Brenda K. Colasanti

Intraocular pressure, ocular toxicity and neurotoxicity after administration of cannabinol or cannabigerol

Cannabinol or cannabigerol was administered to cats topically in doses of 250, 500 and 1000 micrograms as a single drop or chronically via osmotic minipumps (20 micrograms hr-1) over a period of 9 days. While cannabinol had a modest effect on intraocular pressure after a single dose, it caused a more significant reduction in ocular tension during chronic administration. Cannabigerol had similar effects, but the magnitude of response to its chronic administration was greater. Cannabinol but not cannabigerol caused conjunctival erythema and hyperemia. After systemic administration of cannabinol (20, 40 or 80 mg kg-1) to rats, 8-13 Hz polyspike discharges appeared in the electrocorticogram during wakefulness and during rapid eye movement sleep episodes. Cannabigerol (10, 30 and 100 mg kg-1) lacked this effect. These results indicate that chronic administration of these cannabinoids lowers ocular tension considerably. Like marihuana and delta-9-tetrahydrocannabinol, cannabinol produced both ocular toxicity and neurotoxicity. As cannabigerol lacked these toxicities, it appears that the ocular hypotensive effect of this cannabinoid is somewhat dissociable from both the adverse central and ocular effects accompanying marihuana intake.

Effects of marihuana cannabinoids on seizure activity in cobalt-epileptic rats.

Rats rendered chronically epileptic by bilateral implantation of cobalt into frontal cortices were simultaneously prepared with permanent electrodes for longitudinal recording of the electroencephalogram (EEG) and electromyogram (EMG). Delta-8-tetrahydrocannabinol (delta-8-THC; 10 mg/kg), delta-9-tetrahydrocannabinol (delta-9-THC; 10 mg/kg), cannabidiol (CBD; 60 mg/kg), or polyvinylpyrrolidone (PVP) vehicle (2 ml/kg) was administered IP twice daily from day 7 through 10 after cobalt implantation, at which time generalized seizure activity in non-treated cobalt-epileptic rats was maximal. Relative to PVP-treated controls, CBD did not alter the frequency of appearance of seizures during the course of repeated administration. In contrast, both delta-8-THC and delta-9-THC markedly reduced the incidence of seizures on the first and second days of administration. Interictal spiking during this period, on the other hand, was actually enhanced. On the third and fourth days, tolerance to the effect on seizures was evident, with a return of seizure frequency of THC-treated rats to values not significantly different from those of controls. Unlike the effect on seizures, no tolerance developed to the marked suppression of rapid eye movement (REM) sleep induces by delta-8-THC and delta-9-THC. REM sleep remained reduced in the treated animals during the first 2 days after termination of THC administration. In contrast, REM sleep time was unaffected by repeated administration of CBD. These results suggest that delta-8-THC and delta-9-THC exert their initial anticonvulsant effect by limiting the spread of epileptogenic activity originating from the cobalt focus.

Electrocorticogram and behavioral correlates during the development of chronic cobalt experimental epilepsy in the rat.

The ECoG and EMG were recorded continuously for 21 days from rats rendered epileptic by application of cobalt wire to the right parietal cortex. Focal spiking appeared in the ECoG as early as the first few days. All rats developed spontaneous focal seizures with secondary generalization by day 4 to 7, initially more frequent at the end of NREM and REM sleep episodes. Between 6 and 12 days, continuous (in sleep and wakefulness) ECoG spikes and spike‐and‐wave complexes were recorded from the cobalt‐treated hemisphere, accompanied by clonic jerks of the contralateral limbs. Spiking lasted 16 to 48 hr, the amount of REM sleep decreased during this period, and seizures occurred mainly during wakefulness. Seizures subsided by the end of the second week, but ECoG spikes at the cobalt focus remained. These results suggest that the early time period after induction of cobalt epilepsy in the rat may provide a useful basis for studying the neurochemical events associated with the development of local epileptogenesis.

Intraocular pressure, ocular toxicity and neurotoxicity after administration of Δ9-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.

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.

A study of pentylenetetrazol kindling in rats and mice

The effect of repeated injection of pentylenetetrazol on pentylenetetrazol seizure thresholds was determined in mice and rats. Once per week treatment of rats with pentylenetetrazol resulted in the development of a state of kindling. On the other hand, when pentylenetetrazol was administered twice per week, a phenomenon resembling tolerance was observed. In mice, it was not possible to demonstrate kindling under experimental conditions utilizing either one or two treatments with PTZ per week.

Appearance of wet dog shake behavior during cobalt experimental epilepsy in the rat and its suppression by reserpine.

Rats rendered chronically epileptic by the implantation of cobalt in the right parietal cortex were simultaneously prepared with permanent cortical and temporalis muscle electrodes for longitudinal EEG and EMG recording. Animals treated similarly with glass rods served as the controls. Wet dog shakes were quantified by counting the characteristic artifacts produced in the EEG tracings upon their appearance. The number of wet dog shakes exhibited by the control rats remained at a low and constant level over 18 days of recording. In contrast, wet dog shakes in the chronically epileptic rats began to increase by the fourth day after cobalt placement and remained significantly elevated up to the 18th day. Administration of reserpine to naive rats or to cobalt epileptic rats on days 7 and 9 after implantation resulted in an almost complete suppression of wet dog shakes which endured over a period of 3–5 days. These results suggest that the abnormally elevated wet dog shake response of the cobalt-epileptic rats and the spontaneous wet dog shake behavior of normal rats may be mediated by common neural pathways.

Brain concentrations and synthesis rates of biogenic amines during chronic cobalt experimental epilepsy in the rat

Abstract Both the absolute levels and the turnover rates of the monoamines norepinephrine (NE), dopamine (DA), and serotonin (5-HT) were measured in the brains of rats rendered epileptic by the application of cobalt powder to the surface of the cerebral cortex. Throughout the entire 21-day time course studied after cobalt treatment, during which a sustained reduction in the pentylenetetrazol (Metrazol) seizure threshold developed gradually within the first four days, whole brain levels of NE, DA, and 5-HT remained similar to their respective control values. Whereas the turnover rate of NE as well as that of DA in the brains of the cobalt-epileptic rats likewise remained within normal limits, both the rise of brain 5-HT after blockade of its metabolism and its decline from the brain after synthesis blockade followed time courses of change which differed significantly from those of the control groups. The decrease in 5-hydroxyindole acetic acid (5-HIAA) content of the brain caused by blockade of 5-HT catabolism, however, was found to be similar in cobalt-treated and control rats. These results suggest that the involvement of brain biogenic amines in the development and the maintenance of a chronic epileptic state differs markedly from the established role of these potential neurotransmitters in the production of acute seizure activity.

Cholinergic involvement in cobalt-induced epilepsy in the rat

SummaryIn rats with cobalt implanted in the right frontal cerebral cortex, acetylcholine (ACh) levels were depressed in the visually non-necotic, surrounding cortex at 7 and 14 days after surgery in comparison with values for controls treated with glass. At 21 days post-implantation, ACh levels were not different for glass and cobalt treatments.Effects of drugs affecting cholinergic function on electro-corticographic (ECoG) epileptiform activity were determined in rats implanted bilaterally with cobalt. The cholinesterase inhibitors, physostigmine and diisopro-pylfluorophosphate reduced both seizure activity and interictal spiking in these cobalt-treated rats. Hemicholinium-3 (HC-3), given subacutely, initially inhibited seizures, but seizure frequency increased later during treatment. HC-3 did not appear to inhibit interictal spiking. These results suggest an involvement of brain cholinergic system in chronic cobalt experimental epilepsy.Seven days after cobalt implantation, HC-3 was less effective in depleting ACh in cerebral cortex adjacent to the cobalt-lesion than in similar tissue from rats with no cobalt implants. This suggests that the cholinergic neurons adjacent to the implant are not highly active at a time when seizure frequency is maximal.

Effects of diphenylhydantoin and trimethadione on seizure activity during cobalt experimental epilepsy in the rat.

Abstract Rats rendered chronically epileptic by the application of cobalt to the right parietal cortex were simultaneously prepared with permanent cortical and temporalis muscle electrodes for longitudinal recording of the electroencephalogram and electromyogram. Automatic injections of trimethadione (100 mg/kg per 6 hr and 100 mg/kg per 3 hr) or diphenylhydantoin (5 mg/kg per 6 hr and 10 mg/kg per 6 hr) were administered through indwelling intraperitoneal cannulae from days 7–13 after cobalt placement. At this time, spontaneous seizure activity in saline treated cobalt epileptic rats was maximal. Although neither anticonvulsant completely suppressed seizures, the higher dose of diphenylhydantoin and the lower dose of trimethadione caused a significant reduction in the incidence of completely generalized grand mal convulsions. While neither dose of diphenylhydantoin had any influence on the frequency of occurrence of incompletely generalized seizures, the incidence of this type of seizure activity after the lower dose of trimethadione was actually increased. Upon termination of chronic diphenylhydantoin administration at either dosage level, a significant enhancement of incompletely generalized seizure activity occurred. Scizure activity in cobalt-epileptic rats after termination of treatment with either dose of trimethadione, on the other hand, remained similar to that of controls. These results suggest that the chronic model of epilepsy resulting from cerebral cobalt application in the rat may provide a suitable indicator of the effectiveness of anticonvulsants in chronic seizure disorders.