1. Whole-cell patch recordings were made from substantia gelatinosa (SG) neurons in transverse lumbar spinal cord slices of 15- to 30-day-old rats. 2. Endomorphin 1 (EM-1) or EM-2 (≤ 10 μM) hyperpolarized or induced an outward current in 26 of the 66 SG neurons. The I-V relationship showed that the peptide activates an inwardly rectifying K + current. 3. EM-1 or EM-2 (0.3-10 μM) suppressed short-latency excitatory postsynaptic currents (EPSCs) and long-latency inhibitory postsynaptic currents (IPSCs) in nearly all SG neurons tested or short-latency IPSCs in six of the 10 SG neurons. [Met 5] enkephalin or [D-Ala 2, N-Me-Phe 4, Gly 5-ol]-enkephalin (DAMGO) (1-10 μM) depressed EPSCs and IPSCs. EM-1 or EM-2 depressed synaptic responses without causing a significant change in holding currents or inward currents induced by glutamate. 4. Glutamate also evoked a short-latency outward current in five SG neurons or a biphasic current in two neurons; the outward current was blocked by tetrodotoxin (TTX, 0.3 μM) or bicuculline (10 μM). EM-1 or DAMGO (1 or 5 μM) attenuated the glutamate-evoked outward or biphasic currents in four of the seven SG neurons. 5. EM-1 (1 μM) reduced the frequency, but not the amplitude of miniature EPSCs or miniature IPSCs. 6. Naloxone (1 μM) or the selective μ-opioid receptor antagonist β-funaltrexamine (β-FNA, 25 μM) antagonized the action of EM; EM-induced hyperpolarizations persisted in the presence of the κ-opioid receptor antagonist (nor-binaltorphimine dihydrochloride, 1 μM) and/or σ-opioid receptor antagonist (naltrindole hydrochloride, 1 μM). 7. It may be concluded that EM acting on μ-opioid receptors hyperpolarizes a population of SG neurons by activating an inwardly rectifying K + current, and attenuates excitatory and inhibitory synaptic currents evoked in a population of SG neurons, probably by a presynaptic site of action.
| Identifer | oai:union.ndltd.org:ETSU/oai:dc.etsu.edu:etsu-works-15187 |
| Date | 01 November 2003 |
| Creators | Wu, Su Ying, Ohtubo, Yoshitaka, Brailoiu, G. Cristina, Dun, Nae J. |
| Publisher | Digital Commons @ East Tennessee State University |
| Source Sets | East Tennessee State University |
| Detected Language | English |
| Type | text |
| Source | ETSU Faculty Works |
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