Distribution of Calretinin Immunoreactivity in the Lateral Nucleus of the Bottlenose Dolphin (Tursiops truncatus) Amygdala

Abstract

The amgdaloid complex consists of different nuclei, each with unique cytoarchitectonic, chemoarchitectonic and connectional characteristics. Most of the inputs coming from cortical and subcortical areas enter the amygdala via the lateral nucleus, which makes it the main receiving structure of the complex. The activity of its neurons is coordinated and modulated by different inhibitory, GABAergic-interneurons, which can be classified for their expression of various calcium-binding proteins, as well as by morphological characteristics. This research based on the analysis of the amygdala of three bottlenose dolphins, provides the first description of the topography, cytoarchitecture and distribution of calretinin immunoreactivity of the lateral nucleus. Our observations on the bottlenose dolphin confirmed the general topography of the mammalian amygdala and of the lateral nucleus. Notably, we identified six subdivision of the nucleus, more than those reported until now in the rat, monkey and human lateral nucleus. This could reveal an outstanding capability of integration and elaboration of external stimuli. In addition, we observed a strong presence of CR-immunoreactive (-ir) neurons and fibres. CR-ir neurons were mainly non-pyramidal inhibitory neurons; in particular, 80% of IR-cells were represented by large and small polygonal neurons. In the lateral nucleus of the human amygdala, CR-ir neurons form inhibitory synapses on calbindinD28k-IR inhibitory interneurons. Since calbindin-D28k-ir interneurons make inhibitory synapses on the pyramidal cells, the final goal of the CR-ir interneurons could be the synchronization of cells activity, thus playing an important role in the control of information flow in the lateral amygdalar nucleus.

Comparative neuroanatomical study of the amygdala and fear conditioning in Nigerian breeds of Artiodactyla: Sheep (Uda) and goats (Red Sokoto)

“…In the BLC of the amygdala in goats, most neurons are pyramidal while in sheep they are non‐pyramidal of spherical subtype. Sheep showed similarity to the neurons within the BLC of several mammals like human (Sorvari, Soininen, & Pitkanen, 1996), rat (Kemppainen & Pitkanen, 2000; McDonald, 1994), monkey (McDonald, 1994) and bottlenose dolphins (Rambaldi et al, 2008) where the majority of cells consists of small spherical or bipolar/bitufted neurons. However, that of goat was unique and in contrast to the reported mammals.…”

The amygdaloid body of two carnivore species: The feliform banded mongoose and the caniform domestic ferret

“…In both species the amygdaloid body shows a very similar architectural organization, in terms of homologous nuclei and cortical areas, and one that is not significantly different to that observed in more frequently studied mammalian species, including the domestic cat and domestic dog (e.g., Ichinohe & Rockland, 2005; Kemppainen & Pitkänen, 2000; Kosmal & Nitecka, 1977; Krettek & Price, 1978; Limacher‐Burrell, Bhagwandin, Gravett, Maseko, & Manger, 2016; Pitkänen & Amaral, 1993a, 1993b; Pitkänen, Savander, & LeDoux, 1997; Price et al, 1987; Sah et al, 2003; Sorvari et al, 1995), although our analysis of the organization of the domestic ferret amygdaloid body differs in some respects to that previously provided (Radtke‐Schuller, 2018). It is reasonable to conclude that across Eutherian mammals a shared organization of the nuclei and cortical areas of the amygdaloid body is present, although in some cases this organization does present with some specific differences (e.g., Limacher‐Burrell, Bhagwandin, Maseko, & Manger, 2018; Rambaldi et al, 2017). This overall similarity in the organization is strongly suggestive of phylogenetic constraints playing a major role in the evolution of the amygdala and thus the expression of affective behaviors; however, the systems level organization presented here does not account for potential variations in connectivity, which may vary between species that show overall similarities in systems‐level organization (e.g., Dell, Innocenti, Hilgetag, & Manger, 2019a, 2019b, 2019c), and other aspects such as specific patterns of gene and receptor expression that play a crucial role in neural processing.…”