The effect of naloxone (N-allylnoroxymorphone), a narcotic antagonist, on the morphine blockade of ovulation was studied. Female rats were treated with morphine (50 mg/kg) at the critical period, resulting in ovulatory blockade. The administration of naloxone (0.5 mg/kg) effectively reversed the anti-ovulatory effect of morphine. The antagonist reversed the morphine effect when given 1 hour before (75% reversla), simultaneously (75% reversal), and up to 3 hours after morphine treatment (63% reversal). The number of ova shed per animal was not affected by naloxone treatment with or without morphine. When the blockade of ovulation occurred in animals treated with both naloxone and morphine, uterine distension was present in 85% of the animals on the day of estrus.

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Six hours after a single injection of lithium chloride (10 mequiv./kg), the concentration of myo-inositol in the cerebral cortex of the rat is reduced by 30% (Allison and Stewart, 1971). A similar decrease in myo-inositol concentration has been found in rat hypothalamus, hippocampus, caudate nucleus, and adrenal: however, the cerebellum is unaffected (Allison, itnprrblisli~d wsirlts). Under the same conditions, lithium chloride produces a 20-fold i n c w m e in the concentration of myo-inositol 1phosphate (MIP) in rat cerebral cortex . Atropine, an antimuscarinic agent, blocks both the lithium-induced fall in the level of myo-inositol and the increase in concentration of my-inositol I-phosphate Allsion et al., 1976). Furthermore, both the cholinesterase inhibitor physostigmine and the cholinomimetic pilocarpine produce a 1.8-2.8fold elevation in the M l P levels of rat cerebral cortex. We have, thus far, been unable to detect an effect of these cholinergic agents on myo-inositol levels (Allison, 1978).The ability of atropine to block the lithium effect on myo-inositol and M I P levels as well as the ability of cholinergic agents to produce a small increase in M l P levels suggests that the action of lithium may be mediated by cholinergic mechanisms. Indeed, Haas and Ryall (1977) have shown that lithium facilitates transmission when administered iontophoretically to cholinoceptive Renshaw cells and supraspinal neurons in several regions of brain. The role of lithium as a cholinergic agent has been challenged, however (e.g., Vizi, 1975).The possible mediation of the lithium effect through cholinergic mechanisms can be investigated by determining whether the lithium-induced decrease in myoinositol levels is localized in layers of the cerebral cortex known to contain cholinoceptive cells. Krnjevic and Phillis (1963) have shown in cats, rabbits, and monkeys that acetylcholine-sensitive cell bodies are found predominantly in the cerebral cortex layers lying between 0.8 and 1.3 mm below the surface and that few are found in more superficial layers. In addition to studying layers of the cerebral cortex we wished to examine cerebellar layers to determine if the apparent absence of a lithium-induced decrease in myo-inositol levels observed in whole cerebellum was due to the masking of a localized decrease by a larger mass of unreactive tissue. MATERIALS AND METHODS Treatment o f A n ima IsMale Sprague-Dawley rats (Harlan Industries, Indianapolis, Indiana) weighing 200 to 250 g were injected subcutaneously with 0.75 M-LiCI (10 meqikg). The rats were decapitated 6 h after treatment. Control groups either received 0.75 M-NaCI (10 meqikg) or were untreated. Preparcition of Tissue SamplesSamples of frontal cortex corresponding to the areas encompassed by the planes VI and ss (Sugita, 1917) were mounted on aluminum rods and frozen in Freon 12 cooled by liquid nitrogen within 120 sec of the time of decapitation. Cerebellar tissue was similarly prepared. Coronal serial sections, 10-pm thick, were cut in a cryostat at -15°C. E v ...

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