Putative cholinergic projections from the nucleus isthmi and the nucleus reticularis mesencephali to the optic tectum in the goldfish (Carassius auratus)

Abstract

The nucleus isthmi of fish and amphibians has reciprocal connections with the optic tectum, and biochemical studies suggested that it may provide a major cholinergic input to the tectum. In goldfish, we have combined immunohistochemical staining for choline acetyltransferase with retrograde labeling of nucleus isthmi neurons after tectal injections of horseradish peroxidase. Seven fish received tectal horseradish peroxidase injections, and brain tissue from these animals was subsequently processed for the simultaneous visualization of horseradish peroxidase and choline acetyltransferase. In many nucleus isthmi neurons the dense horseradish peroxidase label obscured the choline acetyltransferase reaction product but horseradish peroxidase and choline acetyltransferase were colocalized in 54 cells from nine nuclei isthmi. The somata of nucleus reticularis mesencephali neurons stained so intensely for choline acetyltransferase that we could not determine whether they were labelled also with horseradish peroxidase. However, the large choline acetyltransferase-immunoreactive axons of nucleus reticularis mesencephali neurons stained intensely enough for us to follow them rostrally; the axons are clustered together until the level of the rostral tectum where two groupings form: one travels into the tectum and the other travels rostroventrally to cross the midline and enter the contralateral diencephalic preoptic area. We conclude therefore that cholinergic neurons project to the optic tectum from the nucleus isthmi as well as nucleus reticularis mesencephali in goldfish.

Afferent Connections of the Optic Tectum in Lampreys: An Experimental Study

“…A common feature of the isthmic nucleus in nonmammalian vertebrates is the cholinergic nature of its cells [Brauth et al, 1985;Desan et al, 1987;Ekström, 1987;Brantley and Bass, 1988;Zottoli et al, 1988;Sorenson et al, 1989;Bagnoli et al, 1992;Medina and Smeets, 1992;Medina et al, 1993;Molist et al, 1993;Powers and Reiner, 1993;Medina and Reiner, 1994;González et al, 2002]. Recently, similar cholinergic nuclei have been suggested in elasmobranch chondrostean and teleost fishes [Adrio et al, 2000;Anadón et al, 2000;Pérez et al, 2000], as well as in lampreys [Pombal et al, 2001; see also Rodríguez-Moldes et al, 2002].…”

“…A direct tectal connection from the isthmus has been found in all vertebrates studied so far [Nieuwenhuys et al, 1998]. In most teleosts this connection is only ipsilateral [Ebbesson and Vanegas, 1976;Grover and Sharma, 1981;Luiten, 1981;Sakamoto et al, 1981;Ito et al, 1982b;Northcutt, 1982;Vanegas and Ito, 1983;Zottoli et al, 1988;Yamamoto et al, 1999], as well as in the leopard frog [Wilczynski and Northcutt, 1977]; however, bilateral connections were found in other fish [Dunn-Meynell and Sharma, 1984;Sas and Maler, 1986] and amphibian species [Glasser and Ingle, 1978;Grobstein et al, 1978;Gruberg and Udin, 1978;Gruberg and Lettvin, 1980;Grobstein and Comer, 1983;Desan et al, 1987;Rettig, 1988;Marín et al, 1999].…”

Comparison of Acetylcholinesterase and Choline Acetyltransferase Staining Patterns in the Optic Tectum of the Goldfish <i>Carassius auratus</i>

“…Since ChAT-positive afferents from the nucleus isthmi and possibly other nuclei (e.g. nucleus reticu laris mesencephali [Zottoli et al, 1985]) project to the tectum, the extent and pat terns of type XIV arborization may be partially obscured by the presence of these fibers. However, some individual neurons stained in near isolation of other ChATpositive cell bodies and neurites.…”

“…These results are discussed in the context of the organization of intrinsic and extrin sic sources of cholinergic innervation of the tectum. Preliminary accounts of this research have been reported previously [Zottoli et al, 1985.…”

“…The localization of ChAT within putative cholinergic neurons by immunocytochemical techniques has been made possible by the development of antibodies specific to ChAT. Such anti bodies have been used to characterize ChAT-containing neurons within the tec tum of goldfish [Zottoli et al, 1985; and to locate potential sources of afferent cholinergic innervation .…”