Organization of cortical projections to the medullary subnucleus reticularis dorsalis: A retrograde and anterograde tracing study in the rat

Abstract

The distribution and organization of cortical projections to the subnucleus reticularis dorsalis (SRD), the neighboring cuneate nucleus (Cu), and trigeminal nucleus caudalis (Sp5C) were studied in the rat using microinjections of wheat germ agglutinin-apo horseradish peroxidase-gold and Biotin-Dextran. Cortical cells projecting to the caudal medulla were confined to the contralateral layer V with their descending axons crossing the midline at the level of pyramidal decussation. Cortical afferents to Sp5C originated from cells located mainly in the primary somatosensory cortex (S1) and the insular cortex, whereas cortical projections to the Cu originated mainly from the primary motor cortex (M1), the primary and secondary somatosensory cortex (S1 and S2). The SRD received dense cortical afferents from larger, widespread cortical areas: M1, M2, S1, S2, and the insular cortex. The existence of dense cortico-SRD connections supports the possibility of a pyramidal influence over SRD neurons, which might modify nociceptive information ascending to the cortex itself. This proposal is consistent with the fact that SRD efferents terminate densely in thalamic areas that influence sensorimotor cortical regions which in turn project to the SRD. Moreover, these corticofugal mechanisms could allow the cortex to select its own input by suppressing or augmenting transmission of signals through SRD-hindbrain/forebrain pathways or by coordinating activities in spino-SRD-spinal circuits and thus selecting the relevant information produced by the noxious stimulus.

Changes of Meningeal Excitability Mediated by Corticotrigeminal Networks: A Link for the Endogenous Modulation of Migraine Pain

“…These projections originate unilaterally from pyramidal cells of layer V of areas within S1, S2, and caudal insula. In accordance with other studies (Wise and Jones, 1977;Desbois et al, 1999), descending axons from S1 and Ins terminate in deep (III-V) and superficial (I-IIo) laminae of Sp5C, respectively, as confirmed by their relationship with 5-HT 1D /calcitonin generelated peptide (CGRP) primary afferents (supplemental Fig. S1 A, available at www.jneurosci.org as supplemental material).…”

Reticular Formation and Pain: The Past and the Future

“…The DRt was shown to relay descending pain facilitation from the anterior cingulate cortex (ACC; Zhang et al, 2005). Additionally, the DRt receives dense innervation from cortical areas, namely from the motor (M1 and M2), somatosensory (S1 and S2) and insular cortex (Desbois et al, 1999; Almeida et al, 2002). Our recent work demonstrated that a high percentage of the cortical projections to the DRt were GABAergic (Figure 2) and the release of GABA at the DRt enhanced DRt pain facilitation (Martins et al, 2015a).…”

Three Channels of Corticothalamic Communication during Locomotion

“…Theoretical calculations suggest that currents in the range of 0.1-0.5 mA activate a sphere of tissue with a diameter of Ͻ1 mm (Hentall et al, 1984); nevertheless, we cannot exclude that some of the axons in the reticular formation surrounding the PT were also activated. Both the PT and lower brainstem reticular formation projecting neurons are known to populate only layer V of the motor cortex (Jones and Wise, 1977;Groos et al, 1978;Toyoshima and Sakai, 1982;Kuypers, 1984, 1989;Rapisarda et al, 1985;Ghosh et al, 1988;Nudo and Masterton, 1990;Desbois et al, 1999). All neurons that responded antidromically to stimulation applied to electrodes in the PT will be referred to as pyramidal tract neurons (PTNs).…”