Modulation of dopamine receptors by thyrotropin-releasing hormone in the rat brain

Widening spectrum of neuroleptic malignant syndrome: Case series

Neuroleptic malignant syndrome (NMS) is a rare and rapidly progressive syndrome with mortality rate of 5.6%. The spectrum of onset, progression and outcome is heterogeneous and is associated with number of risk factors. In our case series, we entail the triggers, hospital course and outcome of five interesting in-patient cases that were admitted to our service in a tertiary care hospital in Northern India. This case series is to highlight the first ever reported case of NMS triggered by levosulpiride administration, along with one of the few first cases of NMS after programming of DBS, hypothyroid disorders, levodopa readjustment and selective basal ganglia and cerebellar injury following the hyperthermic syndrome. This is also to bring to attention of clinicians worldwide the atypical risk factors of NMS, and stress the importance of staying vigilant for the same by frequent follow-ups and high degree of clinical suspicion. We also aim to generate epidemiological data about these atypical triggers.

Neuroleptic malignant syndrome with thyroid disorder: An unusual case report

RATIONALE

Neuroleptic malignant syndrome (NMS) is a life threatening neurologic emergency associated with neuroleptic or antipsychotic agent use. NMS is rarely related to thyroid disease.

PATIENT CONCERNS

We report a case of NMS in a 66-year-old male with past medical history of paranoid schizophrenia on chlorpromazine, diabetes, hypertension and asthma, who presented with a humeral fracture after a fall. Patient developed hyperpyrexia, altered consciousness, autonomic instability, elevated serum creatine kinase (CK) without rigidity.

DIAGNOSES

CT head and workup for infection were negative. Electroencephalogram (EEG) showed generalized slow wave activity. Ultrasound revealed a large goiter with nodules.

INTERVENTIONS

Chlorpromazine was stopped due to concern of NMS. Patient was treated with cooling, fluid and electrolyte maintenance.

OUTCOMES

Patient slowly improved and CK level normalized. Thyroid-stimulating hormone (TSH) level trended down from 10.2 mIU/L to 0.02 mIU/L. Patient was discharged with aripiprazole.

LESSONS

Hypothyroidism predisposes patients to NMS by altering central dopaminergic systems. The typical symptoms may be masked by hypothyroidism. Thyroid dysfunction should be excluded in all patients with NMS. Discontinuing antipsychotic agents decreases TSH levels which maybe due to the negative feedback of dopaminergic activity. This is the first case report describing dramatic changes in TSH after discontinuing chlorpromazine in NMS.

A novel analog of TRH, YM14673, causes a decrease in brain TRH receptors in vitro

Biochemical mechanisms by which analogs of thyrotropin-releasing hormone (TRH) produce their potent neuropharmacological actions on the brain remain ill-defined. We tested effects of YM14673, a novel analog of TRH, on TRH receptors in rat brains in vitro. No significant binding of [3H]YM14673 to brain plasma membranes occurred. In contrast, preincubation of membranes with YM14673 caused dose-dependent decreases in TRH binding. This was not due to competition for TRH binding sites or existence of metabolites of YM14673. Preincubation with DN1417 (an another TRH analog), cyclo(His-Pro) or methionine-enkephalin did not affect the binding. Affections of YM14673 on TRH binding were observed when cerebral cortical membranes were studied; those were not seen in membranes prepared from hypothalamus, striatum, midbrain, hippocampus, or pons-medulla. The present data indicate that YM14673 exerts its characteristic neuro-pharmacological functions through interacting with TRH binding sites in the brain.

Influence of thyrotropin-releasing hormone and catecholaminergic interactions on CNS ethanol sensitivity

The role of catecholamine neuronal systems in mediating the analeptic and thermogenic effects of thyrotropin-releasing hormone (TRH) was examined in long-sleep (LS) and short-sleep (SS) mice. TRH [0.1 to 40 micrograms, intracerebroventricularly (icv)] was associated with a reduction in the sleep times of LS mice, but no dose of TRH had any effect on sleep times of SS mice. However, TRH (20 micrograms, icv) produced a 1.0 degree to 1.5 degrees C attenuation of the ethanol-induced hypothermia in both LS and SS mice. TRH did not change the rate of ethanol elimination in either line of mice, suggesting that the reduction in LS sleep times and attenuation of LS and SS hypothermia were due to decreased CNS ethanol sensitivity rather than an increase in the rate of ethanol metabolism. TRH (20 micrograms, icv) given alone produced an activation of central and peripheral catecholamine systems in LS, but not SS mice, as reflected by an increase in the in vivo tyrosine hydroxylase (TH) activity in the brain and adrenal gland. TRH, given with ethanol, prevented or attenuated ethanol-induced decreases in the brain and adrenal gland in vivo TH activity in LS mice but not SS mice. Thus, there was an association between the ability of TRH to produce an activation of catecholamine neuronal systems (increased rate of catecholamine biosynthesis) and the analeptic action of TRH to reduce the CNS depressant effects of ethanol (decreased sleep times).(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroleptic malignant syndrome and hypothyroidism

Two patients with primary hypothyroidism who developed neuroleptic malignant syndrome (NMS) are described. Thyroid disease might predispose to NMS by altering brain dopamine metabolism.

Effect of thyrotropin releasing hormone on the development of tolerance to the analgesic and hyperthermic actions of morphine in the rat

The effect of thyrotropin releasing hormone (TRH) on the development of tolerance to the analgesic and hyperthermic actions of morphine was determined in male Sprague-Dawley rats. The tolerance to morphine was induced by subcutaneous implantation of 6 morphine pellets, each containing 75 mg of morphine free base. Rats serving as controls were implanted with 6 placebo pellets. Subcutaneous injections of TRH (1, 3 or 10 mg/kg) twice a day for 7 days inhibited the development of tolerance to the analgesic, but not to the hyperthermic action of morphine. Doses lower than 1 mg/kg or greater than 10 mg/kg administered twice a day for 7 days did not modify tolerance development. The inability of higher doses of TRH to inhibit tolerance to morphine may be related to rapid down-regulation of TRH receptors. The results suggest that in appropriate doses, TRH can selectively inhibit the development of tolerance to the analgesic action of morphine.

Effect of some peptides on dopaminergic function in man

Thyrotropin-releasing hormone (TRH) (200 micrograms iv) and 1-desamino-8-D-arginine vasopressin (DDAVP) (4 micrograms iv) antagonized the growth hormone (GH) response to apomorphine HCl (Apo) (0.5 mg sc) in 10 normal men. Apo had no effect on basal prolactin (PRL) levels but antagonized the PRL response to TRH. DDAVP plus Apo decreased PRL compared to placebo or DDAVP alone. These observations are compatible with (a) an inhibitory effect of TRH on hypothalamic and pituitary lactotrophe dopamine (DA) function (b) a facilitory effect of DDAVP on lactotrophe DA function and an inhibitory effect on hypothalamic DA function. Whether these are direct or indirect effects on DA mechanisms is unclear.

Brain neuropeptides: actions on central cardiovascular control mechanisms

The many peptides we have not considered (e.g. gastrin, motilin, FMRFamide, carnosine, litorin, dermorphin, casomorphin, eledoisin, prolactin, growth hormone, neuromedin U, proctolin, etc.) were omitted due to lack of information as far as any putative central cardiovascular effects are concerned. However, even for some of these peptide pariahs intriguing snippets of information are available now (e.g. ref. 85), although as we write, the list of possible candidates for investigation grows longer. On an optimistic note, it is becoming clear that many brain neuropeptides may have important effects on cardiovascular regulation. It seems feasible that 'chemically coded' pathways in the brain might be the neuroanatomical correlate of a 'viscerotopic' organization of cardiovascular control mechanisms, whereby the activity of the heart and flows through vascular beds are individually controlled, but in an integrated fashion, utilizing particular combinations of neurotransmitters and neuropeptides within the brain. Such possibilities can only be investigated, properly, by measurement of changes in cardiac output and regional haemodynamics in response to appropriate interventions, in conscious, unrestrained animals.