Lumbar subarachnoid catheterization in rats

Neurexin-2 is a potential regulator of inflammatory pain in the spinal dorsal horn of rats

Chronic pain is one of the serious conditions that affect human health and remains cure still remains a serious challenge as the molecular mechanism remains largely unclear. Here, we used label-free proteomics to identify potential target proteins that regulate peripheral inflammatory pain and reveal its mechanism of action. Inflammation in peripheral tissue was induced by injecting complete Freund's adjuvant (CFA) into rat hind paw. A proteomic method was adopted to compare the spinal dorsal horn (SDH) in peripheral inflammatory pain (PIP) model rats with controls. Differential proteins were identified in SDH proteome by label-free quantification. The role of screened target proteins in the PIP was verified by small interfering RNA (siRNA). A total of 3072 and 3049 proteins were identified in CFA and normal saline (NS) groups, respectively, and 13 proteins were identified as differentially expressed in the CFA group. One of them, neurexin-2, was validated for its role in the inflammatory pain. Neurexin-2 was up-regulated in the CFA group, which was confirmed by quantitative PCR. Besides, intrathecal siRNA-mediated knock-down of neurexin-2 attenuated CFA-induced mechanical and thermal hyperalgesia and reduced the expression of SDH membrane glutamate receptors (eg mGlu receptor 1, AMPA receptor) and postsynaptic density (eg PSD-95, DLG2). These findings increased the understanding of the role of neurexin-2 in the inflammatory pain, implicating that neurexin-2 acts as a potential regulatory protein of inflammatory pain through affecting synaptic plasticity in the SDH of rats.

An improved procedure for catheterization of the thoracic spinal subarachnoid space in the rat

Catheterization of the subarachnoid space provides a convenient means to deliver drugs to, or collect cerebrospinal fluid from, the spinal cord in animal experiments, and has been instrumental to our understanding of spinal mechanisms that underlie anesthesia, analgesia, or cardiovascular regulation. Experience gained over the years has revealed several shortcomings of this technique. We report a procedure that encompasses the benefits of direct subarachnoid catheterization of the rat thoracic spinal cord but circumvents the known shortcomings. An intrathecal catheter was fabricated with a small silicon bead at one end of a PE-10 catheter, which was cannulated with a 4/0 suture that served as a guide. Using the L-shape hook of the suture guide as an anchorage, the catheter was advanced into the subarachnoid space until the silicon bead was lodged on a drilled hole (2 x 2 mm) over the lamina proper on the T13 vertebrae. With less surgical trauma, greater precision of placement and firmer anchorage of the catheter, less leakage of cerebrospinal fluid, and minimal mortality or morbidity, our modified procedure for catheterization of the thoracic spinal subarachnoid space in the rat compared favorably to previously reported methods.

Distribution of intrathecal catheter positions in rat

BACKGROUND

Although drug administration through an intrathecal catheter is widely used in the study of spinal pharmacology, the catheter positions in transverse plane that may cause a limited spread of a solution remain unclear. In the first step to clarify this issue, the distribution of the intrathecal catheter position was investigated in rats.

METHODS

A polyethylene catheter (PE-10) was inserted intrathecally 8.5 cm through the atlanto-occipital membrane, aiming the tip of the catheter to the dorsal surface of the spinal cord. Three or four weeks after the implantation of the catheter, 83 rats were transcardiacally perfused with fixative solution. The catheter positions were investigated longitudinally and transversely by cutting the spinal cord segmentally through the intervertebral disk at different spinal levels.

RESULTS

Seventeen rats were excluded from further data analysis. Transversely, catheters were located in the left lateral subarachnoid space in 23 rats (35%), in the right lateral in 15 (23%), in the dorsal in 22 (33%), and in the ventral in 6 (9%). Longitudinally, catheter position was significantly higher in the ventral group (median, T9) than that in the dorsal group (T11/12) (P<0.01).

CONCLUSION

Chronic intrathecal catheters were variously located in the rat spinal subarachnoid space in the transverse plane, and lateral subarachnoid placement of the catheter (58%) was frequently observed, whereas dorsal subarachnoid placement occurred in 33%.

Hypotension does not alter the antinociceptive effect of nifedipine

We explored the relationship between antinociceptive and hypotensive effects of nifedipine (NIF) injected intraperitoneally ( ip, 15 mg/kg) and epidurally (epi, 20 microM), as compared to verapamil (VER, 10 mg/kg ip) and nitroglycerin (NTG, 0.1 and 0.15 mg/kg ip). The systolic blood pressure (BP) and tail-flick (TF) latencies were measured simultaneously every 10 min for 2 hours and individual values of both measurements were correlated. The highest antinociceptive as well as hypotensive effects were both measured in the group receiving NIF epi., with the correlation coefficient r2=0.2878. Injected ip., NIF revealed similar antinociceptive effect, whereas the other studied drugs were not effective. As to the degree of hypotensive activity, NIF epi was followed by VER, NTG 0.1, NIF ip. and NTG 0.15. No significant correlation was found between BP and TF latencies in any group receiving the drugs. We concluded that the antinociceptive response, measured by the tail-flick technique, is independent of the hypotensive activity of the studied drugs, including NIF.

Differential participation of hippocampal formation in cocaine-induced cortical electroencephalographic desynchronization and penile erection in the rat

We evaluated the role of the hippocampal formation in cocaine-induced cortical electroencephalographic (EEG) desynchronization and penile erection. Adult, male Sprague-Dawley rats anesthetized and maintained by chloral hydrate were used. Intravenous (1.5 or 3.0 mg/kg) administration of cocaine dose-dependently increased intracavernous pressure (ICP), our experimental index for penile erection. This was accompanied by desynchronization of EEG activity recorded from the somatosensory cortex (cEEG), as represented by a decrease in root mean square (RMS) and an increase in mean power frequency (MPF) values. There was a simultaneous increase in the RMS values, without significant changes in the MPF values of EEG signals recorded from the hippocampal formation (hEEG). In animals that received prior application of 10% xylocaine either intrathecally (i.t.) at the L6-S1 spinal levels or directly into the bilateral hippocampal formation, the RMS values of both cEEG and hEEG signals induced by cocaine (1.5 or 3.0 mg/kg, i.v.) were appreciably reduced, along with a further increase in ICP. Unilateral microinjection of cocaine (15 or 30 microg) into the hippocampal formation elicited discernible excitation of both cEEG and hEEG signals. Intriguingly, the ICP underwent a significant and dose-dependent reduction, which was discernibly antagonized by i.t. application of xylocaine. We conclude that cocaine may effect cortical EEG desynchronization but cause a reduction in ICP via an action on the hippocampal formation.

Involvement of spinal adenosine A1 and A2 receptors in fentanyl-induced muscular rigidity in the rat

In the present study, using hydrophilic adenosine antagonists either selective to A1 or A2 receptors, we investigated the central and spinal adenosinergic participation in fentanyl-induced muscular rigidity. Adult Sprague-Dawley rats were anesthetized with ketamine and were under mechanical ventilation. Fentanyl (100 micrograms/kg, i.v.) consistently elicited electromyographic (EMG) activation in the sacrococcygeal dorsalis lateralis muscle. This implied muscular rigidity was not blocked by i.c.v. administration of the adenosine A1 antagonist, 1-allyl-3,7-dimethyl-8-p-sulfophenyl-xanthine (ADSPX; 20 or 40 nmol/2.5 microliters), except at higher dose (80 nmol). Equimolar doses of the adenosine A2 antagonist, 3,7-dimethyl-1-propargylxanthane (DMPX), did not exert any inhibitory effect on fentanyl-induced rigidity. Intrathecal (i.t.) administration of the same doses of ADSPX (20, 40 or 80 nmol/10 microliters) appreciably suppressed the EMG activation. However, the rigidity was only inhibited by 40 or 80 nmol (i.t.) of DMPX, but not by the lowest dose. High-dose (80 nmol, i.t.) adenosine A1 or A2 antagonist per se did not induce motor impairment or hindlimb paralysis in conscious animals. These results suggest that adenosine A1 and A2 receptors in the spinal cord may play a more crucial role than those in the central nervous system (CNS) in fentanyl-induced muscular rigidity in rats.

Effects of NMDA receptor antagonists on inhibition of morphine tolerance in rats: binding at mu-opioid receptors

Past studies have shown antagonists of excitatory amino acid receptors, both N-methyl-D-aspartate (NMDA) and non-NMDA, to produce an antinociceptive effect in vitro and in vivo. Additionally, NMDA receptor antagonists have been demonstrated to prevent morphine tolerance. We had found that one NMDA receptor antagonist, ketamine, potentiates morphine's analgesic effect in post-operative patients. Our latest experiment was performed to examine the modulatory effect of competitive and non-competitive NMDA receptor antagonists on morphine antinociception and tolerance. A PE10 catheter was intrathecally (i.t.) implanted in male Sprague-Dawley rats for drug administration. The antinociceptive effect of morphine, D-(-)-2-amino-5-phosphonovaleric acid (D-AP5) and (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine maleate (MK-801) was measured using the hot-water tail immersion test. Neither competitive nor non-competitive NMDA receptor antagonists had an antinociceptive effect by themselves, but they did potentiate the antinociceptive effect of morphine. Both D-AP5 (AD50 = 0.18 micrograms) and MK-801 (AD50 = 0.57 micrograms) shifted the antinociceptive dose-response curve of morphine (AD50 = 4.2 micrograms) to the left. Both D-AP5 (4 micrograms/h) and MK-801 (10 micrograms/h) when co-administered with i.t. morphine infusions (10 micrograms/h) also inhibited the development of tolerance. In [3H][D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin ([3H]DAMGO) binding assays, MK-801 (Bmax = 32.90 +/- 3.33 fmol/mg) treatment prevented the down-regulation of mu-opioid receptor high-affinity sites induced by continuous morphine infusions alone (Bmax = 13.97 +/- 1.47 fmol/mg). D-AP5 (Bmax = 20.78 +/- 3.36 fmol/mg) did not prevent the reduction of mu-opioid receptor high-affinity sites. However, high-affinity sites in rats treated with D-AP5 and morphine displayed a higher affinity (KD = 0.45 +/- 0.09 nM) than those of control animals (KD = 0.95 +/- 0.08 nM). Results of this study indicate that competitive as well as non-competitive NMDA receptor antagonists enhance morphine's antinociceptive effect, and prevent the development of morphine tolerance. Thus, in our opinion, there opens a new frontier in clinical pain management, especially for those patients who require long-term opioid treatment for pain relief.

Inhibition by intrathecal prazosin but not yohimbine of fentanyl-induced muscular rigidity in the rat

We evaluated the effect of intrathecally administered prazosin, alpha 1-adrenoceptor antagonist, or yohimbine, alpha 2-adrenoceptor antagonist, on fentanyl-induced muscular rigidity. Adult, male Sprague-Dawley rats were anesthetized with ketamine and were under mechanical ventilation. Fentanyl given intravenously (100 micrograms/kg) or microinjected into the bilateral locus coeruleus (LC) (2.5 microgram/50 nl) consistently evoked a significant increase in the electromyographic activity recorded from the sacrococcygeus dorsalis lateralis muscle. This implied muscular rigidity was appreciably antagonized by prior intrathecal (10 microliters) administration of prazosin (5 or 10 nmol), but not equimolar dose of yohimbine. These results suggest that the spinal alpha 1-adrenoceptors in the coerulospinal noradrenergic pathway play a key role in fentanyl-induced muscular rigidity.

The antinociceptive effect of S-(+)-ibuprofen in rabbits: epidural versus intravenous administration

This study was designed to determine whether systemic absorption plays any role in the antinociceptive effect of epidural (EP) sodium S(+)-ibuprofen (IB). One week after surgical implantation of EP catheters, six rabbits were given EP injections with either normal saline (NS) 0.4 mL or IB 10 mg in 0.4 mL NS (Group 1) on separate days. Each animal was injected with IB 10 mg intravenously (i.v.) on another day. Six control rabbits (Group 2) had neither surgery nor any injection. Analgesic testing was performed using electric stimulation through two electrocardiogram (ECG) skin electrodes with built-in adhesive, attached to shaved hip areas using 50 V, 1 Hz, 3 ms, before and 0.5,1,2 and 3 h after injection in Group 1, and in similar times in controls. The 95% confidence intervals (CI) of the mean difference between baseline and maximal nociceptive response latency of all groups were compared using analysis of covariance (ANCOVA) adjusted for baseline measurements. This comparison covered all possible pairs among all groups. Significant antinociceptive effects were seen after EP IB but not after control or i.v. IB. Neither motor dysfunction nor evidence of systemic toxicity or neurotoxicity was observed in any animal.

Antinociception without motor blockade after subarachnoid administration of S-(+)-ibuprofen in rats

This study was designed to determine whether the nonsteroidal anti-inflammatory drug (NSAID) sodium S-(+)-ibuprofen (IB), can be used intrathecally as a substitute analgesic for opiates to avoid the side effects of intrathecal narcotics. One week or more after surgical implantation of subarachnoid catheters, four groups of Sprague-Dawley rats were given 0.05 ml subarachnoid injections containing one of the following: Group A, normal saline (NS); Group B, IB 0.25 mg, 0.5 mg and 1.5 mg; Group C, morphine (M) 0.05 mg and 0.025 mg; Group D received NS or IB 1.5 mg. Animals were sacrificed for spinal cord examination one week after injection. Tail flick response latency (TFL) was determined before and 15, 30, 60, 120 and 180 minutes after each injection. TFL differences were compared. IB 1.5 mg vs NS, IB 0.5 mg vs NS, IB 0.25 mg vs M 0.05 mg, IB 0.25 mg vs M 0.025 mg, M 0.05 mg vs NS, and M 0.025 vs NS showed p < 0.05. IB 1.5 mg vs M 0.05 mg and M 0.025 mg, IB 0.5 mg vs M 0.05 mg and M 0.025 mg revealed no significant difference. No motor impairment was observed in any animal. Light microscopy of the spinal cord revealed no evidence of pathological changes in any animal (group D).