Vulnerability to involuntary movements over a lifetime trajectory of schizophrenia approaches 100%, in association with executive (frontal) dysfunction

This study assessed the prevalence of involuntary movements among older inpatients with severe schizophrenia, many of whom had experienced a lifetime of illness and its treatment, and examined their neuropsychological correlates. The subjects of this study were 128 inpatients with a DSM-IV diagnosis of schizophrenia. They were assessed using the Abnormal Involuntary Movement Scale, the Mini-Mental State Examination for general cognitive impairment and the Executive Interview for executive dyscontrol; additionally, their medical records were reviewed in detail for treatment histories. Prevalence of involuntary movements was examined and their clinical correlates determined in relation to topography of movement disorder using logistic regression. In schizophrenia, prevalence of involuntary movements was: age <65years, 63%; 65-75years, 80%; >75years, 93%. The primary correlate both of overall and of orofacial movements was poor executive function, whereas the primary correlate of limb-trunkal movements was poor general cognitive function. On approaching the limits of human longevity following a lifetime trajectory of illness and its treatment, essentially 'all' patients with schizophrenia appear inherently vulnerable to the emergence of involuntary movements in topographically specific association with cognitive deficits.

Determinants of neurological dysfunction in first episode schizophrenia

BACKGROUND

Although it is well recognized that individuals with schizophrenia display evidence of subtle neurological impairment, its aetiopathological and clinical significance continues to be unclear.

METHODS

Patients presenting with a first episode of schizophrenia or schizophreniform psychosis (DSM-IV criteria) were examined using two previously validated neurological examinations. The majority (N = 35) were examined prior to their 'first ever' dose of neuroleptic while the remaining patients (N = 21) had been medicated for less than one month. The manner in which neurological functioning is influenced by symptomatology and handedness was ascertained.

RESULTS

The majority of patients who were examined neuroleptic-naive displayed evidence of neurodysfunction. A combination of relative hand preference and symptomatology explained a significant proportion of the variance in neurological functioning. Mixed handedness among adults at the time of first presentation with schizophrenia was associated with more severe neurological impairment and a history of poorer scholastic attainment and pre-morbid social adjustment.

CONCLUSIONS

Neurological soft signs are an intrinsic part of schizophrenia rather than a direct consequence of treatment. Early developmental processes are associated with the level of subsequent neurological impairment in first episode schizophrenia. However, symptomatology appears to have an influence on the apparent severity of neurological impairment.

Phenotypic characterization of an alpha 4 neuronal nicotinic acetylcholine receptor subunit knock-out mouse

Neuronal nicotinic acetylcholine receptors (nAChR) are present in high abundance in the nervous system (Decker et al., 1995). There are a large number of subunits expressed in the brain that combine to form multimeric functional receptors. We have generated an alpha(4) nAChR subunit knock-out line and focus on defining the behavioral role of this receptor subunit. Homozygous mutant mice (Mt) are normal in size, fertility, and home-cage behavior. Spontaneous unconditioned motor behavior revealed an ethogram characterized by significant increases in several topographies of exploratory behavior in Mt relative to wild-type mice (Wt) over the course of habituation to a novel environment. Furthermore, the behavior of Mt in the elevated plus-maze assay was consistent with increased basal levels of anxiety. In response to nicotine, Wt exhibited early reductions in a number of behavioral topographies, under both unhabituated and habituated conditions; conversely, heightened levels of behavioral topographies in Mt were reduced by nicotine in the late phase of the unhabituated condition. Ligand autoradiography confirmed the lack of high-affinity binding to radiolabeled nicotine, cytisine, and epibatidine in the thalamus, cortex, and caudate putamen, although binding to a number of discrete nuclei remained. The study confirms the pivotal role played by the alpha(4) nAChR subunit in the modulation of a number of constituents of the normal mouse ethogram and in anxiety as assessed using the plus-maze. Furthermore, the response of Mt to nicotine administration suggests that persistent nicotine binding sites in the habenulo-interpeduncular system are sufficient to modulate motor activity in actively exploring mice.

Long-term adaptive life functioning in relation to initiation of treatment with antipsychotics over the lifetime trajectory of schizophrenia

BACKGROUND

There is evidence that the stage of illness at which antipsychotic treatment is initiated in schizophrenia may have consequences for its subsequent course. How this might relate to impaired adaptive life functioning in the long-term is poorly understood.

METHODS

Thirty-eight inpatients, many of whom had been admitted in the preneuroleptic era, were assessed using the Social-Adaptive Functioning Evaluation (SAFE); constituent clinical and medication phases of the lifetime trajectory of their illnesses were then analyzed to identify predictors of SAFE score using multiple regression modeling.

RESULTS

The primary, independent predictor of SAFE score was duration of initially unmedicated psychosis, which accounted for 22% of variance (p<.001) therein. Conversely, duration of subsequently treated illness, although decades longer, failed to predict SAFE score.

CONCLUSIONS

These findings are consistent with some form of "progressive" process, particularly over the first several years following the emergence of psychosis, which is associated with accrual of deficits in adaptive life functioning.

Topographically based search for an "Ethogram" among a series of novel D(4) dopamine receptor agonists and antagonists

The effects of three selective D(4) antagonists [CP-293,019, L-745, 870, and Ro 61-6270] and two putative selective D(4) agonists [CP-226,269 and PD 168077] were compared with those of the generic D(2)-like [D(2L/S),D(3), D(4)] antagonist haloperidol to identify any characteristic "ethogram," in terms of individual topographies of behavior within the natural rodent repertoire, as evaluated using ethologically based approaches. Among the D(4) antagonists, neither L-745,870 (0.0016-1.0 mg/kg) nor Ro 61-6270 (0.2-25.0 mg/kg) influenced any behavior; whereas, CP-293,019 (0.2-25.0 mg/kg) induced episodes of nonstereotyped sniffing, sifting, and vacuous chewing; there were no consistent effects on responsivity to the D(2)-like agonist RU 24213. Among the putative D(4) agonists, CP-226, 269 (0.2-25.0 mg/kg) failed to influence any behavior; whereas, PD 168077 (0.2-25.0 mg/kg) induced nonstereotyped shuffling locomotion with uncoordinated movements, jerking, and yawning, which were insensitive to antagonism by CP-293,019, L-745,870, or haloperidol. These findings fail to indicate any "ethogram" for selective manipulation of D(4) receptor function at the level of the interaction between motoric and psychological processes in sculpting behavioral topography over habituation of exploration through to quiescence and focus attention on social, cognitive, or other levels of examination.

Determinants of quality of life at first presentation with schizophrenia

BACKGROUND

Quality of life (QOL) has gained importance as a global measure of social and clinical outcome in schizophrenia.

AIMS

To identify the clinical correlates of QOL at the time of first presentation with schizophrenia.

METHOD

Over two years, consecutive first-episode psychosis patients presenting to a catchment area psychiatric service underwent validated clinical assessments of premorbid adjustment, illness duration, symptoms and QOL.

RESULTS

At presentation, subjects already had a diminished QOL. Although independent of gender and age at onset of psychosis, QOL was influenced by premorbid adjustment, duration of untreated psychosis and symptoms.

CONCLUSIONS

Reducing the duration of untreated psychosis may have a beneficial effect on the subsequent QOL of patients presenting with schizophrenia. First-episode patients with a protracted duration of untreated psychosis or impaired premorbid adjustment may warrant specific treatment interventions to prevent the development of secondary handicaps.

Topographical evaluation of behavioural phenotype in a line of mice with targeted gene deletion of the D2 dopamine receptor

The phenotype of spontaneous and dopamine D2-like agonist-induced behaviour was assessed topographically in a line of mice with targeted gene deletion of the D1 receptor. An ethologically-based, rapid time-sampling behavioural check-list technique was used to resolve and quantify all behaviours in the natural repertoire of the mouse. Relative to wildtypes [D2+/+], D2-null [D2-/-] mice evidenced over a 1 h period of initial exploration modest but significant reductions in locomotion, grooming, rearing free and rearing to wall; rearing seated, sniffing, sifting and stillness were not altered. Individual elements of behaviour habituated similarly over a 6 h period for both genotypes. The dose-dependent induction of stereotyped sniffing and ponderous locomotion by the D2-like agonist RU 24213 (0.1-12.5 mg/kg) in wildtypes was essentially absent in D2-null mice. The ethogram of spontaneous behaviour in D2-null mice was characterised by only modest reductions in, and topographical shifts between, certain individual elements of behaviour. Essential abolition of D2-like agonist responsivity in D2-null mice vis-à-vis considerable preservation of spontaneous behavioural topography suggests compensatory processes subsequent to developmental absence of the D2 receptor that are able to sustain function under naturalistic, tonic conditions but not during phasic challenge.

Early cerebro-craniofacial dysmorphogenesis in schizophrenia: a lifetime trajectory model from neurodevelopmental basis to 'neuroprogressive' process

Understanding the temporal origin(s) of schizophrenia, through specifying the earliest identifiable pathology, might indicate when to look for etiological factor(s), what their nature might be, and how course of illness might evolve from these origins. From this premise, earlier formulations are elaborated to offer a rigorously data-driven model that roots schizophrenia in cerebro-craniofacial dysmorphogenesis, particularly along the mid-line but involving other structures, over weeks 9/10 through 14/15 of gestation. However, a brain that has been compromised very early in fetal life is still subject to the normal endogenous programme of developmental, maturational and involutional processes on which a variety of exogenous biological insults and psychosocial stressors can impact adversely over later pregnancy, through infancy and childhood, to maturation and into old age, to sculpt brain structure and function; it should be emphasised that the effects of such endogenous programmes and exogenous insults on such an already developmentally-compromised brain may be different from their effects on a brain whose early fetal origins were unremarkable. From these early origins, a lifetime trajectory model for schizophrenia from developmental basis to 'neuroprogressive' process is constructed. Thereafter, consideration is given to what the model can explain, including cerebral asymmetry and homogeneity, what it cannot explain, what empirical findings would challenge or disprove the model, what cellular and molecular mechanisms might underpin the model, and what are its implications.

Conservation of behavioural topography to dopamine D1-like receptor agonists in mutant mice lacking the D1A receptor implicates a D1-like receptor not coupled to adenylyl cyclase

Though D1-like dopamine receptors [D1A/B] are defined in terms of linkage to the stimulation of adenylyl cyclase, with D1A assumed to be the functionally prepotent subtype, evidence suggests the existence of another, novel D1-like receptor without such coupling. To investigate these issues we challenged mutant mice having targeted gene deletion of the D1A receptor with selective agonists and used an ethologically-based assessment technique to resolve resultant behavioural topography. D1-like-dependent behaviour was substantially conserved in D1A-null mice relative to wild-types following challenge with each of two selective D1-like agents: A 68930 (0.068-2.0 mg/kg s.c.) which exhibits full efficacy to stimulate adenylyl cyclase, and SKF 83959 (0.016-2.0 mg/kg s.c.) which fails to stimulate adenylyl cyclase, and indeed inhibits the stimulation of adenylyl cyclase induced by dopamine. Furthermore, responsivity to the selective D2-like agonist RU 24213 (0.1-12.5 mg/kg s.c.) was conserved in D1A-null mice, indicating the integrity of D1-like:D2-like interactions at the level of behaviour. These data are consistent with behavioural primacy of a D1-like receptor other than D1A [or D1B] that is coupled to a transduction system other than/additional to adenylyl cyclase.

The neurodevelopmental basis of schizophrenia: clinical clues from cerebro-craniofacial dysmorphogenesis, and the roots of a lifetime trajectory of disease

A "read-back" analysis of schizophrenia, from chronic illness, through the first psychotic episode, to psychosocial and neurointegrative abnormalities of childhood and infancy, leads to the intrauterine period as a primary focus for etiological events. Evidence for a characteristic topography of cerebro-craniofacial dysmorphology in schizophrenia is reviewed, and interpreted to estimate: (i) the timing of dysmorphic event(s); (ii) the nature of early cellular and molecular mechanisms which might determine that topography of dysmorphogenesis; and (iii) the population homogeneity of these processes. It is argued that early cerebro-craniofacial dysmorphogenesis in schizophrenia should be conceptualized as a first stage not in a static but rather in a dynamic, lifetime trajectory of disease.

Geographical variation in rate of schizophrenia in rural Ireland by place at birth vs place at onset

This study examined geographical variation in rate of occurrence of schizophrenia by place at birth vs place at onset, among a rural Irish catchment area population of unusual stability and socioeconomic homogeneity. Within a catchment area of 21,520 persons, all cases of schizophrenia were sought using current inpatient and outpatient records and key informants active in the community. Suspected cases were interviewed personally and diagnosed using DSM-III-R criteria. Place at birth and place at onset of psychosis were specified among the 32 District Electoral Divisions constituting the study region. For the 72 cases ascertained, an unremarkable overall prevalence rate/morbid risk obscured substantial and significant geographical variations therein between District Electoral Divisions. Particularly after controlling for high-density families, men demonstrated prominent geographical variation both by place at birth and by place at onset, with most men remaining unmarried and becoming ill at their place of birth; conversely, women demonstrated prominent variation by place at birth but more limited variation by place at onset, despite more frequent transitions from the parental home to the marital home before onset. Even when cases changed their location before the onset of psychosis, geographical variation in rate of occurrence of schizophrenia remained associated more strongly with factors related to the place of their birth.

SK&F 83959 and non-cyclase-coupled dopamine D1-like receptors in jaw movements via dopamine D1-like/D2-like receptor synergism

This study compared the effects of the dopamine D1-like receptor agents SK&F 83959 (3-methyl-6-chloro-7,8-dihydroxy-1-[3-methyl-phenyl]-2,3,4,5-tetrahydro- 1 H-3-benzazepine), which inhibits the stimulation of adenylyl cyclase, and A 68930 ([1R,3S]-1-aminomethyl-5,6-dihydroxy-3-phenyl-isochroman), a full efficacy agonist, in regulating jaw movements in the rat by synergism with dopamine D2-like receptor agonism. When SK&F 83959 and A 68930 were given in combination with quinpirole, there was a synergistic induction of jaw movements. Responsivity to SK&F 83959 + quinpirole was antagonised by the dopamine D1-like receptor antagonists SCH 23390 ([R]-3-methyl-7-chloro-8-hydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-ben zaz epine) and BW 737C ([S]-6-chloro-1-[2,5-dimethoxy-4-propylbenzyl]-7-hydroxy-2-methyl- 1,2,3,4-tetrahydroisoquinoline); synergism was antagonised also by the dopamine D2-like receptor antagonist YM 09151-2 (cis-N-[1-benzyl-2-methyl-pyrrolidin-3-yl]-5-chloro-2-methoxy-4-++ +methyl-aminobenzamide). Responsivity to A 68930 + quinpirole was enhanced by low doses of SCH 23390, BW 737C and YM 09151-2, and antagonised by higher doses of SCH 23390 and YM 09151-2. These results implicate a novel, dopamine D1-like receptor that is coupled to a transduction system other than/additional to adenylyl cyclase, and suggest that its functional role extends to the regulation of jaw movements by synergistic interactions with dopamine D2-like receptors.

Topographical evaluation of the phenotype of spontaneous behaviour in mice with targeted gene deletion of the D1A dopamine receptor: paradoxical elevation of grooming syntax

The phenotype of spontaneous behaviour in mice with targeted gene deletion of the DIA dopamine receptor was investigated topographically. Via direct visual observation, individual elements of behaviour were resolved and quantified using an ethologically-based, rapid time-sampling behavioural check-list procedure. Relative to wildtypes (D1A+/+), D1A-null (-/-) mice evidenced over initial exploration significant reductions in rearing free, sifting and chewing, but significant increases in locomotion, grooming and intense grooming. Sniffing and rearing to a wall habituated less readily in D1A-null mice such that these behaviours occurred subsequently to significant excess: increases in locomotion were persistent. The ethogram of spontaneous behaviour in D1A-null mice was characterised by neither 'hypoactivity' or 'hyperactivity' but, rather, by prominent topographical shifts between individual elements of behaviour that could not be encapsulated by either term. Given the substantial body of evidence that grooming and particularly intense grooming constitute the most widely accepted behavioural index of D1-like receptor function, the elevation of such behaviour in D1A-null mice was paradoxical; it may reflect (over)compensatory processes subsequent to developmental absence of D1A receptors and/or the involvement of a D1-like receptor other than/additional to the D1A subtype.

Mortality in schizophrenia. Antipsychotic polypharmacy and absence of adjunctive anticholinergics over the course of a 10-year prospective study

BACKGROUND

Although increased mortality is one of the most consistent and accepted epidemiological findings in schizophrenia, a high rate of suicide appears unable to account fully for this burden which remains poorly understood.

METHOD

A cohort of 88 in-patients was followed prospectively over a 10-year period and predictors of survival sought among demographic, clinical and treatment variables.

RESULTS

Over the decade, 39 of the 88 patients (44%) died, with no instances of suicide. Reduced survival was predicted by increasing age, male gender, edentulousness and time since pre-terminal withdrawal of antipsychotics; additionally, two indices of polypharmacy predicted reduced survival: maximum number of antipsychotics given concurrently (relative risk 2.46, 95% CI 1.10-5.47; P = 0.03) and absence of co-treatment with an anticholinergic (relative risk 3.33, 95% CI 0.99-11.11; P = 0.05).

CONCLUSIONS

Receiving more than one antipsychotic concurrently was associated with reduced survival, in the face of little or no systematic evidence to justify the widespread use of antipsychotic polypharmacy. Conversely, over-cautious attitudes to the use of adjunctive anticholinergics may require re-evaluation.

Spontaneous abnormal involuntary movements in first-episode schizophrenia and schizophreniform disorder: baseline rate in a group of patients from an Irish catchment area

OBJECTIVE

This study investigated the rate of spontaneous abnormal involuntary movements in a group of patients presenting with a first episode of schizophrenia or schizophreniform psychosis.

METHOD

Seventy-nine patients with a first episode of schizophrenia or schizophreniform psychosis who presented to a catchment area psychiatric service over a 3-year period, and who were neuroleptic-naive or had been medicated for less than 1 month, were examined for the presence of involuntary movements with use of the Abnormal Involuntary Movement Scale.

RESULTS

Six patients (7.6%) had spontaneous dyskinesia as defined by the criteria of Schooler and Kane, and nine other patients had mild orofacial involuntary movements. The patients with spontaneous dyskinesia had completed significantly fewer years of education than the patients without dyskinesia. Spontaneous involuntary movements were unrelated to age at presentation for treatment.

CONCLUSIONS

Spontaneous abnormal involuntary movements were evident among a proportion of patients with first-episode schizophrenia or schizophreniform psychosis at baseline presentation and were associated with reduced educational attainment. This finding supports previous suggestions that abnormal involuntary movements in schizophrenia may be related to the pathophysiology of the illness and therefore cannot be attributed entirely to the adverse effects of neuroleptic medication.

Course of psychopathology, cognition and neurobiological abnormality in schizophrenia: developmental origins and amelioration by antipsychotics?

It is argued that schizophrenia has origins in events occurring during the first or early second trimester that are reflected in minor physical anomalies and which may at least in part predispose to later obstetric complications. This neurodevelopmental basis underlies certain neuromotor and psychosocial abnormalities of infancy and childhood, which are the early manifestations of what will be reconceptualised later as negative symptoms and (particularly frontal) cognitive dysfunction, but gives rise to positive symptoms only on the maturation of other systems necessary for their expression. This later emergence of psychosis may reflect an active morbid process that is associated with increased accrual of negative symptoms and of general (but not frontal) cognitive impairment that may be ameliorated by effective antipsychotic treatment. The psychological or biological basis of this heuristic process is poorly understood. Contemporary re-appraisal of any impact of antipsychotics on the long-term course of schizophrenia must take into account what is known of the origins of the disease process with which such drugs might interact. Much recent work continues to indicate that very early events, during the embryonic/fetal period, are important in, if not fundamental to, the genesis of schizophrenia; i.e. that there is a neurodevelopmental basis to the disorder. The present article seeks to establish a time-line relating early intrauterine adversity and dysmorphogenesis, through the onset of psychosis, to the chronic phase of the illness over adulthood; from this time-line, a schema is elaborated for a beneficial impact of antipsychotics on the course of psychopathology, cognition and, less clearly, neurobiological abnormality.

Heterogeneity of behavioural profile between three new putative selective D3 dopamine receptor antagonists using an ethologically based approach

The effects on behaviour of the putative selective D3 dopamine receptor antagonists GR 103691, nafadotride and U 99194A were compared with those of the generic D2-like antagonist haloperidol, using an ethologically based approach. Neither GR 103691 (0.008-1.0 mg/kg) nor nafadotride (0.025-1.6 mg/kg) influenced any element of behaviour. Conversely, U99194A (1.67-45 mg/kg) effected a dose-dependent stimulation of episodes of non-stereotyped sniffing, locomotion, chewing and eating, with some stimulation of rearing, and reduced baseline levels of grooming; thereafter, as sniffing and locomotion declined, stimulation of episodes of grooming emerged. Haloperidol (0.0008-0.1 mg/kg) failed to promote any element of behaviour and reduced baseline levels of grooming; responsivity to U99194A was antagonised by pretreatment with haloperidol. The lack of effect of GR 103691 (> 100-fold D3/D2 selectivity) and nafadotride (10-fold D3/D2 preference), in contrast to the characteristic "ethogram" for U99194A (25-fold D3/D2 selectivity), indicated a fundamental difference in their mechanisms of action. This topography of responsivity to U99194A overlapped somewhat with the profiles of both D2-like and D1-like agonists, and its sensitivity to antagonism by haloperidol also indicated a dopaminergic basis thereto. However, differences among GR 103691, nafadotride and U99194A bore no relation to their relative selectivities for the D3 receptor, and the basis thereof remains unclear. Theorising as to the behavioural role of the D3 receptor may need to be tempered pending the identification of a range of chemically distinct D3 antagonists of higher selectivity.

Neurodevelopmental and neuroprogressive processes in schizophrenia. Antithetical or complementary, over a lifetime trajectory of disease?

The neurodevelopmental model of schizophrenia maintains ascendancy among current etiopathologic perspectives on schizophrenia. However, inconsistencies across studies and the absence thus far of pathognomic brain changes suggest the need for complex conceptualization of neurodevelopmental arrest, including some reconciliation with the competing neurodegenerative model of schizophrenia. This article critically reviews the preponderance of evidence for each model and provides an account of how these may interact or synergize to produce the characteristic clinical expression of schizophrenia.

The new antipsychotics, and their potential for early intervention in schizophrenia

Over almost four decades, few fundamentally different antipsychotic drugs evolved to challenge classical neuroleptics as the mainstay of the pharmacotherapy of schizophrenia. However, the recent re-emergence of clozapine, together with the emergence of risperidone, portends an increasing number of new antipsychotics which are now either traversing the stages of regulatory approval or else well-advanced in clinical development. This article first evaluates the significance of clozapine and risperidone; it then reviews some of the new antipsychotics and how they might be classified vis-a-vis potential advantages for patients, outlines putative mechanisms and new therapeutic targets, and considers whether such agents may act on any disease process inherent to schizophrenia. One fundamental issue is the extent to which the new antipsychotics might shift materially the risk benefit balance towards intervention, not just at the earliest possible stage following the onset of psychosis but at a yet earlier, 'prodromal' phase of the disorder where there is a considerably greater likelihood of 'treating' behavioural disturbances that prove not to be the harbingers of psychotic illness.

Psychopathology, executive (frontal) and general cognitive impairment in relation to duration of initially untreated versus subsequently treated psychosis in chronic schizophrenia

BACKGROUND

It has been suggested that the expression of psychosis may reflect an active morbid process that is associated with increasingly poor outcome unless ameliorated by antipsychotic drugs.

METHODS

The subjects of this study were 48 in-patients with schizophrenia, many of whom had been admitted before the introduction of antipsychotic drugs to rural Irish psychiatric hospitals in the late 1950s. Each patient was assessed for positive and negative symptoms, and for general and executive (frontal) cognitive function.

RESULTS

After controlling for age and for duration and continuity of subsequent antipsychotic treatment, current severity both of negative symptoms and of general cognitive impairment was predicted strongly by increasing duration of initially untreated psychosis; duration of illness following initiation of antipsychotic medication failed to predict the severity thereof. Neither of these indices of illness duration predicted the severity of positive symptoms or of executive dyscontrol.

CONCLUSIONS

Increasing duration of initially untreated psychosis was associated specifically with heightened accrual of prominent negative symptoms and general cognitive impairment. Executive dyscontrol, though also prominent in these patients, may be 'locked-in' at an earlier phase of the illness.

Psychopharmacological distinction between novel full-efficacy "D1-like" dopamine receptor agonists

The search for full-efficacy agonists selective for the "D1-like" family of dopamine receptor subtypes has recently generated two novel series of compounds: the isochromans, typified by A 68930, and the phenanthridines, typified by dihydrexidine. This study was undertaken to compare systematically the effects of these two agents on the spectrum of unconditioned motor behaviour (i.e., construction of their drug ethograms) in the intact adult rat and to determine the sensitivity of these responses to selective antagonists of "D1-like" (SCH 23390) vs. "D2-like" (YM 09151-2) receptors. A 68930 (0.0625-4.0 mg/kg) readily induced grooming, including intense grooming, the most widely accepted behavioural model of "D1-like" receptor stimulation; it also induced vacuous chewing, a more controversial model thereof, and sniffing. Conversely, dihydrexidine (0.25-16.0 mg/kg) induced grooming, but little intense grooming was evident; it failed to induce vacuous chewing but did induce sniffing. Grooming and sniffing responses to A 68930 were readily blocked by SCH 23390 (0.01-1.0 mg/kg) but were only attenuated or spared by YM 09151-2 (0.005-0.5 mg/kg). Conversely, the grooming and sniffing responses to dihydrexidine were readily blocked both by SCH 23390 and by YM 09151-2. A 68930 and dihydrexidine do not show identical psychopharmacological profiles; they appear to differ in the specificity of their effects on "D1-like" vs. "D2-like" function and may interact differentially with putative subtypes of "D1-like" receptors that are indicated behaviourally.