Phaclofen-reversible effects of GABA in the spinal cord of the rat.

Our earlier observation that intrathecal administration of L- and D-baclofen had different effects on sympathetic output regulating arterial pressure and heart rate in the rat prompted the present study which was designed to determine whether intrathecal administration of GABA elicits a phaclofen-reversible effect on arterial pressure and/or heart rate and whether this effect mimics that of L-baclofen or that of D-baclofen. Following intrathecal administration of the GABAA antagonist, bicuculline (10 nmol), at the T9 level, administration of GABA at a dose of 5 mumol (n = 8) decreased arterial pressure and heart rate by about 25 mm Hg and 45 bpm, respectively. The responses started at 1-2 min and lasted 3-20 min; comparison was made with rats given NaCl (5 mumol; n = 5), which was without effect on arterial pressure and heart rate. In rats pretreated with both bicuculline and the GABAB antagonist, phaclofen (5 mumol intrathecally; n = 9), the effect of GABA on arterial pressure was attenuated and the effect of GABA on heart rate was absent; comparisons were made with rats given bicuculline, phaclofen and NaCl (n = 5) and with rats given bicuculline, NaCl and GABA (n = 6). These data suggest that there is a phaclofen-reversible effect of GABA in spinal pathways regulating sympathetic output and that this effect of GABA resembles that L-baclofen reported in our earlier study.(ABSTRACT TRUNCATED AT 250 WORDS)     

GABA and its receptors in the spinal cord

The importance of the inhibitory neurotransmitter, GABA, within higher centres of the mammalian brain is unquestionable. However, its role within the spinal cord is of equal significance. There have been numerous studies over the past two decades that have established GABA as a neurotransmitter at both post- and presynaptic sites in the cord. Here, Marzia Malcangio and Norman Bowery review the current status of GABA in relation to nociception and skeletal muscle tone, and indicate that its contribution to spinal cord function should not be overlooked.     

Involvement of GABA and opioid peptide receptors in sevoflurane-induced antinociception in rat spinal cord

AIM: The spinal cord is pivotal in immobility induced by volatile anesthetics because the anesthetics depress the activity of motor neurons in the spinal cord. The aim of this study was to observe the effects of sevoflurane on pain processing at the spinal level. METHODS: The firing of the gastrocnemius muscle was evoked by electrical stimulation to the ipsilateral hindpaw in rats. The nociceptive C response of electromyography (EMG) was selected to study. The GABAA receptor antagonist bicuculline (0.1 mg/kg) and opioid receptor antagonist naloxone (0.4 mg/kg) were administered intravenously, either in the presence or in the absence of 1.0% sevoflurane. RESULTS: In rats with transected spinal cord, sevoflurane produced a profound reduction in the C response in a dose- and time-dependent manner. In the presence of 1.0% sevoflurane, the C responses were increased after injections of bicuculline and naloxone. CONCLUSION: Sevoflurane is a volatile anesthetic that acts directly on the spinal cord to suppress the nociceptive reflex. The sevoflurane-induced suppression of the C response is antagonized by either bicuculline or naloxone. The results suggest that spinal GABAA receptors and opioid peptide receptors are involved in the sevoflurane-induced suppression of spinal nociception.     

Nociceptive regulation of GABA(B) receptor gene expression in rat spinal cord

Activation of gamma-aminobutyric acid (GABA) neurotransmission evokes antinociceptive responses in laboratory animals. The recent cloning of GABA(B) receptor gene products makes it possible to examine the regulation of this receptor system as it relates to the mediation of pain-related sensory information. Inasmuch as acute and chronic pain alter the expression of a number of nociception-related receptors, and because such changes are important components in the regulation of pain, the present study was undertaken to determine whether GABA(B) receptor gene expression is altered in sensory systems following a peripheral nociceptive stimulus. Solution hybridization-nuclease protection assays conducted 24 h after formalin injection into the right hindpaw of the rat revealed a significant bilateral increase in GABA(B) R1 and R2 receptor expression in the dorsal lumbar spinal cord, and a significant increase in GABA(B) R1 receptor mRNA in the ipsilateral lumbar dorsal root ganglion. These findings indicate an activity-dependent, differential regulation of GABA(B) R1 and R2 receptor gene expression in spinal sensory systems in response to chemogenic nociceptive activation, suggesting that GABA(B) receptor plasticity may play an important role in regulating the mediation, and perception, of chronic pain.     

The chloride-dependent depression by GABA in the frog spinal cord

Spontaneous activities from ventral and dorsal roots of the isolated perfused spinal cord of the bullfrog were inhibited by GABA. β-Alanine showed a strong and glycine a weaker inhibitory effect. The inhibitory effect of GABA was markedly reduced in a chloride-free medium, whereas glycine and β-alanine still showed an inhibitory effect similar to that seen in normal medium. Employing the sucrose-gap method, a marked depolarization in the dorsal root and a small but obvious hyperpolarization in the ventral root were found by the application of GABA. These results support the view that GABA is one of the transmitters involved in pre- and postsynaptic inhibition of the spinal cord. The postsynaptic hyperpolarizing effect of GABA on motoneurones would be caused directly through increased permeability of the membrane to chloride ion. The depolarizing effect of GABA on primary afferent terminals is discussed in connection with chloride dependency.     

New spinal cord injury model produced by spinal cord compression in the rat

Graded spinal cord injuries were produced in rats by compressing the spinal cord at the level of the T11 vertebra for 5, 15, 30, 60, or 180 min with stainless steel screws of 2-mm diameter and 2.8-mm length, or for 60 min with screws of the same diameter and various lengths (2.5, 2.8, 3.1, or 3.4 mm). The main neurologic symptoms caused by spinal cord compression were motor deficits, sensory deficits, and urinary incontinence. Neurologic scores, based on both motor and sensory deficits, correlated significantly with both the screw length and the duration of compression at every observation point from 4 hr to 21 days after removal of the screw. The incidence of urinary incontinence (from 24 hr to 21 days) and the percentage of rats surviving (from 14 days to 21 days) also correlated closely with the two factors (screw length and duration of compression). These results suggest that the present procedure could be a useful and simple model for studying traumatic spinal cord injury in rats.     

Postnatal development of cyclooxygenase-2 in the rat kidney

Prostaglandins are local mediators/modulators of kinin effects in the kidney. The prostaglandin G2/H2 synthase (cyclooxygenase, COX) is the key regulatory enzyme of prostanoid synthesis pathway. Two COX isoenzymes (constitutive or COX-1 and inducible or COX-2) have been described in the rat kidney. We have demonstrated the presence of COX-2 in a subset of thick ascending limb of Henle (TAL) cells in normal adult rats [Vio, C.P., Cespedes, C., Gallardo, P., Masferrer, J.L., 1997. Renal identification of cyclooxygenase-2 in a subset of thick ascending limb cells. Hypertension 30, 687-692]. The present work was designed to evaluate COX-2 during the postnatal development of the rat kidney. Kidneys from Sprague-Dawley rats were studied during postnatal days 5, 10, 15 days and adult (60 days) (n = 8 each group). Renal tissue was immunostained with specific antibodies against COX-2. COX-2 was observed exclusively in TAL. A small number of COX-2 cells were observed during early postnatal life, increasing from day 5 to 15, and decreasing thereafter to reach adult levels. During maximal expression, near 20% of TAL were COX-2 positive whereas in early postnatal period and adults, only 2% of TAL cells contain COX-2. This transient induction of COX-2 during development suggest that the enzyme is necessary for the postnatal development of the kidney. This change in COX-2 seems to correspond to a derepression of COX-2 gene expression secondary to low levels of glucocorticoids.     

GABA and central neuropathic pain following spinal cord injury

Spinal cord injury induces maladaptive synaptic transmission in the somatosensory system that results in chronic central neuropathic pain. Recent literature suggests that glial-neuronal interactions are important modulators in synaptic transmission following spinal cord injury. Neuronal hyperexcitability is one of the predominant phenomenon caused by maladaptive synaptic transmission via altered glial-neuronal interactions after spinal cord injury. In the somatosensory system, spinal inhibitory neurons counter balance the enhanced synaptic transmission from peripheral input. For a decade, the literature suggests that hypofunction of GABAergic inhibitory tone is an important factor in the enhanced synaptic transmission that often results in neuronal hyperexcitability in dorsal horn neurons following spinal cord injury. Neurons and glial cells synergistically control intracellular chloride ion gradients via modulation of chloride transporters, extracellular glutamate and GABA concentrations via uptake mechanisms. Thus, the intracellular “GABA-glutamate-glutamine cycle” is maintained for normal physiological homeostasis. However, hyperexcitable neurons and glial activation after spinal cord injury disrupts the balance of chloride ions, glutamate and GABA distribution in the spinal dorsal horn and results in chronic neuropathic pain. In this review, we address spinal cord injury induced mechanisms in hypofunction of GABAergic tone that results in chronic central neuropathic pain.This article is part of a Special Issue entitled ‘Synaptic Plasticity & Interneurons’.     

Adrenergic receptors in rat spinal cord

Radioligand binding assays were used to demonstrate the presence of alpha 1, alpha 2 and beta receptors in rat spinal cord. Specific and saturable binding was exhibited for [3H]-WB 4101 (alpha 1), [3H]-aminoclonidine (alpha 2) and [3H]-dihydroalprenolol (beta). Binding was of high affinity and the total number of binding sites (Bmax) were: alpha 1, 66.5 +/- 1.0 fmol/mg protein; alpha 2, 20.0 +/- 0.6 fmol/mg protein; beta, 10.2 +/- 0.3 fmol/mg protein. The data confirms the existence of adrenergic receptors in spinal cord and provides further evidence of the role of catecholaminergic neurons in regulating spinal cord physiology.     

Adrenergic receptors in rat spinal cord

Radioligand binding assays were used to demonstrate the presence of alpha 1, alpha 2 and beta receptors in rat spinal cord. Specific and saturable binding was exhibited for [3H]-WB 4101 (alpha 1), [3H]-aminoclonidine (alpha 2) and [3H]-dihydroalprenolol (beta). Binding was of high affinity and the total number of binding sites (Bmax) were: alpha 1, 66.5 +/- 1.0 fmol/mg protein; alpha 2, 20.0 +/- 0.6 fmol/mg protein; beta, 10.2 +/- 0.3 fmol/mg protein. The data confirms the existence of adrenergic receptors in spinal cord and provides further evidence of the role of catecholaminergic neurons in regulating spinal cord physiology     

银杏内酯B促进体外培养胚胎大鼠脊髓神经细胞生长发育的研究

目的探讨GB对体外培养的胚鼠脊髓神经元存活和生长发育的作用。方法胚胎大鼠脊髓神经细胞原代培养,相差显微镜下进行细胞计数和显微测量,观察GB对神经元存活和生长发育的作用。对培养7d细胞行NSE免疫组化染色,光镜下观察GB对NSE染色阳性神经元生长发育的影响。结果GB及NGF能够促进体外培养胚胎大鼠脊髓神经细胞及NSE染色阳性神经元的存活,促进其细胞及突起的生长。其促进脊髓神经细胞的存活、胞体及突起发育的作用与NGF一致,而其促进神经突起分化与生长的作用强于NGF。结论NGF和GB能促进培养大鼠发育期脊髓神经元存活、分化和生长,并且表现出各自作用的特异性。     

Sympathoinhibitory action of nociceptin in the rat spinal cord

1. Whole-cell patch recordings were made from antidromically identified sympathetic preganglionic neurons (SPN) of immature rat spinal cord slices. Bath application of nociceptin (0.1-1 micromol/L) suppressed excitatory postsynaptic potentials (EPSP) and hyperpolarized a population of SPN; these effects were naloxone (1 micromol/L) insensitive. 2. Nociceptin suppressed the amplitude of EPSP without causing a concomitant change in glutamate-induced depolarizations, suggesting a presynaptic inhibitory action. 3. Analysis of current-voltage relationships showed that nociceptin hyperpolarized SPN by increasing an inwardly rectifying K+ current. 4. Intrathecal injection of nociceptin (3, 10 and 30 nmol) to urethane-anaesthetized rats dose-dependently reduced the mean arterial pressure and heart rate; these effects were not prevented by prior intravenous injection of naloxone (1 mg/kg). 5. Results from our in vitro and in vivo experiments suggest that nociceptin suppresses spinal sympathetic outflow either by attenuating excitatory synaptic responses or hyperpolarizing SPN.     

大鼠脊髓损伤后NEK6表达的实验研究

目的 探讨大鼠急性脊髓损伤后脊髓组织中NEK6的表达变化及意义.方法 采用改良Allen's打击法,构建大鼠脊髓T8-T10撞击伤模型,利用蛋白免疫印迹、免疫荧光双标的方法,研究大鼠脊髓损伤后脊髓组织中NEK6表达的时间和空间分布特征.结果 脊髓损伤后NEK6表达于撞击后2h有轻微抬高趋势,损伤后8h达到高峰,随后逐渐...     

Postnatal development of dopamine deamination in the striatum of the rat.

In the striata of litter-mate rats the development of the monoamine oxidase (MAO) activity towards dopamine in vitro followed a similar time course with age as the tissue concentrations of homovanillic acid and dihydroxphenylacetic acid, the two acid metabolites of dopamine formed by the action of MAO.     

The role of GABA and glycine in the physostigmine-induced alterations of spinal cord reflexes.

The purpose of this study was to determine which inhibitory pathway(s) mediate the alterations in the monosynaptic (MSR) and polysynaptic (PSR) reflexes after two different doses of physostigmine. It was found previously that 0.8 mg/kg physostigmine facilitated the MSR and 2.0 mg/kg initially depressed and then facilitated the MSR. Both doses facilitated the PSR. In this study, the animals were pretreated with either strychnine (0.1 mg/kg) or bicuculline (0.5 mg/kg), prior to the administration of either dose of physostigmine. It was found that both strychnine and bicuculline blocked the facilitation produced by the small dose of physostigmine, while bicuculline alone blocked the depression of the MSR produced by the large dose of physostigmine. Strychnine partially blocked the effects of both doses of physostigmine on the PSR, while bicuculline only partially blocked the effects of the small dose of physostigmine. These data suggest that the depression of the MSR was the result of a GABA-mediated pathway, while the facilitation of MSR involved both glycine and GABA.     

Dissociation between amino-oxyacetic acid-induced depression of spinal reflexes and the rise in cord GABA levels

Amino-oxyacetic acid (AOAA, 15–60 mg/kg produced a slow, dose-dependent depression of all segmentally evoked dorsal and ventral root activity in acute spinal cats. Amino-oxyacetic acid also increased cord gamma-aminobutyric acid (GABA) levels over a similar time course. However, several findings indicate that no causal relationship exists between these two observations. Small doses of AOAA (15 mg/kg) failed to induce depressant actions on spinal reflexes, although they more than doubled cord GABA levels. When 30 mg/kg of AOAA was administered to cats in which GABA synthesis was inhibited by semicarbazideS pretreatment, only a slight increase in cord GABA levels occurred, hut the monosynaptic and polysynaptic reflexes were depressed at the same rate as in unpretreated animals. Though GABA probably serves as a transmitter in pathways mediating primary afferent depolarization, AOAA did not selectively depress presynaptic inhibition. It also failed to augment the dorsal root reflex, an action which would signal an increase in primary afferent depolarization. It is thus concluded that the depressant actions of AOAA on spinal reflexes are not mediated by GABA, and that GABA accumulating in the spinal cord after AOAA administration fails to gain access to GABA receptors.