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Electrophysiological effects of FLFQPQRF amide, an endogenous brain morphine modulating peptide, on cultured mouse
A Guzman1, P Legendre, M Allard
1INSERM U.176, Université de Bordeaux II, France.
Abstract:
Intracellular recordings were made from dissociated fetal mouse spinal cord neurones in primary culture. Micropressure application of FLFQPQRFamide (10(-5) M in the delivery pipette), an endogenous mammalian brain morphine modulating peptide, onto the surface of spinal cord neurones induced, in a dose dependent manner, a transitory hyperpolarization followed by a long lasting depolarization of the membrane potential (n = 37). In contrast, no response was observed when the peptide was applied on dorsal root ganglia neurones (n = 30). The depolarizing phase of this response was underlied by an increase of the input resistance. Extrapolated reversal potential for the depolarizing phase was close to -80 mV while it was close to -40 mV for the hyperpolarizing phase. Increasing extracellular K+ concentration raised the reversal potential value of depolarizing phases to more positive values. The amplitude of the depolarizing phase was reduced by application of tetraethylammonium (50 mM) while it was enhanced by application of 4-aminopyridine (3 mM). CaCl2 application (3 mM) reversibly blocked the hyperpolarization and decreased the subsequent depolarization. In presence of Ba2+ the extrapollated reversal potential of the hyperpolarizing phase was dramatically shifted to a more positive value. Finally FLFQPQRFamide induced response can be partially mimicked by FMRFamide application. Our observations indicate that FLFQPQRFamide can have multiple effects on membrane conductance of mammalian spinal cord neurones by acting on a single class of receptor. These effects of FLFQPQRFamide were found to be mainly excitatory.
Insights
FLFQPQRFamide, a peptide modulating morphine, excites spinal cord neurons by altering membrane potential and conductance. This peptide selectively impacts spinal cord neurons, not sensory ganglia, suggesting specific receptor interactions.
Area of Science:
- Neuroscience
- Molecular Biology
- Pharmacology
Background:
- Endogenous peptides play crucial roles in modulating neuronal activity.
- FLFQPQRFamide is identified as a mammalian brain peptide that influences morphine.
- Understanding peptide-receptor interactions is key to deciphering neuronal signaling pathways.
Purpose of the Study:
- To investigate the electrophysiological effects of FLFQPQRFamide on mammalian spinal cord neurons.
- To determine the specific ion channel mechanisms underlying the peptide's action.
- To explore the selectivity of FLFQPQRFamide's effects on different neuronal populations.
Main Methods:
- Primary cell culture of fetal mouse spinal cord neurons and dorsal root ganglia neurons.
- Intracellular recordings to measure membrane potential and input resistance.
- Micropressure application of FLFQPQRFamide and other pharmacological agents (e.g., tetraethylammonium, 4-aminopyridine, CaCl2, Ba2+).
Main Results:
- FLFQPQRFamide induced a dose-dependent hyperpolarization followed by a long-lasting depolarization in spinal cord neurons.
- The peptide did not elicit a response in dorsal root ganglia neurons.
- The depolarization phase involved increased input resistance, with distinct reversal potentials for hyperpolarizing and depolarizing phases.
- Ion channel blockers and modulators affected the peptide-induced responses, indicating involvement of potassium and calcium channels.
- FLFQPQRFamide's effects were partially mimicked by FMRFamide.
Conclusions:
- FLFQPQRFamide exerts multiple effects on the membrane conductance of mammalian spinal cord neurons.
- These effects are mediated by a single class of receptors and are primarily excitatory.
- The findings highlight FLFQPQRFamide's role in modulating spinal cord neuronal excitability.