Nicolas P. Lapointe

Rotenone induces non-specific central nervous system and systemic toxicity.

We investigated the dopaminergic (DA) neuronal degeneration in animals subjected to systemic treatment of rotenone via subcutaneous delivery. Behavioral observations revealed a hypokinetic period in rats sacrificed at 3 and 5 days, and dystonic episodes in animals sacrificed at 8 days. Less than 20% of the total number of animals given rotenone depicted brain lesions after 8 days of treatment, as demonstrated by a significant loss of DA fibers in the striatum, but not of DA nigral neurons. Tyrosine hydroxylase‐negative striatal territories were characterized by post‐synaptic toxicity as demonstrated by a decreased number of interneurons labeled for choline acetyltransferase, NADPH‐diaphorase, parvalbumin, and projection neurons labeled for calbindin and nerve growth factor inducible‐B (NGFI‐B). Post‐synaptic neurodegeneration was demonstrated further by abundant striatal staining for Fluoro‐Jade. Decrease in the nuclear orphan receptor Nurr1 expression was the only significant change observed at the level of the substantia nigra. Autopsy reports confirmed that animals suffered from severe digestion problems. These data suggest that hypokinesia observed between 3 and 5 days is the result of general health problems rather than a specific motor deficit associated to Parkinsons disease (PD) symptoms. Overall, the effects of rotenone toxicity are widespread, and subcutaneous administration of this toxin does not provide the neuropathological and behavioral basis for a relevant and reliable PD model.

Systemic exposure to paraquat and maneb models early Parkinson's disease in young adult rats.

In recent years, several lines of evidence have shown an increase in Parkinsons disease (PD) prevalence in rural environments where pesticides are widely used. Paraquat (PQ--herbicide) and maneb (MB--fungicide) are among the compounds suspected to induce neuronal degeneration and motor deficits characteristics of PD. Here, we investigated the effects of PQ and MB on dopaminergic (DA) neuron-glia cultures and in vivo in young adult rats. In vitro, PQ led to a loss of DA as compared to non-DA neurons and microglial activation in a dose-dependent manner. Addition of MB had no further effect nor did it lead to microglial activation when used alone. In vivo, 2-month old young adult rats were subjected to intraperitoneal injections of vehicle (n = 4), PQ alone (n = 8), or PQ in combination with MB (n = 8) twice a week for 4 weeks and were sacrificed the day following the last injection. Significant loss of nigral DA neurons was observed in both treatment groups, but a significant decrease in striatal DA fibers was not found. Microglial activation was seen in the nigra of rats subjected to PQ with or without MB. Behavioral analyses demonstrated a mixed pattern of motor impairments, which may have been related to early effects of nigral DA neuronal loss or systemic effects associated with MB exposure in addition to PQ. These results indicate that exposure to PQ with or without MB induces neurodegeneration which might occur via an early inflammatory response in young adult animals.

Contribution of spinal 5-HT1A and 5-HT7 receptors to locomotor-like movement induced by 8-OH-DPAT in spinal cord-transected mice

Growing evidence from in vitro studies suggests that spinal serotonin (5‐HT) receptor subtypes 5‐HTR1A and 5‐HTR7 are associated with an induction of central pattern generator activity. However, the possibility of a specific role for these receptor subtypes in locomotor rhythmogenesis in vivo remains unclear. Here, we studied the effects of a single dose (1 mg/kg, i.p.) of 8‐hydroxy‐2‐(di‐N‐propylamino)‐tetralin (8‐OH‐DPAT), a potent and selective 5‐HTR1A/7 agonist, in mice spinal cord transected at the low‐thoracic level (Th9/10). The results show that 8‐OH‐DPAT acutely induced, within 15 min, hindlimb movements that share some characteristics with normal locomotion. Paraplegic mice pretreated with the selective 5‐HTR1A antagonists, WAY100,135 or WAY100,635, displayed significantly less 8‐OH‐DPAT‐induced movement. A similar reduction of 8‐OH‐DPAT‐induced movements was found in animals pretreated with SB269970, a selective 5‐HTR7 antagonist. Moreover, a near complete blockade of 8‐OH‐DPAT‐induced movement was obtained in wild‐type mice pretreated with 5‐HTR1A and 5‐HTR7 antagonists, and in 5‐HTR7–/– mice pretreated with 5‐HTR1A antagonists. Overall, these results clearly demonstrate that 8‐OH‐DPAT potently induces locomotor‐like movement in the previously paralysed hindlimbs of low‐thoracic‐transected mice. The results, with selective antagonists and knockout animals, provide compelling evidence of a specific contribution of both receptor subtypes to spinal locomotor rhythmogenesis in vivo.

Role of spinal 5-HT2 receptor subtypes in quipazine-induced hindlimb movements after a low-thoracic spinal cord transection

A role of serotonin receptors (5‐HTRs) in spinal rhythmogenesis has been proposed several years ago based mainly upon data showing that bath‐applied 5‐HT could elicit locomotor‐like rhythms in in vitro isolated spinal cord preparations. Such a role was partially confirmed in vivo after revealing that systemically administered 5‐HTR2 agonists, such as quipazine, could induce some locomotor‐like movements (LM) in completely spinal cord‐transected (Tx) rodents. However, given the limited binding selectivity of currently available 5‐HTR2 agonists, it has remained difficult to determine clearly if one receptor subtype is specifically associated with LM induction. In situ hybridization, data using tissues from L1–L2 spinal cord segments, where critical locomotor network elements have been identified in mice, revealed greater 5‐HTR2A mRNA levels in low‐thoracic Tx than non‐Tx animals. This expression level remained elevated for several days, specifically in the lateral intermediate zone, where peak values were detected at 1 week post‐Tx and returned to normal at 3 weeks post‐Tx. Behavioral and kinematic analyses revealed quipazine‐induced LM in 1‐week Tx mice either non‐pretreated or pretreated with selective 5‐HTR2B and/or 5‐HTR2C antagonists. In contrast, LM completely failed to be induced by quipazine in animals pretreated with selective 5‐HTR2A antagonists. Altogether, these results provide strong evidence suggesting that 5‐HTR2A are specifically associated with spinal locomotor network activation and LM generation induced by quipazine in Tx animals. These findings may contribute to design drug treatments aimed at promoting locomotor function recovery in chronic spinal cord‐injured patients.

Synergistic Effects of D1/5 and 5-HT1A/7 Receptor Agonists on Locomotor Movement Induction in Complete Spinal Cord–Transected Mice

Monoamines are well known to modulate locomotion in several vertebrate species. Coapplication of dopamine (DA) and serotonin (5-HT) has also been shown to potently induce fictive locomotor rhythms in isolated spinal cord preparations. However, a synergistic contribution of these monoamines to locomotor rhythmogenesis in vivo has never been examined. Here, we characterized the effects induced by selective DA and 5-HT receptor agonists on hindlimb movement induction in completely spinal cord transected (adult) mice. Administration of the lowest effective doses of SKF-81297 (D 1/5 agonist, 1-2 mg/kg, ip) or 8-OH-DPAT (5-HT 1A/7 agonist, 0.5 mg/kg, ip) acutely elicited some locomotor-like movements (LM) (5.85 +/- 1.22 and 3.67 +/- 1.44 LM/min, respectively). Coadministration of the same doses of SKF-81297 and 8-OH-DPAT led to a significant increase (7- to 10-fold) of LM (37.70 +/- 5.01 LM/min). Weight-bearing and plantar foot placement capabilities were also found with the combination treatment only (i.e., with no assistance or other forms of stimulation). These results clearly show that D 1/5 and 5-HT 1A/7 receptor agonists can synergistically activate spinal locomotor networks and thus generate powerful basic stepping movements in complete paraplegic animals. Although previous work from this laboratory has reported the partial rhythmogenic potential of monoamines in vivo, the present study shows that drug combinations such as SKF-81297 and 8-OH-DPAT can elicit weight-bearing stepping.

Specific role of dopamine D1 receptors in spinal network activation and rhythmic movement induction in vertebrates

Dopamine (DA) is well‐recognized for its determinant role in the modulation of various brain functions. DA was also found in in vitro isolated invertebrate preparations to activate per se the central pattern generator for locomotion. However, it is less clear whether such a role as an activator of central neural circuitries exists in vertebrate species. Here, we studied in vivo the effects induced by selective DA receptor agonists and antagonists on hindlimb movement generation in mice completely spinal cord‐transected (Tx) at the low‐thoracic level (Th9/10). Administration of D1/D5 receptor agonists (0.5–2.5 mg kg−1, i.p.) was found to acutely elicit rhythmic locomotor‐like movements (LMs) and non‐locomotor movements (NLMs) in untrained and non‐sensory stimulated animals. Comparable effects were found in mice lacking the D5 receptor (D5KO) whereas D1/D5 receptor antagonist‐pretreated animals (wild‐type or D5KO) failed to display D1/D5 agonist‐induced LMs. In contrast, administration of broad spectrum or selective D2, D3 or D4 agonists consistently failed to elicit significant hindlimb movements. Overall, the results clearly show in mice the existence of a role for D1 receptors in spinal network activation and corresponding rhythmic movement generation.

Spontaneous recovery of hindlimb movement in completely spinal cord transected mice: a comparison of assessment methods and conditions

Study design:To compare results obtained with a variety of locomotor rating scales in Th9/10 spinal cord transected (Tx) mice.Objectives:To assess spontaneous recovery with a variety of rating scales to find the most sensitive methods for assessing recovery levels in Tx mice and differences associated with gender and condition.Setting:Laval University Medical Center, Neuroscience Unit & Laval University, Department of Anatomy and Physiology, Quebec City, Quebec, Canada.Methods:Scales including the Basso, Beattie and Bresnahan (BBB), the Basso Mouse Score (BMS), the Antri, Orsal and Barthe (AOB), the Motor Function Score (MFS) and the Averaged Combined Score (ACOS) were used to assess, in open-field and treadmill conditions, spontaneous locomotor recovery in male and female Tx mice.Results:The ACOS scale revealed a progressive increase of spontaneous recovery during 5-weeks post-Tx. The other methods detected a progressive increase for the first 2–3 weeks post-Tx without any significant progress in weeks 4 and 5. Generally, scores obtained with each method were nonsignificantly different between males and females or between open-field and treadmill conditions.Conclusion:These results further confirm the existence of a limited but significant increase of locomotor function recovery, occurring without intervention, in Tx animals. Although each method could detect small levels of recovery, the ACOS method was discriminative enough to detect progressive changes up to 5 weeks post-Tx. In conclusion, the ACOS rating scale was the most discriminative method for assessing the spontaneous return of hindlimb movements found in Tx mice, both in open-field and treadmill conditions.

Strain-dependent recovery of spontaneous hindlimb movement in spinal cord transected mice (CD1, C57BL/6, BALB/c).

Reorganization and plasticity after spinal cord injury have been recently shown to take place in sublesional neuronal networks, but the possibility of strain-dependent changes at that level has never been explored. The authors studied the spontaneous return of hindlimb movement in low-thoracic spinal cord transected (Tx) mice from 3 commonly used strains. Without intervention, most CD1, C57BL/6, and BALB/c mice displayed some hindlimb movement recovery after Tx. Although all assessment methods unanimously reported that CD1 displayed higher recovery levels than did the C57BL/6 and BALB/c, higher scores were generally found with the Antri-Orsal-Barthe (M. Antri, D. Orsal, & J. Y. Barthe, 2002) and the Average Combined Score (P. A. Guertin, 2005a) methods. Such spontaneous recovery in low-thoracic Tx mice is likely the result of neuronal plasticity at the lumbosacral spinal cord level, suggesting that these sublesional changes are strain dependent.

Histomorphometric and Densitometric Changes in the Femora of Spinal Cord Transected Mice

Spinal cord injury (SCI) leads generally to significant bone tissue loss within a few months to a few years post–trauma. Although, increasing data from rat models are available to study the underlying mechanisms of SCI‐associated bone loss, little is known about the extent and rapidity of bone tissue changes in mouse models of SCI. The objectives are to characterize and describe quantitatively femoral bone tissue changes during 1 month in adult paraplegic mice. Histomorphometric and densitometric measurements were performed in 3‐ to 4‐month‐old CD1 mice spinal cord transected at the low‐thoracic level (Th9/10). We found a general decrease in bone volume (−22%), trabecular thickness (−10%), and trabecular number (−14%) within 30 days post‐transection. Dual‐energy X‐ray absorptiometric measurements revealed no change in bone mineral density but a significant reduction (−14%) in bone mineral content. These results show large structural changes occurring within only a few weeks post–spinal cord transection in the femora of adult mice. Given the increasing availability of genetic and molecular research tools for research in mice, this murine model may be useful to study further the cellular and molecular mechanisms of demineralization associated with SCI. Anat Rec, 291:303–307, 2008.

Early adaptive changes in chronic paraplegic mice: a model to study rapid health degradation after spinal cord injury

Study design:Literature review.Objective:To describe quantitatively some of most important anatomic, systemic, and metabolic changes occurring soon (one month) after spinal cord trauma in mice.Setting:University Laval Medical Center.Results:Significant changes in weight, mechanical and contractile muscle properties, bone histomorphometry and biomechanics, deep-vein morphology, complete blood count, immune cell count, lipid metabolism and anabolic hormone levels were found occurring within 1 month in completely spinal cord transected (Th9/10) mice.Conclusion:These data reveal that many changes in mice and humans are comparable suggesting, in turn, that this model may be a valuable tool for neuroscientists to investigate the specific mechanisms associated with rapid health degradation post-SCI.