Reduction of frequency of seizures by carbamazepine during cobalt experimental epilepsy in the rat.

Adult female Sprague-Dawley rats rendered epileptic by bilateral cerebral implantation of cobalt wire were simultaneously prepared with permanent cortical and temporalis muscle electrodes for continuous recording of electroencephalogram and electromyogram activities. Carbamazepine (50 or 100 mg/kg) was administered intraperitoneally twice daily days 8-12 after cobalt implantation. The high dose of carbamazepine was effective in decreasing seizure incidence each day of its administration, but the lower dose was effective in decreasing seizure incidence only for 6 h following its administration on days 8 and 9. These results provide additional evidence that cobalt epilepsy in the rat is a valid model for the study of seizure disorders.

Reduction of seizure frequency by clonazepam during cobalt experimental epilepsy.

Adult female Sprague-Dawley rats rendered epileptic by bilateral cerebral implantation of cobalt wire were simultaneously prepared with permanent cortical and temporalis muscle electrodes for continuous recording of electroencephalographic (EEG) and electromyographic (EMG) activities. Clonazepam (4, 10 or 40 mg/kg) dissolved in gum acacia was administered once daily intraperitoneally for 5 days beginning 9 days after cobalt implantation. The 40 mg/kg dose completely suppressed generalized seizure activity. Although no tolerance to this effect developed by the fifth day of treatment, generalized seizure activity two days after the last injection was significantly greater in epileptic rats than in control animals. These results suggest that the cobalt model of epilepsy may be useful in the study of mechanisms underlying both anticonvulsant effectiveness and rebound excitability after anticonvulsant drug withdrawal.

A comparison of the ocular and central effects of delta 9-tetrahydrocannabinol and cannabigerol.

Both delta 9-tetrahydrocannabinol (delta 9-THC) and cannabigerol, two naturally occurring marihuana cannabinoids, produced only a modest fall in intraocular pressure after acute topical application to the eyes of cats. After chronic administration unilaterally to the cornea via Alzet osmotic minipumps and connecting extraocular cannulas, however, a considerable fall in ocular tension amounting to 4 to 7 mm Hg occurred. After systemic administration of delta 9-THC to rats, polyspike discharges appeared in the cortical electroencephalogram initially during wakefulness and behavioral depression. These polyspikes subsequently became evident within rapid eye movement sleep episodes. Cannabigerol was devoid of this effect. After removal of either sympathetic or parasympathetic input to the eyes of cats, the intraocular pressure lowering effect of delta 9-THC was not changed. Neither delta 9-THC nor cannabigerol altered the rate of formation of aqueous humor. On the other hand, both cannabinoids produced a two-to three-fold increase in aqueous outflow facility. These results suggest that cannabigerol and related cannabinoids may have therapeutic potential for the treatment of glaucoma.

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.

Autonomic drug effects after chronic lowering of ocular cholinergic input. II. Intraocular pressure responses.

Cholinergic input to the anterior segment of the eye was chronically reduced by ciliary ganglionectomy in cats and by treatment with hemicholinium-3 in both rabbits and cats. The parasympathetically denervated cat eyes developed super-sensitivity to the intraocular pressure lowering effects of carbachol and echothiophate. On the other hand, responsiveness to the similar effects of norepinephrine, epinephrine, and isoproterenol was not changed. After both acute and chronic treatment of rabbit eyes with hemicholinium-3, intraocular pressure was markedly lowered, but the facility of aqueous outflow after chronic treatment was not changed. During chronic treatment of cat eyes with hemicholinium-3, intraocular pressure was also lowered. Three days after chronic delivery of this acetylcholine synthesis inhibitor to the eyes of cats, the rate of formation of aqueous humor was reduced by 50 percent. These results suggest that chemical compounds lowering ocular cholinergic input may possess a pharmacological profile useful as an alternative means for the treatment of glaucoma.

Autonomic drug effects after chronic lowering of ocular cholinergic input. I. Pupillary responses.

Cholinergic input to the anterior segment of the eye was chronically lowered by ciliary ganglionectomy in cats. Experimental eyes developed supersensitivity to the miotic effects of pilocarpine. In addition, these parasympathetically denervated eyes exhibited a moderate subsensitivity to the mydriatic effects of norepinephrine, epinephrine, and isoproterenol. Iris preparations accordingly afford the unique opportunity to study the two opposite extremes of normal drug sensitivity simultaneously in the same tissue.

GABA receptors, lipids, and gangliosides in cobalt epileptic focus.

The seizure state induced in the rat by cerebral cortical implantation of cobalt metal has been increasingly used to study a variety of neurochemical parameters. This experimental model of epilepsy affords the opportunity to study events prior to the development of seizures, during the period of intense seizure activity, and during the period when seizure activity has essentially terminated. The seizures that occur in this model are intermittent and paroxysmal and share many other similarities with human epilepsy. The crucial question with this model, and indeed with any experimental model of epilepsy, is whether the basic seizure-producing mechanism(s) is similar. This question remains to be answered. There have been studies that show that changes in certain neurochemical parameters parallel the onset, intensity, and decline of seizure activity in cobalt-epileptic animals. Although extremely interesting, by themselves they do not prove a cause-and-effect relationship. Such parallelism is more apparent in the case of GABA than in the cases of lipids and gangliosides. GABA and its synthetic enzyme, glutamic acid decarboxylase (GAD), are both at normal levels prior to the development of seizures, are significantly decreased during the period of seizures, and return toward control values at a time when seizures are no longer apparent. On the other hand, there is no change in postsynaptic GABA binding sites (Bmax) prior to seizures, a significant increase in Bmax during seizure activity, and a return toward normal by 21 days (when seizure activity has terminated). Studies that have been carried out on lipids and gangliosides in cobalt-induced epilepsy are not nearly as extensive nor are the results as positive as those that have been obtained in the case of GABA. They do, however, provide provocative findings that may well be related to the genesis of epilepsy.

Possible mechanisms underlying the differential effects of selective inhibitors of type A and type B monoamine oxidase on intraocular pressure in the cat.

Intraocular pressure and facility of aqueous outflow were measured in adult cats after topical application of clorgyline, a selective inhibitor of type A monoamine oxidase (MAO), or deprenyl, a selective inhibitor of type B of the enzyme. Clorgyline produced a dose-related lowering of intraocular pressure which was associated with a dose-related increase in outflow facility. Sympathetic denervation markedly reduced both these effects of clorgyline. Both effects, on the other hand, persisted after death of the animals. Deprenyl did not lower intraocular pressure; in fact, a tendency toward pressure elevation was apparent 2 hours after its administration. Outflow facility was not significantly changed. These results suggest that an endogenous substrate of type A MAO, presumably norepinephrine, is responsible for the ocular tension lowering effect of clorgyline. Because cessation of circulation after death did not abolish the effect, it is assumed that the trabecular meshwork is the site of action and that sympathetic innervation normally supplies an adrenergic neurotransmitter to the meshwork area. The tendency toward rise in intraocular pressure produced by deprenyl is probably due to alteration of aqueous humor formation rather than to a change in outflow resistance.

Effect of delta 9-tetrahydrocannabinol on intraocular pressure after removal of autonomic input.

Sympathetic input to the anterior segment of the eyes of cats was unilaterally removed by either superior cervical ganglionectomy or treatment with 6-hydroxydopamine. Parasympathetic input was unilaterally removed by extirpation of the ciliary ganglion. delta 9-tetrahydrocannabinol (delta 9-THC; 20 micrograms/hr) was delivered unilaterally to the denervated eyes and to eyes of surgically intact control cats via osmotic minipumps and connecting extraocular cannulas over a total period of nine days. The results indicated that the degree of reduction of intraocular pressure by delta 9-THC was not affected by removal of input from either branch of the autonomic nervous system. Outflow facility during chronic administration of THC showed a two-to-three fold increase. Ciliary ganglionectomy alone produced a moderate decrease in intraocular pressure that endured for one week. These findings indicate that neither adrenergic nor cholinergic input to the cat eye is apparently required for the mediation of the tension lowering effect of THC. They additionally suggest that cholinergic input may normally play a role in the regulation of steady-state intraocular pressure levels, presumably by modulating aqueous humor formation.

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.

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.

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.

Aqueous humor dynamics in the enucleated deer eye.

Facility of outflow of aqueous humor was determined in ten deer (Odocoileus virginianus) eyes enucleated within 1 hr post-mortem. Although both outflow facility and anterior chamber volume were much greater than values reported in the literature for a variety of other species, calculated values for aqueous humor turnover were within the reported range for other animals as well as for man. These results strengthen the hypothesis that the rate of turnover of aqueous humor is quite similar in eyes of vastly differing dimensions.

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.

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.

Loss of supersensitivity of the cat eye to carbachol at prolonged periods after ciliary ganglionectomy.

Adult female cats (2.4-2.8 kg) underwent surgical removal of the left ciliary ganglion under pentobarbital anesthesia. Twenty-one, 560 and 616 days later, pupil size of both left and right (control) eyes was measured in response to progressively increasing doses of carbachol applied topically. By 21 days after denervation, ganglionectomized eyes showed marked supersensitivity to the miotic effects of pilocarpine and carbachol. By 560 days, however, responsiveness of the denervated eyes to lower and intermediate doses of carbachol was the same as that of contralateral control eyes, while responsiveness to higher doses was significantly reduced. Responsiveness to both lower and higher doses of carbachol was significantly less than that of the controls on the 616th day. Ganglionectomized eyes showed no pupillary response to light 14, 562, or 620 days after surgery. Histochemical analysis of iris tissue collected from eyes of these cats 720 days after ganglion removal revealed an almost complete absence of acetylcholinesterase-containing nerve fibers on the denervated side. These findings indicate that the return to normal or lower sensitivity to carbachol of denervated eyes at prolonged periods after ciliary ganglion removal is not due to significant cholinergic reinnervation of the iris sphincter muscle.

Interaction between impulse-flow and delta 9-tetrahydrocannabinol within the septal-hippocampal cholinergic pathway of rat brain.

The role of the cholinergic cell bodies of the medial septum in the transsynaptic reduction of nerve activity elicited by delta 9-tetrahydrocannabinol (THC) in the septal-hippocampal cholinergic pathway was assessed by measuring the ability of delta 9-THC to reduce sodium-dependent high affinity choline uptake in rat hippocampus 2 hr after electrolytic destruction of the cholinergic cell bodies in the septum. delta 9-THC did not reduce choline uptake in rats with electrolytic lesions of the cholinergic cell bodies in the septum. Because lesioning of cholinergic cell bodies itself reduces impulse-flow in cholinergic neurons, this observation has two interpretations: either delta 9-THC acts transynaptically at the cholinergic cell bodies in the septum, or alternatively, requires impulse-flow in the septal-hippocampal cholinergic pathway in order to reduce its activity. To test if delta 9-THC required impulse-flow in order to reduce the activity or the septal-hippocampal cholinergic pathway, the ability of delta 9-THC to reduce choline uptake in hippocampus of rats with cingulate bundle transections, another surgical procedure which reduces impulse-flow iun the septal-hippocampal cholinergic pathway, was measured. In cingulate bundle-transected rats, delta 9-THC did not reduce choline uptake in hippocampus. Taken together with the effects of delta 9-THC in septal-lesioned rats, this observation favors the interpretation that delta 9-THC requires impulse-flow in the septal-hippocampal cholinergic pathway in order to reduce the activity of this pathway.

Involvement of brain monoamines in the delta-9-tetrahydrocannabinol-induced reduction of hippocampal choline uptake.

The role of monoamines in the transsynaptic reduction of neuronal activity produced by delta 9-tetrahydrocannabinol (delta 9-THC) in the septal-hippocampal cholinergic pathway has been investigated. Serotonergic afferents were chemically lesioned by unilateral infusion of 5,7-dihydroxytryptamine. Noradrenergic and dopaminergic inputs were selectively deleted by unilateral infusion of 6-hydroxydopamine into appropriate anatomic sites. Although removal of serotonergic and noradrenergic input did not alter hippocampal choline uptake relative to the contralateral control side, dopaminergic input reduction produced a significant elevation. After administration of delta 9-THC (20 mg/kg), reduction of choline uptake into lesioned hippocampi was not significantly different from that for the controls. These results indicate that monoaminergic afferents do not play a major role in the effect of delta 9-THC on cholinergic activity in the rat hippocampus.

Effects of selective beta 1- and beta 2-adrenoreceptor agonists and antagonists on intraocular pressure in the cat.

Ocular tension of cats was measured after topical administration of the selective beta 1-adrenergic agonist CGP 7760B, the selective beta 1-adrenergic antagonist atenolol, the selective beta 2-adrenergic agonist salbutamol, the selective beta 2-adrenergic antagonist H 35/25, and the mixed beta 1- and beta 2-adrenergic antagonist timolol. Although atenolol did not alter intraocular pressure, CGP 7760B produced a modest decrease amounting to 3 to 4 mm Hg. Salbutamol, H 35/25, and timolol each produced a dose-dependent lowering of ocular tension, with maximal reductions amounting to 7, 5, and 5 mm Hg, respectively. Sympathetically denervated cat eyes showed supersensitivity to the pressure-lowering effect of salbutamol. In contrast, sympathectomy markedly reduced the effects of H 35/25 and timolol on ocular tension. Eyes rendered subsensitive to the pressure-lowering effects of cholinomimetics by chronic echothiophate treatment likewise showed diminished responsiveness to H 35/25 and timolol. Pretreatment with timolol (3 hr) completely abolished the pressure-lowering effect of salbutamol, and pretreatment with atenolol likewise completely antagonized the effect of CGP 7760B. These results suggest that beta-adrenergic receptors in the anterior segment of the cat eye are predominantly beta 2. Although beta-adrenergic antagonists apparently exert their effects on ocular tension by action at beta-adrenergic receptors, a cholinergic mechanism may be involved as well.