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J F Pujol

Publications and source records attributed to J F Pujol.

At least 37 records · Page 2Linked to original sources
PubMed1994

RU24722 induces spatially organized phenotypic plasticity in the locus coeruleus.

The plasticity of tyrosine hydroxylase (TH) expression in rat locus coeruleus (LC) was evaluated after RU24722 TH induction using, as a new parameter of characterization, the quantitative topology of LC defined by TH-positive cells. This new phenotype was spatially organized into cell subpopulations in the medial LC, dorsal and ventro-lateral to the initial perikaryal space. Reserpine and parachlorophenylalanine, which elicited a similar increase in the TH content, failed to induce a significant change in the number of TH-expressing cells. Activation of TH expression is not sufficient to reveal the existence of such a plasticity and some original but still unknown mechanism(s) of control of TH expression is affected by RU24722.

Animals↗
PubMed1994

Ontogeny of tyrosine hydroxylase levels in the neuropil close to locus caeruleus.

We aimed to characterize tyrosine hydroxylase (TH) expression within the pericaerulean area (PCA) during postnatal development. Levels of TH along the caudorostral axis of the locus caeruleus (LC) showed a dramatic increase in the PCA beyond day 21. This was due to the extension of the TH-containing area, particularly organized in the ventrolateral and longitudinal directions. As dendrites of LC neurones were observed at long distances within this PCA, such an increase in TH distribution could affect functions related to the LC.

Animals↗
PubMed1994

Ventilatory acclimatization to chronic hypoxia: relationship to noradrenaline metabolism in the rat solitary complex.

1. The relationship between ventilatory acclimatization to chronic hypoxia (10% O2-90% N2) and noradrenaline metabolism was examined in two regions located immediately caudal and rostral to the obex within the rat solitary complex. 2. Three experimental protocols were established. In protocol 1, the percentage changes in respiratory tidal volume, frequency and minute ventilation elicited by 4, 7, 10 and 14 days of hypoxia were assessed by flow plethysmography in awake rats, and then the content of tyrosine hydroxylase was measured in the solitary complex. In protocol 2, the time course response of tyrosine hydroxylase protein level was determined after 3, 7, 14 and 22 days of hypoxia by using a quantitative immunoblotting method for the protein assay. In protocol 3, the turnover of noradrenaline was estimated in the solitary complex after 14 days of hypoxia. 3. A progressive increase in ventilation was observed to reach a maximum (+105 +/- 15%, mean +/- S.E.M.) above normoxic control after 10 days of hypoxia, at which time it stabilized. Furthermore, tyrosine hydroxylase protein increased progressively and reached a maximal level at 14 days of hypoxia (+36 +/- 4%, mean +/- S.E.M.). Return to the basal level of tyrosine hydroxylase was observed after 22 days of hypoxia. 4. Tyrosine hydroxylase content (+36 +/- 4%) and noradrenaline turnover (+394 +/- 3%) increased exclusively in the caudal part of the solitary complex. 5. The ventilatory acclimatization to chronic hypoxia preceded the increase in tyrosine hydroxylase and these two parameters were significantly correlated. 6. These data suggest that ventilatory acclimatization to chronic hypoxia is associated with topical modifications of the brainstem catecholamine metabolism.

Acclimatization↗
PubMed1994

Relationship between tyrosine hydroxylase content and noradrenergic cell reactivity to piperoxane: an in vivo voltammetric approach in the rat locus coeruleus.

A previous electrochemical study showed that the increase in the tyrosine hydroxylase (TH) content of the locus coeruleus (LC) produced by RU24722 administration was associated with a relative decrease in the catecholaminergic metabolic reactivity of this nucleus to a hypotensive stimulus. Since alpha 2 receptors participate in the regulation of the activity of both LC neurons and TH, the aim of the present work was to evaluate the possible involvement of the autoinhibition mediated by alpha 2 autoreceptors in the inverse relationship between the reactivity of the LC and its TH content. Our study was divided into two successive steps: (i) the electrochemical measurement of the in vivo metabolic activation of LC cells in response to alpha 2-adrenergic receptor blockade, and (ii) the evaluation of the quantity of TH every 100 microns along the caudorostral axis in each recorded LC. The capacity of TH protein to be activated was evaluated by the measurement, using differential normal pulse voltammetry, of the in vivo variations of the extracellular 3,4-dihydroxyphenylacetic acid concentrations in response to six cumulated doses of the alpha 2-antagonist piperoxane. The corresponding dose-response curves, determined in control- and RU24722-treated rats, were expressed as a function of the quantity of TH contained either in the whole recorded LC or in the 100 microns-wide coronal interval surrounding the recording site. It was established that the slopes of the dose-response curves were significantly (P < 0.01) and inversely related to the quantity of TH at the level of the recording site. This result suggests that the negative control of the catecholaminergic metabolic reactivity in a restricted area of the LC could be directly or indirectly dependent on the level of expression of TH protein in this particular area.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1994

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)

Animals↗
PubMed1994

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.

Animals↗
PubMed1994

Regional specificity of the long-term variation of tyrosine hydroxylase protein in rat catecholaminergic cell groups after chronic heat exposure.

The present study was carried out to investigate the effect of chronic heat exposure on tyrosine hydroxylase (TH) protein content in catecholaminergic rat brain-stem areas such as the anterior (LCA) and posterior (LCP) locus coeruleus, the substantia nigra (SN), the ventral tegmental area, and the dorsomedial (DMM) and the ventrolateral medulla and in the adrenal gland (AG). Male Sprague-Dawley rats were exposed to 34 degrees C during 3, 7, or 14 days. Controls were kept at 25 degrees C for the same period. In the LCA, TH content was decreased on day 7 (-34%) and 14 (-37%) of heat exposure. In the SN, TH protein content was decreased on day 7 (-25%) and 14 (-20%) after 34 degrees C. In the DMM cell group, 14 days at 34 degrees C produced a decrease (-20%) of TH content. In all of these structures, TH content variations were correlated with body temperature variations. In the AG, TH content increased progressively to peak (+31%) after 14 days of chronic heat exposure. This increase was also associated with body temperature modification. The selective and body temperature-related response to long-term TH protein content variations following chronic heat exposure observed in the LCA, SN, DMM, and AG could represent an adaptive physiological response of these catecholaminergic cells.

Adrenal Glands↗
PubMed1994

Postnatal development of the tyrosine hydroxylase-containing cell population within the rat locus coeruleus: topological organization andphenotypic plasticity.

The cellular phenotypic characteristics of tyrosine hydroxylase (TH) expression have been studied within the rat locus coeruleus (LC) during postnatal development at six different stages: postnatal day 4 (PND4), PND10, PND14, PND21, PND30, and PND42. Coronal brain sections were selected at intervals of 80 microns along the caudorostral extent of the LC and processed for TH immunohistochemistry. At each anatomical level we (1) reconstructed the mean space of the LC delineated by the TH positive cell bodies, (2) enumerated the mean number of these cell bodies, and (3) determined the mean volume circumscribed by these cell bodies and their density. The topological study revealed a steady remodeling of the structure until the third week, with a progressive reducing of a ventral cellular group in the anterior LC, which was no longer observable at PND21, concomitant to the stretch of the structure toward its caudal limit. We have noted invariant and variant cellular phenotypic characteristics of TH expression. At any stage, the LC could be separated into a posterior and an anterior subregion and its total volume remained quite stable during the studied period. At PND14 and PND21, we observed a transient 33% increase in the total number of TH positive perikarya as compared to PND42. Conjoint analysis of the topological reconstruction and the density of TH positive cells suggested there were three distinct and precisely localized subsets of "quiescent" neurons. TH gene expression in these cells would have lowered between PND14 and PND21 inside two subsets and between PND21 and PND30 inside the last one. So topologically defined populations of cells could be involved in specific functions. If they have not definitively lost their TH expression capacity, they could contribute to increasing TH levels in LC occurring in response to physiological perturbations or pharmacological treatments.

Animals↗
PubMed1994

Quantitative study of tyrosine hydroxylase protein levels within the somatic area of the rat locus coeruleus during postnatal development.

To date only global dosages of tyrosine hydroxylase (TH) protein have been realized in the locus coeruleus (LC) without discriminating the enzyme contained in the cell body area from the one in the surrounding neuropil. The preceding immunohistochemical study (Bezin et al., 1994) revealed a dramatic plasticity of the cellular expression of TH in the LC during the postnatal development of the rat. It was therefore necessary to develop a quantitative biochemical approach, strengthened by a great anatomical resolution, to follow the developmental evolution of TH levels exactly in the space containing the coerulean TH-immunoreactive perikarya. In the present work two biochemical parameters necessary for precisely defining the phenotypic characterization of TH expression within the rat LC have been established during the postnatal development at six different stages: postnatal day 4 (PND4), PND10, PND14, PND21, PND30, and PND42. TH tissue concentration and content were precisely determined along the caudorostral extent of the LC within the previously (Bezin et al., 1994) defined spaces delimited by the TH-containing perikarya. TH tissue concentration remained quite stable during the postnatal development. TH quantity exhibited few age-related variations with a transient peak at PND10 and followed the same evolution as the volume containing the TH-expressing perikarya. The mean cell contribution to the total quantity of TH measured in the whole LC showed important age-related fluctuations with a dramatic peak at PND10 followed by a drastic decrease until PND21.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1993

Quantitative autoradiography of somatostatin receptors in the rat limbic system.

The distribution of somatostatin receptors (SRIF-R) was analyzed in the limbic system of the adult rat by in vitro autoradiography with [125I-Tyr0,DTrp 8]S14 as a radioligand. Precise quantification of the density of binding sites, at 0.2 mm intervals throughout the different areas revealed a marked heterogeneity of labeling in most structures. In particular, SRIF-R were concentrated in the basal (104.4 +/- 3.3 fmol/mg proteins) and basolateral amygdaloid nuclei (94.8 +/- 4.3 fmol/mg proteins), and in the nucleus of the lateral olfactory tract (121.6 +/- 2.4 fmol/mg proteins), whereas moderate densities were detected in the amygdalo-hippocampal nucleus (76.4 +/- 2.8 fmol/mg proteins). The medial (41.3 +/- 1.9 fmol/mg proteins) and the central (24.0 +/- 1.4 fmol/mg proteins) amygdaloid nuclei contained lower SRIF-R concentrations. It appears from these observations, in the light of the anatomical pathways of the amygdala, that intra-amygdalian SRIF-containing neurons project to the amygdalo-hippocampal nucleus, and that SRIF-R in the basolateral complex are the target of afferents from limbic cortical areas. SRIF-R were detected at different levels of the hippocampal formation but their distribution was more restricted than that of SRIF-containing fibers. The maximal density of sites was detected in the ventral and dorsal parts of the subiculum (115.0 +/- 3.4 and 87.0 +/- 2.8 fmol/mg proteins, respectively) and in the parasubiculum (100.1 +/- 5.4 fmol/mg proteins). In Ammon's horn, the stratum oriens and stratum radiatum of the CA1 field were the only sites enriched in SRIF-R (74.1 +/- 2.0 and 74.6 +/- 1.9 fmol/mg proteins, respectively). The apparent lack of receptors in the pyramidal cell layer indicated that, in Ammon's horn, SRIF is involved in intra-hippocampal communication. Low levels of receptors were found in the hippocampal CA2 and CA3 fields. SRIF-R in the dentate gyrus were mainly concentrated in the molecular layer (57.3 +/- 1.2 fmol/mg proteins). A very high density of sites was also observed in the entorhinal cortex (up to 123.1 +/- 1.5 fmol/mg proteins). A clear mismatch between SRIF and SRIF-R was detected in the septum and the habenula. In the profound layers of the cingulum and retrosplenial cortex, a heterogeneous distribution of SRIF-R was observed. High concentrations of sites were detected in the rostral zone of the cingulate cortex (93.4 +/- 2.0 fmol/mg proteins) while the posterior cingulate only exhibited moderate concentrations of sites (66.5 +/- 0.7 fmol/mg proteins).(ABSTRACT TRUNCATED AT 400 WORDS)

Amygdala↗
PubMed1993

Regional specificity of the long-term regulation of tyrosine hydroxylase in some catecholaminergic rat brainstem areas. I. Influence of long-term hypoxia.

The present study was carried out to investigate the influence of long-term hypoxia on tyrosine hydroxylase (TH) protein quantity in some catecholaminergic rat brainstem areas such as the dorsomedial medulla (DMM), the ventrolateral medulla (VLM) and the locus coeruleus (LC). TH protein quantity was also measured in a dopaminergic structure, the substantia nigra (SN). Male Sprague-Dawley rats were exposed to normobaric hypoxia (10% O2/90% N2) for 3, 7, 14 or 22 days. Controls were kept in normoxia for the same period. This study demonstrates that: (1) 3 days of hypoxia produced a 50% and a 26% increase in the quantity of TH protein in the rostral and caudal LC, respectively; (2) 14 days of hypoxia produced a 44% increase of TH protein content exclusively in the caudal part of DMM and a 31% increase in the VLM area; and (3) the stimulus failed to alter the TH protein quantity in the SN. After 14 and 22 days of hypoxia respectively, the TH protein content in the LC and DMM returned to the level of controls. To determine whether the increase in TH protein quantity could be related to a change in norepinephrine (NE) content, the rate constant of disappearance (k) of NE was measured in the catecholaminergic areas of intact or chemodenervated rats submitted to long-term hypoxia. Our results show that hypoxia causes an increase of TH protein quantity within the subpopulations of catecholaminergic areas additionally with an elevation in the NE content. These data suggest a selective response of the TH regulation to long-term hypoxia within the caudal DMM catecholaminergic area which receives chemosensory inputs.

Animals↗
PubMed1993

Regional specificity of long-term regulation of tyrosine hydroxylase in some catecholaminergic rat brainstem areas. II. Effect of a chronic dihydralazine treatment.

Dihydralazine, which is used in the treatment of hypertension, causes a long-lasting hypotensive action by a direct vasodilator effect on arteriolar smooth muscle. The present study was carried out to investigate the effect of a daily single injection of dihydralazine (20 mg/kg, s.c.) for 14 days on the tyrosine hydroxylase (TH) protein quantity in some catecholaminergic rat brainstem areas such as the dorsomedial medulla (DMM), the ventrolateral medulla (VLM) and the locus coeruleus (LC). This study demonstrates that the dihydralazine produced (1) an 85% increase in TH protein quantity exclusively in the rostral part of DMM, (2) a 58% increase of TH protein content exclusively in the rostral part of the LC, and (3) a 37% increase of the TH protein quantity in VLM catecholaminergic area. To determine whether the increase in TH protein quantity could be related to a change in norepinephrine (NE) content, the rate constant of disappearance (k) of NE was measured in the catecholaminergic regions of the same rats treated with dihydralazine. Our results show that dihydralazine causes an increase of the TH protein, in addition to an elevation of NE content, within the subpopulations of catecholaminergic structures. These data suggest a selective response of the TH regulation to dihydralazine within the rostral DMM area which receives barosensory inputs.

Animals↗
PubMed1993

Decrease in the reactivity of locus coeruleus neurons to hypotension after an increase in their tyrosine hydroxylase content: a subregional in vivo voltammetry study in the rat.

The aim of the present work was to determine if noradrenergic neurons of the anterior and the posterior subregions of the locus coeruleus exhibit a difference in reactivity in response to sodium nitroprusside-induced arterial hypotension, and if the pharmacological induction of tyrosine hydroxylase by RU24722 modifies the reactivity of locus coeruleus neurons to this hypotensive stimulus. Previous findings have demonstrated that administration of RU24722 increases the concentration of tyrosine hydroxylase in the rat locus coeruleus by two different mechanisms in the anterior and in the posterior locus coeruleus subregions. The goal of the present study was to measure in vivo the changes in catecholaminergic metabolism in the locus coeruleus after treatment with RU24722 using differential normal pulse voltammetry (DNPV). In vehicle-treated rats, arterial hypotension increased catecholaminergic metabolism with the same pattern in the two locus coeruleus subregions. However, the changes in the magnitude of the catechol oxidation current throughout the recording period were significantly smaller in the posterior subregion (P < 0.001). In the RU24722-pretreated rats, there was a 39% increase in tyrosine hydroxylase and dihydroxyphenylacetic acid in the locus coeruleus. The functional reactivity to hypotension measured by DNPV was significantly decreased (P < 0.001) in both the anterior and posterior locus coeruleus subregions with RU24722 treatment. Therefore, this study suggests that the response of locus coeruleus cells to a hypotensive stimulus depends upon the intracellular tyrosine hydroxylase concentration both in the basal condition and during pharmacological induction of tyrosine hydroxylase gene expression.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

Long-term effect of RU24722 on tyrosine hydroxylase in the rat locus coeruleus: differential effects of two enantiomeric forms.

RU24722, as a racemic mixture, has been found to act on neuronal activity and the long-term regulation of tyrosine hydroxylase in the locus coeruleus of the rat. In this study, the effects of two enantiomeric derivatives of RU24722 (3 alpha and 16 alpha forms), as compared to the racemic form itself, are studied. The short-term effect was estimated 20 min after treatment by measuring variations in 3,4-dihydroxyphenylacetic acid content in the locus coeruleus. The long-term effect was determined by evaluating tyrosine hydroxylase protein concentration in the locus coeruleus 3 days after a single injection. Comparison of actions of both enantiomers showed that the 16 alpha form was 3-fold more potent in eliciting tyrosine hydroxylase protein elevations at three days, whereas the 3 alpha isomer increased 3,4-dihydroxyphenylacetic acid content 2-fold more in the short-term. These results seem to show that the 16 alpha configuration is crucial for the long term regulation of tyrosine hydroxylase protein elicited by RU24722 within the locus coeruleus.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

Microdialysis monitoring of 3,4-dihydroxyphenylalanine accumulation after decarboxylase inhibition: a means to estimate in vivo changes in tyrosine hydroxylase activity of the rat locus ceruleus.

An on-line microdialysis approach was developed to estimate changes in tyrosine hydroxylase activity in the locus ceruleus noradrenergic neurons of anesthetized rats by measuring the 3,4-dihydroxyphenylalanine (DOPA) accumulation in the extracellular fluid during perfusion of an aromatic amino acid decarboxylase inhibitor through a dialysis probe. The aromatic amino acid decarboxylase inhibitor used was difluoromethyl-DOPA, which was shown to be more stable than NSD 1015 or Ro 4-4602 in the perfusion fluid. A 1-h perfusion of a 10(-4) mol/L of difluoromethyl-DOPA solution induced a linear increase in DOPA concentration in the locus ceruleus dialysates that achieved a steady state within 1 h. The identity of DOPA accumulated in dialysates during aromatic amino acid decarboxylase inhibition was confirmed by the disappearance of the chromatographic peak when DOPA formation was blocked by the administration of alpha-methyl-p-tyrosine. Systemic administration of the alpha 2-antagonist piperoxane before difluoromethyl-DOPA perfusion markedly increased the DOPA concentration during both the accumulation and the steady-state periods, showing that the present technique is a suitable in vivo approach to monitor changes in tyrosine hydroxylase activity occurring in the locus ceruleus neurons.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

Further characterization of the long-term effect of RU24722 on tyrosine hydroxylase in the rat locus coeruleus.

Recent data have indicated that the long-lasting increase in tyrosine hydroxylase (TH) protein could be differently expressed in the anterior and posterior locus coeruleus (LC) after a single intraperitoneal injection of RU24722, which has been proposed as a potent activator of catecholaminergic systems. In the present study, we have evaluated the dose and time course responses and the effect of a repeated treatment with RU24722 at 3-day intervals on TH protein level in the anterior and posterior rat LC. The results showed that RU24722 induces a long-lasting increase of TH protein level in the anterior and posterior LC that was maximal 3 days following a single injection of 30 mg/kg. The increase in TH protein was maintained at a constant level after repeated administrations of RU24722 at 3-day intervals. Furthermore, we have investigated whether the effect of the drug on TH protein could be modulated via several hormonal systems. The long-term increase of TH steady-state content after RU24722 was still observed 15 days after castration, adrenalectomy, hypophysectomy, and thyroidectomy. The initial steady-state TH protein level was significantly higher in the anterior LC of thyroid- or hypophysectomized and in the posterior LC of hypophysectomized rats. However, this increase was reversed when animals were housed at 28 degrees C.

Adrenal Glands↗
PubMed1992

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

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

Animals↗