Comparative distribution of messenger RNAs encoding glutamic acid decarboxylases (Mr 65,000 and Mr 67,000) in the basal ganglia of the rat.

Glutamic acid decarboxylase, the enzyme required for GABA synthesis, exists as distinct isoforms, which have recently been found to be encoded by different genes. The relative expression of messenger RNAs encoding two isoforms of glutamic acid decarboxylase (Mr 67,000 and Mr 65,000) was measured at the single-cell level in neurons of the rat basal ganglia with in situ hybridization histochemistry. Both messenger RNAs were expressed in neurons of the striatum, pallidum, and substantia nigra pars reticulata, but marked differences in the relative level of labelling were observed with the two probes. In striatum, efferent neurons were more densely labelled for the messenger RNA encoding glutamic acid decarboxylase (Mr 65,000) than for the messenger RNA encoding glutamic acid decarboxylase (Mr 67,000), whereas the reverse was observed for GABA-ergic interneurons. Neurons of the entopeduncular nucleus were much more densely labelled for messenger RNA encoding glutamic acid decarboxylase (Mr 65,000) than for messenger RNA encoding glutamic acid decarboxylase (Mr 67,000). In addition, labelling for messenger RNA encoding glutamic acid decarboxylase (Mr 65,000) was higher in the entopeduncular nucleus (internal pallidum) than in the globus pallidus (external pallidum), a structure which expressed similar levels of both mRNAs. In contrast to neurons of the internal pallidum, efferent neurons of the substantia nigra pars reticulata expressed slightly more messenger RNA encoding glutamic acid decarboxylase (Mr 67,000) than that encoding the other isoform of the enzyme. The results suggest a differential expression of the messenger RNAs encoding the two isoforms of glutamic acid decarboxylase in subpopulations of basal ganglia neurons in rats.

Clozapine and haloperidol have differential effects on glutamic acid decarboxylase mRNA in the pallidal nuclei of the rat.

The striatum, and one of its targets, the pallidum (globus pallidus and entopeduncular nucleus) are based ganglia nuclei involved in extrapyramidal movement control. Gamma-aminobutyric acid (GABA)ergic neurons of the pallidum may be important for the expression of the effects of agents which alter striatal neurotransmission. In this study, rats were treated once daily for 28 days with either haloperidol or clozapine, two drugs which respectively, do and do not, induce extrapyramidal movement disorders. In situ hybridization histochemistry was used to quantify the levels of labeling for the messenger ribonucleic acid encoding glutamic acid decarboxylase, the main synthesizing enzyme for GABA in neurons of the striatum, globus pallidus, and entopeduncular nucleus. Neither drug treatment altered levels of labeling in the striatum. Haloperidol treatment increased the level of labeling in the entopeduncular nucleus and clozapine treatment increased labeling in the globus pallidus suggesting that these drugs exert different regulatory effects on pallidal neurons.

Behavioral deficits in rats with minimal cortical hypoplasia induced by methylazoxymethanol acetate.

Methylazoxymethanol, a short-acting antimitotic agent, produces marked cortical hypoplasia in fetuses when injected into pregnant rats. These offspring also have increased cortical concentrations of biogenic amines associated with hyperactivity and learning deficits. In this experiment, rats with a relatively mild degree of methylazoxymethanol-induced cortical hypoplasia were studied to determine whether these neurochemical and behavioral abnormalities persisted. Sprague-Dawley pregnant rats were injected intraperitoneally on day 15 of gestation with methylazoxymethanol acetate (25 mg/kg). Total brain weight was reduced by 12% and cortical slab weight by 28% in methylazoxymethanol-exposed offspring. They were more active than control rats and showed a trend toward slower learning in a swim maze. Affected offspring had increased cortical concentrations of norepinephrine, 5-hydroxyindoleacetic acid, and glycine. There was no significant difference in the concentrations of serotonin gamma-aminobutyric acid, aspartic acid, glutamic acid, or glutamine. Methylazoxymethanol-lesioned animals with mild cortical hypoplasia remained measurably hyperactive and may serve as a model for the study of neurotransmitter and neuropathologic abnormalities associated with hyperactivity in children with microcephaly.

Children with self-injurious behavior.

Self-injurious behavior is a serious problem that is not uncommon among individuals with mental retardation. Medical and developmental characteristics of 97 children, adolescents, and young adults (age range 11 months to 21 years, 11 months) assessed and treated for self-injurious behavior in a specialized, interdisciplinary inpatient unit between 1980 and 1988 were reviewed. This population differed from those reported in previous studies in that it was of school age and predominantly community based. Severe or profound mental retardation was present in 82.5% of our patients. The causative diagnoses associated with self-injurious behavior were similar to those of severe mental retardation alone. Associated disabilities represented at greater than expected frequencies included pervasive developmental disorders, visual impairment, and a history of infantile spasms. Most patients (81.4%) engaged in more than one type of self-injurious behavior. The most common topographies were head banging, biting, head hitting, body hitting, and scratching. Physical injury was documented in 77% of cases; the injuries most frequently reported were excoriations, scars/callus formation, hematomas, and local infection. As community placement of handicapped individuals continues to increase, pediatricians will be called upon to monitor patients who engage in self-injurious behavior.

Clozapine decreases enkephalin mRNA in rat striatum.

Typical antipsychotic drugs (i.e. haloperidol) induce extrapyramidal movement disorders while 'atypical' antipsychotics (i.e. clozapine) do not. In situ hybridization histochemistry followed by film autoradiography showed that clozapine treatment (20 mg/kg i.p. daily for 28 days) decreased the level of labelling for preproenkephalin mRNA in the striatum of the rat while haloperidol treatment (1 mg/kg i.p. daily for 28 days) resulted in no change compared with controls. The results suggest that these typical and atypical antipsychotic drugs exert differential effects on the enkephalin-containing striatal projection to the globus pallidus, a pathway critical for the expression of extrapyramidal movement disorders.

Increased glutamic acid decarboxylase (GAD) mRNA and GAD activity in cerebellar Purkinje cells following lesion-induced increases in cell firing.

Lesions of the inferior olive-climbing fiber projection to the cerebellar Purkinje cell were produced in adult rats using the neurotoxin 3-acetylpyridine. At 7 days post-lesion, glutamic acid decarboxylase (GAD) activity in Purkinje cell axons terminating in the lateral division of the deep cerebellar nucleus was significantly increased (+58%) above control levels. GAD mRNA levels in Purkinje cell bodies from the same animals were measured by in situ hybridization histochemistry using a radiolabeled cRNA probe for GAD mRNA. GAD mRNA was significantly elevated (+42%) above control at 7 days post-lesion. Because lesions of the climbing fiber system increase Purkinje cell firing rates, the results suggest that increased Purkinje cell activity induces transcription of GAD mRNA, which in turn results in increased GAD availability in Purkinje cell terminals.

Psychopharmacology in children with developmental disabilities.

A variety of motor and behavioral symptoms may cause functional impairment in children with developmental disabilities. Some of these symptoms, including increased tone, involuntary movements, and disruptive behaviors, may be helped by multimodal treatments that include pharmacotherapy. Treatment with psychopharmacologic agents can also cause unwanted CNS side effects that can be as detrimental as the target symptom, however. Identification and measurement of target symptoms at baseline and maintenance drug conditions, in conjunction with careful medical monitoring, provide the pediatrician and family with the information needed to make decisions about drug treatment.

What is attention-deficit/hyperactivity disorder?

ADHD is a highly prevalent condition with the core symptoms of functionally impairing limitations in sustained attention and impulsivity/overactivity. Other frequent symptoms include overemotionality or overreactivity, academic underachievement, low self-esteem, and interpersonal difficulties. The assessment for and diagnosis of ADHD are complicated by the lack of a specific test or marker for the disorder, the occurrence of symptoms along a continuum in the population, and its frequent association with other neurodevelopmental and psychiatric disorders. Due to the often pervasive effects of these symptoms and their chronicity, treatment generally must be multifaceted and prolonged. Neuropsychological studies suggest that individuals with ADHD may have their most salient difficulties in the areas of organizing, preparing, and inhibiting responses. Neurobiologic studies suggest that the circuitry involving frontal cortical-basal ganglia connections may be structurally or functionally different in individuals with ADHD, although the specificity of these findings has not been researched thoroughly. ADHD symptoms are highly, although not entirely, heritable. Many questions remain as to the specifics of etiology and best treatment practices.

Differential effects of chronic treatment with haloperidol and clozapine on the level of preprosomatostatin mRNA in the striatum, nucleus accumbens, and frontal cortex of the rat.

1. The goal of this work was to determine the effects of typical and atypical neuroleptics on the level of preprosomatostatin messenger RNA (mRNA) in regions of the rat brain innervated by dopaminergic neurons. 2. Quantitative in situ hybridization histochemistry was used to measure the levels of mRNA encoding preprosomatostatin in neurons of the striatum, the nucleus accumbens, and the medial and lateral agranular areas of the frontal cortex in adult rats treated with either haloperidol or clozapine. 3. In untreated animals, the density of neurons containing preprosomatostatin mRNA was higher in the nucleus accumbens than in the striatum and frontal cortex. The intensity of labeling per neuron, however, was higher in the striatum than in the two other areas examined, suggesting that the expression of preprosomatostatin mRNA is differentially regulated in these brain regions. Chronic administration of haloperidol (1 mg/kg for 28 days) induced a significant decrease in the labeling for preprosomatostatin mRNA in neurons of the nucleus accumbens, frontal cortex, and medial but not lateral striatum. Treatment with clozapine (20 mg/kg for 28 days) increased the levels of preprosomatostatin mRNA in the nucleus accumbens but not in the striatum or the frontal cortex. 4. These results support a role for dopamine in the regulation of central somatostatinergic neurons. The differences in the effects of haloperidol, a neuroleptic which induces extrapyramidal side effects, and clozapine, which does not, suggest that somatostatinergic neurons may play an important role in the regulation of motor behavior.

Developmental alterations in 5-hydroxytryptamine concentration and turnover after treatment of neonatal rats with 5,7-dihydroxytryptamine.

Early disruption of the serotonin neurotransmitter system may have important consequences for normal neuro-physiological development. In order to further understand the neurochemical changes which occur after early insults to the system, intracerebroventricular injections of the serotonin-selective toxin, 5,7-dihydroxytryptamine were given to Sprague-Dawley rat pups on day 3 of life. Serotonin and 5-hydroxyindoleacetic acid concentration in cortex, striatum, hippocampus, and brainstem were measured after 4, 8, and 12 weeks. In controls, serotonin concentration in the striatum and cortex increased from 4 to 12 weeks, while it reached adult levels by 4 weeks in the hippocampus. 5-Hydroxyindoleacetic acid increased in cortex and hippocampus and was unchanged after 4 weeks in the striatum. An index of serotonin turnover (5-hydroxyindoleacetic acid/serotonin) decreased in striatum and cortex, but increased in the hippocampus over time. 5,7-Dihydroxytryptamine treatment induced permanent decreases in serotonin and 5-hydroxyindoleacetic acid concentration in all three forebrain regions, but had no region- and time-specific effects on serotonin turnover. In the brainstem of controls, serotonin concentration increased from 4 to 12 weeks, while 5-hydroxyindoleacetic acid concentration was unchanged, resulting in decreasing turnover. After 5,7-dihydroxytryptamine treatment, the brainstem did not show depletions of serotonin concentration in spite of significant serotonin neuronal loss, suggesting that compensatory mechanisms in remaining neurons may permit increased serotonin production. Regional and time-dependent responses to serotonin depletion may have functional implications for the developmental regulation of serotonin transmission after early insults to this neurotransmitter system.

Expression of glutamic acid decarboxylase mRNA in striatum and pallidum in an animal model of tardive dyskinesia.

Long-term administration of neuroleptics can induce tardive dyskinesia in humans. Oral movements with the same distinctive form observed in humans with tardive dyskinesia are observed in rats treated with haloperidol for 8 and 12 months but not 28 days. We have examined the effects of these long-term haloperidol treatments on the levels of mRNA encoding glutamic acid decarboxylase (GAD, M(r) 67,000), the rate-limiting enzyme of GABA synthesis, in the striatum and pallidum of adult rats. Despite the differences in behavior, GAD67 mRNA was increased in the striatum and entopeduncular nucleus (internal pallidum) after both 28 days and 8 months of haloperidol administration. In contrast, only long-term haloperidol treatments (8 and 12 months) decreased GAD67 mRNA in globus pallidus (external pallidum). This effect contrasted with the increased level of GAD67 mRNA we have previously observed in the globus pallidus after short-term haloperidol treatment (3-14 days), a regimen that induces catalepsy. Together with data indicating a loss of GAD activity in target areas of the globus pallidus in humans with tardive dyskinesia, the results suggest that decreased GABAergic transmission in the projection neurons of the external pallidum may play a critical role in the motor side effects associated with long-term neuroleptic therapy.