Cellular localization of tyrosine hydroxylase by immunohistochemistry

Real-time monitoring of chemical transmission in slices of the murine adrenal gland

The real-time electrochemical detection of catecholamine secretion from murine adrenal slices using fast-scan cyclic voltammetry (FSCV) and amperometry at carbon fiber microelectrodes is described. Bright-field and immunofluorescent microscopy supported that chromaffin cells in the adrenal medulla are organized into clusters and positively stain for tyrosine hydroxylase confirming that they are catecholaminergic. Spontaneous exocytotic catecholamine events were observed inside chromaffin cell clusters with both FSCV and amperometry and were modulated by the nicotinic acetylcholine receptor antagonist hexamethonium and low extracellular calcium. Reintroduction of extracellular calcium and pressure ejection of acetylcholine caused the frequency of spikes to increase back to predrug levels. Electrical stimulation caused the synchronous secretion from multiple cells within the gland, which were modulated by nicotinic acetylcholine receptors but not muscarinic receptors or gap junctions. Furthermore, electrically stimulated release was abolished with perfusion of low extracellular calcium or tetrodotoxin, indicating that the release requires electrical excitability. An extended waveform was used to study the spontaneous and stimulated release events to determine their chemical content by FSCV. Consistent with total content analysis and immunohistochemical studies, about two thirds of the cells studied spontaneously secreted epinephrine, whereas one third secreted norepinephrine. Whereas adrenergic sites contained mostly epinephrine during electrical stimulation, noradrenergic sites contained a mixture of the catecholamines showing the heterogeneity of the adrenal medulla.

A biochemical and functional protein complex involving dopamine synthesis and transport into synaptic vesicles

Synaptic transmission depends on neurotransmitter pools stored within vesicles that undergo regulated exocytosis. In the brain, the vesicular monoamine transporter-2 (VMAT(2)) is responsible for the loading of dopamine (DA) and other monoamines into synaptic vesicles. Prior to storage within vesicles, DA synthesis occurs at the synaptic terminal in a two-step enzymatic process. First, the rate-limiting enzyme tyrosine hydroxylase (TH) converts tyrosine to di-OH-phenylalanine. Aromatic amino acid decarboxylase (AADC) then converts di-OH-phenylalanine into DA. Here, we provide evidence that VMAT(2) physically and functionally interacts with the enzymes responsible for DA synthesis. In rat striata, TH and AADC co-immunoprecipitate with VMAT(2), whereas in PC 12 cells, TH co-immunoprecipitates with the closely related VMAT(1) and with overexpressed VMAT(2). GST pull-down assays further identified three cytosolic domains of VMAT(2) involved in the interaction with TH and AADC. Furthermore, in vitro binding assays demonstrated that TH directly interacts with VMAT(2). Additionally, using fractionation and immunoisolation approaches, we demonstrate that TH and AADC associate with VMAT(2)-containing synaptic vesicles from rat brain. These vesicles exhibited specific TH activity. Finally, the coupling between synthesis and transport of DA into vesicles was impaired in the presence of fragments involved in the VMAT(2)/TH/AADC interaction. Taken together, our results indicate that DA synthesis can occur at the synaptic vesicle membrane, where it is physically and functionally coupled to VMAT(2)-mediated transport into vesicles.

Looking at neurotransmitters in the microscope

This review article covers the early period of my career. I first summarize research initiated by the late Nils-Ake Hillarp, after his appointment in 1962 as professor in the Department of Histology at Karolinska Institutet. He only lived for three more years, but during this short period he started up a group of ten students who explored various aspects of the three monoamine transmitters, dopamine, noradrenaline and 5-hydroxytryptamine, using the new formaldehyde fluorescence method developed by Bengt Falck and Hillarp in Lund. This method allowed visualization of the cellular localization in the microscope of these monoamines, which introduced a new discipline in neurobiology-chemical neuroanatomy. I then deal with work aiming at localizing the monoamines at the ultrastructural level, as well as attempts to use radioactively labeled aminoacids, especially gamma-aminobutyric acid (GABA), and autoradiography, to identify, in the microscope, neurons using such transmitters. Finally, our immunohistochemical work together with Kjell Fuxe and the late Menek Goldstein, using antibodies to four monoamine-synthesizing enzymes is summarized, including some aspects on the adrenaline neurons, which had escaped detection with the Falck-Hillarp technique.

Mutant torsinA interacts with tyrosine hydroxylase in cultured cells

A specific mutation (DeltaE302/303) in the torsinA gene underlies most cases of dominantly inherited early-onset torsion dystonia. This mutation causes the protein to aggregate and form intracellular inclusion bodies in cultured cells and animal models. Co-expression of the wildtype and mutant proteins resulted in the redistribution of the wildtype protein from the endoplasmic reticulum to inclusion bodies in cultured HEK293 cells, and this was associated with increased interaction between the two proteins. Expression of DeltaE302/303 but not wildtype torsinA in primary postnatal midbrain neurons resulted in the formation of intracellular inclusion bodies, predominantly in dopaminergic neurons. Tyrosine hydroxylase was sequestered in these inclusions and this process was mediated by increased protein-protein interaction between mutant torsinA and tyrosine hydroxylase. Analysis in an inducible neuroblastoma cell culture model demonstrated altered tyrosine hydroxylase activity in the presence of the mutant but not wildtype torsinA protein. Our results suggest that the interaction of tyrosine hydroxylase and mutant torsinA may contribute to the phenotype and reported dopaminergic dysfunction in torsinA-mediated dystonia.

Complementary developmental expression of the two tyrosine hydroxylase transcripts in zebrafish

Tyrosine hydroxylase (TH) is a rate-limiting enzyme in the biosynthesis of catecholamines. In zebrafish, two genes encoding TH have been identified. We cloned them and studied their expression in zebrafish. In adult tissues, th1 mRNA was more abundant than th2 mRNA in the brain and eyes, whereas th2 mRNA was more abundant in the liver, kidney, heart and gills. In developing brain, th1 mRNA was readily detected at 1 day post-fertilization using qPCR and in situ hybridization, whereas th2 mRNA appeared later. th1 was found in 17 catecholaminergic groups in larval brain, whereas th2 was found in four additional groups. A monoclonal antibody commonly used against TH detected preferentially TH1 protein. The two th genes, probably originated as a result of genome duplication, thus show complementary expression, although th1 is predominant in the brain and th2 in the periphery. th2 may be a novel essential factor in regulation of catecholamine synthesis in zebrafish.

Molecular mechanisms and clinical implications of reversible protein S-glutathionylation

Sulfhydryl chemistry plays a vital role in normal biology and in defense of cells against oxidants, free radicals, and electrophiles. Modification of critical cysteine residues is an important mechanism of signal transduction, and perturbation of thiol-disulfide homeostasis is an important consequence of many diseases. A prevalent form of cysteine modification is reversible formation of protein mixed disulfides (protein-SSG) with glutathione (GSH). The abundance of GSH in cells and the ready conversion of sulfenic acids and S-nitroso derivatives to S-glutathione mixed disulfides suggests that reversible S-glutathionylation may be a common feature of redox signal transduction and regulation of the activities of redox sensitive thiol-proteins. The glutaredoxin enzyme has served as a focal point and important tool for evolution of this regulatory mechanism, because it is a specific and efficient catalyst of protein-SSG deglutathionylation. However, mechanisms of control of intracellular Grx activity in response to various stimuli are not well understood, and delineation of specific mechanisms and enzyme(s) involved in formation of protein-SSG intermediates requires further attention. A large number of proteins have been identified as potentially regulated by reversible S-glutathionylation, but only a few studies have documented glutathionylation-dependent changes in activity of specific proteins in a physiological context. Oxidative stress is a hallmark of many diseases which may interrupt or divert normal redox signaling and perturb protein-thiol homeostasis. Examples involving changes in S-glutathionylation of specific proteins are discussed in the context of diabetes, cardiovascular and lung diseases, cancer, and neurodegenerative diseases.

Evaluation of behavioural effects of a selective NMDA NR1A/2B receptor antagonist in the unilateral 6-OHDA lesion rat model

The degeneration of the dopaminergic nigrostriatal pathway in Parkinson's disease (PD) is associated with altered transmission at striatal NMDA receptors containing NR2B subunits. We investigated a potential novel therapeutic compound, 4-trifluoromethoxy-N-(2-trifluoromethyl-benzyl)-benzamidine (BZAD-01), a selective NMDA NR1A/2B receptor antagonist for PD and compared it with levodopa, the standard treatment for PD. This study also evaluated whether combining levodopa and BZAD-01 gave better improvements of parkinsonian symptoms. Parkinsonism was induced by microinjection of the toxin, 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle (MFB) of 40 Sprague-Dawley rats. Parkinsonism and the efficacy of drugs were assessed using a battery of behavioural tests including balance beam, apomorphine-induced rotation, body axis bias or "curling", head position bias and disengage sensorimotor latency test. Immunohistochemistry was performed on post-mortem tissue to estimate the loss of dopaminergic neurons. The main effects were that BZAD-01 co-administration prevented chronic levodopa-induced potentiation of apomorphine rotation. However levodopa-treated rats were slower than either controls or BZAD-01-treated rats in the locomotor test. The improvement in the apomorphine rotation test suggests that BZAD-01 may be a useful adjunct to levodopa monotherapy.

Dipyridamole promotes changes in calbindin-D28k and tyrosine hydroxylase expression in neonatal rats

BACKGROUND

Perinatal hypoxia alters the concentration of many neurochemicals in the brain, including adenosine, and promotes central nervous system (CNS) disorders in human infants such as periventricular leukomalacia or encephalopathy.

OBJECTIVE

Using the postnatal rat as a model of perinatal human development, we examined the effects of sustained increases in brain adenosine on CNS regions thought to be involved with both planning and execution of motor activity.

METHODS

To simulate hypoxia-induced changes in adenosine, Sprague-Dawley rats were injected twice daily from postnatal day (P) 3 to P14, with the adenosine uptake inhibitor dipyridamole (DIP) or the A(1) adenosine receptor agonist N(6)-cyclopentyladenosine (CPA). Vehicle-injected animals served as controls. Immunohistochemical and morphological analyses were then performed to examine the expression of calbindin D-28k (CB) and the thickness of the external granule cell layer (eGL) in the cerebellum. Additionally tyrosine hydroxylase (TH) expression in the caudate putamen and ventricular size were also examined.

RESULTS

In the cerebellum, both DIP and CPA reduced the number of CB-positive Purkinje cells as well as decreased the thickness of the eGL compared to vehicle. In the caudate putamen we found that DIP but not CPA decreased TH expression when compared to vehicle. Neither agent significantly altered ventricular size when compared to vehicle.

CONCLUSIONS

These observations suggest that elevations in brain adenosine, which can occur following hypoxia, leads to both neurochemical and cellular changes in regions of the brain which control the planning and execution of motor activity. Thus, therapeutic strategies that target brain regions most sensitive to adenosine may prevent or control at least some of the CNS damage observed following perinatal hypoxia.

Predominant surface distribution of neurokinin-3 receptors in non-dopaminergic dendrites in the rat substantia nigra and ventral tegmental area

Neurokinin-3 (NK(3)) receptors are prevalent within the substantia nigra (SN) and ventral tegmental area (VTA), where their activation can affect motor and motivational behaviors as well as cardiovascular function and stress responses. These actions are mediated, in part, by dopaminergic neurons in each region. To determine the relevant sites for activation of these receptors, we examined the electron microscopic localization of NK(3) receptors and tyrosine hydroxylase (TH), the catecholamine synthesizing enzyme in dopaminergic neurons in the SN and VTA of rat brain. In each region, immunogold-silver labeling for NK(3) receptors was detected in many somatodendritic profiles, some of which contained TH-immunoreactivity. NK(3)-immunogold particles were largely associated with endomembranes resembling smooth endoplasmic reticulum, and only occasionally located on the plasma membrane in TH-labeled dendrites. In comparison with these dendrites, non-TH immunoreactive dendrites contained significantly more total (VTA) and more plasmalemmal (VTA and SN) NK(3)-immunogold particles. In each region, NK(3) gold particles also were seen in axonal as well as glial profiles, some of which contacted TH-immunoreactive dendrites. The NK(3)-labeled axon terminals formed either symmetric or asymmetric, excitatory-type synapses, the latter of which were significantly more prevalent in the VTA, compared with SN. These results provide the first ultrastructural evidence indicating that NK(3) receptors are available in cytoplasmic reserve in dopaminergic neurons, but more immediately accessible at the plasmalemmal surface of non-dopaminergic dendrites in both the SN and VTA. The activation of these receptors, together with the NK(3) receptors in either the presynaptic axon terminals or glia may contribute to the diverse physiological effects of tachykinins in each region, and most prominently involving excitatory inputs to the VTA.

Delayed increase of tyrosine hydroxylase expression in rat nigrostriatal system after traumatic brain injury

Tyrosine hydroxylase (TH) is the key enzyme for synthesizing dopamine (DA) in dopaminergic neurons and its terminals. Emerging experimental and clinical evidence support the hypothesis of a disturbance in dopamine neurotransmission following traumatic brain injury (TBI). However, the effect of controlled cortical impact (CCI) injury on TH in the nigrostriatal system is currently unknown. To determine if there is an alteration in TH after CCI injury, we examined TH levels at 1 day, 7 days, and 28 days post-injury by utilizing a commercially available antibody specific to TH. Rats were anesthetized and surgically prepared for CCI injury (4 m/s, 3.2 mm) or sham surgery. Injured (N=6) and sham animals (N=6) were sacrificed and coronally sectioned (35 microm thick) through the striatum and substantia nigra (SN) for immunohistochemistry. Additionally, semiquantitative measurements of TH protein in striatal and SN homogenates from injured (N=6) and sham (N=6) rats sacrificed at the appropriate time post-surgery were assessed using Western blot analysis. TH protein is bilaterally increased at 28 days post-injury in nigrostriatal system revealed by immunohistochemistry in injured rats compared to sham controls. Western blot analysis confirms the findings of immunohistochemistry in both striatum and SN. We speculate that the increase in TH in the nigrostriatal system may reflect a compensatory response of dopaminergic neurons to upregulate their synthesizing capacity and a delayed increase in the efficiency of DA neurotransmission after TBI.

Chronic stress increases the plasmalemmal distribution of the norepinephrine transporter and the coexpression of tyrosine hydroxylase in norepinephrine axons in the prefrontal cortex

Norepinephrine (NE) potently modulates the cognitive and affective functions of the prefrontal cortex (PFC). Deficits in NE transmission are implicated in psychiatric disorders, and antidepressant drugs that block the NE transporter (NET) effectively treat these conditions. Our initial ultrastructural studies of the rat PFC revealed that most NE axons (85-90%) express NET primarily within the cytoplasm and lack detectable levels of the synthetic enzyme tyrosine hydroxylase (TH). In contrast, the remaining 10-15% of PFC NE axons exhibit predominantly plasmalemmal NET and evident TH immunoreactivity. These unusual characteristics suggest that most PFC NE axons have an unrecognized, latent capacity to enhance the synthesis and recovery of transmitter. In the present study, we used dual-labeling immunocytochemistry and electron microscopy to examine whether chronic cold stress, a paradigm that persistently increases NE activity, would trigger cellular changes consistent with this hypothesis. After chronic stress, neither the number of profiles exhibiting NET labeling nor their size was changed. However, the proportion of plasmalemmal NET nearly doubled from 29% in control animals to 51% in stressed rats. Moreover, the expression of detectable TH in NET-labeled axons increased from only 13% of profiles in control rats to 32% of profiles in stressed animals. Despite the consistency of these findings, the magnitude of the changes varied across individual rats. These data represent the first demonstration of activity-dependent trafficking of NET and expression of TH under physiological conditions and have important implications for understanding the pathophysiology and treatment of stress-related affective disorders.

Adverse effects of prenatal tobacco smoke exposure on biological parameters of the developing brainstem

We aimed to study the consequences of chronic exposure to tobacco smoke in utero on the morphological and functional maturation of the brainstem by comparing stillbirths of smoker mothers versus nonsmoker mothers. A total of 42 stillbirths, aged 25-40 gestational weeks, underwent autopsy according to our guidelines (). The brainstem was studied on serial sections and by immunohistochemistry to assay the expression of the EN2 gene, somatostatin (SS) and the tyrosine hydroxylase enzyme (TH). We observed a significant correlation between maternal smoking and sudden intrauterine unexplained death (SIUD), hypoplasia of the ArcN, no immunostaining of the EN2 in the arcuate nucleus (ArcN), and of TH in the locus coeruleus (LC) (P < 0.05). An increased incidence of maternal smoking was also observed in fetuses with SS negativity in the hypoglossus nucleus (HypoglN). Exposure in utero to maternal smoking may strongly interfere with brain biological parameters, giving rise not only to structural developmental abnormalities of the arcuate nucleus, but also to a decrease of noradrenergic activity in the LC, of EN2 gene expression in the ArcN and of SS in the HypoglN.

Cell therapy for neuropathic pain in spinal cord injuries

Cell therapy to treat neuropathic pain after spinal cord injury (SCI) is in its infancy. However, the development of cellular strategies that would replace or be used as an adjunct to existing pharmacological treatments for neuropathic pain have progressed tremendously over the past 20 years. The earliest cell therapy studies for pain relief tested adrenal chromaffin cells from rat or bovine sources, placed in the subarachnoid space, near the spinal cord pain- processing pathways. These grafts functioned as cellular minipumps, secreting a cocktail of antinociceptive agents around the spinal cord for peripheral nerve injury, inflammatory or arthritic pain. These initial animal, and later clinical, studies suggested that the spinal intrathecal space was a safe and accessible location for the placement of cell grafts. However, one major problem was the lack of a homogeneous, expandable cell source to supply the antinociceptive agents. Cell lines that can be reversibly immortalised are the next phase for the development of a practical, homogenous cell source. These technologies have been modelled with a variety of murine cell lines, derived from embryonic adrenal medulla or CNS brainstem, in which cells are transplanted, which downregulate their proliferative, oncogenic phenotype either before or after transplant. An alternative approach for existing human cell lines is the use of neural or adrenal precursors, in which the antinociceptive properties are induced by in vitro treatment with molecules that move the cells to an irreversible neural or chromaffin, and non-oncogenic, phenotype. Although such human cell lines are at an early stage of investigation, their clinical antinociceptive potential is significant given the daunting problem of difficult-to-treat neuropathic SCI pain.

Analysis of the human locus coeruleus in perinatal and infant sudden unexplained deaths. Possible role of the cigarette smoking in the development of this nucleus

We investigated the immunohistochemical expression of the tyrosine hydroxylase (TH) enzyme and the morphometric parameters of the human locus coeruleus (LC) in the brainstems of 32 subjects aged from 17 gestational weeks to 12 postnatal month, died of unknown (sudden unexplained perinatal and infant deaths) and known causes. The goals of this study were: (1) to obtain basic information about the structure and physiology of the LC during the first phases of human nervous system development; (2) to evaluate whether there is altered expression of TH and/or structural alterations of the LC in cases of sudden perinatal and infant death; and (3) to verify if morphological and/or physiological abnormalities of the LC could be related to maternal cigarette smoking. Morphometric analysis showed homogeneous data in cases of sudden perinatal and infant death and in age-matched controls who had died of known aetiology. However, immunohistochemistry demonstrated in a wide subset of sudden and unexplained deaths a negativity or low positivity of TH. High distribution of TH protein were instead detectable in the LC neurons of foetuses aged 17-18 gestational weeks who had died of known causes. Therefore, we postulate the functional importance of the LC in the early phases of central nervous system development. Besides, the observation of a significant correlation between sudden unexplained death, negativity of TH staining and maternal smoking, prompted us to suppose a close relation between smoking in utero and a decrease of the noradrenergic activity of the LC, leading to sudden death in the last part of pregnancy and in the first year of life.

Useful cell lines derived from the adrenal medulla

Five approaches for the preparation of adrenal chromaffin cell lines have been developed. Initially, continuous chromaffin lines were derived from spontaneous pheochromocytoma tumors of the medulla, either from murine or human sources, such as the rat PC12 cell line and the human KNA and KAT45 cell lines. Over the last few decades, more sophisticated molecular methods have allowed for induced tumorigenesis and targeted oncogenesis in vivo, where isolation of specific populations of mouse cell lines of endocrine origin have resulted in model cells to examine a variety of regulatory pathways in the chromaffin phenotype. As well, conditional immortalization with retroviral infection of chromaffin precursors has provided homogeneous and expandable chromaffin cells for transplant studies in animal models of pain. This same strategy of immortalization with conditionally expressed oncogenes has been expanded recently to create the first disimmortalizable chromaffin cells, with an excisable oncogenic cassette, as might be envisioned for the creation of human chromaffin cell lines. Eventually, as we increase our understanding of regulating the phenotypic fate of chromaffin cells in vitro, stem or progenitor adrenal medullary cell lines will be derived as an alternative source for expansion and clinical use.

Numerous GABAergic afferents to locus ceruleus in the pericerulear dendritic zone: possible interneuronal pool

Most nuclei in the CNS are composed of principal neurons that project to other areas and interneurons that serve to integrate information among afferents. The noradrenergic brain nucleus locus ceruleus (LC) has appeared to be an exception to this general rule, because the LC is composed almost entirely of noradrenergic principal neurons. Here, we report that numerous small neurons in the peri-LC region become retrogradely labeled after focal injections of wheat germ agglutinin-apo (inactivated) horseradish peroxidase conjugated to colloidal gold, or pseudorabies virus (PRV), into the nuclear core of the rat LC. A substantial number of these neurons were routinely found within the dendritic field of the LC, in the area surrounding the compact cell-dense region classically defined as LC. Double labeling revealed that a large percentage of these cells stained for GABA. Ultrastructural analyses revealed axodendritic and axosomatic contacts between PRV-labeled afferents and LC neurons labeled with tyrosine hydroxylase immunohistochemistry. In addition, PRV-labeled neurons or axons were immunopositive for GABA in ultrastructural localizations. Analysis of the synaptology of immunopositive profiles demonstrated that these LC afferents in the peri-LC region receive several non-LC synaptic inputs. These results indicate that a population of small GABAergic neurons in the peri-LC dendritic zone may provide interneuronal integration for LC noradrenergic neurons.

Generation of embryonic stem cells and transgenic mice expressing green fluorescence protein in midbrain dopaminergic neurons

We have generated embryonic stem (ES) cells and transgenic mice with green fluorescent protein (GFP) inserted into the Pitx3 locus via homologous recombination. In the central nervous system, Pitx3-directed GFP was visualized in dopaminergic (DA) neurons in the substantia nigra and ventral tegmental area. Live primary DA neurons can be isolated by fluorescence-activated cell sorting from these transgenic mouse embryos. In culture, Pitx3-GFP is coexpressed in a proportion of ES-derived DA neurons. Furthermore, ES cell-derived Pitx3-GFP expressing DA neurons responded to neurotrophic factors and were sensitive to DA-specific neurotoxin N-4-methyl-1, 2, 3, 6-tetrahydropyridine. We anticipate that the Pitx3-GFP ES cells could be used as a powerful model system for functional identification of molecules governing mDA neuron differentiation and for preclinical research including pharmaceutical drug screening and transplantation. The Pitx3 knock-in mice, on the other hand, could be used for purifying primary neurons for molecular studies associated with the midbrain-specific DA phenotype at a level not previously feasible. These mice would also provide a useful tool to study DA fate determination from embryo- or adult-derived neural stem cells.

Cyclin-dependent kinase 11p110 and casein kinase 2 (CK2) inhibit the interaction between tyrosine hydroxylase and 14-3-3

Tyrosine hydroxylase (TH) is regulated by the reversible phosphorylation of serines 8, 19, 31 and 40. Upon initiation of this study, serine 19 was unique due to its requirement of 14-3-3 binding after phosphorylation for optimal enzyme activity, although it has been more recently demonstrated that phosphorylated serine 40 also binds 14-3-3. To identify proteins that interact with TH following phosphorylation of serine 19, this amino acid was mutated to alanine and THS19A was used as bait in a yeast two-hybrid system. From this, mouse-derived cyclin-dependent kinase 11 (CDK11)p110 was identified as an interacting partner with THS19A. The interaction was confirmed using human CDK11p110 cDNA in a mammalian system. Previous research has demonstrated that casein kinase 2 (CK2) interacts with CDK11p110, and both were observed to phosphorylate TH in vitro. In addition, CDK11p110 overexpression was observed to inhibit the interaction between TH and 14-3-3. A mechanism contributing to disruption of the interaction between TH and 14-3-3 may be due to CK2 phosphorylation of specific 14-3-3 isoforms, i.e. 14-3-3 tau. Collectively, these results imply that CDK11p110 and CK2 negatively regulate TH catecholamine biosynthetic activity since phosphoserine 19 of TH requires 14-3-3 binding for optimal enzyme activity and a decreased rate of dephosphorylation.

Ultrastructural interactions between terminals expressing the norepinephrine transporter and dopamine neurons in the rat and monkey ventral tegmental area

The norepinephrine (NE) system is implicated in the etiology and treatment of depression and drugs blocking the NE transporter (NET) are effective antidepressants. It is possible that dopamine (DA) also plays a role in depression and the action of antidepressant drugs, although the mechanisms whereby NE and DA interact have not been fully elaborated. We examined whether NE neurons might alter DA transmission via synaptic projections to cells in the ventral tegmental area (VTA) by using electron microscopic dual labeling immunocytochemistry in the rat and monkey. NET was used as a marker for NE axons, whereas the catecholamine synthetic enzyme, tyrosine hydroxylase (TH), served as a label for DA neurons. We observed three types of spatial relationships between these profiles that were similar in type but varied in frequency between rodent and primate. The most common arrangement involved nonsynaptic appositions between NET-immunoreactive (-ir) axons and TH-ir dendrites. Such relationships may facilitate extrasynaptic actions of NE on DA cell activity. The other commonly observed arrangement involved adjacent profiles that were otherwise separated by glia. These relationships may represent regions where NE is prevented from reaching DA cells. In only a few cases were synapses observed between NET-ir axons and TH-ir dendrites. This finding suggests that NE can synaptically regulate DA neurons, although functional interactions are more likely to involve extrasynaptic mechanisms. Finally, in the VTA of both species the majority of NET-ir axons exhibited no detectable TH immunoreactivity. The latter finding agrees with observations in cortical regions and represents the first report of its type in a subcortical structure.

Anatomy of the pelvic plexus and innervation of the prostate gland

We have examined the anatomy of the pelvic (inferior hypogastric) plexus in six male cadavers, paying particular attention to gross anatomical landmarks that might aid in locating it and have used immunohistochemistry to study the small branches of the plexus that supply the prostate gland. The pelvic plexus was found two finger breadths lateral to the third anterior sacral foramina, lying deep to a line drawn from third sacral vertebra, the conventional level of the recto-sigmoid junction, and the palpable posterior superior surface of the pubic symphysis. Immunohistochemical staining showed small nerve branches from the pelvic plexus entering the prostate gland and the presence of ganglia within the prostate gland that contained both tyrosine hydroxylase positive and negative neuronal cell bodies. This information may be useful in nerve-sparing surgical procedures and in discussions of the functional implications of perturbations of prostate innervation.

Ultrastructural localization of the norepinephrine transporter in superficial and deep layers of the rat prelimbic prefrontal cortex and its spatial relationship to probable dopamine terminals

The prefrontal cortex (PFC) is a likely site of action for the therapeutic efficacy of antidepressants that inhibit norepinephrine (NE) reuptake. Moreover, drugs that block the NE transporter (NET) increase extracellular levels of both NE and dopamine (DA), an interaction that may contribute to their therapeutic properties. To examine the subcellular localization of NET and to investigate the spatial relationships between presumed NE and DA axons within the rat prelimbic PFC, we combined immunogold-silver localization of NET with immunoperoxidase staining for the catecholamine synthetic enzyme tyrosine hydroxylase (TH). An additional aim was to quantify the proportion of profiles dually labeled for NET and TH to test the common observation that TH immunolabeling is relatively selective for DA axons. NET-immunoreactive (NET-ir) axonal profiles were typically unmyelinated and occasionally were observed to form symmetric axodendritic synapses. The majority of immunogold NET labeling was unexpectedly observed in the cytoplasm rather than on the plasma membrane. Furthermore, in tissue dually labeled for both NET and TH, only 8-10% of profiles contained both markers. Unlike observations for singly labeled profiles, gold-silver particles for NET in dually labeled axons were localized primarily to the plasmalemma. A systematic survey of terminals labeled only for TH revealed that they were typically separated by at least 1.2 mum from NET-ir varicosities, and the two profile types were not seen to contact common targets. These results suggest that, in the rat PFC, NE axons (1) contain predominantly cytoplasmic NET, (2) infrequently contain TH immunolabeling, and (3) may interact with probable DA afferents by means of extrasynaptic mechanisms.

Colocalization of gamma-aminobutyric acid-like immunoreactivity and catecholamines in the feeding network of Aplysia californica

Functional consequences of neurotransmitter coexistence and cotransmission can be readily studied in certain experimentally favorable invertebrate motor systems. In this study, whole-mount histochemical methods were used to identify neurons in which gamma-aminobutyric acid (GABA)-like immunoreactivity (GABAli) was colocalized with catecholamine histofluorescence (CAh; FaGlu method) and tyrosine hydroxylase (TH)-like immunoreactivity (THli) in the feeding motor circuitry (buccal and cerebral ganglia) of the marine mollusc Aplysia californica. In agreement with previous reports, five neurons in the buccal ganglia were found to exhibit CAh. These included the paired B20 buccal-cerebral interneurons (BCIs), the paired B65 buccal interneurons, and an unpaired cell with projections to both cerebral-buccal connectives (CBCs). Experiments in which the FaGlu method was combined with the immunohistochemical detection of GABA revealed double labeling of all five of these neurons. An antibody generated against TH, the rate-limiting enzyme in the biosynthesis of catecholamines, was used to obtain an independent determination of GABA-CA colocalization. Biocytin backfills of the CBC performed in conjunction with TH immunohistochemistry revealed labeling of the rostral B20 cell pair and the unpaired CBI near the caudal surface of the right hemiganglion. THli was also present in a prominent bilateral pair of caudal neurons that were not stained with CBC backfills. On the basis of their position, size, shape, and lack of CBC projections, the lateral THli neurons were identified as B65. Double-labeling immunohistochemical experiments revealed GABAli in all five buccal THli neurons. Finally, GABAli was observed in individual B20 and B65 neurons that were identified using electrophysiological criteria and injected with a marker (neurobiotin). Similar methods were used to demonstrate that a previously identified catecholaminergic cerebral-buccal interneuron (CBI) designated CBI-1 contained THli but did not contain GABAli. Although numerous THli and GABAli neurons and fibers were present in the cerebral and buccal ganglia, additional instances of their colocalization were not observed. These findings indicate that GABA and a catecholamine (probably dopamine) are colocalized in a limited number of interneurons within the central pattern generator circuits that control feeding-related behaviors in Aplysia.

Administration of FGF-2 to embryonic mouse brain induces hydrocephalic brain morphology and aberrant differentiation of neurons in the postnatal cerebral cortex

Fibroblast growth factor-2 (FGF-2) was injected into mouse cerebral ventricles at embryonic day (E) 14 in utero and its effects on developing brain morphology and expression of various cell- or differentiation-associated protein markers in the cerebral cortex were examined. High doses of FGF-2 (200 or 300 ng) caused encephalic alternations such as deformation of the calvarium, enlargement of the ventricular spaces, and thinning of the cerebral cortex. There was no gross abnormality in the alignment of the cerebral neuronal layers, however, both cell number and cell density of the upper layers (II/III) and the lower layers (IV-VI) of the cerebral cortex were increased. Brain-derived neurotrophic factor (BDNF), tyrosine hydroxylase, nestin, and microtubule-associated protein 2 were aberrantly or ectopically expressed in the deep areas of the cerebral cortex. A substantial number of these cells coexpressed these antigens. These observations demonstrate that a subpopulation of neurons in the cortical deep layer abnormally differentiated or partly sustained their immature state following a single administration of FGF-2 at E14. Developmental analysis of localization of BDNF-positive cells suggested that the abnormality started around P5. Furthermore, cell migration was not affected by FGF-2 administration. FGF-2 seems to play predominant roles in the proliferation of neuronal precursors and in neuronal differentiation in the developing mouse cerebral cortex even at relatively late stages of brain neurogenesis.

Immunohistochemical studies of the localization of neurons containing the enzyme that synthesizes dopamine, GABA, or gamma-hydroxybutyrate in the rat substantia nigra and striatum

gamma-Hydroxybutyrate (GHB) is an endogenous metabolite of gamma-aminobutyric acid (GABA), which is synthesized in the neuronal compartment of the central nervous system. This substance possesses several properties that support its role as a neurotransmitter/neuromodulator in brain. In particular, it is synthesized by a specific pathway that transforms GABA into succinic semialdehyde via GABA-T activity; then succinic semialdehyde is converted into GHB by a specific succinic semialdehyde reductase (SSR). The last enzyme is considered as a marker for neurons that synthesize GHB. This compound binds in brain to receptors whose distribution, ontogenesis, kinetics, and pharmacology are specific. Endogenous GHB, but also GHB exogenously administered to rats, participate in the regulation of dopaminergic activity of the nigrostriatal pathway. To investigate the distribution of GHB neurons in this pathway and the anatomic relationships between dopaminergic and GHB neurons, immunocytochemical identification of dopamine, GABA, and GHB neurons was carried out in the substantia nigra and striatum of the rat. The following markers for these neurons were used: anti-tyrosine hydroxylase (TH) antibodies for dopamine neurons, anti-glutamate decarboxylase (GAD) antibodies for GABA neurons, and anti-succinic semialdehyde reductase (SSR) antibodies for GHB neurons. GABA neurons were studied because GAD and SSR co-exist frequently in the same neuron, and GABA alone also exerts its own regulatory effects on dopaminergic neurons. This study reveals the co-existence of GAD/SSR and GAD/SSR/TH in numerous neurons of the substantia nigra. However, some neurons appear to be only GAD or SSR positive. In the striatum, TH-positive terminals surround many GHB neurons. GAD innervation is abundant in close contact with unlabeled neurons in the caudate-putamen, whereas distinct SSR-positive punctuates are also present. The existence of SSR-reactive synapses and neurons was confirmed in the striatum at the electron microscopic level. On the basis of these results, a clear anatomo-functional relationship between GHB and dopamine networks cannot be defined; however, we propose the modulation by GHB of striatal intrinsic neurons that could then interfere with the presynaptic control of dopaminergic activity.

Initial characterization of the transplant of immortalized chromaffin cells for the attenuation of chronic neuropathic pain

Cultures of embryonic day 17 (E17) rat adrenal and neonatal bovine adrenal cells were conditionally immortalized with the temperature-sensitive allele of SV40 large T antigen (tsTag) and chromaffin cell lines established. Indicative of the adrenal chromaffin phenotype, these cells expressed immunoreactivity (ir) for tyrosine hydroxylase (TH), the first enzyme in the synthetic pathway for catecholamines. At permissive temperature in vitro (33 degrees C), these chromaffin cells are proliferative, have a typical rounded chromaffin-like morphology, and contain detectable TH-ir. At nonpermissive temperature in vitro (39 degrees C), these cells stop proliferating and express increased TH-ir. When these immortalized chromaffin cells were transplanted in the lumbar subarachnoid space of the spinal cord I week after a unilateral chronic constriction injury (CCI) of the rat sciatic nerve, they survived longer than 7 weeks on the pia mater around the spinal cord and continued to express TH-ir. Conversely, grafted chromaffin cells lost Tag-ir after transplant and Tag-ir was undetectible in the grafts after 7 weeks in the subarachnoid space. At no time did the grafts form tumors after transplant into the host animals. These grafted chromaffin cells also expressed immunoreactivities for the other catecholamine-synthesizing enzymes 7 weeks after grafting, including: dopamine-beta-hydroxylase (DbetaH) and phenylethanolamine-N-methyltransferase (PNMT). The grafted cells also expressed detectable immunoreactivities for the opioid met-enkephalin (ENK), the peptide galanin (GAL), and the neurotransmitters y-aminobutyric acid (GABA) and serotonin (5-HT). Furthermore, after transplantation, tactile and cold allodynia and tactile and thermal hyperalgesia induced by CCI were significantly reduced during a 2-8-week period, related to the chromaffin cell transplants. The maximal antinociceptive effect occurred 1-3 weeks after grafting. Control adrenal fibroblasts, similarly immortalized and similarly transplanted after CCI, did not express any of the chromaffin antigenic markers, and fibroblast grafts had no effect on the allodynia and hyperalgesia induced by CCI. These data suggest that embryonic and neonatal chromaffin cells can be conditionally immortalized and will continue to express the phenotype of primary chromaffin cells in vitro and in vivo; grafted cells will ameliorate neuropathic pain after nerve injury and can be used as a homogeneous source to examine the mechanisms by which chromaffin transplants reverse chronic pain. The use of such chromaffin cell lines that are able to deliver antinociceptive molecules in models of chronic pain after nerve and spinal cord injury (SCI) offers a novel approach to pain management.

Effects of prenatal exposure to diethylstilbestrol on the sympathetic nervous system in the rat ovary

Transplacental exposure to diethylstilbestrol (DES) causes morphological and functional changes including the disruption of follicular maturation in murine ovaries. Since the function of ovarian sympathetic nerves is thought to be related to the follicular maturation, we examined changes in the distribution pattern of the sympathetic nerves between prenatally DES-exposed rat ovaries and normal controls using immunohistochemistry of tyrosine hydroxylase (TH). In the DES-exposed ovaries, the TH-positive nerve innervation was poor and the innervation density was reduced to about half as compared to that in the controls. Simultaneously, follicular maturation was disrupted in the DES-exposed ovaries. These findings suggest that the prenatal DES exposure inhibited the development of ovarian sympathetic nervous system, which might be closely associated with the disruption of follicular maturation.

Direct catecholaminergic-cholinergic interactions in the basal forebrain. I. Dopamine-beta-hydroxylase- and tyrosine hydroxylase input to cholinergic neurons

Immunocytochemical double-labeling techniques were used at the light and electron microscopic levels to investigate whether dopamine-beta-hydroxylase and tyrosine hydroxylase-containing axons contact basal forebrain cholinergic neurons. Dopamine-beta-hydroxylase- and tyrosine hydroxylase-positive fibers and terminals were found in close proximity to cholinergic neurons throughout extensive basal forebrain areas, including the vertical and horizontal limb of the diagonal band nuclei, the sublenticular substantia innominata, bed nucleus of the stria terminalis, ventral pallidum, and ventrolateral globus pallidus. Cholinergic cells in some aspects of the globus pallidus appeared to be contacted by tyrosine hydroxylase-positive but not dopamine-beta-hydroxylase-positive fibers, suggesting dopaminergic input to cholinergic neurons in these regions. Direct evidence for the termination of dopamine-beta-hydroxylase and tyrosine hydroxylase-positive fibers on cholinergic neurons was obtained in electron microscopic double-immunolabeling studies. Using high magnification light microscopic screening, both qualitative and quantitative differences were noted in the catecholaminergic innervation of forebrain cholinergic neurons. For example, while many cholinergic neurons were in close proximity to single dopamine-beta-hydroxylase-positive varicosities, others, particularly those located in the substantia innominatabed nucleus of the stria terminalis continuum, were apparently contacted by labeled fibers in repetitive fashion. The findings of the present study, together with our preliminary biochemical experiments (Zaborszky et al. [1993] Prog. Brain Res. 98:31-49) suggest that catecholaminergic afferents can differentially modulate forebrain cholinergic neurons. Such interactions may be important in learning and memory processes, and their perturbations may contribute to the cognitive decline seen in aging and in disorders such as Alzheimer's and Parkinson's diseases.

Light and electron microscopic immunohistochemical study of dopaminergic terminals in the striatal portion of the pigeon basal ganglia using antisera against tyrosine hydroxylase and dopamine

A dopaminergic projection from the midbrain to the striatal portion of the basal ganglia is present in reptiles, birds, and mammals. Although the ultrastructure of these fibers and terminals within the striatum has been studied extensively in mammals, little information is available on the ultrastructure of this projection in nonmammals. In the present study, we used immunohistochemical labeling with antibodies against tyrosine hydroxylase (TH) or dopamine (DA) to study the dopaminergic input to the striatal portion of the basal ganglia in pigeons (i.e., lobus parolfactorius and paleostriatum augmentatum). At the light microscopic level, the anti-TH and anti-DA revealed a similar abundance and distribution of numerous labeled fine fibers and varicosities within the striatum. In contrast, the use of an antidopamine beta-hydroxylase antiserum (which labels only adrenergic and noradrenergic terminals) labeled very few striatal fibers, which were restricted to visceral striatum. These results demonstrate that anti-TH mainly labels dopaminergic terminals in the striatum. At the electron microscopic level, the anti-TH and anti-DA antisera labeled numerous axon terminals within the striatum (15-20% of all striatal terminals). These terminals tended to be small (with an average length of 0.6 microns) and flattened, and their vesicles tended to be small (35-60 nm in diameter) and pleomorphic. About 50% of the terminals were observed to make synaptic contacts in the planes of section examined, and nearly all of these synaptic contacts were symmetric. Both TH+ and DA+ terminals typically contacted dendritic shafts or the necks of dendritic spines, but a few contacted perikarya. No clear differences were observed between TH+ and DA+ terminals within medial striatum (whose neurons project to the nigra in birds) or between TH+ and DA+ terminals within lateral striatum (whose neurons project to the pallidum in birds). In addition, no differences were observed between medial and lateral striata in either TH+ or DA+ terminals. Thus, there is no evident difference in pigeons between striatonigral and striatopallidal neurons in their dopaminergic innervation. Our results also indicate that the abundance, ultrastructural characteristics, and postsynaptic targets of the midbrain dopaminergic input to the pigeon striatum are highly similar to those in mammals. This anatomical similarity is consistent with the pharmacologically demonstrable similarity in the role of the dopaminergic input to the striatum in birds and mammals.

Induction of midbrain dopaminergic neurons by Sonic hedgehog

Midbrain dopaminergic neurons, whose loss in adults results in Parkinson's disease, can be specified during embryonic development by a contact-dependent signal from floor plate cells. Here we show that the amino-terminal product of Sonic hedgehog autoproteolysis (SHH-N), an inductive signal expressed by floor plate cells, can induce dopaminergic neurons in vitro. We show further that manipulations to increase the activity of cyclic AMP-dependent protein kinase A, which is known to antagonize hedgehog signaling, can block dopaminergic neuron induction by floor plate cells. Our results and those of other studies indicate that SHH-N can function in a dose-dependent manner to induce different cell types within the neural tube. Our results also provide the basis for a potential cell transplantation therapy for Parkinson's disease.

Control of neuronal diversity by the floor plate: contact-mediated induction of midbrain dopaminergic neurons

The notochord and floor plate contribute to patterning the ventral neural tube in part by expressing a diffusible factor that induces motoneurons. To determine the mechanisms that direct the development of other classes of ventral neurons, we studied the development of dopaminergic neurons that reside near motoneurons in the ventral midbrain. We provide evidence that dopaminergic neurons develop in the vicinity of the floor plate and that they can be specified by the floor plate in vitro and in vivo. Unlike motoneurons, efficient induction of dopaminergic neurons requires contact with floor plate cells. These results suggest that neuronal diversification along the dorsal-ventral axis may be achieved partly through the concerted action of diffusible and contact-dependent signals from a single organizing center, the floor plate.

Ultrastructural study of CCK and tyrosine hydroxylase immunoreactivity in the rat nucleus accumbens

The cholecystokinin (CCK)- and tyrosine hydroxylase (TH)-like immunoreactive (LI) axons and boutons were studied in the caudal and medial parts of the rat nucleus accumbens (NAC), using the indirect immunoperoxidase technique, at the electron microscopic level. Both CCK- and TH-LI boutons contained clear synaptic vesicles and large granular vesicles of similar size, but the CCK-LI boutons contained more large granular vesicles than TH-LI boutons. The CCK-LI and TH-LI boutons were heterogeneous. This finding might be related to the various immunoreactive neuronal types innervating the caudomedial NAC. However, the CCK-LI boutons (containing mostly small, round, clear synaptic vesicles) formed mainly asymmetrical synaptic contacts with dendritic spines whereas the TH-LI boutons (containing medium-sized as well as small, round, clear synaptic vesicles) formed mostly symmetrical synaptic contacts with dendritic shafts.

Frequency analysis of catecholamine axonal morphology in human brain. I. Effects of postmortem delay interval

The diverse morphologies of catecholamine axons in the human brain were examined by using tyrosine hydroxylase immunocytochemistry. Human brain tissue was obtained by either rapid autopsy (mean postmortem delay < 1 h) or routine autopsy (mean postmortem delay 5 h). Tissue blocks from the superior frontal cortex (Brodmann area 9), the hippocampal gyrus and the calcarine cortex (Brodmann area 17) were processed for tyrosine hydroxylase immunoreactivity. First, a quantitative method was developed to reliably identify differing morphologies of catecholamine axons in human brain tissue. A total of 625 tyrosine hydroxylase immunoreactive axons were randomly sampled from coded sections and classified into one of six distinct morphological categories. These categories were based upon axonal morphologies which were readily distinguished by trained observers, and moreover, further investigations demonstrated that entire tissue sections could be reliably re-sampled at intervals of up to six months. Second, regional variations in axonal distribution and the effects of increasing postmortem delay in tissue processing on the categories of tyrosine hydroxylase immunoreactive axon morphologies were examined. Postmortem delays of up to 6.5 hours were found to decrease the frequency of fine axons with varicosities (axon type 2) and increase thick-caliber straight axons (axon type 5) in all regions examined. The frequency of other morphological axon types did not change as a function of postmortem delay. In summary, the use of quantitative neuroanatomical measures of the catecholaminergic system in human brain tissue was found to be reliable and valid. It was furthermore demonstrated that postmortem delays affect selected morphological types of catecholamine axons.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular quantification of tyrosine hydroxylase in the rat brain by immunoautoradiography

We developed a rapid and sensitive radioimmunohistochemical method for the quantification of tyrosine hydroxylase (TH) at both the anatomical and cellular level. Coronal tissue sections from fresh-frozen rat brains were incubated in the presence of a TH monoclonal antibody. The reaction was revealed with a 35S-labeled secondary antibody. TH content was quantified in catecholaminergic brain areas by measuring optical density on autoradiographic films or silver grain density on autoradiographic emulsion-coated sections. Regional TH concentrations determined in the locus ceruleus (LC), substantia nigra pars compacta (SNC), and ventral tegmental area (VTA) were significantly increased by 45% after reserpine treatment in the LC but unchanged in the SNC and VTA. Microscopic examination of TH radioimmunolabeling showed a heavy accumulation of silver grains over catecholaminergic cell bodies. In the LC, grain density per cell was heterogeneous and higher in the ventral than in the dorsal part of the structure. After reserpine treatment, TH levels were significantly increased (57%) in the neurons of the LC but not in those of the SNC or VTA. The data support the validity of this radioimmunohistochemical method as a tool for quantifying TH protein at the cellular level and they confirm that TH protein content is differentially regulated in noradrenergic and dopaminergic neurons in response to reserpine.

Comparative single and double immunolabelling with antisera against catecholamine biosynthetic enzymes: criteria for the identification of dopaminergic, noradrenergic and adrenergic structures in selected rat brain areas

Immunodetection of catecholamine biosynthetic enzymes is frequently used for the visualization of central nervous catecholaminergic systems. Because of the method's limited specificity for the different catecholamines, interpretation of the results often presents difficulties. To determine criteria for the identification of dopaminergic, noradrenergic, and adrenergic afferents to the rat amygdaloid complex, comparative immunolabelling for tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine-N-methyl-transferase (PNMT) was carried out using single- and double-labelling for fluorescence, light- and electron microscopy. The observations were complemented by findings in brainstem and hypothalamic areas. The results indicated that TH-labelling detected preferentially dopaminergic afferents in the lateral central and intercalated amygdaloid nuclei. DBH-labelling detected noradrenergic axons in nuclei lacking PNMT-immunoreactive fibres, and PNMT was a marker for adrenergic axons in the entire complex. For nuclei with combined dense dopaminergic, noradrenergic and/or adrenergic innervation, morphological and immunolabelling characteristics were described which, to a certain extent, enabled identification of the different afferents in anti-TH or anti-DBH-preparations. Using a monoclonal TH-antiserum, noradrenergic and adrenergic axons displayed weaker immunoreactivity than dopaminergic ones, and possessed characteristic morphological features. TH-immunoreactivity in noradrenergic axons differed depending on their origin, and showed intra-axonal compartmentalization. The present study provides a basis for the use of the detection of biosynthetic enzymes in future investigations into the ultrastructure and connectivity of the catecholaminergic amygdala innervation.

The postnatal development of tyrosine hydroxylase immunoreactive nerves in rat atrium, studied with immunofluorescence and confocal laser scanning microscopy

The developmental pattern and distribution of tyrosine hydroxylase (TH) immunoreactive nerves in the rat heart has been studied by indirect immunofluorescence. Anti-TH and monoclonal antibodies against the synaptic vesicle antigen SV2 were applied to whole-mount stretch preparations of the right atria from hearts of newborn to 40-day-old animals. Immunofluorescence was studied with confocal laser scanning microscopy (CFLM). Nerve fibres with TH-like immunoreactivity (TH-LI) were present throughout the atria already at birth, with the highest density around the sino-atrial (SA) node, colocalized in most nerve terminal arborizations with the synaptic vesicle marker SV2. Also, TH-positive ganglion cells were present around the openings of the caval veins. In comparison with TH-positive fibres, SV2-positive nerve terminal fibres were more delicate, and the number of fibres larger in all areas studied. In axon bundles, TH-LI was very prominent, while the SV2-LI was weak. A gradual increase in the density of innervation was observed up to the age of 40 days. The density of innervation decreased from the epicardium to the endocardium, confirmed in cross-sections of the cardiac wall. The relative density of TH-positive nerve terminals was estimated in the CFLM from the area around the SA node. At birth, about 600 white (strongly fluorescent) pixels were registered per scanned field, with the pixel number increasing gradually up to 20,000 pixels per frame in 18- and 40-day-old animals. The results show that TH-positive, possibly adrenergic, nerve fibres are present at birth, and that the pattern is qualitatively similar to that observed in adults, with the expression of synaptic vesicle antigen being present some days before the development of noradrenaline neuroeffector maturation, as shown in a number of physiological and pharmacological studies.

A novel population of tyrosine hydroxylase immunoreactive neurones in the basal forebrain of the common marmoset (Callithrix jacchus)

We have observed in the basal forebrain of the common marmoset a group of neurones which display tyrosine hydroxylase immunoreactivity (THir) with three different polyclonal antibodies and one monoclonal antibody, and which express TH mRNA as shown by in situ hybridization histochemistry. The population of cells is composed of large multipolar neurones and is located predominantly in the substantia innominata and at the ventral, medial and lateral margins of the external segment of the globus pallidus. The cell morphology and the distribution of THir cells corresponds closely to the caudal portion of the nucleus basalis of Meynert. Adjacent sections demonstrate both THir and choline acetyltransferase immunoreactivity in the cells in this group, as well as strong acetylcholinesterase activity but not dopamine immunoreactivity. These observations indicate that many cholinergic neurones in the posterior nucleus basalis of Meynert of the marmoset contain tyrosine hydroxylase, and suggest that both acetylcholine and catecholamine may be synthesised as co-localised neurotransmitters within the same magnocellular neurones. We observe no THir cells in similar areas of the basal forebrain of either rhesus or talapoin monkeys.

Resistance of hippocampal CA-1 noradrenergic fibers to five minutes of transient cerebral ischemia in the gerbil

We examined changes in the tyrosine hydroxylase (TH)-immunoreactive fibers following 5 min of cerebral ischemia in gerbils using an immunohistochemical method 1, 3 and 30 days after ischemia. Almost all CA-1 pyramidal neurons were lost 3 days after ischemia, whereas noradrenergic fibers were maintained 30 days after ischemia. The present study demonstrated that TH-immunoreactive fibers and cells were resistant to transient ischemia, and that there was no sprouting or hyperactivity in noradrenergic systems after ischemia.

The distribution of neurotransmitters and neurotransmitter-related enzymes in the dorsomedial telencephalon of the pigeon (Columba livia)

Immunoreactivity to four neurotransmitters/transmitter-related enzymes was found in the dorsomedial telencephalon (hippocampal region) of the pigeon. Putative afferent fibers containing choline acetyltransferase-like, serotonin-like, and tyrosine hydroxylase-like immunoreactivity were seen in a fiber tract passing through the septo-hippocampal junction and along the medial wall of the hippocampal region. The most intensive labeling of neuropil and terminals of all four substances was found in the dorsomedial area of the hippocampal region. Glutamic acid decarboxylase-like immunoreactivity was seen in sparsely scattered cells throughout the region. These results are discussed in relation to hypotheses about the boundaries and subdivisions of the hippocampal region of the pigeon.

Clinical and biochemical aspects of depressive disorders: II. Transmitter/receptor theories

The present document is the second of three parts in a review that focuses on recent data from clinical and animal research concerning the biochemical bases of depressive disorders, diagnosis, and treatment. Various receptor/transmitter theories of depressive disorders are discussed in this section. Specifically, data supporting noradrenergic, serotonergic, cholinergic, dopaminergic, GABAergic, and peptidergic theories, as well as interactions between noradrenergic and serotonergic, or cholinergic and catecholaminergic systems are presented. Problems with the data and future directions for research are also discussed. A previous publication, Part I of this review, dealt with the classification of depressive disorders and research techniques for studying the biochemical mechanisms of these disorders. A future publication, Part III of this review, discusses treatments for depression and some of the controversies in this field.

Co-localization of tyrosine hydroxylase and glutamate decarboxylase in a subpopulation of single nigrotectal projection neurons

The neurotransmitter phenotype(s) of nigral neurons innervating the superior colliculus (SC) in the rat was examined using a combination of immunohistochemical techniques and fluorescent retrograde tracing. After double-immunofluorescent histochemistry for tyrosine hydroxylase (TH) and glutamate decarboxylase (GAD), single cells in the rostral ventrolateral portion of the substantia nigra pars reticulata (SNr) and to a lesser extent the substantia nigra pars lateralis (SN1) displayed immunoreactivity to both antigens. Furthermore, following True blue (TB) injections into the SC and incubation for both TH and GAD immunoreactivity, a considerable number of cells in the SNr retrogradely labeled with TB (approximately 10%) were also immunopositive for both synthetic enzymes. The present study provides evidence for the coexistence of TH and GAD and thus, the coexistence of dopamine and GABA in a subpopulation of single nigrotectal projection cells.

Systematic presence of GABA-immunoreactivity in the tubero-infundibular and tubero-hypophyseal dopaminergic axonal systems: an ultrastructural immunogold study on several mammals

Immunoreactivities for tyrosine hydroxylase (TH), gamma-aminobutyric acid (GABA) and, in some cases, glutamic acid decarboxylase (GAD) were detected by light and electron microscopy in axons projecting into the median eminence and pituitary gland of various mammals (rats, mice, guinea pigs, cats, rabbits and hares). Light microscope immunoperoxidase reactions were performed on adjacent semithin sections of plastic-embedded samples. In the median eminence external zone, the distributions of the TH- and GAD- or GABA-immunoreactive endings were very similar in the anterior and lateral areas, while medially the GABA-labelled endings predominated. Comparable distribution patterns were found in the various species examined. In the pituitary gland, the distributions of GABA- and TH-immunoreactivities were superimposable in the intermediate lobes of all species examined, except in the rabbit and hare in which both types of innervation were lacking. For electron microscopy, the immunogold procedure was applied to sections of lowicryl-embedded samples; simultaneous detection of GABA- and TH-immunoreactivities was enabled by recto-verso double labelling with gold particles of distinct diameters. In the median eminence, GABA-immunoreactivity occurred systematically in the TH-positive endings, while distinct GABA-positive/TH-negative axons were also detected. In the intermediate lobe, the colocalization of TH- and GABA-immunoreactivities was a constant feature of the axons innervating the melanotrophic cells in all the species examined, except in the Leporidae. The functional significance of this colocalization remains to be determined.

Organization of tyrosine hydroxylase-immunoreactive neurons in the di- and mesencephalon of the American bullfrog (Rana catesbeiana) during metamorphosis

We examined the immunocytochemical distribution of tyrosine hydroxylase, the rate-limiting enzyme in catecholamine synthesis, in the di- and mesencephalon of developing bullfrog tadpoles. Special attention was given to catecholaminergic innervation of the median eminence and pituitary. In premetamorphic tadpoles, tyrosine hydroxylase-immunoreactive neurons were visualized in the suprachiasmatic and infundibular hypothalamus, the ventral thalamus, and midbrain tegmentum by Taylor-Kollros stage V. The number of labeled neurons in all these areas increased as metamorphosis progressed. By mid-prometamorphosis, labeled neurons appeared in the preoptic recess organ as well as in the posterior thalamic nucleus. The majority of cells in the preoptic recess organ, as well as occasional neurons in the suprachiasmatic nucleus, exhibited labeled processes which projected through the ependymal lining of the preoptic recess to contact cerebrospinal fluid. The modified CSF-contacting neurons of the nucleus of the periventricular organ were devoid of specific staining. By late prometamorphosis, labeled fibers from the suprachiasmatic nucleus were observed projecting caudally to enter the hypothalamo-hypophysial-tract en route to innervating the median eminence and pituitary. Labeled fibers arising from the dorsal infundibular nucleus projected ventrolaterally to contribute to catecholaminergic innervation of the median eminence and pituitary. Immunoperoxidase staining of tyrosine hydroxylase-immunoreactive fibers and terminal arborizations in the median eminence were restricted to non-ependymal layers, while labeled fibers in the pituitary were observed in the pars intermedia and pars nervosa. Staining of tyrosine hydroxylase-immunoreactive fibers in the median eminence and pituitary was sparse or absent in premetamorphic tadpoles, but became increasingly more intense as metamorphosis progressed.

Development of catecholaminergic projections to the spinal cord in the North American opossum, Didelphis virginiana

The intent of our study was to determine when catecholaminergic axons grow into each of their adult targets in the spinal cord of the North American opossum (Didelphis virginiana) and to identify the origin of catecholaminergic axons in the lumbosacral cord at different stages of development. Tyrosine hydroxylase-like immunoreactive axons, presumed to be catecholaminergic, were demonstrated at different stages of development by the indirect antibody peroxidase-antiperoxidase technique of Sternberger. The neurons giving rise to such axons in the lumbosacral cord were identified by using the retrograde transport of Fast Blue and immunofluorescence for tyrosine hydroxylase-like immunoreactive neurons. At birth, 12-13 days after conception, tyrosine hydroxylase-like immunoreactive axons are present in the marginal zone throughout the length of the spinal cord. Such axons are particularly numerous in the dorsolateral marginal zone, the region containing most of them in adult animals. By postnatal day 3, a few immunoreactive axons are present in the intermediate (mantle) zone of the spinal cord; and by postnatal day 8, they are most concentrated in the presumptive intermediolateral cell column. Laminae I and II of the dorsal horn are not innervated by such axons until approximately postnatal day 15. By postnatal day 44, the distribution of tyrosine hydroxylase-like immunoreactive axons in the spinal cord resembles that in adult animals, although some areas may be hyperinnervated. At birth, tyrosine hydroxylase-like immunoreactive cell bodies are present in all of the brainstem areas providing catecholaminergic projections to the spinal cord in adult animals (Pindzola et al.: Brain Behav. Evol. 32:281-292, '88); and by at least postnatal day 5, lumbosacral injections of Fast Blue retrogradely label tyrosine hydroxylase-like immunoreactive neurons in all such areas. Retrogradely labeled immunoreactive neurons were also found in areas that do not contain them in adult animals. Such areas include the dorsal part of the nucleus coeruleus and certain areas of the reticular formation. During development, spinally projecting tyrosine hydroxylase-like immunoreactive neurons are numerous medial to the nucleus ventralis lemnisci lateralis (the paralemniscal region), whereas only a few are present in the same location in adult animals. Our results suggest that catecholaminergic axons grow into the spinal cord prenatally, that they innervate their adult targets postnatally and over an extended time period, and that during some stages of development they originate from areas that do not supply them in the adult animal.

Anatomic distribution of autonomic neural tissue in the developing dog heart: I. Sympathetic innervation

We used immunocytochemical localization of tyrosine hydroxylase to trace the ontogenesis and anatomic distribution of sympathetic innervation in fetal, neonatal, and mature canine hearts. Sparse tyrosine hydroxylase-positive neural tissue first appeared in the atrium, including sinoatrial and atrioventricular nodes, and the ventricular epicardium at midgestation and progressively increased in extent to reach the adult pattern by 2 months following birth. Sympathetic innervation of the atrioventricular bundle occurred relatively later, with no nerve processes in the neonate but a mature pattern by 2 months. At each developmental stage the atria contained more tyrosine hydroxylase-positive neural tissue than the ventricles. Thus, sympathetic nerve processes appear in the developing canine heart earlier than was previously recognized. The time course of sympathetic innervation as defined by this anatomic study is in accord with electrophysiologic studies indicating progressive neonatal development of sympathetic effect which achieves maturity by 2 months of age.

The monoaminergic innervation of the amygdala in the squirrel monkey: an immunohistochemical study

The monoaminergic innervation of the amygdala of the squirrel monkey (Saimiri sciureus) was studied by using immunohistochemical methods with primary antisera raised against serotonin, and the catecholamine synthesizing enzymes tyrosine hydroxylase, dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase. Serotonin was widely distributed within the amygdala including profuse terminal labeling in central, basolateral and cortical nuclear groups. The accessory basal and medial nuclei were the only two areas receiving relatively poor serotoninergic innervation. Tyrosine hydroxylase was more discretely distributed, with very dense to moderate terminal labeling in central, basal and lateral nuclei, but only scant labeling within accessory basal and corticomedial nuclei, except at the cortical transitional area where dense terminal labeling was noted. Dopamine-beta-hydroxylase immunoreactivity was moderate in central and corticomedial nuclei, but comparatively light in other nuclear groups. Phenylethanolamine-N-methyltransferase was only sparsely distributed in the amygdala. The findings of the present study reveal that the monoaminergic innervation of the primate amygdala is similar to that reported in rodents, although some conspicuous exceptions do exist. Whereas the noradrenergic and serotoninergic neuronal systems ramify profusely within the amygdala, the dopaminergic system appears to be more discretely and topographically organized.

Solitary hypothalamic neurons inherently express vasopressin and tyrosine hydroxylase

Hypothalamic neurons were grown as single cells in three-dimensional culture. Solitary neurons lacking cell contacts were immunocytochemically examined for inherent expression of vasopressin (VP), tyrosine hydroxylase (TH), and luteinizing hormone releasing hormone (LHRH). Immunoreactive VP and TH were detected within a day. Sixty to eighty-five percent of neurons displayed homogeneously distributed reaction product for VP or TH. One percent exhibited intense punctate staining of somas and varicosities. Few neurons stained for LHRH. Results indicate that hypothalamic neurons can express appropriate neuropeptides and transmitter-specific products without contacting other neurons or nonneuronal cells. Thus, this culture system may provide a useful model to study intrinsic neuronal processes.

New perspectives on the molecular pharmacology of affective disorders

Research with antidepressants has emphasized the importance of a delayed deamplification of the linked serotonin (5HT)/norepinephrine (NE) receptor coupled adenylate cyclase system in brain. The basic phenomena of regulation of receptor number and function of the beta adrenoceptor linked adenylate cyclase system in brain are well established, with NE regulating beta adrenoceptors in the high agonist affinity conformation (linked to adenylate cyclase and down-regulated by antidepressants), and with 5HT regulating those receptors in the low agonist affinity conformation. The biochemical effector systems of NE and 5HT are discussed and it is concluded that the final common pathway of signal transduction is protein kinase mediated phosphorylation of cellular proteins. Glucocorticoid receptors are located in the perikarya of aminergic cell bodies and may exert their effects by modifying the genomic expression of the diffusely projecting stress-responsive monoamine systems. The molecular neurobiology of beta adrenoceptors, with its implication for genetic and immunologic investigations, is briefly discussed and further research on stimulus-transcription coupling and regulation of gene expression in brain is suggested as an exciting new direction in central receptor research relevant to the psychopharmacology of affective and other disorders.