Electrophysiological and neurochemical characterization of neurons of the medial preoptic area in Japanese quail ( Coturnix japonica)

Abstract

Intracellular recordings of medial preoptic neurons demonstrated that most neurons show a spontaneous firing, a linear I– V relationship and low-threshold-like events suppressed by the application of Ni 2+. Some neurons had a depolarizing sag of the membrane potential in response to hyperpolarizing current pulses. The majority of the cells exhibited a robust spontaneous synaptic activity suppressed by SR95531 (100 μM), a GABA A receptor antagonist, and/or by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 μM), an ( RS)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate (KA) glutamate receptor antagonist. Most neurons were affected by the application of AMPA (10 μM), kainate (30 μM), N-methyl- d-aspartic acid (NMDA, 10 μM), isoguvacine (a GABA A receptor agonist, 100 μM), dopamine (100 μM), and norepinephrine (100 μM). Biocytin injections coupled to aromatase immunocytochemistry identified 19 recorded neurons including 3 displaying a dense aromatase immunoreactivity. All of them responded to kainate, dopamine, and norepinephrine, while only one responded to isoguvacine and NMDA. Taken together, these results demonstrate a relative electrical and neurochemical homogeneity of the medial preoptic neurons, including a few aromatase-immunoreactive neurons that could be identified by immunocytochemistry after biocytin labeling of the recorded neurons.