A 5′-flanking region of the bovine tyrosine hydroxylase gene is involved in cell-specific expression, activation of gene transcription by phorbol ester, and transactivation by c-Fos and c-Jun

Enhanced Retrieval of Taste Associative Memory by Chemogenetic Activation of Locus Coeruleus Norepinephrine Neurons

The ability of animals to retrieve memories stored in response to the environment is essential for behavioral adaptation. Norepinephrine (NE)-containing neurons in the brain play a key role in the modulation of synaptic plasticity underlying various processes of memory formation. However, the role of the central NE system in memory retrieval remains unclear. Here, we developed a novel chemogenetic activation strategy exploiting insect olfactory ionotropic receptors (IRs), termed "IR-mediated neuronal activation," and used it for selective stimulation of NE neurons in the locus coeruleus (LC). Drosophila melanogaster IR84a and IR8a subunits were expressed in LC NE neurons in transgenic mice. Application of phenylacetic acid (a specific ligand for the IR84a/IR8a complex) at appropriate doses induced excitatory responses of NE neurons expressing the receptors in both slice preparations and in vivo electrophysiological conditions, resulting in a marked increase of NE release in the LC nerve terminal regions (male and female). Ligand-induced activation of LC NE neurons enhanced the retrieval process of conditioned taste aversion without affecting taste sensitivity, general arousal state, and locomotor activity. This enhancing effect on taste memory retrieval was mediated, in part, through α₁- and β-adrenergic receptors in the basolateral nucleus of the amygdala (BLA; male). Pharmacological inhibition of LC NE neurons confirmed the facilitative role of these neurons in memory retrieval via adrenergic receptors in the BLA (male). Our findings indicate that the LC NE system, through projections to the BLA, controls the retrieval process of taste associative memory.SIGNIFICANCE STATEMENT Norepinephrine (NE)-containing neurons in the brain play a key role in the modulation of synaptic plasticity underlying various processes of memory formation, but the role of the NE system in memory retrieval remains unclear. We developed a chemogenetic activation system based on insect olfactory ionotropic receptors and used it for selective stimulation of NE neurons in the locus coeruleus (LC) in transgenic mice. Ligand-induced activation of LC NE neurons enhanced the retrieval of conditioned taste aversion, which was mediated, in part, through adrenoceptors in the basolateral amygdala. Pharmacological blockade of LC activity confirmed the facilitative role of these neurons in memory retrieval. Our findings indicate that the LC-amygdala pathway plays an important role in the recall of taste associative memory.

Characterization of Group I Metabotropic Glutamate Receptors in Rat and Human Adrenal Glands

Glutamate and its receptors have been demonstrated to promote both basal and nicotine-evoked catecholamine release in bovine chromaffin cells. Multiple glutamate receptors, including metabotropic glutamate receptors (mGluRs), are found in the adrenal glands of several species, as well as in chromaffin cells. However, there is limited information available regarding the expression of glutamate metabotropic receptor (GRM)1-8 mRNAs and the detailed localization of group I mGluRs (mGluR1 and mGluR5) in the rat and human adrenal cortex and medulla. Therefore, we examined mRNA expression of GRM1-8 subunits using reverse transcription-polymerase chain reaction (RT-PCR) and the distribution of mGluR1 and mGluR5 by immunostaining. The results showed that the GRM1-8 mRNAs were expressed in both the cortex and medulla of rat and human adrenal glands with the exception of GRM1, which was not detectable in the rat adrenal cortex. Immunostaining of mGluR1 revealed that it was localized only in the adrenal medulla of rats but was present in both the adrenal cortex and medulla in humans. In the adrenal medulla, the central part of the adrenal glands, mGluR1 was detected in chromaffin cells but not in nerve fibers and ganglion cells. Immunoactivity of mGluR5 was visible in the capillary wall throughout the adrenal cortex and medulla in rat and human samples. Its immunoactivity was also observed in ganglion cells in the rat adrenal medulla. There was no mGluR5 immunoactivity detected in chromaffin cells and nerve fibers in the rat and human adrenal medulla. Using dissected rat adrenal medulla as a model, we found that treatment with a mGluR1 agonist activated extracellular signal-regulated kinase (ERK) 1/2 and increased the expression of tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine synthesis. Moreover, these results showed that mGluR1 signaling was involved in hypoxia-induced upregulation of TH in the rat adrenal medulla. This study shows the expression of GRM1-8 mRNAs in rat and human adrenal glands and indicates that glutamate, through the activation of mGluRs, may play various physiological roles in the adrenal gland. Furthermore, mGluR1 may be involved in catecholamine biosynthesis by regulating TH, and mGluR5 may affect cortical and medullar hormone levels by regulating microvascular function.

Integrative nuclear FGFR1 signaling (INFS) pathway mediates activation of the tyrosine hydroxylase gene by angiotensin II, depolarization and protein kinase C

The integrative nuclear FGFR1 signaling (INFS) pathway functions in association with cellular growth, differentiation, and regulation of gene expression, and is activated by diverse extracellular signals. Here we show that stimulation of angiotensin II (AII) receptors, depolarization, or activation protein kinase C (PKC) or adenylate cyclase all lead to nuclear accumulation of fibroblast growth factor 2 (FGF-2) and FGFR1, association of FGFR1 with splicing factor-rich domains, and activation of the tyrosine hydroxylase (TH) gene promoter in bovine adrenal medullary cells (BAMC). The up-regulation of endogenous TH protein or a transfected TH promoter-luciferase construct by AII, veratridine, or PMA (but not by forskolin) is abolished by transfection with a dominant negative FGFR1TK-mutant which localizes to the nucleus and plasma membrane, but not by extracellularly acting FGFR1 antagonists suramin and inositolhexakisphosphate (IP6). Mechanism of TH gene activation by FGF-2 and FGFR1 was further investigated in BAMC and human TE671 cultures. TH promoter was activated by co-transfected HMW FGF-2 (which is exclusively nuclear) but not by cytoplasmic FGF-1 or extracellular FGFs. Promoter transactivation by HMWFGF-2 was accompanied by an up-regulation of FGFR1 specifically in the cell nucleus and was prevented FGFR1(TK-) but not by IP6 or suramin. The TH promoter was also transactivated by co-transfected wild-type FGFR1, which localizes to both to the nucleus and the plasma membrane, and by an exclusively nuclear, soluble FGFR1(SP-/NLS) mutant with an inserted nuclear localization signal. Activation of the TH promoter by nuclear FGFR1 and FGF-2 was mediated through the cAMP-responsive element (CRE) and was associated with induction of CREB- and CBP/P-300-containing CRE complexes. We propose a new model for gene regulation in which nuclear FGFR1 acts as a mediator of CRE transactivation by AII, cell depolarization, and PKC.

The cAMP responsive element and CREB partially mediate the response of the tyrosine hydroxylase gene to phorbol ester

Tyrosine hydroxylase (TH) gene promoter activity is increased in PC12 cells that are treated with the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate (TPA). Mutagenesis of either the cAMP responsive element (CRE) or the activator protein-1 element (AP1) within the TH gene proximal promoter leads to a dramatic inhibition of the TPA response. The TH CRE and TH AP1 sites are also independently responsive to TPA in minimal promoter constructs. TPA treatment results in phosphorylation of cAMP responsive element binding protein (CREB) and activation of cAMP-dependent protein kinase (PKA) in PC12 cells; hence, we tested whether CREB and/or PKA are essential for the TPA response. In CREB-deficient cells, the response of the full TH gene proximal promoter or the independent response of the TH CRE by itself to TPA is inhibited. The TPA-inducibility of TH mRNA is also blocked in CREB-deficient cells. Expression of the PKA inhibitor protein, PKI, also inhibits the independent response of the TH CRE to TPA. Our results support the hypothesis that TPA stimulates the TH gene promoter via signaling pathways that activate either the TH AP1 or TH CRE sites. Both signaling pathways are dependent on CREB and the TH CRE-mediated pathway is dependent on PKA.

Nicotine regulates mRNA level of tyrosine hydroxylase gene but not that of nicotinic acetylcholine receptor genes in PC12 cells

To understand the molecular mechanism of nicotine addiction, we examined the mRNA level of the tyrosine hydroxylase (TH) gene and that of the nicotinic acetylcholine receptor (nAChR) genes by long-term nicotine treatment. The transcript levels of the four subunit genes of the nAChR (alpha3, alpha5, alpha7, and beta4) were down-regulated by the treatment with forskolin, whereas the mRNA levels of the TH gene was increased in PC12 cells. By long-term nicotine treatment, the mRNA level of the nAChR genes did not change, but transcript levels of alpha3, alpha5, alpha7, and beta4 nAChR genes were still negatively regulated by forskolin. However, the mRNA level of TH gene did not change by forskolin under long-term nicotine treatment. The TH gene may be regulated by a nicotine-related signaling pathway, whereas alpha3, alpha5, alpha7, and beta4 nAChR genes may be further regulated by a protein kinase A (PKA) pathway under long-term nicotine treatment.

Stimulation of dopaminergic amacrine cells by stroboscopic illumination or fibroblast growth factor (bFGF, FGF-2) injections: possible roles in prevention of form-deprivation myopia in the chick

Form-deprivation myopia (FDM) in the chick is a popular model for studying the postnatal regulation of ocular growth. Using this model, we have shown previously that dopamine and FGF-2 can counteract the effects of form-deprivation, thereby producing emmetropia. In the present study, we tested the hypothesis that the emmetropizing effects of flickering light and intraocular injections of FGF-2 in the chick are mediated by the activity of dopaminergic retinal amacrine cells. We have assessed the rate of dopamine synthesis in the retina by measuring the accumulation of 3,4-dihydroxyphenylalanine (DOPA). We found that form-deprivation reduces the rate of dopamine synthesis in the light-adapted retina, and that the normal rate of dopamine synthesis in the light can be restored by stroboscopic illumination at frequencies around 10 Hz. By labeling cells immunocytochemically we have shown that the synthesis of c-fos, a putative transcriptional regulator of the tyrosine hydroxylase gene, is induced in dopaminergic amacrine cells by stroboscopic illumination at around 10 Hz. These observations are consistent with a critical role for dopaminergic amacrine cells in the regulation of ocular growth by intermittent illumination. We have found also that intraocular injections of FGF-2 cause emmetropization without altering levels of expression of c-fos, amounts of tyrosine hydroxylase, or rates of dopamine synthesis with respect to vehicle-injected controls. We conclude that FGF acts either in parallel to or downstream from the dopaminergic amacrine cells, rather than through them. We observed that intravitreal injection per se induces high levels of c-fos expression in both form-deprived and non-deprived retinas, and causes partial emmetropization in form-deprived eyes, while inhibiting dopamine synthesis in non-deprived retinas. It is likely, therefore, that injection stimulates the production and/or release of unknown factors whose diverse effects on ocular growth and dopamine metabolism are mediated by complex pathways. Taken together, our results are consistent with the view that the retinal circuitry that controls postnatal ocular growth in the chick involves multiple messengers and pathways.

Acute repeated nicotine injections increase enkephalin and decrease AP-1 DNA binding activity in rat adrenal medulla

Previously we reported that a single injection of nicotine decreased AP-1 DNA binding activity in adrenal medullae, although chronic bidaily nicotine (and saline) injections increased this binding activity [15]. Repeated acute nicotine injections (3 mg/kg i.p., 7 injections equi-spaced over a 3 h period) effectively increased adrenal tyrosine hydroxylase [3] and [Met5]enkephalin levels and also profoundly decreased adrenal medulla AP-1 DNA binding activity for over 8 h.

Hemodynamic regulation of tyrosine hydroxylase messenger RNA in medullary catecholamine neurons: a c-fos-guided hybridization histochemical study

Medullary catecholamine cell groups are involved in multiple modes of cardiovascular regulation and display indices of functional activation, including widespread c-fos expression, in response to hypotensive hemorrhage. Assessments of the impact of such challenges on transmitter-related gene expression are complicated by the biochemical and connectional heterogeneity that characterize these cell groups. Quantitative hybridization histochemical methods were used to follow the effects of 15% hemorrhage on levels of messenger RNA encoding tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, in medullary aminergic neurons; concurrent staining for nuclear Fos-immunoreactivity permitted comparisons between cells that ostensibly were and were not targeted by the challenge. Increased levels of tyrosine hydroxylase messenger RNA were detected in Fos-immunoreactive neurons in all cell groups examined. Mean maximal increases ranged between 133 and 192% of control values, and were attained within 0.5-1 h post-hemorrhage in noradrenergic (A1 and A2) cell groups, and at 2 h in adrenergic ones (C1, C2, and C2d or dorsal strip). By 4 h after the challenge, tyrosine hydroxylase messenger RNA levels in Fos-immunoreactive neurons in all cell groups had returned to control values. By contrast, tyrosine hydroxylase messenger RNA in non-Fos-immunoreactive cells either did not change significantly over the course of the experiment (C2 and C2d), or showed a rapid and transient increase, whose magnitude tended to be less than that seen in Fos-immunoreactive cells. c-fos messenger RNA was prominently induced in catecholaminergic neurons in each of the medullary cell groups examined at 0.5 h after hemorrhage, suggesting that the early tyrosine hydroxylase messenger RNA response to hemorrhage in non-Fos-immunoreactive cells preceded the capacity of responsive neurons to manifest detectable Fos protein expression. These findings indicate that hemorrhage up-regulates tyrosine hydroxylase messenger RNA levels in medullary catecholaminergic cell groups which have access to adaptive neuroendocrine and/or autonomic control systems. The approach employed here should prove of general utility in assessing the impact of environmental events on messenger RNA expression in connectionally heterogeneous cell groups that share a common biochemical phenotype.

The transient nicotinic stimulation of tyrosine hydroxylase gene transcription in bovine adrenal chromaffin cells is independent of c-fos gene activation

The nicotinic agonist dimethylphenylpiperazinium (DMPP) transiently stimulates tyrosine hydroxylase (TH) gene transcription in cultured bovine adrenal chromaffin cells (Craviso et al., J. Neurochem., 59 (1992) 2285-2296). The present studies examined the mechanism of this stimulation, exploring the hypothesis that c-fos- and/or cyclic AMP-related mechanisms are involved. As determined by nuclear run-on assay, exposure of chromaffin cells to DMPP (1 microM) induced c-fos and TH gene transcription fivefold and twofold, respectively. Nitrendipine (20 microM) blocked both responses, indicating a similar dependency of each on extracellular calcium. Both c-fos and TH gene transcription rates were also elevated by entry of calcium due to the presence of the calcium ionophore A23187 (5 microM). Comparison of the time dependence of the DMPP stimulation of c-fos and TH gene transcription revealed similar time courses. Both were rapid and transient, peaking within 10-30 min of nicotinic receptor occupancy and returning to control values by 1 h. This simultaneous activation of the TH and c-fos genes indicates that Fos induction cannot be responsible for the stimulation of TH gene transcription. This conclusion was further supported by a failure of anisomycin (100 microM) pretreatment of chromaffin cells, which blocked protein synthesis 99%, to have any effect on either the rapid stimulation of TH gene transcription or the length of time that the TH gene was activated by DMPP. Thus, neither Fos nor other high turnover-rate transcription factors appear to be responsible for the stimulation, or return to control level, of TH gene activity following nicotinic stimulation of chromaffin cells. In other experiments, treating chromaffin cells with a combination of maximally effective concentrations of DMPP and forskolin was found to produce no greater stimulation of TH gene transcription than either agent alone, suggesting that DMPP acts through the same mechanism as forskolin. Taken together, these results support the conclusion that the mechanism of TH gene activation in chromaffin cells by DMPP involves a cyclic AMP-dependent process and not the induction of transcription factors such as Fos.

Bovine tyrosine hydroxylase gene-promoter regions involved in basal and angiotensin II-stimulated expression in nontransformed adrenal medullary cells

The tyrosine hydroxylase gene is expressed specifically in catecholaminergic cells, and its activity is regulated by afferent stimuli. To characterize molecular mechanisms underlying those regulations, we have constructed chimeric genes consisting of bovine tyrosine hydroxylase gene promoters (wild-type or deletion mutants) and a luciferase reporter gene. The basal expression of these genes and their regulation by angiotensin II were examined in cultured bovine adrenal medullary cells. Luciferase activity was normalized to the amount of transfected plasmid DNA. A pTHgoodLUC plasmid containing the -428/+21-bp fragment of the tyrosine hydroxylase gene promoter expressed luciferase activity at severalfold higher levels than the promoterless pOLUC plasmid. Deletion of the -194/-54-bp promoter fragment containing POU/Oct, SP1, and other putative regulatory elements increased luciferase expression fivefold. An additional deletion further upstream (-269/-194 bp), including a 12-O-tetradecanoylphorbol 13-acetate (TPA)-responsive element (TRE)-like site, reduced promoter activity. These results indicate the presence of negatively and positively acting regions in the bovine tyrosine hydroxylase gene promoter controlling basal promoter activity in adrenal medullary cells. Angiotensin II stimulated the expression of endogenous tyrosine hydroxylase gene and pTHgood-LUC approximately threefold without affecting the expression of pOLUC. A comparable threefold stimulation was observed following the deletion of the -194/-54-bp promoter region, despite the increase in basal promoter activity. Additional deletion of the -269/-194-bp promoter fragment reduced stimulation by angiotensin II to 1.5-fold. These results indicate that the angiotensin II receptor-responsive element is located in the -269/-194-bp promoter region containing the TRE-like site. Additional angiotensin II-responsive site(s) may be present outside this region. Gel mobility shift assays demonstrated constitutive and angiotensin II-induced protein binding to the tyrosine hydroxylase gene promoter. Some DNA-protein complexes were displaced with c-Fos antibodies. The results suggest that c-Fos-related antigens support basal promoter activity and mediate activation of tyrosine hydroxylase by angiotensin II receptor.

Regulation of tyrosine hydroxylase gene expression in depolarized non-transformed bovine adrenal medullary cells: second messenger systems and promoter mechanisms

Activation of the tyrosine hydroxylase (TH) gene in the adrenal medulla during stress is mediated by trans-synaptic mechanisms and may involve cholinergic receptors. Stimulation of nicotinic receptors in adrenal medullary cells induces cell depolarization, influx of Ca2+ ions and increases levels of cAMP. We have shown that both cAMP and membrane depolarization produce an increase in the expression of the TH gene in cultured bovine adrenal medullary cells (BAMC). Others have proposed that transcriptional activation of the TH gene by cAMP is mediated through the sequence homologous to a cAMP responsive element (CRE) located in the proximal region of the TH gene promoter. In the present study we have examined the mechanisms by which membrane depolarization increases the TH gene activity. Treatment of serum-free BAMC cultures with the depolarizing agent, veratridine, increased the extracellular concentration of catecholamines, Met5-enkephalin, and the relative abundance of TH mRNA. Veratridine treatment also increased the levels of mRNAs for the catecholamine biosynthetic enzyme phenylethanolamine N-methyltransferase (PNMT), and proenkephalin A (PEK). Treatment for longer than 3 h was required to increase TH mRNA levels. By contrast, our previous studies indicated that cAMP stimulation for 2 h produces a maximal increase in TH mRNA levels in BAMC. The effects of veratridine and forskolin on TH mRNA levels were additive, further indicating that depolarization and cAMP activate TH gene expression via different pathways. Calmidazolium, an antagonist of calmodulin, had no effect on the veratridine-induced increase in TH mRNA levels. Similarly sphingosine treatment or preincubation with PMA, which reduce protein kinase C (PKC) activity and attenuate the induction of TH mRNA by PMA or the hormone, angiotensin II, did not affect the induction by veratridine. To identify promoter mechanisms of TH gene activation in depolarized cells we transfected BAMC with a plasmid pTHgoodLuc and treated with veratridine for 24 h. pTHgoodLUC contains a luciferase reporter gene linked to a -428/+21 bp fragment of the bovine TH gene promoter (relative to the transcription start site). Veratridine increased the expression of luciferase from the TH promoter 2.5-fold. Deletion of the -194/-54 bp promoter region containing SP-1 and POU/Oct sites reduced veratridine stimulation by 40%. Additional deletion of the -269 to -190 bp promoter segment, including an AP-1 element, further reduced veratridine stimulation to a statistically non-significant level. In conclusion, activation of TH gene expression upon depolarization is not mediated by calmodulin and PKC. Promoter sequences involved in this activation are located upstream from the CRE. Depolarization may activate TH gene transcription by acting on more than one regulatory region.