The effects of clozapine on behavioural responses to the selective 'D1-like' dopamine receptor agonist, A 68930, and to the selective 'D2-like' agonist, RU 24213

1. The influence of the atypical antipsychotic clozapine on D1 dopamine receptor-mediated function was examined in terms of its effects on behavioural responses to the new isochroman selective D1 agonist, A 68930, and to the selective D2 agonist, RU 24213. 2. In rat striatal membrane preparations, radioligand binding studies with [3H]-SCH 23390 and [3H]-spiperone confirmed clozapine to show weak and non-selective affinity for both D1 and D2 receptors. 3. Using a rapid time-sampling behavioural check list technique, clozapine (4.0-36.0 mg kg-1) exerted only modest antagonism of RU 24213 (15.0 mg kg-1)-induced sniffing and locomotion, and weakly released some episodes of myoclonic jerking; such antagonism with release of jerking has been shown previously to occur only during concurrent stimulation of D2 receptors and attenuation of D1 function. 4. Over the same dose-range, clozapine completely blocked A 68930 (0.25 mg kg-1)-induced intense grooming but failed to influence the vacuous chewing response; this profile was similar to that demonstrated previously for selective D1 antagonists. 5. On the basis of complete blockade of typical D1 agonist-induced grooming and weak release of atypical jerking to D2 agonism in the face of modest reduction in typical D2-stimulated behaviours, clozapine appears to exert some preferential but not selective attenuation of D1 receptor-mediated function. Clozapine may attenuate activity through a classical D1 receptor at a level beyond the recognition site, for which it has little affinity, or by way of new, putative 'D1-like' site(s) that subserve distinct elements of dopaminergic behaviour.

Evidence for a gender-specific decline in the rate of schizophrenia in rural Ireland over a 50-year period

The issue of whether the incidence rate of schizophrenia may have declined over recent decades has generated considerable controversy. This study sought to ascertain and interview all patients who satisfied contemporary diagnostic criteria for schizophrenia within a defined and unusually homogeneous region of rural Ireland having a total population of 25,178 people; morbid risk for schizophrenia was then examined by quinquennia of birth from 1920-24 to 1965-69. Morbid risk appeared essentially constant for persons born between 1920 and 1939 but fell by 37% for those born between 1940 and 1969, the fall being considerably more prominent in females (-56%) than in males (-19%). Attention is focused on sexual dimorphism in cerebral development and on temporal changes in endogenous or exogenous factors that influence the rate of occurrence of schizophrenia in females.

Cognitive dysfunction in schizophrenia: organic vulnerability factor or state marker for tardive dyskinesia?

The literature on the putative association between cognitive dysfunction in schizophrenia and the presence of tardive dyskinesia is critically reviewed, focusing on potential artifacts and specific relationships to a particular topography of involuntary movements. These issues are exemplified via a study of cognitive function in 64 schizophrenic patients, in which impaired cognitive flexibility was identified as the primary measure distinguishing those with tardive orofacial dyskinesia. The significance of such an association with cognitive dysfunction is considered in relation to competing hypotheses of organic vulnerability to vs. state marker for this movement disorder.

Gender specificity of geographical variation in morbid risk for schizophrenia in rural Ireland

The morbid risk for schizophrenia was determined separately for men and women within each of 36 contiguous district electoral divisions of a rural Irish county in which all cases of schizophrenia satisfying DSM-III-R criteria had been sought. The distribution of morbid risk values for men (0.0-19.2 per 1000) was in accordance with a statistical model for random occurrences in space, while for women (0.0-38.3 per 1000) it deviated markedly from such a model; thus, morbid risk for schizophrenia showed very prominent geographical variations in women, but not in men. These findings may have a basis in factors that can show both spatial inhomogeneity and gender specificity in their consequences for schizophrenia.

Behavioural effects of the putative D-3 dopamine receptor agonist 7-OH-DPAT in relation to other "D-2-like" agonists

The putative D-3 dopamine receptor agonist 7-OH-DPAT (10 micrograms/kg, s.c.) reduced spontaneous activity in rats, without inducing yawning; higher doses (0.1-10.0 mg/kg, s.c.) stimulated non-stereotyped sniffing, locomotion and chewing, which were attenuated by the selective D-1 antagonist BW 737C (5.0 mg/kg, s.c.) without release of any atypical behaviours. Low doses of 7-OH-DPAT may act on inhibitory D-3 receptors, while higher doses may act at stimulatory D-3 or other "D-2-like" receptors that participate in cooperative but not oppositional interactions with D-1 receptors.

Grooming and vacuous chewing induced by SK&F 83959, an agonist of dopamine 'D1-like' receptors that inhibits dopamine-sensitive adenylyl cyclase

The benzazepine SK&F 83959 demonstrates high affinity for dopamine D1 receptors and potently inhibits the stimulation of adenylyl cyclase by dopamine. This compound induced the same intense grooming behaviour identified previously as a characteristic response to typical dopamine D1 receptor agonists such as SK&F 77434 that stimulate adenylyl cyclase; it also induced vacuous chewing. These findings constitute direct evidence for a behaviourally relevant subtype of 'D1-like' receptor that is not linked to adenylyl cyclase.

Magnetic resonance imaging of schizophrenia-like psychoses associated with cerebral trauma: clinicopathological correlates

Three patients with schizophrenia-like psychosis and two with schizoaffective-like psychosis who experienced cerebral trauma before the onset of their illness underwent clinical and magnetic resonance imaging evaluation. Each patient with a schizophrenia-like psychosis, but neither of those with a schizoaffective-like psychosis, showed abnormalities confined to or including the left temporal lobe. These observations complement recent findings in schizophrenia.

Neurodynamics of abnormalities in cerebral metabolism and structure in schizophrenia

Much evidence points to the importance of intrauterine events in the etiology of schizophrenia and suggests a complex interplay between dysfunctional and intact neurons in the pathophysiology of the disorder. This article contrasts what is known of the topographies of metabolic and structural brain abnormalities in schizophrenia at differing stages of the illness. From these contrasts, a schema is elaborated by which subtle neurodevelopmental perturbation in early to middle gestation might give rise to functional and structural abnormalities that ultimately release the diagnostic symptoms of schizophrenia. An interaction between those mechanisms mediating the expression of psychosis and the initially subtle stages of normal aging is posited to act on the substrate of a brain that is already developmentally compromised. Such a process might masquerade as "progression" in the absence of any active disease directly attributable to the original etiological event.

Behavioural evidence for "D-1-like" dopamine receptor subtypes in rat brain using the new isochroman agonist A 68930 and isoquinoline antagonist BW 737C

The full efficacy, high potency isochroman D-1 agonist A 68930 demonstrated greater than 220-fold selectivity for D-1 over D-2 receptors. A 68930 (0.06 and 0.25 mg/kg) readily induced intense grooming, together with vacuous chewing; these responses became less evident following higher doses (1.0 and 4.0 mg/kg) and sniffing became prominent. Intense grooming was blocked by three D-1 antagonists, the benzazepines SCH 23390 (0.01-1.0 mg/kg) and NNC-756 (0.01-1.0 mg/kg), and the isoquinoline BW 737C (0.2-5.0 mg/kg); however, vacuous chewing was not antagonised by SCH 23390 and NNC-756, but was blocked by BW 737C. Intense grooming was attenuated by the D-2 antagonist YM 09151 (0.005-0.5 mg/kg) while vacuous chewing was enhanced. These data suggest that intense grooming is mediated by a "D-1 like" receptor that recognises all known chemical classes of D-1-selective compounds, while vacuous chewing may be mediated by a pharmacologically distinct subtype of "D-1-like" receptor that recognises preferentially the isochromans and isoquinolines.

Schizophrenia, Genetic Retrenchment, and Epidemiologic Renaissance

A distinctive feature of these workshops, in addition to those noted in the introductory overview, is the selection of a relatively isolated location for a 1-week period. This, together with a rich and varied program and an ethos of informality, encourages participants to discuss not only the work presented but also their unpublished work and their intuitions based on preliminary data and analyses. Such an interchange is of inestimable value to the schizophrenia research community. In scientific terms, a panel of concluding discussants (Drs Kendell, Torrey, and Waddington) were in some measure of agreement that genetics, particularly molecular genetics, appears to be experiencing a period of retrenchment, while epidemiology is experiencing something of a renaissance. Maternal influenza was a prominent theme, although the data were far from consistent. It was argued by Dr Wessely that risk for schizophrenia putatively attributable to maternal influenza might be 5% to 10% of all cases, indicating a modest effect. Eclectically, Dr Kendell believed the effect to be "real" but slight and fragile, it being sought against large aggregates that almost inevitably result in differing findings from differing countries or from different data bases within a given country. Gender differences were also among the more prominent themes, not just in an epidemiologic context but also in a variety of other studies. This points anew to disturbances in schizophrenia of factors that regulate, or are intimately associated with, sexual dimorphism in brain development. Abnormalities in cerebral asymmetry continue to pervade a variety of research findings and point further to neurodevelopmental anomalies.(ABSTRACT TRUNCATED AT 250 WORDS)

Risk of schizophrenia in adults born after obstetric complications and their association with early onset of illness: a controlled study

OBJECTIVE

To determine whether obstetric complications occur to excess in the early histories of individuals who go on to develop schizophrenia when compared with controls, and to seek clinical correlates of any such excess.

DESIGN

Contemporaneous maternity hospital records were identified and extracted verbatim, and these extracts evaluated for obstetric complications by two independent assessors who were blind to subjects' status.

SUBJECTS

65 patients having an ICD-9 diagnosis of schizophrenia, the records of the previous same sex live birth being deemed to be those of a control subject.

MAIN OUTCOME MEASURE

Presence of one or more obstetric complications recorded in maternity notes of patients and controls.

RESULTS

When two recognised scales for specifying obstetric complications were used the patients with schizophrenia were significantly more likely than controls to have experienced at least one obstetric complication (odds ratio 2.44, 95% confidence interval 1.08 to 6.03). Patients also showed a greater number and severity of and total score for obstetric complications, fetal distress being the only complication to occur to significant individual excess (present in five (8%) patients, absent in controls). There was a marked sex effect, male patients being more vulnerable (odds ratio 4.24, 1.39 to 12.90) to such complications. Obstetric complications in patients were unrelated to family history or season of birth but were associated with a significantly younger age at onset of illness (mean difference--4.5 years,--1.2 to--7.8 years).

CONCLUSIONS

Patients with schizophrenia, particularly males, have an excess of obstetric complications in their early developmental histories, and such complications are associated with a younger age at onset of their disease. Though the data are not conclusive, they also suggest that obstetric complications may be secondary to yet earlier events.

Abnormalities of Cerebral Structure in Schizophrenia on Magnetic Resonance Imaging: Interpretation in Relation to the Neurodevelopmental Hypothesis

The nature of abnormalities of cerebral structure evident in schizophrenia on magnetic resonance imaging is considered in relation to the neurodevelopmental hypothesis of the disorder. While schizophrenic patients showed increased ventricular volume, the extent of increase with age was comparable with that evident in controls and was unrelated to duration of illness. Conversely, cortical atrophy was evident only in patients, and this increased markedly with age and duration of illness. Such findings could be suggestive of two distinct pathophysiological processes in schizophrenia, but a schema for their reconciliation with the neurodevelopmental hypothesis is elaborated.

Two directions of dopamine D1/D2 receptor interaction in studies of behavioural regulation: a finding generic to four new, selective dopamine D1 receptor antagonists

A range of new, chemically distinct D1 dopamine receptor antagonists, SCH 39166, NO 756, A-69024 and BW 737C, were studied for their effects on behavioural responses to the selective D2 agonist RU 24213. Each D1 antagonist not only blocked typical sniffing and locomotor responses to RU 24213 but also released atypical myoclonic jerking behaviour, while the selective D2 antagonist YM 09151 blocked these typical responses but did not release jerking. The rank order of effectiveness of these D1 antagonists to release such D2 agonist-induced jerking was similar to that of their selectivities as D1 antagonists; also, the action of BW 737C showed complete enantioselectivity, the inactivity of its R-antipode BW 736C paralleling enantioselective blockade of D1 but not D2 receptors. It appears that while tonic activity through D1 receptors is necessary for the expression of typical D2-stimulated behaviour, via well-known cooperative/synergistic D1:D2 interactions, D1 tone also normally inhibits, via oppositional D1:D2 interactions, the expression of atypical D2-stimulated behaviours such as jerking. Oppositional D1:D2 interactions are evident using all of the classes of selective D1 antagonist currently known, and appear to constitute another general mode of dopaminergic regulation.

New classes of selective D-1 dopamine receptor antagonist provide further evidence for two directions of D-1:D-2 interaction

Initial notions of cooperative/synergistic interactions between D-1 and D-2 dopamine receptors have been followed by recent evidence suggesting more complex forms of D-1:D-2 interaction. Each of the new, putative selective D-1 antagonists SCH 39166, NO 756 and A-69024 antagonised typical behavioural responses to the selective D-2 agonist RU 24213 and concurrently released atypical behaviour. These data extend new notions of both cooperative/synergistic and oppositional D-1:D-2 interactions in the regulation of typical and atypical behaviours, which may involve further subtypes of D-1 and of D-2 receptor.

Agonist and antagonist interactions with D1 dopamine receptors: agonist-induced masking of D1 receptors depends on intrinsic activity

The effects of agonist and antagonist compounds on the equilibrium binding of the D1 antagonist ligand [3H]SCH 23390 were examined in membranes from the striatum of the rat. The antagonist SK&F 83566 interacted with D1 receptors in the manner of a competitive antagonist, causing a decrease in the affinity of the binding of [3H]SCH 23390, without altering the maximum number of binding sites (Bmax). The interaction of agonist compounds with the D1 receptor appeared to be more complex. The drug SK&F 75670, a weak partial agonist, also acted competitively at D1 sites. However, agonists with moderate (SK&F 38393, CY 208-243) or full (dopamine) intrinsic activity to stimulate adenylate cyclase, interacted with D1 binding sites in a mixed competitive/non-competitive manner, causing both a decrease in ligand affinity and a decrease in Bmax. The benzazepine analogue, which also has full agonist activity, SK&F 82958, only caused a reduction in Bmax. Furthermore, there was a positive relationship between the intrinsic activity of agonists and the magnitude of the reductions in Bmax which they induced. In the presence of the GTP analogue, Gpp(NH)p, CY 208-243 no longer caused an apparent reduction in the number of receptors. These data suggests that the apparent loss of D1 receptors, induced by agonists, may result from an interaction with a guanine-nucleotide sensitive, high affinity agonist binding site and that the degree of interaction with this site depends on the intrinsic D1 activity of the agonist.

D-1 dopamine receptors and the topography of unconditioned motor behaviour: studies with the selective, 'full efficacy' benzazepine D-1 agonist SKF 83189

Approaches to studying the role of the D-1 receptor in the regulation of unconditioned motor behaviour, and the current status of results derived therefrom, are reviewed; the desirability of utilizing drug tools other than the benzazepine partial D-1 agonist SKF 38393 is emphasized, particularly the need for studies with full D-1 agonists. Behavioural responses to the benzazepine putative full D-1 agonist SKF 83189 were compared with those to its high potency but only partial agonist counterpart SKF 77434. Both agents produced qualitatively and generally quantitatively similar behavioural responses, particularly intense grooming in the absence of vacuous chewing; thus, their behavioural properties appeared entirely unrelated to their efficacies to stimulate adenylate cyclase, the classical definition of a D-1 agonist. There may be complex interactions between selectivity, intrinsic activity and CNS penetrability, or a high D-1 receptor reserve ('spare' receptors); however, these results point towards the notion of behaviourally relevant subtypes of D-1 receptor, possibly utilizing transduction mechanisms other than, or additional to, adenylyl cyclase, for which there is emerging evidence.