Morphology and connectivity of parabrachial and cortical inputs to gustatory thalamus in rats

Abstract

Ventroposterior medialis parvocellularis (VPMpc) of thalamus, the thalamic relay nucleus for gustatory sensation, receives primary input from parabrachial nucleus, and projects to insular cortex. To reveal unique properties of gustatory thalamus in comparison to archetypical sensory relay nuclei, this study examines the morphology of synaptic circuitry in VPMpc, focusing on parabrachiothalamic driver input and corticothalamic feedback. Anterogradely visualized parabrachiothalamic fibers in VPMpc bear large swellings. At electron microscope resolution, parabrachiothalamic axons are myelinated and make large boutons, forming multiple asymmetric, adherent and perforated synapses onto large caliber dendrites and dendrite initial segments. Labeled boutons contain dense-core vesicles, and they resemble a population of calcitonin gene-related peptide containing terminals within VPMpc. As typical of primary inputs to other thalamic nuclei, parabrachiothalamic terminals are over 5 times larger than other inputs, while constituting only 2% of all synapses. Glomeruli and triadic arrangements, characteristic features of other sensory thalamic nuclei, are not encountered. As revealed by anterograde tracer injections into insular cortex, corticothalamic projections in VPMpc form a dense network of fine fibers bearing small boutons. Corticothalamic terminals within VPMpc were also observed to synapse on cells that were retrogradely filled from the same injections. The results constitute an initial survey in describing unique anatomical properties of rodent gustatory thalamus.

Characterization of McDonald's intermediate part of the Central nucleus of the amygdala in the rat

“…It is specifically used to visualize CGRP in brain cells. This antibody produced the same staining pattern in the rat brain as previously reported for other CGRP antibodies (Shimada et al, 1985;Yasui, Saper, & Cechetto, 1991;Holtz, Fu, Loflin, Corson, & Erisir, 2015).…”

Central taste anatomy and physiology

“…Inputs, Outputs, and Internal Connectivity-The parvicellular portion of the ventropostero-medial nucleus of the thalamus (VPMpc) is the main thalamic gustatory relay to cortex (Mufson and Mesulam, 1984). Gustatory information reaches the VPMpc via projections from the NST in primates (Beckstead et al, 1980) and the parabrachial nucleus (PBN) in rodents (Holtz et al, 2015;Karimnamazi et al, 2002). In primates, no gustatory connection to the PBN has been demonstrated so far.…”

“…The VPMpc receives inhibitory inputs from the gustatory portion of the reticular thalamus (Hayama et al, 1994) and a strong contingent of excitatory fibers from the GC (Allen et al, 1991;Holtz et al, 2015). The GC projects to the VPMpc directly (Allen et al, 1991;Holtz et al, 2015) and indirectly via the RT (Hayama et al, 1994). As is the case for many other sensory thalamic nuclei, the VPMpc also receives fibers from neuromodulatory centers.…”

“…With regard to the projections out of the PBN, the two major taste-related PBN targets are the thalamus and the CeA (Bernard et al, 1993;Fulwiler and Saper, 1984;Halsell, 1992;Holtz et al, 2015;Ogawa et al, 1984;Tokita et al, 2010). Anterograde tracing studies have shown that PBN-thalamic projections mainly terminate in the ipsilateral gustatory thalamus (Halsell, 1998).…”

The mouse olfactory peduncle 4: Development of synapses, perineuronal nets, and capillaries

“…Images were only taken in regions containing at least one labeled synapse. For all BDAlabeled presynaptic terminals, synapse length and terminal area were measured (Holtz, Fu, Loflin, Corson, & Erisir, 2015). Across three mice, 20 synapses and 14 terminals were measured.…”