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

Abstract

The thalamic intergeniculate leaflet (IGL) is involved in mediating effects of both photic and nonphotic stimuli on mammalian circadian rhythms. IGL neurons containing neuropeptide Y (NPY) have been implicated in mediating nonphotic effects, but little is known about those involved in photic entrainment. We used juxtacellular recording/labeling in rats to characterize both photic responses and neurochemical phenotypes of neurons in the lateral geniculate area, focusing on the IGL and ventral lateral geniculate (VLG). Single neurons were recorded to characterize photic responsiveness and were labeled with Neurobiotin (Nb); tissue was stained for Nb, NPY, and in some cases for orexin A. Three classes of neurons were identified in the IGL/VLG. Type I neurons lacked NPY and showed sustained activations during retinal illumination and moderate firing rates in darkness. Type II neurons contained large amounts of NPY throughout the soma and showed varied responses to illumination: suppression, complex responses, or no response. Type III neurons had patches of NPY both on the external soma surface and within the soma, apparently representing internalization of NPY. Type III neurons resembled type I cells in their sustained activation by illumination but were virtually silent during the intervening dark period. These neurons appear to receive NPY input, presumably from other IGL cells, which may suppress their activity during darkness. These results demonstrate the presence of several classes of neurons in the IGL defined by their functional and anatomical features and reinforce the role of the IGL/VLG complex in integrating photic and nonphotic inputs to the circadian system.

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.…”

“…Burst spike firing can be evoked in IGL neurons in vivo by retinal illumination (Ying et al, 1993;Thankachan and Rusak, 2005), and rhythmic oscillations can spontaneously occur under constant light (Werhun and Lewandowski, 2009) and can be evoked in slices by optic stimulation (Blasiak et al, 2009). Here we demonstrated that IGL neurons spontaneously fired LTS bursts when the membrane was hyperpolarized; such burst firing formed a rhythmic oscillation with a burst frequency of 0.5-2.6 Hz (Fig.…”

Photic induction of c-Fos in enkephalin neurons of the rat intergeniculate leaflet innervated by retinal PACAP fibres

“…However, light induces c-Fos mainly in non-immunoreactive cells. Recently, using juxtacellular recordings/labelling methods and NPY immunostaining, Thankachan and Rusak (2005) have classified three types of cells, which respond differently to retinal illumination, in the rat IGL. Type I neurons lacking NPY show sharp increases in firing at light onset, sustained activation during continued illumination and moderate firing rates in darkness.…”

Age-related changes in neurochemical components and retinal projections of rat intergeniculate leaflet

“…Both types are likely involved in mediating IGL photic adjustments to SCN. In contrast, type II neurons presented large NPY amounts and heterogeneous response to illumination and mediate the IGL non-photic function (Thankachan and Rusak 2005). Since we found a decrease in both IGL retinal projections and NPY-IR, we believe these three types of IGL neurons are functionally disrupted within the aging process, type I and type III in its activation by light input and type II in NPY expression, which points the adjustments IGL provides to central clock, by integration of photic and non-photic clues, are hindered with aging.…”

“…Moreover, Thankachan and Rusak (2005) characterized three classes of IGL neurons according to its activation by light and NPY presence. Among these classes, type I and type III neurons presented sustained activation by light and absence of NPY synthesis, differing in activation during darkness.…”