To investigate the intracellular calcium concentration ([Ca²⁺]_i) in mouse hypothalamic oxytocin neurons co- regulated by cyclic adenosine diphosphate ribose (cADPR) and thermal stimulation.

Oxytocin neurons were separated from supraoptic nucleus of mice and cultured in vitro. Under different temperature gradients (with a temperature gradient of 2 degrees Celsius and target temperatures set to 28, 34, 37 and 39 degrees Celsius) , the neurons were treated with extracellular cADPR and inhibitors (Ryanodine, 8- bromo- cADPR, 2- APB). Calcium fluorescence imaging system was used to detect [Ca²⁺ ]_i). In addition, the change in [Ca²⁺]_i) in the heat- sensitive neurons were measured after stimulation of extracellular oxytocin.

An increased in [Ca²⁺]_i with 100 μmol/L extracellular cADPR was noted when the temperature was raised to 37 degrees Celsius, and became even more significant when the temperature was raised to 39 degrees Celsius, corresponding to 125% and 151% times, respectively, the basic level of [Ca²⁺]_i (P<0.05). Under the same conditions, adenosine diphosphate ribose and nicotinamide adenine dinucleotide may also induce similar changes in [Ca²⁺]_i as did cADPR, but with weaker actions. These actions were obviously blocked by the transient receptor potential M2 channel (TRPM2) blocker 2- APB. 100 nmol/L oxytocin stimulation of the heat-sensitive neurons was noted to induce a relatively flat and steady increase in [Ca²⁺]_i.

Temperature - dependent activity of cADPR/TRPM2 - mediated calcium influx may underlie the regulation of increased [Ca²⁺]_i in oxytocin neurons, which may contribute to production of oxytocin.

Cyclic adenosine diphosphate ribose; Transient receptor potential M2; Calcium; Hypothalamus; Oxytocin