Hemispheric differences in the number of parvalbumin-positive neurons in subdivisions of the rat basolateral amygdala complex

Abstract

The amygdala is a bilateral temporal lobe brain region which plays an important role in emotional processing. Past studies on the amygdala have shown hemispheric differences in amygdalar processes and responses associated with specific pain and fear behaviors. Despite the functional differences in the amygdala, few studies have been performed to characterize whether anatomical differences exist between the left and right amygdala. Parvalbumin (PV) is a phenotypic marker for an inhibitory interneuronal population in cortical brain structures such as the basolateral amygdala complex (BLC). This study examined the number of PV-positive neurons in the left and right BLC of adult, male Long-Evans rats using unbiased stereology. Coronal sections through the rostral-caudal extent of the BLC were immunohistochemically-stained for PV and the optical fractionator method was used to obtain an unbiased estimate of the number of PV-positive neurons in subdivisions through the BLC. The lateral and basolateral amygdala divisions of the BLC were analyzed, were subdivided into the dorsolateral, ventrolateral and ventromedial and the posterior, anterior and ventral subdivisions, respectively. The results indicate that there are significantly more PV-positive neurons in the left basolateral amygdala compared to the right, with a significant difference specifically in the posterior subdivision. This difference in PV neuronal number could help explain the distinct hemispheric roles of the BLC in the behavioral processing following exposure to painful and fearful stimuli.

Predominant synaptic potentiation and activation in the right central amygdala are independent of bilateral parabrachial activation in the hemilateral trigeminal inflammatory pain model of rats

“… 65 Functional and morphological asymmetry has been reported for various structures in the rodent, fish, and human brain. 66 – 71 Although the functional and cellular mechanisms underlying such asymmetry remains largely undetermined (but see Ukai et al. 67 ), this would imply asymmetric ontogenic mechanisms during network formation in the embryonic stage.…”

It Is All in the Right Amygdala: Increased Synaptic Plasticity and Perineuronal Nets in Male, But Not Female, Juvenile Rat Pups after Exposure to Early-Life Stress

“…In adults rodents, glutamatergic synaptic output of BLA pyramidal cells is directly modulated by inhibitory GABAergic interneurons expressing the calcium-binding protein parvalbumin (PV) (Berdel and Mory s, 2000). PV cells form approximately half of the interneurons in the adult BLA (Woodruff and Sah, 2007b), display hemispheric asymmetry in numbers (Butler et al, 2018), and mature between PND14 and PND30 (Berdel and Mory s, 2000). PV interneurons in the BLA are encapsulated by proteoglycan-rich specializations of the extracellular matrix called perineuronal nets (PNNs) that reach adult levels by PND28 (Gogolla et al, 2009).…”

Low-threshold spiking interneurons perform feedback inhibition in the lateral amygdala

“…The most salient parallels between BLA and other cortical regions with respect to their interneurons exist with respect to parvalbumin (PV) and somatostatin (SOM) positive interneurons. For instance, PV+ interneurons form perisomatic baskets or axoaxonic synapses on principal neurons and constitute around 50% of the total interneuron population (McDonald and Mascagni 2001;McDonald and Bettette 2001;Rainnie et al 2006;Vereczki et al 2016;Butler et al 2018) and play significant roles in fear learning (Lucas et al 2016). Remarkably, these PV+ interneurons exhibit a close correspondence in their electrophysiology to their cortical counterparts (Rainnie et al 2006;Woodruff and Sah 2007).…”