Calcium and cAMP mediated stimulation of Fos in cultured hypothalamic tyrosine hydroxylase-immunoreactive neurons

In vitro regulated expression of tyrosine hydroxylase in ventral midbrain neurons from Nurr1-null mouse pups

The transcription factor Nurr1, an orphan member of the steroid-thyroid hormone nuclear receptor superfamily, is essential for the proper terminal differentiation of ventral midbrain dopaminergic neurons. Disruption of the Nurr1 gene in mice by homologous recombination abolishes synthesis of dopamine (DA) and expression of DA biosynthetic enzymes, including tyrosine hydroxylase (TH), in the ventral midbrain without affecting the synthesis of DA in other areas of the brain. At birth, however, dopaminergic neuron precursors in Nurr1 null (-/-) pups remain as shown by continued expression of residual, untranslated Nurr1 mRNA not altered by homologous recombination. Since Nurr1 disruption is lethal shortly after birth, to further investigate the developmental properties of these neurons, dissociated ventral midbrain neurons from newborn pups were grown for 5 days on an astrocyte feeder layer, subjected to various treatments and then evaluated for expression of TH by fluorescent immunocytochemistry. Initially, a small percentage of neurons (0.26% +/- 0.07%) from the ventral midbrain of Nurr1 -/- pups were TH-immunoreactive (TH-IR). No change in TH expression was observed in the presence of glial cell line-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), or DA alone or in combination. Treatment with forskolin (Fsk), however, significantly increased the percentage of TH-IR neurons (1.36% +/- 0.15%). Combination of Fsk, BNDF, and DA further increased the percentage of TH-IR neurons (2.58% +/- 0.50%). Therefore, these data suggest that dopaminergic neuron precursors, which develop in vivo without Nurr1, remain in an undifferentiated condition that is permissive to the induction of TH in vitro. J. Neurosci. Res. 64:322-330, 2001. Published 2001 Wiley-Liss, Inc.

Role of calcium/calmodulin-dependent protein kinases in expression of Fos protein in the nucleus tractus solitarii after sustained hypertension

We investigated the role of calcium/calmodulin-dependent protein kinases in the phosphorylation of cyclic AMP response element binding protein and subsequent induction of c-fos gene elicited by sustained hypertension in neurons of the nucleus tractus solitarii of anesthetized rats. Activation of glutamate receptors in the nucleus tractus solitarii significantly increased the number of neurons that were immunoreactive to phosphorylated cyclic AMP response element binding protein and Fos protein. Microinjection bilaterally into the nucleus tractus solitarii of the calcium/calmodulin-dependent protein kinase inhibitor, 1-[N,O-bis(5-isoquinolinesulfonyl-N-methyl-L-tyrosyl]-4-phenylpiperazine , appreciably blunted such an increase. This inhibitor also attenuated the augmented immunoreactivity for phosphorylated cyclic AMP response element binding protein or Fos protein in the same nucleus induced by sustained hypertension. These results were comparable to those observed after blockade of either N-methyl-D-aspartate or non-N-methyl-D-aspartate ionotropic glutamate receptors in the nucleus tractus solitarii. Reverse transcription-polymerase chain reaction further indicated that the calcium/calmodulin-dependent protein kinase blocker attenuated the expression of Fos protein induced by sustained hypertension in the nucleus tractus solitarii by suppressing the transcription of c-fos messenger RNA. The present results suggest that activation of calcium/calmodulin-dependent protein kinases may represent an important step in the cascade of intracellular events that leads to phosphorylation of cyclic AMP response element binding protein and subsequent induction of c-fos gene after activation of ionotropic glutamate receptors by baroceptive signals in the nucleus tractus solitarii.

Phosphorylation of transcription factor cyclic-AMP response element binding protein mediates c-fos induction elicited by sustained hypertension in rat nucleus tractus solitarii

We investigated the role of cyclic-AMP response element binding protein signaling in the induction of the immediate-early gene c-fos by baroreceptor activation in neurons of the nucleus tractus solitarii of anesthetized rats. Activation of the arterial baroreceptors with sustained hypertension significantly increased the number of neurons in the caudal nucleus tractus solitarii that were immunoreactive to an antiserum that detects Ser133-phosphorylated cyclic-AMP response element binding protein. This implied increase in phosphorylation of cyclic-AMP response element binding protein was subsequently followed by an elevation in the expression of Fos protein in neurons of the nucleus tractus solitarii. Microinjection bilaterally into the nucleus tractus solitarii of a phosphorothioated antisense oligonucleotide directed against the initiation site of cyclic-AMP response element binding protein messenger RNA discernibly reduced the manifested immunoreactivity of phosphorylated cyclic-AMP response element binding protein in response to baroreceptor activation. This was accompanied by a decline in the transcription of c-fos messenger RNA and the expression of Fos protein, along with an appreciable potentiation of the baroreceptor reflex response. Control injections of the sense oligonucleotide or artificial cerebrospinal fluid were ineffective. These findings suggest that phosphorylation of cyclic-AMP response element binding protein is crucial to Fos expression in the nucleus tractus solitarii elicited by sustained hypertension. As such, phosphorylation of cyclic-AMP response element binding protein may be an important early nuclear event that mediates the long-term inhibitory modulation of the baroreceptor reflex response by Fos protein at the nucleus tractus solitarii.

Behavioural, autonomic and endocrine responses associated with C-fos expression in the forebrain and brainstem after intracerebroventricular infusions of endothelins

Endothelins are a range of peptides (endothelin-1, endothelin-2, and endothelin-3) well known to act peripherally as powerful cardiovascular-regulating agents. Recently, they have been shown to be localized in CSN, where they may act as central neurotransmitters. A variety of putative roles has been ascribed to them in the CNS. To identify those regions of the brain capable of responding to these peptides, the expression of c-fos (an immediate-early gene), has been used to map patterns of activation following intracerebroventricular (i.c.v.) infusions of endothelins in Lister-hooded rats. This has been correlated with changes in heart rate, core temperature and plasma corticosterone levels. Endothelin-3 i.c.v. (50 pmol) decreased both heart rate and core temperature (both recorded by telemetry). This effect lasted for about 30-45 min. Endothelin-1 (10 pmol) or endothelin-3 (50 pmol) i.c.v. induced c-fos expression in the specific regions in the forebrain and brainstem. Strong expression was found in the septum, bed nucleus of the stria terminalis, parvicellular paraventricular nucleus, the central nucleus of the amygdala, dorsal motor nucleus of the vagus and solitary nucleus. There was less marked c-fos expression in other areas of the basal forebrain, such as the organum vasculosum of the lamina terminals, median preoptic nucleus, supraoptic nucleus and the magnocellular. There are two classes of endothelin receptor (A and B). An endothelin-A receptor antagonist, BQ-123, abolished c-fos expression in all structures in the forebrain and brainstem following endothelin-1 infusions. However, an endothelin-B agonist (TetraAla endothelin-1) did not induce discernible c-fos expression in the forebrain or brainstem. These results suggest that the endothelin-A receptor is responsible for endothelin-dependent c-fos induction in the brain. Interactions between endothelins and angiotensin II were also studied. The pattern of c-fos induced by endothelin-3 and angiotensin II was different (particularly in the anteroventral region of the third ventricle). Furthermore, prior infusions of endothelin-3 interfered with the expression of c-fos induced by subsequent angiotensin II, and also suppressed the latter's dipsogenic effect. These results show that endothelin-3 and angiotensin II interact at both behavioural and cellular levels, and that endothelins may play significant roles in the central control of fluid balance and autonomic activity.

In vitro autoradiography of receptor-activated G proteins in rat brain by agonist-stimulated guanylyl 5'-[gamma-[35S]thio]-triphosphate binding

Agonists stimulate guanylyl 5'-[gamma-[35S]thio]-triphosphate (GTP[gamma-35S]) binding to receptor-coupled guanine nucleotide binding protein (G proteins) in cell membranes as revealed in the presence of excess GDP. We now report that this reaction can be used to neuroanatomically localize receptor-activated G proteins in brain sections by in vitro autoradiography of GTP[gamma-35S] binding. Using the mu opioid-selective peptide [D-Ala2,N-MePhe4,Gly5-ol]enkephalin (DAMGO) as an agonist in rat brain sections and isolated thalamic membranes, agonist stimulation of GTP[gamma-35S] binding required the presence of excess GDP (1-2 mM GDP in sections vs. 10-30 microM GDP in membranes) to decrease basal G-protein activity and reveal agonist-stimulated GTP[gamma-35S] binding. Similar concentrations of DAMGO were required to stimulate GTP[gamma-35S] binding in sections and membranes. To demonstrate the general applicability of the technique, agonist-stimulated GTP[gamma-35S] binding in tissue sections was assessed with agonists for the mu opioid (DAMGO), cannabinoid (WIN 55212-2), and gamma-aminobutyric acid type B (baclofen) receptors. For opioid and cannabinoid receptors, agonist stimulation of GTP[gamma-35S] binding was blocked by incubation with agonists in the presence of the appropriate antagonists (naloxone for mu opioid and SR-141716A for cannabinoid), thus demonstrating that the effect was specifically receptor mediated. The anatomical distribution of agonist-stimulated GTP[gamma-35S] binding qualitatively paralleled receptor distribution as determined by receptor binding autoradiography. However, quantitative differences suggest that variations in coupling efficiency may exist between different receptors in various brain regions. This technique provides a method of functional neuroanatomy that identifies changes in the activation of G proteins by specific receptors.

Fos activation in cultured tyrosine hydroxylase and oxytocin immunoreactive neurons

Fos and other immediate early gene products are used as markers for neuronal activity. We identified Fos immunocytochemically after KCI-induced depolarization of cultured hypothalamic neurons. Five-day cultures were treated for 1 h with 50 mM KCI or media and fixed at 0, 0.5, 1, 2, and 4 h posttreatment. Sequential immunocytochemistry was performed to identify Fos immunoreactivity in tyrosine hydroxylase (TH)-immunoreactive (-ir) or oxytocin (OT)-ir neurons. Activated neurons [brown cells (TH-ir or OT-ir) with purple nuclei (Fos-ir)] were counted microscopically. KCI treatment resulted in an increased percentage of Fos-ir TH-ir and OT-ir neurons over control levels over the time course examined. Fos-ir peaked in TH-ir neurons at 0.5 to 1 h posttreatment, with levels returning to baseline at 4 h. Fos-ir in OT-ir neurons peaked at 2 h, and remained elevated at 4 h, showing prolonged activation. These results demonstrate that KCI-induced depolarization of cultured hypothalamic neurons increases Fos with a different time course in TH-ir vs. OT-ir neurons.