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Intergeniculate leaflet and suprachiasmatic nucleus organization and connections in the golden hamster
- L.P. Morin, J. Blanchard, R.Y. Moore
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- Journal:
- Visual Neuroscience / Volume 8 / Issue 3 / March 1992
- Published online by Cambridge University Press:
- 02 June 2009, pp. 219-230
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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.
Forebrain connections of the hamster intergeniculate leaflet: Comparison with those of ventral lateral geniculate nucleus and retina
- L.P. MORIN, J.H. BLANCHARD
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- Journal:
- Visual Neuroscience / Volume 16 / Issue 6 / November 1999
- Published online by Cambridge University Press:
- 07 July 2001, pp. 1037-1054
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The hamster intergeniculate leaflet (IGL), part of the circadian rhythm regulatory system, has very extensive interconnections with subcortical visual nuclei. The present investigation describes IGL connections with the hamster diencephalon and telencephalon and compares them with ventral lateral geniculate nucleus (VLG) connections and retinal projections. Connections of the geniculate nuclei were evaluated using anterograde transport of iontophoretically injected Phaseolus vulgaris leucoagglutinin and by retrograde transport of cholera toxin β fragment. The cholera fragment was also injected intraocularly to trace retinal efferents. The IGL has ipsilateral and contralateral projections to the anterior and posterior hypothalamic nuclei, the ventral preoptic, lateral and dorsal hypothalamic areas, but not to the core ventromedial nucleus and very sparsely to the paraventricular nucleus. There are also IGL projections to the medial and lateral zona incerta, anteroventral, anterodorsal, reuniens, parataenial, paraventricular, centrolateral, central medial, and laterodorsal thalamic nuclei. IGL projections to the telencephalon are found in the horizontal limb of the diagonal band, olfactory tubercle, nucleus of the lateral olfactory tract, posterior bed nucleus of the stria terminalis, ventral pallidum, and in nuclei of the medial amygdala. The only substantial VLG projections are to bed nucleus of the stria terminalis, IGL, medial zona incerta, central medial and laterodorsal thalamic nuclei. Several of the IGL targets, the bed nucleus of the stria terminalis and zona incerta in particular, send projections back to the IGL and VLG. In addition, cells are present in the caudal cingulate cortex that project to both nuclei. Retinal projections are found in many of the regions receiving IGL innervation, including nuclei of the medial basal telencephalon, the posteromedial bed nucleus of the stria terminalis, and nuclei of the hypothalamus. A retinal projection is also visible in the lateral olfactory tract from which it extends rostrally, then medially along the base of the rhinal fissure. Fibers also extend caudally, in a superficial location, to perirhinal cortex. The results further demonstrate the widespread connections of the IGL and support the idea that the IGL modulates olfactory, photic, and circadian rhythm regulation of regulatory physiology and behavior.