Jeannette C. Miller

Induction of c‐fos mRNA Expression in Rat Striatum by Neuroleptic Drugs

The effect of selective dopamine D2 receptor‐acting drugs on striatal c‐fos mRNA expression in the rat has been investigated by Northern hybridization and autoradiography to determine a possible role for c‐fos in the initiation of adaptive changes in D2 receptor number by neuroleptic drugs. The neuroleptic drug haloperidol, a D2 receptor antagonist, was found to produce a rapid and transient induction of c‐fos mRNA expression as compared with the expression in animals treated with saline. This induction by haloperidol was found to be dose dependent and D2 receptor mediated, inasmuch as a D2 agonist completely reversed the induction and the inactive isomer of the neuroleptic butaclamol, which does not produce an increase in D2 receptors, had no effect on c‐fos mRNA expression. From these data, it can be concluded that c‐fos expression in striatum is under dopamine D2 receptor‐mediated inhibitory control. It is suggested that c‐fos may play a role in the initiation of the increase in D2 receptor number produced by chronic neuroleptic drug treatment.

Noradrenergic activation of immediate early genes in rat cerebral cortex

Previous studies have shown that stimulation of adrenergic receptors in the brain increases the expression of the immediate early gene (IEG), c-fos, in vivo (Mol. Brain Res., 6(1989) 39-45). The present study was undertaken to determine whether this also holds for other IEGs which have been shown to be activated in brain cell culture by adrenergic agonists. Both yohimbine injection and stressful stimulation, two treatments causing brain norepinephrine (NE) release, were found to cause a parallel, transient activation of at least 5 IEGs (c-fos, nur77, tis-7, zif-268 and tis-21) in the rat cortex. Genes that are not immediate early (beta-actin, NGF and HSP70) were found not to be affected in the interval used (6 h). The responses were mediated predominantly by beta-adrenoceptors with some contribution from alpha 1 receptors. The parallel activation of multiple genes by noradrenergic receptors may enable the coding of different biochemical responses to the activation of different receptors.

Sex differences in dopaminergic and cholinergic activity and function in the nigro-striatal system of the rat

Possible sex differences in the balance between dopaminergic and cholinergic activity in the rat striatum were investigated. Female rat show a greater vulnerability to neuroleptic-induced catalepsy compared to male rats. This vulnerability to neuroleptics has a human counterpart in that women show an increased frequency of neuroleptic-induced extrapyramidal syndrome (EPS) compared to men. In humans, EPS can be alleviated by increasing dopaminergic activity or by decreasing cholinergic activity. Conversely, EPS can be precipitated by decreasing dopaminergic activity with neuroleptics, and pre-existing EPS can be made worse with cholinergic agonists. Thus, the presence of EPS in humans or catalepsy in animals, as a result of neuroleptic agents, appears to be related to low dopaminergic and/or high cholinergic activity. In the present studies of sex differences it was found that: (1) cycling female rats had fewer striatal dopamine receptors than did male rats. Estradiol treatment significantly reduced the number in males and also reduced the number, although not significantly in ovariectomized (OVX) rats; (2) cycling female rats had lower apomorphine-induced stereotypy during phases with high estrogen levels as compared to phases with low estrogen levels. Estrogen treatment of male or OVX rats resulted in attenuation of induced stereotypy compared to untreated male or OVX rats; (3) female rats had a significantly higher affinity of striatal cholinergic receptors of 3H-QNB than did males and also had higher choline acetyltransfease activity than male rats. The data from these experiments provide the first direct evidence that estrogen plays a role in shifting the balance toward cholinergic predominance in the striatum, a state that favors the development of cataleposy in female rats and EPS in women.

Prenatal neurotransmitter programming of postnatal receptor function.

Publisher Summary This chapter focuses on the prenatal neurotransmitter programming of postnatal receptor function. The biogenic amine transmitter systems in the brain have far-reaching regulatory influence on both motor and mental function. A role for catecholamines dopamine (DA) in mediating certain mental functions is inferred from the actions of neuroleptic drugs, and agents such as amphetamine, on the DA system. A role for norepinephrine (NE) and serotonin in mediating mood, level of arousal and sleep is inferred from the actions of antidepressant drugs, agents whose biochemical activity resides in their inhibitory action on noradrenergic and serotonergic reuptake and on other presynaptic mechanisms. In contrast to postnatal animals, in which a reduction in transmitter supply results in a homeostatic increase in receptor density, the prenatal animal responds to similar conditions with a decrease in receptor density. It is very interesting, from this standpoint, that the cholinergic system is central in primary information transfer in the brain.

Dopamine receptor-coupled modulation of the K+-depolarized overflow of 3H-acetylcholine from rat striatal slices: alteration after chronic haloperidol and alpha-methyl-p-tyrosine pretreatment.

Abstract The effect of dopamine on the K + -depolarized overflow of 3 H-acetylcholine from rat striatal slices was investigated to determine whether drug-induced changes in neuronal sensitivity to dopamine might be manifested in changes in striatal cholinergic activity. Dopamine was found to produce a dose-dependent inhibition of the K + -evoked release of 3 H-Ach. This inhibition could be blocked by prior exposure of the slices to haloperidol, a dopamine receptor blocker. Dopamine receptors localized on striatal cholinergic axon terminals and possibly postsynaptic dopamine receptors on cholinergic perikarya and dendrites may mediate the DA inhibition of 3 H-Ach release induced by high K + . Chronic pretreatment with haloperidol followed by alpha-methyl-p-tyrosine resulted in a significant shift to the left in the dose-dependent inhibition of K + -stimulated overflow of 3 H-Ach by dopamine. This shift to the left in the dose-response curve may be the result of an increase in the number of striatal dopamine receptors produced by chronic dopamine receptor blockade and inhibition of dopamine synthesis.

Role of maternal biochemistry in fetal brain development: effect of maternal thyroidectomy on behaviour and biogenic amine metabolism in rat progeny.

Few studies have addressed the role of biochemicals of maternal origin on fetal neurodevelopment and behavioural outcome. Thyroid deficiency in the thyroidectomized pregnant rat provides an excellent model to study fetal effects of maternal chemistry, as this condition is known to be associated with deficits in motor and cognitive behaviour in human offspring. Based on evidence that thyroid hormone of maternal origin may be an important determinant in regulating these behaviours, we assessed neurobehaviours and regional brain biogenic amine levels in offspring of rats thyroidectomized (Tx) prior to conception. Cross-fostering techniques were used to isolate fetal effects of maternal thyroid deficiency from possible neonatal effects during nursing by thyroid-deficient dams. The progeny of Tx dams showed significant deficits in maze learning, were less cautious in emotionality testing, and were more active in open-field exploration. Tx females appeared to be more vulnerable to the effects on learning. Learning in Tx males was only slightly impaired. Serotonin and dopamine metabolism was also affected in a brain region-specific manner in Tx progeny. Levels of 5-HIAA were reduced in the olfactory tubercle and cortex. HVA levels were lower in olfactory tubercle, but were elevated in the hippocampus. As these neurotransmitters play a functional role in activity, mood and learning, the findings may be pertinent to the observed behavioural impairments. The results are consistent with the hypothesis that an adequate in utero thyroid hormone environment may be essential for early fetal neurodevelopment even if the fetus is euthyroid.

Restraint stress influences AP-1 and CREB DNA-binding activity induced by chronic lithium treatment in the rat frontal cortex and hippocampus.

The therapeutic efficacy of mood stabilizers may involve the regulation of gene expression mediated by transcription factor activation. In this study, we investigated AP-1 and cAMP response element-binding protein (CREB) DNA-binding activity in the rat frontal cortex and hippocampus of rats fed a control diet, a lithium diet for 7 wk, or 6 wk of lithium, followed by withdrawal for 7 d. Subsequently, animals were exposed to restraint stress or no stress and the DNA-binding activities assessed at 2, 8 and 24 h post-stress. AP-1 activity was increased in both brain regions by lithium, an effect that persisted with lithium discontinuation. Restraint stress induced AP-1 activity in the frontal cortex of the control group. This stress-induced effect on AP-1 activity was attenuated in lithium-treated and lithium-withdrawn animals. AP-1 DNA binding was also induced by stress in the hippocampus of control animals and the activity diminished over time in the lithium and lithium-withdrawn groups. CREB activity also increased in the frontal cortex and hippocampus of the lithium-treated group. Stress increased CREB activity in the frontal cortex of the controls, and was slightly attenuated with lithium treatment. CREB activity in the hippocampus was insensitive to stress. The proteins involved in the AP-1 and CREB transcription complexes were also characterized. Our findings of increased AP-1 and CREB binding after lithium are consistent with lithiums inhibitory effect on glycogen synthase kinase-3beta, which has been show to negatively regulate AP-1 and CREB transcriptional activity.

Development of specificity and stereoselectivity of rat brain dopamine receptors

Prenatal exposure to the neuroleptic haloperidol has been reported to produce an enduring decrement in the number of dopamine D2 receptors in rat striatum and a persistent diminution of a dopamine dependent behavior, stereotypy.17 The ontogeny of rat brain dopamine binding sites has been studied in terms of the kinetic properties and phenotypic specificity in rat fetal brain through early postnatal development. Sites showing some properties of the D2 binding site can be found prior to gestational day (GD) 18, can be labeled with [3H]dopamine or [3H]spiroperidol and can he displaced with dopaminergic agonists and antagonists.5 Saturation kinetics for specific [3H]spiroperidol has previously been found to occur on or about GD 18.1.5 It is of interest that the critical period for the prenatal effect of haloperidol to reduce striatal D2 binding sites. CDs 15–18.18 coincides with the period during which dopamine binding sites lack true specificity, but can be labeled with dopaminergic ligands.

Prenatal Neuroleptic Exposure Alters Postnatal Striatal Cholinergic Activity in the Rat

Previous studies in our laboratory have shown that prenatal exposure to a neuroleptic during a critical period of gestation in the rat results in a marked deficit in the number of striatal dopamine-binding sites and in a diminution of dopamine agonist-induced stereotyped behavior. In the present studies, we examined the effect of prenatal neuroleptic exposure on biochemical parameters of cholinergic activity to determine whether the balance between striatal dopaminergic and cholinergic activity might be altered. The number of muscarinic cholinergic-binding sites and the specific activity of choline acetyltransferase were found to be significantly increased by prenatal treatment with the neuroleptics haloperidol or (+)-butaclamol. From the present studies and previous observations made in our laboratory, it is concluded that the ability of a neuroleptic to affect the number of muscarinic cholinergic receptors in postnatal life may be a result of the phenotypically undifferentiated state of the developing dopamine-binding site. Our findings of increased striatal cholinergic activity accompanied by a marked decrease in dopaminergic activity may have implications for an increased vulnerability to extrapyramidal motor disturbances during postnatal development.

Basal and stimulated C-fos mRNA expression in the rat brain: effect of chronic dietary lithium.

The mechanisms underlying the therapeutic efficacy of lithium in affective disorders are poorly understood; however, previous studies have established an influence of lithium on receptor-coupled and postreceptor signal transduction mechanisms, including the transcription factor c-fos. We investigated the effect of chronic lithium on basal, stress-, muscarinic-, and haloperidol-induced c-fos mRNA expression in various rat brain regions. Chronic lithium produced significant reductions in basal c-fos expression in the frontal cortex and hippocampus, confirming our previous report. Stress-induced c-fos was significantly attenuated in the frontal cortex, hippocampus, and pituitary, was increased in the occipital cortex, and unchanged in the hypothalamus by chronic lithium. Pilocarpine-induced c-fos was significantly reduced in the frontal cortex and hippocampus by chronic lithium, but was enhanced in the occipital cortex and hypothalamus. Haloperidol-induced c-fos was augmented in the striatum and pituitary, but reduced in the frontal cortex by chronic lithium treatment. In regions in which haloperidol did not induce fos expression in control animals, fos levels after haloperidol were reduced after chronic lithium. One week after discontinuation of the lithium treatment, basal c-fos levels remained significantly lower in the frontal cortex and hippocampus, whereas the effects of stress, pilocarpine, or haloperidol on fos were normalized in most regions, except in the hippocampus, where the attenuated fos response to injection stress persisted. We suggest that repression of basal fos expression and inhibition and activation of inducible fos may be factors to be considered in the longer-term effects of lithium, leading to changes in expression of genes that regulate fos and are regulated by Fos, and ultimately to alterations in the functional activity of neural systems involved in the pathophysiology of affective disorder.