Habenula

Habenula
Medial aspect of human brain showing location of the habenula in front of the pineal gland or body in the epithalamus shown in red The habenular commissure is labelled shown connecting the habenula.
Habenula shown in blue just in front of the pineal gland shown in red
Identifiers
MeSHD019262
NeuroNames294
NeuroLex IDbirnlex_1611
TA98A14.1.08.003
TA25662
FMA62032
Anatomical terms of neuroanatomy

The habenula (diminutive of Latin habena meaning rein) is a small bilateral neuronal structure in the brain of vertebrates, that has also been called a microstructure since it is no bigger than a pea. The naming as little rein describes its elongated shape in the epithalamus, where it borders the third ventricle, and lies in front of the pineal gland.[1]

Although it is a microstructure each habenular nucleus is divided into two distinct regions of nuclei, a medial habenula (MHb), and a lateral habenula (LHb) both having different neuronal populations, inputs, and outputs.[2][3] The medial habenula can be subdivided into five subnuclei, the lateral habenula into four subnuclei.[4] Research has shown morphological complexity in the MHb and LHb. Different inputs to the MHb are discriminated between the different subnuclei.[5] In the two regions of nuclei there is a difference in gene expression giving different functions to each.[6]

The habenula is a conserved structure across vertebrates. In mammals it is highly symmetric, and in fish, amphibians and reptiles it is highly asymmetric in size, molecular composition, and connections.[1] The habenular nuclei are a major component in the limbic system pathways.[1] The fasciculus retroflexus pathway between the habenula and the interpeduncular nucleus is one of the first major nerve tracts to form in the developing brain.[1]

The habenula is a central structure that connects forebrain regions to midbrain regions, and acts as a hub or node for the integration of emotional and sensory processing.[2] It integrates information from the limbic system, sensory and basal ganglia to guide appropriate and effective responses.[5] The habenula is involved in the regulation of monoamine neurotransmittters notably dopamine and serotonin.[2][3] Both of these neurotransmitters are strongly associated with anxiety disorders, and avoidance behaviours.[2] The functions of the habenula are also involved in motivation, emotion, learning, and pain.[2] The MHb plays an important role in depression, stress, memory, and nicotine withdrawal, as well as a role in cocaine, methamphetamine and alcohol addiction.[6] The MHb shows a high level of nicotinic acetylcholine receptors (nAChRs), that are involved in many forms of addiction. Previously their expression was only noted in other structures associated with addiction. Their expression in the MHb has become a later focus of research.[6]

  1. ^ a b c d Antolin-Fontes, B; Ables, JL; Görlich, A; Ibañez-Tallon, I (September 2015). "The habenulo-interpeduncular pathway in nicotine aversion and withdrawal". Neuropharmacology. 96 (Pt B): 213–22. doi:10.1016/j.neuropharm.2014.11.019. PMC 4452453. PMID 25476971.
  2. ^ a b c d e Antunes, GF; Campos, ACP; Martins, DO; Gouveia, FV; Rangel Junior, MJ; Pagano, RL; Martinez, RCR (27 June 2023). "Unravelling the Role of Habenula Subnuclei on Avoidance Response: Focus on Activation and Neuroinflammation". International Journal of Molecular Sciences. 24 (13): 10693. doi:10.3390/ijms241310693. PMC 10342060. PMID 37445871.
  3. ^ a b Boulos, LJ; Darcq, E; Kieffer, BL (15 February 2017). "Translating the Habenula-From Rodents to Humans". Biological Psychiatry. 81 (4): 296–305. doi:10.1016/j.biopsych.2016.06.003. PMC 5143215. PMID 27527822.
  4. ^ Cite error: The named reference Ables2023 was invoked but never defined (see the help page).
  5. ^ a b Juárez-Leal, I; Carretero-Rodríguez, E; Almagro-García, F; Martínez, S; Echevarría, D; Puelles, E (16 June 2022). "Stria medullaris innervation follows the transcriptomic division of the habenula". Scientific Reports. 12 (1): 10118. Bibcode:2022NatSR..1210118J. doi:10.1038/s41598-022-14328-1. PMC 9203815. PMID 35710872.
  6. ^ a b c Viswanath, H; Carter, AQ; Baldwin, PR; Molfese, DL; Salas, R (2013). "The medial habenula: still neglected". Frontiers in Human Neuroscience. 7: 931. doi:10.3389/fnhum.2013.00931. PMC 3894476. PMID 24478666.