Astrocytes in 17β-estradiol treated mixed hippocampal cultures show attenuated calcium response to neuronal activity

Abstract

Glial cells in the brain are capable of responding to hormonal signals. The ovarian steroid hormone 17β-estradiol, in addition to its actions on neurons, can directly affect glial cells. Estrogen receptors have been described on both neurons and astrocytes, suggesting a complex interplay between these two in mediating the effects of the hormone. Astrocytes sense and respond to neuronal activity with a rise in intracellular calcium concentration ([Ca²⁺]i). Using simultaneous electrophysiology and calcium imaging techniques, we monitored neuronal activity evoked astrocyte ([Ca²⁺]i) changes in mixed hippocampal cultures loaded with fluo-3 AM. Action potential firing in neurons, elicited by injecting depolarizing current pulses, was associated with ([Ca²⁺]i) elevations in astrocytes, which could be blocked by 200 μM MCPG and also 1 μM TTX. We compared astrocytic ([Ca²⁺]i) transients in control and 24-hour estradiol treated cultures. The amplitude of the ([Ca²⁺]i) transient, the number of responsive astrocytes, and the ([Ca²⁺]i) wave velocity were all significantly reduced in estradiol treated cultures. ([Ca²⁺]i) rise in astrocytes in response to local application of the metabotropic glutamate receptor (mGluR) agonist t-ACPD was attenuated in estradiol treated cultures, suggesting functional changes in the astrocyte mGluR following 24-h treatment with estradiol. Since astrocytes can modulate synaptic transmission by release of glutamate, the attenuated ([Ca²⁺]i) response seen following estradiol treatment could have functional consequences on astrocyte-neuron signaling.