Brain-derived neurotrophic factor treatment failed to induce any change in the levels of both messengers per neuron in the septal area. In contrast, daily intraventricular administration of nerve growth factor upregulated both choline acetyltransferase and trkA messenger RNA expression in individual neurons. This upregulation was evident on ipsilateral and contralateral sides, suggesting that nerve growth factor is able to upregulate these markers in intact and injured cholinergic cells in the basal forebrain. Similar to the situation in the septum, brain-derived neurotrophic factor did not upregulate choline acetyltransferase or trkA expression in the striatum. However, nerve growth factor administration strongly upregulated choline acetyltransferase messenger RNA expression by individual cholinergic neurons of the striatum. A medial to lateral gradient decrease in this upregulation was detected in the striatum ipsilateral to the side of administration, suggesting a limited diffusion of the nerve growth factor protein from the ventricle into brain parenchyma. In contrast to the strong effect on choline acetyltransferase expression, nerve growth factor treatment was ineffective in altering trkA messenger RNA in the striatum. The contrasting findings between septum and striatum suggest different regulatory mechanisms for trkA messenger RNA expression in the two cholinergic populations. Since nerve growth factor was found to upregulate the expression of its trkA receptor, we tested whether brain-derived neurotrophic factor administration had similar effects on the regulation of its trkB receptor.(ABSTRACT TRUNCATED AT 400 WORDS)

Tetrahydrobiopterin cofactor biosynthesis: GTP cyclohydrolase I mRNA expression in rat brain and superior cervical ganglia

GTP cyclohydrolase I (GTPCH) is the rate-limiting enzyme in the biosynthesis of tetrahydrobiopterin, the reduced pteridine cofactor required for catecholamine (CA), indoleamine, and nitric oxide biosynthesis. We have used the reverse transcription-polymerase chain reaction technique, based on the published cDNA sequence for rat liver GTPCH, to clone a portion of the GTPCH transcript from rat adrenal gland mRNA and have used this clone for the analysis of GTPCH mRNA in brain and other tissues of the rat by northern blot, nuclease protection assay, and in situ hybridization. Two GTPCH mRNA transcripts of 1.2 and 3.8 kb in length were detected by northern blot, with the 1.2-kb form predominating in the liver and the 3.8-kb form in the pineal gland, adrenal gland, brainstem, and hypothalamic neurons maintained in culture. In situ hybridization studies localized GTPCH mRNA to CA-containing perikarya in the locus ceruleus, ventral tegmental area, and substantia nigra, pars compacta. Levels of GTPCH mRNA in central and peripheral catecholamine neurons determined by nuclease protection assay were increased twofold 24 h after a single injection of the CA-depleting drug reserpine; both the 1.2- and 3.8-kb transcripts were increased in the adrenal gland. Low levels of GTPCH mRNA were also detected by nuclease protection assay in the striatum, hippocampus, and cerebellum, brain regions that do not contain monoaminergic perikarya.

A combined in situ hybridization and immunofluorescence procedure allowing visualisation of peptide mRNA and serotonin in single sections

We describe a novel procedure for combining immunocytochemistry with in situ hybridisation. In contrast to previously published procedures, the technique involves immunofluorescence followed by in situ hybridization and is particularly suitable for antigens which are labile or sensitive to in situ hybridization processing. We have evaluated the technique using 5-hydroxytryptamine (5-HT, serotonin) immunofluorescence and neuropeptide in situ hybridization employing 35S-labelled oligonucleotide probes. Successful double labelling was obtained and showed that galanin messenger RNA (mRNA) is expressed by 5-HT immunoreactive cells in the dorsal raphe nucleus of the rat. In contrast, somatostatin mRNA in the same region is expressed by a separate non-serotonergic cell population. Double-labelled preparations produced using this technique can be conveniently viewed using epipolarised combined with epifluorescent illumination. Careful analysis of procedural variables revealed that it is not possible to carry out high-sensitivity 5-HT immunocytochemistry following in situ hybridization. The immunostaining is much poorer on slide-mounted sections than on free-floating sections, and 5-HT appears to be lost during the in situ hybridization steps of dehydration/delipidation and incubation in hybridization buffer. The procedure we describe avoids these problems but with a slight loss of in situ hybridization sensitivity.

Chronic intranigral administration of brain-derived neurotrophic factor produces striatal dopaminergic hypofunction in unlesioned adult rats and fails to attenuate the decline of striatal dopaminergic function following medial forebrain bundle transection

The present study determined the effects of chronic intranigral injections of recombinant human brain-derived neurotrophic factor (1 micrograms) every second day for 19 days on the functional capacity of dopaminergic neurons of the nigrostriatal pathway of unlesioned adult rats. In animals chronically treated with brain-derived neurotrophic factor, we observed amphetamine (5 mg/kg)-induced circling behavior directed toward the neurotrophin-injected side (33 turns/5 min). The behavioral asymmetry was paralleled by reductions of striatal [3H]dopamine uptake (27%), tyrosine hydroxylase activity (68%), dopamine content (36%) and [3H]mazindol binding site density (35%) on the same side as brain-derived neurotrophic factor treatment. While chronic injections of brain-derived neurotrophic factor produced a modest decrease in the number of tyrosine hydroxylase-positive cell bodies in the vicinity of the injection site, a similar reduction in cell number was observed in animals injected with a control protein, cytochrome c. However, in contrast to the animals treated with brain-derived neurotrophic factor, rats treated with the control protein showed no amphetamine-induced circling behavior, and there were no significant reductions in neurochemical parameters of striatal dopaminergic function. Lastly, we found that in brain-derived neutrophic factor-injected animals there was a 30% decrease of tyrosine hydroxylase messenger RNA levels in the ventral mesencephalon. We also determined the effects of brain-derived neurotrophic factor treatment on animals with transections of the medial forebrain bundle. Medial forebrain bundle-lesioned animals challenged with amphetamine circled (55 turns/5 min) ipsilateral to the lesioned side. The medial forebrain lesions decreased the following markers of striatal dopaminergic function: [3H]opamine uptake (65%), tyrosine hydroxylase activity (79%), dopamine content (80%) and [3H]mazindol binding site density (52%), induced a pronounced loss of tyrosine hydroxylase-positive cell bodies within the substantia nigra and also reduced tyrosine hydroxylase messenger RNA levels. Chronic intranigral brain-derived neurotrophic factor treatment did not attenuate nor did it exacerbate the medial forebrain bundle lesion-induced decreases of dopaminergic parameters in either the substantia nigra or striatum. The results of the present study indicate that chronic intranigral administration of brain-derived neurotrophic factor to normal adult rats induces a dopaminergic hypofunction in the striatum which is manifested behaviorally by amphetamine-induced rotations. The brain-derived neurotrophic factor-induced striatal function is not the result of significant cell loss at the levels of the substantia nigra, but seems to be related to brain-derived neurotrophic factor-induced down-regulation of dopaminergic-specific proteins.(ABSTRACT TRUNCATED AT 400 WORDS)

BDNF mRNA expression in the developing rat brain following kainic acid-induced seizure activity

Brain-derived neurotrophic factor (BDNF) mRNA expression was studied in the hippocampus at various developmental stages in normal rats and following kainic acid (KA)-induced seizure activity. Systemic administration of KA strongly elevated BDNF mRNA levels in all hippocampal subregions after postnatal day 21. In contrast, even though KA induced intense behavioral seizure activity at postnatal day 8, the seizures were not associated with elevations of BDNF mRNA levels, indicating a clear dissociation between behavioral seizures and increases in BDNF mRNA levels and contradicting the view that BDNF mRNA expression is principally regulated by neuronal activity. In the dentate gyrus at postnatal day 13, intense BDNF mRNA expression was limited to a defined area at the border between granule cell and molecular layers, suggesting the possibility that segregation of BDNF mRNA into defined subcellular compartments may play a role in establishing the well-delineated patterns of innervation in the hippocampus.

Somatotopic organization of tyrosine hydroxylase expression in the rat locus coeruleus: long term effect of RU24722

Tyrosine hydroxylase (TH) tissue concentration was determined by immunostaining of tissue sections directly transferred onto nitrocellulose membranes in the restricted region of the noradrenergic perikarya of the locus coeruleus (LC) along its postero-anterior axis. TH containing cells were systematically counted on adjacent post fixed sections stained by immunohistochemistry. The absolute quantity of TH was estimated in each section and was found to be linearly related to the number of TH immuno-positive cells found in the adjacent section. The ratio between these two parameters was thus used as an index of the cellular concentration of TH in noradrenergic cells. In the LC of control rats, the TH cellular concentration was lower (-39%) in the anterior than in the posterior half of the structure. Three days after an injection of 20 mg/kg of RU24722, an eburnamine derivative known to increase the quantity of TH in the LC, increases in quantities of TH were found in both portions of the LC. Moreover in the posterior LC the increase in the amount of TH resulted from a significant increase in the number of TH-immunopositive cells. In the anterior part, however, it was primarily the result of a significant increase in TH cellular concentration. Throughout the LC there was an increase in the cellular concentration of TH which was inversely proportional to the concentrations found in control animals. TH mRNA content was measured by a quantitative in situ hybridization in sections of both the posterior and anterior LC one day after a single injection of RU24722 at the same dose. The quantity of TH mRNA was significantly increased in both parts. The number of TH mRNA-expressing neurons also increased, especially in the anterior LC. Thus the effects at the level of TH protein and TH mRNA were strikingly parallel though increase in TH protein occurred later than the increase in the TH mRNA. These results suggest that in the rat LC: (1) there is a significant population of 'sleeping cells' in which TH expression is either inactivated or, at a low level of activation; (2) TH cellular concentration could exert a retrocontrol on its own expression in cells of the LC that contained TH and (3) TH expression appears to be regulated by different selective mechanisms in these two different subpopulations of noradrenergic cells within the LC.

Changes in tyrosine hydroxylase mRNA levels in medullary A1 and A2 neurons and locus coeruleus following castration and estrogen replacement in rats

Temporal changes in tyrosine hydroxylase (TH) mRNA levels in medullary A1 and A2 neurons and locus coeruleus (LC) cells were studied 6, 12 and 24 h following orchidectomy in rats. Brains from intact controls and sham castrated rats also were evaluated at these same time periods. In situ hybridization histochemistry and quantitative image analysis techniques were used to quantitate levels of cytoplasmic TH mRNA. Neither the time of day nor the stress of sham castration affected TH mRNA levels in A1, A2 and LC neurons. In contrast, 6 h following castration, TH mRNA levels in A1 neurons had declined significantly. Thereafter, there was a linear increase in A1 message levels such that, by 24 h, TH mRNA values were significantly higher than those obtained in intact controls. Placement of Silastic estrogen capsules immediately after castration prevented the 6 h decline in A1 message levels. At 12 h, TH mRNA levels in A1 neurons were significantly higher in estrogen-treated rats compared to those of the castrate or intact control groups. By 24 h, message levels in A1 neurons of steroid-treated rats were comparable to the intact control. Neither castration nor estrogen treatment altered TH mRNA levels in A2 neurons. TH mRNA levels in LC neurons increased significantly 6 h after castration and estrogen produced a further significant increase in message levels. Six hours later (12 h), TH mRNA values were still higher than controls but, in the estrogen-treated group, these levels had declined to those observed in the 12 h castrate group.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of reserpine on tyrosine hydroxylase mRNA levels in locus coeruleus and medullary A1 and A2 neurons analyzed by in situ hybridization histochemistry and quantitative image analysis methods

These studies examined the effects of reserpine on concentrations of norepinephrine (NE), dopamine (DA) and epinephrine (EPI) and on levels of tyrosine hydroxylase (TH) mRNA in locus coeruleus (LC) and medullary A1 and A2 neurons. Noradrenergic neurons in these regions first were identified by immunocytochemistry and, thereafter, by in situ hybridization histochemistry. Levels of TH mRNA were measured by quantitative image analysis methods. Changes in catecholamine concentrations in micropunches of these brain regions were analyzed by HPLC. Epinephrine was not detected in any of the nuclei examined. Twenty-four hours after reserpine treatment, NE concentrations declined in A1, A2 and LC neurons by 46, 69 and 34% respectively while DA declined only in the region of A2 neurons. This reserpine-induced depletion of NE was accompanied by a 2- to 3-fold increase in TH mRNA levels in LC and A1 neurons but no change in message levels occurred in A2 cells 24 h after reserpine. Forty eight hours later, message levels in A1 and LC neurons did not differ significantly from the elevated 24 h values but TH mRNA levels in A2 neurons now were significantly elevated compared to 24 h values. TH mRNA levels 72 h after reserpine did not differ from 48 h values in A1, A2 and LC neurons. Thus, TH gene expression in A1 neurons increases after reserpine treatment in a manner equivalent to that observed in LC, adrenal medulla and superior cervical ganglia. The reason why it required 48 h for TH mRNA to increase in A2 neurons remains unclear.

Regionally specific and rapid increases in brain-derived neurotrophic factor messenger RNA in the adult rat brain following seizures induced by systemic administration of kainic acid

In situ hybridization techniques were used to analyse the spatiotemporal pattern of brain-derived neurotrophic factor messenger RNA elevation associated with kainic acid-induced seizure activity in the rat. Pronounced increases in hippocampal brain-derived neurotrophic factor messenger RNA levels were observed as early as 30 min following the onset of behavioral seizures. The greatest increase (10-fold) occurred in the dentate granule cell layer, while pyramidal layers CA1, CA3, and CA4 exhibited increases of two- to six-fold. Peak elevation of brain-derived neurotrophic factor messenger RNA in CA1 hippocampal region was evident at 4 h in CA3, and in the dentate granule layer at 30 min postseizure. Elevations persisted in the dentate and hilar regions to four days, while the increases in CA1 and CA3 returned to control levels by 16 h following seizure. Significant increases in brain-derived neurotrophic factor messenger RNA were also observed in the superficial layers of cortex (II and III) and in the piriform cortex which reached peak elevations by 8 h. No detectable changes were observed in the dorsomedial thalamus. Although histologically defined pyramidal and granule cell layers displayed relatively uniform increases in brain-derived neurotrophic factor messenger RNA in response to kainate, a closer examination of the labeling patterns using emulsion autoradiography revealed discrete areas of high grain densities overlapping uniform, moderate hybridization densities in the dentate granule cell layer and CA3, suggesting that the capacity to upregulate brain-derived neurotrophic factor messenger RNA in these regions may differ among individual neurons. In conclusion, our studies revealed that brain-derived neurotrophic factor messenger RNA induction in response to systemic kainate administration differs in hippocampal and cortical areas, in magnitude, time of onset and duration. The observed temperospatial pattern does not correspond in a simple way to increases in metabolic or electrical activity associated with seizures or neuronal vulnerability coincident with the seizures.

Slow changes of tyrosine hydroxylase gene expression in dopaminergic brain neurons after neurotoxin lesioning: a model for neuron aging

Slow neuron regression develops during the adult phase of life in select brain systems of mammals. We describe a model in adult rats that resolves several phases in a slow atrophic process that differentially influences levels of mRNA and protein for tyrosine hydroxylase (TH). Responses of striatal dopaminergic markers to 6-hydroxydopamine (6-OHDA) lesions in rats indicated that the striatal terminals maintained TH protein, despite greater than 3-fold loss of TH mRNA in the substantia nigra pars compacta (SNC) cell bodies whose axons project to the striatum. The loss of TH mRNA/cell was progressive up to 9 months, whereas SNC cell body shrinkage stabilized by 3 months post-lesioning. Consideration of possible mechanisms in protein turnover motivated a search for PEST motifs in the TH of rats and other vertebrates that could be a point of regulation by altering the rate of TH protein turnover.

Sulfated glycoprotein-2 (SGP-2) mRNA is expressed in rat striatal astrocytes following ibotenic acid lesions

A combination of in situ hybridization and immunocytochemistry (ICC) was used to identify the cells that contained mRNA for sulfated glycoprotein-2 (SGP-2) in adult male rats after striatal ibotenic acid (IA) lesioning. Astrocytic responses were monitored by ICC for glial fibrillary acidic protein (GFAP). IA lesioning that caused death of striatal neurons also stimulated astrocytic responses as monitored by GFAP and SGP-2. The SGP-2 immunoreactivity showed punctate deposits in the lesioned striatum without any apparent cellular localization. By in situ hybridization combined with ICC, SGP-2 mRNA was localized in astrocytes that were GFAP-immunopositive. These data suggest that reactive astrocytes may express SGP-2 which may be eventually secreted.

Astrocytic apolipoprotein E mRNA and GFAP mRNA in hippocampus after entorhinal cortex lesioning

Entorhinal cortex lesions (ECL) that damage the perforant path to the hippocampus induce rapid increases of apolipoprotein E (apo E) mRNA in the hippocampus. Apo E mRNA was localized in astrocytes by in situ hybridization in combination with immunocytochemistry for glial fibrillary acidic protein (GFAP). Unilateral ECL also increased hippocampal GFAP mRNA, with increases preceding those of apo E mRNA. The apo E mRNA and GFAP mRNA responses were transiently bilateral in non-denervated zones. The timing of response in apo E mRNA to deafferentation supports suggestions that apo E has roles in membrane remodelling during responses to neuron injury.

Tyrosine hydroxylase mRNA expression by dopaminergic neurons in culture: effect of 1-methyl-4-phenylpyridinium treatment

To enable us to study expression of tyrosine hydroxylase [TH; tyrosine 3-monooxygenase; L-tyrosine tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating); EC 1.14.16.2] as a measure of dopaminergic neuron function in future experiments, methods were developed to quantify TH mRNA levels in cultures of dopaminergic mesencephalic cells. The model of selective dopaminergic toxicity of 1-methyl-4-phenylpyridinium (MPP+) was used to verify the specificity of our methods. Fetal (embryonic day 15) rat ventral mesencephalic cell cultures were treated with 15 microM MPP+ for 48 h, conditions previously shown to reduce the number of TH-immunoreactive neurons, TH activity, and dopamine uptake to 5-10% of control values. This treatment decreased the number of neurons labeled by TH in situ hybridization to 9% of untreated controls and caused a strong reduction of the abundance of TH mRNA in Northern blots. Our findings establish TH mRNA expression as a parameter for future studies of toxic and trophic effects on cultured dopaminergic neurons, and they support the view that MPP+ destroys dopaminergic neurons.

Tyrosine hydroxylase mRNA concentration in midbrain dopaminergic neurons is differentially regulated by reserpine

Tyrosine hydroxylase (TH)-mRNA, assayed by in situ hybridization combined with TH immunocytochemistry, showed a selective increase in the ventral tegmental area (A-10) but not in the substantia nigra (A-9) midbrain dopaminergic (DAergic) neurons 3 days after reserpine treatment. TH-mRNA in locus ceruleus noradrenergic (A-4) neurons was increased by reserpine, as confirmed by RNA blot hybridization. These findings show that TH-mRNA is differentially regulated in midbrain DAergic neurons in response to reserpine.