BACKGROUND AND PURPOSE3-Iodothyronamine (T1AM), an endogenous derivative of thyroid hormones, is regarded as a rapid modulator of behaviour and metabolism. To determine whether brain thyroid hormone levels contribute to these effects, we investigated the effect of central administration of T1AM on learning and pain threshold of mice either untreated or pretreated with clorgyline (2.5 mg·kg -1 , i.p.), an inhibitor of amine oxidative metabolism. EXPERIMENTAL APPROACHT1AM (0.13, 0.4, 1.32 and 4 mg·kg -1 ) or vehicle was injected i.c.v. into male mice, and after 30 min their effects on memory acquisition capacity, pain threshold and curiosity were evaluated by the following tests: passive avoidance, licking latency on the hot plate and movements on the hole-board platform. Plasma glycaemia was measured using a glucorefractometer. Brain levels of triiodothyroxine (T3), thyroxine (T4) and T1AM were measured by HPLC coupled to tandem MS. ERK1/2 activation and c-fos expression in different brain regions were evaluated by Western blot analysis. RESULTST1AM improved learning capacity, decreased pain threshold to hot stimuli, enhanced curiosity and raised plasma glycaemia in a dose-dependent way, without modifying T3 and T4 brain concentrations. T1AM effects on learning and pain were abolished or significantly affected by clorgyline, suggesting a role for some metabolite(s), or that T1AM interacts at the rapid desensitizing target(s). T1AM activated ERK in different brain areas at lower doses than those effective on behaviour. CONCLUSIONS AND IMPLICATIONST1AM is a novel memory enhancer. This feature might have important implications for the treatment of endocrine and neurodegenerative-induced memory disorders. AbbreviationsCREB, cyclic AMP-responsive element binding; PBST, PBS plus Tween; T1AM, 3-iodothyronamine; T3, triiodothyroxine; T4, thyroxine; TA1 receptor, trace amine-associated receptor 1

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Rett Syndrome (RTT) is a severe neurodevelopmental disorder associated with mutations in either MECP2, CDKL5 or FOXG1. The precise molecular mechanisms that lead to the pathogenesis of RTT have yet to be elucidated. We recently reported that expression of GluD1 (orphan Glutamate receptor Delta-1 subunit) is increased in iPSC-derived neurons obtained from patients with mutations in either MECP2 or CDKL5. GluD1 controls synaptic differentiation and shifts the balance between excitatory and inhibitory synapses towards the latter. Thus, an increase in GluD1 might be a critical factor in the etiology of RTT by affecting the excitatory/inhibitory balance in the developing brain. To test this hypothesis, we generated iPSC-derived neurons from FOXG1+/− patients. We analyzed mRNA and protein levels of GluD1 together with key markers of excitatory and inhibitory synapses in these iPSC-derived neurons and in Foxg1+/− mouse fetal (E11.5) and adult (P70) brains. We found strong correlation between iPSC-derived neurons and fetal mouse brains, where GluD1 and inhibitory synaptic markers (GAD67 and GABA AR-α1) were increased, while the levels of a number of excitatory synaptic markers (VGLUT1, GluA1, GluN1, PSD-95) were decreased. In adult mice, GluD1 was decreased along with all GABAergic and glutamatergic markers. Our findings further the understanding of the etiology of RTT by introducing a new pathological event occurring in the brain of FOXG1+/− patients during embryonic development and its time-dependent shift toward a general decrease in brain synapses.

BACKGROUND AND PURPOSE3-Iodothyroacetic acid (TA1) is an end product of thyroid hormone metabolism. So far, it is not known if TA1 is present in mouse brain and if it has any pharmacological effects. EXPERIMENTAL APPROACHTA1 levels in mouse brain were measured by HPLC coupled to mass spectrometry. After i.c.v. administration of exogenous TA1 (0.4, 1.32 and 4 μg·kg −1 ) to mice, memory acquisition-retention (passive avoidance paradigm with a light-dark box), pain threshold to thermal stimulus (51.5°C; hot plate test) and plasma glucose (glucorefractometer) were evaluated. Similar assays were performed in mice pretreated with s.c. injections of the histamine H1 receptor antagonist pyrilamine (10 mg·kg ) and the corresponding WT strain. KEY RESULTSTA1 was found in the brain of CD1 but not of HDC mice. Exogenous TA1 induced amnesia (at 0.4 μg·kg ). All these effects were modulated by pyrilamine and zolantidine. In HDC −/− mice, TA1 (1.32 and 4 μg·kg −1) did not increase plasma glucose or induce hyperalgesia. CONCLUSIONS AND IMPLICATIONSBehavioural and metabolic effects of TA1 disclosed interactions between the thyroid and histaminergic systems. AbbreviationsT3, tri-iodothyronine; TA1, 3-iodothyroacetic acid; TA1M, 3-iodothyronamine; TRIAC, tri-iodothyroacetic acid

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