Alpha 1-adrenergic receptors in neuronal cultures from rat brain: increased expression in the spontaneously hypertensive rat

The potential of metabolomic analysis techniques for the characterisation of α1-adrenergic receptors in cultured N1E-115 mouse neuroblastoma cells

Several studies of neuropathic pain have linked abnormal adrenergic signalling to the development and maintenance of pain, although the mechanisms underlying this are not yet fully understood. Metabolomic analysis is a technique that can be used to give a snapshot of biochemical status, and can aid in the identification of the mechanisms behind pathological changes identified in cells, tissues and biological fluids. This study aimed to use gas chromatography-mass spectrometry-based metabolomic profiling in combination with reverse transcriptase-polymerase chain reaction and immunocytochemistry to identify functional α1-adrenergic receptors on cultured N1E-115 mouse neuroblastoma cells. The study was able to confirm the presence of mRNA for the α1D subtype, as well as protein expression of the α1-adrenergic receptor. Furthermore, metabolomic data revealed changes to the metabolite profile of cells when exposed to adrenergic pharmacological intervention. Agonist treatment with phenylephrine hydrochloride (10 µM) resulted in altered levels of several metabolites including myo-inositol, glucose, fructose, alanine, leucine, phenylalanine, valine, and n-acetylglutamic acid. Many of the changes observed in N1E-115 cells by agonist treatment were modulated by additional antagonist treatment (prazosin hydrochloride, 100 µM). A number of these changes reflected what is known about the biochemistry of α1-adrenergic receptor activation. This preliminary study therefore demonstrates the potential of metabolomic profiling to confirm the presence of functional receptors on cultured cells.

The sigma-1 antagonist BMY-14802 inhibits L-DOPA-induced abnormal involuntary movements by a WAY-100635-sensitive mechanism

RATIONALE

Levodopa (L-DOPA), the gold standard treatment for Parkinson's disease (PD), eventually causes L-DOPA-induced dyskinesia (LID) in up to 80% of patients. In the 6-hydroxydopamine (6-OHDA) rat model of PD, L-DOPA induces a similar phenomenon, which has been termed abnormal involuntary movement (AIM). We previously demonstrated that BMY-14802 suppresses AIM expression in this model.

OBJECTIVES

Although BMY-14802 is widely used as a sigma-1 antagonist, it is also an agonist at serotonin (5-HT) 1A and adrenergic alpha-1 receptors. The current study was conducted to determine which of these mechanisms underlies BMY-14802's AIM-suppressing effect. This characterization included testing the 5-HT1A agonist buspirone and multiple sigma agents. When these studies implicated a 5-HT1A mechanism, we subsequently undertook a pharmacological reversal study, evaluating whether the 5-HT1A antagonist WAY-100635 counteracted BMY-14802's AIM-suppressing effects.

RESULTS

Buspirone dose-dependently suppressed AIM, supporting past findings. However, no AIM-suppressing effects were produced by drugs with effects at sigma receptors, including BD-1047, finasteride, SM-21, DTG, trans-dehydroandrosterone (DHEA), carbetapentane, and opipramol. Finally, we show for the first time that the AIM-suppressing effect of BMY-14802 was dose-dependently prevented by WAY-100635 but not by the alpha-1 antagonist prazosin.

CONCLUSIONS

BMY-14802 exerts its AIM-suppressing effects via a 5-HT1A agonist mechanism, similar to buspirone. Other 5-HT1A agonists have failed clinical trials, possibly due to submicromolar affinity at other receptors, including D2, which may exacerbate PD symptoms. BMY-14802 is a promising candidate for clinical trials due to its extremely low affinity for the D2 receptor and lack of extrapyramidal effects during prior clinical trials for schizophrenia.

Lack of cross talk between alpha1-adrenergic and angiotensin type 1 receptors in neurons of spontaneously hypertensive rat brain

Norepinephrine causes downregulation of angiotensin II (Ang II) receptors in Wistar-Kyoto rat (WKY) brain neuronal cultures. The aim of this study was to compare the cross talk between Ang II and alpha1-adrenergic receptors in these neuronal cultures. Norepinephrine causes a 66 percent decrease in Bmax of Ang II type 1 (AT1) receptors in neuronal cultures of WKY brain. This decrease is mediated by the interaction of norepinephrine with the alpha1a-adrenergic receptor subtype. Norepinephrine also causes a decrease in mRNA levels for AT1 receptors. A maximal decrease of 83 percent in AT1, receptor mRNA is observed in 8 hours with 100 micromol/L norepinephrine, is blocked by 5-methyluradipil, and involves inhibition of AT1 receptor transcription. Furthermore, decreases in the AT1 receptor and its mRNA are associated with a significant attenuation of AT1 receptor-mediated stimulation of norepinephrine transporter mRNA in WKY brain neurons. In contrast, norepinephrine does not decrease AT1 receptors or mRNA and has no effect on Ang II stimulation of norepinephrine transporter mRNA in neuronal cultures of spontaneously hypertensive rat brain. Thus, these data show that norepinephrine-mediated downregulation of AT1 receptors is associated with a parallel decrease in AT1 mRNA and Ang II stimulation of norepinephrine transporter mRNA and involves the alpha1a-adrenergic receptor in neurons of WKY brain. This cross talk between the two receptors is lacking in neurons of spontaneously hypertensive rat brain.

Alpha 1-adrenergic receptors in the brain: characterization in astrocytic glial cultures and comparison with neuronal cultures

Binding of [125I]HEAT to membranes prepared from primary cultures of astrocytic glial cells was time-dependent and 70-85% specific. Various adrenergic agonists and antagonists competed for [125I]HEAT binding according to the potencies of prazosin greater than, yohimbine greater than or equal to, clonidine, norepinephrine (NE), and propranolol. Scatchard analysis showed the Bmax of 209 fmol/mg protein and a Kd of 184 pM for [125I]HEAT binding by astrocytic glial membranes. Pretreatment of astrocytes with NE resulted in a dose-dependent downregulation of [125I]HEAT binding sites with a maximal response observed after 8 h at 100 microM NE. Removal of NE from cultures after pretreatment resulted in a time- and protein synthesis-dependent recovery of binding sites to control levels within 120 h. Incubation of astrocytic glial cultures with NE stimulated phosphoinositide (PI) hydrolysis in a time- and dose-dependent manner with a maximal stimulation of 2-fold observed in 60 min by 100 microM NE. Clonidine expressed differential effects on alpha 1-adrenergic receptors of the neuronal and astrocytic glial cultures. Pretreatment with 10 microM clonidine caused a 40% decrease in the Bmax of [125I]HEAT binding without influencing the Kd value in neuronal cultures. This downregulatory effect of clonidine was associated with a reduction in the ability of NE to stimulate PI hydrolysis in clonidine pretreated cells. In contrast to neuronal cultures, clonidine neither downregulated [125I]HEAT binding sites nor stimulated PI hydrolysis in glial cultures.

Alpha-1-adrenergic receptors in the nucleus tractus solitarii region of rats with experimental and genetic hypertension

The binding of the alpha 1-adrenergic receptors antagonist, 125I-HEAT, to membranes of nucleus tractus solitarii (NTS) regions of the brains of neurogenic hypertensive, spontaneously hypertensive (SH), and deoxycorticosterone (DOCA)/salt hypertensive rats and their respective controls was studied to quantitate the expression of alpha 1-adrenergic receptors. Scatchard analysis of the binding studies revealed a 1.8-fold increase in the Bmax of alpha 1-adrenergic receptors in NTS region membranes of SH rats when compared to their Wistar-Kyoto (WKY) control without significant difference in the Kd for 125I-HEAT. A decrease in the Kd with no difference in Bmax of receptors for 125I-HEAT was observed in the NTS region membranes of neurogenic hypertensive rats when compared with their sham-operated controls. In contrast, comparison of the Bmax and Kd values for 125I-HEAT binding in NTS region membrane of the DOCA/salt hypertensive rats and its sham-operated control showed no significant differences. We suggest that alterations in baroreceptor afferent activity may be related to alterations in central alpha 1-adrenergic receptors binding in SH rats and rats with neurogenic hypertension.

Lack of alpha-1-adrenergic receptor-mediated downregulation of angiotensin II receptors in neuronal cultures from spontaneously hypertensive rat brain

Neuronal cells from Wistar Kyoto (WKY) and spontaneously hypertensive (SH) rat brains were established in culture to compare the expression of angiotensin II (Ang II) specific receptors and their regulation by norepinephrine (NE). Neurons from SH rat brains possess twice more Ang II specific receptors and expressed a proportional increase in Ang II stimulated [3H]-NE uptake compared with WKY neurons. NE caused a dose-dependent decrease in 125I-Ang II binding in WKY neurons, an effect not observed when neurons from SH rat brains were incubated with NE. These observations suggest that the lack of NE-induced downregulation of Ang II receptors in neuronal cultures is genetically regulated.

Kindling in spontaneous hypertensive rats

Vasopressin is a neurohormone and neuromodulator with many effects on behavior. Rats lacking vasopressin have been found to develop kindled seizures more slowly with amygdala stimulation. In the present study the spontaneous hypertensive (SH) rat and rats from the parent strain, the Wistar-Kyoto (WKY) rat received amygdala and pyriform kindling. The SH rat has been reported to have increased plasma vasopressin and increased brain vasopressin release. Plasma vasopressin, osmolality and hematocrit were also measured in blood samples obtained through chronic, indwelling catheters implanted in SH, WKY normal and Sprague-Dawley rats. SH rats were found to kindle with fewer afterdischarges than WKY normal rats with both amygdala and pyriform cortex stimulation. The total afterdischarge duration required to reach each kindling stage was significantly shorter in the SH rat. Plasma osmolality and vasopressin were significantly higher in the SH rats compared to WKY normal rats and Sprague-Dawley rats. These findings provide additional evidence that vasopressin may influence the establishment of enduring behaviors such as kindled seizures.

Vasopressin in neuronal cultures from neonatal rat brain

This study was performed to characterize and quantify vasopressin in neuron-enriched primary cultures of whole brains from 1-day-old rats and to compare such cultures between spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Vasopressin was extracted from cells and evaluated by radioimmunoassay and high-pressure liquid chromatography. Radioimmunoassay of high-pressure liquid chromatography fractions from cell extracts showed that the major peak of immunoreactivity comigrated with synthetic vasopressin. Cell vasopressin content increased in a graded manner when one to six dishes (plated 8 x 10(6) cells/dish) were pooled (8.7 +/- 0.5 to 67.7 +/- 8.2 pg/dish). When the number of plated cells per dish was increased (2 to 16 x 10(6) cells), there was also a graded rise in dish vasopressin content (3.4 +/- 0.4 to 15.3 +/- 3.9 pg). Treatment of cultures with 100 aM to 1 nM of angiotensin II for 5 minutes caused a dose-dependent decrease in cell vasopressin content. Furthermore, the decrease in cell vasopressin content of cultures treated with 1 nM angiotensin II (12.6 +/- 0.8 to 7.0 +/- 1.0 pg/10(6) cells, p less than 0.05) corresponded with the increase in medium vasopressin concentration (3.8 +/- 0.5 to 7.5 +/- 2.3 pg/ml) and this vasopressin-releasing effect of angiotensin II was blocked by [Sar1, Thr8]angiotensin II. Treatment of cultures with potassium chloride (56 mM) and acetylcholine chloride (5.5 microM) also resulted in significant decreases in cell vasopressin content.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced pressor response to GABA in the nucleus tractus solitarii of the spontaneously hypertensive rat

A previous study from this laboratory demonstrated that ongoing GABAergic neurotransmission in the nucleus tractus solitarii (NTS) functions to maintain baseline arterial pressure (AP). In that study, bilateral microinjection of nipecotic acid into the NTS was observed to elevate AP. Since nipecotic acid is a selective GABA uptake blocker, changes in GABA release should be reflected by changes in the response to nipecotic acid. The present study utilized this approach to assess endogenous GABA activity within the NTS of the spontaneously hypertensive rat (SHR). Male SHR, 16-20 weeks of age, were anesthetized with chloralose, paralyzed and ventilated. Age-matched Wistar-Kyoto (WKY) rats were studied as controls. Bilateral microinjection of nipecotic acid (10 nmol in 100 nl; a maximally effective dose) into the NTS elicited a pressor response which was significantly greater in the SHR than the response observed in the WKY rats. Similarly, direct stimulation of GABAB receptors in the NTS with (-)-baclofen 40 pmol, a maximally effective dose) elicited an increase in AP which was significantly greater in the SHR. In contrast, bilateral microinjection of the direct acting GABAA agonist muscimol (160 pmol, a maximally effective dose) resulted in a similar elevation of AP in both the SHR and WKY rats. These results suggest that the enhanced pressor response caused by endogenous GABA in the NTS of the SHR is due to a greater response evoked by stimulation of GABAB receptors. Thus, enhanced GABAB receptor-mediated neural transmission in the NTS may contribute to the expression or maintenance of hypertension in this genetic model of hypertension.

Increased density of perivascular nerves to the major cerebral vessels of the spontaneously hypertensive rat: differential changes in noradrenaline and neuropeptide Y during development

Fluorescence and immunohistochemical techniques were used to study the pattern and density of perivascular nerves containing noradrenaline (NA) and neuropeptide Y (NPY) supplying the major cerebral arteries of 4-, 6-, 8- and 12-week-old spontaneously hypertensive rats (SHR) and normotensive Wistar (WIS) controls. Levels of NA and NPY in the superior cervical ganglia were measured. The density of nerves containing NA and NPY was greater in the hypertensive animals at all ages studied. However, the developmental changes in the density of innervation showed similar trends in both SHR and WIS groups. With few exceptions, there was a significant increase in the density of nerves containing NA from 4 to 6 weeks and from 8 to 12 weeks of age. This was in contrast to a low expression, and in some vessels a significant decrease in the number of NPY-containing nerves from 4 to 6 weeks. The density of nerve fibres containing NPY increased significantly in almost all vessels between 6 and 8 weeks of age and then stabilized. Thus there is a differential time course for the appearance of NA and NPY during development. Furthermore, the hyperinnervation of cerebral vessels in SHR by nerves containing NA and NPY precedes the onset of hypertension and associated medial hypertrophy. High-performance liquid chromatography and enzyme-linked immunosorbant assays show that the NA and NPY contents of the superior cervical ganglion do not reflect the changes in innervation pattern seen in the terminal fibres in the cerebral arteries. This tends to support the view that a local neurovascular mechanism is involved in the maintenance of hypertension. The possibility that increase in NPY as well as NA in cerebral perivascular nerves of hypertensive animals is involved in the protection of the blood-brain barrier against oedema and cerebral haemorrhage is raised.

Increased expression of alpha 1-adrenergic receptors in the hypothalamus of spontaneously hypertensive rats

The specificity and molecular weights of alpha 1-adrenergic receptors in various tissues of spontaneously hypertensive (SH) rat were compared with normotensive controls (Wistar-Kyoto; WKY) with the use of [125I]HEAT and [125I]azidoprazosin, specific alpha 1-adrenergic receptor antagonists. Binding of [125I]HEAT to membranes prepared from SH rat brain hypothalamus was significantly higher, due to a 75% increase in the Bmax, than the WKY control. In contrast, the Bmax and Kd of [125I]HEAT binding to brainstem and liver membranes from SH rats were not significantly different from those of WKY controls. Competition-inhibition data suggested similar pharmacological specificity with potencies in the order of prazosin greater than yohimbine greater than propranolol for both WKY and SH rat membranes prepared from liver, hypothalamus, brainstem and neuronal cultures. Photoaffinity labeling of alpha 1-adrenergic receptors from hypothalamus, brainstem and neuronal cultures using [125I]azidoprazosin followed by SDS-PAGE and autoradiography showed the presence of one major band with a molecular weight (MW) of 105,000 Da for both WKY and SH rats. In contrast, labeling of liver alpha 1-adrenergic receptors revealed one major band with a MW of 60,000 Da. Quantitation of the 105,000-Da band from SH rat hypothalamic membranes demonstrated a 52% higher intensity compared with WKY controls. Neuronal cultures prepared from 1-day-old SH rats showed a similarly greater intensity of the 105,000-Da band compared with WKY controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Phorbol esters inhibit agonist-stimulated phosphoinositide hydrolysis in neuronal primary cultures

The effects of phorbol esters on neurotransmitter-stimulated phosphoinositide (PI) hydrolysis in neurons in primary culture were investigated. Ten-day-old neuronal cultures were incubated with [3H]inositol for 2-3 days, exposed to phorbol esters, and the release of [3H]inositol phosphates was measured in the presence of 10 mM lithium. Pretreatment of the neuronal cultures with 1 microM phorbol myristate acetate (PMA) inhibited alpha 1, muscarinic, and glutamate receptor-mediated PI hydrolysis in a time-dependent manner with maximal inhibition observed after a 20-30 min preincubation. The active beta-phorbol didecanoate inhibited stimulated PI hydrolysis, but its stereo-isomer alpha-phorbol didecanoate was without effect at 1 microM. PMA was about 10 times more potent at inhibiting PI hydrolysis stimulated by norepinephrine and glutamate compared to carbachol. The order of potency of the various phorbol esters for inhibition of stimulated PI hydrolysis and the differences between active and inactive stereoisomers suggests that the activation of protein kinase C may mediate the inhibitory effects. Thus, stimulation of neuronal protein kinase C may represent a mechanism for the regulation of agonist-stimulated PI hydrolysis.

Norepinephrine metabolism in neuronal cultures is increased by angiotensin II

In this study we have examined the actions of angiotensin II (ANG II) on catecholamine metabolism in neuronal brain cell cultures prepared from the hypothalamus and brain stem. Neuronal cultures prepared from the brains of 1-day-old Sprague-Dawley rats exhibit specific neuronal uptake mechanisms for both norepinephrine (NE) and dopamine (DA), and also monoamine oxidase (MAO) and catechol O-methyltransferase (COMT) activity. Separate neuronal uptake sites for NE and DA were identified by using specific neuronal uptake inhibitors for each amine. In previous studies, we determined that ANG II (10 nM-1 microM) stimulates increased neuronal [3H]NE uptake by acting at specific receptors. We have confirmed these results here and in addition have shown that ANG II (1 nM-10 microM, 10-120 min) has no significant effects on neuronal [3H]DA uptake. These results suggest that the actions of ANG II are restricted to the NE transporter in neuronal cultures. It is possible that ANG II stimulates the intraneuronal metabolism of at least part of the NE that is taken up, because the peptide stimulates MAO activity, an effect mediated by specific ANG II receptors. ANG II had no effect on COMT activity in neuronal cultures. Therefore, the use of neuronal cultures of hypothalamus and brain stem we have determined that ANG II can specifically alter NE metabolism in these areas, while apparently not altering DA metabolism.

Protein kinase C agonists increase the expression of angiotensin II receptors in neuronal cultures

Previous studies have shown that norepinephrine is important in the regulation of central angiotensin II receptors, an effect mediated by alpha 1-adrenergic receptors. Because alpha 1-adrenergic stimulation leads to inositol phospholipid hydrolysis and activation of protein kinase C, we have examined a possible role of this enzyme in the regulation of central angiotensin II (Ang II) receptors. In the present study, we have examined the effects of protein kinase C activators, phorbol esters, on the expression of Ang II receptors in neuronal cultures prepared from 1-day-old rat brains. The active phorbol ester phorbol-12-myristate-13-acetate (TPA) caused time- and concentration-dependent increases in the specific binding of [125I]Ang II to its receptors in neuronal cultures of normotensive and spontaneously hypertensive rat brains. The stimulatory effect of TPA on Ang II receptors was apparent within 15 min and reached a maximum between 1 and 2 h. Ang II specific binding had returned to control levels by 24 h. Various phorbol esters increased [125I]Ang II binding in accordance with their order of potency in stimulating protein kinase C activity. Saturation and Scatchard analysis revealed that the phorbol ester-induced increase in [125I]Ang II binding was due to an increase in the number of Ang II receptors. These observations indicate that activation of protein kinase C results in an increased expression of Ang II receptors in neuronal cultures from both normotensive and spontaneously hypertensive rat brains. The results suggest a possible role of phosphorylation in Ang II receptor expression in neuronal cultures.