Abstract
The midbrain tegmentum is the source of cholinergic innervation of the thalamus and has been associated with arousal and control of the sleep/wake cycle. In general, the innervation arises bilaterally from the pedunculopontine tegmental nucleus (PPT) and the laterodorsal tegmental nucleus (LDT). While this pattern has been observed for many thalamic nuclei, a projection from the LDT to the medial geniculate body (MG) has been questioned in some species. We combined retrograde tracing with immunohistochemistry for choline acetyltransferase (ChAT) to identify cholinergic projections from the brainstem to the MG in guinea pigs. Double-labeled cells (retrograde and immunoreactive for ChAT) were found in both the PPT (74%) and the LDT (26%). In both nuclei, double-labeled cells were more numerous on the ipsilateral side. About half of the retrogradely labeled cells were immunonegative, suggesting they are non-cholinergic. The distribution of these immunonegative cells was similar to that of the immunopositive ones: more were in the PPT than the LDT and more were on the ipsilateral than the contralateral side. The results indicate that both the PPT and the LDT project to the MG, and suggest that both cholinergic and non-cholinergic cells contribute substantially to these projections.
Highlights
The medial geniculate body (MG) is part of the auditory thalamus and serves as the primary source of ascending input to the auditory cortex
The latter areas included the cochlear nucleus, superior olivary complex, ventral nucleus of the lateral lemniscus and adjacent paralemniscal area, nucleus sagulum, and a region dorsal to the dorsal nucleus of the lateral lemniscus
Only the nuclei of the pontomesencephalic tegmentum (PMT) contained retrogradely labeled cells that were immunopositive for choline acetyltransferase (ChAT) (Figure 2)
Summary
The medial geniculate body (MG) is part of the auditory thalamus and serves as the primary source of ascending input to the auditory cortex. The cholinergic projections form part of the ascending arousal system and, as such, control the firing mode of thalamic cells through both nicotinic and muscarinic effects (Tebecis, 1972; McCormick and Prince, 1987; Steriade et al, 1988; Jones, 2005). These effects control the flow of information to the cortex and underlie changes in thalamic responsiveness during the sleep-wake cycle and at varying levels of arousal during wakefulness (Edeline, 2003; Steriade, 2004; Hennevin et al, 2007). The possible lack of a projection from the LDT to the MG suggests that the auditory thalamus may be exceptional in receiving a unique pattern of cholinergic inputs from the brainstem
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
