GABAergic circuitry in the dorsal division of the cat medial geniculate nucleus

Coomes, Diana L.; Bickford, Martha E.; Schofield, Brett R.

doi:10.1002/cne.10387

Cited by 13 publications

(20 citation statements)

References 81 publications

(185 reference statements)

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“…This value is similar to that in cats but rather different from rats (the two other species for which similar data are available; Figure 6). As mentioned in the Introduction, it was postulated that a high percentage of GABAergic tectothalamic cells may compensate for the relative absence of interneurons (Coomes et al, 2002). In cats, 25% of MG neurons are GABAergic interneurons (Huang et al, 1999), and about 20% of the tectothalamic cells are GABAergic.…”

Section: Discussionmentioning

confidence: 99%

“…Coomes et al (2002) suggested that rats may have a higher percentage of GABAergic cells in the tectothalamic pathway to compensate for the near absence of MG interneurons in that species (<1% of MG neurons; Winer and Larue, 1988). In contrast, cats have more interneurons (about 25% of MG neurons; Huang et al, 1999) and relatively fewer GABAergic tectothalamic cells.…”

Section: Introductionmentioning

confidence: 99%

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Distribution of GABAergic cells in the inferior colliculus that project to the thalamus

et al. 2014

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A GABAergic component has been identified in the projection from the inferior colliculus (IC) to the medial geniculate body (MG) in cats and rats. We sought to determine if this GABAergic pathway exists in guinea pig, a species widely used in auditory research. The guinea pig IC contains GABAergic cells, but their relative abundance in the IC and their relative contributions to tectothalamic projections are unknown. We identified GABAergic cells with immunochemistry for glutamic acid decarboxylase (GAD) and determined that ~21% of IC neurons are GABAergic. We then combined retrograde tracing with GAD immunohistochemistry to identify the GABAergic tectothalamic projection. Large injections of Fast Blue, red fluorescent beads or FluoroGold were deposited to include all subdivisions of the MG. The results demonstrate a GABAergic pathway from each IC subdivision to the ipsilateral MG. GABAergic cells constitute ~22% of this ipsilateral pathway. In addition, each subdivision of the IC had a GABAergic projection to the contralateral MG. Measured by number of tectothalamic cells, the contralateral projection is about 10% of the size of the ipsilateral projection. GABAergic cells constitute about 20% of the contralateral projection. In summary, the results demonstrate a tectothalamic projection in guinea pigs that originates in part from GABAergic cells that project ipsilaterally or contralaterally to the MG. The results show similarities to both rats and cats, and carry implications for the role of GABAergic tectothalamic projections vis-à-vis the presence (in cats) or near absence (in rats and guinea pigs) of GABAergic interneurons in the MG.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Distribution of GABAergic cells in the inferior colliculus that project to the thalamus

et al. 2014

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“…The GABA antibody used for this report has been used in numerous brain areas and numerous species, including guinea pigs, rats, rabbits, cats and mice (Coomes et al, 2002; Ruiz et al, 2004; Ponti et al, 2008; Luzzati et al, 2009; Brown et al, 2012; Smith et al, 2012). The ultrastructural features of GABA+ profiles in the present study (boutons, cell bodies, dendrites, spines and axon trunks) are similar to other descriptions of GABAergic structures in the IC, including studies that used antibodies to glutamic acid decarboxylase (GAD), a different marker for GABAergic neurons (Roberts and Ribak, 1987; Oliver and Beckius, 1992).…”

Section: Discussionmentioning

confidence: 99%

“…Based upon our measurements of the maximum size of the synaptic densities in the guinea pig IC we determined that a spacing of 600 nm was sufficient to avoid taking multiple sections of the same synapse. Each section was collected on a 300-mesh nickel grid and immunostained for GABA as described previously (Coomes et al, 2002). Briefly, grids with ultrathin sections were incubated overnight in anti-GABA antibody (rabbit anti-GABA, Sigma, St. Louis, MO) diluted 1:500 or 1:1000 in 0.05 M Tris-buffered saline with 0.1% Triton X-100, pH 7.6 (TBST), washed in TBST pH 7.6, then TBST pH 8.2, and placed into a secondary antibody conjugated to 15 nm gold particles (goat anti-rabbit, diluted 1:25 in TBST pH 8.2; Ted Pella Inc., Redding, CA).…”

Section: Methodsmentioning

confidence: 99%

Analysis of excitatory synapses in the guinea pig inferior colliculus: A study using electron microscopy and GABA immunocytochemistry

et al. 2013

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The inferior colliculus (IC) integrates ascending auditory input from the lower brainstem and descending input from auditory cortex. Understanding how IC cells integrate these inputs requires identification of their synaptic arrangements. We describe excitatory synapses in the dorsal cortex, central nucleus, and lateral cortex of the IC in guinea pigs. We used electron microscopy (EM) and post-embedding anti-GABA immunogold histochemistry on aldehyde-fixed tissue from pigmented adult guinea pigs. Excitatory synapses were identified by round vesicles, asymmetric synaptic junctions, and GABA-immunonegative presynaptic boutons. Excitatory synapses constitute ~ 60% of the synapses in each IC subdivision. Three types can be distinguished by presynaptic profile area and number of mitochondrial profiles. Large excitatory (LE) boutons are more than 2 μm2 in area and usually contain 5 or more mitochondrial profiles. Small excitatory (SE) boutons are usually less than 0.7 μm2 in area and usually contain 0 or 1 mitochondria. Medium excitatory (ME) boutons are intermediate in size and usually contain 2 to 4 mitochondria. LE boutons are mostly confined to the ICc, while the other two types are present throughout the IC. Dendritic spines are the most common target of excitatory boutons in the IC dorsal cortex, whereas dendritic shafts are the most common target in other IC subdivisions. Finally, each bouton type terminates on both GABA+ and GABA-negative (i.e., glutamatergic) targets, with terminations on GABA-negative profiles being much more frequent. The ultrastructural differences between the 3 types of boutons presumably reflect different origins and may indicate differences in postsynaptic effect. Despite such differences in origins, each of the bouton types contact both GABAergic and non-GABAergic IC cells, and could be expected to activate both excitatory and inhibitory IC circuits.

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“…Every seventh section was collected (this spacing is greater than the dimensions of synaptic zones in the IC, ensuring that a single synapse was not included in more than one ultrathin section for the quantitative analyses; Nakamoto et al, 2013). Individual sections were collected on 300-mesh nickel grids and immunostained for GABA, as described previously (Coomes et al, 2002). Grids with ultrathin sections were incubated overnight in anti-GABA antibody (rabbit anti-GABA, Sigma, St. Louis, MO) diluted 1:500 or 1:1000 in 0.05 M Tris-buffered saline with 0.1% Triton X-100 (TBST) pH 7.6, washed in TBST pH 7.6, then TBST pH 8.2, and placed into a secondary antibody conjugated to 15 nm gold particles (goat anti-rabbit, diluted 1:25 in TBST pH 8.2; Ted Pella Inc., Redding, CA).…”

Section: Methodsmentioning

confidence: 99%

Ultrastructural examination of the corticocollicular pathway in the guinea pig: a study using electron microscopy, neural tracers, and GABA immunocytochemistry

Nakamoto¹,

Mellott²,

Killius³

et al. 2013

Front. Neuroanat.

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Projections from auditory cortex (AC) can alter the responses of cells in the inferior colliculus (IC) to sounds. Most IC cells show excitation and inhibition after stimulation of the AC. AC axons release glutamate and excite their targets, so inhibition is presumed to result from cortical activation of GABAergic IC cells that inhibit other IC cells via local projections. However, it is not known whether cortical axons contact GABAergic IC cells directly. We labeled corticocollicular axons by injecting fluorescent dextrans into the AC in guinea pigs. We visualized the tracer with diaminobenzidine and processed the tissue for electron microscopy. We identified presumptive GABAergic profiles with post-embedding anti-GABA immunogold histochemistry on ultrathin sections. We identified dextran-labeled cortical boutons in the IC and identified their postsynaptic targets according to morphology (e.g., spine, dendrite) and GABA-reactivity. Cortical synapses were observed in all IC subdivisions, but were comparatively rare in the central nucleus. Cortical boutons contain round vesicles and few mitochondria. They form asymmetric synapses with spines (most frequently), dendritic shafts and, least often, with cell bodies. Excitatory boutons in the IC can be classified as large, medium or small; most cortical boutons belong to the small excitatory class, while a minority (~14%) belong to the medium excitatory class. Approximately 4% of the cortical targets were GABA-positive; these included dendritic shafts, spines, and cell bodies. We conclude that the majority of cortical boutons contact non-GABAergic (i.e., excitatory) IC cells and a small proportion (4%) contact GABAergic cells. Given that most IC cells show inhibition (as well as excitation) after cortical stimulation, it is likely that the majority of cortically-driven inhibition in the IC results from cortical activation of a relatively small number of IC GABAergic cells that have extensive local axons.

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GABAergic circuitry in the dorsal division of the cat medial geniculate nucleus

Cited by 13 publications

References 81 publications

Distribution of GABAergic cells in the inferior colliculus that project to the thalamus

Distribution of GABAergic cells in the inferior colliculus that project to the thalamus

Analysis of excitatory synapses in the guinea pig inferior colliculus: A study using electron microscopy and GABA immunocytochemistry

Ultrastructural examination of the corticocollicular pathway in the guinea pig: a study using electron microscopy, neural tracers, and GABA immunocytochemistry

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