Descending projections from the dysgranular zone of rat primary somatosensory cortex processing deep somatic input

Abstract

In the mammalian somatic system, peripheral inputs from cutaneous and deep receptors ascend via different subcortical channels and terminate in largely separate regions of the primary somatosensory cortex (SI). How these inputs are processed in SI and then projected back to the subcortical relay centers is critical for understanding how SI may regulate somatic information processing in the subcortex. Although it is now relatively well understood how SI cutaneous areas project to the subcortical structures, little is known about the descending projections from SI areas processing deep somatic input. We examined this issue by using the rodent somatic system as a model. In rat SI, deep somatic input is processed mainly in the dysgranular zone (DSZ) enclosed by the cutaneous barrel subfields. By using biotinylated dextran amine (BDA) as anterograde tracer, we characterized the topography of corticostriatal and corticofugal projections arising in the DSZ. The DSZ projections terminate mainly in the lateral subregions of the striatum that are also known as the target of certain SI cutaneous areas. This suggests that SI processing of deep and cutaneous information may be integrated, to a certain degree, in this striatal region. By contrast, at both thalamic and prethalamic levels as far as the spinal cord, descending projections from DSZ terminate in areas largely distinguishable from those that receive input from SI cutaneous areas. These subcortical targets of DSZ include not only the sensory but also motor-related structures, suggesting that SI processing of deep input may engage in regulating somatic and motor information flow between the cortex and periphery.

Organization of Cerebral Projections to Identified Cerebellar Zones in the Posterior Cerebellum of the Rat

“…deed, various sources of mossy fibers, such as the dorsal column nuclei, trigeminal nuclei, lateral reticular nucleus and paramedian reticular formation have been reported to receive cortical input (Allen and Tsukahara, 1974;Lee and Kim, 2012). Although CTb-labeled cells were noted in many of these areas, their full analysis fell outside the scope of the present study.…”

“…For example, it seems remarkable that climbing fiber responses in vermal lobule VII may be triggered from the prelimbic cortex (Watson et al, 2009) which does not qualify as a major disynaptic source to this region. Of course, although to some extent the cerebro-olivo-cerebellar pathway is disynaptic (Lee and Kim, 2012), it usually involves more synapses (Baker et al, 2001;Pardoe et al, 2004).…”

Cerebellum and Cerebellar Connections

“…It is of interest that these areas are also the recipients of cerebellar input as has been demonstrated in the cat (Bull and Berkley, 1991). The IOD also receives a direct and somatotopically organized input from the somatosensory and dysgranular cortices (Swenson et al, 1989;Lee and Kim, 2012). In the rat it has been shown that the anterior interposed nucleus (IntA) of the cerebellum III.…”

“…The homology between the situation in the cat and that in the rat has not yet been specifically investigated (see also the section below "Afferents to the principal olivary nucleus"). Direct input to the IOM has been described to originate from the sensory and supplementary motorcortices (Swenson et al, 1989;Lee and Kim, 2012). Prominent GABAergic projections arise from the contralateral IntP Fredette and Mugnaini, 1991).…”

Thalamic Bursts Down-regulate Cortical Theta and Nociceptive Behavior

“…Here, our choice of stimulation at 10 Hz corresponds to the physiological spontaneous firing rate of TRN neurons in vivo 25, 30, 42 , noting that the effects of TRN stimulation in the current mouse model are known to be frequency-specific 27–29 . With regards to a mechanistic explanation for how spatiotemporal dynamics in the thalamocortical network can alter a nociceptive spinal reflex, we note a possible role for descending corticospinal projections such as from areas 3b, 1 and 2 of SI terminating in superficial laminae I-II of the dorsal horn, as well as projections from areas 3a and 4 terminating in deeper laminae III-V 43–45 . In rats, electrical stimulation in SI inhibits wide-dynamic range neurons in dorsal horn 46 , which is thought to be mediated by presynaptic inhibition of C-fiber afferents via the corticospinal tract 47, 48 .…”