The ascending projections of the nuclei of the descending trigeminal tract (nTTD) in the zebra finch (Taeniopygia guttata)

• Published in: Journal of comparative neurology (1911) Vol. 525; no. 13; pp. 2832 - 2846
• Main Authors: Faunes, Macarena, Wild, J. Martin
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01-09-2017
• Subjects: Afferent Pathways - physiology; Animals; Biotin - analogs & derivatives; Biotin - metabolism; Birds; Brain Mapping; Cerebellum - metabolism; Cerebellum - physiology; Cholera; Cholera toxin; Cholera Toxin - metabolism; Dextran; Dextrans - metabolism; DIVA; Female; Finches - anatomy & histology; Hyperstriatum; Male; Nucleus basalis; Retrograde transport; RRID: AB_10013220; Somatosensory system; Song; songbird; Telencephalon; Thalamic Nuclei - anatomy & histology; Thalamus; Trigeminal Nuclei - anatomy & histology; Trigeminal Nuclei - physiology; Uva; DIVA; Uva; Birds; somatosensory system; RRID: AB_10013220; songbird
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.24247

In our traditional view of the avian somatosensory system, input from the beak and head reaches the telencephalon via a disynaptic pathway, involving projections from the principal sensory nucleus (PrV) directly to nucleus basorostralis (previously called nucleus basalis), whereas input from the rest of the body follows a trisynatic pathway similar to that in mammals, involving projections from the dorsal column nuclei to the thalamus, and thence to somatosensory wulst. However, the role of the nuclei of the descending trigeminal tract (nTTD) in this scenario is unclear, partly because their ascending projections have been examined in only one species, the mallard duck. Here we examine the ascending projections of the nTTD in the zebra finch, using in vivo injections of biotinylated dextran amine and verification of projections by means of retrograde transport of the beta subunit of cholera toxin. The results show a high degree of interconnectivity within the nTTD, and that these nuclei project to PrV. We also find a projection from nTTD to the contralateral thalamic nucleus uvaeformis, a multi‐sensory nucleus connected to the song system. Furthermore, our finding of a projection from nTTD to the contralateral somatosensory thalamic nucleus dorsalis intermedius ventralis anterior (DIVA) is consistent with the well‐known projection in mammals from nTTD to the ventrobasal thalamus, suggesting that the ascending trigeminal pathways in birds and mammals are more similar than previously thought.
The projections of the nTTD were examined in a songbird, using in vivo injections of sensitive neural tracers. The results revealed a high degree of intra‐trigeminal connectivity (blue) and demonstrated ascending projections to the contralateral thalamus (red), similar to those in mammals.