Dopamine D1 receptor behavioral responsitivity following selective lesions of the striatal patch compartment during development

Histamine H3 receptor agonist- and antagonist-evoked vacuous chewing movements in 6-OHDA-lesioned rats occurs in an absence of change in microdialysate dopamine levels

In rats lesioned neonatally with 6-hydroxydopamine (6-OHDA), repeated treatment with SKF 38393 (1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol), a dopamine D(1)/D(5) receptor agonist, produces robust stereotyped and locomotor activities. The gradual induction of dopamine D(1) receptor supersensitivity is known as a priming phenomenon, and this process is thought to underlie not only the appearance of vacuous chewing movements in humans with tardive dyskinesia, but also the onset of motor dyskinesias in L-dihydroxyphenylalanine (L-DOPA)-treated Parkinson's disease patients. The object of the present study was to determine the possible influence of the histaminergic system on dopamine D(1) agonist-induced activities. We found that neither imetit (5.0 mg/kg i.p.), a histamine H(3) receptor agonist, nor thioperamide (5.0 mg/kg i.p.), a histamine H(3) receptor antagonist/inverse agonist, altered the numbers of vacuous chewing movements in non-primed-lesioned rats. However, in dopamine D(1) agonist-primed rats, thioperamide alone produced a vacuous chewing movements response (i.e., P < 0.05 vs SKF 38393, 1.0 mg/kg i.p.), but did not modify the SKF 38393 effect. Notably, both imetit and thioperamide-induced catalepsy in both non-primed and primed 6-OHDA-lesioned rats, comparable in magnitude to the effect of the dopamine D(1)/D(5) receptor antagonist SCH 23390 (7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine; 0.5 mg/kg i.p.). Furthermore, in primed animals both imetit and thioperamide intensified SCH 23390-evoked catalepsy. In vivo microdialysis established that neither imetit nor thioperamide altered extraneuronal levels of dopamine and its metabolites in the striatum of 6-OHDA-lesioned rats. On the basis of the present study, we believe that histaminergic systems may augment dyskinesias induced by dopamine receptor agonists, independent of direct actions on dopaminergic neurons.

Behavioral effects of dopamine agonists and antagonists in MPTP-lesioned D3 receptor knockout mice

To test the modulatory role of D(3) receptors in normal and dopamine-depleted mice, D(3) receptor KO mice and wild-type (WT) littermates were administered saline, L-dopa/carbidopa (20/2 mg/kg ip), a preferential D(3)>D(2) agonist S32504, a D1+D(2)/D(3) agonist apomorphine, a selective D(3) antagonist S33084, or apomorphine with S33084 prior to and after administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We monitored lines crossed in a 55-min session, average number of rears, and average number of grooming bouts. MPTP treatment produced equivalent 70% losses of dopamine fibers in the caudate putamen (CPu) and nucleus accumbens (NAC) of WT and D(3) KO mice as compared to their control (vehicle injected) counterparts. D(3) receptors were absent in KO mice, and the number of D(3) receptors was unaffected by MPTP-induced loss of DA terminals in WT mice. The results support a lack of involvement of the D(3) receptor for D1:D2 receptor-mediated behavioral activity (synergy). First, S32504 inhibited all behaviors and to a similar degree in D(3) KO and WT mice. Second, S33084 at the higher concentration increased number of lines crossed in response to high dose apomorphine in both D(3) KO and WT mice. Third, in nonlesioned mice, apomorphine-induced gnawing stereotypies were inhibited by S33084 in both D(3) KO and WT mice. Interestingly, the inhibition of apomorphine-induced gnawing was not apparent in MPTP-lesioned mice, and this stereotypy was elevated in D(3) KO-MPTP-lesioned mice. Thus, the suppressive effects of S32504 could be via D2 autoreceptor inhibition of DA release, and D2 receptor blockade by S33084 leads to release of that inhibition. This may be more apparent in MPTP-lesioned partially DA denervated mice.

Effect of prenatal administration of haloperidol, risperidone, quetiapine and olanzapine on spatial learning and retention in adult rats

The typical antipsychotic haloperidol and atypical antipsychotics olanzapine, quetiapine and risperidone were administered to pregnant Sprague-Dawley dams in the drinking water from Days 8 to 18 of gestation. When the offspring reached adulthood (2 months), spatial learning and short-term retention were examined using the radial arm maze. Results showed that prenatal administration of haloperidol, risperidone and quetiapine impaired learning but only haloperidol and risperidone disrupted short-term retention.

Timing: A critical determinant of the functional consequences of neonatal 6-OHDA lesions

Previous data have indicated that intrastriatal (IS) lesions of the dopamine (DA) system early in development result in a selective effect on D1 receptor expression and sensitivity, which is not seen with adult lesions or lesions made later in development. The purpose of the present study was to test the hypothesis that the timing of the lesion is a critical determinant of the consequences of DA depletion during development. Rats received IS injections of 6-hydroxydopamine (6-OHDA) on day of birth/postnatal day 1 (P0/1) or P7, which resulted in similar decreases in the number of DA uptake sites (> or =70% loss), a measure of DA terminal density. As adults, lesioned rats were challenged with DA receptor agonists to examine the functional sensitivity of D1 and D2 receptors. In adulthood, P0/1-lesioned rats exhibited increases in oral dyskinesias and rearing behavior following treatment with the partial D1 receptor agonists, SKF38393 and SKF77434, whereas rats lesioned on P7 exhibited increases in grooming. P7-lesioned rats also exhibited increases in gnawing, explosive jumping, and self-biting behavior following treatment with the full D1 receptor agonist SKF82958, which were not observed in the other groups. The results support the hypothesis that the timing of DA denervation is of paramount importance for governing the functional consequences of neonatal lesions, as measured by the incidence of DA agonist-induced behaviors in adulthood.

There is a limited critical period for dopamine's effects on D1 receptor expression in the developing rat neostriatum

Neonatal lesions of the dopamine (DA) system have different behavioral and neurochemical effects than lesions made in adulthood. Previous data from this laboratory have indicated that in the early postnatal period, lesions to the DA system induced by instrastriatal 6-hydroxydopamine (6-OHDA) result in a rapid and permanent loss of striatal D1 binding sites, but D2 receptor binding is unaffected. The length of the postnatal period within which neonatal instrastriatal 6-OHDA administration is effective in modulating D1 receptor binding is not known. To determine when D1 and D2 receptors are vulnerable to lesions of the DA system, we administered 6-OHDA intrastriatally to damage the DA innervation at different ages in the early postnatal period, at day of birth/postnatal day 1 (P0/1), P7 or P15 and examined DA receptor binding at P90 with quantitative autoradiography. Using [3H]mazindol binding to DA transporters (DAT) to verify the extent of the lesion, we then quantified the number of D1 binding sites using [3H]SCH23390 and D2 sites with [3H]spiroperidol. There were significant reductions in DAT sites at P0/1 (78 to 88%) and P7 (67 to 81%) but less significant changes at P15 (34 to 50% losses). The lesions were most effective for the dorsal caudate-putamen than more ventrally or in the nucleus accumbens. Our results demonstrate a significant reduction in D1 sites in all regions of the neostriatum following lesions at P0/1. The dorsal caudate-putamen was affected the most (51% loss, and the nucleus accumbens (41%) and ventral caudate-putamen less so (31%). No significant changes in D1 receptors were found at P7 or P15 and D2 receptors were unaffected with lesions in any of the age groups. The results indicate that there is a critical period for affecting expression of D1 receptors and this effect may, in addition, be related to the pattern of DA loss. Additionally, regulation of D2 receptors by this degree of loss of DA innervation does not occur during the first two weeks postnatally.

Functional and molecular differentiation of the dopamine system induced by neonatal denervation

The administration of the neurotoxin 6-hydroxydopamine (6-OHDA) to damage the mesostriatal dopamine (DA) system in the neonate results in different neurochemical and behavioral consequences as compared to lesions made in adulthood. There have been few direct data to support the conclusion that the behavioral changes following neonatal 6-OHDA lesions reflect plasticity of the DA system. It is our hypothesis that the plasticity of the developing DA system is fundamentally different from that of the adult. Responses to 6-OHDA lesions can only be understood within the context of the status of the mesostriatal DA system at the time of the lesion. There are stages of development in the early postnatal period when certain components of the mesostriatal DA system are differentially sensitive to 6-OHDA lesions. These "windows" of vulnerability can be predicted from an analysis of the developmental expression of DA receptors and the maturation of the subpopulation of the mesostriatal DA system that innervates them. We review the differences in the behavioral plasticity of the adult and neonate sustaining 6-OHDA lesions to the mesostriatal DA system, the mechanisms responsible for the behavioral plasticity in the adult, and our conceptualization of which mechanisms are affected in the neonate.

Independent mediation of unconditioned motor behavior by striatal D1 and D2 receptors in rats depleted of dopamine as neonates

The effects of systemic administration of DA receptor antagonists suggest that unconditioned motor behavior in rats depleted of DA as neonates continues to be dependent upon dopaminergic transmission, yet the specific contribution of D1 and D2 receptors to these behaviors has been altered. The purpose of the present study was to determine whether these depletion-induced receptor changes are occurring at the level of striatal DA terminals and their targets. The ability of bilateral intrastriatal injections (0.5 microliter) of DA receptor antagonists to induce motoric deficits was determined in adult rats treated with vehicle or 6-OHDA (100 micrograms, intraventricular) on postnatal day 3. Administration of the D1-like antagonist SCH 23390 (0.5-2.0 micrograms) or the D2-like antagonist clebopride (1.0-4.0 micrograms) induced dose-dependent akinesia, catalepsy, and somatosensory neglect in vehicle-treated controls. In contrast, neither antagonist produced deficits in rats depleted of forebrain DA as neonates. However, combined administration of SCH 23390 + clebopride induced similar akinesia, catalepsy, and somatosensory neglect in both controls and DA depleted animals. Animals depleted of DA were more sensitive than controls to the low doses of this combined D1 + D2 antagonism. These results demonstrate that activation of striatal DA receptors remains necessary for unconditioned motor behavior in rats depleted of DA as neonates. However, the specific contributions of D1- and D2-like receptors to these behaviors differ between intact animals and those depleted of DA as neonates. The ability of endogenous DA acting at either D1 or D2 receptors to support spontaneous motor behavior in rats depleted of DA as neonates may contribute to their relative sparing from parkinsonian deficits.

Neonatal 6-hydroxydopamine lesions lead to opposing changes in the levels of dopamine receptors and their messenger RNAs

Previous studies have established that selective damage to the early-developing components of the mesostriatal dopamine system produces profound changes in dopamine D1 receptor-mediated behaviors, while decreasing D1 receptor density. In order to better understand the effects of early intrastriatal 6-hydroxydopamine lesions, we studied the ontogenetic expression (postnatal days 7, 14, 35 and 90) of D1 and D2 receptors, and their corresponding messenger RNAs, in rats that had received intrastriatal 6-hydroxydopamine or vehicle lesions on postnatal day 1. Using receptor autoradiography, significant (P < 0.05) decreases in [3H]SCH 23390 binding to D1 receptors in the rostral and caudal dorsomedial and ventromedial caudate of 6-hydroxydopamine-lesioned animals were evident by postnatal day 7, and remained depressed at all future time points. A significant decrease in D1 receptor concentration occurred in the dorsolateral caudate at later time points (postnatal days 35 and 90). [3H]Spiperone binding to D2 receptor sites was unchanged throughout the entire study. In situ hybridization for D1 and D2 messenger RNA expression showed contrasting results. 6-Hydroxydopamine induced significant decreases of D1 messenger RNA levels in the dorsolateral and dorsomedial caudate by postnatal day 7. By postnatal day 14, messenger RNA expression was significantly elevated in the dorsomedial and ventromedial caudate of the 6-hydroxydopamine group, and remained elevated thereafter. D1 messenger RNA levels became elevated in the lateral caudate at later time points (postnatal days 35 and 90). The opposing changes in D1 receptor concentrations and the messenger RNA encoding the protein did not occur as a consequence of increased transport of D1 receptors to striatonigral terminals. D2 messenger RNA levels in the dorsal caudate were significantly decreased on postnatal day 7, and became higher than controls at postnatal day 14, but were unchanged from controls at later time points. Together, the D1 receptor and D1 messenger RNA findings suggest that the normal relationship between levels of D1 receptor transcript and D1 receptor protein is permanently altered following the early loss of dopamine. In contrast, the results indicate that dopamine plays a minor role in the early postnatal development of the D2 receptor protein and transcript. These findings suggest that dopamine may be involved in the coordinated expression of some dopamine receptors and their corresponding messenger RNAs during development.

Ontogeny of the D1 dopamine receptor in the rat striatonigral system: an immunohistochemical study

Antibodies were raised against a recombinant protein to analyse the pre- and postnatal ontogeny of the neurons expressing the D1 dopamine receptor in the striatum by immunohistochemistry. We report that D1 immunoreactivity is detectable from gestational day (G) 15 and is distributed homogeneously throughout the striatum from G15 to G18. From G19-20 to postnatal day (P) 3, D1 immunoreactivity becomes heterogeneous and predominates in cell bodies of the patch compartment while very limited immunoreactivity is detectable in the matricial compartment. The differential intensity between patches and matrix reaches its peak around P0. From P2, the pattern of D1 immunoreactivity progressively assumes the homogeneous distribution characteristic of the adult striatum. The expression of D1 mRNA in striatal neurons, as investigated by in situ hybridization, displays a similar pattern during this period. Substance P mRNA is also preferentially expressed in the patch compartment during the same period. D1 immunoreactivity appears at G17 in the substantia nigra as clusters of fibres and increases subsequently until reaching its adult form during the first postnatal week. These results demonstrate that the two compartments of the developing striatum display differential transcriptional and translational activity for the D1 gene and consequently two different and successive patterns of expression of D1 protein: patch neurons first express D1 receptor intensely while matrix neurons express it later and in smaller amounts so that D1 receptor appears transiently during the perinatal period as a marker of the patch compartment.

Dopamine receptor supersensitivity

Dopamine (DA) receptor supersensitivity refers to the phenomenon of an enhanced physiological, behavioral or biochemical response to a DA agonist. Literature related to ontogenetic aspects of this process was reviewed. Neonatal 6-hydroxydopamine (6-OHDA) destruction of rat brain DA neurons produces overt sensitization to D1 agonist-induced oral activity, overt sensitization of some D2 agonist-induced stereotyped behaviors and latent sensitization of D1 agonist-induced locomotor and some stereotyped behaviors. This last process is unmasked by repeated treatments with D1 (homologous "priming") or D2 (heterologous "priming") agonists. A serotonin (5-HT) neurotoxin (5,7-dihydroxytryptamine) and 5-HT2C receptor antagonist (mianserin) attenuate some enhanced behavioral effects of D1 agonists, indicating that 5-HT neurochemical systems influence D1 receptor sensitization. Unlike the relative absence of change in brain D1 receptor number, DA D2 receptor proliferation accompanies D2 sensitization in neonatal 6-OHDA-lesioned rats. Robust D2 receptor supersensitization can also be induced in intact rats by repeated treatments in ontogeny with the D2 agonist quinpirole. In these rats quinpirole treatments produce vertical jumping at 3-5 wk after birth and subsequent enhanced quinpirole-induced antinociception and yawning. The latter is thought to represent D3 receptor sensitization. Except for enhanced D1 agonist-induced expression of c-fos, there are no changes in the receptor or receptor-mediated processes which account for receptor sensitization. Adaptive mechanisms by multiple "in series" neurons with different neurotransmitters may account for the phenomenon known as receptor supersensitivity.

D1- and D2-receptor mediation of motoric behavior in rats depleted of DA as neonates: effects of age and size of depletion

The D1/D2 mediation of motor behavior in rats is qualitatively altered following large forebrain dopamine (DA) depletions on postnatal day 3. These animals are markedly subsensitive, relative to controls or animals depleted of DA as adults, to the motoric deficits produced by individual D1- or D2-like antagonists but are impaired following combined D1 +D2 antagonists. In order to determine the extent of DA depletion necessary to produce this subsensitivity to individual antagonists, we compared the motoric effects of D1 and D2 antagonists in adult animals sustaining a wide range of DA depletions on day 3. Only animals with striatal depletions of > or = 95% demonstrated this subsensitivity to individual antagonists. Moreover, since important changes in DA receptor ontogeny occur during the first postnatal week, we compared the ability of the D1-like antagonist, SCH 23390 (0.2 mg/kg), or the D2-like antagonists, clebopride (10.0 mg/kg) and haloperidol (1.0 mg/kg), to induce akinesia or catalepsy in adults depleted of DA on either day 1 or on day 3. Rats depleted of striatal DA (> 95%) at either age exhibited similar subsensitivity to D1 or D2 antagonists. These findings suggest that large DA depletions are necessary to alter the roles of D1 and D2 receptors in the expression of motor behavior and that this plasticity is comparable in animals depleted on day 1 or day 3.

D1 and D2 dopamine receptors do not up-regulate in response to neonatal intrastriatal 6-hydroxydopamine lesions

The extent of dopamine (DA) depletion appears to exert important influences on the plasticity of the DA system following lesions made in adulthood. The aim of this study was to determine if the extent of DA depletion has long-term effects on DA receptor regulation after early neonatal lesions. Early intrastriatal injections of 6-hydroxydopamine (6-OHDA) caused a dose-dependent loss of high-affinity DA uptake sites and mu-opioid receptor patches evident in adulthood. DA receptors did not up-regulate in response to any degree of neonatal DA depletion. A patchy loss of D1 binding was evident following the neonatal lesions, although the loss was somewhat more severe and uniform with the highest dose of 6-OHDA (20 micrograms per striatum). There was also a slight decrease in D2 binding which was not dose-dependent. These results suggest that the consequences of early neonatal DA lesions are not dependent upon the degree of DA depletion, as the effects on DA receptor expression were similar regardless of the extent of the lesions.

The dopamine hypothesis of schizophrenia: limbic interactions with serotonin and norepinephrine

The "dopamine hypothesis" of schizophrenia has been the predominant guiding theoretical construct for driving studies of the neurobiology of schizophrenia. There has, however, been much interest in the contributions of non-dopamine systems to the clinical symptoms of schizophrenia, in particular, norepinephrine and serotonin. However, direct evidence for altered transmission in monoamine systems has been quite limited. In part this reflects a focus on specific brain regions for different transmitters, in contrast to a "neural systems" approach. Thus, evidence for the dopamine hypothesis has been derived from studies of the basal ganglia in schizophrenic cases and infrequently from other (e.g. cortical) regions. Recent studies have suggested that disturbances in the organization or development of the temporal lobe may underlie certain aspects of the symptoms of schizophrenia In particular, the hippocampus may show cellular loss or disturbances in cell orientation. These results are supported by the work that has identified neuropsychological and in vivo brain disturbances in schizophrenia specific to the medial temporal lobe. However, not all cases show such pathology and it is likely that these disorders could, in addition, involve an important afferent and/or efferent system associated with the temporal lobe. This model is based on the currently held view that parallel cortico-striatal-pallidal-thalamo circuits form an important basis for information processing in the brain. One such circuit involves the primary efferent of the hippocampus, the subiculum, and associated cortical regions that project onto the ventral striatum. Many of the cortical regions that project directly to the ventral striatum also project to the hippocampus via the entorhinal cortex. These include the anterior cingulate, posterior cingulate, superior temporal cortex, and inferior temporal cortex. The ventral striatum, made up of the nucleus accumbens, olfactory tubercle, and ventral putamen, has as its target the ventral pallidum. The ventral pallidum projects to the medial dorsal nuclei of the thalamus, which, in turn, projects to the anterior prefrontal cortical area. This loop has been referred to as the limbic loop. The patterns of innervation and expression of monoamine receptors in the brain have been delineated for the non-human primate and are being unraveled in the human. We, and other, have described the patterns of receptor expression in the limbic circuit. However, few studies have been published to date that detail what the neurochemical counterparts of the neuronal and neuropsychological disturbances in the limbic circuit might be. We have explored the possibility that monoamine systems are altered at more than one synaptic station in this circuit.(ABSTRACT TRUNCATED AT 400 WORDS)

Neonatal 6-OHDA Lesions differentially affect striatal D1 and D2 receptors

Lesions to the dopamine (DA) system in early postnatal development have different behavioral consequences compared to lesions made in adulthood. Intrastriatal injections of the neurotoxin 6-hydroxydopamine (6-OHDA) on the day of birth (PO) or postnatal day 1 (P1) produce a selective supersensitivity to D1 receptor agonists and a subsensitivity to D1 antagonists (Neal and Joyce, 1991a). In this paper, we describe the long-term effects of early DA loss on DA receptor regulation. Pups received bilateral intrastriatal injections of the neurotoxin 6-OHDA (4 micrograms per striatum) on PO or P1. Adult rats were killed at 90 days of age and the brains were processed for quantitative autoradiography (QAR) or tyrosine hydroxylase (TH) immunocytochemistry. Cohorts were tested for the behavioral responses to the selective D1 receptor agonist SKF38393 (10 mg/kg). Neonatally lesioned rats exhibited increases in abnormal perioral movements in response to D1 receptor stimulation. There was a heterogenous and patchy loss (40-50%) of [3H]mazindol binding to high-affinity DA uptake sites (a marker of DA terminal density) and a similar loss of TH-like immunoreactivity within the striata of the neonatally lesioned rats. There was also a reduction in the number of mu-opioid receptor patches (labelled with [3H]naloxone), a marker for the striatal patch compartment, and a similar patchy loss of D1 binding sites (labeled with [3H]SCH23390). The binding of [3H]spiroperidol to D2 sites was not altered. This is in contrast to the changes observed following adult 6-OHDA lesions, wherein there is a significant increase in the number of D2 binding sites (Joyce, 1991a,b). The results are discussed with respect to the behavioral consequences of neonatal lesions and the differences between neonatal and adult lesions.