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Introduction: Many invasive and noninvasive neurotechnologies are being developed to help treat neurological pathologies and disorders. Making a brain implant safe, stable, and efficient in the long run is one of the requirements to conform with neuroethics and overcome limitations for numerous promising neural treatments. A main limitation is low biocompatibility, characterized by the damage implants create in brain tissue and their low adhesion to it. This damage is partly linked to friction over time due to the mechanical mismatch between the soft brain tissue and the more rigid wires. Methods: Here, we performed a short biocompatibility assessment of bio-inspired intra-cortical implants named "Neurosnooper" made of a microelectrode array consisting of a thin, flexible polymer-metal-polymer stack with microwires that mimic axons. Implants were assembled into poly-lactic-glycolic acid (PLGA) biodegradable needles for their intra-cortical implantation. Results and Discussion: The study of glial scars around implants, at 7 days and 2 months post-implantation, revealed a good adhesion between the brain tissue and implant wires and a low glial scar thickness. The lowest corresponds to electrode wires with a section size of 8 μm × 10 μm, compared to implants with the 8 μm × 50 μm electrode wire section size, and a straight shape appears to be better than a zigzag. Therefore, in addition to flexibility, size and shape parameters are important when designing electrode wires for the next generation of clinical intra-cortical implants., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Darlot, Villard, Salam, Rousseau and Piret.)

Rationale: The risk of becoming addicted to tobacco varies greatly from individual to individual, raising the possibility of behavioural biomarkers capable of predicting sensitivity to nicotine reward, a crucial step in the development of nicotine addiction. Amongst all of nicotine's pharmacological properties, one of central importance is the enhancement of cognitive performances, which depend on the balance between attentional processes and inhibitory control. However, whether the cognitive enhancement effects of nicotine are predictive of sensitivity to its rewarding properties is still unknown., Objective: Using male and female mice, we investigated whether the effects of nicotine on cognitive performances are predictive of sensitivity to the rewarding properties of nicotine and, if so, whether this relationship is sex dependent., Methods: Naïve male and female mice were first assessed for their performances in both baseline conditions and following nicotine injection (0.15 and 0.30 mg/kg) in a cued-Fixed Consecutive Number task (FCNcue) measuring both optimal (attention) and premature (inhibitory control) responding. Next, all mice underwent nicotine-induced conditioned place preference (CPP) in order to evaluate inter-individual differences in response to nicotine reward (0.30 mg/kg)., Results: Results showed that males and females benefited from the effect of nicotine as a cognitive enhancer in the FCNcue task. However, only those males displaying poor inhibitory control, namely high-impulsive animals, subsequently displayed sensitivity to nicotine reward. In females, sensitivity to nicotine reward was independent of FCNcue performances, in both basal and nicotine conditions., Conclusion: Thus, our study suggests that poor inhibitory control and its modulation by nicotine may be a behavioural biomarker for sensitivity to nicotine reward and consequent vulnerability to nicotine addiction in males but not females., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Rationale: Tobacco products are very addictive, partly because they contain nicotine which is reinforcing, but also because they include appealing aromas and tastes. Flavor additives are such sensory stimuli which enhance attractiveness, as well as use and abuse of tobacco and vaping products. Yet, the interaction between these flavor additives and nicotine remains poorly understood., Objectives: We want to understand how flavors may reduce nicotine' aversive taste and how it may enhance its voluntary oral self-administration in mice., Methods: We first studied the effect of flavor additives on nicotine solution palatability in a free bottle choice paradigm. Second, we investigated the effect of vanilla flavoring on the different stages of nicotine (40 μg/ml) oral self-administration in mice., Results: We show that adding flavors increase nicotine palatability and facilitate acquisition and maintenance of oral self-administration when compared to nicotine-alone group. Mice adapt their operant behavior depending on changes in nicotine concentration. All mice reinstate nicotine seeking upon presentation of associated cues. Nevertheless, vanilla-flavored nicotine was not more reinforcing than vanilla-flavored water which was reinforcing enough to drive similar operant response rates., Conclusions: Flavor additives increase nicotine oral consumption and help maintaining operant behavior in mice. Moreover, flavors can be very attractive and can have high reinforcing value by themselves. Thus, it is crucial that the investigation on how taste signals play an important role in modulating oral nicotine intake in rodent models remains explored., (© 2021. This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply.)

One of the hallmarks of addiction is the enduring vulnerability to relapse. Following repeated use, cocaine (COC) induces neuroadaptations within the dopamine (DA) system, arguably underlying several aspects of COC-seeking behavior. Peripheral stimulation of D2, but not D1, receptors induces relapse. However, where in the brain these effects occur is still matter of debate. The D1 and D2 receptors (D1R; D2R) are highly expressed in the nucleus accumbens (NAcc) and the dorsolateral striatum (DLS), but their specific involvement in the reinstatement of COC-seeking remains elusive. We assessed the reinstating effects of intracerebral infusions of agonists of D1R (SKF82958) or D2R (quinelorane) within the NAcc or DLS of rats after extinction of COC self-administration (COC SA). To assess whether we could block peripheral D2 agonist (quinelorane) induced reinstatement, we simultaneously infused either a D1R (SCH23390) or a D2R (raclopride) antagonist within the NAcc or DLS. When infused into the NAcc, but not into the DLS, SKF82958 induced reinstatement of COC-seeking; conversely, quinelorane had no effect when injected into the NAcc, but induced reinstatement when infused into the DLS while the D1R agonist has no effect. While administration of raclopride into the NAcc or DLS impedes the reinstating effect of a systemic quinelorane injection, the infusion of SCH23390 into the NAcc or DLS surprisingly, blocks the reinstatement induced by the peripheral D2R stimulation. Our results point to a double dissociation between D1R and D2R of the NAcc and DLS, highlighting their complex interactions within both structures, in the reinstatement of COC-seeking behavior., (Copyright © 2020. Published by Elsevier Ltd.)

Adolescence represents a critical period characterized by major neurobiological changes. Chronic stimulation of the reward system during adolescence might constitute an important factor of vulnerability to pathological development. Increasing evidences suggest that adolescent overconsumption of sweet palatable foods impact reward-based processes. However, the neurobiological bases of these deficits remain poorly understood. Previous studies have demonstrated motivational deficits for palatable foods after sweet diet exposure during adolescence that might involve the dopamine (DA) system, a central actor in incentive processes. In the present study, the impact of adolescent sugar overconsumption on the sensitivity of the DA system was tested using pharmacological (Experiment 1) and receptor expression approaches (Experiment 2). Adolescent rats received free and continuous access to 5% sucrose solution from post-natal day 30-46. At adulthood, the functionality of the DA system in motivational processes was tested using systemic injections of specific DA receptors D1R or D2R agonists and antagonists during a motivation-dependent progressive ratio task (Experiment 1). Sucrose-exposed rats showed a lower motivation for saccharin and a decreased sensitivity to the effects of both D1R and D2R stimulation and blockade. In Experiment 2, Sucrose-exposed animals presented a lower expression of both D1R and D2R in the nucleus accumbens, a central brain region for incentive processes, but not in dorsal striatum or prefrontal cortex. These findings highlight the impact of sucrose overconsumption during adolescence on DA system that may support deficits in reward-related disorders., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Following central nervous system lesion, the ability of injured axons to regrowth may depend on the level and duration of the injured cell body response (CBR). Therefore, to investigate whether axotomized brainstem neurons maintain a durable growth-competent state after spinal cord injury, we studied the effect of a chronic C2 hemisection in rats on the expression of various CBR markers involved in axon regeneration, such as c-Jun, ATF-3, HSP27, NO synthase (NOS), and also of the neural mature phenotype marker NeuN, in the bulbospinal respiratory neurons as compared to the gigantocellularis nucleus. Both at 7 and 30 days post-lesion (DPL), c-Jun and HSP27 were present in, respectively, ~60 and ~20% of the axotomized respiratory neurons, whereas the apoptotic factor caspase 3 was not detected in these cells. NOS appeared belatedly, and it was detected in ~20% of the axotomized respiratory neurons at 30DPL. At 30DPL, these different CBR markers were strongly colocalized in a sub-population of axotomized respiratory neurons and also in a sub-population of injured neurons within the gigantocellularis nucleus. Such CBR was also accompanied by a sustained alteration of the neural mature phenotype, as indicated by a loss of NeuN immunoreactivity selectively in HSP27 + bulbospinal neurons at 7DPL and 30DPL. Altogether, this study shows that a subset of axotomized medullary respiratory neurons remains in a growth-competent state after a chronic injury, suggesting that they may play a preferential role in long-lasting respiratory neuroplasticity processes., (© 2017 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

In this study, we explored the effects of a longer term application, up to 12 weeks, of photobiomodulation in normal, naïve macaque monkeys. Monkeys (n = 5) were implanted intracranially with an optical fibre device delivering photobiomodulation (red light, 670 nm) to a midline midbrain region. Animals were then aldehyde-fixed and their brains were processed for immunohistochemistry. In general, our results showed that longer term intracranial application of photobiomodulation had no adverse effects on the surrounding brain parenchyma or on the nearby dopaminergic cell system. We found no evidence for photobiomodulation generating an inflammatory glial response or neuronal degeneration near the implant site; further, photobiomodulation did not induce an abnormal activation or mitochondrial stress in nearby cells, nor did it cause an abnormal arrangement of the surrounding vasculature (endothelial basement membrane). Finally, because of our interest in Parkinson's disease, we noted that photobiomodulation had no impact on the number of midbrain dopaminergic cells and the density of their terminations in the striatum. In summary, we found no histological basis for any major biosafety concerns associated with photobiomodulation delivered by our intracranial approach and our findings set a key template for progress onto clinical trial on patients with Parkinson's disease.

The CXCL4 paralog CXCL4L1 is a less studied chemokine that has been suggested to exert an antiangiogenic function. However, CXCL4L1 is also expressed in patient tumors, tumor cell lines, and murine xenografts, prompting a more detailed analysis of its role in cancer pathogenesis. We used genetic and antibody-based approaches to attenuate CXCL4L1 in models of pancreatic ductal adenocarcinoma (PDAC). Mechanisms of expression were assessed in cell coculture experiments, murine, and avian xenotransplants, including through an evaluation of CpG methylation and mutation of critical CpG residues. CXCL4L1 gene expression was increased greatly in primary and metastatic PDAC. We found that myofibroblasts triggered cues in the tumor microenvironment, which led to induction of CXCL4L1 in tumor cells. CXCL4L1 expression was also controlled by epigenetic modifications at critical CpG islands, which were mapped. CXCL4L1 inhibited angiogenesis but also affected tumor development more directly, depending on the tumor cell type. In vivo administration of an mAb against CXCL4L1 demonstrated a blockade in the growth of tumors positive for CXCR3, a critical receptor for CXCL4 ligands. Our findings define a protumorigenic role in PDAC development for endogenous CXCL4L1, which is independent of its antiangiogenic function. Cancer Res; 76(22); 6507-19. ©2016 AACR., (©2016 American Association for Cancer Research.)

We have reported previously that intracranial application of near-infrared light (NIr) reduces clinical signs and offers neuroprotection in a subacute MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) monkey model of Parkinson's disease. In this study, we explored whether NIr reduces the gliosis in this animal model. Sections of midbrain (containing the substantia nigra pars compacta; SNc) and striatum were processed for glial fibrillary acidic protein (to label astrocytes; GFAP) and ionised calcium-binding adaptor molecule 1 (to label microglia; IBA1) immunohistochemistry. Cell counts were undertaken using stereology, and cell body sizes were measured using ImageJ. Our results showed that NIr treatment reduced dramatically (~75 %) MPTP-induced astrogliosis in both the SNc and striatum. Among microglia, however, NIr had a more limited impact in both nuclei; although there was a reduction in overall cell size, there were no changes in the number of microglia in the MPTP-treated monkeys after NIr treatment. In summary, we showed that NIr treatment influenced the glial response, particularly that of the astrocytes, in our monkey MPTP model of Parkinson's disease. Our findings raise the possibility of glial cells as a future therapeutic target using NIr.

We have reported previously that intracranial application of near-infrared light (NIr) - when delivered at the lower doses of 25J and 35J - reduces clinical signs and offers neuroprotection in a subacute MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) monkey model of Parkinson's disease. In this study, we explored whether a higher NIr dose (125J) generated beneficial effects in the same MPTP monkey model (n=15). We implanted an NIr (670nm) optical fibre device within a midline region of the midbrain in macaque monkeys, close to the substantia nigra of both sides. MPTP injections (1.8-2.1mg/kg) were made over a five day period, during which time the NIr device was turned on and left on continuously throughout the ensuing three week survival period. Monkeys were evaluated clinically and their brains processed for immunohistochemistry and stereology. Our results showed that the higher NIr dose did not have any toxic impact on cells at the midbrain implant site. Further, this NIr dose resulted in a higher number of nigral tyrosine hydroxylase immunoreactive cells when compared to the MPTP group. However, the higher NIr dose monkeys showed little evidence for an increase in mean clinical score, number of nigral Nissl-stained cells and density of striatal tyrosine hydroxylase terminations. In summary, the higher NIr dose of 125J was not as beneficial to MPTP-treated monkeys as compared to the lower doses of 25J and 35J, boding well for strategies of NIr dose delivery and device energy consumption in a future clinical trial., (Copyright © 2016 Elsevier B.V. All rights reserved.)

OBJECT The authors of this study used a newly developed intracranial optical fiber device to deliver near-infrared light (NIr) to the midbrain of 6-hydroxydopamine (6-OHDA)-lesioned rats, a model of Parkinson's disease. The authors explored whether NIr had any impact on apomorphine-induced turning behavior and whether it was neuroprotective. METHODS Two NIr powers (333 nW and 0.16 mW), modes of delivery (pulse and continuous), and total doses (634 mJ and 304 J) were tested, together with the feasibility of a midbrain implant site, one considered for later use in primates. Following a striatal 6-OHDA injection, the NIr optical fiber device was implanted surgically into the midline midbrain area of Wistar rats. Animals were tested for apomorphine-induced rotations, and then, 23 days later, their brains were aldehyde fixed for routine immunohistochemical analysis. RESULTS The results showed that there was no evidence of tissue toxicity by NIr in the midbrain. After 6-OHDA lesion, regardless of mode of delivery or total dose, NIr reduced apomorphine-induced rotations at the stronger, but not at the weaker, power. The authors found that neuroprotection, as assessed by tyrosine hydroxylase expression in midbrain dopaminergic cells, could account for some, but not all, of the observed behavioral improvements; the groups that were associated with fewer rotations did not all necessarily have a greater number of surviving cells. There may have been other "symptomatic" elements contributing to behavioral improvements in these rats. CONCLUSIONS In summary, when delivered at the appropriate power, delivery mode, and dosage, NIr treatment provided both improved behavior and neuroprotection in 6-OHDA-lesioned rats.

Adolescence is a critical period characterized by major neurobiological changes. Chronic stimulation of the reward system might constitute an important factor in vulnerability to pathological development. In spite of the dramatic increase in the consumption of sweet palatable foods during adolescence in our modern societies, the long-term consequences of such exposure on brain reward processing remain poorly understood. Here, we investigated in rats the long-lasting effects of sugar overconsumption during their adolescence on their adult reactivity to the hedonic properties of sweet rewards. Adolescent rats with continuous access to 5% sucrose solution (from postnatal day 30-46) showed escalating intake. At adulthood (post-natal day 70), using two-bottle free choice tests, sucrose-exposed rats showed lower intake than non-exposed rats suggesting decreased sensitivity to the rewarding properties of sucrose. In Experiment 1, we tested their hedonic-related orofacial reactions to intraoral infusion of tasty solutions. We showed that sucrose-exposed rats presented less hedonic reactions in response to sweet tastes leaving the reactivity to water or quinine unaltered. Hence, in Experiment 2, we observed that this hedonic deficit is associated with lower c-Fos expression levels in the nucleus accumbens, a brain region known to play a central role in hedonic processing. These findings demonstrate that a history of high sucrose intake during the critical period of adolescence induces long-lasting deficits in hedonic treatment that may contribute to reward-related disorders., (© 2016 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

Objective: To examine whether near-infrared light (NIr) treatment reduces clinical signs and/or offers neuroprotection in a subacute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkey model of Parkinson disease., Methods: We implanted an optical fiber device that delivered NIr (670 nm) to the midbrain of macaque monkeys, close to the substantia nigra of both sides. MPTP injections (1.5-2.1mg/kg) were made over a 5- to 7-day period, during which time the NIr device was turned on. This was then followed by a 3-week survival period. Monkeys were evaluated clinically (eg, posture, bradykinesia) and behaviorally (open field test), and their brains were processed for immunohistochemistry and stereology., Results: All monkeys in the MPTP group developed severe clinical and behavioral impairment (mean clinical scores = 21-34; n = 11). By contrast, the MPTP-NIr group developed much less clinical and behavioral impairment (n = 9); some monkeys developed moderate clinical signs (mean scores = 11-15; n = 3), whereas the majority--quite remarkably--developed few clinical signs (mean scores = 1-6; n = 6). The monkeys that developed moderate clinical signs had hematic fluid in their optical fibers at postmortem, presumably limiting NIr exposure and overall clinical improvement. NIr was not toxic to brain tissue and offered neuroprotection to dopaminergic cells and their terminations against MPTP insult, particularly in animals that developed few clinical signs., Interpretation: Our findings indicate NIr to be an effective therapeutic agent in a primate model of the disease and create the template for translation into clinical trials., (© 2015 American Neurological Association.)

We explored whether 810nm near-infrared light (NIr) offered neuroprotection and/or improvement in locomotor activity in an acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse model of Parkinson's disease. Mice received MPTP and 810nm NIr treatments, or not, and were tested for locomotive activity in an open-field test. Thereafter, brains were aldehyde-fixed and processed for tyrosine hydroxylase immunohistochemistry. Our results showed that MPTP-treated mice that were irradiated with 810nm NIr had both greater locomotor activity (∼40%) and number of dopaminergic cells (∼20%) than those that were not. In summary, 810nm (as with 670nm) NIr offered neuroprotection and improved locomotor activity in MPTP-treated mice., (Copyright © 2014 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.)

Spinal cord injury (SCI) causes an interruption of descending motor and autonomic nervous tracts. However, a partial injury, and particularly a unilateral section, is generally followed by spontaneous locomotor and respiratory recovery. Although locomotor functional recovery has been correlated to spontaneous anatomical plasticity of the corticospinal tract, the remodeling of the bulbospinal tract that sustains respiratory improvement is unknown and has therefore been investigated here after chronic lateral cervical injury in rats (90 days post-lesion by comparison to 7 days post-lesion). We show that chronic lateral C2 SCI leads both to a decreased thickness of the ipsilateral ventrolateral funiculus at sus and sub-lesional levels and to an opposite effect on the contralateral side. At C1 level, the number of ventrolateral bulbospinal fibers, stained with anterograde tracer was reduced within the ipsilateral ventrolateral funiculi while collateral arborization toward the gray matter and growth associated protein-43 levels was increased. At C2 lesional level, fibers rerouting toward the gray matter were also identified for 5% of the axotomized axon terminals. Despite these chronic sprouting processes respiratory bulbospinal projections to ipsilateral phrenic nucleus remained poor (less than 10% compared to non-injured conditions). Retrograde labeling of projections onto the phrenic nucleus revealed, after chronic injury, an increased recruitment of C1 propriospinal interneurons which moreover received more contacts from bulbospinal collaterals. This chronic remodeling was correlated with chronic diaphragm recovery under conditions of respiratory stress. Thus, despite extensive axonal loss and absence of direct phrenic reinnervation by bulbospinal respiratory neurons, sprouting processes toward cervical propriospinal neurons may contribute to the observed partial respiratory recovery., (Copyright © 2012 Elsevier Inc. All rights reserved.)

In several populations of adult central nervous system neurons, axon damage can lead to an up-regulation of some transcription factors among which is c-Jun, known to be a key regulator of neuron cell body response to injury and of its intrinsic potential for axon regeneration. Thus, cervical spinal hemisection leads to c-Jun up-regulation in bulbospinal and rubrospinal axotomized neurons. The aims of the present study were to specify, after a unilateral cervical spinal cord injury, the expression of another marker of the neuronal stress response, heat shock protein 27 (HSP27) in axotomized neurons of the medulla (labeled by fluorogold retrograde tracer), and to compare it to that of c-Jun. In the medulla of injured rats, HSP27 and phospho-HSP27 were expressed in sub-populations of axotomized neurons, principally in the rostral ventral respiratory group (rVRG) (20%), the dorsal part of the gigantocellularis (Gi) (50%), and vestibular nucleus, but seldom in the ventral Gi and raphe nucleus, indicating a heterogeneous post-lesion cell body response between these different neuron populations. By contrast, phospho-c-Jun was up-regulated in axotomized neurons in all nuclei containing bulbospinal neurons, including the rVRG and Gi. In these areas, phospho-c-Jun was also up-regulated in uninjured bulbospinal neurons which project caudal to the spinal cord injury (labeled by fluorogold retrograde tracer). In contrast to phospho-c-Jun, HSP27 immunoreactivity was generally not present in neurons with spared axons. Our results show that various bulbospinal neuron populations react differentially to the injury and that spinal cord injury affects also bulbospinal neurons that are spared by the injury. However, the molecular cell body response of spared neurons is distinct from that of axotomized neurons since they can up-regulate c-Jun but not HSP27.

To evaluate the plasticity processes occurring in the spared and injured tissue after partial spinal cord injury, we have compared the level of axon growth markers after a C2 cervical hemisection in rats between the contralateral (spared) and ipsilateral (injured) cervical cord using western blotting and immunohistochemical techniques. In the ipsilateral spinal cord 7 days after injury, although GAP-43 levels were increased in the ventral horn caudal to the injury, they were globally decreased in the whole structure (C1-C6). By contrast, in the contralateral intact side 7 days and 1 month after injury, we have found an increase of GAP-43 and betaIII tubulin levels, suggesting that processes of axonal sprouting may occur in the spinal region contralateral to the injury. This increase of GAP-43 in the contralateral spinal cord after cervical hemisection may account, at least partially, to the spontaneous ipsilateral recovery observed after a cervical hemisection.

Schwann cells (Sc), associated axons, and nearby vascular endothelium constitute a functional trilogy of major importance during the development and regrowth of peripheral vascular nerves. The goal of the present study is to provide a technique of triple fluorescence confocal imaging of these cell types along renal preglomerular vessels. We took advantage of a protein S100B/EGFP transgenic mouse to visualize Sc. The endothelium was labeled with an intravenous injection of fluorescently tagged lectin, and after tissue processing, adrenergic nerves were revealed with an antibody against the marker protein synaptophysin. As a validation step, we found that EGFP-positive perivascular cells with prominent cell bodies and extensive, multidirectional cell processes were protein S100B positive. They were identified as Sc and indirectly assumed to be unmyelinated Sc. By contrast, we found strong EGFP expression in proximal epithelial cells and in the epithelium lining thin limbs of Henle. This epithelial fluorescence was not associated with immunoreactive protein S100B and thus corresponded to ectopic EGFP expressions in this mouse strain. Sc were organized in bundles or as a meshwork surrounding the preglomerular vasculature from arcuate arteries to afferent arterioles. No Sc were detected in the medulla. Although most Sc were closely apposed to adrenergic varicosities, many varicosities were not associated with detectable Sc processes. The present technique, and the capacity of confocal microscopy to yield three-dimensional imaging, allow the study of the microtopology of Sc and related sympathetic axons in the renal perivascular interstitium.

High cervical spinal cord injury (SCI) interrupts bulbospinal respiratory pathways innervating phrenic motoneurons, and induces an inactivation of phrenic nerves (PN) and diaphragm. We have previously shown that the ipsilateral (ipsi) PN was inactivated following a lateral C2 SCI, but was spontaneously partially reactivated 7 days post-SCI. This phrenic reactivation depended on contralateral (contra) descending pathways, located laterally, that cross the spinal midline. We analysed here whether long-term post-lesional changes may occur in the respiratory network. We showed that ipsi PN reactivation was greater at 3 months compared with 7 days post-SCI, and that it was enhanced after acute contra phrenicotomy (Phx), which also induced a substantial reactivation of the ipsi diaphragm (not detected at 7 days post-SCI). At 3 months post-SCI (compared with 7 days post-SCI), ipsi PN activity was only moderately affected by ipsi Phx or by gallamine treatment, a nicotinic neuromuscular blocking agent, indicating that it was less dependent on ipsi sensory phrenic afferents. After an additional acute contra SCI (C1) performed laterally, ipsi PN activity was abolished in rats 7 days post-SCI, but persisted in rats 3 months post-SCI. This activity thus depended on new functional descending pathways located medially rather than laterally. These may not involve newly recruited neurons as retrograde labelling showed that ipsi phrenic motoneurons were innervated by a similar number of medullary respiratory neurons after a short and long post-lesional time. These results show that after a long post-lesional time, phrenic reactivation is reinforced by an anatomo-functional reorganization of spinal respiratory pathways.