Figure 1.
MAC of isoflurane and desflurane.
Anesthetics were separately delivered to P7 rats in air and oxygen (FiO2 50%) as previously described6, 9. Tail-clamping occurred every 15 minutes, and anesthetic concentration was adjusted to 1 MAC. As before6, 9, MAC decreases with increasing duration of anesthesia for both agents.
Figure 2.
For each task, except allocentric object-place recognition, subjects are introduced at and facing the wall away from the objects. (A) Novel object recognition. Two identical objects are presented in the exposure, and one (right) is replaced with a novel object in the test phase. (B) Object-place recognition. Two different objects are presented, followed by two identical objects. In the test phase, the right object appears in a novel location within the context. (C) In the allocentric version of object-place recognition, subjects are again introduced at and facing the south wall (S) in the exposure. However, for the test phase, subjects are placed at and facing either the east (E) or west (W) wall. (D) Object-context recognition. Two different pairs of objects are presented in two different contexts, so each object is associated with a particular context. In the test phase, one object (right object, top row; left object, bottom row) appears within a context in which it has not been explored. (E) Object-place-context recognition. Two different objects are first presented in a context. The object locations are then reversed and presented in a different context. Thus, after two exposures, each object is seen in both contexts and both locations (left and right). In the test phase, two objects are presented in either context, so one (right object, top row; left object, bottom row) appears in a novel configuration of place and context.
Figure 3.
A to F) Exposure to either anesthetic – desflurane or isoflurane – led to significantly increased neuronal death in each brain region. The degree of neurodegeneration was similar in desflurane and isoflurane-treated subjects. Sample images from brains at 20X magnification are shown alongside graphs comparing total cell death for each structure. G) The average increases in neuronal death relative to controls are shown. *P<0.05.
Figure 4.
Novel object and object-place recognition.
A) Subjects all demonstrated successful object recognition and preferentially explored the novel object. B) Each group’s DI was significantly greater than zero, and there was no difference in DIs. C) Subjects were also able to identify an object in a novel location, demonstrated by a relative increase in investigation of that object. D) Again, DIs for all subjects were greater than zero with no differences identified. *P<0.05, **P<0.01, ***P<0.001, CON = control, DES = desflurane, ISO = isoflurane.
Figure 5.
Object-context and social recognition.
A) Isoflurane-treated animals were impaired in associating an object with a particular context. Animals exposed to desflurane, on the other hand, recognized when an object appeared in a different context and spent more time with that object. B) The DI for anesthetized subjects in this task did not differ from zero, and, within this group, only the desflurane DI significantly exceeded zero. C) Desflurane-treated subjects also had no change in social recognition ability, spending more time with the novel animal, while isoflurane-treated animals had deficient social memory. D) DI for both control and anesthetized animals exceeded zero, although DI for the subset of isoflurane-treated subjects did not. *P<0.05, **P<0.01, ***P<0.001, n.s. = not significant.
Figure 6.
Allocentric object-place and object-place-context recognition.
A) Exposure to isoflurane or desflurane led to impairment in identifying an object’s location when the site of entry into the context was changed. The varied entry points forced subjects to rely on allocentric cues to identify the object’s location. B) DI of control animals was significantly greater than that of anesthetized subjects. Neither desflurane nor isoflurane DI significantly exceeded zero. C) Isoflurane and desflurane-treated subjects were also impaired in recognition of an object that required association of its place and context. D) Again, control DI was greater than anesthetized DI. Neither subset of anesthetized subjects – desflurane or isoflurane – had DI greater than zero. *P<0.05, **P<0.01, n.s. = not significant.
Table 1.
Summary of behavioral testing.