Abstract
We studied the cellular organization of the piriform network [comprising the piriform cortex (PC) and endopiriform nucleus (EP)] of the ferret (Mustela putorius)—a highly excitable region prone to seizures—and, more specifically, the distribution and morphology of different types of gamma-aminobutyric acid (GABA)ergic neurons, and the distribution and ratio of glutamatergic and GABAergic boutons, and we compared our findings to those in primary visual area 17, and secondary areas 18 and 19. We accomplished this by using cytochrome oxidase and immunohistochemistry for mature neuronal nuclei (NeuN), GABAergic neurons [glutamic acid decarboxylase-67 (GAD67), calretinin (CR) and parvalbumin (PV)], and for excitatory (vesicular glutamate transporter 1; VGluT1) and inhibitory (vesicular GABA transporter; VGAT) boutons. In the ferret, the cellular organization of the piriform network is similar to that described in other species such as cats, rats and opossums although some differences also exist. GABAergic immunolabeling showed similarities between cortical layers I–III of the PC and visual areas, such as the relative distribution of GABAergic neurons and the density and area of VGluT1- and VGAT-immunoreactive boutons. However, multiple differences between the piriform network and visual areas (layers I–VI) were found, such as the percentage of GABAergic neurons with respect to the total number of neurons and the ratio of VGluT1- and VGAT-immunoreactive boutons. These findings are relevant to better understand the high excitability of the piriform network.
Highlights
Ferrets (Mustela putorius) are a useful model for research on cortical development and plasticity because they are born with an immature state of corticogenesis compared to other mammals such as monkeys, cats and rodents (Jackson et al, 1989; Chapman et al, 1996; Noctor et al, 1997)
To gain insights into the cytoarchitectonic and functional organization of the inhibitory system in the ferret piriform cortex (PC) and endopiriform nucleus, and its involvement in epilepsy, excitability and propagation of neural information in mammalian seizures, we studied the morphology and distribution of two types of GABAergic neurons such as parvalbumin (PV) and calretinin (CR) immunoreactive neurons, as well as the distribution and ratio of vesicular glutamate transporter 1 (VGluT1)-ir and vesicular gamma-aminobutyric acid (GABA) transporter (VGAT)-ir boutons in the PC and endopiriform nucleus, and we compared these data with our findings in visual areas 17, 18 and 19
Our findings show that glutamic acid decarboxylase-67 (GAD67)-ir neuron proportion was 14.6% in the piriform network; it was 31.1% in primary visual area 17, and 29.4 and 24.6% in secondary areas 18 and 19, respectively
Summary
Ferrets (Mustela putorius) are a useful model for research on cortical development and plasticity because they are born with an immature state of corticogenesis compared to other mammals such as monkeys, cats and rodents (Jackson et al, 1989; Chapman et al, 1996; Noctor et al, 1997). Anatomical studies characterizing the cerebral cortex in adult ferrets are relatively scarce, some reports have described the anatomical and functional organization in several primary and associative sensory cortical areas (Weliky et al, 1995; McLaughlin et al, 1998; Innocenti et al, 2002; Manger et al, 2002a,b, 2004; Dell et al, 2019a,b,c) These studies have uncovered some functional similarities with other mammals such as rats (Ekstrand et al, 2001b), opossums (Haberly, 1983), cats (Witter et al, 1988) and monkeys (Neville and Haberly, 2004). Despite the interest for developmental and functional studies, data on the gamma-aminobutyric acid (GABA)ergic and excitatory/inhibitory organization of the cortex in adult ferrets are scarce
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