Thalamus

The thalamus is a part of the dienchephalon, together with the epithalamus, subthalamus, metathalamus and hypothalamus. The thalamus develops from the embryonic dienchephalon. It is a coordination-relay center, the vast majority of ascending sensory pathways targeting the cerebral cortex relays here.

The paired oval-shape thalamus is located around the third ventricle in both hemispheres. Its complex structure consists of several groups of nuclei: the anterior nuclei, the medial nuclei (parvocellular, magnocellular, medialis dorsalis and caudal nuclei), the lateral group of nuclei (involving the complex lateralis and ventralis nuclei), the reticular thalamic nucleus, the intralaminar nuclei (e.g. centromedial nucleus), as well as the the metathalamic nuclei (medial and lateral geniculate nuclei). The nuclei of subthalamus (zona incerta, subthalamic (Luysi) nucleus and Forel-zones) are located between the midbrain and thalamus.

Functionally, the thalamic nuclei can be divided to specific relay and association nuclei (that receive afferents from certain pathways and project to certain parts of the cerebral cortex) and to non-specific nuclei (basically the intralaminar and reticular thalamic nuclei; they receive afferents from the brainstem reticular formation and other thalamic nuclei and diffusely project to the cerebral cortex).

The thalamus has multiple functions. It relays sensory information, includes motor signals to the cerebral cortex, but it is also involved in the regulation of consciousness, sleep or alertness, and affects emotions.

Figure 1, Schematic drawing of the human brain, indicating the location of thalamus around the third ventricle from a sagittal view.

The transcriptome analysis shows that 79% (n=15510) of all human protein-coding genes (n=19670) are expressed in the human thalamus. Human one-to-one orthologues were investigated in pig and mouse brain, suggesting that 11799 of all mouse one-to-one orthologues (n=15160) are expressed in the mouse thalamus and that 12270 of all pig orthologues (n=14656) are expressed in the pig thalamus.

The transcriptome analysis shows that 79% (n=15510) of all human proteins (n=19670) are expressed in the thalamus.

Only 14 genes are classified as regionally elevated in thalamus. The elevated genes are all classified as group enriched, as shown in Table 1. Many group enriched genes are shared with brainstem regions, such as midbrain or pons and medulla.

Table 1: Number of genes within the different categories of regionally elevated expression, in human thalamus

The mouse thalamus is anatomically similar to the human thalamus, with similar topography of complexes of nuclei.

The transcriptome analysis shows that 60% (n=11799) of all mouse one-to-one homologue genes (n=15160)are expressed in the thalamus and 68 genes show an elevated expression in thalamus compared to other regions of the brain.

Table 2: Number of genes within the different categories of regionally elevated expression, in mouse thalamus.

Figure 2. Schematic drawing of the mouse brain, indicating the location of thalamus from a sagittal view.

The pig thalamus is anatomically similar to the human thalamus, with similar topography of complexes of nuclei.

The transcriptome analysis shows that 62% (n=12270) of all pig one-to-one human orthologue genes (n=14656) are expressed in the thalamus and 28 genes show an elevated expression in thalamus compared to other regions of the brain.

Table 5: Number of genes within the different categories of regionally elevated expression, in pig thalamus.

Figure 3. Schematic drawing of the pig brain, indicating the location of thalamus from a sagittal view.