Nuclear Terminations of Corticoreticular Fiber Systems in Rats; pp. 253–264

Abstract

Corticoreticular fiber systems were examined in adult albino and hooded rats using anterograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) and anterograde degeneration. WGA-HRP injections were made stereotactically into the medial prefrontal cortex, the medial agranular cortex, the anterior cingulate cortex, the face motor cortex, the forelimb motor cortex, the trunk-hindlimb motor cortex, the face somatosensory cortex, the primary auditory cortex, the secondary visual cortex and the primary visual cortex. With the exception of the cingulate cortex (which is relatively inaccessible to lesioning methods) and the primary visual cortex, electrocautery lesions were made into these same cortical areas. The precise locations of cortical injection/lesion sites were corroborated on the basis of cortical cytoarchitectonic criteria, patterns of retrograde and anterograde thalamic labeling, and patterns of anterograde labeling in nonreticular brainstem nuclei such as the red nucleus, trigeminal nuclei and dorsal column nuclei.The heaviest corticoreticular projections arise from the medial agranular cortex. The medial prefrontal cortex also gives rise to consistently strong corticoreticular projections. The anterior cingulate cortex sends robust corticoreticular projections to the upper brainstem but relatively weak projections to the lower brainstem. With respect to the primary motor cortex, the face area gives rise to the densest corticoreticular projections, rivaling those emanating from the medial agranular cortex. The trunk-hindlimb area gives rise to substantial corticoreticular projections, but those originating from the forelimb area are modest and directed chiefly to midbrain and medullary levels. The face area of the somatosensory cortex gives rise to rather weak corticoreticular projections, while those arising from the primary auditory cortex are fewer still. Descending projections from the secondary visual cortex are sparse, with labeled terminals occurring in a few pontine and medullary reticular nuclei. Only one brainstem reticular nucleus (nucleus cuneiformis) was found to receive projections from the primary visual cortex, and this input was extremely sparse.Corticoreticular projections to the upper brainstem terminate predominately ipsilateral to the cortical injection site, whereas medullary corticoreticular projections distribute bilaterally. Corticoreticular fibers from the medial agranular, face motor and trunk-hindlimb motor cortex terminate heavily in somatomotor brainstem reticular nuclei such as the pontis oralis, the pontis caudalis and the gigantocellularis. Corticoreticular fibers from the prefrontal and cingulate cortices also target these nuclei but in addition send dense projections to autonomic brainstem reticular nuclei such as the A1-lateral reticular complex and the paragigantocellularis lateralis. The face area of the motor cortex projects to medullary reticular nuclei closely associated with the trigeminal system, such as the reticularis parvocellularis and the do...

Anterograde Projections of the Motorcortical Tongue Area in the Saddle-Back Tamarin <i>(Saguinus fuscicollis)</i>

“…All species studied until now show a projection of the motorcortical face area into the caudodorsal medullary reticular formation [Kuypers, 1958a, c;Newman et al, 1989;Enomoto et al, 1995;Alipour et al, 1997], and this area is directly connected with the hypoglossal motoneurons [Ugolini, 1995;Fay and Norgren, 1997;Popratiloff et al, 2001]. It therefore may be assumed that the direct cortico-motoneuronal connection found in higher primates developed out of a cortico-reticulo-motoneuronal connection during primate evolution.…”

Central mechanisms regulating coordinated cardiovascular and respiratory function during stress and arousal

“…The evidence for this hypothesis has been discussed in detail in previous reviews (see Refs. 4 or 42) but can be briefly summarized as follows: 1) the dlPAG is the only PAG subregion that receives inputs related to visual, auditory, and olfactory signals (10,113,118) (Fig. 5); 2) auditory, visual, or olfactory threatening stimuli (e.g., ultrasound application, the sight or odor of a cat) that are known to trigger defensive behavior in rats also evoke strong c-Fos expression in the dlPAG but much less expression in other PAG regions (21,50,89,113); 3) lesions of the dorsal PAG that include the dlPAG reduce the behavioral and cardiovascular response to the sight or odor of a cat (51); and 4) activation of neurons in the dlPAG, but not other PAG subregions, evoke increases in sympathetic activity and respiratory rate that closely resemble responses naturally evoked by psychological stressors (79).…”

Anatomical connections of the periaqueductal gray: specific neural substrates for different kinds of fear

“…In the rat, primary motor areas of forelimbs ( Figure 2F), hind limbs and trunk (Figure 2G) project exclusively to the lateral PAG and vlPAG, while primary auditory ( Figure 2B) and secondary visual ( Figure 2C) cortices preferentially innervate the dlPAG (42). Perirhinal, anterior cingulate (43) ( Figure 2D) and agranular lateral retrosplenial cortices (41) (Figure 2E) project almost exclusively to the dlPAG.…”