Subcollicular projections to the auditory thalamus and collateral projections to the inferior colliculus.
superior olive; medial geniculate nucleus; binaural; brain evolution; lateral lemniscus; paralemniscal area; parallel pathways; reticular formation
Experiments in several species have identified direct projections to the medial geniculate nucleus (MG) from cells in subcollicular auditory nuclei. Moreover, many cochlear nucleus cells that project to the MG send collateral projections to the inferior colliculus (IC) (Schofield et al., 2014). We conducted three experiments to characterize projections to the MG from the superior olivary and the lateral lemniscal regions in guinea pigs. For experiment 1, we made large injections of retrograde tracer into the MG. Labeled cells were most numerous in the superior paraolivary nucleus, ventral nucleus of the trapezoid body, lateral superior olivary nucleus, ventral nucleus of the lateral lemniscus, ventrolateral tegmental nucleus, paralemniscal region and sagulum. Additional sources include other periolivary nuclei and the medial superior olivary nucleus. The projections are bilateral with an ipsilateral dominance (66%). For experiment 2, we injected tracer into individual MG subdivisions. The results show that the subcollicular projections terminate primarily in the medial MG, with the dorsal MG a secondary target. The variety of projecting nuclei suggest a range of functions, including monaural and binaural aspects of hearing. These direct projections could provide the thalamus with some of the earliest (i.e., fastest) information regarding acoustic stimuli. For experiment 3, we made large injections of different retrograde tracers into one MG and the homolateral IC to identify cells that project to both targets. Such cells were numerous and distributed across many of the nuclei listed above, mostly ipsilateral to the injections. The prominence of the collateral projections suggests that the same information is delivered to both the IC and the MG, or perhaps that a common signal is being delivered as a preparatory indicator or temporal reference point. The results are discussed from functional and evolutionary perspectives.
Schofield Brett R; Mellott Jeffrey G; Motts Susan D
Frontiers in neuroanatomy
2014
1905-7
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.3389/fnana.2014.00070" target="_blank" rel="noreferrer noopener">10.3389/fnana.2014.00070</a>
Perineuronal nets in subcortical auditory nuclei of four rodent species with differing hearing ranges.
guinea pig; inferior colliculus; mouse; naked mole-rat; plasticity; rat; RRID: AB141637; RRID: AB1500687; RRID: AB2336066; RRID: AB2336874; RRID: AB2336881; RRID: AB90460; superior olive; thalamus
Perineuronal nets (PNs) are aggregates of extracellular matrix molecules that surround some neurons in the brain. While PNs occur widely across many cortical areas, subcortical PNs are especially associated with motor and auditory systems. The auditory system has recently been suggested as an ideal model system for studying PNs and their functions. However, descriptions of PNs in subcortical auditory areas vary, and it is unclear whether the variation reflects species differences or differences in staining techniques. Here, we used two staining techniques (one lectin stain and one antibody stain) to examine PN distribution in the subcortical auditory system of four different species: guinea pigs (Cavia porcellus), mice (Mus musculus, CBA/CaJ strain), Long-Evans rats (Rattus norvegicus), and naked mole-rats (Heterocephalus glaber). We found that some auditory nuclei exhibit dramatic differences in PN distribution among species while other nuclei have consistent PN distributions. We also found that PNs exhibit molecular heterogeneity, and can stain with either marker individually or with both. PNs within a given nucleus can be heterogeneous or homogenous in their staining patterns. We compared PN staining across the frequency axes of tonotopically organized nuclei and among species with different hearing ranges. PNs were distributed non-uniformly across some nuclei, but only rarely did this appear related to the tonotopic axis. PNs were prominent in all four species; we found no systematic relationship between the hearing range and the number, staining patterns or distribution of PNs in the auditory nuclei.
Beebe Nichole L; Schofield Brett R
The Journal of comparative neurology
2018
2018-04
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1002/cne.24383" target="_blank" rel="noreferrer noopener">10.1002/cne.24383</a>