Abstract
Abstract The present study was taken to test the hypothesis that the medial nucleus of the trapezoid body (MNTB) of echolocating neotropical bats with different foraging behavior will exhibit morphological variations in relative size, degree of complexity and spatial distribution. The brains were collected from six male adult bats of each species: Noctilio leporinus (fish-eating), Phyllostomus hastatus (carnivorous/ omnivorous) and Carollia perspicillata (fruit-eating) and were double-embedded and transverse serial sections were cut and stained with cresyl fast violet. The results showed that the MNTB is well developed in all the bats in general and the mean length of the MNTB was 1160 ± 124 µm in N. leporinus, 400 ± 59 µm in P. hastatus and 320 ± 25µm in C. perspicillata. The body and brain weight do not reflect proportionately on the size of the MNTB in the present study. The hearing frequency spectrum did not covary with the size of the MNTB among the bats studied. The MNTB is clearly demarcated from the ventral nucleus of the trapezoid body (VNTB) only in P. hastatus. The MNTB comprised mainly three types of cells in all three bats: dense-staining multipolar cells (12.5 µm and 25.0 µm diameter); light-staining multipolar cells measuring (12.5 µm and 25.0 µm diameter) and light-staining round cells (5.0 µm diameter). The large sized MNTB was observed in N. leporinus, which suggests that it relies heavily on echolocation whereas P. hastatus and C. perspicillata use echolocation as well but also rely on hearing, smell and vision.
Highlights
The medial nucleus of the trapezoid body (MNTB) is a major auditory nucleus in the brainstem located in the hind brain next to superior olive
The large diameter axons of globular bushy cells (GBCs) pass in the acoustic stria and decussate at the midline within the trapezoid body (Smith et al, 1991) and terminate on principal neurons of the MNTB via a type of giant calyceal axo-somatic terminal, calyx of Held (Morest, 1968; Held, 1893) The MNTB is a major source of glycinergic inhibition to the ipsilateral medial and lateral superior olivary nuclei (MSO, lateral superior olive (LSO), respectively), the ventral and dorsal nuclei of the lateral lemniscus (VNLL, DNLL, respectively), and other targets (Harrison and Warr, 1962; Elverland, 1978; Spangler et al, 1985)
The body and brain weight do not reflect proportionately on the size of the MNTB in the present study as the body and brain weight of the P. hastatus measured as 73.24 ± 7.25 g and 8.57 ± 0.67 g respectively which is higher than the N. leporinus 48.1 ± 3.5 g and 6.93 ± 0.47 g, whereas the length of the MNTB measured 400 ± 59 μm in P. hastatus and 1160 ± 124 μm in N. leporinus
Summary
The medial nucleus of the trapezoid body (MNTB) is a major auditory nucleus in the brainstem located in the hind brain next to superior olive It consists of several type of neurons and the calyces of Held, the large synaptic endings of certain auditory neurons of the anterior ventral cochlear nucleus (AVCN). The large diameter axons of GBCs pass in the acoustic stria and decussate at the midline within the trapezoid body (Smith et al, 1991) and terminate on principal neurons of the MNTB via a type of giant calyceal axo-somatic terminal, calyx of Held (Morest, 1968; Held, 1893) The MNTB is a major source of glycinergic inhibition to the ipsilateral medial and lateral superior olivary nuclei (MSO, LSO, respectively), the ventral and dorsal nuclei of the lateral lemniscus (VNLL, DNLL, respectively), and other targets (Harrison and Warr, 1962; Elverland, 1978; Spangler et al, 1985). Three types of neurons viz., stellate, elongate and principal cells were identified in the MNTB of cats and rats (Morest, 1968) with a majority (82%) of principal cells in rats (Casey and Feldman, 1985)
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