Electrophysiology of mammalian spinal cord in vitro

1 The monosynaptic reflex (MSR), recorded in vitro from the neonatal rat spinal cord, was depressed by 5-hydroxytryptamine (5-HT), 5-carboxamidotryptamine (5-CT), methysergide and R( + )-8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), and also by the selective 5-HTlD agonists, sumatriptan and N-methyl-3-(1-methyl-1-piperidinyl)-1H-indole-5-ethane sulphonamide (GR 85548).2 Ketanserin (1 gM) and methiothepin (1 gM) reduced the duration of depressions elicited by 5-CT, but not those produced by 5-HT, sumatriptan, GR 85548, methysergide or 8-OH-DPAT.3 The IC50 for MSR depression by 5-CT was 3.6, 2.1 -6.2nM (n=4), by sumatriptan was 15.2, 12.9-18.0nM (n=32), by GR 85548 was 18.4, 11.7-29.1 nM (n =12), by methysergide was 29.8, 10.2-87.1nM (n=4) and by 8-OH-DPAT was 0.21, 0.11-0.43 MM (n=3) (geometric means and 95% confidence limits). 4 Ketanserin (0.1 or 1 UM) antagonized competitively responses to sumatriptan (apparent pA2 7.8 ± 0.1, n = 5), GR 85548 (apparent pA2 7.6, unpaired data, n = 5), methysergide (apparent pA2 7.9 ± 0.12, n=4) and 8-OH-DPAT (apparent pA2 8.3 ± 0.1, n= 3). Concentration-response curves to 5-CT showed a smaller, parallel shift to the right (apparent pA2 6.8 ± 0.1, n = 4), but responses to 5-HT were unaffected by ketanserin (1 gM) (n = 4). Neither with these concentrations nor with concentrations in the range 1-3 nm was there any unequivocal blockade of responses to sumatriptan. 9 It is concluded that sumatriptan, GR 85548, methysergide and 8-OH-DPAT depress the MSR in the neonate rat spinal cord via ketanserin-sensitive receptors, which have some similarities to 5-HTLIT1 receptors but which are not blocked by GR 127935. 5-HT released by tryptaminergic pathways may act via the same receptors to depress the MSR. 5-HT applied to the cord probably acts via a different, possibly novel 5-HT receptor to depress the MSR.

Section: Introductionmentioning

confidence: 99%

Ketanserin‐sensitive depressant actions of 5‐HT receptor agonists in the neonatal rat spinal cord

Manuel¹,

Wallis²,

Crick³

1995

“…Electrical stimulation of the dorsal root of the neonatal rat hemisected spinal cord preparation evokes a ventral root potential (DR-VRP) in the corresponding ipsilateral ventral root (Otsuka & Konishi, 1974). There are several distinct components of the DR-VRP which can be measured over progressively longer time sweeps (Figure 1 (Akagi et al, 1985).…”

mentioning

confidence: 99%

“…Methods Spinal cords were prepared from neonatal SpragueDawley rats (aged between 3 and 6 days, 8-14 g body weight) as previously described (Otsuka & Konishi, 1974). The hemiAuthor for correspondence.…”

mentioning

confidence: 99%

Depression of glutamatergic transmission by nociceptin in the neonatal rat hemisected spinal cord preparation in vitro

Faber¹,

Chambers²,

Evans³

et al. 1996

104

The present study explored the action of nociceptin, the putative endogenous ligand for the orphan opioid receptor (ORLI), on the rat hemisected spinal cord preparation. Electrical stimulation of a dorsal root evokes a glutamatergic population ventral root potential (DR-VRP) in the corresponding ventral root. Low intensity stimulation evokes two A fibre-mediated components; a compound action potential of motonuerones superimposed on a population e.p.s.p. (excitatory postsynaptic potential); at higher stimulus intensities sufficient to activate C fibres a more prolonged population e.p.s.p. is evoked. All three components were depressed by nociceptin in a concentration-dependent manner with IC50 values (s.e.mean) of 119 + 2 nM (n = 4), 241 + 3 nM (n = 4) and 32 + 2 nM (n = 4), respectively. The depressant actions of nociceptin (30 nM and 300 nM) were not reversed by the opioid antagonist naloxone (1 gM).Nociceptin (100 nM and 300 nM) had no effect on the afferent volleys in the dorsal root. Nociceptin therefore appears to be acting as an inhibitory peptide at the spinal level through a naloxone-insensitive opioid receptor.

“…Isolated spinal cord preparation Under ether anaesthesia, the spinal cord below the middle thoracic level together with spinal nerve roots (L3 -L5) was isolated, hemisected, and placed in a recording chamber of 0.3 ml volume (Otsuka & Konishi, 1974). The chamber was perfused with artificial cerebrospinal fluid (CSF) at a rate of 2.5 ml min-'.…”

Section: Preparationsmentioning

confidence: 99%

Muscarinic excitatory and inhibitory mechanisms involved in afferent fibre‐evoked depolarization of motoneurones in the neonatal rat spinal cord

Kurihara

Suzuki

Yanagisawa

et al. 1993

1 The involvement of acetylcholine and muscarinic receptors in spinal synaptic responses evoked by electrical and noxious sensory stimuli was investigated in the neonatal rat spinal cord in vitro. 2 Potentials were recorded extracellularly from a ventral root (L3-L5) of the isolated spinal cord, spinal cord-cutaneous nerve, and spinal cord-skin preparations of 1-to 4-day-old rats. Spinal reflexes were elicited by electrical stimulation of the ipsilateral dorsal root or the cutaneous saphenous nerve, or by noxious skin stimulation.3 Single shock stimulation of supramaximum intensity of a dorsal root induced a mono-synaptic reflex in the corresponding ventral root. Bath-application of the muscarinic agonists, muscarine (0.3-30 9M) and (+ )-cis-dioxolane (0.1-100 9AM), produced an inhibition of the mono-synaptic reflex and a depolarization of motoneurones. Other muscarinic agonists, arecoline (10 nM-10 AM) and oxotremorine (1OnM-1 tM), inhibited the mono-synaptic reflex with little or no depolarization of motoneurones.Repetitive stimulation of the saphenous nerve at C-fibre strength induced a slow depolarizing response lasting about 30 s of the L3 ventral root. This slow ventral root potential (VRP) was also inhibited by arecoline (10 nM-1I0 AM) and oxotremorine (10 nM-1 9AM). 4 In the spinal cord-saphenous nerve-skin preparation, a slow VRP was evoked by application of capsaicin (0.5 9AM), bradykinin (3 9AM), or noxious heat (47°C) to skin. This slow VRP was depressed by the muscarinic agonists, arecoline (3 9AM) and oxotremorine (1 9AM). 5 Of the (+)-cis-dioxolane-induced inhibition of mono-synaptic reflex and motoneurone depolarization, the M2 antagonists, AF-DX 116 (0.1-1I9M) and methoctramine (100-300 nM), preferentially blocked the former response, whereas the M3 antagonists, 4-DAMP (3-10 nM) and p-F-HHSiD (0.3-3 AM), preferentially blocked the latter response. AF-DX 116 (0.1-1I9M) and methoctramine (100-300 nM) also effectively antagonized the arecoline-and oxotremorine-induced inhibition of the slow VRP. The pA2 values of AF-DX 116 and methoctramine against the arecoline-induced inhibition of the mono-synaptic reflex were both 6.79, and that of 4-DAMP against the (+)-cis-dioxolane-induced motoneurone depolarization was 8.16. 6 In the spinal cord-cutaneous nerve preparation, the saphenous nerve-evoked slow VRP was augmented by the anticholinesterase, edrophonium (5 9AM). (1 AM) and methoctramine (100 nM) also potentiated the slow VRP, whereas 4-DAMP (10 nM) depressed the response. 4-DAMP (5-10 nM) depressed the capsaicin-induced slow VRP in the spinal cord-skin preparation. 7 Oxotremorine (0.3 9lM) and arecoline (1 AM) markedly depressed the depolarization of motoneurones evoked by application of capsaicin (3 9AM) to the spinal cord, whereas they depressed only slightly the depolarization induced by substance P (10 nM). 8 The present study suggests that both excitatory (via M3-type receptors) and inhibitory (via M2-type receptors) muscarinic mechanisms are involved in afferent fibre-evoked nociceptive tr...