Amygdala afferents monosynaptically innervate corticospinal neurones in rat medial prefrontal cortex

Gabbott, Paul; Warner, Tracy-Ann; Brown, Jacki; Salway, Philip; Gabbott, Thomas and Busby, Sarah (2012). Amygdala afferents monosynaptically innervate corticospinal neurones in rat medial prefrontal cortex. Journal of Comparative Neurology, 520(11) pp. 2440–2458.



The amygdala provides the medial prefrontal cortex (mPFC; areas 25, 32 and 24b) with salient emotional information. This study investigated the synaptic connectivity of identified amygdalocortical boutons (ACBs), (labelled anterogradely following injections of Phaseolus vulgaris leucoagglutinin into the basolateral nucleus of the amygdala), with the dendritic processes of identified layer 5 corticospinal neurones in rat mPFC. The corticospinal (CS) neurones in mPFC had been retrogradely labelled with rhodamine fluorescent latex microspheres and subsequently intracellularly ‘filled’ with biotinylated lucifer yellow to visualise their basal and apical dendrites.

Two main classes of mPFC CS neurones were identified – Type 1 cells had apical dendrites bearing numerous dendritic spines with radiate basal dendritic arbors. Type 2 cells possessed apical dendrites with greatly reduced spine densities and a broad range of basal dendritic tree morphologies.

Identified ACBs made asymmetric synaptic junctions with labelled dendritic spines and the labelled apical and basal dendritic shafts of identified CS neurones. On average, 8 ACBs were closely associated with the labelled basal dendritic arbors of Type 1 CS neurones and 5 ACBs with Type 2 CS basal dendrites. The mean Scholl distance of ACBs from CS somata (for both Types 1/2 cells) was 66µm – coinciding with a region containing the highest length density of CS neurone basal dendrites.

These results indicate that neurones in the BLA can monosynaptically influence CS neurones in mPFC that project to autonomic regions of the thoracic spinal cord and probably to other additional subcortical target regions, such as the lateral hypothalamus.

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