Question: 

Oxytocin (OT) attenuates stress and anxiety-related behaviors, when administered into the hypothalamus. However, the intracellular signaling mediating these effects remained to be uncovered. This study is aimed to investigate the effect of OT on ion channel activity in hypothalamic neurons.

Methodology: 

Ion channel activity was analyzed by calcium imaging and whole-cell patch clamp recordings, gene-expression experiments were done using RT-PCR.

Results: 

Analysis of intracellular calcium concentration ([Ca²⁺]_i) in cultured hypothalamic neurons revealed the presence of two cell populations: Cells with stable resting [Ca²⁺]_i and cells displaying spontaneous Ca²⁺-oscillations. Oscillations disappeared in extracellular Ca²⁺-free (25mM EGTA) conditions and extracellular application of lanthanum (100mM). Oscillating cells showed a higher frequency of OT responses (70%) compared to that of not oscillating cells (<10%). OT increased basal [Ca²⁺]_i and changed the amplitude and frequency of oscillation. These effects were dependent on extracellular free Ca²⁺. Additionally, OT activated inward currents. The primary cell culture expressed the TRP channels TRPC1-6 and TRPV1,-2,-4 and -6. Blocking of TRPV2 and TRPC6 channels by SKF96365 (100mM) and additional application of OT resulted in a strong decrease of [Ca²⁺]_i and stopped oscillations. The voltage-clamp data show an activation of outwardly rectifying potassium channels in response to OT.

Conclusion: 

Predominantly cells with autonomous Ca²⁺-oscillations react to OT, by an increase of [Ca²⁺]_i and/or a change of Ca²⁺-waves. The OT effect depends on the influx of extracellular calcium into the cell, involving TRPV2 and/or TRPC6 channels and an activation of outwardly rectifying potassium channels.