Fine structure of the visual dorsolateral anterior thalamic nucleus of the pigeon (Columba livia): A hodological and GABA‐immunocytochemical study

Abstract

The ultrastructure of the lateroventral subcomponent of the visual dorsolateral anterior thalamic nucleus of the pigeon (DLLv) was analyzed using hodological techniques and GABA-immunocytochemistry. Two types of GABA-immunonegative hyperpalliopetal neurons and a single type of strongly GABA-immunoreactive (-ir) interneuron were identified, the latter displaying long dendrites with some containing synaptic vesicles (DCSV). Ten types of axon terminal were identified and divided into two categories. The first, GABA-immunonegative and making asymmetrical synaptic contact, contain round (RT1, RT2, RT3) or pleiomorphic synaptic and many dense-core vesicles (DCT). RT1 terminals are retinothalamic and RT2 terminals hyperpalliothalamic; both mainly contact dendrites of projection neurons (72% and 78% respectively), less frequently dendrites of interneurons and sometimes DCSV; RT1 terminals are rarely involved in synaptic triads. The second category are consistently GABA-immunopositive. Four types (PT1-4), distinguished by their pleiomorphic synaptic vesicles, make symmetrical synaptic contact essentially with dendrites of projection neurons, more rarely on dendrites of interneurons (PT2). PT1 terminals are very probably those of interneurons, whereas the rare PT4 terminals are of retinal origin. A fifth type (RgT) contains round synaptic vesicles and makes asymmetrical synaptic contact with dendrites of projection neurons and interneurons. PT2 and RgT terminals occasionally contact DCSV of interneurons, which are sometimes involved in synaptic triads. Two final subcategories (DCgT1-2) contain many dense-core vesicles. Our findings are compared with those of previous studies concerning the fine structure and neurochemical properties of the GLd of reptiles and mammals, with special reference to the origin of the extraretinal and extracortical projections to this structure.

Synaptic circuitry in the retinorecipient layers of the optic tectum of the lamprey (Lampetra fluviatilis). A combined hodological, GABA and glutamate immunocytochemical study

“…On the other hand, the functional anatomical data concerning the retinotectal system are sufficiently extensive to reveal many similarities between Gnathostomes and Agnathans. Thus, with the exception of a small number of GABAergic retinal terminals (Kenigfest et al 1998;Miceli et al 2008 for reviews) which are absent in lampreys (present results), the retinotectal terminals of all vertebrates are glutamatergic, have rounded synaptic vesicles, and make asymmetrical synaptic contact with three types of profile. The first of these are the dendrites of glutamatergic efferent neurons, which are activated by the retinal terminals.…”

“…Miceli et al 2008). In addition, the microcircuits represented by the synaptic triads involving retinal terminals (optic terminal ?…”

“…It has been shown that the same is true not only of retinotectal or retinocollicular terminals in all major groups of Gnathostomes (fish, Kageyama and Meyer 1989;amphibians, Gábriel and Straznicky 1995;reptiles, Repé-rant et al 1997;birds, Morino et al 1996;mammals, Ortega et al 1995;Mize and Butler 1996) but also of all retinal terminals in general (Repérant et al 1997;Kenigfest et al 1998 for review), with the exception of a small population of GABAergic visual terminals (Kenigfest et al 1998;Miceli et al 2008 for review) of which we found not the slightest trace in the lamprey.…”

“…They have been described, without comment, in the corresponding tectal layers of the viper (Rio et al 1995), in the isthmo-optic nucleus of the pigeon Rio et al 2002), the nucleus dorsolateralis anterior of the same species (Miceli et al 2008), and in the nucleus geniculatus lateralis dorsalis of mammals (Papadopoulos and Parnavelas 1990;Pásik et al 1988). In the latter cases it has been shown that they correspond to serotoninergic terminals.…”

“…The two polyclonal antibodies used in this study have already been characterised in previous investigations; the anti-glutamate antibody (Chemicon) by Sherry and Ulshafer (1992) and Kalloniatis and Fletcher (1993), and the anti-GABA antibody (Immunotech) by Seguela et al (1984) and Miceli et al (2008); they were generated in rabbit against glutamate or GABA coupled to BSA with glutaraldehyde. The cross-reactivities were determined using ELISA or RIA techniques.…”