Intergeniculate leaflet and suprachiasmatic nucleus organization and connections in the golden hamster

Abstract

The intergeniculate leaflet (IGL) is a distinct subdivision of the lateral geniculate complex which receives retinal input and projects upon a circadian pacemaker, the suprachiasmatic nucleus (SCN). In the present study, we have analyzed the organization of the IGL and its connections in the hamster, a species commonly used in circadian rhythm studies. The location of the IGL is defined by the presence of retinal afferents demonstrated by anterograde transport of cholera toxin-HRP, neuropeptide Y-containing neurons and axons, cells retrogradely labeled from the regions of the SCN and contralateral IGL, and substance P-containing axons. It is a long nucleus extending the entire rostrocaudal axis of the geniculate. The most rostral IGL lies between the lateral dorsal thalamus, ventrolateral part, and the horizontal cerebral fissure. It then enlarges ventral to the rostral dorsal lateral geniculate, medial to the optic tract. The mid-portion of the leaflet is a thin lamina intercalated between the dorsal and ventral geniculate nuclei. The extended caudal portion of the nucleus lies lateral and ventral to the medial geniculate and is contiguous with the zona incerta and the lateral terminal nucleus. The IGL contains populations of neuropeptide Y (NPY+) and enkephalin (ENK+) neurons which project to the retinorecipient portion of the SCN. In addition to the immunoreactive perikarya, the IGL contains plexuses of NPY+, ENK + , substance P-, serotonin-, and glutamic acid decarboxylase-immunoreactive axons.Retrograde transport studies demonstrate that, in addition to the NPY+ neurons, there is a population of non-NPY+ neurons projecting upon the SCN. There is also a reciprocal projection upon the IGL from neurons in the SCN region, particularly the retrochiasmatic area. The hamster SCN differs from the rat in containing a distinct subdivision of substance P-immunoreactive neurons.

PIP2-Mediated HCN3 Channel Gating Is Crucial for Rhythmic Burst Firing in Thalamic Intergeniculate Leaflet Neurons

“…Staining for neuropeptide Y (NPY) in the IGL is much stronger than that for surrounding regions (Card and Moore, 1989;Morin et al, 1992;Moore and Card, 1994;Thankachan and Rusak, 2005). In our experiments, the NPY-labeled IGL (see Fig.…”

Exploring Spatiotemporal Organization of SCN Circuits

“…The SCN shell contains neurons expressing arginine vasopressin (AVP) in most species, including mouse, rat, hamster, lemur and humans, although not in mink (Larsen and Mikkelsen 1993) or mole rat (Rosen et al 2007). The SCN core is rich in vasoactive intestinal polypeptide (VIP) and gastrin-releasing peptide (GRP) in mouse, rat, and hamster (Morin et al 1992;Moore 1996;Abrahamson and Moore 2001). Other peptides in the SCN core, however, are more variable among species (Card and Moore 1984;Hartwich et al 1994;Silver et al 1999;Abrahamson and Moore 2001), likely reflecting functional species specializations.…”

Both Neuropeptide Y and Serotonin Are Necessary for Entrainment of Circadian Rhythms in Mice by Daily Treadmill Running Schedules

“…Two afferent pathways to the SCN that may contribute to phase shifting and entrainment by arousing, nonphotic stimuli include the geniculohypothalamic tract, which is a set of fibers containing NPY, GABA, and possibly other transmitters emanating from the thalamic intergeniculate leaflet (IGL) (Harrington et al, 1985;Morin et al, 1992), and a serotonergic input from the midbrain raphe nuclei (Azmitia and Segal, 1978;Meyer-Bernstein and Morin, 1996). Elimination of NPY input to the SCN by IGL ablation in hamsters and mice is reported to attenuate nonphotic shifting or prevent entrainment in response to running induced by triazolam, novel wheels, or home cage wheels (Johnson et al, 1988;Janik and Mrosovsky, 1994;Wickland and Turek, 1994;Edgar et al, 1997).…”