Tolerance of guinea pig hippocampal slice CA1 neurons to hyperthermia evaluated by orthodromic and antidromic responses

Abstract

The tolerance of electrical responses in the CA1 neurons of guinea pig hippocampal slices to elevated temperatures was studied by recording orthodromic and antidromic responses of the population spike (PS). Increasing the temperature of the perfusing medium from 30°C to 49°C resulted in a decreased amplitude of both the orthodromic and antidromic PS, the former disappearing at 42.0 ± 1.8°C and the latter at 46.2 ±1.3°C (n = 8 for both). When the temperature was increased to 44°C, maintained at this level for less than 27 min, then lowered to 30°C, both the orthodromic and antidromic PS recovered within 60 min. When the temperature was increased to 45–49°C, marked irreversible effects were seen with the orthodromic PS, recovery being dependent on the maximum temperature and duration of exposure, the change becoming irreversible after 13 min at 45°C, 6 min at 46°C, 4min at 47°C or 2.5 min at 48°C. In contrast, the antidromic PS, recorded simultaneously, recovered on lowering the temperature to 30°C in all cases tested, except when the temperature was increased to 46°C and maintained at this level for 25–27 min. These results indicate that, in CA1 neurons, temperatures above 44°C have more potent irreversible effects on synaptic transmission than on axonal or somal function.

Key Words:

• Hyperthermia
• synaptic transmission
• orthodromic and antidromic responses
• hippocampal slices