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

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

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

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

Pharmacological modulations of adrenergic phenotype in medullary C2 and C3 cell groups of adult rat.

The adrenergic phenotype was analysed in the rat's rostral dorsomedial medulla under normal conditions and 3 days after a single intraperitoneal injection of an eburnamine derivative, RU 24722, which increases tyrosine hydroxylase protein expression in the rostral portion of the nucleus tractus solitarius. This approach was investigated by a double immunofluorescence labelling of tyrosine hydroxylase and phenylethanolamine N-methyltransferase proteins. Under normal conditions, most adrenergic cell bodies are anatomically distributed in the dorsal and rostral medulla oblongata between the rostral part of the dorsal motor nucleus of the vagus nerve and the medial longitudinal fasciculus. Adrenergic neurons detected in this medullar region were distributed between both cell groups. Three days after the pharmacological RU 24722 treatment, an upregulation in tyrosine hydroxylase and phenylethanolamine N-methyltransferase protein expression was detected in both cell groups characterized by a highly increased number of tyrosine hydroxylase- and phenylethanolamine N-methyltransferase-containing cell bodies. The number of TH-mRNA containing neurons was also increased, indicating the transcriptional level of this regulation. These results demonstrated a particular neuronal plasticity of adrenergic phenotype in the medullary cell groups of adult rat.

Phenotypic characteristics of expressed tyrosine hydroxylase protein in the adult rat nucleus tractus solitarius: plasticity revealed by RU24722 treatment.

The phenotypic characteristics of expressed tyrosine hydroxylase protein have been precisely analysed in the rat nucleus tractus solitarius, which contains the majority of A2 noradrenergic and C2 adrenergic neurons of the medulla oblongata. This study was based upon quantitative analysis of immunohistochemical and immunoradioautographic staining of tyrosine hydroxylase protein in serial coronal sections. In control rats, there were few tyrosine hydroxylase-expressing cell bodies which express less than 2% of the immunoradiolabeled tyrosine hydroxylase protein measured in the structure. These cell bodies were scattered throughout an extensive immunopositive neuropile, which precisely delimited the topological space of the nucleus tractus solitarius quantiatively reconstructed using a polar coordinate system. The quantification of tyrosine hydroxylase tissue concentration from immunoradioautograms allowed us to subdivide the structure into two distinct regions. The posterior region of the nucleus tractus solitarius, which mainly corresponds to the A2 cell group, contains a relatively high tissue concentration of tyrosine hydroxylase protein (18.56 +/- 0.154 units per mg of tissue). The anterior region, which mainly corresponds to the C2 cell group, exhibits a relatively low concentration (12.09 +/- 0.81) of this protein. Three days after an intraperitoneal injection of RU24722, there was a strong increase (90 +/- 17%) in tyrosine hydroxylase protein content only in the anterior region of the nucleus tractus solitarius. This increase was associated with a dramatic elevation (142 +/- 20%) in the number of tyrosine hydroxylase-expressing cell bodies. The additional cell bodies were mainly located inside the initial perikarya-containing area.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis of [3',5'-3H2]-alpha-fluoromethyl-tyrosine as a radioactive specific label of rat brain tyrosine hydroxylase.

The [3',5']-ditritio-alpha-fluoromethyl-tyrosine 4 (specific activity 15.0 Ci/mmol) has been synthesized and used as a radioactive probe for rat neuronal tyrosine hydroxylase (TH). The route of synthesis for the preparation of 3 and 4 allowed us to not only introduce a fluorine atom into 3/4 using an inorganic source of fluorine (CsF), but also to take advantage of the high-yielding cyclization of (alpha,beta)-acetamido alcohols mediated by diethylaminosulfur trifluoride (DAST) to give the corresponding oxazolines. The distribution and metabolism of 4 have been studied in control conditions within the rat locus caeruleus (LC). Intracisternal injection of 20 microCi of 4 was followed by a rapid disappearance of 4 (t1/2 = 1.5 h) and by a specific accumulation of radioactivity into the LC anatomical limits. This was investigated each 140 microns along the caudo-rostral axis of the noradrenergic nucleus. In each anatomical interval, its distribution correlated nicely with already described caudo-rostral distribution of TH in noradrenergic cells. Thus, 4 may provide a reliable measure of TH activity in such catecholamine structures.