Strychnine-sensitive glycine responses in neurons of the lateral amygdala: An electrophysiological and immunocytochemical characterization

Electrophysiological and staining techniques in the in vitro slice preparation of the rat and guinea-pig lateral amygdala were combined with immunocytochemical approaches, in order to characterize the neuronal substrate, the ionic basis and the pharmacological properties of glycine- mediated responses, and to map the distribution and composition of the mediating glycine receptors. Glycine was locally applied to spiny, pyramidal- like cells in the lateral amygdala, which possessed electrophysiological properties typical of projection neurons. Glycine induced a membrane hyperpolarization from rest and associated decrease in input resistance, and an interruption of spike firing and calcium-mediated high-threshold oscillations. The glycine-mediated response persisted during blocked synaptic transmission, reversed close to the presumed somatic chloride equilibrium potential and shifted during altered transmembrane CI- gradients as expected for an increase in membrane chloride conductance. Responses to glycine were reversibly blocked by strychnine, but were insensitive to picrotoxin and bicuculline. Strychnine-sensitive components of spontaneous activity, but not of evoked synaptic responses, were frequently observed. Similar responses to glycine occurred in neurons of the guinea-pig and rat lateral amygdala, as well as in the central amygdala. The localization and composition of glycine receptors were examined through the use of monoclonal antisera directed against the binding protein (gephyrin), the α1 subunits (mAb2b) and α/β subunits (mAb4a) of glycine receptors. A dense to moderate immunostaining for gephyrin was observed throughout the amygdaloid complex, whereas mAb4a immunofluorescent neurons, displaying strong punctate labelling around the soma and proximal dendrites, were confined to the lateral amygdala. No immunoreactivity was obtained with mAb2b antibodies in the amygdala. It is concluded that pyramidal-like projection cells in the lateral amygdala express functional glycine receptors at somatic and proximal dendritic sites, which are composed of β and α subunits other than the α1 type, and which may play a functional role in the control of excitatory activity in the amygdala, particularly during periods of decreased GABAergic influence.