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

Abstract

This study provides an analysis of the cytoarchitecture, myeloarchitecture, and chemoarchitecture of the diencephalon (dorsal thalamus, ventral thalamus, and epithalamus) of the banded mongoose (Mungos mungo) and domestic ferret (Mustela putorius furo). Using architectural and immunohistochemical stains, we observe that the nuclear organization of the diencephalon is very similar in the two species, and similar to that reported in other carnivores, such as the domestic cat and dog. The same complement of putatively homologous nuclei were identified in both species, with only one variance, that being the presence of the perireticular nucleus in the domestic ferret, that was not observed in the banded mongoose. The chemoarchitecture was also mostly consistent between species, although there were a number of minor variations across a range of nuclei in the density of structures expressing the calcium-binding proteins parvalbumin, calbindin, and calretinin. Thus, despite almost 53 million years since these two species of carnivores shared a common ancestor, strong phylogenetic constraints appear to limit the potential for adaptive evolutionary plasticity within the carnivore order. Apart from the presence of the perireticular nucleus, the most notable difference between the species studied was the physical inversion of the dorsal lateral geniculate nucleus, as well as the lateral posterior and pulvinar nuclei in the domestic ferret compared to the banded mongoose and other carnivores, although this inversion appears to be a feature of Abbreviations: 3V, third ventricle; 3n, rootlets of oculomotor nerve; A, lamina A of dorsal lateral geniculate nucleus; A1, lamina A1 of dorsal lateral geniculate nucleus; AD, anterodorsal nucleus of the thalamus; AM, anteromedial nucleus of the thalamus; Amyg, amygdaloid complex; AOL, lateral accessory optic terminal nucleus; AV, anteroventral nucleus of the thalamus; bic, brachium of the inferior colliculus; BIN, nucleus of the brachium of the inferior colliculus; C, lamina C of dorsal lateral geniculate nucleus; Ca, caudate nucleus; ca, cerebral aqueduct; cc, corpus callosum; CeM, central medial nucleus of the thalamus; CL, central lateral nucleus of the thalamus; CM, center médian nucleus; csc, commissure of the superior colliculus;

Transient neurochemical features of the perigeniculate neurons during early postnatal development of the cat

“…It is also wider on the dorsal side, which is cell-free in adult animals and has sparsely located cells during the first postnatal weeks (Figure 2b). This separation from the main body of the TRN is a peculiarity of carnivores, as shown previously (Baldauf, 2010;Fitzgibbon, 2002;Pillay et al, 2021). In addition to the structures observed by other authors, our double-staining of the PRV and NeuN revealed a new anatomical feature-a PRV-free locus at the anterior pole of the…”

“…Except for parvalbumin, Ca 2+ ‐binding proteins (calbindin and calretinin) are labeled within the PGN in carnivores (Mitrofanis, 1992; Pillay et al., 2021). For this reason, calbindin and calretinin immunolabeling was documented in this study.…”

“…The main neurochemical marker for perigeniculate neurons is glutamic acid decarboxylase (GAD) enzyme (Fitzpatrick et al., 1984; Houser et al., 1980; Stichel et al., 1988; Montero & Singer, 1984), which is involved in the synthesis of gamma‐aminobutyric acid (GABA) and Ca 2+ ‐binding protein parvalbumin (Mitrofanis, 1994). However, two related Ca 2+ ‐binding proteins of the EF‐family (calretinin and calbindin) hypothetically marking the interneuronal populations were also detected in the perigeniculate neurons (Mitrofanis, 1992; Pillay et al., 2021). Thus, we investigated the postnatal development of the immunohistochemical status of the PGN neurons using several functional markers: (1) Ca 2+ ‐binding proteins (parvalbumin, calretinin, and calbindin); (2) GAD; and (3) a common neuronal marker (NeuN antibodies).…”