Descending projections of the hamster intergeniculate leaflet: Relationship to the sleep/arousal and visuomotor systems

Abstract

The intergeniculate leaflet (IGL), homolog of the primate pregeniculate nucleus, modulates circadian rhythms. However, its extensive anatomical connections suggest that it may regulate other systems, particularly those for visuomotor function and sleep/arousal. Here, descending IGL-efferent pathways are identified with the anterograde tracer, Phaseolus vulgaris leucoagglutinin, with projections to over 50 brain stem nuclei. Projections of the ventral lateral geniculate are similar, but more limited. Many of the nuclei with IGL afferents contribute to circuitry governing visuomotor function. These include the oculomotor, trochlear, anterior pretectal, Edinger-Westphal, and the terminal nuclei; all layers of the superior colliculus, interstitial nucleus of the medial longitudinal fasciculus, supraoculomotor periaqueductal gray, nucleus of the optic tract, the inferior olive, and raphe interpositus. Other target nuclei are known to be involved in the regulation of sleep, including the lateral dorsal and pedunculopontine tegmentum. The dorsal raphe also receives projections from the IGL and may contribute to both sleep/arousal and visuomotor function. However, the locus coeruleus and medial vestibular nucleus, which contribute to sleep and eye movement regulation and which send projections to the IGL, do not receive reciprocal projections from it. The potential involvement of the IGL with the sleep/arousal system is further buttressed by existing evidence showing IGL-efferent projections to the ventrolateral preoptic area, dorsomedial, and medial tuberal hypothalamus. In addition, the great majority of all regions receiving IGL projections also receive input from the orexin/hypocretin system, suggesting that this system contributes not only to the regulation of sleep, but to eye movement control as well.

Juxtacellular Recording/Labeling Analysis of Physiological and Anatomical Characteristics of Rat Intergeniculate Leaflet Neurons

“…The functional significance of these two classes of IGL neurons is unknown. Also unknown are the cell types that contribute to the widespread IGL connections with other brain regions and contribute to possible noncircadian functions of this nucleus (Mikkelsen, 1990;Moga and Moore, 1997;Vrang et al, 2003;Morin and Blanchard, 2005).…”

Immunocytochemical characterization of the pregeniculate nucleus and distribution of retinal and neuropeptide Y terminals in the suprachiasmatic nucleus of the Cebus monkey

“…In rodents, the IGL is a structure with a distinctive immunohistochemical profile and a characteristic pattern of efferents and afferents (Card and Moore, 1989;Harrington et al, 1987;Hickey and Spear, 1976;Morin and Blanchard, 2005). In rats and hamsters, the IGL can be identified as the region that divides the LGN into its dorsal and ventral parts, contains NPY-IR cells, receives bilateral retinal input (Morin et al, 1992Muscat et al, 2003;Pickard, 1985), and projects to the SCN and the contralateral IGL (Card and Moore, 1989).…”

Spatial and temporal requirements for sonic hedgehog in the regulation of thalamic interneuron identity

“…4A) (Vue et al, 2007). Thalamic neurons derived from pTH-R progenitors are thought to contribute to two dorsolaterally positioned thalamic nuclei, the ventrolateral geniculate nucleus (vLG) and the intergeniculate leaflet (IGL), neither of which projects axons to the cerebral cortex (Horowitz et al, 2004;Morin and Blanchard, 2005;Vue et al, 2007;Jones, 2007). We examined first the expression of thalamic progenitor markers at E12.5 and observed that genes expressed in the pTH-R domain (Nkx2.2, Gsx1, Ascl1, Tal1) were partially reduced in Shh SBE1/SBE1 embryos and almost completely downregulated in Shh SBE1/-mutants ( Fig.…”

“…The rostral population of thalamic progenitors, pTH-R, consists of a narrow band of cells sandwiched between pTH-C and the zli. Thalamic neurons derived from pTH-R progenitors are thought to contribute to two dorsolaterally positioned thalamic nuclei with incompletely understood functions: the ventrolateral geniculate nucleus (vLG) and the intergeniculate leaflet (IGL), neither of which projects axons to the cortex (Horowitz et al, 2004;Morin and Blanchard, 2005;Vue et al, 2007;Vue et al, 2009;Jones, 2007).…”