The efferent connections of the pupillary constriction area in the rat medial frontal cortex

Interhemispheric claustral circuits coordinate sensory and motor cortical areas that regulate exploratory behaviors

The claustrum has a role in the interhemispheric transfer of certain types of sensorimotor information. Whereas the whisker region in rat motor (M1) cortex sends dense projections to the contralateral claustrum, the M1 forelimb representation does not. The claustrum sends strong ipsilateral projections to the whisker regions in M1 and somatosensory (S1) cortex, but its projections to the forelimb cortical areas are weak. These distinctions suggest that one function of the M1 projections to the contralateral claustrum is to coordinate the cortical areas that regulate peripheral sensor movements during behaviors that depend on bilateral sensory acquisition. If this hypothesis is true, then similar interhemispheric circuits should interconnect the frontal eye fields (FEF) with the contralateral claustrum and its network of projections to vision-related cortical areas. To test this hypothesis, anterograde and retrograde tracers were placed in physiologically-defined parts of the FEF and primary visual cortex (V1) in rats. We observed dense FEF projections to the contralateral claustrum that terminated in the midst of claustral neurons that project to both FEF and V1. While the FEF inputs to the claustrum come predominantly from the contralateral hemisphere, the claustral projections to FEF and V1 are primarily ipsilateral. Detailed comparison of the present results with our previous studies on somatomotor claustral circuitry revealed a well-defined functional topography in which the ventral claustrum is connected with visuomotor cortical areas and the dorsal regions are connected with somatomotor areas. These results suggest that subregions within the claustrum play a critical role in coordinating the cortical areas that regulate the acquisition of modality-specific sensory information during exploration and other behaviors that require sensory attention.

Suppression of activity in the forelimb motor cortex temporarily enlarges forelimb representation in the homotopic cortex in adult rats

After forelimb motor cortex (FMC) damage, the unaffected homotopic motor cortex showed plastic changes. The present experiments were designed to clarify the electrophysiological nature of these interhemispheric effects. To this end, the output reorganization of the FMC was investigated after homotopic area activity was suppressed in adult rats. FMC output was compared after lidocaine-induced inactivation (L-group) or quinolinic acid-induced lesion (Q-group) of the contralateral homotopic cortex. In the Q-group of animals, FMC mapping was performed, respectively, 3 days (Q3D group) and 2 weeks (Q2W group) after cortical lesion. In each animal, FMC output was assessed by mapping movements induced by intracortical microstimulation (ICMS) in both hemispheres (hemisphere ipsilateral and contralateral to injections). The findings demonstrated that in the L-group, the size of forelimb representation was 42.2% higher than in the control group (P < 0.0001). The percentage of dual forelimb-vibrissa movement sites significantly increased over the controls (P < 0.0005). The dual-movement sites occupied a strip of the map along the rostrocaudal border between the forelimb and vibrissa representations. This form of interhemispheric diaschisis had completely reversed, with the recovery of the baseline map, 3 days after the lesion in the contralateral FMC. This restored forelimb map showed no ICMS-induced changes 2 weeks after the lesion in the contralateral FMC. The present results suggest that the FMCs in the two hemispheres interact continuously through predominantly inhibitory influences that preserve the forelimb representation and the border vs. vibrissa representation.

Plastic changes in the vibrissa motor cortex in adult rats after output suppression in the homotopic cortex

After motor cortex damage, the unaffected homotopic cortex shows changes in motor output. The present experiments were designed to clarify the nature of these interhemispheric effects. We investigate the vibrissa motor cortex (VMC) output after activity suppression of the homotopic area in adult rats. Comparison was made of VMC output after lidocaine inactivation (L-group) or quinolinic acid lesion (Q-group) of the homotopic cortex. In the Q-group, VMC mapping was performed 3 days (Q3Ds group), 2 weeks (Q2Ws group) and 4 weeks (Q4Ws group) after cortical lesion. In each animal, VMC output was assessed by mapping movements induced by intracortical microstimulation (ICMS) in both hemispheres (hemisphere ipsilateral and contralateral to injections). Findings demonstrated that, in the L-group, the size of vibrissal representation was 39.5% smaller and thresholds required to evoke vibrissa movement were 46.3% higher than those in the Control group. There was an increase in the percentage of ineffective sites within the medial part of the VMC and an increase in the percentage of forelimb sites within the lateral part. Both the Q3Ds group and the L-group led to a similar VMC reorganization (Q3Ds vs. L-group, P > 0.05). In the Q2Ws group the VMC representation showed improvement in size (83.4% recovery compared with controls). The VMC showed recovery to normal output at 4 weeks after lesion (Control vs. Q4Ws group, P > 0.05). These results suggest that the VMC of the two hemispheres continuously interact through excitatory influences, preserving the normal output and inhibitory influences defining the border with the forelimb representation.

Short-term reorganization of input-deprived motor vibrissae representation following motor disconnection in adult rats

It has been proposed that abnormal vibrissae input to the motor cortex (M1) mediates short-term cortical reorganization after facial nerve lesion. To test this hypothesis, we cut first the infraorbital nerve (ION cut) and then the facial nerve (VII cut) in order to evaluate M1 reorganization without any aberrant, facial-nerve-lesion-induced sensory feedback. In each animal, M1 output was assessed in both hemispheres by mapping movements induced by intracortical microstimulation. M1 output was compared in different types of peripheral manipulations: (i) contralateral intact vibrissal pad (intact hemispheres), (ii) contralateral VII cut (VII hemispheres), (iii) contralateral ION cut (ION hemispheres), (iv) contralateral VII cut after contralateral ION cut (ION + VII hemispheres), (v) contralateral pad botulinum-toxin-injected after ION cut (ION + BTX hemispheres). Right and left hemispheres in untouched animals were the reference for normal M1 map (control hemispheres). Findings demonstrated that: (1) in ION hemispheres, the mean size of the vibrissae representation was not significantly different from those in intact and control hemispheres; (2) reorganization of the vibrissae movement representation clearly emerged only in hemispheres where the contralateral vibrissae pad had undergone motor output disconnection (VII cut hemispheres); (3) the persistent loss of vibrissae input did not change the M1 reorganization pattern during the first 48 h after motor paralysis (ION + VII cut and ION + BTX hemispheres). Thus, after motor paralysis, vibrissa input does not provide the gating signal necessary to trigger M1 reorganization.

Postnatal development of vibrissae motor output following neonatal infraorbital nerve manipulation

Using the model of infraorbital nerve (IoN) injury, we have studied the role IoN signals have on the developing vibrissal motor system. To this end, in ten rats, the IoN was severed on the day of birth: in five rats, the IoN was repaired to promote axon regeneration (Reinnervated group) while axon regeneration was prevented in the remaining five rats (Deafferented group). In another five rats, the isolated IoN was left intact (Sham group) and still another group of five rats was left untouched (Control group). After these rats had reached adulthood, the compound muscle action potential (MAP) was recorded from the vibrissa muscle and intracortical microstimulation (ICMS)-evoked movements were mapped in the frontal cortex contralateral to the operated side. We found: (i) no difference between Control, Sham and Reinnervated groups in the integrated MAPs and in the size and excitability of the M1 vibrissal representation. (ii) the Deafferented group showed a 42.9% decrease in the integrated MAP plus a 47.2% and 36.9% reduction, respectively, in the size and excitability of the M1 vibrissae representation. We conclude that, during perinatal life, IoN signals regulate the development of both the peripheral and central vibrissal motor system and that IoN reinnervation restores sensory signals able to stabilize normal development of the vibrissal motor system.

The vibrissal motor output following severing and repair of the facial nerve in the newborn rat reorganises less than in the adult

This study examined the ability of facial motoneurons and motor cortex to reorganise their relationship with the somatic musculature following the severing and repair of the facial nerve in rats at birth. In each adult rat, the organisation of the facial nucleus and the cortical motor output corresponding to the normal side were compared with those corresponding to the reinnervated side. Labelling was used to reveal reinnervation-induced long-term changes in the motoneuron pool supplying vibrissal muscles. Cortical motor output was assessed by mapping the vibrissal movement area extension and thresholds evoked by intracortical microstimulation. After facial nerve reinnervation: (i) the proportion of labelled cell profiles decreased by 85.2% of that in the control side and cortical representation of vibrissal movement decreased by 66.3% of that in control hemispheres; (ii) the reorganised vibrissal representation was shrunken to the medialmost portion of the normal vibrissal representation and there was a medial extension of the forelimb representation, and a more modest lateral extension of eye representation, into the vibrissal territory; (iii) the normal pattern of contralateral vibrissal movement was observed in only 10% of the vibrissal sites, whereas ipsilateral vibrissal movement was found in 53% of the vibrissal sites; (iv) there was an increase in the mean threshold required to evoke contralateral vibrissal movement (32.5+/-11.1 vs. 20.5+/-6.9 microA). Thresholds to evoke other types of movement were similar to normal. These changes indicate that an incomplete motor axon regeneration at birth does not restore normal innervation and normal cortical control over the vibrissal muscles.

Time course for the reappearance of vibrissal motor representation following botulinum toxin injection into the vibrissal pad of the adult rat

The present study investigates the time course and pattern of movement representation recovery in the motor cortex during the recovery after a peripheral paralysis. To this end a transitory flaccid paralysis of the vibrissae muscle was induced in adult rats that underwent two unilateral injections of 8 U of botulinum toxin (BTX) into a vibrissal pad, at a duration of 12 days from one another. The compound muscle action potential (MAP) of the vibrissae muscle began to reappear 4 weeks after the first BTX injection. Intracortical microstimulation (ICMS) was used to map rat motor cortices 4, 5, 6, 7 and 8 weeks after the first BTX injection. Findings demonstrated that: (i) contralateral vibrissae movement reappears in the medial part of its normal cortical territory when the MAP is almost 10% of the control value; in the remaining part, ICMS elicits eye, ipsilateral vibrissae, neck and forelimb movements; (ii) the contralateral vibrissae movement reappears in sites where ipsilateral vibrissae and/or neck movement are co-represented; (iii) as MAP recovers, the vibrissae representation expands until it recovers the 90.8% of its territory after 7 weeks, when the MAP was almost 43.4% of the control value; (iv) from 4 to 7 weeks, the ICMS-evoked contralateral vibrissae movement shows a significantly higher electrical threshold vs. the control group; (v) recovery of the baseline excitability uniformly involves the vibrissae representation 1 week later, after its cortical territory has recovered 93.1% of the control value and the MAP has returned to 78.8% of the baseline value.

Long-term motor cortex reorganization after facial nerve severing in newborn rats

Using the model of facial nerve injury, we have compared the effect of injury in newborn and adult rats on the adult rat motor cortex (M1). To this end, the facial nerve was severed in 10 newborn rats 2 days after birth (Newborn group) and in 10 adult rats (Adult group). In both the Control (contralateral to untouched nerve) and the Experimental (contralateral to severed nerve) hemisphere of each rat, the M1 output organization was assessed by intracortical microstimulation. Our findings demonstrated that: (i) there is no statistical difference in the percentage of movement sites and in current thresholds required to evoke movement in Control hemispheres between the Adult and Newborn groups of rats; (ii) in Adult Experimental hemispheres, neck sites expand in the medial part of the vibrissae representation more extensively than shown in Newborn Experimental hemispheres; (iii) in Newborn Experimental hemispheres eye sites expand in the medial part of the vibrissae representation more extensively than in Adult Experimental hemispheres (these sites overlap the cortical region where electrical stimulation evokes neck movement in Adult Experimental hemispheres) and (iv) in both Newborn and Adult Experimental hemispheres, forelimb sites expand similarly thereby overlapping the same cortical region, corresponding to the lateral part of the vibrissae representation. We conclude that, when the facial nerve injury is performed in the newborn rat, the pattern of movement representation differs from that obtained with the same lesion in the mature brain only in the frontal cortex corresponding to the medial part of the normal vibrissae representation.

Organization of retrosplenial cortical projections to the anterior cingulate, motor, and prefrontal cortices in the rat

The retrosplenial cortex (areas 29a-29d) has been implicated in spatial memory, which is essential for performing spatial behavior. Despite this link with behavior, neural connections between areas 29a-29d and frontal association and motor cortices--areas also essential for spatial behavior--have been analyzed only to a limited extent. Here, we report an analysis of the anatomical organization of projections from areas 29a-29d to area 24 and motor and prefrontal cortices in the rat, using the axonal transport of biotinylated dextran amine (BDA) and cholera toxin B subunit (CTb). Area 29a projects to rostral area 24a, whereas area 29b projects to caudodorsal area 24a and ventral area 24b. Caudal area 29c projects to mid-rostrocaudal area 24b, whereas rostral area 29c projects to caudal areas 24a and 24b and caudal parts of primary and secondary motor areas. Caudal area 29d projects to mid-rostrocaudal areas 24a and 24b, whereas rostral area 29d projects to the caudalmost parts of areas 24a and 24b and the secondary motor area and to the mid-rostrocaudal part of the primary motor area. Area 29d also projects weakly to the prefrontal cortex. These differential corticocortical projections may constitute important pathways that transmit spatial information to particular frontal cortical regions, enabling an animal to accomplish spatial behavior.