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The basic circuit of the IC: tectothalamic neurons with different patterns of synaptic organization send different messages to the thalamus.

Ito T, Oliver DL - Front Neural Circuits (2012)

Bottom Line: Although LG neurons are most numerous in the central nucleus of the IC (ICC), an analysis of their distribution suggests that they are not specifically associated with one set of ascending inputs.Neurons in the dorsal cochlear nucleus, superior olivary complex, intermediate nucleus of the lateral lemniscus, and IC itself that express the gene for VGLUT2 only are the likely origin of the dense VGLUT2 axosomatic terminals on LG tectothalamic neurons.SG neurons evidently target other auditory structures.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy, Faculty of Medical Sciences, University of Fukui Eiheiji, Japan.

ABSTRACT
The inferior colliculus (IC) in the midbrain of the auditory system uses a unique basic circuit to organize the inputs from virtually all of the lower auditory brainstem and transmit this information to the medial geniculate body (MGB) in the thalamus. Here, we review the basic circuit of the IC, the neuronal types, the organization of their inputs and outputs. We specifically discuss the large GABAergic (LG) neurons and how they differ from the small GABAergic (SG) and the more numerous glutamatergic neurons. The somata and dendrites of LG neurons are identified by axosomatic glutamatergic synapses that are lacking in the other cell types and exclusively contain the glutamate transporter VGLUT2. Although LG neurons are most numerous in the central nucleus of the IC (ICC), an analysis of their distribution suggests that they are not specifically associated with one set of ascending inputs. The inputs to ICC may be organized into functional zones with different subsets of brainstem inputs, but each zone may contain the same three neuron types. However, the sources of VGLUT2 axosomatic terminals on the LG neuron are not known. Neurons in the dorsal cochlear nucleus, superior olivary complex, intermediate nucleus of the lateral lemniscus, and IC itself that express the gene for VGLUT2 only are the likely origin of the dense VGLUT2 axosomatic terminals on LG tectothalamic neurons. The IC is unique since LG neurons are GABAergic tectothalamic neurons in addition to the numerous glutamatergic tectothalamic neurons. SG neurons evidently target other auditory structures. The basic circuit of the IC and the LG neurons in particular, has implications for the transmission of information about sound through the midbrain to the MGB.

No MeSH data available.


Related in: MedlinePlus

DCN neurons projecting to the IC express VGLUT2 but not VGLUT1. After an injection of Fluorogold (FG) into the IC, large DCN neurons, presumably fusiform and giant cells, show immunoreactivity for FG (brown). Their cell bodies are positive for VGLUT2 mRNA (dark blue in A), and negative for VGLUT1 mRNA (B) Note that numerous granule cells express VGLUT1 only. Bar: 40 μm.
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Figure 4: DCN neurons projecting to the IC express VGLUT2 but not VGLUT1. After an injection of Fluorogold (FG) into the IC, large DCN neurons, presumably fusiform and giant cells, show immunoreactivity for FG (brown). Their cell bodies are positive for VGLUT2 mRNA (dark blue in A), and negative for VGLUT1 mRNA (B) Note that numerous granule cells express VGLUT1 only. Bar: 40 μm.

Mentions: To test whether specific VGLUT-expressing cells project to the IC, we performed in situ hybridization for VGLUT1 and VGLUT2 combined with retrograde tracing (Ito and Oliver, 2010). After an injection of Fluorogold (FG), a fluorescent retrograde tracer, into the IC, retrogradely labeled neurons were found throughout the auditory pathways and cortex. Four patterns of VGLUT gene expression in FG-positive cells were found; (1) VGLUT1 only, (2) VGLUT2 only (For example, fusiform cells of the DCN; Figure 4), (3) co-expressed VGLUT1&2, and (4) no VGLUT expression. FG-positive cells expressing VGLUT1 alone were found only in the auditory cortex. Nuclei that had a substantial number of FG-positive cells expressing VGLUT are shown in Figure 52. The most likely sources of the VGLUT2 axosomatic terminals on LG neurons (Figure 5, red) were the ipsilateral INLL, the contralateral LSO, the contralateral DCN, and the IC, since other nuclei have fewer neurons that express VGLUT2 only. These sources may also produce the numerous VGLUT2-positive terminals on dendrites in the IC.


The basic circuit of the IC: tectothalamic neurons with different patterns of synaptic organization send different messages to the thalamus.

Ito T, Oliver DL - Front Neural Circuits (2012)

DCN neurons projecting to the IC express VGLUT2 but not VGLUT1. After an injection of Fluorogold (FG) into the IC, large DCN neurons, presumably fusiform and giant cells, show immunoreactivity for FG (brown). Their cell bodies are positive for VGLUT2 mRNA (dark blue in A), and negative for VGLUT1 mRNA (B) Note that numerous granule cells express VGLUT1 only. Bar: 40 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3405314&req=5

Figure 4: DCN neurons projecting to the IC express VGLUT2 but not VGLUT1. After an injection of Fluorogold (FG) into the IC, large DCN neurons, presumably fusiform and giant cells, show immunoreactivity for FG (brown). Their cell bodies are positive for VGLUT2 mRNA (dark blue in A), and negative for VGLUT1 mRNA (B) Note that numerous granule cells express VGLUT1 only. Bar: 40 μm.
Mentions: To test whether specific VGLUT-expressing cells project to the IC, we performed in situ hybridization for VGLUT1 and VGLUT2 combined with retrograde tracing (Ito and Oliver, 2010). After an injection of Fluorogold (FG), a fluorescent retrograde tracer, into the IC, retrogradely labeled neurons were found throughout the auditory pathways and cortex. Four patterns of VGLUT gene expression in FG-positive cells were found; (1) VGLUT1 only, (2) VGLUT2 only (For example, fusiform cells of the DCN; Figure 4), (3) co-expressed VGLUT1&2, and (4) no VGLUT expression. FG-positive cells expressing VGLUT1 alone were found only in the auditory cortex. Nuclei that had a substantial number of FG-positive cells expressing VGLUT are shown in Figure 52. The most likely sources of the VGLUT2 axosomatic terminals on LG neurons (Figure 5, red) were the ipsilateral INLL, the contralateral LSO, the contralateral DCN, and the IC, since other nuclei have fewer neurons that express VGLUT2 only. These sources may also produce the numerous VGLUT2-positive terminals on dendrites in the IC.

Bottom Line: Although LG neurons are most numerous in the central nucleus of the IC (ICC), an analysis of their distribution suggests that they are not specifically associated with one set of ascending inputs.Neurons in the dorsal cochlear nucleus, superior olivary complex, intermediate nucleus of the lateral lemniscus, and IC itself that express the gene for VGLUT2 only are the likely origin of the dense VGLUT2 axosomatic terminals on LG tectothalamic neurons.SG neurons evidently target other auditory structures.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy, Faculty of Medical Sciences, University of Fukui Eiheiji, Japan.

ABSTRACT
The inferior colliculus (IC) in the midbrain of the auditory system uses a unique basic circuit to organize the inputs from virtually all of the lower auditory brainstem and transmit this information to the medial geniculate body (MGB) in the thalamus. Here, we review the basic circuit of the IC, the neuronal types, the organization of their inputs and outputs. We specifically discuss the large GABAergic (LG) neurons and how they differ from the small GABAergic (SG) and the more numerous glutamatergic neurons. The somata and dendrites of LG neurons are identified by axosomatic glutamatergic synapses that are lacking in the other cell types and exclusively contain the glutamate transporter VGLUT2. Although LG neurons are most numerous in the central nucleus of the IC (ICC), an analysis of their distribution suggests that they are not specifically associated with one set of ascending inputs. The inputs to ICC may be organized into functional zones with different subsets of brainstem inputs, but each zone may contain the same three neuron types. However, the sources of VGLUT2 axosomatic terminals on the LG neuron are not known. Neurons in the dorsal cochlear nucleus, superior olivary complex, intermediate nucleus of the lateral lemniscus, and IC itself that express the gene for VGLUT2 only are the likely origin of the dense VGLUT2 axosomatic terminals on LG tectothalamic neurons. The IC is unique since LG neurons are GABAergic tectothalamic neurons in addition to the numerous glutamatergic tectothalamic neurons. SG neurons evidently target other auditory structures. The basic circuit of the IC and the LG neurons in particular, has implications for the transmission of information about sound through the midbrain to the MGB.

No MeSH data available.


Related in: MedlinePlus