Endocrine Abstracts

The endogenous thyroid hormone derivative 3-iodothyronamine (T₁AM), and its metabolite 3-iodothyroacetic acid (TA₁) are known to stimulate learning and induce hyperalgesia in mice. Recently, it has been demonstrated that exogenous T₁AM is able to rescue synaptic impairment after transient ischemia in the entorhinal cortex (EC), a brain area crucially involved in learning and memory, and early affected during Alzheimer’s disease. However, it is still controversial whether T₁AM and its metabolites are produced and released locally at brain level. Here, we sought to assess the release of T₁AM and TA₁ in a mouse model of ischemia-induced EC synaptic dysfunction. EC brain slices were obtained from 3-4 months old C57BL/6 male mice (n = 5), using a vibratome (Leica VT1200S). All steps were performed in ice-cold oxygenated artificial cerebrospinal fluid (aCSF). Slices were perfused at 2–3 ml/min rate with oxygenated aCSF at 33 ± 1 °C. Field excitatory postsynaptic potentials were evoked by a concentric bipolar stimulating electrode in the layer II of the EC. After 10 min of stable baseline recordings, slices were perfused with deoxygenated glucose-free aCSF to obtain a transient oxygen-glucose deprivation (OGD). After 10 min of OGD slices were reperfused with aCSF for 50 min. Effluent aCSF was collected over 10 min intervals during the whole duration of experiments, and assayed by tandem mass spectrometry coupled with liquid chromatography (LC-MS/MS). In additional experiments electrical stimulation was omitted and/or amine oxidase inhibitors were included in aCSF. T₁AM release was not observed in any experiment, however a significant release of its metabolite TA₁ was detected during OGD (0.41±0.04 ng/ml) and during the first 10 min of reperfusion with aCSF (0.24±0.04 ng/ml), but not at the baseline. Notably, no TA₁ release was observed if EC were subjected to OGD in the absence of electrical stimulation. Moreover, preliminary experiments showed that semicarbazide, an amine oxidase inhibitor, was able to block TA₁ release. We conclude that in functional, but not in electrically silent, EC, simulated ischemia elicits TA₁ release. TA₁ might be produced by oxidative deamination of an endogenous precursor, possibly T₁AM. To our knowledge, this is the first report of TA₁ production and release in a pathophysiological relevant condition.