Forelimb motor cortical projections in normal rats and after neonatal hemicerebellectomy: An anatomical study based upon the axonal transport of WGA/HRP

Abstract

Cerebral cortical projections from the forelimb motor cortex, as defined by intracortical microstimulation where movements were evoked at low current intensities (less than 15 microA), were examined in normal rats and in adult rats that sustained neonatal hemicerebellectomy. The distribution pattern of cortical efferent projections in normal rats generally appeared more restricted than previously described. This restricted distribution is attributed to the use of WGA/HRP as the axonal tracing method and to the electrophysiological definition of the injection site as the motor cortex. The observed remodeling of the corticobulbar projections, seen after cerebellar lesions in the young, largely confirmed previous reports. Moreover, no alterations in the laterality of distribution in corticospinal projection were found. Aberrant corticospinal projections were sought in an effort to provide an anatomical basis to a previous description of abnormally low-threshold ipsilateral forelimb responses evoked from the motor cortex in adult rats after neonatal cerebellar lesions. This apparent absence of corticospinal tract remodeling after neonatal hemicerebellectomy suggests that the abnormal responses are mediated by the normal corticospinal pathways. This possibility is discussed in terms of an alteration in the spinal circuits that may change the responsiveness of spinal motoneurons to a given pyramidal discharge.

Efferents from the lateral frontal cortex to spinomedullary target areas, trigeminal nuclei, and spinally projecting brainstem regions in the hedgehog tenrec

“…Projecting throughout the length of the spinal cord, the cat's periaqueductal gray has recently been suggested to play a role in the control of the axial musculature during threat display (Mouton and Holstege, 1994). The periaqueductal gray itself is controlled particularly from limbic regions (for references see Beart et al, 1990;Holstege, 1995) but afferents from cortical somatosensorimotor areas have also been demonstrated (Martin et al, 75;Flindt-Egebak, 1979;O'Donoghue et aL, 1987;Newman et al, 1989, Miyashita et al, 1994. The findings in the tenrec are compatible with these data.…”

“…This high density corticotrigeminal projection is to be expected in view of the relatively extensive injection fields, of the fact that forelimb representations may also project to TrC (Wold and Brodal, 1973;Flindt-Egebak, 1979;O'Donoghue et al, 1987) and of the dominant role the orofacial region is thought to have in exploratory behavior in insectivores. On the other hand, one has to mention that the size index of the TrC in Et is among the lowest of insectivores (91 as compared to the average of 159; for review see, Stephan et al, 1991), and the relative density of corticotrigeminal projections in the erinaceous hedgehog is much less than in Et (Broere, 1971).…”

“…In the rat these projections were shown to originate predominantly in the insular and the medial prefrontal he., infralimbic) cortex; solitary projections arising from the somatosensorimotor cortex, however, have also been mentioned, including some from its area of forelimb representation (Flindt-Egebak, 1979;Dunn and Tolbert, 1982;O'Donoghue et al, 1987;M'hamed et al, 1993).…”

Hemicerebellectomy

“…Neonatal HCb is associated with anomalous increases in crossed sensorimotor corticopontine (O'Donoghue et al 1987) and rubro-olivary projections (Swenson and Castro 1982). This pattern is also observed in ascending pathways.…”

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

“…This suggests that SI processing of deep somatic input may preferentially influence information processing in APT. The APT was also shown to receive input from the MI forepaw and whisker areas (O'Donoghue et al, 1987;Miyashita et al, 1994;Alloway et al, 2010). However, these MI projections terminate more dorsally in APT.…”