Functional Internal Complexity of Amygdala: Focus on Gene Activity Mapping After Behavioral Training and Drugs of Abuse

Abstract

The amygdala is a heterogeneous brain structure implicated in processing of emotions and storing the emotional aspects of memories. Gene activity markers such as c-Fos have been shown to reflect both neuronal activation and neuronal plasticity. Herein, we analyze the expression patterns of gene activity markers in the amygdala in response to either behavioral training or treatment with drugs of abuse and then we confront the results with data on other approaches to internal complexity of the amygdala. c-Fos has been the most often studied in the amygdala, showing specific expression patterns in response to various treatments, most probably reflecting functional specializations among amygdala subdivisions. In the basolateral amygdala, c-Fos expression appears to be consistent with the proposed role of this nucleus in a plasticity of the current stimulus-value associations. Within the medial part of the central amygdala, c-Fos correlates with acquisition of alimentary/gustatory behaviors. On the other hand, in the lateral subdivision of the central amygdala, c-Fos expression relates to attention and vigilance. In the medial amygdala, c-Fos appears to be evoked by emotional novelty of the experimental situation. The data on the other major subdivisions of the amygdala are scarce. In conclusion, the studies on the gene activity markers, confronted with other approaches involving neuroanatomy, physiology, and the lesion method, have revealed novel aspects of the amygdala, especially pointing to functional heterogeneity of this brain region that does not fit very well into contemporarily active debate on serial versus parallel information processing within the amygdala.

Gutsy Moves: The Amygdala as a Critical Node in Microbiota to Brain Signaling

“…[13,14] It is also surprisingly complex in structure, being composed of several networked regions that have different connectivities, neurochemical characteristics, and cyto-architecture. [15] There is some debate over exactly how to define these regions but it is generally agreed that there are at least 13 sub-nuclei that can be grouped, according to their embryological origins, into the centromedial Figure 1). [15] From its central location in the temporal lobe, the amygdaloid complex is highly connected with several brain regions.…”

“…[15] There is some debate over exactly how to define these regions but it is generally agreed that there are at least 13 sub-nuclei that can be grouped, according to their embryological origins, into the centromedial Figure 1). [15] From its central location in the temporal lobe, the amygdaloid complex is highly connected with several brain regions. It receives sensory inputs from the thalamus and cortical areas as well as extensive inputs from other regions in the limbic system, including the prefrontal cortex and hippocampus, [15] both of which are markedly altered in germ-free (GF) animals.…”

“…[15] From its central location in the temporal lobe, the amygdaloid complex is highly connected with several brain regions. It receives sensory inputs from the thalamus and cortical areas as well as extensive inputs from other regions in the limbic system, including the prefrontal cortex and hippocampus, [15] both of which are markedly altered in germ-free (GF) animals. [10,12,16] In fact, the connectivity between these three major regions, not just the function of the individual structures, is fundamental to appropriate emotional responses.…”

“…From here, numerous and complex intra-amygdaloid projections allow substantial communication between subdivisions, often following a lateral to medial direction until signals reach the CeA, from which the majority of efferent projections originate. [15] These efferent projections connect the amygdala to a wide variety of brain areas such as the brainstem, cortical areas, and subcortical nuclei including the hypothalamus and bed nucleus of the stria terminalis. [15,17] The amygdaloid complex undergoes ongoing development well into postnatal life.…”

“…[15] These efferent projections connect the amygdala to a wide variety of brain areas such as the brainstem, cortical areas, and subcortical nuclei including the hypothalamus and bed nucleus of the stria terminalis. [15,17] The amygdaloid complex undergoes ongoing development well into postnatal life. Rodent studies have demonstrated that the soma size and number of dendritic spines on BLA neurons reach adult levels by early adolescence, while there are ongoing changes in dendritic morphology into adulthood that parallel electrophysiological maturation of neurons in this region.…”