Effect of triiodothyronine on 5-HT1A and 5-HT1B receptor expression in rat forebrain and on latency to feed in the novelty suppressed feeding test

Investigation of rhodamine derivative on behavioral impairment in a double neurotoxin lesion of substantia nigra and locus coeruleus dysfunctional mice

Although multiple mechanisms have been studied, there is still a lack of effective treatment on non-motor symptoms in Parkinson's disease (PD) patients. Therapeutic effects of 5-(4-hydroxy-3-dimethoxybenzylidene)-thiazolidinone (RD-1), one of rhodamine derivatives, on motor recovery have been previously demonstrated, but its effects on non-motor symptoms remain unclear. Herein, we explored the beneficial effects of RD-1 on PD-related non-motor symptoms and changes in synaptic plasticity in the mesencephalon. To investigate its therapeutic effects in the non-motor symptoms of Parkinsonian model, we employed male C57BL/6N mice and double injection with noradrenergic specific neurotoxin N-2-Chloroethyl-N-ethyl-2-bromobenzylamine hydrochloride, followed 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Next, we performed behavioral tests, histological analyses and immunoblotting. Our findings showed that RD-1 significantly alleviated locomotor abnormality, motor disturbance, anxiety/depression-like behavior and memory deficit. It rescued the levels of tyrosine hydroxylase in substantia nigra, and striatum. Moreover, RD-1 upregulated expression levels of α-synuclein, synapsin II, postsynaptic density 95 and vesicle-associated membrane protein 2. The restoration of synaptic function may underlie the neuroprotective effects of RD-1 in double lesioned mice, confirming its protective effect for dopaminergic neurodegeneration.

Effect of triiodothyronine (T(3)) augmentation of acute milnacipran administration on monoamine levels: an in vivo microdialysis study in rats

BACKGROUND

Up to 30% of depressed patients are partially or totally resistant to antidepressant therapy. The administration of triiodothyronine (T(3)) to antidepressant nonresponders can be an effective augmentation strategy, although the mechanism is not fully understood.

METHODS

In vivo microdialysis was used to examine the effect of T(3) augmentation of the antidepressant, milnacipran. Basal extracellular serotonin, norepinephrine, and dopamine levels were measured before and after acute milnacipran administration in the medial prefrontal cortex and amygdala of rats which had received subchronic (7 days) T(3) treatment or control saline.

RESULTS

Subchronic administration of T(3) at 0.1 mg/kg significantly increased basal extracellular levels of serotonin in the medial prefrontal cortex, but not in the amygdala. In contrast, subchronic administration of T(3) at 0.2 mg/kg did not alter basal extracellular serotonin levels in the medial prefrontal cortex. Basal extracellular levels of norepinephrine and dopamine were not modified by either dose of T(3) in either region. Acute administration of milnacipran, a serotonin-norepinephrine reuptake inhibitor, to control animals resulted in a significant increase of extracellular levels of serotonin, norepinephrine, and dopamine. When administered to animals treated subchronically with T(3) at 0.1 mg/kg, milnacipran produced an additional increase in extracellular serotonin levels but not in levels of norepinephrine or dopamine in the medial prefrontal cortex of rats.

CONCLUSION

These results suggest that the mechanism of the augmentation effect of milnacipran by T(3) administration occurs via enhancement of serotonergic neurotransmission, but not through noradrenergic or dopaminergic neurotransmission.

Thyroid disorders

All forms of thyroid diseases are much more frequently observed in women than men, although the reasons are still not completely elucidated.Hyperthyroidism is defined by elevated circulating free thyroid hormones. The prevalence is about 2 % in women and 0.2 % in men. The most frequent causes are various forms of thyroid autonomy in elderly women and Graves' disease, which occurs mostly in younger women.Hypothyroidism is defined by a lack of thyroid hormones. It is a common endocrine disorder caused by autoimmune thyroiditis (Hashimoto thyroiditis), iodine deficiency or following surgery or radioiodine therapy. Thyroxine requirements depend on fat-free mass and are, therefore, somewhat higher in males who are more often undersubstituted. In pregnancy lower TSH-reference ranges have to be considered and thyroid function should be monitored throughout pregnancy to avoid harm to the foetus caused by maternal thyroid dysfunctions. If overtreated women more often feature fractures, whereas males more often develop atrial fibrillation.

Effect of triiodothyronine on antidepressant screening tests in mice and on presynaptic 5-HT1A receptors: mediation by thyroid hormone α receptors

Although triiodothyronine (T3) is widely used clinically, preclinical support for its antidepressant-like effects is limited, and the mechanisms are unknown. We evaluated 1) the antidepressant-like effects of T3 in the novelty suppressed feeding test (NSFT), tail suspension test (TST), and forced swim test (FST), 2) the role of presynaptic 5-HT(1A) receptors in the antidepressant-like mechanism of T3 by the hypothermic response to the 5-HT(1A) receptor agonist, 8-hydroxy-N,N-dipropyl-2-aminotetralin (8-OH-DPAT), 3) the thyroid hormone receptor type mediating the antidepressant-like effects by concurrent administration of the specific thyroid hormone α receptor (TRα) antagonist, dronedarone, and 4) the presence of these effects in both genders. Male and female BALB/c mice were administered 1) T3 (20, 50, 200, or 500 μg/kg per day) or vehicle or 2) T3 (50 μg/kg per day), dronedarone (100 μM/day), or the combination intraperitoneally for 21 days and then underwent a behavioral test battery. The NSFT showed a shortened latency to feed in males at the two lower T3 doses. The TST and FST showed decreased immobility in male mice at T3 doses >20 μg/kg per day and in females at all T3 doses. Concurrent dronedarone prevented T3 effects in males on the NSFT and in the TST and FST in both genders. Attenuation of 8-OH-DPAT-induced hypothermia was observed in males only and may be reduced by concurrent dronedarone. These findings support an antidepressant-like effect of T3. Attenuation of 8-OH-DPAT-induced hypothermia in males only suggests the need to evaluate a possible gender disparity in the role of presynaptic 5-HT(1A) receptors in T3 antidepressant mechanisms. Blockade by dronedarone of the antidepressant-like effects of T3 suggests that these effects are TRα receptor-mediated.