Gianfranco Franchi

Blockade of Nociceptin/Orphanin FQ Receptor Signaling in Rat Substantia Nigra Pars Reticulata Stimulates Nigrostriatal Dopaminergic Transmission and Motor Behavior

A multidisciplinary approach was followed to investigate whether the opioid-like peptide nociceptin/orphanin FQ (N/OFQ) regulates the nigrostriatal dopaminergic pathway and motor behavior. Nigrostriatal dopaminergic cells, which express N/OFQ peptide (NOP) receptors, are located in the substantia nigra pars compacta and extend their dendrites in the substantia nigra pars reticulata, thereby modulating the basal ganglia output neurons. In vitro electrophysiological recordings demonstrated that N/OFQ hyperpolarized the dopaminergic cells of the substantia nigra pars compacta and inhibited their firing activity. In vivo dual-probe microdialysis showed that N/OFQ perfused in the substantia nigra pars reticulata reduced dopamine release in the ipsilateral striatum, whereas UFP-101 ([Nphe1,Arg14,Lys15]N/OFQ(1-13)-NH2) (a selective NOP receptor peptide antagonist) stimulated it. N/OFQ microinjected in the substantia nigra pars reticulata impaired rat performance on a rotarod apparatus, whereas UFP-101 enhanced it. Electromyography revealed that N/OFQ and UFP-101 oppositely affected muscle tone, inducing relaxation and contraction of triceps, respectively. The selective NOP receptor nonpeptide antagonist J-113397 (1-[3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H benzimidazol-2-one), either injected intranigrally or given systemically, also elevated striatal dopamine release and facilitated motor activity, confirming that these effects were caused by blockade of endogenous N/OFQ signaling. The inhibitory role played by endogenous N/OFQ on motor activity was additionally strengthened by the finding that mice lacking the NOP receptor gene outperformed wild-type mice on the rotarod. We conclude that NOP receptors in the substantia nigra pars reticulata, activated by endogenous N/OFQ, drive a physiologically inhibitory control on motor behavior, possibly via modulation of the nigrostriatal dopaminergic pathway.

Complex Movement Topography and Extrinsic Space Representation in the Rat Forelimb Motor Cortex as Defined by Long-Duration Intracortical Microstimulation

Electrical stimulation of the motor cortex in the rat can evoke complex forelimb multi-joint movements, including movement of limb and paw. In this study, these movements have been quantified in terms of 3D displacement and kinematic variables of two markers positioned on the wrist and middle digits (limb and paw movement, respectively). Electrical microstimulation was applied to the motor cortex using a pulse train of 500 ms duration. Movements were measured using a high-resolution 3D optical system. Five classes of limb movements (abduction, adduction, extension, retraction, elevation) and four classes of paw movements (opening, closure, opening/closure sequence, supination) were described according to their kinematics. A consistent topography of these classes of movements was presented across the motor cortex together with a topography of spatial locations to which the paw was directed. In about one-half of cortical sites, a specific pattern of limb–paw movement combination did exist. Four categories of limb–paw movements resembling behavioral repertoire were identified: reach-shaping, reach-grasp sequence, bring-to-body, and hold-like movement. Overall, the forelimb motor region included: (1) a large caudal forelimb area dominated by reach-shaping movement representation; (2) a small rostral area containing reach-grasp sequence and bring-to-body movement representation; and (3) a more lateral portion where hold-like movement was represented. These results support the view that, in rats, the motor cortex controls forelimb movements at a relatively complex level and suggest that the orderly representation of complex movements and their dynamics/kinematics emerge from the principles of forelimb motor cortex organization.

Time course of motor cortex reorganization following botulinum toxin injection into the vibrissal pad of the adult rat

The present experiment studies representation patterns in the motor cortex (M1) of adult rats, 1, 3, 6, and 12 days after unilateral injection of Botulinum Toxin (BTX) into the vibrissa pad. Intracortical microstimulation (ICMS) was used to evidence changes in the representation over time and in the current thresholds required to evoke movements inside the disconnected vibrissa region. After 1 day, isolated as well as contiguous negative sites were observed within the motor cortex corresponding to the disconnected vibrissa region. Thereafter the percentage of unresponsive sites decreased so that after 6 days, the number of unresponsive sites was not significantly higher than those in the control hemispheres. Within the disconnected vibrissa region, electrical stimulation elicited forelimb, eye, ipsilateral vibrissa and neck movements. Following BTX injection, the enlargement of the forelimb representation into the disconnected vibrissa representation began during the first day and stabilized during the second week after injection. In the first days, stimulation thresholds in expanded forelimb sites were higher than those required for similar movement in normal M1 forelimb representation. These thresholds then declined so that in ∼6 days they were similar to normal. There was no clear evidence that stimulation of sites in the medial part of disconnected vibrissa‐cortex evoked eye movements during the first 6 days after BTX injection. After this time, thresholds required to evoke eye movement in expanded sites were generally similar to, and never higher than, those needed to evoke this movement in control sites. Intermingled ipsilateral vibrissa and neck movement occupies part of the medial vibrissa region. Over the 12 days, extension of the ipsilateral vibrissa representation shrank while the representation of neck movement remained unchanged. Throughout the entire time there was no change in the excitability of these sites and the thresholds remained higher than that needed to elicit the vibrissa movement normally represented in this cortical region. No significant differences in threshold were found over time for any of the other movement categories represented in M1. These results indicate that, over time, the new movements inside the disconnected vibrissa region develop differently in M1 following peripheral motor disconnection. The implications for mechanisms involved in cortical plasticity are discussed.

Persistence of vibrissal motor representation following vibrissal pad deafferentation in adult rats

Abstract. The effect of sensory vibrissal pad denervation on M1 organization was studied in adult rats 2 weeks after the infraorbital nerve was severed. Cortical motor output organization was assessed mapping the representation size and thresholds of vibrissa movements evoked by intracortical electrical microstimulation (ICMS). Motor cortex output patterns of control and sham groups of rats were compared with those of rats that had received unilateral or bilateral infraorbital nerve lesions. The mean size of the vibrissa representation in both unilateral and bilateral input-deprived hemispheres was not significantly different from those in control and sham hemispheres. The mean threshold required to evoke vibrissa movements was significantly higher in both groups of deafferented hemispheres than in control and sham groups of hemispheres. In contrast, the mean threshold required to evoke other types of movements from both groups of input-deprived hemispheres were similar to those found in the control and sham groups of hemispheres. These results indicate that input-deprived vibrissal motor representation reflects lower-than-normal excitability, although the size and topographic relationship with neighboring representations are normal.

Nociceptin/Orphanin FQ Modulates Motor Behavior and Primary Motor Cortex Output Through Receptors Located in Substantia Nigra Reticulata

This study was set to investigate whether motor effects of nociceptin/orphanin FQ (N/OFQ) can be related to changes in primary motor cortex output. N/OFQ injected i.c.v. biphasically modulated motor performance, low doses being facilitating and higher ones inhibitory. These effects were counteracted by the N/OFQ receptor antagonist [Nphe1 Arg14,Lys15]N/OFQ-NH2 (UFP-101) confirming the specificity of N/OFQ action. However, UFP-101 alone facilitated motor performance, suggesting that endogenous N/OFQ inhibits motor function. N/OFQ and UFP-101 injected into the substantia nigra reticulata but not motor cortex replicated these effects, suggesting motor responses were mediated by subcortical circuits involving the basal ganglia. Intracortical microstimulation technique showed that i.c.v. N/OFQ also biphasically modulated motor cortex excitability and movement representation. Low N/OFQ doses caused a leftward shift of threshold distribution curve in the forelimb area without affecting the number of effective sites. Conversely, high N/OFQ doses increased unresponsive and reduced excitable (movement) sites in vibrissa but not forelimb area. However, increased threshold currents and rightward shift of threshold distribution curve were observed in both areas, suggesting an overall inhibitory effect on cortical motor output. UFP-101 alone evoked effects similar to low N/OFQ doses, suggesting tonic inhibitory control over forelimb movement by endogenous N/OFQ. As shown in behavioral experiments, these effects were replicated by intranigral, but not intracortical, N/OFQ or UFP-101 injections. We conclude that N/OFQ receptors located in the substantia nigra reticulata mediate N/OFQ biphasic control over motor behavior, possibly through changes of primary motor cortex output.

Progressive Motor Cortex Functional Reorganization Following 6-Hydroxydopamine Lesioning in Rats

Many studies have attempted to correlate changes of motor cortex activity with progression of Parkinsons disease, although results have been controversial. In the present study we used intracortical microstimulation (ICMS) combined with behavioral testing in 6-hydroxydopamine hemilesioned rats to evaluate the impact of dopamine depletion on movement representations in primary motor cortex (M1) and motor behavior. ICMS allows for motor-effective stimulation of corticofugal neurons in motor areas so as to obtain topographic movements representations based on movement type, area size, and threshold currents. Rats received unilateral 6-hydroxydopamine in the nigrostriatal bundle, causing motor impairment. Changes in M1 were time dependent and bilateral, although stronger in the lesioned than the intact hemisphere. Representation size and threshold current were maximally impaired at 15 d, although inhibition was still detectable at 60–120 d after lesion. Proximal forelimb movements emerged at the expense of the distal ones. Movement lateralization was lost mainly at 30 d after lesion. Systemic l-3,4-dihydroxyphenylalanine partially attenuated motor impairment and cortical changes, particularly in the caudal forelimb area, and completely rescued distal forelimb movements. Local application of the GABAA antagonist bicuculline partially restored cortical changes, particularly in the rostral forelimb area. The local anesthetic lidocaine injected into the M1 of the intact hemisphere restored movement lateralization in the lesioned hemisphere. This study provides evidence for motor cortex remodeling after unilateral dopamine denervation, suggesting that cortical changes were associated with dopamine denervation, pathogenic intracortical GABA inhibition, and altered interhemispheric activity.

Somatic receptive-field properties of single fibres in the rostral portion of the corpus callosum in awake cats

SummaryIn fifteen awake, chronic cats single-unit recordings were obtained from 316 fibres isolated in the rostral portion of the corpus callosum (CC). Altogether, 304 units were reactive to peripheral stimuli. They were fired by hair bending, light touch or light pressure (S units; 79.3%) or by gentle rotation of joints and/or by pressure on muscle bellies or tendons (D units; 20.7%). All the reactive units were endowed with small and unilateral receptive fields (RFs) located in trigeminal (49.7%) or segmentai (50.3%) regions. Trigeminal and forepaw units had the smallest RFs. All the trigeminal units were of the S type. Their RFs were located in either the ophthalmic, maxillar, and mandibular face districts or in the oral vestible. The vast majority of segmental units (146 out 153 fibres) had RFs in the forelimb. Very few units were fired by stimulation of the trunk (6 fibres), and only one had its RF in the tail. Almost half of the forelimb units (69 fibres) were fired by stimulation of the most proximal parts of the forelimb and of the shoulder; about one third (57 fibres) exhibited RFs located in the forepaw; the remaining units (20 fibres) had their RFs in the intermediate region of the forelimb. Neither the trigeminal nor segmental RFs ever extended across the midline. The distribution of the fibres within the CC conformed to a somatotopic pattern. The representations of the trigeminal and segmental regions were largely coextensive. Along the rostro-caudal axis of the CC, units with RFs in the mandibular, maxillar and ophthalmic divisions of the trigeminal region tended to lie in this order in the rostralmost 4 mm. Segmental representation extended over the rostralmost 6 mm. Shoulder fibres were mainly found in the rostral half, whereas forepaw units were segregated in the caudal half.

Changes in motor representation related to facial nerve damage and regeneration in adult rats.

Abstract. The present study examined how facial nerve regeneration shapes movement representation patterns in previously disconnected motor cortices. Electrical microstimulation was used to bilaterally map the motor cortices of adult rats subjected to unilateral facial nerve lesion and reanastomosis stamps at the stylomastoid foramen level. The motor cortex output patterns of two groups of experimental hemispheres (contralateral to lesioned side) were compared before and after facial nerve reinnervation. The motor cortex output patterns in the control hemispheres (ipsilateral to the lesioned side) were used as reference. Before facial nerve reinnervation, the motor cortex forelimb and eye output area extended into the vibrissa area; such enlargement did not occupy the medial part of the former vibrissa area where ipsilateral vibrissa or neck movements were represented. After facial nerve reinnervation, the contralateral vibrissa movement reorganized into a shrunken cortical area corresponding to the medial portion of the former vibrissa representation, i.e., where the ipsilateral vibrissa and neck movements were mainly represented prior to facial nerve reinnervation. The enlargement of the forelimb and eye representation remained unchanged, even after the vibrissa motor innervation was reactivated. Before facial nerve reinnervation into expanded forelimb and eye representations, a minimal current was required to evoke these movements, which did not vary from the normal range. A higher current was necessary to evoke the ipsilateral vibrissa and neck movements in the medial part of the vibrissa representation than the threshold needed to elicit the vibrissa movement normally represented in this cortical region. After facial nerve reinnervation, the overall current required to evoke movement remained the same as that which evoked movement before the vibrissa motor innervation was reactivated.

Low threshold unilateral and bilateral facial movements evoked by motor cortex stimulation in cats

Organizational features of the ipsilateral representation in the cat face motor cortex were investigated by using the technique of intracortical microstimulation (less than 30 microA). In 4 intact animals, 61 efferent zones controlling facial muscles were identified. They were devoted to contralateral muscles (contralateral efferent zones; n = 35), ipsilateral muscles (ipsilateral efferent zones; n = 8) or symmetrical muscles of both sides (bilateral efferent zones; n = 18). Contralateral efferent zones were found within both the rostral part of the coronal gyrus and the lateral bank of the presylvian sulcus, whereas ipsilateral and bilateral efferent zones were exclusively localized to the rostromedial region of the face motor cortex. Movement thresholds proved to be lowest at the contralateral efferent zones and highest at the ipsilateral efferent zones, with intermediate values at the bilateral efferent zones. Latencies of suprathreshold EMG responses evoked from contralateral and ipsilateral efferent zones were the shortest and the longest, respectively; intermediate values were found upon stimulation of sites from bilateral efferent zones. The efferent zones identified in 3 lesioned animals (two cats with contralateral motor cortex ablation and one cat with transection of the rostral two thirds of the corpus callosum) were contralateral (n = 14), bilateral (n = 13), and ipsilateral (n = 9). Mean thresholds of effective sites from bilateral and ipsilateral efferent zones in lesioned preparations were not significantly higher than those in intact animals. This would thus suggest that extracallosal pathways may account for ipsilateral responses.

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.