Behavioral effects of THC as a function of environment and prior drug experience

Holtzman albino rats were divided into 4 groups, and on 5 consecutive days each group was exposed to one of 4 conditions. The drug-adapted group was given delta-9-tetrahydrocannabinol (THC) (0.0, 0.5, 2.5 or 5.0 mg/kg PO) in their home cages, while the environment-adapted group was given vehicle and placed for one hr in the chamber where they were later tested. The naive group was given vehicle in their home cages and the drug + environment adapted group was given THC and placed in the test chamber. One week later, all rats were given either 0.0, 0.5, 2.5, or 5.0 mg/kg THC and placed in the test chamber where standing, sitting, and behavioral activity were measured. The results showed that the behavioral effects of THC are a function of environmental familiarity in rats who are drug naive but not in rats given prior exposure to THC.

Effects of delta-9-tetrahydrocannabinol, chlordiazepoxide (Librium), and their combination on pregnancy and offspring in mice [correction of rats]

Delta-9-tetrahydrocannabinol (THC), chlordiazepoxide hydrochloride (Librium) or a combination of these drugs, were administered to pregnant mice on gestation days 6 to parturition. Levels of THC in blood were dose-related and approximated levels attained in humans after smoking one to two marijuana cigarettes. Blood cannabinoid levels in mice were elevated by concurrent administration of chlordiazepoxide. Maternal weight gain was significantly reduced by THC but not by chlordiazepoxide. Neither drug affected implantations, but THC significantly increased resorptions. Both THC and chlordiazepoxide decreased fetal weight. There was no indication of synergism between the two drugs for any of the measures examined in this study.

Delta-9-tetrahydrocannabinol during pregnancy in the rat: I. Differential effects on maternal nutrition, embryotoxicity, and growth in the offspring

Either 15 or 50 mg/kg of delta-9-tetrahydrocannabinol (THC) in sesame oil was administered by gastric intubation to gravid rats during the last two weeks of gestation. A pair-fed control group was administered the vehicle alone and allowed to eat and drink only the amount consumed by the 50 mg/kg group on the same gestation days. A nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. Among the dams receiving 50 mg/kg of THC, food and water intake was initially reduced to 75-80% of nontreated controls but then recovered over 3-4 days to approximately a 15-20% reduction until term. Compared with the nontreated dams, both THC dose-level groups and pair-fed control dams gained significantly less body weight from conception to term. Offspring mortality did not differ between the nontreated and pair-fed controls but was significantly higher among both dose-level THC exposed groups. In addition, there was a dose-related increase in the sex-ratio of live male to female offspring as well as significant effects on rate of growth for both sexes. The results are discussed with respect to published animal and clinical studies of cannabinoid exposure during pregnancy.

Delta-9-tetrahydrocannabinol during pregnancy in the rat: II. Effects on ontogeny of locomotor activity and nipple attachment in the offspring

Either 15 or 50 mg/kg delta-9-tetrahydrocannabinol (THC) in sesame oil was administered by gastric intubation to gravid rats during the last two weeks of gestation. A pair-fed control group was administered the vehicle alone and allowed to eat and drink only the amount consumed by the 50 mg/kg group on the same gestation days. A nontreated control group was left undisturbed during pregnancy. All treated and control litters were fostered at birth to untreated dams. Intact litters from the two THC treated and the two control groups were tested at 3-day intervals from birth to 32 days of age for differences in locomotor activity. In addition, pups were tested for nipple attachment on days 2, 5, 8, 11, and 14 of age. There were no differences in locomotor activity among any of the groups although activity level varied during development. Pups from dams exposed to 50 mg/kg of THC, as well as the pair-fed controls, displayed significantly longer latencies to attach to a nipple. These results suggest that the impaired nipple attachment observed among the high-dose offspring was not a primary effect of THC, but rather was secondary to the significant reduction of food and water intake among the dams. The behavioral findings are discussed with respect to other animal and clinical reports of prenatal cannabinoid exposure.

Effects of delta 9-THC, the principal psychoactive component of marijuana, during pregnancy in the rhesus monkey

The effect of delta 9-tetrahydrocannabinol (THC), the principal psychoactive component in marijuana, was studied in pregnant and lactating rhesus monkeys. THC (2.5 mg/kg/d) or vehicle was administered during different periods of gestation, and effects on pregnancy outcome and hormone concentrations during pregnancy were studied. The most obvious effects were observed with administration early in pregnancy; three of five pregnancies aborted within days after the drug injections began, and one pregnancy resulted in a stillbirth at term. The three abortions were associated with a rapid decrease in chorionic gonadotropin and a subsequent fall in progesterone concentrations to nondetectable levels. In the two pregnancies that continued until term, estradiol concentrations were significantly higher than in vehicle control pregnancies. Daily THC administration during the middle or third portion of gestation resulted in lesser pregnancy loss (one premature birth and four live births at term with THC treatment during the middle portion; two premature births and three live births at term with THC treatment during the third portion). All the premature infants died within two weeks of birth. The weights of the infants at birth and weaning were not significantly different for the infants from vehicle control pregnancies and for full-term infants exposed to THC during gestation. Also, no effects on intrauterine growth and development were detected with ultrasound in the drug-treated pregnancies. With acute administration, THC readily crossed the placenta at term in rhesus monkeys and was transferred into the milk of nursing mothers. Significant blood levels of THC and depressant effects were observed in both mothers and neonates when the drug was administered to the mothers one hour before birth or during lactation.

Increased marihuana-induced fetotoxicity by a low dose of concomitant alcohol administration

Many pregnant women use both alcohol and marihuana. To evaluate the effects of this combination on fetotoxicity, pregnant mice in the experimental group were injected with a relatively low dose of alcohol (1 g/kg) and with one of two doses of marihuana extract (equivalent of 50 or 100 g/kg delta 9-THC). Control mice received marihuana extract or alcohol alone. The combination of alcohol and the high dose of marihuana produced a greater effect on fetotoxicity (83%) than either marihuana or alcohol alone or that due to the additive effects of either of these substances (63%). The combination of alcohol and the lower dose of marihuana extract did not increase fetotoxicity significantly. Doses of alcohol that are otherwise without effect on pregnancy may thus have the potential for greatly increasing the effects of drugs on pregnancy outcome.

Maternal cannabinoid exposure. Effects on spermatogenesis in male offspring

Maternal exposure to cannabinoids influenced spermatogenesis and fertility in their male offspring examined at 60-80 days of age. Approximately 20% less spermatozoa were found in males whose mothers had received either the non-psychoactive cannabinol (CBN) or cannabidiol (CBD) on day 1 postpartum. Males exposed to the major psychoactive component of marihuana, delta 9-tetrahydrocannabinol (THC) appeared to have spermatozoa in number comparable to controls. This finding may be consistent with the additional observation that CBN or CBD, but not THC, reduced the percentage of successful impregnations by cannabinoid-exposed males. However, males exposed to each of these cannabinoids produced significantly less live offspring compared to controls. Plasma levels of testosterone and luteinizing hormone (LH) were reduced significantly in mice exposed to THC on day 12 of gestation, while testicular weight was reduced in adult mice exposed either on day 12 of gestation to CBD or on day 1 post-partum to THC. These results indicate that perinatal exposure to psychoactive and non-psychoactive components of marihuana can produce long-term disruption of testicular function including the spermatogenic as well as the steroidogenic components.

Marijuana smoking--possible cause of head and neck carcinoma in young patients

Six cases of advanced head and neck cancer in young patients, who were regular marijuana users, are presented. Numerous carcinogens, as well as respiratory irritants, are found in marijuana smoke. The active euphoria-producing agent, delta-9 tetrahydrocanabinol, has been implicated in altered DNA, RNA, and protein synthesis and consequent chromosomal aberrations.

Perinatal cannabinoid exposure: effects on hepatic cytochrome P-450 and plasma protein levels in male mice

Maternal exposure to the major psychoactive delta 9-tetrahydrocannabinol (THC), or to the nonpsychoactive cannabinol (CBN) or cannabidiol (CBD) on day 12 of gestation, or on day 1 postpartum, affected the concentrations of hepatic cytochromes P-450 in adult male offspring. Levels of P-450 were significantly increased in adult males prenatally exposed to cannabinoids, but were reduced after postnatal exposure. The response to exogenous testosterone was also differentially affected by perinatal cannabinoid exposure, with reduced plasma androgen in males prenatally exposed to THC, but increased levels of hormone in mice exposed postnatally to THC or CBN. There was a concomitant decrease in plasma albumin and increased gamma-globulin in adult males postnatally exposed to CBN. Beta-globulin levels were also significantly increased in adult males exposed to cannabichromene (CBC) on day 1 postpartum. Cannabinoid exposure during perinatal periods of development exert effects on hepatic function, plasma androgen levels, and on the immune system. These effects may reflect the ability of perinatal cannabinoid exposure to interfere with androgen-mediated processes of differentiation.

Delta 9-tetrahydrocannabinol decreases alpha/beta interferon response to herpes simplex virus type 2 in the B6C3F1 mouse

This study was undertaken to determine the effect of delta 9-tetrahydrocannabinol (delta 9-THC) on polyinosinic:polycytidylic acid [poly(I):poly(C)]-induced, and on herpes simplex virus type 2 (HSV-2)-induced, alpha/beta interferon in the B6C3F1 mouse. Animals were administered delta 9-THC, or the diluent, intraperitoneally for 4 consecutive days or at various time intervals prior to administration of the interferon inducer. Poly(I):poly(C) or HSV-2 was injected intravenously on Day 4. Animals receiving poly(I):poly(C) and treated with delta 9-THC at doses ranging from 5 to 100 mg/kg exhibited significantly lower titers of interferon than mice given poly(I):poly(C) and the diluent. Diminished interferon titers occurred in HSV-2-infected animals treated with delta 9-THC in doses exceeding 15 mg/kg when compared to virus-infected animals given the diluent. This suppression of early interferon persisted through 24 hr.

The effect of intragastric administration of delta 9-tetrahydrocannabinol on the growth and development of fetal mice of the A/J strain

Pregnant A/J mice were intubated with vehicle (sesame oil:Tween 80:water) or 60, 120, or 240 mg/kg of delta 9-tetrahydrocannabinol on Days 11 and 12, 12 and 13, or 13 and 14 (vehicle and 240 mg doses only) of gestation. Mice were killed on Day 20 of gestation, and examined for number of corpora lutea and live and resorbed fetuses. Fetuses were weighed and examined for gross external and internal malformations. Each treatment group consisted of a minimum of 10 litters with about 10 pups per litter. In a few groups the effects of feed deprivation on Day 12 or of glucocorticoid administration on Days 12 and 13 (positive control) were assessed. Intubation with vehicle or delta 9-tetrahydrocannabinol, or feed deprivation did not affect number of live fetuses, incidence of resorption, fetal weights, or gross malformations other than cleft palate. Intubation of delta 9-tetrahydrocannabinol on gestational Days 12 and 13 or 13 and 14 increased the mean frequency of cleft palate formation. The increase was 2- to 2.5-fold at the 240-mg dose, being significant (p = 0.05) in the Days 12 and 13 group. Cortisone acetate and corticosterone injection induced both resorption and cleft palate formation. Other developmental or reproductive parameters were not influenced by delta 9-tetrahydrocannabinol treatment. We conclude that delta 9-tetrahydrocannabinol administered by gavage during Days 12 and 13 of gestation retards normal palatal development.

Effects of acute and subchronic delta 9-tetrahydrocannabinol administration on the plasma catecholamine, beta-endorphin, and corticosterone levels and splenic natural killer cell activity in rats

The effect of acute (1 day) or subchronic (25 days) treatment with delta 9-tetrahydrocannabinol (THC), the major psychoactive constituent of marihuana, on plasma norepinephrine (NE), epinephrine (E), corticosterone, beta-endorphin (beta-end), and splenic natural killer (NK) cell activity of the rat was studied. Groups of animals received subcutaneously, either THC in corn oil + saline (3 mg THC/kg); oil + saline; or THC + naloxone (2 mg naloxone/kg and 3 mg THC/kg). Acute injection of THC with or without naloxone did not significantly change plasma levels of NE, E corticosterone, beta-end, or the NK cell activity. However, subchronic treatment with THC significantly reduced plasma levels of NE, E, corticosterone, and NK cell activity, compared to controls. The plasma beta-end levels were significantly elevated in the THC-treated animals. In the THC + naloxone group of animals, the plasma hormone levels (corticosterone and beta-end) were similar to control levels and the NK cell activity was significantly higher than in THC-treated animals. These results indicate that subchronic exposure to THC results in suppression of splenic NK cell activity. The interaction of THC with the endogenous opiate system appears to be a contributing factor leading to the NK cell suppression in rats. A direct suppressive action of THC or its metabolites on the NK cell is not ruled out by this study.

Intraocular pressure, ocular toxicity and neurotoxicity in response to 11-hydroxy-delta 9-tetrahydrocannabinol and 1-nantradol

Both acute and chronic effects on intraocular pressure of 11-hydroxy- delta 9-tetrahydrocannabinol (11-OH-delta 9-THC; a metabolite of delta 9-THC) and 1-nantradol (a synthetic cannabinoid) have been examined in the cat. Acute effects of these cannabinoids on ocular tension have also been determined in the monkey. Single dose effects of several other hydroxylated delta 9-THC metabolites have been evaluated in either the cat or the monkey. Results indicated that 11-OH-delta 9-THC and 1-nantradol produced similar acute effects in both species, with 1-nantradol significantly lowering intraocular pressure and 11-OH- delta 9-THC producing no change. Neither 11-OH- delta 9-THC nor 1-nantradol lowered ocular tension chronically when delivered for nine days to cats eyes via osmotic minipumps and connecting extraocular cannulas. Neither cannabinoid likewise produced ocular toxicity, although both produced neurotoxicity, as assessed by evaluation of electroencephalograms recorded from rats. Both 8-beta-OH- delta 9-THC and 8-beta-11-diOH- delta 9-THC were inactive with regard to acute effects on ocular tension. These results support previous findings suggesting that hydroxylation of the terpene portion of the delta 9-THC molecule significantly reduces intraocular pressure lowering activity. In addition, results from these and earlier studies suggest that structural requirements for tension lowering effects, ocular toxicity, and neurotoxicity, may well be distinctively different.

Long-term delta-9-tetrahydrocannabinol treatment. Computed tomography of the brains of rhesus monkeys

High-resolution computed tomographic (CT) scanning of the brain was performed on three groups of rhesus monkeys for the detection of ventricular or cisternal enlargement. These three groups comprised four age-matched controls that had no prior drug usage--four monkeys receiving short-term (two to ten months) orally administered delta-9-tetrahydrocannabinol (delta 9-THC [now known nonproprietarily as dronabinol] and four monkeys receiving long-term (five years) orally administered delta 9-THC. Our results show a statistically significant enlargement of the frontal horns and the bicaudate distance in the long-term group as compared with the control and less significant enlargement of these areas in the long-term group compared with the short-term group. These findings suggest atrophy of the head of the caudate nucleus and the frontal portion of the brain of rhesus monkeys receiving long-term treatment with delta 9-THC.

Pharmacological activity of the basic fraction of marihuana whole smoke condensate alone and in combination with delta-9-tetrahydrocannabinol in mice

This basic fraction (BF) of marihuana whole smoke condensate was subjected to pharmacological testing in males, Swiss-Webster mice. In a general pharmacological activity screen looking at behavioral, neurologic, and autonomic parameters, BF, at iv doses of 5, 10, and 20 mg/kg, caused impairment of visual placing, increase in tail pinch response, decrease in tail elevation, and induction of piloerection. These effects, although statistically significant, were slight and not consistently dose dependent. In a second study with doses ranging from 10 to 29 mg/kg, BF caused a decrease in spatial locomotion, rearing behavior, and urination incidence. In a third study, body temperatures of mice were measured periodically for 2 hr following administration of BF (1.2, 2.4, and 4.8 mg/kg) alone or in combination with 1.0 mg/kg delta-9-tetrahydrocannabinol (THC). BF did not alter body temperature, nor did it affect THC-induced hypothermia. These results, although suggesting that the basic fraction of marihuana whole smoke condensate has pharmacological activity in mice, offers little evidence for the presence of highly active compounds.

Early cannabinoid exposure influences neuroendocrine and reproductive functions in mice: II. Postnatal effects

Maternal exposure to delta 9-tetrahydrocannabinol (THC), the major psychoactive component in marihuana, or to the non-psychoactive cannabinol (CBN) or cannabidiol (CBD) alters male reproductive functions and brain biogenic amines in male and female offspring. Postnatal exposure to THC or CBN reduced body weights, while testicular weights were lower in CBD-exposed mice. Testicular testosterone (T) levels were also lower in CBN- and CBD-exposed animals. Postnatal cannabinoid exposure reduced plasma luteinizing hormone (LH) levels in intact and castrated adults. Although basal T production in vitro was not affected by postnatal cannabinoid exposure, testes from CBD-exposed males were more responsive to gonadotropin stimulation. In contrast, in vivo responsiveness to intratesticular human chorionic gonadotropin (hCG) administration was significantly reduced in THC- and CBD-exposed males. Pituitary weights and their basal LH production in vitro was higher in THC- or CBN-exposed mice. Pituitaries from cannabinoid-exposed males were less responsive to LH releasing hormone (RH) stimulation, however, hypothalamic LHRH content was significantly higher in the THC-exposed males. Hypothalamic dopamine (DA) levels were significantly lower in CBN-exposed castrated mice, compared to castrated controls. The reduction in hypothalmic norepinephrine (NE) in THC- and CBN-exposed castrates after alpha-methylparatyrosine (alpha-MPT) was significantly less than that observed in control castrates. Hypothalamic DA levels were depleted to a greater extent in CBD-exposed males. Brain levels of serotonin (5-HT) and 5-HIAA were significantly higher in castrated, than in intact THC-exposed males. In ovariectomized CBN-exposed females, hypothalamic NE levels were lower, while the alpha-MPT-induced depletion of NE was less in CBD-exposed, compared to control females. Levels of 5-HT were lower only in THC-exposed females. Plasma levels of LH were significantly higher in CBN-exposed, while plasma levels of FSH were reduced in THC- and CBD females. Maternal exposure to psychoactive or non-psychoactive cannabinoids on the day of parturition results in long term alterations in neuroendocrine function in male and female offspring. It is possible that the observed alterations in biogenic amines may mediate the effects of cannabinoids on pituitary and gonadal function.

Intraocular pressure, ocular toxicity and neurotoxicity after administration of delta 9-tetrahydrocannabinol or cannabichromene

delta-9-Tetrahydrocannabinol (delta 9-THC) or cannabichromene, a structurally diverse naturally occurring cannabinoid, was delivered unilaterally to the corneas of cats either acutely by application of single drops or chronically via osmotic minipumps over a period of nine days. While delta 9-THC only reduced intraocular pressure (IOP) minimally after acute administration, this cannabinoid produced substantial reductions in ocular tension during the entire period of chronic administration. Ocular toxicity during chronic treatment, however, was pronounced; conjunctival chemosis, erythema, and hyperemia were sustained, and corneal opacities approximating the site of drug delivery became evident within three to five days. In contrast, cannabichromene did not significantly alter IOP either acutely or during the nine days of chronic administration, and ocular toxicity was not apparent. After systemic administration of delta 9-THC to rats, a dose-related increase in the appearance of 8-13 Hz polyspike discharges became evident in the electrocorticogram during wakefulness and behavioral depression. These polyspikes subsequently reappeared during rapid eye movement (REM) sleep episodes. Cannabichromene was devoid of this effect. These results indicate that, in contrast with acute administration, chronic delivery of delta 9-THC to cat eyes produces substantial reductions in IOP. The tension lowering effect, however, is accompanied by considerable ocular toxicity and neurotoxicity. As cannabichromene lacked these activities, the terpenoid portion of the cannabinoid structure appears to be important for their mediation.

Early cannabinoid exposure influences neuroendocrine and reproductive functions in male mice: I. Prenatal exposure

Maternal exposure to delta 9-tetrahydrocannabinol (THC), the major psychoactive constituent in marihuana, or to the non-psychoactive cannabinol (CBN) or cannabidiol (CBD) alters endocrine functions and concentrations of brain biogenic amines in their male offspring. Prenatal CBN exposure on day 18 of gestation resulted in decreased plasma FSH levels, testicular testosterone (T) concentrations, and seminal vesicles weights, but increased plasma levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) post-castration in adulthood. Prenatal exposure to THC significantly enhanced the responsiveness of the testes to intratesticular LH injection in vivo and tended to increase human chorionic gonadotropin (hCG)-stimulated T production by decapsulated testes in vitro. In the CBN-exposed mice, hCG-stimulated T production was enhanced, while CBD exposure had no effect. Prenatal THC exposure altered the negative feedback effects of exogenous gonadal steroids in castrated adults, with lower plasma T and FSH levels after 20 micrograms T than in castrated controls. In contrast, CBD-exposed mice had higher levels of LH in plasma post-castration. In CBN-exposed adults, two weeks post-castration the concentration of norepinephrine (NE) and dopamine (DA) in hypothalamus and remaining brain were reduced, while levels of serotonin (5-HT) and its metabolite, 5-HIAA, were elevated compared to that in castrated OIL-controls. Prenatal CBD-exposure also reduced NE and elevated 5-HT and 5-HIAA, but did not affect DA levels post-castration. Concentrations of brain biogenic amines were not influenced by prenatal THC exposure in the present study. A single prenatal exposure to psychoactive or non-psychoactive components of marihuana results in long term alterations in the function of the hypothalamo-pituitary-gonadal axis. Changes in the concentrations of brain biogenic amines may be related to these effects of prenatal cannabinoids on endocrine function in adult male mice.

Effects of delta 9-THC on pregnancy and offspring in rats

Pregnant rats were intubated with increasing doses of delta 9-THC (5-50 mg/kg/day) up to gestation day 5. On gestation day 5, these animals continued to receive either 50 or 150 mg/kg/day of delta 9-THC. Animals receiving the 50 mg/kg/day dose and a control group of vehicle (olive oil) treated animals were pair-fed and pair- watered to animals given the 150 mg/kg/day dose. A second control group served as nontreated, ad lib control animals. Animals were tested postnatally for spontaneous alteration, avoidance learning and rotarod behavior to determine if delta 9-THC was behaviorally teratogenic. Drug treatments produced a dose-related decrease in pregnancies carried to term, weight gain during pregnancy, and birth weight. However, since no viable litters were born to animals in the high dose-group, their data was not included in statistical analyses. Nevertheless, the effects of drug treatment (50 mg/kg/day) were still statistically significant for weight gain during pregnancy and birth weight. Drug treatment (50 mg/kg/day) did not affect litter size or weight at 21 days of age, nor did it affect any of the behavioral tests.

Ocular hypotension, ocular toxicity, and neurotoxicity in response to marihuana extract and cannabidiol

Marihuana extract containing 21.3% delta-9-tetrahydrocannabinol (100 micrograms/hr), delta-9-tetrahydrocannabinol (20 micrograms/hr), cannabidiol (20 micrograms/hr), or the polyethylene glycol vehicle (1 microliter/hr) was delivered topically to cat eyes via osmotic minipumps over a 9-day period. Intraocular pressure differences between treated and untreated eyes of cats receiving marihuana extract remained 3-4 mmHg lower than those for vehicle controls, while differential values for the delta 9-THC-treated group remained reduced by 3-5 mmHg; data for these two groups did not differ statistically. Pressure differences between treated and untreated eyes of cats receiving cannabidiol were likewise 3-4 mmHg lower than values for controls. Ocular toxicity after delta 9-THC, consisting of conjunctival erythema and chemosis as well as corneal opacification, was quite severe. Although these changes also occurred after marihuana extract, their intensity was much reduced. In contrast, no ocular toxicity became apparent during administration of cannabidiol. While marihuana extract and delta 9-THC produced a dose-related increase in the appearance of 8-13 Hz polyspike discharges in the electrocorticograms of rats, both polyethylene glycol and cannabidiol lacked this effect. These results indicate that the ocular and central effects of marihuana extract and delta 9-THC are qualitatively similar. In addition, it appears that the ocular hypotensive effect produced by cannabidiol is relatively dissociable from both the ocular toxicity and the neurotoxicity associated with marihuana extract.

Effects of chronic administration of delta-9-tetrahydrocannabinol on early embryogenesis of the mouse

The effects of chronic administration of delta-9-tetrahydrocannabinol (THC), the major psychoactive component of marihuana, on embryogenesis were investigated in the mouse treated with THC prior to sexual maturation. The study was designed to imitate the prolonged abuse of marihuana by sexually immature and adolescent girls. Female Swiss-Webster mice were injected, intraperitoneally, with THC 5 mg/kg per day or with the vehicle for 21 consecutive days, starting on the 30th day of life, which is prior to their sexual maturation. The dose of THC was approximately equivalent to that absorbed by a man smoking 1 to 2 marihuana cigarettes per day. Superovulation was then induced, and the mice were mated with untreated males. Ova were recovered from the oviducts just prior to the first cleavage division, and at about the time of the second cleavage division. The incidence of degenerative ova increased from 13.6% in the controls to 19.1% in the THC-treated group (P less than 0.001) at the time of the second cleavage division, but there was no difference in the incidence of morphologically abnormal ova between the two groups just prior to the first cleavage division. The rate of successful completion of the first cleavage division, but not the second cleavage division, was adversely affected by THC, resulting in accumulation of morphologically abnormal ova at the later stage. In view of the known disruptive effect of THC on the process of cell division, it was postulated that THC might have adversely affected meiosis, leading to the inability of the ova to undergo the first cleavage division.