Inositol phospholipid hydrolysis in rat cerebral cortical slices: I. Receptor characterisation

Reflections on 60 years of publication of the Journal of Neurochemistry

This review reflects on the origins, development, publishing trends, and scientific directions of the Journal of Neurochemistry over its 60 year lifespan as seen by key contributors to the Journal's production. The Journal first appeared in May 1956 with just two issues published in that inaugural year. By 1963, it appeared monthly and, by 2002, 24 hard copy issues were published yearly. In 2014, the Journal became online only. For much of its time, the Journal was managed through two separate editorial offices each with their respective Chief Editor (the 'Western' and 'Eastern' hemispheres). The Journal was restructured to operate through a single editorial office and Editor-in-Chief from 2013. Scientifically, the Journal progressed through distinct scientific eras with the first two decades generally centered around developments in methodology followed by a period when publications delved deeper into underlying mechanisms. By the late 1980s, the Journal had entered the age of genetics and beyond, with an increasing focus on neurodegenerative diseases. Reviews have played a regular part in the success of J Neurochem with focused special and virtual issues being a highlight of recent years. Today, 60 years and onwards, J Neurochem continues to be a leading source of top-quality, original and review articles in neuroscience. We look forward to its continued success at the forefront of neurochemistry in the decades to come. This article celebrates 60 years of publication of Journal of Neurochemistry including personal reminiscences from some of the Chief Editors, past and present, as well as input from some of the key contributors to the Journal over this period. We highlight the scientific, technological, and publishing developments along the way, with reference to key papers published in the Journal. The support of the Journal toward the aims and objectives of the International Society for Neurochemistry (ISN) is also emphasized. This article is part of the 60th Anniversary special issue.

Effects of dopamine on phosphoinositide hydrolysis in slices of rat striatum and cortex

Phosphoinositide hydrolysis was studied in slices of rat striatum and frontal cortex which had been incubated with [(3)H]inositol to prelabel the inositol phospholipids. Dopamine (100 ?M to 10 mM) increased phosphoinositide hydrolysis to a maximum of about 200% compared to control in both areas. Noradrenaline (1 ?M to 1 mM) stimulated [(3)H]inositol phosphate formation to about 400% of control. Dopamine-stimulated phosphoinositide hydrolysis was completely blocked by prazosin; while spiperone and SCH 23390 were partial inhibitors. The ability of noradrenaline (5 to 100 ?M) to stimulate phosphoinositide hydrolysis was antagonized by co-incubation with dopamine (1-10 mM). Low concentrations of dopamine (10 nM and 1 ?M) did not affect total [(3)H]inositol phosphate formation, and ion exchange chromatography of the [(3)H]inositol phosphates failed to show any inhibitory effects on the individual fractions (mono-, bis- and tris-phosphates). Ten mM dopamine, on the other hand, increased the production of [(3)H]inositol mono- and bis-phosphates compared to control. It was concluded that dopamine acts as partial ?(1)-agonist in both the rat striatum and frontal cortex. As such, it increased phosphatidylinositol hydrolysis. Dopamine partially inhibited noradrenaline-stimulated phosphatidylinositol hydrolysis, but it did not inhibit basal rates of phosphatidylinositol hydrolysis.

Assay of receptor-stimulated phosphoinositide turnover

The stimulation of phosphoinositide turnover is one of the key means by which receptors evoke responses in target cells and tissues. This is true for both G protein-coupled receptors and receptors that couple via tyrosine kinase activity. The protocols in this unit allow for pharmacological analysis of receptors coupled to phosphoinositide turnover. In general, the [(3)H]myo-inositol prelabeling methodology (described for both tissue slices and cultured cells) is the more widely applicable, since it requires fewer experimental steps and typically gives rise to a better signal-to-noise ratio. Individual inositol phosphates can also be determined as described by chromatographic separation on ion-exchange columns. In some circumstances (for example, when rapid responses to receptor stimulation are to be investigated or when the absolute levels of the active inositol phosphate are to be examined), it is preferable to use the mass assay described here for inositol (1,4,5)-trisphosphate from either tissue slices and cultured cells. This unit also provides support protocols for the preparation of [(3)H]myo-inositol, chromatography columns, tissue slices, and the IP(3)-binding protein.

Selegiline, an MAO-B inhibitor, attenuates airway smooth muscle contraction in the rat trachea

Selegiline is widely used for Parkinson's disease and sometimes for Alzheimer's disease. It is reported to affect intracellular Ca2+ concentration. Since intracellular Ca2+ is partly regulated by phosphatidylinositol (PI) response and is important for smooth muscle contraction, selegiline may affect airway smooth muscle tension. We examined the effects of selegiline on acetylcholine (ACh)- and KCl-induced contractile and PI responses in rat trachea. The trachea was cut into 3-mm-wide ring segments or 1-mm-wide slices. ACh (3 μM, 50% effective dose) or KCl (40mM) was added, and ring relaxation was induced by the addition of selegiline. Tracheal slices were incubated with [3H]myo-inositol and 3 μM ACh in the presence of selegiline, and [3H]inositol monophosphate (IP1) was measured. Selegiline dose-dependently attenuated ACh- and KCl-induced tracheal ring contractions. Fifty-percent inhibitory doses (ID50) of selegiline against ACh- and KCl-induced contraction were 120±30 μM and 80±20 μM, respectively. Basal and ACh-induced IP1 accumulation were 2.20±0.20 Bq and 7.88±0.23 Bq, respectively, and selegiline at a dose of 1000 μM attenuated ACh-induced IP1 accumulation (5.44±0.30 Bq). These results suggest that selegiline inhibits contractile responses through the inhibition of voltage-operated Ca2+ channels and the PI response.

TRPC Channels Mediate a Muscarinic Receptor-Induced Afterdepolarization in Cerebral Cortex

Activation of muscarinic cholinergic receptors on pyramidal cells of the cerebral cortex induces the appearance of a slow afterdepolarization that can sustain autonomous spiking after a brief excitatory stimulus. Accordingly, this phenomenon has been hypothesized to allow for the transient storage of memory traces in neuronal networks. Here we investigated the molecular basis underlying the muscarinic receptor-induced afterdepolarization using molecular biological and electrophysiological strategies. We find that the ability of muscarinic receptors to induce the inward aftercurrent underlying the slow afterdepolarization is inhibited by expression of a Galpha(q-11) dominant negative and is also markedly reduced in a phospholipase C beta1 (PLCbeta1) knock-out mouse. Furthermore, we show, using a genetically encoded biosensor, that activation of muscarinic receptor induces the breakdown of phosphatidylinositol 4,5-bisphosphate in pyramidal cells. These results indicate that the Galpha(q-11)/PLCbeta1 cascade plays a key role in the ability of muscarinic receptors to signal the inward aftercurrent. We have shown previously that the muscarinic afterdepolarization is mediated by a calcium-activated nonselective cation current, suggesting the possible involvement of TRPC channels. We find that expression of a TRPC dominant negative inhibits, and overexpression of wild-type TRPC5 or TRPC6 enhances, the amplitude of the muscarinic receptor-induced inward aftercurrent. Furthermore, we find that coexpression of TRPC5 and T-type calcium channels is sufficient to reconstitute a muscarinic receptor-activated inward aftercurrent in human embryonic kidney HEK-293 cells. These results indicate that TRPC channels mediate the muscarinic receptor-induced slow afterdepolarization seen in pyramidal cells of the cerebral cortex and suggest a possible role for TRPC channels in mnemonic processes.

Effects of amitriptyline, a tricyclic antidepressant, on smooth muscle reactivity in isolated rat trachea

PURPOSE

This study was designed to investigate the action of amitriptyline, a tricyclic antidepressant, on airway smooth muscle reactivity and its underlying mechanisms.

METHODS

In isolated rat trachea, isometric force was recorded to examine the effects of amitriptyline on the contractile response to acetylcholine (ACh), electrical field stimulation (EFS), calyculin A (a myosin light chain phosphatase inhibitor), and sphingosylphosphorylcholine (SPC; a Rhokinase activator). In addition, inositol monophosphate (IP1) accumulation was measured to examine its effects on inositol 1, 4, 5-trisphosphate (IP(3)) production during stimulation with ACh.

RESULTS

Amitriptyline inhibited the contractile responses to ACh, EFS, calyculin A, and SPC, with the concentrations of amitriptyline (mean +/- SD) required to exert 50% inhibition (IC(50)) being 4.3 +/- 1.3 microM, 3.2 +/- 1.6 microM, 256.4 +/- 106.4 microM, and 98.2 +/- 21.8 microM, respectively. In addition, amitriptyline (10 microM) eliminated the ACh (10 microM)-induced IP(1) accumulation.

CONCLUSION

The results suggest that amitriptyline does not influence tracheal smooth muscle reactivity at clinical concentrations (<1 microM), but attenuates the reactivity at supraclinical concentrations (> or =1 microM). The attenuated response to ACh brought about by amitriptyline is presumably due, at least in part, to the inhibition of phosphatidylinositol (PI) metabolism. The ability of amitriptyline to inhibit the calyculin Ainduced contraction suggests that amitriptyline also inhibits the Ca(2+)-calmodulin-myosin light chain pathway independently of the inhibition of PI metabolism. Finally, the difference between the IC(50) values for SPC-induced contraction and those for calyculin A-induced contraction suggests that amitriptyline may also inhibit the Rho-kinase pathway.

High-affinity neurotensin receptor is involved in phosphoinositide turnover increase by inhibition of sodium pump in neonatal rat brain

Phosphoinositide (PI) metabolism is enhanced in neonatal brain by activation of neurotransmitter receptors and by inhibition of the sodium pump with ouabain or endogenous inhibitor termed endobain E. Peptide neurotensin inhibits synaptosomal membrane Na(+), K(+)-ATPase activity, an effect blocked by SR 48692, a selective antagonist for high-affinity neurotensin receptor (NTS1). The purpose of this study was to evaluate potential participation of NTS1 receptor on PI hydrolysis enhancement by sodium pump inhibition. Cerebral cortex miniprisms from neonatal Wistar rats were preloaded with [(3)H]myoinositol in buffer during 60 min and further preincubated for 0 min or 30 min in the absence or presence of SR 48692. Then, ouabain or endobain E were added and incubation proceeded during 20 or 60 min. Reaction was stopped with chloroform/methanol and [(3)H]inositol-phosphates (IPs) accumulation was quantified in the water phase. After 60-min incubation with ouabain, IPs accumulation values reached roughly 500% or 860% in comparison with basal values (100%), if the preincubation was omitted or lasted 30 min, respectively. Values were reduced 50% in the presence of SR 48692. In 20-min incubation experiments, IPs accumulation by ouabain versus basal was 300% or 410% if preincubation was 0 min or 30 min, respectively, an effect blocked 23% or 32% with SR 48692. PI hydrolysis enhancement by endobain E was similarly blocked by SR 48692, being this effect higher when sample incubation with the endogenous inhibitor lasted 60 min versus 20 min. Present results indicate that PI hydrolysis increase by sodium pump inhibition with ouabain or endobain E is partially diminished by SR 48692. It is therefore suggested that NTS1 receptor may be involved in cell signaling system mediated by PI turnover.

High concentrations of landiolol, a beta(1)-adrenoceptor antagonist, stimulate smooth muscle contraction of the rat trachea through the Rho-kinase pathway

PURPOSE

Gradually progressing contraction of airway smooth muscle is suggested to be due to the Rho-kinase signaling pathway. In our preliminary study in rat tracheas, landiolol, a beta(1)-adrenoceptor antagonist, at high doses caused gradually progressing contraction, and this contraction reached a plateau after 20 min. Therefore, this study was carried out to clarify whether landiolol could stimulate the Rho-kinase pathway or the phosphatidylinositol (PI) response in the rat trachea.

METHODS

Seventy-eight male Wistar rats weighing 250-350 g were used for the experiments. Their tracheas were cut into 3-mm-wide ring segments or 1-mm-wide slices. Measurements of isometric tension and [(3)H] inositol monophosphate (IP(1)) production were conducted, using these tracheal rings or slices. Data values are expressed as means +/- SD, and statistical significance (P < 0.05) was determined using analysis of variance (ANOVA).

RESULTS

Landiolol (700 microM)-induced contraction was completely inhibited by fasudil at 30 microM, while the landiolol-induced contraction was not inhibited by 4-diphenylacetoxy-N-methyl-piperidine methobromide (4-DAMP), ketanserin, or nicardipine. Landiolol did not stimulate IP(1) production.

CONCLUSION

These results suggest that high concentrations of landiolol could cause airway smooth muscle contraction through the Rho-kinase pathway, but not through the PI response coupled with muscarinic M(3) receptors, 5-HT receptors or the activation of L-type Ca(2+) channels.

Tandem regulation of phosphoinositide signaling and acute behavioral effects induced by antidepressant agents in rats

RATIONALE

Antidepressants increase synaptic monoamine concentrations, but the subsequent signaling events that produce the beneficial clinical effects remain unclear. Diverse antidepressants increase CDP-diacylglycerol, a crucial step in phosphoinositide signaling. Serotonin 5HT(2) receptors, implicated in depression or the actions of some antidepressants, signal through phosphoinositide hydrolysis. Thus, cross talk between antidepressant-induced CDP-diacylglycerol and 5HT(2) signaling could contribute to the antidepressant mechanism.

OBJECTIVE

The objective of the study was to test the hypotheses that antidepressants enhance net signaling via 5HT(2) receptors by augmenting the supply of phosphoinositide substrates and that this action contributes to the behavioral effects of the drugs.

MATERIALS AND METHODS

Brain slices pre-labeled with [(3)H]inositol in the presence of various antidepressant concentrations were washed and incubated with the 5HT(2) agonist, alpha-methylserotonin, followed by measuring phosphoinositide synthesis and inositol phosphate accumulation. Further, rats administered antidepressants after pretreatment with neomycin to inhibit metabolic utilization of phosphoinositides were behaviorally evaluated in the forced swim test.

RESULTS

Diverse antidepressants significantly enhanced phosphoinositide synthesis. While alpha-methylserotonin increased inositol phosphate accumulation, this effect was significantly accentuated in hippocampal or cortical tissues pre-incubated in the presence of imipramine, desipramine, fluoxetine, paroxetine, or maprotiline. Drug-induced behavioral antidepressant effects were reversed by neomycin pretreatment, whereas neomycin alone did not alter basal immobility times.

CONCLUSIONS

Antidepressants probably exert tandem neurochemical effects by increasing synaptic monoamine concentrations and by producing phosphoinositides used in 5HT(2) receptor signaling. This combination of actions may constitute the mechanism of at least the acute behavioral effects of the drugs and could implicate aberrant neurolipid signaling in the pathophysiology of depression.

Succinylcholine potentiates acetylcholine-induced contractile and phosphatidylinositol responses of rat trachea

PURPOSE

Although succinylcholine (SCh) is often used as a muscle relaxant in electroconvulsive therapy, its influence on airway reactivity has not been fully investigated. We examined the effects of SCh on acetylcholine (ACh)-, carbachol (CCh)-, and electrical field stimulation (EFS)-induced contractions, and on the ACh-induced phosphatidylinositol (PI) response of rat trachea.

METHODS

Thirty-two male Wistar rats weighing 250-350 g were used. The trachea was rapidly isolated and cut into 3-mm-wide rings. The resting tension was adjusted periodically to 1.0 g during the equilibration period. ACh, 1 microM; carbachol (CCh), 0.05 microM; or neither of them, was added, and SCh was then added at 1-300 microM final concentrations, and ring tension was examined. Contractions were elicited by EFS in the presence or absence of 100 microM SCh. Tracheal slices were incubated with [3H] myo-inositol, 1 microM ACh, and various concentrations of SCh. The accumulation of [3H] inositol monophosphate (IP1) was measured.

RESULTS

SCh did not affect the tension by itself without ACh, or with CCh, but SCh potentiated the ACh-induced contraction of rat trachea at concentrations of 10 microM or more (50% effective concentration [EC50]; 43.6 microM). SCh produced a significant increase in the amplitude and duration of EFS-induced contractions. SCh, at concentrations of 10 microM and 100 microM, potentiated ACh-induced IP1 accumulation.

CONCLUSION

SCh potentiated ACh-induced, but not CCh-induced, contractile and PI responses, and enhanced EFS-induced contraction of rat trachea, suggesting that competition for butyrylcholinesterase (BChE) in airway smooth muscle could be involved in the potentiation by SCh of ACh-induced airway smooth muscle contraction.

Phosphoinositide hydrolysis increase by angiotensin-(1–7) in neonatal rat brain

Angiotensin (Ang)-(1-7) is an endogenous peptide hormone of the renin-angiotensin system which exerts diverse biological actions, some of them counterregulate Ang II effects. In the present study potential effect of Ang-(1-7) on phosphoinositide (PI) turnover was evaluated in neonatal rat brain. Cerebral cortex prisms of seven-day-old rats were preloaded with [(3)H]myoinositol, incubated with additions during 30 min and later [(3)H]inositol-phosphates (IPs) accumulation quantified. It was observed that PI hydrolysis enhanced 30% to 60% in the presence of 0.01 nM to 100 nM Ang-(1-7). Neither 10 nM [D-Ala(7)]Ang-(1-7), an Ang-(1-7) specific antagonist, nor 10 nM losartan, an angiotensin II type 1 (AT(1)) receptor antagonist, blocked the effect of 0.1 nM Ang-(1-7) on PI metabolism. The effect of 0.1 nM Ang-(1-7) on PI hydrolysis was not reduced but it was even significantly increased in the simultaneous presence of [D-Ala(7)]Ang-(1-7) or losartan. PI turnover enhancement achieved with 0.1 nM Ang-(1-7) decreased roughly 30% in the presence of 10 nM PD 123319, an angiotensin II type 2 (AT(2)) receptor antagonist. The antagonists alone also enhanced PI turnover. Present findings showing an increase in PI turnover by Ang-(1-7) represent a novel action for this peptide and suggest that it exerts a function in this signaling system in neonatal rat brain, an effect involving, at least partially, angiotensin AT(2) receptors.

Anticholinesterase Drugs Stimulate Smooth Muscle Contraction of the Rat Trachea Through the Rho-Kinase Pathway

We performed this study to determine the effects of Rho-kinase inhibitors, Y-27632 and fasudil, on the anticholinesterase (anti-ChE)-induced contractile and phosphatidylinositol responses of the rat trachea. In vitro measurements of isometric tension and [3H] inositol monophosphate (IP1) that was formed were conducted by using rat tracheal rings or slices. Neostigmine- and pyridostigmine-induced contractions were almost completely inhibited by Y-27632 and fasudil at 30 microM each, whereas acetylcholine-induced contraction was inhibited incompletely, i.e., by 56% by Y-27632 and by 51% by fasudil, at 100 microM for each, respectively. The inhibitory effects of fasudil on neostigmine- and acetylcholine-induced contractions were completely reversed by calyculin-A, a myosin phosphatase inhibitor. Neostigmine-induced IP1 accumulation was attenuated by fasudil at 100 microM. The results suggest that anti-ChEs cause airway smooth muscle contraction, in part, through activation of the Rho-kinase pathway.

G-protein-coupled receptors: past, present and future

The G-protein-coupled receptor (GPCR) family represents the largest and most versatile group of cell surface receptors. Drugs active at these receptors have therapeutic actions across a wide range of human diseases ranging from allergic rhinitis to pain, hypertension and schizophrenia. This review provides a brief historical overview of the properties and signalling characteristics of this important family of receptors.

Effects of (±)-huprine Y and (±)-huprine Z, two new anticholinesterasic drugs, on muscarinic receptors

The cholinergic profile of (+/-)-huprine Y and (+/-)-huprine Z on muscarinic receptors has been determined. Displacement of [3H]-pirenzepine and [3H]-QNB plus pirenzepine was performed in rat hippocampus. Both compounds showed a higher degree of affinity to M1 muscarinic receptors (P < 0.01) than to M2 muscarinic receptors. To determine the M1 agonist or antagonist role of the two huprines, studies of inositol phosphates (IP) production were performed. Both huprines significantly stimulated IP accumulation in a concentration-dependent manner. The reversion of this effect by different antagonists showed that M1 muscarinic receptors were activated by (+/-)-huprine Y and (+/-)-huprine Z, but some other mechanisms, such as alpha1-adrenoceptors or nicotinic receptors, were involved.

High-affinity neurotensin receptor is involved in phosphoinositide hydrolysis stimulation by carbachol in neonatal rat brain

Ontogenetic studies indicate that inositol phosphate accumulation in rodent brain tissue by cholinergic muscarinic agonists as well as expression of high-affinity neurotensin receptor (NTS1) peak at 7 days after birth. Herein, potential participation of this receptor in such effect was investigated. Cerebral cortex prisms of 7-day-old rats were preloaded with [3H]myoinositol and later incubated during 60 or 20 min in the presence of muscarinic agonist carbachol plus neurotensin and SR 48692, a non-peptide NTS1 antagonist. In 60-min incubation experiments, inositol phosphate accumulation by 10(-3) M carbachol was roughly 320%, an effect which remained unaltered plus 10(-6) M to 10(-4) M neurotensin but partially decreased with equimolar SR 48692 concentration. In 20-min incubation experiments, inositol phosphate accumulation by 10(-3) M carbachol was circa 240%, a value which attained 320-360% plus 10(-7) M neurotensin; this effect was totally blocked by 10(-7) M SR 48692. It was concluded that in inositol phosphate accumulation by carbachol, besides the cholinergic muscarinic receptor, the NTS1 receptor is likewise involved; findings at 60 min are attributable to the effect of endogenous neurotensin whereas those at 20 min most likely involve both endogenous and exogenously added peptide.

Noradrenergic regulation of prolactin secretion at the level of the paraventricular nucleus of the hypothalamus: functional significance of the alpha-1b and beta-adrenergic receptor subtypes

Previous research has demonstrated that in the Siberian hamster, both photoperiod and estrous cyclicity alter the profile of noradrenergic activity with the paraventricular nucleus of the hypothalamus (PVN), and that noradrenergic activity is correlated with changes in circulating levels of prolactin. Work from our laboratory has demonstrated an inhibitory role for norepinephrine (NE) acting at the alpha-2 receptor subtype within the PVN on serum prolactin levels; however, the functional significance of other adrenergic receptor subtypes on this system is unknown. The purpose of this study was to investigate the functional significance of the alpha-1b and beta-adrenergic receptor subtypes at the level of the PVN on circulating levels of prolactin. These experiments were performed in male Siberian hamsters using reverse microdialysis coupled with serial blood sampling. In Experiment 1, infusion of l-phenylephrine hydrochloride (alpha-1b agonist) initiated a dose-dependent increase in circulating prolactin, whereas infusion of chloroethylclonidine (alpha-1b antagonist) induced a significant dose-dependent decline in prolactin. In Experiment 2, intraparaventricular administration of propranolol (beta antagonist) initiated a significant increase in prolactin levels in a dose-dependent manner, whereas isoproterenol (beta agonist) induced a dose-dependent decline in prolactin. The results of this study indicate that both the alpha-1b and beta-adrenergic receptor subtypes have a significant role in regulating circulating levels of prolactin at the level of the PVN in the Siberian hamster.

Pharmacological characteristics of Ro 115-1240, a selective alpha1A/1L-adrenoceptor partial agonist: a potential therapy for stress urinary incontinence

OBJECTIVE

To describe the preclinical pharmacology of Ro 115-1240, a peripherally acting selective alpha1A/1L-adrenoceptor (AR) partial agonist, compared with the alpha1A/1L-AR full agonist amidephrine, as AR agonists have some utility in the treatment of stress urinary incontinence (SUI) but are limited by undesirable cardiovascular and central nervous system side-effects.

RESULTS

In radioligand-binding studies Ro 115-1240 had greater affinity for alpha1A than for alpha1B and alpha1D subtypes. The potency and intrinsic activity of amidephrine and Ro 115-1240 relative to noradrenaline were determined in native and cell-based assays using human recombinant alpha1-ARs; they acted as selective alpha1A/1L-AR full and partial agonists, respectively. In anaesthetized micropigs and rabbits, amidephrine and Ro 115-1240 produced non-selective, dose-dependent increases in intraurethral and arterial blood pressures but the magnitude of the pressure increases evoked by Ro 115-1240 were about a third of those with amidephrine. In conscious micropigs both agents produced dose-dependent increases in urethral tension. Again, the magnitude of the urethral response to Ro 115-1240 was about a third of that with amidephrine. More importantly, only amidephrine produced dose-dependent increases in blood pressure and decreases in heart rate. Ro 115-1240 produced a maximum increase in urethral tension with no effect on blood pressure or heart rate.

CONCLUSION

These results show that by combining selectivity for the alpha1A/1L-AR subtype with a reduction in intrinsic agonist efficacy, Ro 115-1240 has reduced haemodynamic effects while retaining to some degree the contractile effects on urethral smooth muscle. These studies indicate that Ro 115-1240 may be useful as a novel treatment for SUI.

Chronic methamphetamine administration reduces histamine-stimulated phosphoinositide hydrolysis in mouse frontal cortex

In the present study, it was hypothesized that in vivo pretreatment with repeated methamphetamine would alter the agonist-stimulated phosphoinositide hydrolysis in mouse frontal cortical slices. Male ICR mice that received the methamphetamine injection (1.0mg/kg, intraperitoneally) once a day for five consecutive days showed behavioral sensitization to the same dose of methamphetamine 5 days after the last injection of the initial chronic treatment regimen (test day 10). On test day 10, the reduction of histamine (0.1-1.0mM)-stimulated phosphoinositide hydrolysis in the mouse frontal cortex was observed. The reduction was specific to histamine, but not to norepinephrine (10 microM-0.1mM) or L-glutamate (0.1-0.5mM). The reduction occurred without any change in the expression level of histamine H(1) receptor mRNA. The reduction recovered 25 days after the last injection of the initial chronic treatment regimen (test day 30). The direct application to the slices of a pharmacologically effective concentration of methamphetamine in vitro (10 microM) did not alter the histamine signal transduction. The present results suggest that the reduction is probably one of neuroadaptations in the frontal cortex contributing to behavioral sensitization.

Metabotropic glutamate receptor involvement in phosphoinositide hydrolysis stimulation by an endogenous Na(+), K(+)-ATPase inhibitor and ouabain in neonatal rat brain

The mechanism of action of an endogenous Na(+), K(+)-ATPase inhibitor, termed endobain E, on phosphoinositide hydrolysis was studied in neonatal rat brain cortex and compared with that of ouabain. Lack of additivity for endobain E and glutamate paired stimulation on inositol phosphates accumulation suggested that they share at least a common step on inositol phosphate metabolism, as previously advanced for ouabain. In addition, Cd(2+) sensitivity of endobain E and ouabain effects strengthened the involvement of glutamate receptors. The participation of ionotropic glutamate receptors on endobain E- and ouabain-induced phosphoinositide hydrolysis seems untenable, since antagonists dizocilpine and CNQX proved unable to inhibit these effects. However, the endobain E effect was blocked by 2 x 10 (-4) M L-AP3 (an antagonist for group I mGluRs) when at least a 15-min preincubation protocol was employed. Maximal inhibition of endobain E effect (42%) occurred when L-AP3 preincubation was extended to 60 min, as already shown with glutamate, but only a trend to decrease was recorded with ouabain. At variance, the ouabain effect was reduced to 50% employing 5 x 10 (-4) M MCPG (a competitive antagonist for group I mGluRs), whereas no blockade was observed with endobain E or glutamate. In addition, MPEP (a selective mGluR5 antagonist) partially reduced ouabain, endobain E and glutamate responses and the selective mGluR1 antagonist LY367385 showed no activity at all. To sum up, the present findings support the involvement of mGluR5 in both endobain E and ouabain phosphoinositide hydrolysis stimulation in neonatal rat brain, in spite of dissimilar response to tested antagonists.

Long-term Activation of Phosphoinositide Turnover Associated with Increased Release of Amino Acids in the Dentate Gyrus and Hippocampus Following Classical Conditioning in the Rat

The release of amino acids and the hydrolysis of inositol phospholipids were examined in parallel in three hippocampal areas following classical conditioning. Paired or unpaired tone(CS) - shock(US) presentations were given to animals engaged in a previously acquired food-motivated lever-pressing task. Conditioned suppression of lever-pressing was the behavioural measure of conditioning. Twenty-four hours after the last conditioning session, the dentate gyrus and areas CA3 and CA1 of the hippocampus were removed bilaterally from conditioned and pseudoconditioned animals, and slices cut and stored in liquid nitrogen for subsequent analysis. Crude synaptosomal pellets were prepared to investigate: (i) potassium-stimulated release of preloaded [3H]glutamate and [14C]aspartate in the presence and absence of extracellular Ca2+; (ii) [3H]inositol labelling of phosphoinositides and inositol phosphates; and (iii) [14C]arachidonic acid labelling of 1,2-diacylglycerol (1,2-DG). Potassium-stimulated, Ca2+-dependent release of [3H]glutamate in synaptosomes prepared from the dentate gyrus and area CA3 was significantly greater in conditioned animals than in pseudoconditioned animals. In area CA1, K+-stimulated, Ca2+-dependent release of [14C]aspartate was significantly increased in conditioned animals. These results confirm in synaptosomes, and extend to a period of 24 h our previous report of an increased release of transmitter in the dentate gyrus and hippocampus associated with classical conditioning. In parallel with the increased release of amino acids, learning was associated with a significant increase in labelling of phosphoinositides and inositol phosphates by [3H]inositol and a significant increase in labelling of 1,2-DG by [14C]arachidonic acid in the three hippocampal areas examined. It is suggested that a long-lasting presynaptic activation of inositol lipid metabolism may contribute to the learning-dependent increase in the capacity of hippocampal terminals to release transmitter and hence to the maintenance of a neurochemical trace which may, at least in part, underlie lasting changes in synaptic function built up during associative learning.

Time-related Changes in Basal Phosphoinositide Turnover after Induction of Long-term Potentiation in the Dentate Gyrus are Blocked by Commissural Stimulation

We have examined basal phosphoinositide turnover in synaptosomes obtained from the dentate gyrus of anaesthetized rats in which long-term potentiation was induced unilaterally in perforant path-granule cell synapses. Relative to the unpotentiated side, [3H]myo-inositol labelling of inositol phosphates was significantly enhanced 45 min and 3 h after induction of long-term potentiation, but reduced after 2.5 min. Similarly, [14C]arachidonic acid labelling of 1,2-diacylglycerol was increased 45 min and 3 h after induction of long-term potentiation, but reduced after 2.5 min. In a second series of experiments, induction of long-term potentiation was blocked by stimulation of the commissural projection to granule cells. In synaptosomes prepared from this tissue, there was no difference in phosphoinositide turnover between tetanized and control sides at any of the three post-tetanic intervals. We conclude that in the dentate gyrus, long-term potentiation is associated with an increase in phosphoinositide turnover which is established between 2.5 min and 45 min post-tetanus and which persists for at least 3 h.

Stimulatory effects of pituitary adenylate cyclase-activating polypeptide on inositol phosphates accumulation in avian cerebral cortex and hypothalamus

This study has demonstrated that the short and long form of the pituitary adenylate cyclase-activating polypeptide (PACAP), i.e. PACAP(27) and PACAP(38), moderately but significantly, and in a concentration (0.5-5 microM)-dependent manner, stimulated inositol phosphates (IPs) accumulation in myo-[(3)H]inositol-prelabeled cerebral cortical and hypothalamal slices of chick and duck, and in slices of rat cerebral cortex; both peptides had no effect on IPs formation in rat hypothalamus. Vasoactive intestinal peptide (VIP; 0.5-5 microM) weakly enhanced IPs accumulation in chick hypothalamus, had no significant action in chick cerebral cortex (in fact there was a tendency to attenuate the IPs response in this tissue), and slightly, but significantly, inhibited the IPs accumulation in rat cerebral cortex. VIP showed no activity in rat hypothalamus. It is concluded that the stimulatory action of PACAP on phosphoinositide metabolism in avian cerebral cortex, similar to rat cerebral cortex, is mediated via phospholipase C-linked PAC(1) type receptors. In chick hypothalamus, however, there may be a component of VPAC type receptors stimulating IPs formation.

Pharmacological properties and SAR of new 1,4-disubstituted piperazine derivatives with hypnotic-sedative activity

Preparation, pharmacological properties and structure-activity relationships of new pyrimidyl-piperazine derivatives, exhibiting sedative and hypnotic activity in mice, are reported. The hypnotic activity of the compounds was comparable with that of zopiclone (the known hypnotic-sedative agent), their interaction with ethanol, however, being much lower. The obtained results suggested that zopiclone and pyrimidylpiperazines 2, 4 and 5 exerted their pharmacological activity through a different mechanism - zopiclone through the interaction with benzodiazepine receptors and compounds 2, 4 and 5 through an unidentified molecular target. The pharmacological properties of compound 3 could be the result of a mixed mechanism of action, combining the properties of zopiclone and those of compounds 2, 4 and 5. A common feature of zopiclone and compounds 2 and 3 was that, after their systemic administration, independently of mechanism of action, together with the hypnotic effect a reduction of the 5-HT turnover in the mouse brain was observed. Minimum structural requirements for the hypnotic activity were formulated. Structural considerations have shown that removing the alpha-carbonyl group did not influence the drug's ability to inhibit the locomotor activity. However, it did influence its ability to disturb motor coordination or abolish the righting reflex within non-lethal doses.

An endogenous Na+, K+-ATPase inhibitor enhances phosphoinositide hydrolysis in neonatal but not in adult rat brain cortex

The effect of an endogenous Na+, K+-ATPase inhibitor, termed endobain E, on phosphoinositide hydrolysis was studied in rat brain cortical prisms and compared with that of ouabain. As already shown for ouabain, a transient effect was obtained with endobain E; maximal accumulation of inositol phosphates induced by endobain E was 604 +/- 138% and 186 +/- 48% of basal values in neonatal and adult rats, respectively. The concentration-response plot for the interaction between endobain E and phosphoinositide turnover differed from that of ouabain, thus suggesting the involvement of distinct mechanisms. In the presence of endobain E plus ouabain at saturating concentrations, no additive effect was recorded, suggesting that both substances share at least a common step in their activation mechanism of inositol phosphates metabolism or that they enhance phosphatidylinositol 4,5-biphosphate breakdown from the same membrane precursor pool, until its exhaustion. Experiments with benzamil, a potent blocker of Na+/Ca2+ exchanger, showed that it partially and dose-dependently inhibited endobain E effect. These results indicate that the endogenous Na+, K+-ATPase inhibitor endobain E, like ouabain, is able to stimulate phosphoinositide turnover transiently during postnatal brain development.

Clonidine attenuates the carbachol-induced contractile and phosphatidylinositol responses of rat trachea

Although clonidine is known to affect vascular smooth muscle, its effects on airway smooth muscle are not fully understood. This study was designed to examine the effects of clonidine on carbachol-induced contractile and phosphatidylinositol responses of rat trachea. Clonidine, at a dose of 100 microM or greater, attenuated carbachol-induced contraction and the accumulation of carbachol-induced inositol monophosphate (IP1). Clonidine also attenuated the accumulation of aluminium fluoride-induced IP1. The concentration-effect relationship of IP1 accumulation was similar to that of carbachol-induced contraction; r = 0.797, P < 0.001. These results suggest that clonidine attenuates contractile responses, at least in part, through the inhibition of phospholipase C (coupled with G-proteins) in phosphatidylinositol responses.

The effects of the peptide-coupling agent, EEDQ, on 5-HT2A receptor binding and function in rat frontal cortex

This ex vivo study in rat frontal cortex determined the influence of 5-HT receptor agonists and antagonists on EEDQ-induced depletion of 5-HT2A binding sites and reduction in their functional coupling to phospholipid hydrolysis. Twenty-four hours after EEDQ (6 mg/kg) administration a marked reduction (66%) of cortical 5-HT2A binding sites with no change in binding affinity was observed. The 5HT2A antagonists ritanserin (1 mg/kg), ketanserin (1 and 5 mg/kg), metergoline (3 mg/kg) or the 5HT2A agonist, DOI (3 and 10 mg/kg) also significantly reduced (by 15-44%) these binding sites 24 h after injection. Thirty minute pretreatment with ritanserin, ketanserin, metergoline or DOI (at the doses above) afforded 49-65% protection against the loss of 5-HT2A binding sites induced by EEDQ (6 mg/kg). DOI (10 mg/kg) pretreatment (-24 h) decreased by 26% the accumulation of [3H]inositol phosphates (IPs) evoked by 5-HT (100 microM), but did not affect that produced by DOI (100 microM). Ketanserin (5 mg/kg, -24 h) decreased 5-HT- and DOI-induced IP formation by 65% and 53%, respectively. The EEDQ (6 mg/kg, -24 h)-evoked reductions (-50%) of 5-HT- and DOI-induced IP formation were not altered by DOI (10 mg/kg) or ketanserin (5 mg/kg) given 30 min before EEDQ. G-protein-stimulated IP accumulation was unaffected by EEDQ (6 mg/kg). Overall, EEDQ reduces 5-HT2A binding sites and function in rat frontal cortex, whereas its effects on binding were attenuated by various 5-HT receptor antagonists and agonists, its effects on function was unaltered by these drugs.

Comparative pharmacology of recombinant human M3 and M5 muscarinic receptors expressed in CHO-K1 cells

1. Affinity estimates were obtained for several muscarinic antagonists against carbachol-stimulated [3H]-inositol phosphates accumulation in Chinese hamster ovary (CHO-KI) cells stably expressing either human muscarinic M3 or M5 receptor subtypes. The rationale for these studies was to generate a functional antagonist affinity profile for the M5 receptor subtype and compare this with that of the M3 receptor, in order to identify compounds which discriminate between these two subtypes. 2. The rank order of antagonist apparent affinities (pK(B)) at the muscarinic M5 receptor was atropine (8.7) > or =tolterodine (8.6) = 4-diphenylacetoxy-N-methylpiperidine (4-DAMP, 8.6)> darifenacin (7.7) > or =zamifenacin (7.6)>oxybutynin (6.6)= para-fluorohexahydrosiladifenidol (p-F-HHSiD, 6.6)>pirenzepine (6.4) > or = methoctramine (6.3)=himbacine (6.3)>AQ-RA 741 (6.1). 3. Antagonist apparent affinities for both receptor subtypes compare well with published binding affinity estimates. No antagonist displayed greater selectivity for the muscarinic M5 subtype over the M3 subtype, but himbacine, AQ-RA 741, p-F-HHSiD, darifenacin and oxybutynin displayed between 9- and 60 fold greater selectivity for the muscarinic M3 over the M5 subtype. 4. This study highlights the similarity in pharmacological profiles of M3 and M5 receptor subtypes and identifies five antagonists that may represent useful tools for discriminating between these two subtypes. Collectively, these data show that in the absence of a high affinity M5 selective antagonist, affinity data for a large range of antagonists is critical to define operationally the M5 receptor subtype.

In vitro alpha1-adrenoceptor pharmacology of Ro 70-0004 and RS-100329, novel alpha1A-adrenoceptor selective antagonists

It has been hypothesized that in patients with benign prostatic hyperplasia, selective antagonism of the alpha1A-adrenoceptor-mediated contraction of lower urinary tract tissues may, via a selective relief of outlet obstruction, lead to an improvement in symptoms. The present study describes the alpha1-adrenoceptor (alpha1-AR) subtype selectivities of two novel alpha1-AR antagonists, Ro 70-0004 (aka RS-100975) and a structurally-related compound RS-100329, and compares them with those of prazosin and tamsulosin. Radioligand binding and second-messenger studies in intact CHO-K1 cells expressing human cloned alpha1A-, alpha1B- and alpha1D-AR showed nanomolar affinity and significant alpha1A-AR subtype selectivity for both Ro 70-0004 (pKi 8.9: 60 and 50 fold selectivity) and RS-100329 (pKi 9.6: 126 and 50 fold selectivity) over the alpha1B- and alpha1D-AR subtypes respectively. In contrast, prazosin and tamsulosin showed little subtype selectivity. Noradrenaline-induced contractions of human lower urinary tract (LUT) tissues or rabbit bladder neck were competitively antagonized by Ro 70-0004 (pA2 8.8 and 8.9), RS-100329 (pA2 9.2 and 9.2), tamsulosin (pA2 10.4 and 9.8) and prazosin (pA2 8.7 and 8.3 respectively). Affinity estimates for tamsulosin and prazosin in antagonizing alpha1-AR-mediated contractions of human renal artery (HRA) and rat aorta (RA) were similar to those observed in LUT tissues, whereas Ro 70-0004 and RS-100329 were approximately 100 fold less potent (pA2 values of 6.8/6.8 and 7.3/7.9 in HRA/RA respectively). The alpha1A-AR subtype selectivity of Ro 70-0004 and RS-100329, demonstrated in both cloned and native systems, should allow for an evaluation of the clinical utility of a 'uroselective' agent for the treatment of symptoms associated with benign prostatic hyperplasia.

Human cloned alpha1A-adrenoceptor isoforms display alpha1L-adrenoceptor pharmacology in functional studies

The recombinant alpha1A-adrenoceptor displays a distinct pharmacological profile ('classical alpha1A-adrenoceptor') in homogenate binding assays, but displays the properties of the so-called alpha1L-adrenoceptor in functional studies in whole cells at 37 degrees C. As three splice variants of the human alpha1A-adrenoceptor have been described previously (alpha1A-1, alpha1A-2 and alpha1A-3), we have compared their functional pharmacological profiles, when expressed stably in Chinese hamster ovary (CHO-K1) cells (antagonist inhibition of noradrenaline-stimulated [3H]inositol phosphates accumulation). A fourth, novel isoform (alpha1A-4) has also been studied: alpha1A-4 mRNA predominates in several human tissues including prostate, liver, heart and bladder. In homogenate binding studies, all four isoforms displayed essentially identical affinity profiles, with prazosin (1-(4-amino-6,7-dimethoxy-2-quinazolinyl)-4-(2-furoyl)piperazine), tamsulosin (5-[2-[[2-(2-ethoxyphenoxy)ethyl]-amino]propyl]-2-methoxybenzen esulfonamide), RS-17053 (N-[2-(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro-alpha,alphad imethyl-1H-indole-3-ethanamine hydrochloride), WB 4101 ((2,6-dimethoxyphenoxyethyl)aminomethyl-1,4-benzodioxane hydrochloride) and 5-Me-urapidil (5-methyl-6[[3-[4-(2-methoxyphenyl)-1-piperazinyl]propyl]amino]-1,3-d imethyuracil) all displaying subnanomolar affinities. In functional studies, noradrenaline accelerated [3H]inositol phosphates production with potencies (p[A]50) of between 5.8 and 6.6. The affinities of prazosin, RS-17053, WB 4101 and 5-Me-urapidil, at antagonizing responses to noradrenaline, were reduced by approximately 10-fold (cf. binding data), while those for tamsulosin and indoramin (N-[1-[2-(1H-indol-3-yl)ethyl]-4-piperidinyl]benzamide) remained constant or increased, consistent with the previously described alpha1L-adrenoceptor. Thus, all four human recombinant alpha1A-adrenoceptor isoforms display the pharmacology of the alpha1L-adrenoceptor when studied in functional assays, consistent with the hypothesis that the putative alpha1L-adrenoceptor represents a functional phenotype of the alpha1A-adrenoceptor.

Inhibition of receptor-mediated calcium responses by corticotrophin-releasing hormone in the CATH.a cell line

A region of the brain believed to be important in the CNS response to stress is the locus coeruleus, the predominant site of noradrenergic cell bodies. Corticotrophin releasing hormone (CRH) is the primary hypothalamic releasing hormone responsible for the activation of the pituitary-adrenal axis in response to stress and, in this study, we employed a locus coeruleus-like cell line, CATH.a, to investigate the modulation of receptor signalling pathways by CRH. Pituitary adenylyl cyclase-activating polypeptide (PACAP) (10 nM), vasoactive intestinal peptide (VIP) (1 microM) and carbachol (1 mM) produced transient increases in intracellular [Ca2+]. The inhibition of the carbachol (1 mM) response by CRH was concentration-dependent (EC50 = 154 +/- 1.8 nM). Calcium responses to sub-maximally effective concentrations of PACAP (5 nM), VIP (400 nM) and carbachol (1 mM) were abolished by prior exposure to CRH (1 microM). At the concentrations employed, CRH and VIP both substantially increased intracellular [3H]-cyclic AMP accumulation. The adenylyl cyclase activator forskolin (10 microM) was also effective at eliminating the agonist-induced calcium responses. Incubation with the cell permeant cyclic AMP analogue dibutyryl cyclic AMP (dbcAMP) (1 mM), an activator of protein kinase A (PKA), for 12 min prior to agonist exposure similarly abolished the intracellular calcium response to carbachol. Carbachol increased [3H]-inositol phosphate ([3H]-IP) accumulation to a maximum of 2.4 +/- 0.11-fold basal (EC50 = 6.75 +/- 0.26 microM). PACAP produced a much greater accumulation (19.9 +/- 2.1 fold basal; EC50 = 24 nM). In the presence of forskolin (10 microM), neither carbachol- nor PACAP-induced [3H]-IP accumulation was significantly different from in its absence. These results demonstrate that CRH inhibits receptor-mediated intracellular calcium responses in a locus coeruleus-like cell line possibly via activation of PKA. This modulation could be important in controlling neuronal function in vivo in stressful situations in which the levels of CRH are increased in the locus coeruleus.

Contractile and phosphatidylinositol responses of rat trachea to anticholinesterase drugs

PURPOSE

Some anticholinesterases (anti-ChE) such as neostigmine and pyridostigmine but not edrophonium, stimulate phosphatidylinositol (PI) response. Although a direct relationship was suggested between the increase in PI response and airway smooth muscle contraction, there are no data regarding the effects of anti-ChE drugs on airway smooth muscle. Thus, we examined the contractile properties and PI responses produced by anti-ChE drugs.

METHODS

Contractile response. Rat tracheal ring was suspended between two stainless hooks in Krebs-Henseleit (K-H) solution. (1) Carbachol (CCh), anti-ChE drugs (neostigmine, pyridostigmine, edrophonium) or DMPP (a selective ganglionic nicotinic agonist) were added to induce active contraction. (2) The effects of 4-diphenylacetoxy-N-methyl-piperidine methobromide (4-DAMP), an M3 muscarinic receptor antagonist, on neostigmine- or pyridostigmine-induced contraction of rat tracheal ring were examined. (3) Tetrodotoxin (TTX) was tested on the anti-ChE drugs-induced responses. PI response. The tracheal slices were incubated in K-H solution containing LiCl and 3[H]myo-inositol in the presence of neostigmine or pyridostigmine with or without 4-DAMP, an M3 muscarinic receptor antagonist. 3[H]inositol monophosphate (IP1) formed was counted with a liquid scintillation counter.

RESULTS

Carbachol (0.1 microM), neostigmine (1 microM), pyridostigmine (10 microM) but not edrophonium or DMPP, caused tracheal ring contraction. 4-DAMP, but not tetrodotoxin, inhibited neostigmine and pyridostigmine-induced contraction. Neostigmine- or pyridostigmine-induced IP1, accumulation was inhibited by 4-DAMP.

CONCLUSIONS

The data suggest that anti-ChE drugs activate the M3 receptors at the tracheal effector site.

Characterization of prostanoid receptor-evoked responses in rat sensory neurones

1. Prostanoid receptor-mediated sensitization, or excitation, of sensory nerve fibres contributes to the generation of hyperalgesia. To characterize the prostanoid receptors present on sensory neurones, biochemical assays were performed on primary cultures of adult rat dorsal root ganglia (DRG) and the F-11 (embryonic rat DRG x neuroblastoma hybrid) cell line. 2. In DRG cultures, the IP receptor agonists, cicaprost and carbaprostacyclin (cPGI2) stimulated cyclic AMP accumulation. Prostaglandin E2 (PGE2) also increased cyclic AMP levels, but to a lesser extent, while carbocyclic thromboxane A2 (cTxA2), PGD2 and PGF2alpha had negligible effects. The rank order of agonist potency was cicaprost>PGE2=BMY45778=cPGI2=PGI2. In the F-11 cells, the rank order of agonist potency for the stimulation of cyclic AMP accumulation was: cicaprost>iloprost=cPGI2=PGI2=BMY45778>PGE2=cTXA2++ +. In DRG cultures, cicaprost induced significantly more accumulation of inositol phosphates than PGE2. 3. To examine the effects of prostanoids on C-fibre activity, extracellular recordings of d.c. potentials from the rat isolated vagus nerve were made with the 'grease-gap' technique. PGI2 (0.1 nM-10 microM) produced the largest depolarizations of the nerve. The rank order of agonist potency was: PGI2=cPGI2=PGE1>cTXA2>PGE2=PGD2=TXB2>PGF2alpha. 4. Prior depolarization of nerves with either forskolin (10 microM) or phorbol dibutyrate (1 microM) alone significantly reduced the response to PGI2 (10 microM), while simultaneous application of both forskolin and phorbol dibutyrate attenuated PGI2 responses almost completely. 5. Putative EP1 and/or TP receptor-selective antagonists had no effect on the responses to PGI2, cPGI2 or PGE2 in the three preparations studied. 6. Collectively, these data are consistent with a positive coupling of IP receptors to both adenylyl cyclase and phospholipase C in sensory neurones. These findings suggest that IP receptors play a major role in the sensitization of rat sensory neurones.

Adenosine A1 receptor activation inhibits basal accumulation of inositol phosphates in rat hippocampus

The ability of the adenosine A1 receptor selective agonist, N6-cyclopentyladenosine, to modify basal accumulation of inositol phosphates in rat hippocampal slices, was investigated. Cyclopentyladenosine (10-300 nM) inhibited the basal accumulation of total [3H]inositol phosphates, with an EC50 of 10 nM and an Emax of 24%. This effect of cyclopentyladenosine was prevented by the adenosine A1 receptor selective antagonist, 1,3-dipropyl-8-cyclopentylxanthine (30 nM). Cyclopentyladenosine (100 nM) also inhibited histamine (300 nM)-stimulated accumulation of [3H]inositol phosphates, this effect being quantitatively similar to that observed on basal [3H]inositol phosphates accumulation. The results suggest that adenosine A1 receptor activation is able, per se, to inhibit the formation of phosphatidylinositol-derived second messengers in hippocampus.

Molecular cloning, genomic characterization and expression of novel human alpha1A-adrenoceptor isoforms

We have isolated and characterized from human prostate novel splice variants of the human alpha1A-adrenoceptor, several of which generate truncated products and one isoform, alpha(1A-4), which has the identical splice site as the three previously described isoforms. Long-PCR on human genomic DNA showed that the alpha(1A-4) exon is located between those encoding the alpha(1A-1) and alpha(1A-3) variants. CHO-K1 cells stably expressing alpha(1A-4) showed ligand binding properties similar to those of the other functional isoforms as well as agonist-stimulated inositol phosphate accumulation. Quantitative PCR analyses revealed that alpha(1A-4) is the most abundant isoform expressed in the prostate with high levels also detected in liver and heart.

Disruption of the m1 receptor gene ablates muscarinic receptor-dependent M current regulation and seizure activity in mice

Muscarinic acetylcholine receptors are members of the G protein-coupled receptor superfamily expressed in neurons, cardiomyocytes, smooth muscle, and a variety of epithelia. Five subtypes of muscarinic acetylcholine receptors have been discovered by molecular cloning, but their pharmacological similarities and frequent colocalization make it difficult to assign functional roles for individual subtypes in specific neuronal responses. We have used gene targeting by homologous recombination in embryonic stem cells to produce mice lacking the m1 receptor. These mice show no obvious behavioral or histological defects, and the m2, m3, and m4 receptors continue to be expressed in brain with no evidence of compensatory induction. However, the robust suppression of the M-current potassium channel activity evoked by muscarinic agonists in sympathetic ganglion neurons is completely lost in m1 mutant mice. In addition, both homozygous and heterozygous mutant mice are highly resistant to the seizures produced by systemic administration of the muscarinic agonist pilocarpine. Thus, the m1 receptor subtype mediates M current modulation in sympathetic neurons and induction of seizure activity in the pilocarpine model of epilepsy.

Disruption of the m1 receptor gene ablates muscarinic receptor-dependent M current regulation and seizure activity in mice

Muscarinic acetylcholine receptors are members of the G protein-coupled receptor superfamily expressed in neurons, cardiomyocytes, smooth muscle, and a variety of epithelia. Five subtypes of muscarinic acetylcholine receptors have been discovered by molecular cloning, but their pharmacological similarities and frequent colocalization make it difficult to assign functional roles for individual subtypes in specific neuronal responses. We have used gene targeting by homologous recombination in embryonic stem cells to produce mice lacking the m1 receptor. These mice show no obvious behavioral or histological defects, and the m2, m3, and m4 receptors continue to be expressed in brain with no evidence of compensatory induction. However, the robust suppression of the M-current potassium channel activity evoked by muscarinic agonists in sympathetic ganglion neurons is completely lost in m1 mutant mice. In addition, both homozygous and heterozygous mutant mice are highly resistant to the seizures produced by systemic administration of the muscarinic agonist pilocarpine. Thus, the m1 receptor subtype mediates M current modulation in sympathetic neurons and induction of seizure activity in the pilocarpine model of epilepsy.

Transient global brain hypoxia-ischemia in adult rats: neuronal damage, glial proliferation, and alterations in inositol phospholipid hydrolysis

A model of ischemic-hypoxic brain injury which combines bilateral occlusion of common carotid arteries for 10 min and mild hypoxia (15% O2 for 10 min before and during occlusion) was developed. Global ischemia was assessed by a simplified EEG recording indicating isoelectric line, i.e. full arrest of cortical electrical activity. Histological examination of brain 7 days after ischemic insult showed from moderate to severe damage, mainly in the cerebral cortex (layers III, V and VI) and hippocampus (mainly CA1 subfield). The injury consisted of neuronal degeneration and necrosis with nuclear pyknosis and karyorrhexis. Immunohistochemical staining for gliofibrillar acidic protein showed a marked glial proliferation in the cerebral cortex and hippocampus. In the cortical slices, inositol phosphates accumulation stimulated by excitatory amino acid agonists (ACPD, ibotenate and quisqualate), as well as by norepinephrine and carbachol, was enhanced significantly (p < 0.01) with respect to sham-operated rats 7 days, but not 24 h, after the ischemic insult. The overall data show that the relatively simple transient brain hypoxia/ischemia rat model produces full arrest of cortical EEG, histopathological alterations and those relative to post-receptor neurochemical mechanisms characteristic of four-vessel occlusion model.

Pharmacological pleiotropism of the human recombinant alpha1A-adrenoceptor: implications for alpha1-adrenoceptor classification

1. Three fully-defined alpha1-adrenoceptors (alpha1A, alpha1B and alpha1D) have been established in pharmacological and molecular studies. A fourth alpha1-adrenoceptor, the putative alpha1L-adrenoceptor, has been defined in functional but not molecular studies, and has been proposed to mediate contraction of human lower urinary tract tissues; its relationship to the three fully characterized alpha1-adrenoceptors is not known. 2. In the present study, binding affinities were estimated by displacement of [3H]-prazosin in membrane homogenates of Chinese hamster ovary (CHO-K1) cells stably expressing the human alpha1A-, alpha1B- and alpha1D-adrenoceptors and were compared with affinity estimates obtained functionally in identical cells by measuring inhibition of noradrenaline (NA)-stimulated accumulation of [3H]-inositol phosphates. 3. For the alpha1A-adrenoceptor, binding studies revealed a pharmacological profile typical for the classically defined alpha1A-adrenoceptor, such that prazosin, RS-17053, WB 4101, 5-methylurapidil, Rec 15/2739 and S-niguldipine all displayed subnanomolar affinity. A different profile of affinity estimates was obtained in inositol phosphates accumulation studies: prazosin, WB 4101, 5-methylurapidil, RS-17053 and S-niguldipine showed 10 to 40 fold lower affinity than in membrane binding. However, affinity estimates were not 'frameshifted', as tamsulosin, indoramin and Rec 15/2739 yielded similar, high affinity estimates in binding and functional assays. 4. In contrast, results from human alpha1B- and alpha1D-adrenoceptors expressed in CHO-K1 cells gave antagonist affinity profiles in binding and functional assays that were essentially identical. 5. A concordance of affinity estimates from the functional (inositol phosphates accumulation) studies of the alpha1A-adrenoceptor in CHO-K1 cells was found with estimates published recently from contractile studies in human lower urinary tract tissues (putative alpha1L-adrenoceptor). These data show that upon functional pharmacological analysis, the cloned alpha1A-adrenoceptor displays pharmacological recognition properties consistent with those of the putative alpha1L-adrenoceptor. Why this profile differs from that obtained in membrane binding, and whether it explains the alpha1L-adrenoceptor pharmacology observed in many native tissues, requires further investigation.

[3H]8-OH-DPAT labels a 5-HT site coupled to inhibition of phosphoinositide hydrolysis in the dorsal raphe

The present study was undertaken to compare the properties of the [3H]8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin) binding site in the dorsal raphe nucleus with the hippocampal 5-HT1A receptor. In both tissues inclusion of 1 mM Mg2+ enhanced specific [3H]8-OH-DPAT binding, while 1 mM GTP decreased radioligand binding. [3H]8-OH-DPAT appears to bind to a single population of binding sites in both the hippocampus and the dorsal raphe nucleus, although the K(d) for the radioligand at the dorsal raphe site was five times that observed at the hippocampal 5-HT1A receptor. Similarly, although 5-HT and selective 5-HT1A receptor ligands displayed high affinity for the [3H]8-OH-DPAT binding site in the dorsal raphe nucleus, the affinity at the dorsal raphe site was less than that observed at the hippocampal 5-HT1A receptor. 8-OH-DPAT inhibited forskolin-stimulated adenylyl cyclase activity in the hippocampus, but did not alter enzyme activity in the dorsal raphe nucleus. Conversely, 8-OH-DPAT inhibited the accumulation of [3H]inositol phosphates in the dorsal raphe nucleus, but not in the hippocampus. An inhibition of phosphoinositide hydrolysis in the dorsal raphe nucleus also was found with the putative 5-HT1A receptor selective ligands, flesinoxan and gepirone. However, addition of another putative 5HT1A receptor selective ligand, buspirone, did not alter the generation of [3H]inositol phosphates, but blocked the inhibitory effect of 8-OH-DPAT on phosphoinositide hydrolysis. These studies demonstrate that the 8-OH-DPAT binding site in the dorsal raphe nucleus displays a binding profile which is similar to the hippocampal 5-HT1A receptor, but unlike this 5-HT1A receptor the binding site in the dorsal raphe nucleus is negatively coupled to phosphoinositide turnover.

Sensitive measurement of agonist-stimulated [3H]inositol monophosphate accumulation in rat cortical miniprisms

Phosphoinositide (PI) breakdown is an important transmembrane signaling mechanism in rat brain and numerous transmitter receptors are linked to this mechanism. Since agonist-stimulated PI breakdown is often changed after drug pretreatment, assessment of changes in PI breakdown represents an important tool in drug development. PI breakdown is commonly monitored by assaying [3H]inositol monophosphate ([3H]IP1) accumulation in the presence of lithium as an inhibitor of inositol monophosphatase. The present protocol presents a lithium-inhibited [3H]IP1 accumulation assay that enhances relatively weak agonist-stimulated [3H]IP1 accumulation signals by thorough oxygenation during agonist stimulation. The protocol is particularly useful in the measurement of [3H]IP1 accumulation after in vitro exposure to relatively weak stimulants, such as serotonin (5-HT), and/or after animal pretreatments that decrease the response to the agonist. In the case of 5-HT stimulation the monoamine oxidase (MAO) inhibitor, tranylcypromine, was added to the incubation medium to inhibit breakdown of exogenous serotonin. We used this protocol to measure 5-HT- and carbachol-stimulated [3H]IP1 accumulation in cortical miniprisms obtained from rats pretreated with D-fenfluramine. D-Fenfluramine is a drug that acutely releases 5-HT into the synaptic cleft and blocks its reuptake.