Paired pulse facilitation of corticogeniculate EPSCs in the dorsal lateral geniculate nucleus of the rat investigated in vitro

Abstract

To investigate paired pulse facilitation of corticogeniculate EPSCs, whole‐cell patch‐clamp recordings were made from principal cells in the rat dorsal lateral geniculate nucleus (dLGN) in vitro. Thalamic slices, oriented so that both corticogeniculate and retinogeniculate axons could be stimulated, were cut from young (16‐ to 37‐day‐old) DA‐HAN rats. Corticogeniculate EPSCs displayed pronounced paired pulse facilitation at stimulus intervals up to 400 ms. The facilitation had a fast and a slow component of decay with time constants of 12 ± 7 and 164 ± 47 ms (means ±s.d.), respectively. Maximum paired pulse ratio (EPSC2× EPSC1−1) was 3.7 ± 1.1 at the 20‐30 ms interval. Similar to other systems, the facilitation was presynaptic. Retinogeniculate EPSCs recorded in the same dLGN cells displayed paired pulse depression at intervals up to at least 700 ms. The two types of EPSCs differed in their calcium response curves. At normal [Ca2+]o, the corticogeniculate synapse functioned over the early rising part of a Hill function, while the retinogeniculate synapse operated over the middle and upper parts of the curve. The paired pulse ratio of corticogeniculate EPSCs was maximal at physiological [Ca2+]o. The facilitation is proposed to have an important role in the function of the corticogeniculate circuit as a neuronal amplifier.

Homeostatic Plasticity in the Visual Thalamus by Monocular Deprivation

“…A paired-pulse stimulation paradigm was used to activate corticothalamic (CT) and optic tract (OT) axons while recording the evoked synaptic responses in CDE and COE regions. As shown in Figure 6A, responses evoked by CT stimulation led to facilitation whereas those by OT produced depression (Turner and Salt, 1998; Granseth et al, 2002; Chen and Regehr, 2003; Govindaiah and Cox, 2004). However, the amplitudes of the CT evoked (e) EPSCs in the CDE region were significantly larger compared to those recorded in the COE region of the opposite hemisphere (Figure 6B, top).…”

“…For example, it is well known that a progressive increase in CT stimulus intensity gives rise to graded responses, indicating that dLGN cells receive convergent input from several individual corticogeniculate cells (Turner and Salt, 1998; Granseth et al, 2002; Granseth and Lindstrom, 2003; Li et al, 2003). As shown in Figure 7, our results are consistent with these reports and further reveal that these relations are unaffected by MD.…”

“…Previous reports indicate that these parameters are near optimal for evoking the peak of both paired-pulse facilitation and depression at the corticothalamic and retinogeniculate synapses, respectively (Turner and Salt, 1998; Granseth et al, 2002; Chen and Regehr, 2003; Granseth and Lindstrom, 2003; Govindaiah and Cox, 2004; Alexander et al, 2006). Recordings were limited to dLGN regions corresponding to the monocular segment of dLGN (Coleman et al, 2009).…”

“…Initially, single synaptic responses evoked once every 20 seconds across a range of stimulus intensities (0.1– 0.3 ms, 0.1–1 mA) were obtained, and the stimulus producing the maximal response was used for a paired pulse protocol. Since CT stimulation gives rise to graded responses (Figure 7), and to minimize such variability, it was necessary to choose a stimulus intensity that recruited as many fibers as possible (Granseth et al, 2002; Granseth and Lindstrom, 2003). …”

Synaptic organization of the tectorecipient zone of the rat lateral posterior nucleus

“…In addition, stimulation of cortical inputs to the rostral LPN elicits two types of excitatory postsynaptic responses (EPSPs). Type I responses facilitate with increasing stimulation frequency (Li et al, 2003b), similar to corticogeniculate EPSPs (Lindstrom and Wrobel, 1990; Turner and Salt, 1998; von Krosigk et al, 1999; Granseth et al, 2002), while type II responses depress with increasing stimulation frequency (Li et al, 2003a), similar to retinogeniculate responses (Turner and Salt, 1998; Chen et al, 2002; Chen and Regehr, 2003). Thus, it appears that the rostral LPN should be considered higher order in that the morphology and physiology of synaptic terminals that originate from cortical layer 5 are quite similar to the ascending sensory inputs of first order nuclei.…”