Modification of the behavioural effects of haloperidol and of dopamine receptor regulation by altered thyroid status

Baclofen and Tizanidine Adverse Effects Observed Among Community-Dwelling Adults Above the Age of 50 Years: A Systematic Review

OBJECTIVE

This review highlights adverse effects of baclofen and tizanidine in older community-dwelling adults.

DATA SOURCES

A literature search was conducted, including search terms of "adverse effect," "baclofen," "elderly," "falls," "fractures," and "tizanidine." Studies were included if they described community-dwelling adults aged 50 years and older who received oral baclofen or tizanidine. The Federal Drug Administration Adverse Event Reporting System (FAERS) data were compiled for adverse effect incidence.

STUDY SELECTION AND DATA EXTRACTION

The literature search was completed in July 2019 and updated in June 2023. Reviews performed by 2 independent reviewers yielded 15 records. FAERS identified 486 (baclofen) and 305 (tizanidine) adverse effects of interest.

DATA SYNTHESIS

Two retrospective cohort studies evaluating baclofen use in older adults showed increased hospitalizations for encephalopathy in chronic kidney disease (7.2% vs 0.1%) and end-stage renal disease (daily dose 20 mg or more; relative risk [RR] 19.8, 95% CI = [14.0-28.0]). Other articles were case reports; 10 articles reported dyskinesias, encephalopathy or disorientation, and drowsiness associated with baclofen, and 5 articles reported bradycardia and/or hypotension with tizanidine. The FAERS Public Dashboard revealed 12.1% and 28.7% overall incidence of adverse effects of interest, with a 27.8% and 29.2% incidence of falls for baclofen and tizanidine, respectively. Baclofen and tizanidine are associated with concerning adverse effects in older adults. Alternative agents should be considered, but, if necessary, providers should start at lower doses and increase slowly.

CONCLUSIONS

This review highlights the importance of using baclofen and tizanidine with caution in older adults.

Thyroid hormones mediate the impact of early-life stress on ventral tegmental area gene expression and behavior

Proper thyroid function is essential to the developing brain, including dopamine neuron differentiation, growth, and maintenance. Stress across the lifespan impacts thyroid hormone signaling and anxiety disorders and depression have been associated with thyroid dysfunction (both hypo- and hyper-active). However, less is known about how stress during postnatal development impacts thyroid function and related brain development. Our previous work in mice demonstrated that early-life stress (ELS) transiently impinged on expression of a transcription factor in dopamine neurons, Otx2, shown to be regulated by thyroid hormones. We hypothesized that thyroid hormone signaling may link experience of ELS with transcriptional dysregulation within the dopaminergic midbrain, and ultimately behavior. Here, we find that ELS transiently increases thyroid-stimulating hormone levels (inversely related to thyroid signaling) in both male and female mice at P21, an effect which recovers by adolescence. We next tested whether transient treatment of ELS mice with synthetic thyroid hormone (levothyroxine, LT4) could ameliorate the impact of ELS on sensitivity to future stress, and on expression of genes related to dopamine neuron development and maintenance, thyroid signaling, and plasticity within the ventral tegmental area. Among male mice, but not females, juvenile LT4 treatment prevented hypersensitivity to adult stress. We also found that rescuing developmental deficits in thyroid hormone signaling after ELS restored levels of some genes altered directly by ELS, and prevented alterations in expression of other genes sensitive to the second hit of adult stress. These findings suggest that thyroid signaling mediates the deleterious impact of ELS on VTA development, and that temporary treatment of hypothyroidism after ELS may be sufficient to prevent future stress hypersensitivity.

Thyroid hormones mediate the impact of early-life stress on ventral tegmental area gene expression and behavior

Proper thyroid function is essential to the developing brain, including dopamine neuron differentiation, growth, and maintenance. Stress across the lifespan impacts thyroid hormone signaling and anxiety disorders and depression have been associated with thyroid dysfunction (both hypo- and hyper-active). However, less is known about how stress during postnatal development impacts thyroid function and related brain development. Our previous work in mice demonstrated that early-life stress (ELS) transiently impinged on expression of a transcription factor in dopamine neurons shown to be regulated by thyroid hormones. We hypothesized that thyroid hormone signaling may link experience of ELS with transcriptional dysregulation within the dopaminergic midbrain, and ultimately behavior. Here, we find that ELS transiently increases thyroid-stimulating hormone levels (inversely related to thyroid signaling) in both male and female mice at P21, an effect which recovers by adolescence. We next tested whether transient treatment of ELS mice with synthetic thyroid hormone (levothyroxine, LT4) could ameliorate the impact of ELS on sensitivity to future stress, and on expression of genes related to dopamine neuron development and maintenance, thyroid signaling, and plasticity within the ventral tegmental area. Among male mice, but not females, juvenile LT4 treatment prevented hypersensitivity to adult stress. We also found that rescuing developmental deficits in thyroid hormone signaling after ELS restored levels of some genes altered directly by ELS, and prevented alterations in expression of other genes sensitive to the second hit of adult stress. These findings suggest that thyroid signaling mediates the deleterious impact of ELS on VTA development, and that temporary treatment of hypothyroidism after ELS may be sufficient to prevent future stress hypersensitivity.

Associations of C-Reactive Protein, Free Triiodothyronine, Thyroid Stimulating Hormone and Creatinine Levels with Agitation in Patients with Schizophrenia: A Comparative Cross-Sectional Study

PURPOSE

Agitation is prevalent among inpatients with schizophrenia. The aim of this study was to investigate whether biochemical parameters are associated with agitation in schizophrenia.

PATIENTS AND METHODS

Agitation was evaluated by the Positive and Negative Syndrome Scale-Excited Component questionnaire (PANSS-EC). Fasting serum levels of C-reactive protein (CRP), free triiodothyronine (FT3), free thyroxine (FT4), thyroid-stimulating hormone (TSH), uric acid (UA), creatinine, glucose and lipids were measured.

RESULTS

The analysis included 154 inpatients with schizophrenia (71 with agitation, 83 without agitation) and 75 healthy control subjects. Patients with schizophrenia and agitation had higher serum levels of CRP, FT3, FT4 and UA as well as lower levels of serum TSH and creatinine than patients without agitation (all P < 0.05). Multivariate logistic regression analysis indicated that serum CRP (odds ratio [OR] = 1.470, P = 0.001), FT3 (OR = 13.026, P < 0.001), TSH (OR = 0.758, P = 0.033) and creatinine (OR = 0.965, P = 0.004) were significantly associated with agitation in schizophrenia. CRP, FT3, TSH and creatinine achieved an area under the ROC curve of 0.626, 0.728, 0.620 and 0.663 respectively in discriminating schizophrenia with or without agitation.

CONCLUSION

Increased serum CRP and FT3 levels and decreased serum TSH and creatinine levels are independent risk factors for agitation in hospitalized patients with schizophrenia. Inflammation, thyroid hormones and renal function may be involved in the pathogenesis of agitation in schizophrenia.

Neuroprotective Effect of Ashwagandha Extract against the Neurochemical Changes Induced in Rat Model of Hypothyroidism

The current aim is to evaluate the effect of ashwagandha root extract (AE) on the neurochemical changes induced in the cortex and hippocampus as a consequence of thyroid dysfunction induced by propylthiouracil (PTU). Male Wistar rats were divided into; control, AE treated rats, rat model of hypothyroidism and rat model of hypothyroidism treated with either AE or L-thyroxine (T4) for 1 month. Rat model of hypothyroidism showed a significant decrease in serum levels of tri-iodothyronine (T3) and T4 and a significant increase in cortical and hippocampal lipid peroxidation (MDA), nitric oxide (NO), superoxide dismutase (SOD) and catalase (CAT). However, reduced glutathione (GSH) decreased significantly. This was associated with a significant increase in hippocampal tumor necrosis factor-α (TNF-α) and cortical dopamine levels. Both L-thyroxine and AE restored T3 and T4 levels. In the hippocampus L-Thyroxine prevented the increase in MDA and restored GSH but failed to restore the increased NO and TNF-α. In the cortex L-thyroxine didn't change the increased MDA and NO and the decreased GSH induced by PTU. L-thyroxine increased cortical and hippocampal SOD and CAT. AE prevented the increased hippocampal MDA, NO and TNF-α and the decreased GSH level induced by PTU. In the cortex AE failed to restore MDA and NO but prevented the decrease in GSH. The increase in cortical dopamine level induced by PTU was ameliorated by L-thyroxine and improved by AE. The present data indicate that AE could prevent thyroid dysfunction and reduce its complications on the nervous system including oxidative stress and neuroinflammation.

Triiodothyronine accelerates and enhances the antipsychotic effect of risperidone in acute schizophrenia

In acute psychotic schizophrenia patients we investigated if the combination of triiodothyronine (T3) plus risperidone was more effective when compared to risperidone monotherapy. Thirty-two in-patients meeting the DSM-IV-TR diagnostic criteria for schizophrenia and without thyroid disease received risperidone (flexibly adjusted dose for tolerability) and were randomized to additionally receive either T3 (25 μg daily; risperidone plus T3 group) or placebo (risperidone plus placebo group). Treatment lasted until meeting the response to treatment criteria defined as score of ≤ 3 on the Clinical Global Impression Severity and Improvement scales. Acute psychotic episode symptom severity was evaluated using the Brief Psychiatric Rating Scale (BPRS) at treatment initiation and at the final study assessment. Fourteen patients were randomized to receive risperidone plus T3 and eighteen to receive risperidone plus placebo. The time until treatment response was shorter in the risperidone plus T3 group relative to the risperidone plus placebo group (25.5 ± 4.4 days vs 32.2 ± 8.2 days, respectively; p = 0.001). Moreover, there was a greater reduction of BPRS-total score (p = 0.01) in the risperidone plus T3 group relative to the risperidone plus placebo group. Treatment with T3 was associated with shorter time to treatment response (β = -0.440, p = 0.022) and with greater improvement in BPRS score (β = 0.240, p = 0.053), independent of patients' gender, age, baseline BPRS score and mean risperidone dose. The study confirms that addition of T3 to risperidone was associated with accelerated and enhanced treatment response in acutely psychotic schizophrenic patients.

Myxedema madness complicating postoperative follow-up of thyroid cancer

Although hypothyroidism is associated with an increased prevalence of psychiatric manifestations, myxedema madness is rarely observed. We report the case of a 62-year-old woman with no prior history of psychiatric disorders, who presented to the emergency department with psychomotor agitation 6 weeks after total thyroidectomy for papillary thyroid cancer. Serum thyroid stimulating hormone (TSH) on admission was 62.9 mIU/L and free T4 was < 0.35 ng/dL, indicating severe hypothyroidism. After ruling out other possible causes, the diagnosis of myxedema madness was considered; hence, antipsychotic drug treatment and intravenous levothyroxine were prescribed. Behavioral symptoms returned to normal within 4 days of presentation, while levels of thyroid hormones attained normal values 1 week after admission. Recombinant TSH (Thyrogen®) was used successfully to prevent new episodes of mania due to thyroid hormone withdrawal in further controls for her thyroid cancer. This case illustrates that myxedema madness can occur in the setting of acute hypothyroidism, completely reverting with levothyroxine and antipsychotic treatment. Recombinant TSH may be a useful tool to prevent myxedema madness or any severe manifestation of levothyroxine withdrawal for the follow-up of thyroid cancer.

Levothyroxine Augmentation in Clozapine Resistant Schizophrenia: A Case Report and Review

There are many reports that show different thyroid abnormalities in schizophrenia without clear establishment of their role in etiology and treatment outcome of schizophrenia. Among these reports, there are only a few that consider a role for thyroid hormones as augmenting agents in the treatment with antipsychotic drugs. This case report outlines symptom subsidence of a patient with clozapine refractory paranoid schizophrenia and normal thyroid function who added levothyroxine to clozapine and found that symptoms of psychosis returned once levothyroxine was discontinued. Although this observation needs to be confirmed in controlled clinical trials, we aimed to discuss possible hypothesized mechanisms underlying this observation.

Antithyroid medications and psychosis

INTRODUCTION

Antithyroid drugs (ATDs) are used in the treatment of hyperthyroidism. Very rarely ATDs were reported to trigger acute psychosis in patients with no history of psychiatric disturbances. Our aim is to review the literature on psychosis as a side effect of ATD and to give a personal opinion on this issue.

AREAS COVERED

The cases of acute psychosis elicited by ATD are few and most were reported many years ago, before radioimmunoassay for thyroid-stimulating hormone (TSH) and thyroid hormones was introduced. Most of those cases lack a description of serum thyroid hormone profile before, during and after the appearance of the psychiatric disorder; hence, an abrupt shift from hyperthyroidism to euthyroidism or hypothyroidism cannot be excluded. In addition, patients underwent specific psychiatric therapy, so that it is difficult to attribute the disappearance of the mental disorders to the withdrawal of ATD per se.

EXPERT OPINION

Patients who develop mental disorders while under ATD should be followed by an accurate evaluation of TSH, free triiodothyronine (FT3), and free thyroxine (FT4) levels throughout the course of the psychiatric disease. The use of new imaging techniques could be helpful in ruling out the encephalopathy associated with autoimmune thyroid diseases and other cerebral pathologies that might be possible causes of these mental disorders.

Revisiting thyroid hormones in schizophrenia

Thyroid hormones are crucial during development and in the adult brain. Of interest, fluctuations in the levels of thyroid hormones at various times during development and throughout life can impact on psychiatric disease manifestation and response to treatment. Here we review research on thyroid function assessment in schizophrenia, relating interrelations between the pituitary-thyroid axis and major neurosignaling systems involved in schizophrenia's pathophysiology. These include the serotonergic, dopaminergic, glutamatergic, and GABAergic networks, as well as myelination and inflammatory processes. The available evidence supports that thyroid hormones deregulation is a common feature in schizophrenia and that the implications of thyroid hormones homeostasis in the fine-tuning of crucial brain networks warrants further research.

An animal model of extrapyramidal side effects induced by antipsychotic drugs: relationship with D2 dopamine receptor occupancy

1. Muscle rigidity was assessed quantitatively and objectively as increases in electromyographic (EMG) activity (muscle rigidity) in the hindlimb muscles of the rat following subcutaneous administration of haloperidol, fluphenazine and thioridazine. 2. Behavioural changes were assessed as increases in the catalepsy score, defined as the time taken for an animal to move off an inclined grid. 3. Increased tonic EMG activity, or the presence of catalepsy was related to the level of occupancy of dopamine D2 receptors in the striatum and substantia nigra of the brain, measured using ex vivo quantitative autoradiography. 4. Increases in tonic EMG activity and the induction of catalepsy were associated with >80% occupancy of striatal and nigral D2 receptors by fluphenazine, while haloperidol increased tonic EMG activity at D2 occupancies of >57%. 5. Thioridazine at doses ranging from 1-15 mg/kg failed to increase EMG activity and occupied <61% of striatal D2 receptors. 6. Overall the findings support the hypothesis that muscle rigidity is observed when a threshold level of D2 receptors in the striatum and substantia nigra are occupied by antipsychotic drugs. 7. This conclusion is consistent with the results of positron emission tomography (PET) studies in humans, and those from our past studies in rats using raclopride, chlorpromazine and clozapine, in which a threshold of approximately 70% striatal and nigral D2 receptor occupancy has been demonstrated.

GABA uptake is inhibited by thyroid hormones: implications for depression

Studies of the effects of thyroid hormones on the uptake of neurotransmitters by homogenates of rat cerebral cortex have revealed a significant competitive inhibition of neuronal uptake of [3H]GABA by thyroid hormones (T3 greater than T4 greater than rT3). The IC50 for inhibition of GABA uptake by T3 was estimated at 4 microM and that of T4 at 11 microns. GABA uptake in homogenates of cerebral cortex from hypothyroid rats was significantly enhanced over that of controls; however, uptake in tissues from hyperthyroid rats was not significantly diminished.

The hypothalamic-pituitary-thyroid axis in patients with schizophrenia

Serum concentrations of thyroxine (T(4)), triiodothyronine (T(3)), reverse triiodothyronine (rT(3)) and thyrotropine (TSH) were measured in 31 acutely ill in-patients with schizophrenia before and after four weeks of treatment with the phenothiazine derivative perazine. The serum levels of all the above hormones were also determined in 19 schizophrenic patients in remission who were receiving no medication, 20 schizophrenic patients in remission taking neuroleptic drugs, and 24 patients with residual-type schizophrenia. The serum levels of T(4) of acutely ill schizophrenic patients were elevated, while those of T(3), rT(3) and TSH were normal. Their T(4) levels showed a positive correlation with the severity of illness and the degree of clinical response to neuroleptic treatment. There was a significant fall in serum concentrations of T(4) and rT(3) during four weeks of drug treatment and the decrease was significantly correlated to clinical response. No abnormalities in the serum concentrations of any of the hormones measured were found in schizophrenic patients in remission or in residual-type schizophrenia. In conclusion, our results indicate that the elevated serum levels of T(4) may be specific for acutely ill schizophrenic patients and that neuroleptic medication may affect thyroid hormone metabolism, this interaction being involved in the mechanism of action of these drugs.

The subchronic effects of the TRH analog TA-0910 and bromocriptine on alcohol preference in alcohol-preferring rats: development of tolerance and cross-tolerance

In a previous study, we showed that a single injection of the thyrotropin-releasing hormone analog TA-0910 dose-dependently reduced alcohol intake in alcohol-preferring (P) rats and increased their water intake over a 24-hr period. In the present study, the effects of seven consecutive, once-daily injections of TA-0910 (0.75 mg/kg, ip) on alcohol preference were determined. P rats developed tolerance to the attenuating effects of TA-0910 on alcohol intake within 3-5 days. Following the development of tolerance to TA-0910, rats were injected with the dopamine agonist bromocriptine (0.5 mg/kg, sc). In the presence of tolerance to TA-0910, the attenuating effect of bromocriptine on alcohol intake was reduced. When rats were made tolerant to the attenuating effects of bromocriptine, they exhibited tolerance to the attenuating effects of TA-0910. These findings indicate that tolerance to the effects of TA-0910 on alcohol intake occurs and suggest dopamine involvement in the mechanism of action of TA-0910 in reducing alcohol intake in P rats.

Triiodothyronine (T3) modifies cholinergic-induced hypothermia and tremor in rats

Hypothermia and tremor responses of oxotremorine and eserine were studied in rats after several T3 treatment regimens. The T3 antagonized oxotremorine-induced hypothermia and failed to antagonize eserine hypothermic effect, but potentiated oxotremorine- and eserine-induced tremors. Acetylcholinesterase activity was not altered in T3 rats. The hypothetical mechanisms to explain changes of central cholinergic responses caused by T3 are discussed.

Effects of thyroid state on preference for and sensitivity to ethanol in Fischer-344 rats

1. It has been reported by several groups that thyroid status can alter ethanol preference in rats. However, results using different methods and different strains of rats have not been consistent. 2. In this study, thyroidectomy or T4 augmentation was used to produce hypothyroidism or hyperthyroidism, respectively, in adult male Fischer-344 rats. 3. Preference for weak solutions (4 or 5%) of ethanol or tap water and ethanol-induced sedation and hypothermia were compared in hypothyroid, hyperthyroid and euthyroid rats. 4. No significant differences in preference indices (the ratios of ethanol to total liquid consumed) among the three groups were observed; however, for ethanol to contribute a greater portion of total calories ingested by hypothyroid rats than by euthyroid or hyperthyroid rats. 5. The duration of sleep resulting from a single i.p. injection of 2.5 mg/kg ethanol was increased (by 34%) in hyperthyroid rats and decreased (by 16%) in hypothyroid rats compared to euthyroid controls. Only the effect of hyperthyroidism was significant at the 0.05 level. 6. Colonic temperatures differed with thyroid state (hyperthyroid > euthyroid > hypothyroid) but the decrease produced by ethanol did not differ by thyroid state. 7. Observed differences in ethanol-induced sedation are consistent with differences in brain TRH levels and effects on neurotransmitter systems associated with different thyroid states.

Manic episode, thyroid gland function and lithium

This paper addresses the issue of (recurrent) mania in relation to an increased T4-value, whether or not influenced by lithium. Lithium has an anti-TSH-effect on the thyroid gland by inhibiting the intracellular enzyme adenylate cyclase. This might cause hypothyroidism. Moreover, lithium is also known to have a direct stabilizing effect on (behavioral manifestations) of dopamine receptor supersensitivity. The hypothesis regarding the relation between thyroid function and affective disturbances is that the altered thyroid function may cause a change in the availability of the central dopamine receptors. Dopamine is known to be able to cause a manic state. TSH and TRH are also involved in this mechanism. It is, therefore, very likely that an increased thyroid function, whether or not caused by discontinuation of lithium-therapy, could induce a (recurrent) mania.

The hypothyroid rat as a model of increased sensitivity to dopamine receptor agonists

Control and hypothyroid rats were challenged with a range of doses (0.5-4 mumol/kg) of either the nonselective dopamine agonist, apomorphine, or the selective D2 receptor agonist. LY 171555, and their stereotyped head-down sniffing (SHDS) responses measured. The dose-response curves for both agonists were shifted to the left in the hypothyroid rats compared to water-treated controls. Increasing doses of the selective D2 antagonist, raclopride, caused a parallel shift to the right in the LY 171555-induced SHDS dose-response curve. Schild analysis revealed a decreased sensitivity to raclopride in the hypothyroid animals. The selective D1 antagonist SCH 23390 was observed to decrease the maximal response elicited by LY 171555 in a dose-dependent manner and the hypothyroid rats were more sensitive to this effect. It was concluded that hypothyroid rats showed an apparent increased sensitivity to D2 receptor agonists and a decreased sensitivity to D2 antagonists. In addition, the facilitation effect of the D1 receptor on the D2 receptor appeared less tightly coupled in the hypothyroid rats.

Effects of sex, thyro-parathyroidectomy, and light regime on levels and circadian rhythms of wheel-running in rats

Intact and thyro-parathyroidectomized (TPX) Sprague-Dawley rats of both sexes were observed for 24 days under a 12:12 light:dark cycle (Entrainment), followed by 20 days in constant dim red light (Free-Run). Circadian periods and levels of wheel-running activity were examined. Intact females and TPX males were significantly more active and had significantly shorter free-running circadian periods than intact males, and the effects of TPX in females were different from those in males. Circadian periods in TPX females were slightly, but not significantly, shorter than in intact females, and activity levels in TPX females were nonsignificantly depressed relative to intact females. It was also found that day versus night activity levels differed more in TPX animals than in intact animals, especially during entrainment, suggesting that TPXs may be more sensitive to some effects of light. A number of possible explanations for the effects of TPX are considered, including changes in thyroid and calcitonin levels, interactions with gonadal hormones, and possible developmental effects of thyroid hormones on the circadian system. It is also possible that rhythm changes are secondary to alterations in activity levels. Human manic depressives reportedly have an unusually high incidence of thyroid, parathyroid, and calcium regulation abnormalities, display shortened circadian sleep-wake rhythms and abnormal levels of activity, and may also be hypersensitive to some effects of light; in addition, depression predominates in women, whereas mania predominates in men. The present results suggest that thyroid dysfunction could be partially responsible for the some of these abnormalities, and for sex differences in the manifestations of these disorders.

Evidence for post-synaptic changes mediating increased behavioural sensitivity to dopamine receptor agonists in hypothyroid rats

1. Hypothyroidism was maintained for four weeks in male rats by administration of PTU daily. 2. Hypothyroid rats showed increased behavioural responses to apomorphine, a mixed D1/D2 dopamine receptor agonist, LY 171555, a selective D2 agonist and to SKF 38393, a selective D1 agonist, compared with euthyroid controls. 3. Responses to the selective D1 antagonist, SCH 23390, were decreased, but were increased to the D2 antagonist, haloperidol, in hypothyroid rats. 4. Ligand binding studies showed no significant differences in the affinity and concentration of D1 or D2 receptor sub-types in the striatum of hypothyroid compared with euthyroid rats. 5. However, hypothyroid rats had a greater increase in dopamine stimulated cyclic AMP in the striatum than euthyroid controls. 6. It is concluded that the changes in behavioural sensitivity observed in hypothyroid rats may be associated with these alterations in post-synaptic events.

Post-synaptic changes and increased dopamine receptor sensitivity in hypothyroid rats

Hypothyroid rats showed increased behavioral sensitivity to both selective and non-selective dopamine agonists. Ligand binding analysis revealed no differences in concentration or affinity of striatal dopamine receptor subtypes in hypothyroid rats. Measurement of striatal cAMP levels however, indicated that hypothyroid rats showed a greater increase in cAMP production in response to stimulation by dopamine. It is concluded that the changes in behavioural sensitivity observed may be associated with alterations in post-synaptic mechanisms.

Hypothyroidism leads to increased dopamine receptor sensitivity and concentration

Rats treated with iodine-131 were confirmed to be hypothyroid by their reduced baseline core body temperatures, reduced serum thyroxine concentrations and elevated serum thyroid stimulating hormone concentrations. When hypothyroid rats were compared to euthyroid controls they were more sensitive to the effects of apomorphine (1.0 mumol/kg) on stereotypy, operant responding and body temperature and showed a smaller reduction in locomotor activity after injection of haloperidol (0.25 mumol/kg). Receptor binding studies on striatal homogenates indicated that hypothyroid rats had increased concentrations of D2 dopamine receptors but there was no change in the affinity. It is concluded that hypothyroidism increases dopamine receptor sensitivity by increasing receptor concentration.

The neuroendocrinology of mania

The paper reviews the endocrine findings in manic patients and the effects of treatment, as well as the association between endocrine conditions or hormonal treatments and abnormal states of elation resembling mania. The findings are discussed in relation to hypotheses about the neurochemical basis of mania, particularly the mesolimbic dopamine hypothesis.

Alterations in the dopaminergic system and behaviour in rats reared on iodine-deficient diets

Male rats raised on an iodine-deficient diet were found to be retarded in growth rate, to have lowered body temperature, and to have poorer memory retention of a passive avoidance task than rats raised on a similar diet but with adequate iodine concentration. In addition, the iodine deficient rats showed increased locomotor activity and sniffing frequency after the dopamine agonist, apomorphine; while their operant performance was inhibited to a greater degree after apomorphine. However, the hypothermic effects of apomorphine were comparable in both iodine-deficient and normal rats. At sacrifice the iodine-deficient rats were found to have significantly depressed thyroxine levels (less than 10% of normal), significantly elevated TSH levels (greater than 700% of normal), and a significantly greater concentration of dopamine receptors in the striatum (28% increase). Thus, rats raised on iodine-deficient diets have considerable behavioural and physiological alterations, including an increased concentration of dopamine receptors.