Sub-chronic treatment with classical but not atypical antipsychotics produces morphological changes in rat nigro-striatal dopaminergic neurons directly related to `early onset' vacuous chewing Giorgio Marchese, 1 Maria Antonietta Casu, 1 Francesco Bartholini, 1 Stefania Ruiu, 1 Pierluigi Saba, 3 Gian Luigi Gessa 1,2,3 and Luca Pani 1,2 1 Neuroscienze S.c.a.r.l., 2 Institute of Neurogenetics, Neuropharmacology, C.N.R. and 3 `B.B. Brodie' Department of Neuroscience, University of Cagliari, Italy Keywords: neurotoxicity, Parkinson, tardive dyskinesia Abstract In the present work, we investigated if an impairment of dopaminergic neurons after subchronic haloperidol treatment might be a possible physiopathologic substrate of the `early onset' vacuous chewing movements (VCMs) in rats. For this purpose, different antipsychotics were used to analyse a possible relationship between VCMs development and morphological alterations of tyrosine-hydroxylase-immunostained (TH-IM) neurons. Rats treated twice a day with haloperidol displayed a signi®cant increase of VCMs that was both time- (2±4 weeks) and dose (0.1±1 mg/kg) dependent. Immunocytochemical analysis showed a shrinkage of TH-IM cell bodies in substantia nigra pars compacta and reticulata and a reduction of TH-immunostaining in the striatum of haloperidol treated rats with the arising of VCMs. No differences were observed in TH-IM neurons of ventral tegmental area and nucleus accumbens vs. control rats. The atypical antipsychotics risperidone (2 mg/kg, twice a day), amisulpride (20 mg/kg, twice a day) and clozapine (10 mg/kg, twice a day) did not produce any nigro-striatal morphological changes or VCMs. TH-IM nigro-striatal neuron morphological alterations and VCMs were still present after three days of withdrawal in rats treated for four weeks with haloperidol (1 mg/kg). Both the main morphological changes and the behavioural correlate disappeared after three weeks of withdrawal. These results suggest that haloperidol induces a morphological impairment of the dopaminergic nigro-striatal neurons which is directly associated with the arising, permanency and disappearance of VCMs in rats. Introduction Neuroleptic drugs are chronically used in the treatment of schizo- phrenia and other psychotic disorders but, unfortunately, their use is often associated with acute and delayed motor side-effects, including parkinsonism, akathisia and tardive dyskinesia (TD). TD, character- ized by involuntary movements predominantly in the orofacial region, develops in up to 20% of patients chronically treated with classical neuroleptics such as haloperidol (Klawans & Rubovits, 1972; Tarsy & Baldessarini, 1974, 1977; Jeste & Wyatt, 1979). Although the relationship between TD and long-term haloperidol treatment has been established, the pathophysiology of this motor disturbance is still unknown. A peculiar characteristic of this syndrome is that TD generally persists after haloperidol withdrawal and occasionally becomes irreversible, indicating that haloperidol has produced long lasting changes in brain function that are no longer related to the presence of the drug (Meshul et al., 1992, 1994). Rats treated with repeated high doses of haloperidol develop vacuous chewing movements (VCMs), a syndrome similar to human TD for time course and signs (Ellison & See, 1989; Tamminga et al., 1990; Waddington, 1990, 1997; Egan et al, 1996). Enhanced oral activity has been reported after subchronic (3±4 weeks) exposure to haloperidol (early onset VCMs) (Egan et al., 1996; Diana et al, 1992) or only after chronic (6±12 months) drug administration (tardive VCMs) (Waddington, 1990; Egan et al., 1996). Differences in these reports led to different interpretations of the results (Egan et al., 1996; Ikeda et al., 1999) and several hypotheses have been formulated to explain the development of VCMs, including the existence of a dopaminergic receptor supersensitivity (Klawans & Rubovits, 1972, 1977; Tarsy & Baldessarini, 1974; Burt et al., 1977), a dopamine D1/D2 receptor imbalance (Casey, 1995; Peacock & Gerlach, 1997; Waddington, 1997) and a g-aminobutyric acid (GABA) de®ciency (Gale, 1980; Fibiger & Lloyd, 1984). All these studies considered VCMs as a consequence of the haloperidol mediated receptor blockade and focused their attention on basal ganglia circuits and on the altered neurotransmitter-receptor equilib- rium in these areas. Recently, the emphasis on VCMs studies has shifted from neurotransmitter models to an approach that considers haloperidol-induced VCMs as a consequence of a direct neurotoxic effect mediated by haloperidol itself (De Keyser, 1991). Ex vivo studies have reported neuropathological alterations in basal ganglia of Correspondence: Dr Luca Pani, as above. E-mail: panil@unica.it Received 22 August 2001, revised 3 January 2002, accepted 8 February 2002 European Journal of Neuroscience, Vol. 15, pp. 1187±1196, 2002 ã Federation of European Neuroscience Societies