Changes in CNS responsiveness during hibernation

The ability of the midbrain reticular formation (MRF) to produce thermogenic responses and to trigger arousal from hibernation was tested during successive quarters of individual hibernation bouts. Golden-mantled ground squirrels (Citellus lateralis) were implanted with bilateral cannula guides into the MRF. Single, bilateral, 1-mul injections of acetylcholine (ACh) at concentrations of 50, 100, or 200 mug/mul were delivered in each quarter of the same bout or in selected quarters of different bouts. The results show that the magnitude of thermogenic responses evoked by ACh stimulation of the MRF was depressed during the early portion of the bout and increased as time in the bout elapsed. Furthermore, the magnitude of responses evoked during hibernation was depressed in comparison to those evoked during euthermia, indicating the influence of inhibition on the responsiveness of the CNS during hibernation. We suggest that during hibernation, a progressive change in responsiveness of the CNS, perhpas focused in the MRF, controls the duration of each hibernation bout.

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Characterization of midbrain component of the trigger for arousal from hibernation

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1976.230.2.368 ◽

1976 ◽

Vol 230 (2) ◽

pp. 368-375 ◽

Cited By ~ 19

Author(s):

AL Beckman ◽

E Satinoff ◽

TL Stanton

Keyword(s):

Body Temperature ◽

Ambient Temperature ◽

Reticular Formation ◽

Functional Organization ◽

Ground Squirrels ◽

Anterior Hypothalamus ◽

Midbrain Reticular Formation ◽

Citellus Lateralis ◽

Arousal Mechanism

The ability of the midbrain reticular formation (MRF) to trigger arousal from hibernation and to change body temperature (Tb) during euthermia was tested in golden-mantled ground squirrels (Citellus lateralis). During hibernation (ambient temperature 5-6 degrees C) microinjections of cholinomimetic compounds (acetylcholine and carbachol) triggered full arousal or produced transient increases in Tb in 15 out of 19 tests; MRF microinjections of norepinephrine (NE) and 5-hydroxytryptamine (5-HT), at the same concentrations that produced full arousal when microinjected into the preoptic/anterior hypothalamus (PO/AH) area in previous experiments, has no effect on Tb in 13 out of 16 tests. In experiments on euthermic ground squirrels tested at an ambient temperature of 25 degrees C, MRF microinjections of acetylcholine raised Tb, whereas the monoamines had no significant effects. These results show that cholinoceptive neurons in the MRF can trigger arousal from hibernation and increase Tb during euthermia. The failure of NE and 5-HT to produce any significant effects at the same doses that were reported to be effective in the PO/AH indicates that the functional organization of the MRF portion of the arousal mechanism is different from that reported for the PO/AH.

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Evoked potentials in the hypothalamus

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1959.196.6.1163 ◽

1959 ◽

Vol 196 (6) ◽

pp. 1163-1167 ◽

Cited By ~ 47

Author(s):

Shaul Feldman ◽

Charles S. Van der Heide ◽

Robert W. Porter

Keyword(s):

Sciatic Nerve ◽

Evoked Potentials ◽

Reticular Formation ◽

Short Latency ◽

High Frequency Stimulation ◽

Midbrain Reticular Formation ◽

Long Latency ◽

Prolonged Recovery ◽

Frequency Stimulation ◽

Stimulation Of

The distribution and some properties of the evoked potentials in the hypothalamus from stimulation of the sciatic nerve were investigated in 60 cats. In the posterior and lateral hypothalamus biphasic positive-negative responses of 7–10 msec. latency were found, while in the anterior and medial hypothalamus the stimuli evoked monophasic negative waves of 20–35 msec. latency. The threshold of activation of the hypothalamic potentials corresponded to the upper range of activation of group A fibers in the sciatic nerve. The hypothalamic evoked potentials had a very prolonged recovery time on double stimulation, were sensitive to pentobarbital even to a greater degree than the evoked potentials in the midbrain reticular formation, and were abolished by high frequency stimulation of the midbrain reticular formation. The long latency potentials in the hypothalamus were similar to those evoked in the midbrain reticular formation, while the short latency potentials had properties similar to those of the lemniscal potentials. This fact suggested that the short latency potentials signaled the arrival of impulses from lemniscal collaterals.

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