Multi-receptor analysis of the macaque lateral geniculate nucleus

2166 

Abstract Submission 

Marina Saito^1,2,3, Lucjia Rapan⁴, Meiqi Niu⁴, Ling Chao⁴, Sei-ichi Tsujimura², Nicola Palomero-Gallagher^4,5, Hiromasa Takemura^1,6,7

¹National Institute for Physiological Sciences, Okazaki, Japan, ²Nagoya City University, Nagoya, Japan, ³Japan Society for the Promotion of Science, Tokyo, Japan, ⁴Research Centre Jülich, Jülich, Germany, ⁵Heinrich Heine University Düsseldorf, Düsseldorf, Germany, ⁶The Graduate Institute of Advanced Studies, SOKENDAI, Hayama, Japan, ⁷Center for Information and Neural Networks (CiNet), Advanced ICT Research Institute, NICT, Suita, Japan

Marina Saito  
National Institute for Physiological Sciences|Nagoya City University|Japan Society for the Promotion of Science
Okazaki, Japan|Nagoya, Japan|Tokyo, Japan

Lucjia Rapan  
Research Centre Jülich
Jülich, Germany

Meiqi Niu  
Research Centre Jülich
Jülich, Germany

Ling Chao  
Research Centre Jülich
Jülich, Germany

Sei-ichi Tsujimura  
Nagoya City University
Nagoya, Japan

Nicola Palomero-Gallagher  
Research Centre Jülich|Heinrich Heine University Düsseldorf
Jülich, Germany|Düsseldorf, Germany

Hiromasa Takemura  
National Institute for Physiological Sciences|The Graduate Institute of Advanced Studies, SOKENDAI|Center for Information and Neural Networks (CiNet), Advanced ICT Research Institute, NICT
Okazaki, Japan|Hayama, Japan|Suita, Japan

The lateral geniculate nucleus (LGN) is one of the thalamic nuclei which process visual information from the retina and transmit visual signals to the cortex. The LGN is composed of three subdivisions: the magnocellular, parvocellular and koniocellular (Figure 1A). Although the structure and function of LGN has been extensively studied through various methods (Hubel & Livingstone, 1990; Denison et al., 2014; Oishi et al., 2023), its receptor architecture has not yet been fully understood so far. As the regional and laminar distribution patterns of different receptors in the cerebral cortex has been shown to be a powerful tool for understanding the potential functional segregation as well as hierarchical organization among different brain areas (Rapan et al., 2022), here we aim to elucidate the receptor architecture of the LGN by analyzing receptor autoradiographs obtained from macaque monkey brains for better understanding underlying relationship between receptor architecture and function of the LGN (Palomero-Gallagher & Zilles, 2018).

We analyzed coronal sections from four hemispheres of three adult male Macaca fascicularis (Rapan et al., 2022). We quantified the densities of 15 receptors visualized by in vitro receptor autoradiography using previously established protocols (Palomero-Gallagher & Zilles, 2018; Zilles et al., 2002). We delineated LGN sublayers as regions-of-interest (ROIs) in both cell-body stained sections and the adjacent receptor autoradiographs and extracted the density of each receptor type in each, the borders between each layer were charted on the pseudocolor-coded autoradiographs (Figure 1B). The magnocellular, parvocellular, and koniocellular layers were defined as ROIs, the densities of each ROI were measured by calculating the average receptor densities from their component sublayers, respectively. Finally, the mean densities of all receptors were visualized for each ROI separately in a polar plot as a 'receptor fingerprint'. To evaluate differences in receptor architecture between the LGN and visual cortex, we compared the receptor fingerprints with those of primary visual areas published by Rapan et al., 2021.

The color-coded autoradiographs of representative sections in Figure 1B show the exemplary receptor distribution patterns of the LGN. We found a considerably higher concentration of acetylcholine M₂ and α₄β₂ receptors in the LGN than in the cortex. Furthermore, the distinct cytoarchitectonic layers in the LGN are clearly reflected by the receptor architecture. The receptor fingerprints of all three ROIs were similar in shape, but differ in size (Figure 2A): magnocellular part exhibited the highest densities, while the koniocellular ones exhibited the lowest densities, whereby M₂ receptors presented the highest overall receptor densities, followed by the M₃, α₄β₂. Lowest densities were measured for the AMPA and M₁ receptors. This balance resulted in fingerprints that differed considerably in both size and shape from those of the dorsal and ventral parts of V1 (Figure 2B), where the highest densities are reached by the GABAergic and glutamate receptors.

The present study showed that the LGN presents considerably higher M₂, and α₄β₂ receptor densities than does V1 and its three subdivisions differ in their averaged densities. The high density of LGN in M₂ and α₄β₂ receptors may be related to the functional roles of acetylcholine during sensory information processing, such as involvement with improving signal-to-noise ratio of neural response to sensory stimuli, by decreasing noise correlation among neurons and improving encoding efficiency (Minces et al., 2017). Our results suggest that the receptor architecture of the LGN may be geared towards improving the encoding efficiency of visual information before it is forwarded to cortical visual areas.

Transmitter Receptors ¹

Perception: Visual ²

Acetylcholine

GABA

Neurotransmitter

RECEPTORS

Vision