Neocortical neuronal morphology in the newborn giraffe (Giraffa camelopardalis tippelskirchi) and African elephant (Loxodonta africana)

Abstract

Although neocortical neuronal morphology has been documented in the adult giraffe (Giraffa camelopardalis tippelskirchi) and African elephant (Loxodonta africana), no research has explored the cortical architecture in newborns of these species. To this end, the current study examined the morphology of neurons from several cortical areas in the newborn giraffe and elephant. After cortical neurons were stained with a modified Golgi technique (N = 153), dendritic branching and spine distributions were analyzed by using computer-assisted morphometry. The results showed that newborn elephant neurons were considerably larger in terms of all dendritic and spine measures than newborn giraffe neurons. Qualitatively, neurons in the newborns appeared morphologically comparable to those in their adult counterparts. Neurons in the newborn elephant differed considerably from those observed in other placental mammals, including the giraffe, particularly with regard to the morphology of spiny projection neurons. Projection neurons were observed in both species, with a much larger variety in the elephant (e.g., flattened pyramidal, nonpyramidal multipolar, and inverted pyramidal neurons). Although local circuit neurons (i.e., interneurons, neurogliaform, Cajal-Retzius neurons) resembled those observed in other eutherian mammals, these were usually spiny, which contrasts with their adult, aspiny equivalents. Newborn projection neurons were smaller than the adult equivalents in both species, but newborn interneurons were approximately the same size as their adult counterparts. Cortical neuromorphology in the newborn giraffe is thus generally consistent with what has been observed in other cetartiodactyls, whereas newborn and adult elephant morphology appears to deviate substantially from what is commonly observed in other placental mammals.

Comparative morphology of gigantopyramidal neurons in primary motor cortex across mammals

“…In accordance with the well‐documented limitations of quantitative Golgi investigations (Braak & Braak, ; Jacobs et al, ; Jacobs, Harland, et al, ; Jacobs, Lee, et al, ; Williams, Ferrante, & Caviness, ), the present study is constrained by tissue fixation/storage issues, dendritic truncation in sectioning, and the small sample size of individual specimens and reconstructed neurons. The type of fixation (i.e., perfusion vs. immersion) is known to affect the quality of Golgi impregnations, as is the duration that tissue is stored prior to staining (de Ruiter, ; Friedland, Los, & Ryugo, ; Johnson et al, ).…”

“…Traced neurons ( N = 617) conformed to established selection criteria (Anderson et al, ; Jacobs et al, , Jacobs, Harland, et al, ; Jacobs, Lee, et al, ; Johnson et al, ), with an isolated soma near the center of the 120‐μm‐thick section and relatively well‐impregnated, unobscured, and as complete as possible (i.e., non‐truncated) dendritic projections. In addition to gigantopyramidal neurons, identified by relative size and dendritic morphology (Scheibel & Scheibel, ; Scheibel et al, ), both superficial (primarily layer III) and deep (primarily layer V) pyramidal neurons were traced for comparative purposes.…”

Neocortical neuronal morphology in the Siberian Tiger (Panthera tigris altaica) and the clouded leopard (Neofelis nebulosa)

“…Traced neurons conformed to established selection criteria (Anderson et al, ; Jacobs et al, , ), with an isolated soma near the center of the 120‐μm section and relatively well impregnated, unobscured, and complete (i.e., nontruncated) dendritic projections. To provide a comprehensive morphological analysis, neurons were selected to encompass representative typologies in each species.…”

“…Descriptively, neurons were classified according to somatodendritic criteria (Ferrer et al, ; Jacobs et al, , ) by considering factors such as soma size and shape, presence of spines, laminar location, and general morphology. Quantitatively, a centrifugal nomenclature was used to characterize branches extending from the soma as first‐order segments, which bifurcate into second‐ and then third‐order segments, and so on (Bok, ; Uylings et al, ).…”

“…Despite such extensive exploration of the domestic cat neocortex, nondomestic feliforms have received little attention in neuroscience research (Manger et al, ), presumably for practical reasons. Recently, however, studies of neuronal morphology across a variety of previously unexplored large‐brained mammals in both cerebellar (Jacobs et al, ) and cerebral cortex (Jacobs et al, , ; Butti et al, ) have revealed not only similarities but also some striking differences across species. To characterize further neuronal diversity across mammalian evolution, the present investigation extends existing knowledge of felid neocortex by examining the neocortical neuronal morphology of the Siberian tiger ( Panthera tigris altaica ) and the clouded leopard ( Neofelis nebulosa ).…”