Cholinergic and GABAergic neuronal elements in the pineal organ of lampreys, and tract-tracing observations of differential connections of pinealofugal neurons

Abstract

The putative cholinergic and GABAergic elements of the pineal organ of lampreys were investigated with immunocytochemistry to choline acetyltransferase (ChAT) and gamma-aminobutyric acid (GABA), and by acetylcholinesterase (AChE) histochemistry. For comparison we also carried out immunocytochemistry to serotonin (5-HT) and a tract-tracing investigation of the two types of projecting cells, i. e., ganglion cells and long-axon photoreceptors. Most photoreceptors were ChAT-immunoreactive (ChAT-ir) and AChE-positive, while ganglion cells and the pineal tract were ChAT-negative and AChE-negative or only faintly positive. These results strongly suggest the presence of a cholinergic system of photoreceptors in the lamprey pineal organ. GABA-ir fibers that appear to originate from faintly to moderately stained ganglion cells were observed in the pineal stalk. Immunocytochemistry to 5-HT indicated the presence of two types of 5-HT-ir cells, bipolar cells and ganglion-like cells. The connections of the ganglion cells and long-axon photoreceptors were also studied by application of DiI to the pineal stalk in fixed brains or of biotinylated dextran amine (BDA) to one of the main targets of pinealofugal fibers (optic tectum or mesencephalic tegmentum) in isolated brains in vitro. Some long-axon photoreceptors and ganglion cells were labeled from the optic tectum. However, BDA application to the tegmentum exclusively labeled ganglion cells in the pineal organ. These results indicate that the two morphological types of afferent pineal neuron have different projections. No labeled cells were observed in the parapineal organ in BDA experiments, indicating that this organ and the pineal organ are involved in different neural circuits.

Afferent and Efferent Connections of the Pineal Organ in the European Sea Bass <i>Dicentrarchus labrax:</i> A Carbocyanine Dye Tract-Tracing Study

“…This lipophilic fluorescent tracer diffuses along cell membranes in paraformaldehyde-fixed brains, thus avoiding in vivo surgery [Vercelli et al, 2000]. Moreover, DiI reveals with high resolution the connections of small, relatively inaccessible structures, including the pineal organ [Honig and Hume, 1986;Godement et al, 1987;Holmqvist et al, 1992;Yáñez et al, , 1997Yáñez et al, , 1999Yáñez and Anadón, 1998;Pombal et al, 1999;Mandado et al, 2001;Folgueira et al, 2002Folgueira et al, , 2003Folgueira et al, , 2004aYáñez et al, 2009].…”

“…The efferent labeling in the posterior tubercle represents a shared feature of lampreys, elasmobranchs and bony fishes [Hafeez and Zerihun, 1974;Puzdrowski and Northcutt, 1989;Yáñez et al, 1993;Jiménez et al, 1995;Yáñez and Anadón, 1998;Pombal et al, 1999;Mandado et al, 2001;Yáñez et al, 2009]. In the sea bass, the paraventricular organ contains serotonin-and dopamine-immunoreactive cells [Batten et al, 1993], which might play a role in mediating the central actions of the pineal organ.…”

“…Since the introduction of the lipophilic carbocyanine dyes [i.e. 1,1 -dioctadecyl-3,3,3 ,3 -tetramet hylindocarbocyanine perchlorate (DiI), 3,3 -dioctadecyloxacarbocyanine perchlorate and 4-[4-(dihexadecylamino)styryl]-N-meth ylpyridinium iodide] as neuronal tracers, the study of pineal projections has been considerably facilitated [Yáñez et al, 1993Yáñez and Anadón, 1998;Pombal et al, 1999;Mandado et al, 2001;Yáñez et al, 2009]. The carbocyanine dyes permit one to delineate neural projections of those structures not easily accessible for the in vivo surgery required in the classical tracing methods [Godement et al, 1987;Holmqvist et al, 1992].…”

“…To date, the pineal projections have been investigated in several vertebrate species including lampreys [Puzdrowski and Northcutt, 1989;Yáñez et al, 1993;Pombal et al, 1994Pombal et al, , 1999, elasmobranchs [Mandado et al, 2001], sturgeons [Yáñez and Anadón, 1998] and some teleosts [Hafeez and Zerihun, 1974;Ekström andvan Veen, 1983, 1984;Holmqvist et al, 1994;Jiménez et al, 1995;Yáñez et al, 2009]. In those animals, the pineal tract has been observed as bilateral projections coursing through the habenula to reach different diencephalic (preoptic area, pretectum, thalamus, hypothalamus) and mesencephalic areas (optic tectum, tegmentum, torus semicircularis, raphe) [Ekström and Meissl, 1997].…”

Evolution of photosensory pineal organs in new light: the fate of neuroendocrine photoreceptors

“…In lampreys they appear to be fairly randomly distributed in the pineal organ, possibly with a predominance in the distal atrium (Samejima et al 1989;Pombal et al 1999). One central target for the long photoreceptor axons appears to be the optic tectum demonstrating the presence of more than one photopigment in several species (Meissl & Dodt 1981;Ekströ m & Meissl 1997).…”