title: The isthmic nuclei providing parallel feedback connections to the avian tectum have different neurochemical identities: Expression of glutamatergic and cholinergic markers in the chick (Gallus gallus).
abstract: Retinal inputs to the optic tectum (TeO) triggered by moving stimuli elicit synchronized feedback signals from two isthmic nuclei: the isthmi parvocelullaris (Ipc) and isthmi semilunaris (SLu). Both of these nuclei send columnar axon terminals back to the same tectal position receiving the retinal input. The feedback signals from the Ipc seem to act as an attentional spotlight by selectively boosting the propagation of retinal inputs from the tectum to higher visual areas. Although Ipc and SLu nuclei are widely considered cholinergic because of their immunoreactivity for choline acetyltransferase (ChAT), contradictory findings, including the expression of the vesicular glutamate transporter 2 (VGluT2) mRNA in Ipc neurons, have raised doubts about the purely cholinergic nature of this nucleus. In this study, in chicks, we revise the neurochemical identity of the isthmic nuclei by using in situ hybridization assays for VGluT2 along with three cholinergic markers: the vesicular acetylcholine transporter (VAChT), the high-affinity choline transporter (CHT1) and ChAT. We found that neurons in the SLu showed strong mRNA expression of all three cholinergic markers, whereas the expression of VAChT mRNA in the Ipc was undetectable in our essays. Instead, Ipc neurons exhibited a strong expression of VGluT2 mRNA. Immunohistochemistry assays showed VGluT2 immunoreactivity in the TeO codistributing with anterogradely labeled Ipc axon-terminal boutons, further supporting a glutamatergic function for the Ipc nucleus. Therefore, our results strongly suggest that, in the chick, whereas the feedback from the SLu to the TeO is indeed cholinergic, the feedback from the Ipc has a marked glutamatergic component.
authors.affiliation: Department of Biology, Faculty of Sciences, University of Chile, Santiago, Chile.
authors.forename: Cristian
authors.initials: C
authors.lastname: González-Cabrera
authors.forename: Florencia
authors.initials: F
authors.lastname: Garrido-Charad
authors.forename: Alejandro
authors.initials: A
authors.lastname: Roth
authors.forename: Gonzalo J
authors.initials: GJ
authors.lastname: Marín
mesh_terms: D000818:Animals; D030161:Avian Proteins / Q000378:metabolism; D002645:Chickens / Q000033:anatomy & histology / Q000378:metabolism*; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D025461:Feedback, Physiological / Q000502:physiology*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D026901:Membrane Transport Proteins / Q000378:metabolism; D056347:Neuroanatomical Tract-Tracing Techniques; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D013477:Superior Colliculi / Q000033:anatomy & histology / Q000378:metabolism*; D050494:Vesicular Acetylcholine Transport Proteins / Q000378:metabolism; D050599:Vesicular Glutamate Transport Protein 2 / Q000378:metabolism; D014795:Visual Pathways / Q000033:anatomy & histology / Q000378:metabolism*
chemical_list: D030161:Avian Proteins; D026901:Membrane Transport Proteins; D012333:RNA, Messenger; D050494:Vesicular Acetylcholine Transport Proteins; D050599:Vesicular Glutamate Transport Protein 2; C065637:choline transporter; D002795:Choline O-Acetyltransferase
keywords: RRID: nif-0000-24345; RRID:AB_10562420; RRID:AB_10562715; RRID:AB_2239153; RRID:AB_2313581; RRID:AB_2315140; RRID:AB_2336126; RRID:AB_514497; RRID:AB_90661; RRID:OMICS_02343; RRID:nlx_84100; RRID:nlx_84530; neurochemical identity; nucleus isthmi; spatial attention; tectofugal pathway