Large intercalated neurons of amygdala relay noxious sensory information.
Various GABAergic neuron types of the amygdala cooperate to control principal cell firing during fear-related and other behaviors, and understanding their specialized roles is important. Among GABAergic neurons, the so-called intercalated cells (ITCcs) are critically involved in the expression and extinction of fear memory. Tightly clustered small-sized spiny neurons constitute the majority of ITCcs, but they are surrounded by sparse, larger neurons (L-ITCcs) for which very little information is known. We report here a detailed neurochemical, structural and physiological characterization of rat L-ITCcs, as identified with juxtacellular recording/labeling in vivo. We supplement these data with anatomical and neurochemical analyses of nonrecorded L-ITCcs. We demonstrate that L-ITCcs are GABAergic, and strongly express metabotropic glutamate receptor 1α and GABAA receptor α1 subunit, together with moderate levels of parvalbumin. Furthermore, L-ITCcs are innervated by fibers enriched with metabotropic glutamate receptors 7a and/or 8a. In contrast to small-sized spiny ITCcs, L-ITCcs possess thick, aspiny dendrites, have highly branched, long-range axonal projections, and innervate interneurons in the basolateral amygdaloid complex. The axons of L-ITCcs also project to distant brain areas, such as the perirhinal, entorhinal, and endopiriform cortices. In vivo recorded L-ITCcs are strongly activated by noxious stimuli, such as hindpaw pinches or electrical footshocks. Consistent with this, we observed synaptic contacts on L-ITCc dendrites from nociceptive intralaminar thalamic nuclei. We propose that, during salient sensory stimulation, L-ITCcs disinhibit local and distant principal neurons, acting as "hub cells," to orchestrate the activity of a distributed network.
The group of Marco Capogna, in collaboration with other Unit members and with the group of the ex-Unit member Francesco Ferraguti report in the Journal of Neuroscience 35 (5): 2044-2057, 2015 the organisation of a novel GABAergic neuron type of the rodent amygdala, the so-called large intercalated cell (L-ITCc). They identified them with juxtacellular recording/labelling in vivo.
Coordination of neuronal activity between two brain areas, the amygdala and the hippocampus, as well as precisely-timed integration of sensory inputs in the amygdala, are critical for emotional memories. Amygdala neurons that release the inhibitory neurotransmitter GABA (GABAergic cells) are expected to play key roles in these events, but their precise identity and function are not known.