Actions of mu, delta and kappa opioid agonists and antagonists on mouse primary afferent neurons in culture.

The effects of selective mu, delta and kappa opioid agonists and antagonists were studied on somatic calcium-dependent action potentials recorded from mouse dorsal root ganglion (DRG) neurons grown in dissociated cell culture. The mu selective agonist, PL 017, and the delta selective agonist, [D-Pen2, L-Pen5] enkephalin (DPLPE), reduced action potential duration of a subpopulation (21/56) of DRG neurons. Leucine-enkephalin reduced action potential duration of all neurons sensitive to PL 017 or DPLPE, whereas 85% of neurons responding to leucine-enkephalin responded to either PL 017 or DPLPE. Only 15% of neurons responded to both PL 017 and DPLPE. There was no significant difference in the response to PL 017 or DPLPE when compared to leucine-enkephalin. In another experiment, the kappa selective agonist dynorphin A (DYN A), PL 017 and DPLPE reduced action potential duration of a subpopulation (15/67) of DRG neurons. There was a heterogeneous response among neurons to PL 017, DPLPE and DYN A inasmuch as 21.4% of neurons responded to all three agonists, 35.7% responded to PL 017 and DYN A, 35.7% responded only to PL 017 and 7.1% responded only to DYN A. Responses to the mu selective agonist PL 017 were antagonized by the reversible opioid antagonist naloxone and the selective mu antagonist SMS 201-995 in a concentration-dependent fashion. Responses to PL 017 were not altered by the selective delta antagonist ICI 174864. Responses to PL 017 were reduced by the irreversible, selective mu antagonists beta-funaltrexamine and naloxonazine in a concentration-dependent fashion.(ABSTRACT TRUNCATED AT 250 WORDS)

Activators of adenylate cyclase and cyclic AMP prolong calcium-dependent action potentials of mouse sensory neurons in culture by reducing a voltage-dependent potassium conductance.

The effects of compounds that activate adenylate cyclase and of cAMP on calcium-dependent action potentials recorded from mouse dorsal root ganglion neurons were assessed. Application of compounds that stimulate the adenylate cyclase system (forskolin, cholera toxin, and prostaglandin E1) increased action potential duration with an associated decrease in afterhyperpolarization. An adenylate cyclase inhibitor, 2',5'-dideoxyadenosine, partially inhibited the responses to forskolin and cholera toxin. cAMP analogs mimicked the effect of forskolin, and the phosphodiesterase inhibitor theophylline enhanced the response to forskolin. Following intracellular injection of the potassium channel blocker cesium, the forskolin response was reduced. Forskolin did not significantly alter resting membrane potential or conductance. The action potential responses to forskolin were voltage dependent, being reduced when the membrane was held at less negative (less than -50 mV) potentials. The data suggest that activators of adenylate cyclase and cAMP prolong calcium-dependent action potentials by blocking a voltage-dependent potassium conductance that is responsible, in part, for action potential repolarization and that inactivates at membrane potentials less negative than -50 mV.

Forskolin and phorbol esters reduce the same potassium conductance of mouse neurons in culture.

Second messenger systems may modulate neuronal activity through protein phosphorylation. However, interactions between two major second messenger pathways, the cyclic AMP and phosphatidylinositol systems, are not well understood. The effects of activators of cyclic AMP-dependent protein kinase and protein kinase C on resting membrane properties, action potentials, and currents recorded from mouse dorsal root ganglion neurons and cerebral hemisphere neurons grown in primary dissociated cell culture were investigated. Neither forskolin (FOR) nor phorbol 12,13-dibutyrate (PDBu) altered resting membrane properties but both increased the duration of calcium-dependent action potentials in both central and peripheral neurons. By means of the single-electrode voltage clamp technique, FOR and PDBu were shown to decrease the same voltage-dependent potassium conductance. This suggests that two independent second messenger systems may affect the same potassium conductance.

Modification of cardiac activity in response to dehydration in the terrestrial slug, Limax maximus.

The level of body hydration in the terrestrial slug Limax maximus modifies several aspects of behavior such as pneumostome activity, feeding responsiveness, huddling, and contact-rehydration. The relationship between water balance and pneumostome activity and respiratory function suggested that cardiac activity might also be affected. To pursue this possibility, intact slugs and isolated heart-central nervous system (CNS) preparations were used to investigate cardiac responses to the increase in hemolymph osmolality which occurs during dehydration. In intact animals, heart rate increased in response to progressive air-dehydration and to increases in hemolymph osmolality resulting from injections of hyperosmotic solutions of mannitol or NaCl. In isolated preparations, the heart or CNS were separately exposed to hyperosmotic saline. Exposure of the heart alone to hyperosmotic saline resulted in decreased heart rate while exposure of only the CNS resulted in an increase in heart rate. These observations suggest that the increase in heart rate that is observed in intact air-dehydrated slugs is primarily mediated by the CNS.

Culturing spinal cord explants in a collagen gel.

A new method for culturing spinal cord slices or explants is presented which entails the use of a commercially available purified collagen, Vitrogen. Vitrogen provides a stable three-dimensional matrix for culturing spinal cord explants which is superior to the conventional method of applying explants to moist dishes coated with rat tail collagen. The use of Vitrogen facilitated the culturing of spinal cord explants which remain viable for over 2 1/2 weeks in culture, in addition to enhancing neuritic growth.

Effects of temperature on the endogenous activity and synaptic interactions of the salivary burster neurones in the terrestrial slug Limax maximus.

(1) The activity of the endogenously active salivary burster neurones (SBs) shows temperature acclimation and has characteristic cold and warm blockade temperatures. (2) Temperature acclimation affects the upper and lower limits of the temperature range over which SBs are active. The absolute range, in centigrade degrees, during warming, is unaffected by acclimation. (3) Acclimatization of burster activity is a slow response to the mean ambient temperature. (4) There is increased synchrony of activity between the right and left salivary bursters at low temperature which is correlated with an increased electrical coupling between the SBs and protractor motoneurones (B7s). There is a corresponding increase in the input resistance of B7 at low temperatures.