Neonatal paracetamol treatment reduces long-term nociceptive behaviour after neonatal procedural pain in rats.

BACKGROUND: Pain from skin penetrating procedures (procedural pain) during infancy in the neonatal intensive care unit (NICU) may result in changes of nociceptive sensitivity in later life. This supports the need for pain management during such vulnerable periods in life. This study, therefore, analyses the short- and long-term consequences of neonatal paracetamol (acetaminophen) treatment on pain behaviour in an experimental rat model of neonatal procedural pain. METHODS: A repetitive needle-prick model was used, in which neonatal rats received four needle pricks into the left hind paw per day from postnatal day 0 to day 7 (P0-P7). Paracetamol (50 mg/kg/day s.c.) was administered daily (P0-P7), and sensitivity to mechanical stimuli was compared with a needle-prick/saline-treated group and to a tactile control group. At 8 weeks of age, all animals underwent an ipsilateral paw-incision, modelling postoperative pain, and the duration of hypersensitivity was assessed. RESULTS: Neonatal paracetamol administration had no effect upon short-term mechanical hypersensitivity during the first postnatal week or upon long-term baseline sensitivity from 3 to 8 weeks. However, neonatal paracetamol administration significantly reduced the postoperative mechanical hypersensitivity in young adults, caused by repetitive needle pricking. CONCLUSION: Paracetamol administration during neonatal procedural pain does not alter short-term or long-term effects on mechanical sensitivity, but does reduce the duration of increased postoperative mechanical hypersensitivity in a clinically relevant neonatal procedural pain model. WHAT DOES THIS STUDY ADD: Paracetamol can be used safely in neonatal rats. Neonatal paracetamol treatment had no effect upon short-term mechanical hypersensitivity during the first postnatal week, nor upon long-term baseline sensitivity from 3 to 8 weeks. Paracetamol treatment during the first postnatal week significantly reduced the postoperative mechanical hypersensitivity in young adult rats.

The CatWalk method: a detailed analysis of behavioral changes after acute inflammatory pain in the rat.

Experimental pain research is often complicated by the absence of an objective and detailed method to analyze behavioral changes. In the present study, acute pain was induced into the right knee of the rat (n=15) through the injection of 2mg carrageenan (CAR) in saline. A control group received vehicle injection into the knee (n=15). With the use of an automated quantitative gait analysis system, the CatWalk, it was possible to quantitatively analyze behavioral changes at post-injection time 2.5, 4, 24 and 48h. The CatWalk analysis of individual paw parameters like the intensity of the paw print or the time contact with the floor showed a significant effect after CAR injection into the knee. These CatWalk parameters were highly correlated with von Frey data and thus representative for the development of mechanical allodynia. Furthermore, detailed CatWalk analysis of the gait (i.e. coordinated interaction between left and right hindlimb) showed very fine, accurate and significant coordination changes in the experimental rats from 4h post-injection. In conclusion, the CatWalk method allows an objective and detailed detection of both pain-induced gait adaptations as well as the development of mechanical allodynia in an acute inflammatory pain model.

Effect of spinal cord stimulation in an animal model of neuropathic pain relates to degree of tactile "allodynia".

Spinal cord stimulation (SCS) is an established treatment for chronic neuropathic pain. However, in recent studies conflicting results regarding the effect of SCS were noted in a selected group of patients suffering from complex regional pain syndrome and mechanical allodynia. In the present study we investigated the pain relieving effect of SCS in a rat experimental model of neuropathic pain as related to the severity of mechanical allodynia. Adult male rats (n=45) were submitted to a unilateral sciatic nerve ligation. The level of allodynia was tested using the withdrawal response to tactile stimuli with the von Frey test. A portion of these rats developed marked tactile hypersensitivity in the nerve-lesioned paw (von Frey test), similar to "tactile allodynia" observed after nerve injury in humans. Prior to SCS treatment the rats were subdivided into three groups based on the level of allodynia: mild, moderate and severe. All allodynic rats were treated with SCS (n=27) for 30 min (f=50 Hz; pulse width 0.2 ms and stimulation at 2/3 of motor threshold) at 16 days post-injury. Our data demonstrate a differential effect of SCS related to the severity of the mechanical allodynia. SCS leads to a faster and better pain relief in mildly allodynic rats as compared with the more severely allodynic rats. Thus, we suggest that the selection and subdivision of patient groups similar to those defined in our experimental setting (mild, moderate and severe allodynic) may provide better pre-treatment prediction of possible therapeutic benefits of SCS.

Olfactory ensheathing cells, olfactory nerve fibroblasts and biomatrices to promote long-distance axon regrowth and functional recovery in the dorsally hemisected adult rat spinal cord.

Cellular transplantation, including olfactory ensheathing cells (OEC) and olfactory nerve fibroblasts (ONF), after experimental spinal cord injury in the rat has previously resulted in regrowth of severed corticospinal (CS) axons across small lesion gaps and partial functional recovery. In order to stimulate CS axon regrowth across large lesion gaps, we used a multifactorial transplantation strategy to create an OEC/ONF continuum in spinal cords with a 2-mm-long dorsal hemisection lesion gap. This strategy involved the use of aligned OEC/ONF-poly(D,L)-lactide biomatrix bridges within the lesion gap and OEC/ONF injections at 1 mm rostral and caudal to the lesion gap. In order to test the effects of this complete strategy, control animals only received injections with culture medium rostral and caudal to the lesion gap. Anatomically, our multifactorial intervention resulted in an enhanced presence of injured CS axons directly rostral to the lesion gap (65.0 +/- 12.8% in transplanted animals versus 13.1 +/- 3.9% in control animals). No regrowth of these axons was observed through the lesion site, which may be related to a lack of OEC/ONF survival on the biomatrices. Furthermore, a 10-fold increase of neurofilament-positive axon ingrowth into the lesion site as compared to untreated control animals was observed. With the use of quantitative gait analysis, a modest recovery in stride length and swing speed of the hind limbs was observed. Although multifactorial strategies may be needed to stimulate repair of large spinal lesion gaps, we conclude that the combined use of OEC/ONF and poly(D,L)-lactide biomatrices is rather limited.

Chronically injured corticospinal axons do not cross large spinal lesion gaps after a multifactorial transplantation strategy using olfactory ensheathing cell/olfactory nerve fibroblast-biomatrix bridges.

Transplantation of mixed cultures containing olfactory ensheathing cell (OEC) and olfactory nerve fibroblasts (ONF) has been shown to stimulate regrowth of both acutely and chronically injured corticospinal (CS) axons across small spinal cord lesion gaps. Here, we used a multifactorial transplantation strategy to stimulate regrowth of chronically injured CS axons across large spinal cord lesion gaps. This strategy combined the transplantation of aligned OEC/ONF-biomatrix complexes, as described previously (Deumens et al. [2004] Neuroscience 125:591-604), within the lesion gap with additional OEC/ONF injections rostral and caudal to the lesion site. We show an enhanced presence of injured CS axons directly rostral to the lesion gap, with no effects on injured CS axons at or caudal to the lesion gap. Furthermore, injured CS axons did not penetrate the OEC/ONF-biomatrix complex within the lesion gap. The enhanced presence of CS axons rostral to the lesion gap was not accompanied by any recovery of behavioral parameters assessed with the BBB locomotor rating scale or CatWalk gait analysis. We conclude that our multifactorial transplantation strategy should be optimized to create an OEC/ONF continuum in the injured spinal cord and thereby stimulate regrowth of injured CS axons across large spinal lesion gaps.

Alignment of glial cells stimulates directional neurite growth of CNS neurons in vitro.

Olfactory ensheathing cells (OECs) together with olfactory nerve fibroblasts (ONFs) and neonatal astrocytes are potent stimulators of neurite growth in adulthood and during development, respectively. Since it is known that alignment of glial cells is important for the correct outgrowth of axon tracts, it was hypothesized that the alignment of glial cells stimulates directional and enhanced neurite outgrowth. Adult OEC/ONF and neonatal astrocytes were cultured either on biodegradable poly(d,l)-lactide matrices or in Petri dishes for 4 days. Thereafter neonatal cerebral cortical neurons were added. After a 2-days coculture period the cultures were fixed and processed for a combined MAP-2 and phosphorylated neurofilament (RT97) staining. The neurite growth (neurite elongation and neurite formation) and the neurite direction were assessed. We show that (1). OEC/ONF cultures are more potent in stimulating the length of the longest neurite of cocultured neurons, (2). alignment of glial is achieved in vitro on our biomatrices, (3). aligned glial/biomatrix complexes do not enhance neurite growth, and (4). aligned glial/biomatrix complexes direct neurite outgrowth. These data have significant implications for in vivo experiments focusing on glial transplantation. Transplanting glial/biomatrix complexes may stimulate the directional regrowth of severed axons across a lesion site.