Cellular quantification of tyrosine hydroxylase in the rat brain by immunoautoradiography

Reduction in Nesfatin-1 Levels in the Cerebrospinal Fluid and Increased Nigrostriatal Degeneration Following Ventricular Administration of Anti-nesfatin-1 Antibody in Mice

Nesfatin-1 is one of several brain-gut peptides that have a close relationship with the central dopaminergic system. Our previous studies have shown that nesfatin-1 is capable of protecting nigral dopaminergic neurons against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity. A recent study also revealed a reduced blood level of nesfatin-1 in patients with Parkinson’s disease (PD). The current study was designed to investigate whether reduced nesfatin-1 in cerebrospinal fluid (CSF) induces nigrostriatal system degeneration. An intra-cerebroventricular (ICV) injection technique was used to administer anti-nesfatin-1 antibody directly into the lateral ventricle of the brain. Enzyme-linked immunosorbent assay (ELISA) results showed that ICV injection of anti-nesfatin-1 antibody into the lateral ventricle of the brain once daily for 2 weeks caused a significant reduction in nesfatin-1 levels in the CSF (93.1%). Treatment with anti-nesfatin-1 antibody resulted in a substantial loss (23%) of TH-positive (TH+) dopaminergic neurons in the substantia nigra pars compacta (SNpc), as shown by immunofluorescence staining, a depletion in dopamine and its metabolites in the striatum detected by high-performance liquid chromatography (HPLC), and obvious nuclear shrinkage and mitochondrial lesions in dopaminergic neurons in the SNpc detected by transmission electron microscopy (TEM). Furthermore, the results from our Western blot and ELISA experiments demonstrated that anti-nesfatin-1 antibody injection induced an upregulation of caspase-3 activation, increased the expression of p-ERK, and elevated brain-derived neurotrophic factor (BDNF) levels in the SNpc. Taken together, these observations suggest that reduced nesfatin-1 in the brain may induce nigrostriatal dopaminergic system degeneration; this effect may be mediated via mitochondrial dysfunction-related apoptosis. Our data support a role of nesfatin-1 in maintaining the normal physiological function of the nigrostriatal dopaminergic system.

Transcription Factors Phox2a/2b Upregulate Expression of Noradrenergic and Dopaminergic Phenotypes in Aged Rat Brains

The present study investigated the effects of forced overexpression of Phox2a/2b, two transcription factors, in the locus coeruleus (LC) of aged rats on noradrenergic and dopaminergic phenotypes in brains. Results showed that a significant increase in Phox2a/2b mRNA levels in the LC region was paralleled by marked enhancement in expression of DBH and TH per se. Furthermore, similar increases in TH protein levels were observed in the substantial nigra and striatum, as well as in the hippocampus and frontal cortex. Overexpression of Phox2 genes also significantly increased BrdU-positive cells in the hippocampal dentate gyrus and NE levels in the striatum. Moreover, this manipulation significantly improved the cognition behavior. The in vitro experiments revealed that norepinephrine treatments may increase the transcription of TH gene through the epigenetic action on the TH promoter. The results indicate that Phox2 genes may play an important role in improving the function of the noradrenergic and dopaminergic neurons in aged animals, and regulation of Phox2 gene expression may have therapeutic utility in aging or disorders involving degeneration of noradrenergic neurons.

Norepinephrine upregulates the expression of tyrosine hydroxylase and protects dopaminegic neurons against 6-hydrodopamine toxicity

As a classic neurotransmitter in the brain, norepinephrine (NE) also is an important modulator to other neuronal systems. Using primary cultures from rat ventral mesencephalon (VM) and dopaminergic cell line MN9D, the present study examined the neuroprotective effects of NE and its effects on the expression of tyrosine hydroxylase (TH). The results showed that NE protected both VM cultures and MN9D cells against 6-hydroxydopamine-caused apoptosis, with possible involvement of adrenal receptors. In addition, treatment with NE upregulated TH protein levels in dose- and time-dependent manner. Further experiments to investigate the potential mechanisms underlying this NE-induced upregulation of TH demonstrated a marked increase in protein levels of the brain-derived neurotrophic factor (BDNF) and the phosphorylated extracellular signal-regulated protein kinase 1 and 2 (pERK1/2) in VM cultures treated with NE. In MN9D cells, a significantly increase of TH and pERK1/2 protein levels were observed after their transfection with BDNF cDNA or exposure to BDNF peptides. Treatment of VM cultures with K252a, an antagonist of the tropomyosin-related kinase B, blocked the upregulatory effects of NE on TH, BDNF and pERK1/2. Administration of MEK1 & MEK2 inhibitors also reversed NE-induced upregulation of TH and pERK1/2. Moreover, ChIP assay showed that treatment with NE or BDNF increased H4 acetylation in the TH promoter. These results suggest that the neuroprotection and modulation of NE on dopaminergic neurons are mediated via BDNF and MAPK/ERK pathways, as well as through epigenetic histone modification, which may have implications for the improvement of therapeutic strategies for Parkinson's disease.

Dual use of immunohistochemistry for film densitometry and light microscopy

In the present study, we applied the principles of immunoblotting and light microscopy immunohistochemistry to develop a combined methodology that allows obtaining optical density data in films, as well as morphological and protein distribution data on slides using the same brain tissue section, thus maximizing the data obtained from a single sample. This is especially important when experiments are performed using very valuable or unique tissue samples, which is a very common case in the study of the human brain. The ideal methodology should combine the possibility of measuring levels of expression of a marker, and the capability to map accurately the distribution of that marker in the region of interest. To achieve this, two things are required: first, the technique needs to be sensitive enough to obtain optical density or intensity measurements of the marker, and second, a good preservation of the tissue is needed for the study of distribution patterns and morphological analysis. Here we show that our combined methodology produced reliable results for different tissue preservation conditions (fresh-frozen and fixed tissue), in different species (rat and human), in different brain areas (substantia nigra and striatum), and for the detection of different markers (tyrosine hydroxylase and μ-opioid receptor). This methodology also combines the accuracy of optical density data acquisition in film with obtaining histological slides from the same sample. In summary, the methodology proposed here is very versatile and does not require the use of specialized equipment, other than the routine equipment present in an anatomy laboratory.

Corticosterone up-regulates expression and function of norepinephrine transporter in SK-N-BE(2)C cells

Glucocorticoids affect cellular and molecular events in brains by modulating the expression of many genes during stress. In the present study, we examined the regulatory effect of corticosterone on the expression and function of the norepinephrine transporter (NET) in vitro. The results show that exposure of SK-N-BE(2)C cells to corticosterone for 14 days significantly increased mRNA (up to 43%) and protein (up to 71%) levels of NET in the concentration-dependent manner. Longer exposure (21 days) resulted in greater increases in the levels of mRNAs (up to about 160%) and proteins (up to about 250%) of the NET. The up-regulatory effect of corticosterone on NET expression lasted a persistent period after cessation of exposure. Associated with the corticosterone-induced enhancement in NET expression, there was a parallel increase in the uptake of [(3)H]norepinephrine by SK-N-BE(2)C cells. Increased NET expression and function were abolished after exposure of cells to corticosterone in combination with mifepristone or spironolactone, two specific antagonists of corticosteroid receptors. This is consistent with the hypothesis that corticosterone-induced NET up-regulation is mediated by corticosteroid receptors. Nevertheless, there was no synergistic effect for a combination of both corticosteroid receptor antagonists. A similar up-regulation of NET protein levels was also observed after exposing PC12 cells to corticosterone. The present findings demonstrate that corticosterone up-regulates the expression and function of NET in vitro, indicating the action of corticosterone on the noradrenergic phenotype may play an important role in the correlation between stress and the development of depression.

Increased extracellular DA and normal evoked DA release in the rat striatum after a partial lesion of the substantia nigra

After injection of 6-hydroxydopamine into the lateral part of the rat substantia nigra, tissue dopamine (DA), dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were reduced in the corresponding lateral part of the ipsilateral caudate/putamen (CP) complex (13, 40 and 56% of controls, respectively). In this region, tyrosine hydroxylase (TH, the rate limiting enzyme of the DA synthesis) immunoautoradiography decreased by more than 80% as was the case for the binding of tritiated GBR12935 (a specific marker of the DA-carrier protein). In the medial region of the CP, only very moderate reductions of DA, DOPAC and HVA (77, 76 and 84% of controls, respectively) were observed. In this region, TH immunoautoradiography and GBR12935 binding were only reduced by about 20% reflecting weak DA denervation. However, using in vivo voltammetry, extracellular basal DA levels were found to be particularly high in the medial region of CP complex when compared to unoperated animals (up to 235%). In the medial region, TH activity was also significantly increased (161%) but the electrical stimulation of DA fibers produced the same DA overflow in control and lesioned animals. From these results, it may be concluded that elevated basal DA levels in this region cannot be attributed to the reduced DA uptake and/or to an increased ability of DA neurons to release DA in response to impulse flow.

Hypothalamo-pituitary-adrenocortical dysregulation in aging F344/Brown-Norway F1 hybrid rats

Hypothalamo-pituitary-adrenocortical (HPA) axis aging was studied in young (3 mo), middle aged (15 mo) and aged (30 mo) F344/Brown Norway hybrid rats. This strain was selected to obviate HPA-relevant pathologies found in other aging models. Aged, unstressed rats showed enhanced central HPA drive, marked by elevated ACTH release and decreased pituitary proopiomelanocortin and corticotropin-releasing factor receptor 1 (CRH-R1) mRNAs. Acute corticosterone responses to spatial novelty were exacerbated in aged rats; however, responses to restraint or hypoxia were not affected. Chronic stress exposure also differentially increased HPA drive in aged animals, marked by elevated paraventricular nucleus CRH peptide levels and pituitary proopiomelanocortin mRNA. Plasma ACTH and pituitary POMC and CRH-R1 mRNA expression in middle-aged rats were intermediate those of young and aged animals. Middle-aged animals responded to chronic stress with disproportionate increases in CRH mRNA levels, and increased corticosterone secretion following hypoxia but not novelty. The results suggest a gradual increase in HPA tone across the aging process, culminating in marked hyperresponsivity to both acute and chronic stress in senescence.

Regulation of hippocampal glucocorticoid receptor gene transcription and protein expression in vivo

Glucocorticoid receptors (GRs) are glucocorticoid-activated transcription factors that modulate expression of a variety of neuronal genes. Appropriate control of GR expression is therefore critical for maintenance of cellular and organismic homeostasis. The present study assessed glucocorticoid regulation of the GR at the gene, mRNA, and protein level. Removal of circulating glucocorticoids (adrenalectomy) increased GR mRNA expression in CA1 and dentate gyrus (DG). Corticosterone (CORT) replacement normalized GR mRNA expression, whereas high doses slightly decreased GR mRNA in CA1. Parallel increases were observed using a probe complementary to the distal 3' untranslated region, indicating that mRNA changes were not attributable to selection of alternative polyadenylation site. Expression of a GR intronic sequence was also increased by adrenalectomy, consistent with increased gene transcription. Analysis of regional GR protein expression by immunoautoradiography did not reveal changes in GR protein in pyramidal cell layers; however, increased GR signal was seen in the stratum radiatum, indicating redistribution of GR to the cytosol. Western blot analysis confirmed adrenalectomy-induced increases in hippocampal GR levels. Administration of the mineralocorticoid receptor (MR) antagonist spironolactone increased both GR mRNA and protein in CA1 and DG, consistent with MR-mediated inhibition of GR transcription. However, high-dose CORT treatment did not decrease GR mRNA or protein levels. Chronic stress exposure did not downregulate GR mRNA or protein in hippocampus. The results suggest that the hippocampal GR is subject to heterologous regulation by the MR. In contrast, GR autoregulation is only evident during prolonged exposure to high-circulating glucocorticoid levels.

Neurochemical characterization of individual vulnerability to addictive drugs in rats

Rats exposed to a low-light, low-noise, novel environment exhibit differences in individual locomotor response to the novelty stressor. The categorization of rats in a locomotor screening procedure as low- (LR) or high-responders (HR), where LRs are in the low locomotor range while HRs belong to the high locomotor range, is significant in that HRs show higher activity in mesencephalic dopaminergic projection neurons, and also show a higher propensity to self-administer psychostimulants and other drugs of abuse compared with LRs. In this study, we examined the neurobiological basis of dopaminergic hyperactivity by comparing in HRs and LRs the steady-state differences in regulatory inputs to mesencephalic (substantia nigra and ventral tegmental area: VTA) dopaminergic neurons. In particular, using in situ hybridization, we studied levels of mRNA for tyrosine hydroxylase (TH) and cholecystokinin (CCK) in the mesencephalon, and for preprodynorphin (DYN), preproenkephalin (PPE), and preprotachykinin (PPT) in the striatum and nucleus accumbens (Acb). We also evaluated TH levels by radioimmunocytochemistry (TH-RIC) in striatal, accumbal and mesencephalic regions. HRs versus LRs had lower levels of neurochemicals belonging to the intrinsic inhibitory input to dopaminergic neurons in the VTA, e.g. lower TH-RIC (-25%) and CCK-mRNA (-48%). In contrast, HRs showed higher levels of parameters belonging to extrinsic facilitating inputs, e.g. higher PPE-mRNA (+37%). In addition, HRs had higher DYN-mRNA in Acb (+61%), which has been shown to be positively correlated with higher dopaminergic activity. These results enhance our knowledge of the neurobiological correlates of individual rats' propensities to develop drug-intake and provide some putative mechanisms for the dopaminergic hyperactivity that characterizes drug-prone animals.

Ventral subiculum regulates hypothalamo-pituitary-adrenocortical and behavioural responses to cognitive stressors

The hippocampus plays an important role in central stress integration. The present study tests the hypothesis that the ventral subiculum, as a principal source of hippocampal efferents, is involved in co-ordination of hypothalamo-pituitary-adrenocortical and behavioural responses to cognitively-processed information. Basal hypothalamo-pituitary-adrenocortical activation appears to be normal in ventral subiculum lesion rats, as basal corticosterone and adrenocorticotropic hormone secretion, anterior pituitary pro-opiomelanocortin and type 1 corticotropin-releasing hormone receptor messenger RNA expression, adrenal and thymus weight, and splenic mitogen activity are not affected by lesion. Lesions of the ventral subiculum induce glucocorticoid hypersecretion following restraint stress or open field exposure, whereas responses to ether inhalation are unaffected. Interestingly, ventral subiculum lesion does not affect fast glucocorticoid negative feedback inhibition of restraint-induced adrenocorticotropic hormone release. Corticotropin-releasing hormone immunoreactivity is increased in the hypothalamic paraventricular nucleus of ventral subiculum lesion rats, and is differentially depleted by acute stress exposure (relative to sham-lesion rats). However, ventral subiculum lesion does not affect basal and stress-induced corticotropin-releasing hormone, arginine vasopressin and cFOS messenger RNA expression in paraventricular nucleus neurons. Behavioural analysis reveals that ventral subiculum lesion rats are hyper-responsive to open field exposure, showing decreased total ambulation and reduced incidence of central square entry. The results suggest that the ventral subiculum plays a specific role in integrating cognitively-processed stimuli (e.g., restraint and open field exposure) into appropriate neuroendocrine and behavioural responses to stress. Enhanced stress-induced glucocorticoid secretion and increased corticotropin-releasing hormone biosynthesis are likely due to removal of oligosynaptic inhibitory input to the paraventricular nucleus subsequent to ventral subiculum lesion.

Chronic levodopa is not toxic for remaining dopamine neurons, but instead promotes their recovery, in rats with moderate nigrostriatal lesions

Orally administered levodopa remains the most effective symptomatic treatment for Parkinson's disease (PD). The introduction of levodopa therapy is often delayed, however, because of the fear that it might be toxic for the remaining dopaminergic neurons and, thus, accelerate the deterioration of patients. However, in vivo evidence of levodopa toxicity is scarce. We have evaluated the effects of a 6-month oral levodopa treatment on several dopaminergic markers, in rats with moderate or severe 6-hydroxydopamine-induced lesions of mesencephalic dopamine neurons and sham-lesioned animals. Counts of tyrosine hydroxylase (TH)-immunoreactive neurons in the substantia nigra and ventral tegmental area showed no significant difference between levodopa-treated and vehicle-treated rats. In addition, for rats of the sham-lesioned and severely lesioned groups, immunoradiolabeling for TH, the dopamine transporter (DAT), and the vesicular monoamine transporter (VMAT2) at the striatal level was not significantly different between rats treated with levodopa or vehicle. It was unexpected that quantification of immunoautoradiograms showed a partial recovery of all three dopaminergic markers (TH, DAT, and VMAT2) in the denervated territories of the striatum of moderately lesioned rats receiving levodopa. Furthermore, the density of TH-positive fibers observed in moderately lesioned rats was higher in those treated chronically with levodopa than in those receiving vehicle. Last, that chronic levodopa administration reversed the up-regulation of D2 dopamine receptors seen in severely lesioned rats provided evidence that levodopa reached a biologically active concentration at the basal ganglia. Our results demonstrate that a pharmacologically effective 6-month oral levodopa treatment is not toxic for remaining dopamine neurons in a rat model of PD but instead promotes the recovery of striatal innervation in rats with partial lesions.

Nod factor internalization and microtubular cytoskeleton changes occur concomitantly during nodule differentiation in alfalfa

Reorganization of the plant cytoskeleton is thought to play an important role during nodule ontogeny. In situ immunolocalisation of tubulin reveals that important cytoskeletal changes, implying a transient disorganization followed by a newly patterned reorganization, occur in indeterminate and determinate nodules. In alfalfa nodules, cytoskeletal changes closely parallel the symbiotic differentiation features related to cell infection, bacterial release, endopolyploidization, cell enlargement, cell spatial organization and organelle ultrastructure and positioning. Moreover, the fact that microtubule disorganization can be correlated with Nod factor internalization in central infected cells suggests that Nod factors are possibly involved in the control of cytoskeletal changes which direct the differentiation of bacteria-containing cells.

Controlled targeting of tyrosine hydroxylase protein toward processes of locus coeruleus neurons during postnatal development

Dendrites of locus coeruleus (LC) neurons laying within the pericoerulean neuropil (PCA) organize the major site where tyrosine hydroxylase (TH) is present throughout postnatal development. Those dendrites constitute the neuronal compartment in which TH levels increase beyond postnatal day (P) 21 or after RU24722-induced TH expression. Distal LC dendrites are present in the PCA by at least P20 but are devoid of TH and can rapidly accumulate TH protein when gene induction is triggered. Contrasting with the increase in TH levels within LC perikarya and dendrites, TH-mRNA concentration remains constant in LC perikarya from P4 to P42. Thus, supposing TH synthesis and degradation are also constant, any change in TH levels targeted toward axons might be balanced by a shift in the TH deposition within LC dendrites. This mechanism may be crucial in functions that the different processes of LC neurons have at critical steps of postnatal ontogeny.

AP-1 mediates trans-synaptic induction of tyrosine hydroxylase gene expression in adrenal medulla but not in superior cervical ganglia

Reserpine treatment leads to a rapid trans-synaptic increase of the tyrosine hydroxylase (TH) gene transcription rate and mRNA levels in catecholaminergic tissues including the adrenal medulla (AM) and the superior cervical ganglia (SCG). In the AM, the formation of a specific protein complex with the TPA-responsive element located in the proximal region of the TH gene was enhanced between 30 min and 8 hr following the injection. This complex appears to contain a member of the Fos family and an antigenically related Jun protein. Moreover, the prolonged and enhanced expression of the c-Fos protein in the AM and its phosphorylation are likely to contribute to the increased TH transcription following reserpine treatment. Most strikingly, in the SCG, the trans-synaptic induction of TH transcription is transduced by totally different mechanisms, since no AP-1 complex and only minute amounts of c-Fos immunoreactivity were detected. Our study provides the first demonstration that, following the same stimulus, the induced expression of a single gene is mediated by different cis- and trans-acting factors in two distinct tissues sharing the same embryonic origin.

Collateral sprouting of central noradrenergic neurons during aging: histochemical and neurochemical studies in intraocular triple transplants

The sprouting capacity of aged noradrenergic neurons of the brain-stem nucleus locus coeruleus (LC) was examined using intraocular transplants of fetal tissues. Fetal hippocampal tissue (E18) and LC tissue (E15) were transplanted together as a double transplant into the anterior chamber of the eye of young adult Fischer 344 rats. The double transplants were allowed to mature for 14-18 months, after which an additional fetal hippocampal transplant was placed next to the LC graft. The triple transplants were monitored for overall growth and vascularization for an additional 2-6 months. Immunohistochemical examinations showed that both young (2-6 months old) and aged (16-24 months old) hippocampal cografts contained a plexus of thin varicose tyrosine hydroxylase (TH)-immunoreactive fibers extending throughout the grafted hippocampal tissues. However, the aged hippocampal grafts contained a denser uniform plexus of TH-positive fibers compared to the young transplants. Immunohistochemistry with synapsin antibodies demonstrated that both the young and the aged hippocampal transplants contained much higher densities of synaptic elements than the LC grafts. In vivo electrochemical measurements of potassium-evoked overflow of norepinephrine (NE) in the grafts showed that similar amounts of NE overflow were detected in both the young and the aged hippocampal grafts. HPLC-EC measurements of NE levels in the grafts revealed that there were similar amounts of NE in the young and the aged grafts, and the grafts did not contain serotonin or dopamine. In summary, the findings of the present study show that aged LC neurons are capable of undergoing collateral sprouting producing a functional NE neuronal system when introduced to an appropriate young target.

Pharmacology and distribution of norepinephrine transporters in the human locus coeruleus and raphe nuclei

The norepinephrine transporter (NET) is a site of action for tricyclic antidepressant drugs and for drugs of abuse such as amphetamine and cocaine. In this study, the binding of [3H]nisoxetine to NETs in the noradrenergic cell group, the locus coeruleus, and the serotonergic cell groups, the dorsal raphe nuclei, was measured autoradiographically in postmortem human brain. [3H]nisoxetine binding was unevenly distributed along the rostral-caudal axis of the locus coeruleus and correlated positively with numbers of neuromelanin-containing (noradrenergic) cells along the axis of the locus coeruleus within individuals. Binding densities of [3H]nisoxetine in dorsal raphe nuclei were similar to that in the locus coeruleus. [3H]nisoxetine binding was unevenly distributed along the entire rostral-caudal extent of the dorsal raphe, with the highest binding occurring in the interfascicular and ventral nuclei. A moderate amount of [3H]nisoxetine binding was also observed in the median raphe nucleus. The specificity of [3H]nisoxetine binding to NETs in monoaminergic nuclei was assessed by measuring the inhibition of its binding by desipramine, imipramine, or citalopram. The order of affinities of these drugs was identical in the locus coeruleus and dorsal and median raphe and was characteristic of binding to NETs (desipramine > imipramine > citalopram). Thus, high levels of NETs and an uneven distribution of NETs occur in the locus coeruleus as well as in the dorsal raphe nuclei of the human.

Immunoautoradiographic evidence for a loss of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate-preferring non-N-methyl-D-aspartate glutamate receptors within the medial temporal lobe in schizophrenia

Decreased expression of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-preferring non-N-methyl-D-aspartate (non-NMDA) glutamate receptors (GluRs) occurs in the medial temporal lobe of schizophrenics in terms of reduced abundance of GluR1 and GluR2 subunit mRNAs. To investigate further these receptors in schizophrenia, we have performed a quantitative immunoautoradiographic study in medial temporal lobe sections of 11 schizophrenics and 10 well-matched controls. GluR1 and GluR2/3 were detected with polyclonal antisera coupled to 35S-labeled secondary antibodies. Both subunits were vulnerable to a prolonged postmortem interval and poor agonal state as indicated by brain pH. GluR1 also tended to decline with increasing age. These factors were therefore used as covariates. GluR1 abundance was reduced in schizophrenics in parahippocampal gyrus (p < .025), while GluR2/3 was lower in most subfields in the schizophrenics, significantly so in CA4 (p < .02). The present data extend the evidence for decreased expression of the AMPA subtype of non-NMDA receptors in the medial temporal lobe in schizophrenia, although the magnitude and spatial extent of the loss is smaller than that affecting the encoding mRNAs. Impaired AMPA receptor expression is consistent with a neurodevelopmental origin and with hypotheses of glutamatergic hypofunction in the disease; however, its true pathophysiological significance and relationship to the other neuropathological and pathochemical abnormalities in the medial temporal lobe in schizophrenia remain to be determined.

Distribution of alpha 2-adrenoceptors in the human locus coeruleus

Recent reports of specific topographic patterns of cell loss in the locus coeruleus (LC) in psychiatric and neurologic disorders underscores the need for detailed neurochemical analyses of this cell group. In this study, the anatomical distribution of alpha 2-adrenoceptors and its relationship to the distribution of noradrenergic neurons in the human LC was studied. Quantitative autoradiography was used to assess the binding of [125I]p-iodoclonidine ([125I]PIC) to alpha 2-adrenoceptors coordinately with counts of neuromelanin-containing cells in tissue sections cryocut at 10-13 levels along the rostrocaudal axis of the LC. Pontine brain tissue was obtained postmortem from 7 subjects dying of natural or accidental causes, ranging in age from 26 to 78 years. Both the binding of [125I]PIC and number of neuromelanin-containing cells were differentially distributed along the LC axis (P < 0.01) with almost identical topographical patterns. The highest concentration of binding and the greatest number of neuromelanin-containing cells per section occurred near the middle portion of the nucleus. There was a significant correlation between the number of neuromelanin-containing cells per section and the specific binding of [125I]PIC at any particular level of the LC (r2 = 0.56; P < 0.0001). The highest and lowest amounts of [125I]PIC binding in the LC were observed in the youngest and oldest subjects, respectively, and this trend was parallelled by a significant negative correlation between the number of neuromelanin-containing cells at a given level and age (r2 = 0.85; P < 0.003). The uneven distribution of alpha 2-adrenoceptors in the LC demonstrates the importance of anatomical specificity when performing quantitative studies of LC protein chemistry in psychiatric and neurologic disorders.

Immunoautoradiographic and in situ hybridization analysis of corticotropin-releasing hormone biosynthesis in the hypothalamic paraventricular nucleus

Corticotropin-releasing hormone (CRH) gene transcription and mRNA expression are keyed to stimuli activating the pituitary-adrenocortical axis, suggesting a connection between neuronal activation and synthesis of active peptide. However, the relationship between CRH mRNA and levels of CRH peptide remains to be definitively established. The present report characterizes an immunoautoradiographic (IAR) strategy to assess CRH peptide expression in an anatomical context. Non-fixed tissue sections through the rat hypothalamus were reacted with a primary antibody against rat CRH, followed by incubation with [35S] or [125I] labeled secondary antibody. Autoradiography performed on reacted sections revealed that CRH immunoreactivity could be detected in CRH-containing regions of the hypothalamus and amygdala. Generation of CRH signal was blocked by preabsorption of primary antibody with CRH peptide, demonstrating antibody specificity. IAR performed on nitrocellulose blotted with synthetic CRH peptide revealed a linear relationship between peptide quantity and intensity of autoradiographic signal, verifying that this method is appropriate for semi-quantitative analysis of CRH peptide regulation. Assessment of CRH peptide regulation revealed a significant increase in CRH content in adrenalectomized rats (ADX) relative to sham-adrenalectomized (SHAM) controls (196%). In situ hybridization performed on adjacent sections revealed a similar increase in CRH mRNA expression in ADX rats (256%), and a significant correlation between CRH peptide and mRNA measures (r = 0.68). No ADX induced changes were seen in median eminence, dorsomedial hypothalamus or central amygdaloid nucleus. The results of this study indicate that CRH biosynthesis appears to be driven by amount of available mRNA, rather than changes in translational efficacy. In addition, the IAR technique appears ideally suited to allow concomitant assessment of mRNA and protein expression within defined populations of CNS neurons.

Reserpine affects differentially the density of the vesicular monoamine transporter and dihydrotetrabenazine binding sites

We have studied the effect of a single injection of reserpine (5 mg/kg, s.c.) on the synaptic vesicle monoamine transporter (VMAT) density in the rat striatum, using two labelling procedures: radioimmunolabelling with an antibody against VMAT, and binding of the specific ligand [(3)H]dihydrotetrabenazine ([(3)H]TBZOH). In the rostral and medial striatum, the distribution of VMAT immunoreactivity displayed the highest density in the lateral subregions. In the caudal part of the striatum, VMAT immunoreactivity showed increasing density from dorsal to ventral subregions. The VMAT immunoreactivity was not altered 2 and 30 days after the reserpine injection, whereas [(3)H]TBZOH binding site density, measured on adjacent slices, showed a dramatic decrease at day 2 and a moderate recovery at day 30, suggesting that despite a persistent blockade of [(3)H]TBZOH binding sites, VMAT protein density was unchanged.

Decreased synaptophysin in the medial temporal lobe in schizophrenia demonstrated using immunoautoradiography

Synaptic alterations have been suggested, largely on theoretical grounds, to occur in the brain in schizophrenia. The messenger RNA encoding synaptophysin, a presynaptic terminal protein, is reduced in the medial temporal lobe in the disease, but immunocytochemical and immunoblotting data have not produced clear evidence for a loss of the encoded protein. Here we have used immunoautoradiography with an antisynaptophysin monoclonal antibody and a 35S-labelled secondary antibody in medial temporal lobe sections from 11 schizophrenics and 14 matched controls. In the schizophrenic cases there was an overall loss of synaptophysin (P < 0.02). Analysis by subfield showed significant reductions in the right dentate gyrus molecular layer, subiculum and parahippocampal gyrus, with similar trends in most other subfields. These data confirm that synaptophysin expression is decreased within the medial temporal lobe in schizophrenia. In the respect that synaptophysin is a marker of synaptic density, our findings suggest that reduced synaptic density may be a feature of the molecular neuropathology of the disease.

Effects of chronic social stress on tyrosine hydroxylase mRNA and protein levels

Males housed in mixed sex groups quickly form dominance hierarchies; subordinates can be further subdivided into stress responsive subordinates (SRS) and non-responsive subordinates (NRS) based on corticosterone responses to a novel stressor. Tyrosine hydroxylase (TH) mRNA levels measured with in situ hybridization were elevated in locus coeruleus (LC) of NRS compared to singly or pair-housed controls; NRS also had higher TH levels than dominants. TH protein levels determined by immunoautoradiography were also higher in LC of NRS and SRS versus pair-housed controls.

Differential expression of tyrosine hydroxylase and membrane dopamine transporter genes in subpopulations of dopaminergic neurons of the rat mesencephalon

Dopaminergic (DA) cells of the substantia nigra pars compacta (SNC) and the ventral tegmental area (VTA) display differences in their topography, biochemistry and susceptibility to pathological processes. Neuronal dopamine concentration is regulated in large part by tyrosine hydroxylase (TH), the rate-limiting enzyme of dopamine synthesis, and by the dopamine reuptake system. In the present study, TH protein, TH mRNA and dopamine membrane transporter (DAT) mRNA were quantified at cellular level in 4 arbitrary subregions of the rat ventral mesencephalon (lateral, middle, medial SNC and VTA), using in situ hybridization and immunoautoradiography. The distribution of labelling for TH protein and TH mRNA was almost superimposable and close to that of DAT mRNA in mesencephalic neurons. Lower values of cellular expression in TH protein, TH mRNA and DAT mRNA were observed in the lateral part of the SNC compared to the other subregions. TH and DAT expression were correlated in SNC but not in VTA. Indeed DA cells in this region expressed low levels of DAT mRNA in comparison to the middle and medial SNC. These results suggest a heterogeneity of DA metabolism among populations of mesencephalic cells. The relative lower expression of the DAT gene in VTA neurons suggests a less efficient dopamine reuptake capacity, which may partly account for the relative sparing of the mesolimbic system reported in Parkinson's disease and MPTP-treated animals.