Calcagnetti D J, Schechter M D
Department of Pharmacology, Northeastern Ohio Universities College of Medicine, Rootstown 44272-0095.
Brain Res Bull. 1994;35(1):37-40. doi: 10.1016/0361-9230(94)90213-5.
When a rat is returned to a context associated with mild electric foot shock (1 mA/0.75 s), the environmental cues elicit a species-specific defensive behavior termed freezing. Genetically divergent strains of rats given identical shock conditioning differ in the degree of freezing observed. The acquisition of freezing appears to be mediated, at least in part, by endogenous opioids since the duration that a rat spends freezing is increased by pretreatment prior to training with naltrexone (NTX), an opioid receptor antagonist. The objective of the present studies was to compare the shock-induced freezing and its enhancement with NTX in two unique strains of rats, viz., N/Nih and Fawn Hooded (FH), with that seen in the more commonly employed Sprague-Dawley strain (SPD). Age-matched female rats from these three strains were observed for freezing after shock conditioning. Separate groups of rats from each strain were treated with NTX (7.0 mg/kg) prior to shock. Vehicle (VEH; 0.9% saline)-treated SPD and N/Nih rats were observed freezing for approximately 30% of the testing duration, whereas FH rats froze for only 15% of the test duration. NTX-treated SPD and N/Nih rats displayed an equivalent 130% increase in freezing in comparison to their respective saline controls. Freezing in NTX treated FH rats did not differ from VEH. Collectively, these results suggest that the level of freezing and NTX enhancement of freezing in the N/Nih rat strain are equivalent to SPD. In comparison, FH rats show deficits in freezing and are insensitive to NTX enhancement of freezing.
当一只大鼠被放回与轻度足部电击（1毫安/0.75秒）相关的环境中时，环境线索会引发一种特定物种的防御行为，称为僵住不动。给予相同电击条件的基因不同品系的大鼠，所观察到的僵住不动程度有所不同。僵住不动行为的习得似乎至少部分是由内源性阿片类物质介导的，因为在用阿片受体拮抗剂纳曲酮（NTX）进行训练前预处理，会增加大鼠僵住不动的持续时间。本研究的目的是比较两种独特品系的大鼠，即N/Nih和小鹿帽鼠（FH），与更常用的斯普拉格-道利品系（SPD）在电击诱导的僵住不动及其经NTX增强方面的情况。对来自这三个品系的年龄匹配的雌性大鼠在电击条件反射后观察其僵住不动情况。来自每个品系的单独一组大鼠在电击前用NTX（7.0毫克/千克）处理。用赋形剂（VEH；0.9%生理盐水）处理的SPD和N/Nih大鼠在大约30%的测试时间内出现僵住不动，而FH大鼠仅在15%的测试时间内僵住不动。与各自的生理盐水对照组相比，经NTX处理的SPD和N/Nih大鼠的僵住不动增加了130%。经NTX处理的FH大鼠的僵住不动情况与用赋形剂处理的大鼠没有差异。总体而言，这些结果表明，N/Nih大鼠品系的僵住不动水平及其经NTX增强的僵住不动情况与SPD相当。相比之下，FH大鼠在僵住不动方面存在缺陷，并且对NTX增强僵住不动不敏感。
