Charles R. Craig

The role of biogenic amines in the reserpine-induced alteration of minimal electroshock seizure thresholds in the mouse

A single injection of reserpine (1 mgkg i.p.) produced an increased susceptibility to minimal electroshock seizures, as well as a decrease in whole brain levels of norepinephrine (NE), dopamine (DA), and serotonin (5-HT). The return to normal seizure susceptibility correlated well with the return of the ability of whole brain tissue to synthesize and retain 3H-amine formed from either 3H-3,5-l-tyrosine or 3H-5-hydroxy-dl-tryptophan. Selective inhibition of catecholamine synthesis with α-methyl-p-tyrosine, following reserpine administration, prevented the return to normal both of seizure susceptibility and NE and DA levels. The combination of disulfiram and reserpine also prevented the return to normal seizure susceptibility. After the latter treatment, levels of DA were elevated while NE remained depressed. Selective inhibition of 5-HT synthesis following reserpine similarly prevented the return of normal seizure susceptibility. Our study suggests that NE and 5-HT, but not DA, are important in regulating minimal electroshock seizure susceptibility.

Concentration of Amino Acids in the Brain of Cobalt‐Epileptic Rat

The concentrations of 12 amino acids were measured in brains of rats rendered epileptic by implantation of cobalt wire in parietal cortex; at 7 days there was a marked decrease in the level of glutamic acid, aspartic acid and taurine and an increase in lysine and alanine levels at the site of the lesion. In homotopic contralateral cortex 19 days after implantation of cobalt there were no differences from controls. The findings in rats are thus similar to those reported in other species and in epileptogenic cerebral tissue of man.

Studies on gamma-aminobutyric acid transport in cobalt experimental epilepsy in the rat

Abstract: Crude brain homogenates and cerebral tissue slices from rats with cobalt metal implanted in right and left cerebral cortices were used to examine high‐ and low‐affinity GABA transport. High‐affinity GABA transport was maximally reduced to 34% of controls 7 days after cobalt implantation, a time that coincides with peak seizure activity in this model. Kinetic analysis of high‐affinity GABA transport, using brain homogenates, revealed a significant change in Vmax 7 days after cobalt implantation. (Vmax= 446.4 ± 26.2 pmol/mg prot./min, cobalt, versus 787.8 ± 67.3, control). An analysis of the low‐affinity system revealed no depression of Km, or Vmax parameters. Administration of valproic acid at a concentration as high as 1 mM in vitro or a dose of 300 mg/kg in vivo had no effect on high‐ or low‐affinity GABA transport. The results obtained from cobalt‐treated rats provide additional evidence for an involvement of GABA in experimental epilepsy.

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.

ALTERATIONS IN CATION LEVELS AND NA‐K ATPase ACTIVITY IN RAT CEREBRAL CORTEX DURING THE DEVELOPMENT OF COBALT‐INDUCED EPILEPSY

Abstract— This study was carried out to ascertain what biochemical changes might be present in cobalt‐induced epilepsy in the rat. Sodium, potassium, calcium, magnesium, Na‐K ATPase activity, water content, protein content and the ability of the tissue to utilize oxygen were measured in (1) the area of the cerebral cortex in which the cobalt was implanted; (2) in an area adjacent to but not including the area of the lesion; and (3) in the homotopic area of the contralateral cerebral cortex. The greatest changes were observed in the area of the lesion itself, with marked increases in calcium, magnesium and sodium contents and decreases in potassium content, Na‐K ATPase activity, protein content and the ability of the tissue to utilize oxygen. The only significant findings in the area adjacent to the lesion and in the contralateral cortex were a modest elevation of sodium and a modest decrease in potassium at different time periods after implantation of the cobalt. We feel that the changes observed at the site of cobalt implantation may reflect tissue destruction which is unrelated to the epileptic process.

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.