Relay of affective stimuli from amygdala to thalamus parallels sensory pathways
Date
2018
DOI
Authors
Timbie, C.
Garcia-Cabezas, M.
Zikopoulos, Vasileios
Barbas, H.
Version
Published version
OA Version
Citation
C. Timbie, M. Garcia-Cabezas, V. Zikopoulos, H. Barbas. "Relay of affective stimuli from amygdala to thalamus parallels sensory pathways." Society for Neuroscience. San Diego, CA, https://www.abstractsonline.com/pp8/#!/4649/presentation/33787.
Abstract
The amygdala, the emotional sensor of the brain, is strongly connected with
the posterior orbitofrontal cortex (pOFC), forming a pathway activated by
reward learning. In addition, the amygdala innervates neurons in the
mediodorsal thalamic nucleus (MD) that project to pOFC, forming a second,
indirect route for the amygdala to inuence the pOFC sector of the prefrontal
cortex. The indirect pathway that connects the amygdala and pOFC through
the thalamus may be similar to sensory pathways connecting peripheral
receptors with sensory cortices through sensory relay thalamic nuclei. The
indirect pathway is morphologically distinct from the direct pathway; amygdalar
pathway terminals in MD are larger than those in the pOFC, and likely derive
from separate neuronal populations in the amygdala (Timbie and Barbas,
Society for Neuroscience, 2013; J Neurosci, 2015). The synaptic interactions
and potential specializations of amygdalar terminals in MD have not yet been
described in comparison to other thalamic afferents. We addressed this issue
by labeling amygdalar axons in MD in rhesus monkeys and compared them
with retinal axons terminating in the lateral geniculate nucleus (LGN). We
studied axon terminations in MD and LGN using serial section electron
microscopy and analyzed pre- and post-synaptic elements by morphology. All
amygdalar terminals in MD and retinal ganglion terminals in LGN contained
multiple mitochondria, and were classed as round, large (RL) boutons.
Amygdalar and retinal RL boutons contained excitatory type vesicles and
formed several asymmetric (excitatory) synapses with dendrites of
thalamocortical relay neurons and dendrites of inhibitory interneurons. In a
significant proportion of these multi-synaptic arrangements, the inhibitory
dendrites contained vesicles and formed symmetric synapses with the
dendrite of the thalamocortical neuron. These novel findings reveal that
amygdalar terminals in MD form synaptic triads, reminiscent of those found in
sensory thalamic relay nuclei, like LGN. Our findings suggest that amygdalar
inputs to MD can drive signals to cortex, ensuring efficient transmission of
salient emotional information, akin to sensory thalamic relays.