Mattson M P, Taylor-Hunter A, Kater S B
Department of Anatomy and Neurobiology, Colorado State University, Fort Collins 80523.
J Neurosci. 1988 May;8(5):1704-11. doi: 10.1523/JNEUROSCI.08-05-01704.1988.
In identified Helisoma neurons, intracellular calcium can regulate neurite elongation and growth cone motility. Neurotransmitters such as 5-HT suppress both neurite elongation and the filopodial and lamellipodial movements of growth cones by causing increases in intracellular calcium (Haydon et al., 1984; Cohan et al., 1987; Mattson and Kater, 1987). Since an additional second messenger, cyclic AMP (cAMP), is known to mediate many physiological effects of neurotransmitters, we tested (1) the possible involvement of cAMP in the regulation of neurite outgrowth from Helisoma buccal neurons and (2) calcium-cAMP interrelationships in the regulation of outgrowth. The cAMP-elevating agents forskolin (5 x 10(-6)-10(-4) M) and dibutyryl cAMP (dbcAMP; 5 x 10(-3)-10(-2) M) suppressed neurite elongation and growth cone movements in identified neurons B19 (5-HT sensitive) and B5 (5-HT insensitive); the suppression was reversible. Exposure of these particular identified neurons to the calcium channel blocker La3+ (10(-5) M) or a culture medium with reduced calcium prevented and reversed the suppressive effects of forskolin and dbcAMP. In order to determine if the results on neurons B5 and B19 were representative of all neurons or only a subset, we examined a larger population of neurons. Calcium ionophore A23187 suppressed outgrowth from all neurons in mass dissociate cultures of buccal neurons, while forskolin or dbcAMP plus IBMX suppressed outgrowth from only one-half of buccal neurons. Finally, we found that 2 subpopulations exist among the neurons whose outgrowth is suppressed by cAMP: One subpopulation requires calcium influx for cAMP to act, while the other does not. Thus, even within the relatively small population of neuronal types comprising the buccal ganglion of Helisoma, second messengers within different neurons can act and interact in different ways to regulate outgrowth.
在已识别的椎实螺神经元中，细胞内钙可调节神经突伸长和生长锥运动。5-羟色胺等神经递质通过引起细胞内钙增加，抑制神经突伸长以及生长锥的丝状伪足和片状伪足运动（海登等人，1984年；科汉等人，1987年；马特森和卡特，1987年）。由于另一种第二信使环磷酸腺苷（cAMP）已知可介导神经递质的许多生理效应，我们测试了（1）cAMP在调节椎实螺颊神经元神经突生长中的可能作用，以及（2）在生长调节中钙 - cAMP的相互关系。提高cAMP水平的试剂福斯可林（5×10⁻⁶ - 10⁻⁴ M）和二丁酰cAMP（dbcAMP；5×10⁻³ - 10⁻² M）抑制了已识别的B19神经元（对5-羟色胺敏感）和B5神经元（对5-羟色胺不敏感）的神经突伸长和生长锥运动；这种抑制是可逆的。将这些特定的已识别神经元暴露于钙通道阻滞剂La³⁺（10⁻⁵ M）或钙含量降低的培养基中，可预防并逆转福斯可林和dbcAMP的抑制作用。为了确定对B5和B19神经元的研究结果是代表所有神经元还是仅代表一个子集，我们检查了更多的神经元群体。钙离子载体A23187抑制了颊神经元大规模解离培养物中所有神经元的生长，而福斯可林或dbcAMP加异丁基甲基黄嘌呤仅抑制了一半颊神经元的生长。最后，我们发现，在其生长受到cAMP抑制的神经元中存在两个亚群：一个亚群需要钙内流才能使cAMP发挥作用，而另一个则不需要。因此，即使在构成椎实螺颊神经节的相对较少的神经元类型群体中，不同神经元内的第二信使也可以以不同方式起作用和相互作用来调节生长。
