Ontogeny of tyrosine hydroxylase and dopamine-beta-hydroxylase activity in discrete limbic and hypothalamic structures of female rats

Tyrosine hydroxylase (TOH) and dopamine-ß-hydroxylase (DBH) activities were measured in the mediocortical amygdala (AMY), hippocampus (HPC), nucleus accumbens (ACB), medial preoptic area (MPO), and anterior and posterior parts of the mediobasal hypothalamus (AMBH and PMBH) in female rats of various postnatal ages. Serum LH, FSH and prolactin levels were also measured. In a previous study it was shown that dopamine (DA) and norepinephrine (NE) turnover rates in the MPO and the MBH increase between days 20 and 30 after birth and decrease thereafter. The cause for increased DA turnover was shown to be increasing serum prolactin levels. The activity of TOH in the ACB, MPO, AMBH and PMBH did not parallel DA turnover rates. Around day 20 after birth, when serum prolactin levels and preoptic and hypothalamic DA turnover increase, TOH activity also increased in the ACB and PMBH. In adult, diestrous animals, however, which have low serum prolactin levels and low preoptic and hypothalamic DA turnover, TOH activity was higher than in immature rats. The activity of DBH in the MPO, AMBH, AMY and HPC was high in 15-day-old animals, decreased between days 20 and 30 and then increased again to adult values. This pattern is just opposite to the one observed for serum prolactin levels and for preoptic and hypothalamic NE turnover. It is concluded that activity of both enzymes is not a good measure for neuronal activity of those NE and DA cells which innervate limbic and hypothalamic structures.     

Nigrostriatal and mesolimbic dopaminergic activities were modified throughout the ovarian cycle of female rats

Summary In this work, we have studied the changes in the functional state of nigrostriatal (NSDA) and mesolimbic (MLDA) dopaminergic neurons during the estrous cycle of the female rat. The activity of tyrosine hydroxylase (TH), the turnover rate (K_t) after inhibition of dopamine (DA) synthesis and the ratio between the contents of this amine and its metabolite, L-3,4 dihydroxyphenylacetic acid (DOPAC), were used as indices of neuronal activity. The neuronal activity of NSDA neurons rose during estrous and declined during proestrous, as reflected by the values of K_t and DOPAC/DA ratio measured during both phases. Interestingly, the course of variations in striatal TH activity was similar, although retarded in relation to the changes in neuronal activity. Thus, TH activity was high during diestrous, whereas it was low during estrous. The activity of MLDA neurons was reduced during proestrous. This can be concluded from the decreased K_t and DOPAC/DA ratio measured in this phase and it was accompanied by a low TH activity. Thereupon, both K_t and TH activity increased during estrous. These results indicate the existence of physiological changes in the functional state of both dopaminergic systems during the ovarian cycle, which are partially different for each neuronal pathway. This supports the existence of a specific regulation, and not indiscriminate effects, by the hormones involved in this cycle, mainly estradiol and progesterone.     

Central administration of serotonin decreases tyrosine hydroxylase catalytic activity and messenger ribonucleic Acid signal levels in the hypothalamus of female rats

We investigated the effect of central serotonin (5-hydroxytryptamine, 5-HT) administration on hypothalamic tuberoinfundibular dopamine neurons and related changes in neuronal activity to circulating prolactin (PRL) levels. Ovariectomized rats were treated with either vehicle or 5-HT through a lateral ventricular cannula in one of two dose paradigms: 1) a bolus of 20 μg, with tissues taken at 30 min, or 2) the same bolus immediately followed by 20 μg/30 min via a syringe pump for 120 min, and tissues taken at 120 min. Blood samples were taken throughout experiments and plasma PRL determined by radioimmunoassay. Under both paradigms, NSD 1015, a dihydroxyphenylalanine (DOPA) decarboxylase inhibitor (25 mg/kg intraarterially) was injected 10 min before decapitation and brain excision followed by stalk-median eminence dissection. The rate of DOPA accumulation, determined by measuring DOPA levels in the stalk-median eminence by high-performance liquid chromatography with electrochemical detection was used as a measure of tyrosine hydroxylase (TH) catalytic activity. Stalk-median eminence DOPA accumulation in control rats was 29.9 ± 4.2 and 28.8 ± 4,4 ng/mg protein (30 and 120 min experiments, respectively). DOPA accumulation in 5-HT-treated rats was significantly reduced (P<0.05) after 30 min to 17.8 ± 1.2 ng/mg protein, but it was similar (21.7 ± 3.9) to controls after 120 min of 5-HT infusion. 5-HT levels in the stalk-median eminence of rats treated with 5-HT were 13- to 17-fold greater than controls (16.9 to 18.5 ng/mg protein). Plasma PRL levels in both groups increased 10-fold after 5-HT treatment with a peak at 5 min, returning to baseline by 120 min. TH mRNA levels were determined by in situ hybridization in a second group of rats which were treated with the 20μg bolus and subsequent 120 min infusion of 5-HT. TH mRNA signal levels in the arcuate nucleus of control rats averaged 144 ± 21 grains/cell. After treatment with 5-HT, TH mRNA levels in the arcuate nucleus were significantly lower (P<0.0001) with 69±14 grains/cell. In a third group of rats, the effects of the 30 min 5-HT treatment on TH catalytic activity and circulating PRL levels was challenged with two 5-HT(2) receptor antagonists, LY53857 (5 mg/kg intraperitoneally) or ketanserin (10 mg/kg intraperitoneally). Neither the 5-HT-induced decrease in TH catalytic activity nor the increase in PRL was altered by pretreatment (120 min) with 5-HT(2) antagonists. These data suggest that central 5-HT is capable of decreasing TH activity and TH mRNA levels in the tuberoinfundibular dopamine neurons and that the decrease in dopaminergic neuronal activity may contribute to the 5-HT-induced PRL rise. The changes in TH catalytic activity and PRL after intracerebroventricular administration of 5-HT do not appear to be mediated by 5-HT(2) receptors.     

Effects of dexamethasone and other glucocorticoid steroids on tyrosine hydroxylase activity in the superior cervical ganglion

Dexamethasone is known to elicit an increase of tyrosine hydroxylase activity in the superior cervical ganglion. The details of such a glucocorticoid effect were investigated in the present study. Of 4 glucocorticoids (dexamethasone, corticosterone, hydrocortisone and triamcinolone) examined in rats, only the synthetic steroid dexamethasone was found to be effective in increasing ganglionic tyrosine hydroxylase activity (by 50% at 48 h after drug administration). Corticosterone even at doses as high as 50 mg/kg failed to show an effect. Since recent reports indicate that a cytoplasmic glucocorticoid receptor is not present in the sympathetic ganglion, it is unlikely that the dexamethasone effect involves a receptor-mediated mechanism. Moreover, the dexamethasone effect was totally blocked by chlorisondamine, a nicotinic cholinergic receptor antagonist. The possibility of an enhanced impulse flow from the CNS, however, was excluded by the finding that decentralization immediately prior to dexamethasone administration did not prevent the increase of ganglionic tyrosine hydroxylase activity, although earlier decentralization (24 h or longer) abolished the steroid effect. Significantly, in the freshly decentralized ganglia, the increase of tyrosine hydroxylase activity by dexamethasone was still blocked by chlorisondamine. Since synaptic activity in terminals is known to continue for a brief period following nerve transection, our data support the contention that the primary site of the dexamethasone effect may be the preganglionic terminals.     

Reduced tyrosine hydroxylase activity in nigrostriatal system of sinoaortic-denervated rats

Tyrosine hydroxylase activity was measured in the caudate nucleus and substantia nigra (pars compacta) of sinoaortic-denervated (SAD) and sham-operated (SO) rats 3 days after operation. The SAD groups had approximately a 50%, statistically significant, reduction of enzyme activity in both regions and also a significant reduction of dopamine in caudate nucleus. These results suggest a probable link between cortico-somatomotor integration and neural input from arterial baroreceptor neural pathways.     

In vitro effects of catecholamines and catecholestrogens on brain tyrosine hydroxylase activity and kinetics in the female catfish Heteropneustes fossilis

Effects of catecholamines and catecholestrogens on tyrosine hydroxylase (TH) activity and kinetics were investigated in the telencephalon and hypothalamus of female Heteropneustes fossilis in gonad quiescent (resting) and recrudescent (preparatory) phases. Dopamine, noradrenaline and adrenaline and the catecholestrogen, 2-hydroxyestradiol-17 beta inhibited TH activity in a concentration-dependent manner in both resting and preparatory phases, with a higher effect in the resting phase. Two- methoxyestradiol-17 beta did not alter TH activity in any season. The catecholamines inhibited TH in a competitive manner increasing apparent K(m) values significantly without altering the apparent V(max). Two-hydroxyestradiol-17 beta inhibited significantly the enzyme in a noncompetitive manner and decreased apparent V(max) without altering apparent K(m) values. The apparent K(i) is higher for dopamine than noradrenaline or adrenaline. The apparent K(i) for 2-hydroxyestradiol-17 beta is not significantly different from that of noradrenaline. The present results suggest an interaction between oestradiol-17beta (E2) and catecholamine metabolism at the level of tyrosine hydroxylation and E2 effects on catecholamines may be mediated through its 2-hydroxylation.     

Harmonal regulation of adult sympathetic neurons: the effects of castration on tyrosine hydroxylase activity

The effects of the hormone testosterone on neurotransmitter synthesis in peripheral sympathetic ganglia were examined in adult male Sprague-Dawley rats. Tyrosine hydroxylase (T-OH), the rate limiting enzyme in catecholamine biosynthesis was examined in the hypogastric (HG), coeliac (CG), and superior cervical ganglion (SCG) subsequent to castration. Initial studies indicated that 2 weeks after surgery, HG T-OH activity fell to approximately 30% of control. In order to more clearly define the pattern of testosterone effects, HG was examined 1, 2 and 4 weeks after surgery. T-OH activity was 67%, 50% and 11% of control at these 3 respective time points, and the observed alteration in T-OH activity appeared to parallel changes in the size of pelvic target organs. Similar hormonal effects did not occur in other peripheral sympathetic ganglia; T-OH activity was unchanged in SCG and CG when examined 1 month after castration. Enzyme activity was restored following replacement therapy with testosterone, whereas the neural metabolite 17-beta estradiol was without effect. The recovery in T-OH activity was associated with partial recovery of target organ size. These studies suggest that hormonal factors regulate neurotransmitter synthesizing enzymes in adult sympathetic neurons and may do so via consequences of alterations in target organs. These observations parallel similar events in the developing nervous system.     

Reserpine induction of tyrosine hydroxylase in paraplegia

Reserpine induction of tyrosine hydroxylase (TH) activity reflects the biochemical adaptability of sympathetic neurons. Midthoracic spinal cord transection in adult animals precludes TH induction in the sixth lumbar (L6) ganglion, a ganglion innervated by spinal segments caudal to the lesion. However, in animals receiving lesions as neonates, an elevation in L6 ganglion TH activity occurred after reserpine. This retained biochemical adaptability indicates an increased recuperative capacity of developing neurons.     

Adrenal influence on tyrosine hydroxylase activity in superior cervical ganglion

The involvement of adrenal hormones as regulatory factors in maintaining physiological levels of tyrosine hydroxylase (TH) was examined in mouse superior cervical ganglion. Following bilateral adrenalectomy, TH activity in the ganglion fell at a slow but steady rate, reaching 60-65% of the control levels after 2 weeks. Decentralization is known also to reduce TH activity in the ganglion. The effects of adrenalectomy and decentralization were therefore compared, and they were found to be additive, indicating different mechanisms in the two cases. The reduction of TH activity following adrenalectomy was not prevented by replacement with corticosterone (0.5 mg/kg, daily). However, replacement with epinephrine (4 mg/kg, daily) completely prevented the fall of TH activity in adrenalectomized animals. Isoproterenol, a beta-adrenergic receptor agonist, was as effective as epinephrine in preventing the reduction of TH activity following adrenalectomy. Furthermore, in intact animals, chronic administration of SKF 64139, an inhibitor of adrenal PNMT which depletes circulating epinephrine levels, also reduced ganglionic TH activity to the same level as that after adrenalectomy. These results indicate that epinephrine, but not corticosterone, is the adrenal factor required for physiological maintenance of normal levels of TH in the superior cervical ganglion.     

Ultrastructural immunocytochemical localization of tyrosine hydroxylase in the neostriatum

The morphology and synaptic associations of dopaminergic axons in the n. caudate-putamen (neostriatum) of the adult rat brain are examined. Identification of dopaminergic axons is based upon the electron microscopic immunocytochemical localization of the catecholamine synthesizing enzyme, tyrosine hydroxylase. Immunoreactivity for the enzyme is detected in unmyelinated axons and axon terminals in serial sections collected throughout the neostriatum. The labeled terminals range from 0.1 to 1.5 micron in diameter and have peroxidase reaction product located around closely packed, round vesicles with a diameter of 40-60 nm. The tyrosine hydroxylase containing axon terminals constitute approximately 21% of the total number of terminals in the n. caudatus-putamen and include 3 types which differ in size and synaptic specializations. The most prevalent (82% of total), type I, is small (0.15-0.39 micron in diameter) and forms symmetric junctions with dendrites and dendritic spines. The other two terminal types (II and III) have a medium to large diameter (0.4-1.5 micron) and show either no membrane specializations or asymmetric junctions with dendrites. The axon terminals without observable membrane densities are occasionally oriented so as to suggest an association with dopaminergic and non-dopaminergic axon terminals. These findings indicate that while the dopaminergic terminals may form axoaxonic connections, the primary synaptic contacts are with dendrites of intrinsic neurons in all regions of n. caudatus-putamen.     

Homospecific activity (activity per enzyme protein) of tyrosine hydroxylase increases in parkinsonian brain

Summary Tyrosine hydroxylase (TH) contents in the caudate nucleus, putamen, and substantia nigra from control and parkinsonism brains were measured for the first time by a sandwich enzyme immunoassay. Both the TH protein content and TH activity (V_max) were decreased in parallel in the parkinsonian brains as compared with those of the control brains. In contrast, TH homospecific activity (activity per enzyme protein) was significantly increased in the parkinsonian brains. The results indicate that the decrease of TH activity in parkinsonian brains is due to the decrease of TH protein content as a result of cell death. The increase in the homospecific activity of residual TH in parkinsonian brain suggests such molecular changes in TH molecules as result in a compensatory increase in TH activity.     

Localization of immunoreactive tyrosine hydroxylase in the goldfish brain

This report describes the distribution of tyrosine hydroxylase immunoreactive (TH-ir) structures in the brain of the goldfish (Carassius auratus). The localization of TH-ir cell groups revealed by immunocytochemical techniques is largely in accordance with catecholamine distribution previously reported in teleosts by using monoamine fluorescence; however, in the telencephalon and diencephalon, several new cell groups are elucidated. In the telencephalon, TH-ir cell bodies are observed in the olfactory bulb, area ventralis telencephali, and the central zone of the area dorsalis telencephali. TH-ir fibers and terminals are moderately dense throughout the telencephalon except for a sparse innervation of the area dorsalis, pars medialis. Immunostained cells are present in the suprachiasmatic nucleus and magnocellular and parvicellular components of the preoptic nucleus. Immunoreactive fibers from preoptic cells can be traced caudally in two main tracts to the infundibulum. Dense immunoreactivity around cells in the pituitary provides anatomical support for catecholamine involvement in the neuroendocrine axis probably via preopticohypophysial connections. At middiencephalic levels, immunoreactive cells are present in the ventral thalamus, nucleus pretectalis periventricularis, pars ventralis, and paraventricular organ pars anterioris. In the caudal diencephalon, TH-ir cells are seen within the posterior tuberal nuclei and dorsal to posterior recess. No immunostained cells are observed in the midbrain. In the hindbrain, tyrosine hydroxylase containing cells comprise three groups similar to that described using Falck-Hillarp histofluorescence (Parent et al., '78), i.e., isthmal, central medullary, and medullospinal groups. Tyrosine hydroxylase immunoreactivity is interpreted as evidence for the presence of catecholamines and not only provides an anatomical basis for the functional significance of catecholamines in teleosts, but may be useful in elucidating homologous structures in tetrapod vertebrates, although certain sites of immunoreactivity may prove to be unique to teleosts.     

Ultrastructural localization of tyrosine hydroxylase in rat nucleus accumbens

Immunocytochemical localization of tyrosine hydroxylase (TH) was used to determine the ultrastructural morphology and synaptic associations of catecholaminergic terminals in the nucleus accumbens of the rat. The brains were fixed by vascular perfusion with 4% paraformaldehyde and 0.2% glutaraldehyde. Coronal sections cut with a vibrating microtome were incubated with rabbit antiserum to TH then immunocytochemically labeled by the peroxidase-antiperoxidase method. Immunoreactivity for the enzyme was found within unmyelinated axons and axon terminals. These terminals contained either all small clear or combined small clear and large dense core vesicles. Approximately 40% of the labeled terminals formed symmetric synapses with unlabeled proximal or distal dendritic shafts. The dendrites showed a spare distribution of spines. Axosomatic synapses and axonal associations of the TH-containing terminals also were detected. The recipient perikarya were usually 10-20 micrometers in diameter and contained an indented nucleus and abundant cytoplasm. The content of large dense vesicles and synaptic associations with somata and proximal dendrites suggest that a certain proportion of the TH-containing terminals within the nucleus accumbens are morphologically distinct from catecholaminergic terminals within the dorsal striatum. These differences are discussed in relation to neuropeptides and functions of the dopaminergic mesolimbic and nigrostriatal pathways.     

Coexistence of oxytocin and tyrosine hydroxylase in the rat hypothalamus,an immunocytochemical study

Summary Immunocytochemical double labelling was used to determine the structural relationship of oxytocin (OT) and tyrosine hydroxylase (TH) containing perikarya and processes in the rat hypothalamus. Extrahypothalamic TH fibers, as well as parvocellular TH neurons were found to form contacts with OT cells. A fraction of the OT neurons contained TH immunoreactivity. It is likely that in addition to the classical mesencephalic afferences also hypothalamic interneurons and magnocellular dopaminergic neurons control the hypothalamo neurohypophysial system.     

Effect of starvation on hypothalamic tyrosine hydroxylase activity in adult male rats

The activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in norepinephrine synthesis, was determined in the mediobasal hypothalamus of adult male rats during acute and semistarvation. 3,4-Dihydroxyphenylalanine (DOPA) formed by TH was measured using high-performance liquid chromatography (HPLC). Acute starvation, as well as 3 weeks of semistarvation on a high-protein low-carbohydrate diet (CST PR) reduced TH activity significantly. Three weeks of a low-protein high-carbohydrate diet (CST KH) did not affect TH activity. While maximal velocity (Vmax) is significantly diminished in acute starvation and in semistarvation with a high-protein low-carbohydrate diet, Kd-values for tyrosine were not changed. These results suggest that TH activity in the brain contributes to decreased norepinephrine (NE) turnover in starvation.     

Immunocytochemical localization of tyrosine hydroxylase in rat adrenal medulla by the peroxidase labeled antibody method: effects of enzyme activation on ultrastructural distribution of the enzyme

A monospecific antibody against tyrosine hydroxylase (TH), purified from a transplantable rat pheochromocytoma, was produced in rabbits. Immunohistochemical techniques were employed in order to determine if a relationship exists between the subcellular distribution of TH and the level of activation of the enzyme in the rat adrenal medulla. Tyrosine hydroxylase activity in adrenals removed from non-stressed rats following pentobarbital anesthesia was found to be 12.9 +/- 1.0 nmol DOPA formed x mg protein-1. The use of ether anesthesia (17.9 +/- 2.0 nmol DOPA formed x mg protein-1), and the administration of electroconvulsive shock (ECS) followed by decapitation (35.9 +/- 2.0 nmol DOPA formed x mg protein-1) was associated with an acute activation of adrenal TH. The subcellular distribution of TH within the cytosol of chromaffin cells from animals subjected to anesthesia or ECS, as determined by immunocytochemical techniques, was similar. In all treatment groups chromaffin cells were found which had TH associated with some chromaffin granules. The percentage of chromaffin granules which appeared to contain TH was lower in animals subjected to ECS plus decapitation as compared with anesthetized animals. These observations suggest that the activation of adrenal medullary TH is not associated with a shift in the subcellular distribution of the enzyme from the cytosol to membranous structures.     

Levodopa‐induced dyskinesias in tyrosine hydroxylase deficiency

The objective of this study was to characterize levodopa (l‐ dopa)–induced dyskinesias in patients with tyrosine hydroxylase deficiency. Clinical observation was carried out on 6 patients who were diagnosed with tyrosine hydroxylase deficiency and were treated with escalating doses of l‐ dopa. All 6 patients showed l ‐dopa‐induced dyskinesias of variable intensity early in the course of treatment and regardless of the age of initiation. l ‐Dopa–induced dyskinesias were precipitated by increases in the dose of l ‐dopa and also by febrile illnesses and stress. They caused dysfunction and distress in 2 patients. The dyskinesias were improved by decreasing the l ‐dopa dose or by slowing its titration upward. Increasing the dose frequency was helpful in 2 patients, and introducing amantadine was helpful in another 2 patients. l ‐Dopa–induced dyskinesias are a common phenomenon in tyrosine hydroxylase deficiency. The current observations show that l‐ dopa–induced dyskinesias are frequent in a dopamine‐deficient state in the absence of nigrostriatal degeneration. Although l ‐dopa–induced dyskinesias in tyrosine hydroxylase deficiency are phenomenologically similar to those that occur in Parkinson's disease, they are different in a number of other respects, suggesting intrinsic differences in the pathophysiologic basis of l‐ dopa–induced dyskinesias in the 2 conditions. © 2013 Movement Disorder Society     

Depolarizing stimuli increase tyrosine hydroxylase in the mouse locus coeruleus in culture

The influence of membrane depolarization on the development and regulation of brain noradrenergic neurons was studied in explant cultures of the mouse locus coeruleus (l.c.). Exposure to the depolarizing agents veratridine or elevated K+ significantly increased the catalytic activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. The effects of veratridine were prevented by tetrodotoxin, suggesting that transmembrane Na+ influx was necessary for the rise in TH. Morphometric analysis indicated that the rise in TH activity was not accompanied by altered TH-positive cell number or cell diameter. Rather, TH fluorescence intensity increased in each neuron, suggesting that depolarization increased TH per neuron. Immunoblot and densitometric analysis indicated that depolarization did, indeed, increase TH immunoreactive protein. Moreover, depolarization elevated enzyme activity in cultured neurons expressing the normal developmental increase in TH, as well as those in which plateau levels had already been attained. We conclude that depolarization and/or Na+ influx regulates a critical transmitter macromolecule in brain neurons, as in the periphery, by altering enzyme molecule number.