Organization of the projections from the pericruciate cortex to the pontomedullary reticular formation of the cat: A quantitative retrograde tracing study

Abstract

Dextran-amines were used as retrograde tracers to investigate the organization of cortical projections to different cytoarchitectonic regions of the pontomedullary reticular formation of the cat. Injections into the nucleus reticularis pontis oralis resulted in labelling of neurones in the proreus cortex and area 6a beta of the premotor cortex, with little labelling in the motor cortex (area 4). This labelling was predominantly ipsilateral to the injection site. In contrast, injections into the nucleus reticularis pontis caudalis (NRPc), nucleus reticularis gigantocellularis (NRGc), and nucleus reticularis magnocellularis (NRMc) resulted in bilateral labelling--primarily in areas 6a beta, 6a gamma, and in the rostromedial region of area 4--with little labelling in the proreus cortex. In general, the cortical projections to the caudal NRGc and the NRMc were larger than those to the NRPc. More than 25% of the total projections to each of the latter three reticular regions arose from the medial part of area 4. Labelling in the hindlimb regions of area 4 was largest following the NRMc injections and smallest after injections in the NRPc. The projections to the NRPc originated from more medial parts of areas 4 and 6 than did the projections to the caudal region of the NRGc. These results suggest that areas 4 and 6 may be able to differentially activate different regions of the pontomedullary reticular formation depending on the movement that is made and perhaps also on the context of that movement.

Evidence for a role of the reticulospinal system in recovery of skilled reaching after cortical stroke: initial results from a model of ischemic cortical injury

“…The decreased responsiveness of the left PMRF to electrical stimulation found in both subjects is consistent with the observation that the majority of corticoreticular projections are ipsilateral (Rho et al 1997). Electrical stimulation in gray matter is thought to excite output neurons through two means.…”

“…Following damage to corticospinal projections, recovery of arm function could be mediated by strengthening of PMRF effectiveness via corticoreticular pathways from intact ipsilesional cortical motor areas (Jankowska et al 2005;Jankowska and Edgley 2006;Rho et al 1997). Recovery of arm function could also be mediated by increased effectiveness of corticoreticular projections from contralesional homologous cortical motor regions.…”

Strategies for the Integration of Posture and Movement During Reaching in the Cat

“…In this case, it seems that the movement and the accompanying postural response are initiated by a single motor command (see Massion 1992). This suggestion is supported by our recent studies on the organization of the corticoreticulospinal system (Kably and Drew 1998a;Matsuyama and Drew 1997;Rho et al 1997), which shows that neurons in the motor cortex that are implicated in the control of movement send collateral branches to the PMRF (Kably and Drew 1998b) where they could initiate postural responses adapted in time and magnitude to the focal movement (Drew et al 2003;Prentice and Drew 2001).…”

Independent and Convergent Signals From the Pontomedullary Reticular Formation Contribute to the Control of Posture and Movement During Reaching in the Cat

“…16). On the basis of the known functional anatomy of the corticoreticular system (Berrevoets and Kuypers 1975;Canedo and Lamas 1993;Kably and Drew 1998a;Matsuyama and Drew 1997;Rho et al 1997) and of previous studies performed in this laboratory in walking cats (Kably and Drew 1998b), it is probable that both the phasic and tonic signals related to movement arise as feed-forward signals transmitted by corticoreticular axons. The corollary nature of this discharge would ensure that the timing and the magnitude of these postural adjustments are appropriately related to the exact nature of the movement being made.…”