lucifer-yellow and cytisine

1. Nicotinic responses and actions on excitatory synaptic activity were studied in eighty-four neurones in the region dorsal to the central canal (lamina X) in transverse thoracolumbar spinal cord slices of neonate (P2-P10) rats by using the whole-cell patch-clamp technique. 2. Neurones (n = 15) labelled with Lucifer Yellow, showed the typical morphology of sympathetic preganglionic neurones (SPNs) in the central autonomic area (CA). Unlabelled neurones of comparable morphology were visually identified and recorded. 3. All neurones recorded responded to the nicotinic acetylcholine receptor (nAChR) agonist, DMPP. Under current-clamp conditions, pressure ejections of DMPP depolarized cells and induced the discharge of action potentials. Tetrodotoxin suppressed action potentials but not DMPP-induced depolarization. 4. Under voltage-clamp conditions at a holding potential (Vh) of -50 mV, DMPP induced a transient inward current (which reversed around 0 mV) and an increase in membrane current noise in 50% of the recorded neurones. In the others, DMPP increased membrane current noise without measurable inward current. The current-voltage relationship showed strong inward rectification at holding potentials more positive than 0 mV. 5. In neurones displaying a detectable current response to DMPP, the following agonist rank order potency could be established: DMPP = nicotine > cytisine > ACh. The DMPP response could be blocked by mecamylamine but was insensitive to methyllycaconite. 6. Pressure application of glutamate induced inward currents in all cells tested at a Vh of -50 mV. This response reversed at 10 mV, displayed a region of negative slope conductance at Vh more negative than -30 mV and was partially blocked by CNQX. Pressure application of DMPP transiently increased the amplitude of the glutamate-induced current in six out of nine cells tested. This potentiation persisted in the presence of tetrodotoxin. 7. Forty per cent of the recorded neurones displayed spontaneous excitatory postsynaptic currents (sEPSCs). At a Vh of -50 mV the sEPSCs had a mean amplitude of -19.3 pA and occurred at a frequency below 0.5 Hz. sEPSCs were blocked by CNQX and inverted around 0 mV. Brief application of DMPP increased the discharge frequency of sEPSCs without affecting their kinetics. Additionally, in some cells DMPP increased mean sEPSC amplitude. 8. Focal electrically evoked EPSCs reversed close to 10 mV and were sensitive to CNQX. They occurred with a constant latency,

Topics: Acetylcholine; Alkaloids; Animals; Azocines; Cholinergic Agonists; Dimethylphenylpiperazinium Iodide; Evoked Potentials; Glutamic Acid; Isoquinolines; Mecamylamine; Neurons; Nicotine; Patch-Clamp Techniques; Quinolizines; Rats; Rats, Wistar; Receptors, Cholinergic; Spinal Cord; Synaptic Transmission; Tetrodotoxin