Neuroscience Letters, 129 (1991) 81-85 ADONIS 030439409100399J
81
NSL 07919
Chronic haloperidol treatment attenuates receptor-mediated phosphoinositide turnover in rat brain slices R e n a Li 1, L a u r e n L. W i n g 1, Y o n g Shen 1, R i c h a r d J. W y a t t 1, Darrell G. K i r c h ~ a n d D e - M a w C h u a n g 2 Neuropsychiatry Branch, NIMH Neuroscience Center at St. Elizabeths, Washington, DC 20032 (U.S.A.) and 2Biological Psychiatry Branch, NIMH, Bethesda, MD 20892 (U.S.A.)
(Received 11 December1990;Revisedversionreceived19 April 1991;Accepted24 April 1991) Key words: Haloperidol;Carbachol; Norepinephrine;Phosphoinositideturnover; Frontal cortex; Hippocampus;Striatum
The long-termeffectsof haloperidol on phosphoinositideturnover in rat brain sliceswere investigated.Continuoustreatment with haloperidol decanoate (21 mg/kg I.M. biweeklyfor 6 weeks)significantlyattenuatedcarbachol-and norepinephrine(NE)-inducedinositolphosphate accumulation in rat frontal cortex and hippocampus. In the striatum, the haloperidol treatment also significantlydecreased carbachol-stimulatedinositol phosphate levelbut did not significantlyaffectNE-sensitivephosphoinositideturnover. These effectswere not observed in rats treated with a single dose of haloperidol (1.5 mg/kg).Basallevelsof inositolphosphate in these 3 brain regionsdid not changefollowingcontinuousor singlehaioperidol doses.
While it has been proposed that the antipsychotic effects of haloperidol and other neuroleptics may be related to blockade of dopamine D2 receptors, the mechanism of the clinical effects of haloperidol is not known. The D2 receptor is known to be negatively coupled to adenylyl cyclase [6] and stimulation of the D2 receptor has been shown to be associated with an attenuation of basal and receptor agonist-induced phosphoinositide (PI) turnover [8, 14, 19]. The latter may be an indirect effect, secondary to a decrease in intracellular calcium levels following D2 receptor stimulation. Alternately, the haloperidol PI effects may be produced by activity at other central neurotransmitter receptor sites. For example, haloperidol has been shown to interact with muscarinic, ~q-adrenergic, Dl-dopaminergic, GABAergic and sigma receptors [12, 16], and long-term administration of neuroleptics may induce decreased function of striatal cholinergic receptors as well as inducing dopamine receptor supersensitivity [7, 13, 18]. Since the hydrolysis of membrane-bound PIs following agonist stimulation of various neurotransmitter receptor subtypes is an important signal transduction mechanism, long-term effects of haloperidol on brain receptor-mediated PI metabolism have been studied. It has been reported that when haloperidol is given to rats for 4 weeks [11] or one year [17] there is no effect on basal or receptor-mediated PI turnover in brain slices. In Correspondence: D.-M. Chuang, Biological Psychiatry Branch, NIMH, Bldg. 10, Rm. 3N212, Bethesda,MD 20892, U.S.A.
light of recent reports that long-term treatment of rats with lithium, another psychotropic drug with anti-manic activity, produces an inhibition of receptor-mediated and fluoride-sensitive PI turnover in rat brain [4, 9, 10], we examined the effects of long-term haloperidol treatment on carbachol- and norepinephrine (NE)-stimulated PI turnover in frontal cortex, hippocampus and striatum. Male Sprague-Dawley rats, weighing 275-325 g, were treated with haloperidol decanoate (21 mg/kg i.m., biweekly) or the sesame oil vehicle for 6 weeks in the longterm study. In the single-dose study, rats were given an injection of haloperidol (1.5 mg/kg, s.c.) or vehicle and were sacrificed by decapitation 1.5 h later. Brains were rapidly removed and dissected on ice. The hippocampus, striatum and frontal cortex were sliced into 350 x 350/zm cubes. Slices were transferred to Krebs-Hensleit buffer (KHB) containing (in mM): NaCI 118, KCI 4.8, KH2PO4 1.2, CaCI2 1.3, MgSO4 1.2, glucose 11 and NaHCO3 25. After incubation at 37°C for 45 min in KHB, slices were equilibrated with O2/CO2 (95%/5%, v/v). Brain slices were labeled with 0.3/zM of myo-[2-3H]inositol for 60 min and then washed extensively to remove the myo-[23H]inositol label. Forty/zl of the gravity packed slices were pipetted into 250/zl of KHB containing 5 mM LiC1. After a 20-min pre-incubation period, 1 mM of indicated agonist or vehicle was added. The stimulation was terminated 45 min later by the addition of 0.9 ml CHCI3:MeOH (1:2, v/v). [3H]inositol phosphate (IP) formation was determined
82
by using a Dowex anion exchange resin (AG, 1 x 8 formate form, 100-200 mesh, Biorad Labs) according to the method of Berridge et al. [2]. To measure the incorporation of [3H]inositol into phospholipids, a 200-/~1 aliquot of the organic phase was air-dried and counted. NE or carbachol (1 mM) increased [3H]IP accumulation in hippocampal, striatal and cortical slices approximately 4-fold over basal levels (Fig. 1). However, carbachol-induced IP accumulation was significantly ( P < 0.01) attenuated by long-term treatment with haloperidol in the 3 brain regions examined (29%, 40% and 38% decreases in the hippocampus, striatum and frontal cortex, respectively) (Fig. 2A). Chronic treatment with haloperidol also resulted in significant (P
81
NSL 07919
Chronic haloperidol treatment attenuates receptor-mediated phosphoinositide turnover in rat brain slices R e n a Li 1, L a u r e n L. W i n g 1, Y o n g Shen 1, R i c h a r d J. W y a t t 1, Darrell G. K i r c h ~ a n d D e - M a w C h u a n g 2 Neuropsychiatry Branch, NIMH Neuroscience Center at St. Elizabeths, Washington, DC 20032 (U.S.A.) and 2Biological Psychiatry Branch, NIMH, Bethesda, MD 20892 (U.S.A.)
(Received 11 December1990;Revisedversionreceived19 April 1991;Accepted24 April 1991) Key words: Haloperidol;Carbachol; Norepinephrine;Phosphoinositideturnover; Frontal cortex; Hippocampus;Striatum
The long-termeffectsof haloperidol on phosphoinositideturnover in rat brain sliceswere investigated.Continuoustreatment with haloperidol decanoate (21 mg/kg I.M. biweeklyfor 6 weeks)significantlyattenuatedcarbachol-and norepinephrine(NE)-inducedinositolphosphate accumulation in rat frontal cortex and hippocampus. In the striatum, the haloperidol treatment also significantlydecreased carbachol-stimulatedinositol phosphate levelbut did not significantlyaffectNE-sensitivephosphoinositideturnover. These effectswere not observed in rats treated with a single dose of haloperidol (1.5 mg/kg).Basallevelsof inositolphosphate in these 3 brain regionsdid not changefollowingcontinuousor singlehaioperidol doses.
While it has been proposed that the antipsychotic effects of haloperidol and other neuroleptics may be related to blockade of dopamine D2 receptors, the mechanism of the clinical effects of haloperidol is not known. The D2 receptor is known to be negatively coupled to adenylyl cyclase [6] and stimulation of the D2 receptor has been shown to be associated with an attenuation of basal and receptor agonist-induced phosphoinositide (PI) turnover [8, 14, 19]. The latter may be an indirect effect, secondary to a decrease in intracellular calcium levels following D2 receptor stimulation. Alternately, the haloperidol PI effects may be produced by activity at other central neurotransmitter receptor sites. For example, haloperidol has been shown to interact with muscarinic, ~q-adrenergic, Dl-dopaminergic, GABAergic and sigma receptors [12, 16], and long-term administration of neuroleptics may induce decreased function of striatal cholinergic receptors as well as inducing dopamine receptor supersensitivity [7, 13, 18]. Since the hydrolysis of membrane-bound PIs following agonist stimulation of various neurotransmitter receptor subtypes is an important signal transduction mechanism, long-term effects of haloperidol on brain receptor-mediated PI metabolism have been studied. It has been reported that when haloperidol is given to rats for 4 weeks [11] or one year [17] there is no effect on basal or receptor-mediated PI turnover in brain slices. In Correspondence: D.-M. Chuang, Biological Psychiatry Branch, NIMH, Bldg. 10, Rm. 3N212, Bethesda,MD 20892, U.S.A.
light of recent reports that long-term treatment of rats with lithium, another psychotropic drug with anti-manic activity, produces an inhibition of receptor-mediated and fluoride-sensitive PI turnover in rat brain [4, 9, 10], we examined the effects of long-term haloperidol treatment on carbachol- and norepinephrine (NE)-stimulated PI turnover in frontal cortex, hippocampus and striatum. Male Sprague-Dawley rats, weighing 275-325 g, were treated with haloperidol decanoate (21 mg/kg i.m., biweekly) or the sesame oil vehicle for 6 weeks in the longterm study. In the single-dose study, rats were given an injection of haloperidol (1.5 mg/kg, s.c.) or vehicle and were sacrificed by decapitation 1.5 h later. Brains were rapidly removed and dissected on ice. The hippocampus, striatum and frontal cortex were sliced into 350 x 350/zm cubes. Slices were transferred to Krebs-Hensleit buffer (KHB) containing (in mM): NaCI 118, KCI 4.8, KH2PO4 1.2, CaCI2 1.3, MgSO4 1.2, glucose 11 and NaHCO3 25. After incubation at 37°C for 45 min in KHB, slices were equilibrated with O2/CO2 (95%/5%, v/v). Brain slices were labeled with 0.3/zM of myo-[2-3H]inositol for 60 min and then washed extensively to remove the myo-[23H]inositol label. Forty/zl of the gravity packed slices were pipetted into 250/zl of KHB containing 5 mM LiC1. After a 20-min pre-incubation period, 1 mM of indicated agonist or vehicle was added. The stimulation was terminated 45 min later by the addition of 0.9 ml CHCI3:MeOH (1:2, v/v). [3H]inositol phosphate (IP) formation was determined
82
by using a Dowex anion exchange resin (AG, 1 x 8 formate form, 100-200 mesh, Biorad Labs) according to the method of Berridge et al. [2]. To measure the incorporation of [3H]inositol into phospholipids, a 200-/~1 aliquot of the organic phase was air-dried and counted. NE or carbachol (1 mM) increased [3H]IP accumulation in hippocampal, striatal and cortical slices approximately 4-fold over basal levels (Fig. 1). However, carbachol-induced IP accumulation was significantly ( P < 0.01) attenuated by long-term treatment with haloperidol in the 3 brain regions examined (29%, 40% and 38% decreases in the hippocampus, striatum and frontal cortex, respectively) (Fig. 2A). Chronic treatment with haloperidol also resulted in significant (P
