Figure 1.
Comparison of the facial anatomy and trigeminal sensory complex of a hairy-tailed mole (Parascalops breweri) and star-nosed mole (Condylura cristata).
A. A hairy-tailed mole has the typical body plan for a mole, with large forelimbs, small eyes, and a prominent but unspecialized nose. B. A horizontal section through the brainstem of a hairy tailed mole showing the trigeminal nerve (V), principal trigeminal sensory nucleus (PrV), and the spinal trigeminal nuclei (Sp50 – oral subnucleus, Sp5I - interpolar subnucleus, Sp5C - caudal subnucleus). The brainstem trigeminal nuclei of the hairy-tailed mole are similar to those of laboratory mice and rats. C. The star-nosed mole with an elaborate, mechanosensory nose. D. A horizontal section through the brainstem of a star-nosed mole. In star-nosed moles, PrV is greatly expanded in both rostral and medial-lateral directions. Note that the sections in B and D were cut horizontally relative to the separated brainstem, such that the ventral surface defined the horizontal plane.
Figure 2.
A parasagittal section of the star-nosed mole brain showing the relative size and location of the trigeminal nuclei, cranial nerve 5 (V) and the trigeminal ganglion (Vg).
Figure 3.
A star pattern visible in PrV.
A. Half of the star rotated 90 degrees counterclockwise showing the 11 rays that ring the nostril. The relatively small 11th ray acts as the tactile fovea. B. When the brainstem is properly oriented (see materials and methods) sections reveal 11 distinct modules in PrV.
Figure 4.
Microelectrode recordings from PrV related to brainstem anatomy.
A–F. A series of sections through the brainstem showing the representation of the star in PrV and the locations of 2 microlesions made during the recordings (L1, L2). G. Drawing of the brainstem showing the star subnucleus in PrV and the locations of the microlesions made during recordings. H. Receptive fields for neurons responding at lesioned sites L1 and L2. Axes are approximate in “G” as the brainstem was rotated to obtain favorable sections (see materials and methods).
Figure 5.
Microelectrode recordings from PrV related to brainstem anatomy.
A–I. A series of sections through the brainstem showing the representation of the star in PrV and the locations of 3 microlesions made during the recordings (L1, L2, L3). J. Drawing of the brainstem showing the star subnucleus in PrV and the locations of the microlesions made during recordings. K. Receptive fields for neurons responding at lesioned sites L1, L2, and L3.
Figure 6.
Comparison of myelinated fiber counts, PrV ray volumes, and cortical ray areas.
A–B. A section of the principal nucleus (PrV) containing the star representation compared to a flattened section of cortex showing the primary somatosensory representation of the star (S1 Cortex), both processed for cytochrome oxidase. The areas of the ray representations in “A” are similar to the total PrV volumes of the ray representations from reconstructions of serial sections. Thus these images illustrate the general finding that ray 11, the tactile fovea, is more greatly over-represented at the level of the cortex (B) than in the brainstem (A). C. The mean PrV volumes for each ray representation (1–11) from the 4 reconstructed cases. D. Myelinated fiber counts for the 11 rays of 4 moles from a previous study [17]. E. Areas of cortex representing the rays of 4 moles from a previous study [17]. F. The mean volume of each ray representation in PrV per fiber (ratio of C to D). G. The mean S1 cortex per fiber for each ray representation (ratio of E to D). Note that D, E, and G (darker histograms) are from a previous investigation in 4 moles (adapted from[17]), whereas C and F are from the present study in 4 different moles. Bars in C–G are SEM.