Elsevier

Brain Research

Volume 1023, Issue 1, 8 October 2004, Pages 54-63
Brain Research

Research report
Clozapine increases both acetylcholine and dopamine release in rat ventral hippocampus: role of 5-HT1A receptor agonism

https://doi.org/10.1016/j.brainres.2004.07.009Get rights and content

Abstract

Atypical antipsychotic drugs (APDs) such as clozapine, but not the typical APD haloperidol, improve some aspects of cognition in schizophrenia. This advantage has been attributed, in part, to the ability of the atypical APDs to markedly increase acetylcholine (ACh) and dopamine (DA) release in rat medial prefrontal cortex (mPFC), while producing a minimal effect in the nucleus accumbens (NAC) or striatum. The atypical APD-induced preferential release of DA, but not ACh, in the mPFC is partially inhibited by the selective 5-HT1A antagonist WAY100635. However, little is known about these effects of atypical APDs in the ventral hippocampus (vHIP), another possible site of action of atypical APDs with regard to cognitive enhancement. The present study demonstrates that clozapine (10 mg/kg) comparably increases both ACh and DA release in the vHIP and mPFC. The increases in DA, but not ACh, release in both regions were partially attenuated by WAY100635 (0.2 mg/kg), which had no effect by itself on the release of either neurotransmitter in either region. Tetrodotoxin (TTX; 1 μM), a Na+ channel blocker, in the perfusion medium, eliminated the clozapine (10 mg/kg)-induced ACh and DA release in the vHIP, indicating their neuronal origin. Haloperidol produced a slight increase in ACh release in the vHIP at 1 mg/kg, and DA release in the mPFC at 0.1 mg/kg. In conclusion, clozapine increases ACh and DA release in the vHIP and mPFC, whereas haloperidol has minimal effects on the release of these two neurotransmitters in either region. These differences may contribute, at least in part, to the superior ability of clozapine, compared to haloperidol, to improve cognition in schizophrenia. 5-HT1A agonism is important to the ability of clozapine and perhaps other atypical APDs to increase DA, but not ACh, release in the vHIP, as well as the mPFC. The role of hippocampus in the cognitive effects of atypical APDs warrants more intensive study.

Introduction

The hippocampus (HIP), which has a principal role in learning and memory [18], [19], [50], has been suggested to be important for the neurocognitive deficits and possibly psychotic symptoms in schizophrenia as well [28], [31], [32], [33], [48], [63], complementing the contribution of the prefrontal cortex (PFC) and nucleus accumbens (NAC) to these abnormalities [13]. The neonatal excitotoxic lesions in the ventral (v)HIP of rats have been reported to produce dysfunction of the PFC in adulthood [54]. This may be the result of disrupting glutamatergic pyramidal neurons, which project to the medial (m)PFC [6], [44], [50], [70]. Disruption of the vHIP–mPFC circuit produced by reversible inactivation of the vHIP in rats may produce temporary working memory abnormalities in adults [20], [64], and decreased prepulse inhibition of acoustic startle [77], which has been proposed as a model of the sensorimotor deficit in schizophrenia [73]. Disruption of the vHIP, which receives a dopaminergic projection from the ventral tegmental area (VTA) [24], and is also the origin of glutamatergic pyramidal neurons, which project to the NAC shell [29], [66], [67], [75], has been suggested as a possible animal model for psychosis in schizophrenia [21], [22], [26], [27], [63]. These considerations suggest that the HIP could be another target for the therapeutic benefit for APDs [62]. Specifically, atypical APDs may improve neurocognitive deficits and psychosis in schizophrenia [52], [55], at least in part, via their effects in the vHIP.

Dopamine (DA) [1], [43] and acetylcholine (ACh) [8], [31] are critically important for cognition. Furthermore, there is evidence for decreased cortical dopaminergic [13], [45], [46], [56], [76] and cholinergic [10], [11], [12], [15], [16] activity in patients with schizophrenia. Thus, a possible explanation for the beneficial effect of some atypical APDs on neurocognitive deficits in patients with schizophrenia may be their ability to produce greater increases in DA and ACh release in the mPFC, compared to the NAC, whereas typical APDs such as haloperidol, S(−)-sulpiride and thioridazine have little effect on the release of either neurotransmitter in the mPFC [36], [37], [38], [39], [40], [49], [57].

Despite the interest in the HIP in neurocognition and schizophrenia, little is known about the effect of APDs on DA and ACh release in the vHIP. Shirazi-Southall et al. [65] have recently reported that the atypical APDs, clozapine, olanzapine and risperidone, increased ACh release in the vHIP, whereas another atypical APD, ziprasidone, did not; haloperidol, as well as other typical APDs, thioridazine and chlorpromazine, produced modest increases in ACh release in the vHIP. These authors suggested that the ability to increase ACh release in the vHIP may not distinguish atypical APDs from typical APDs. However, it should be noted that neostigmine, an AChesterase inhibitor, was included in the perfusion medium in that study [65], in order to achieve detectable dialysate ACh concentrations. We have suggested that levels of ACh in this range significantly influence drug-induced ACh release [35], [38]. Interestingly, some, but not all, drugs such as piribedil, an α2 adrenoceptor antagonist, have been reported to produce comparable effects on ACh release in the mPFC and dorsal HIP, in the absence of AChesterase inhibition [25]. Because the highest density of 5-HT1A receptors in rat brain is shown in the HIP, followed by the mPFC [2], [7], it is possible that WAY100635, a selective 5-HT1A receptor antagonist, attenuates clozapine-induced DA release in the vHIP, as well as the mPFC [36]. Stimulation of 5-HT1A receptors has been reported to increase DA and ACh release in the HIP [23], [42], [47], [58], [61], [65] as well as in the mPFC [9], [36], [39], [47], [61]. Some, but not all, drugs produce comparable effects on DA and ACh release in both vHIP and mPFC, and there are mono- and trans-synaptic connections between these two regions: the hippocampo-PFC circuit [51], [71]. It is important to determine whether APDs increase DA and/or ACh release in the vHIP, and whether WAY100635 attenuates clozapine-induced ACh release in the vHIP. Specifically, it should be noted that no in vivo data have been provided regarding the effect of APDs on DA release in the vHIP. The present study was designed to compare the effects of clozapine and haloperidol on the release of DA and ACh in the vHIP and the mPFC, and whether WAY100635 attenuates clozapine-induced DA and ACh release in the vHIP. Preliminary data from this study have been reported in abstract form elsewhere [8].

Section snippets

Animals

Male Sprague–Dawley albino rats (Zivic-Miller Laboratories, Porterville, PA) weighing 250 to 350 g were housed two to three per cage and maintained in a controlled 12:12-h light–dark cycle and under constant temperature at 22 °C, with free access to food and water.

Surgery

Rats were anesthetized with the modified Equithesin mixture (3 ml/kg body weight i.p.) that was made by dissolving 2.125 g chloral hydrate and 1063 g magnesium sulphate, adding 8.1 ml Nembutal (50 mg/ml sodium pentobarbital) and 5.0

Basal levels in the absence of AChesterase inhibition

ACh levels were 6.82±0.46 (fmol/10 μl) in the vHIP (N=48), and 9.84±0.82 in the mPFC (N=44). DA levels were 1.42±0.08 (fmol/10 μl) in the vHIP (N=47), and 2.11±0.11 in the mPFC (N=50). Basal ACh and DA levels are significantly lower in the vHIP than the mPFC (F(1,90)=10.81, p=0.001, and F(1,95)=25.98, p<0.001, respectively). ACh and DA concentrations were not significantly different between treatment groups in each region. Interestingly, basal ACh and DA levels in the mPFC obtained with a

Discussion

A major finding of this study is that clozapine increases DA and ACh in the vHIP. This is the first in vivo evidence that clozapine increases DA release in the vHIP. We confirmed a previous report that clozapine increases ACh release in the vHIP [65]. Activation of 5-HT1A receptor-mediated mechanism(s) contributes to the ability of clozapine to increase DA, but not ACh, release in both the vHIP and mPFC, as indicated by attenuation of the increases in DA release by WAY100635, a selective 5-HT1A

Acknowledgments

This study was supported, in part, by grants from the Ritter Foundation, the Warren Foundation, and Mr. Donald Test.

References (77)

  • H.J. Groenewegen et al.

    Organization of the projections from the subiculum to the ventral striatum in the rat. A study using anterograde transport of Phaseolus vulgaris leucoagglutinin

    Neuroscience

    (1987)
  • C. Hagger et al.

    Improvement in cognitive functions and psychiatric symptoms in treatment-refractory schizophrenic patients receiving clozapine

    Biol. Psychiatry

    (1993)
  • M.E. Hasselmo et al.

    Acetylcholine and memory

    Trends Neurosci.

    (1993)
  • J. Ichikawa et al.

    DOI, a 5-HT2A/2C receptor agonist, attenuates clozapine-induced cortical dopamine release

    Brain Res.

    (2001)
  • J. Ichikawa et al.

    Atypical, but not typical, antipsychotic drugs increase cortical acetylcholine release without an effect in the nucleus accumbens or striatum

    Neuropsychopharmacology

    (2002)
  • J. Ichikawa et al.

    5-HT1A and 5-HT2A receptors minimally contribute to clozapine-induced acetylcholine release in rat medial prefrontal cortex

    Brain Res.

    (2002)
  • J. Ichikawa et al.

    A typical antipsychotic drugs, quetiapine, iloperidone, and melperone, preferentially increase dopamine and acetylcholine release in rat medial prefrontal cortex: role of 5-HT1A receptor agonism

    Brain Res.

    (2002)
  • J. Ichikawa et al.

    Cholinergic modulation of basal and amphetamine-induced dopamine release in rat medial prefrontal cortex and nucleus accumbens

    Brain Res.

    (2002)
  • T.M. Jay

    Dopamine: a potential substrate for synaptic plasticity and memory mechanisms

    Prog. Neurobiol.

    (2003)
  • M.B. Knable et al.

    Multivariate analysis of prefrontal cortical data from the Stanley Foundation Neuropathology Consortium

    Brain Res. Bull.

    (2001)
  • T. Koyama et al.

    Enhancement of cortical and hippocampal cholinergic neurotransmission through 5-HT1A receptor-mediated pathways by BAYx3702 in freely moving rats

    Neurosci. Lett.

    (1999)
  • E.E. Krieckhaus et al.

    Paranoid schizophrenia may be caused by dopamine hyperactivity of CA1 hippocampus

    Biol. Psychiatry

    (1992)
  • S. Leucht et al.

    Efficacy and extrapyramidal side-effects of the new antipsychotics olanzapine, quetiapine, risperidone, and sertindole compared to conventional antipsychotics and placebo. A meta-analysis of randomized controlled trials

    Schizophr. Res.

    (1999)
  • J.-F. Liégeois et al.

    5-HT2A receptor antagonism potentiates haloperidol-induced dopamine release in rat medial prefrontal cortex and inhibits that in the nucleus accumbens in a dose–dependent manner

    Brain Res.

    (2002)
  • B. Scatton

    Differential changes in DOPAC levels in the hippocampal formation, septum and striatum of the rat induced by acute and repeated neuroleptic treatment

    Eur. J. Pharmacol.

    (1981)
  • S. Shirazi-Southall et al.

    Effects of typical and atypical antipsychotics and receptor selective compounds on acetylcholine efflux in the hippocampus of the rat

    Neuropsychopharmacology

    (2002)
  • A.I. Weike et al.

    Effective neuroleptic medication removes prepulse inhibition deficits in schizophrenia patients

    Biol. Psychiatry

    (2000)
  • C.R. Yang et al.

    Hippocampal signal transmission to the pedunculopontine nucleus and its regulation by dopamine D2 receptors in the nucleus accumbens: an electrophysiological and behavioural study

    Neuroscience

    (1987)
  • C.R. Yang et al.

    Developing a neuronal model for the pathophysiology of schizophrenia based on the nature of electrophysiological actions of dopamine in the prefrontal cortex

    Neuropsychopharmacology

    (1999)
  • W.-N. Zhang et al.

    Prepulse inhibition in rats with temporary inhibition/inactivation of ventral or dorsal hippocampus

    Pharmacol. Biochem. Behav.

    (2002)
  • S.J. Boyson et al.

    Quantitative autoradiographic localization of the D1 and D2 subtypes of dopamine receptors in rat brain

    J. Neurosci.

    (1986)
  • F.P. Bymaster et al.

    Muscarinic receptors as a target for drugs treating schizophrenia

    Curr. Drug Targets-CNS Neurol. Disord.

    (2002)
  • D.B. Carr et al.

    Hippocampal afferents to the rat prefrontal cortex: synaptic targets and relation to dopamine terminals

    J. Comp. Neurol.

    (1996)
  • Y.-C. Chung et al.

    Clozapine, an atypical antipsychotic, increases acetylcholine and dopamine release in rat ventral hippocampus and medial prefrontal cortex, whereas the effect of typical antipsychotic haloperidol is minimal: role of 5-HT1A receptor agonism

    Soc. Neurosci. Abstr.

    (2003)
  • J.M. Crook et al.

    Low muscarinic receptor binding in prefrontal cortex from subjects with schizophrenia: a study of Brodmann's areas 8, 9, 10, and 46 and the effects of neuroleptic drug treatment

    Am. J. Psychiatr.

    (2001)
  • K.L. Davis et al.

    Dopamine in schizophrenia: a review and reconceptualization

    Am. J. Psychiatr.

    (1991)
  • R.M. Deacon et al.

    Equithesin without chloral hydrate as an anaesthetic for rats

    Psychopharmacology

    (1996)
  • B. Dean et al.

    Muscarinic1 and 2 receptor mRNA in the human caudate-putamen: no change in m1 mRNA in schizophrenia

    Mol. Psychiatry

    (2000)
  • Cited by (85)

    View all citing articles on Scopus
    View full text