The effects of baclofen on calcium channel currents in dorsal sensory cells of the spinal cord in the lamprey

Abstract

Dorsal sensory cells isolated from the spinal cord of the lamprey species Ichthyomyzon unicuspis and Lampetra fluviatilis were used for whole-cell patch-clamp studies of the effects of baclofen on calcium channel currents, evoked in conditions in which Na+, K+ currents were blocked, by depolarizing membranes from constant holding potentials of -100 or -80 mV to +30 mV. Ba ions were used as carriers of currents through calcium channels. These studies demonstrated that baclofen (0.5 mM) decreased the peak amplitude of the Ba2+ current by an average of 22.5 +/- 4.2% (n = 12) in dorsal sensory cells of the lamprey Ichthyomyzon unicuspis and by 28.4 +/- 3.3% in the dorsal sensory cells of Lampetra fluviatilis (n = 25). The conductivity of dorsal sensory cell membranes in the presence of baclofen (and GABA) did not change. The blocking action of baclofen persisted in the presence of bicuculline (100 microM) and was lifted by addition of delta-aminovaleric acid and 2-hydroxysaclofen to the perfusing solution. These results are interpreted as evidence for the presence of GABAB receptors in dorsal sensory cell membranes. The data were compared with published results, and the question of the functional significance of GABAB receptors in the dorsal sensory cells (primary afferent cells) of cyclostomata is discussed.

GABA promotes survival and axonal regeneration in identifiable descending neurons after spinal cord injury in larval lampreys

“…The drugs were applied in the water where the animals were left after the SCI surgical procedures (GABA at a concentration of 500 µM, GABOB at a concentration of 50 µM and baclofen at a concentration of 125 µM). These concentrations were based on previous electrophysiological studies in lampreys (Batueva et al, 1999;Bussières and El Manira, 1999;Grillner, 1999, 2000).…”

Calcium currents and GABAB receptors in the dorsal sensory cells of the lamprey spinal cord

“…the chloride current was not activated [2]. The absence of changes in membrane permeability in response to application of GABA and glycine to lamprey dorsal sensory cells has previously been demonstrated by Homma and Rovainen [34].…”

“…Despite this very important role, the properties of Ca 2+ channels in lamprey dorsal sensory cells have thus far received little study. The membranes of these cells are known to contain two types of Ca 2 § channel, low-threshold and highthreshold [19], and data have also been obtained indicating that the Ca 2+ current in dorsal sensory cells depends not only on the membrane potential, but can also be modulated by neurotransmitters such as GABA [1,40] and dopamine [37]. These substances decrease the Ca 2+ influx current, which may reduce the quantity of mediator released.…”