Effects of naloxone and morphine on cerebral ischemia in gerbils

The effects of naloxone on cerebral blood flow and cerebral function during relative cerebral ischemia

CBF and somatosensory evoked potentials (SEPs) were measured in a model of moderate cerebral ischemia in anesthetized spontaneously hypertensive rats. The rats were bled to reduce SEP amplitudes to about 50% of prebleeding control. The consequent blood pressure fall reduced CBF to 77% of control as measured by the laser-Doppler technique. Naloxone (5 mg kg-1 i.v. plus 25 mg kg-1 h-1 i.v. for 30 min) caused a significant increase in SEP amplitudes, while CBF did not change significantly. In addition, the latency of the first SEP component decreased toward prebleeding values. Heart rate (HR) decreased, but MABP was held constant by a pressure-regulating reservoir. In unbled rats, naloxone (5 mg kg-1 i.v.) caused a transient small increase in MABP and SEP amplitudes and decrease in HR. These results indicate that sensory input is regulated by opioid systems. Increased opioid activity may inhibit ascending sensory pathways during relative cerebral ischemia and thereby depress SEP responses. Thus, naloxone can release this inhibition and enhances SEP independently of CBF during relative cerebral ischemia. Similar mechanisms might explain the apparently beneficial effects of naloxone in some stroke models.

Levallorphan and dynorphin improve motor dysfunction in Mongolian gerbils with unilateral carotid occlusion: the first application of the inclined plane method in the experimental cerebral ischemia

Levallorphan and dynorphin were effective on the motor dysfunction in the gerbil model of unilateral cerebral ischemia. The effect of opioids, levallorphan (mixed agonist-antagonist), dynorphin (kappa-receptor agonist) and naloxone (mu-receptor antagonist), on neurological impairment was evaluated using the unilateral cerebral ischemia model of gerbil. Motor function was evaluated quantitatively by using the inclined plane method. Both levallorphan-treated group and dynorphin-treated group showed a significant improvement of the motor dysfunction compared with saline-control group. On the other hand, naloxone-treated group did not differ from saline-control group. The beneficial effect of these opioids on motor dysfunction might be mediated by the kappa-opioid receptor. This study also showed the potential usefulness of the inclined plane method for the investigation on the cerebral ischemia.

Endogenous opiates: 1986

This is the ninth installment of our annual review of research involving the endogenous opiate peptides. It is restricted to the non-analgesic and behavioral studies of the opiate peptides published in 1986. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic processes; mental illness; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; activity; sex, pregnancy, and development; and some other behaviors.