Antagonism of the effects on thermoregulation of delta9-tetrahydrocannabinol by clomipramine in the rat

1 The effect of pretreatment with clomipramine hydrochloride (15 mg/kg, i.p.) on the (--)-trans-delta9-tetrahydrocannabinol (delta9-THC)-induced changes in body temperature and brain amines of the rat was investigated. 2 A dose of 0.05 mg/kg of delta9-THC produced hyperthermia and a decrease in whole brain concentration of 5-hydroxyindoleacetic acid (5-HIAA). Doses of 2 and 5 mg/kg produced hypothermia and increases in brain 5-HIAA whereas 0.5 mg/kg did not affect either parameter. delta9-THC, at any of the doses, did not affect the whole brain concentrations of dopamine, noradrenaline or 5-hydroxytryptamine. 3 Clomipramine modified these responses of delta9-THC in that the dose-response curves appeared to be shifted to the right. 4 It is concluded that clomipramine acts as an antagonist to these actions of delta9-THC by interfering with entry of delta9-THC into tryptaminergic neurones.

Neuronal responses to extracellularly applied cyclic AMP:Role of the adenosine receptor

At low doses, theophylline blocks the neuronal depressant effects of 5'-AMP, but not cyclic AMP. Higher doses (100 mg/kg) block cyclic AMP responses and reduce the effects of noradrenaline and GABA. It is concluded that cyclic AMP does not depress neurones via the adenosine receptor.

Relationship between body temperature and brain monoamines during the development of tolerance to delat9-tetrahydrocannabinol in the rat

The development of tolerance to delat9-tetrahydrocannabinol (delta9-THC) was examined. Rats with permanently indwelling intravenous catheters were injected daily with delta9-THC, 2 mg/kg, for up to 10 days and on each day subjective behaviour and body weight of each rat were noted. Tolerance appeared to develop to both the excitatory and depressant behavioural effects of delta9-THC, whereas the rate of gain in body weight of delta9-THC treated rats was retarded and tolerance to this phenomenon did not develop over the experimental period. On days 1, 2, 3, 5, 6, and 10 body temperature was recorded continuously for at least 2 h after delta9-THC and in other groups of rats the brain levels of noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) were measured spectrophotofluorimetrically 1 h after delta9-THC. Tolerance developed to the delta9-THC-induced hypothermia by day 3, and on days 6 and 10 hyperthermia was observed. delta9-THC did not markedly affect the brain levels of NA or DA over the experimental period. The brain levels of 5-HT were unchanged on days 1--5 but there was a decrease on days 6 and 10. On days 1, 2, and 3 brain levels of 5-HIAA were raised, whereas on day 6 there was a decrease. These results show that delta9-THC induces tolerance to the hypothermia and elevation of brain 5-HIAA levels in a linear manner. An inverse relationship appears to exist between these two parameters.

The nature of adrenoceptors in the guinea pig cerebral cortex: a microiontophoretic study

1. Noradrenaline, isoprenaline, and phenylephrine have been applied my microiontophoresis to neurones in the guinea pig cerebral cortex. All three compounds produced depression of neuronal firing, and all could be antagonized to some extent by phentolamine or propranolol. 2. The responses to isoprenaline were substantially reduced in size after a few applications. Noradrenaline and phenylephrine responses were partially reduced at the time of isoprenaline insensitivity, and the responses could now be blocked completely by phentolamine. 3. The results suggest that two kinds of receptors are present in the guinea pig cerebral cortex, with properties similar to alpha and beta receptors in the periphery. A single receptor with intermediate properties would not readily explain the present results. 4. The results are not consistent with the proposal that alpha receptors mediate neuronal excitation, and beta receptors inhibition in the cerebral cortex. 5. It is also suggested that the failure of some previous studies on guinea pig cortex in vitro to demonstrate the presence of beta receptors may be due to the particularly rapid desensitization of these receptors.

Biphasic nature of the effects of delta9-tetrahydrocannabinol on body temperature and brain amines of the rat

The effects of i.v. injected delta9-tetrahydrocannabinol (delta9-THC) on behaviour, body temperature and levels of brain monoamines, measured spectrophotofluorimetrically, of the rat were determined. Doses of delta9-THC in the range of 0.05--5.0 mg/kg produced biphasic changes in behaviour, body temperature and levels of 5-hydroxyindoleacetic acid (5-HIAA). The whole brain levels of dopamine (DA), noradrenaline (NA) and 5-hydroxytryptamine (5-HT) were not altered by delta9-THC. The subjective behavioural biphasic responses did not appear to be dose related, whereas the biphasic changes in body temperature and brain levels of 5-HIAA were dose-related. Low doses of delta9-THC (0.05 and 0.1 mg/kg) caused hyperthermia, while doses of 1.0, 2.0 and 5.0 mg/kg induced hypothermia. On the other hand, 0.05 mg/kg delta9-THC significantly reduced, whereas doses of 1.0, 2.0 and 5.0 mg/kg significantly increased the 5-HIAA levels in a dose-related manner. It is concluded that an inverse relationship exists between delta9-THC-induced changes in body temperature and alterations in brain 5-HIAA levels.

The effect of delta9-tetrahydrocannabinol on body temperature and brain amine concentrations in the rat at differnt ambient temperatures

1. Rats were injected intravenously with 2 mg/kg (-)-trans-delta9-tetrahydrocannabinol (delta9-THC) at ambient temperatures of 4 degrees, 21 degrees, 31 degrees and 37 degrees C. 2. The general behavior exhibited by rats treated with delta9-THC was similar at all four ambient temperatures. 3. Body temperatures were recorded continuously before and after drug administration. At 4 degrees and 21 degrees C, delta9-THC caused hypothermia whereas no change in body temperature occurred at 31 degrees and 37 degrees C. 4. The concentrations in the whole brain of noradrenaline (NA), dopamine, 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined spectrophotofluorimetrically 1 h after drug administration. At 4 degrees C delta9-THC caused an increase of 5-HT, at 21 degrees C an increase of 5-HIAA, at 21 degrees C an increase of 5-HIAA AND A decrease of NA, and at 37 degrees C an increase of 5-HT and 5-HIAA. 5. At all ambient temperatures, delta9-THC increased the brain levels of 5-HT and/or 5-HIAA. A correlation between the delta9-THC-induced hypothermic response and the possible alteration of brain 5-HT metabolism cannot be excluded.

Microiontophoretic studies of the effects of cylic nucleotides on excitability of neurones in the rat cerebral cortex

1. Responses of cerebral cortical neurones to the microiontophoretic application of acetylcholine, noradrenaline, cyclic adenosine 3',5'-monophosphate (cyclic AMP) and cyclic guanosine 3',5'-monophosphate (cyclic GMP) were examined.2. The application of acetylcholine and cyclic GMP to identified pyramidal tract neurones resulted in an increased frequency of firing in a large number of cells. Upon application of both substances to cells which could not be identified as pyramidal tract cells, a reduction in the frequency of spontaneous firing was sometimes observed.3. Careful current controls had no effect on the cells discussed here, indicating that the observed responses were not due to the iontophoretic currents. Also, the electro-osmotic ejection of cyclic GMP (outward current) produced similar changes of cell firing to those which followed iontophoretic application (inward current).4. The microiontophoretic application of atropine resulted in a blockade of acetylcholine responses while leaving responses to cyclic GMP unaffected. This suggests that cyclic GMP was not acting indirectly by releasing acetylcholine from presynaptic endings.5. Ejection of cyclic GMP from solutions containing calcium ions produced responses comparable to those produced by cyclic GMP alone. It is unlikely therefore that cyclic GMP was causing excitation by chelating calcium.6. Applications of noradrenaline and cyclic AMP produced a reduction in the spontaneous discharge rate of most neurones tested.7. Phosphodiesterase inhibitors such as ICI 63,197 caused a potentiation of the noradrenaline responses of pyramidal tract neurones.8. 5'-adenosine monophosphate produced a powerful depression of all cells to which it was applied. This action was blocked by aminophylline, suggesting the effect was mediated through an adenosine receptor. Responses to cyclic AMP were usually not abolished, but were reduced by about 50% in amplitude.9. These results are consistent with the hypothesis that cyclic AMP may mediate some neuronal effects of noradrenaline and cyclic GMP may mediate some effects of acetylcholine. The results are also consistent with the suggestion that the two nucleotides may sometimes mediate opposite cellular responses to humoral stimuli.

Effect of identity in the multiletter matching task

This study was concerned with the nature of the character-comparison process involved in same-different judgments of arrays of letters. One condition replicated the standard matching task, with subjects pressing one key to indicate that the two arrays of letters were identical in all positions, and another key to indicate difference in one or more positions. A second condition reversed the standard decision rule and required the subjects to distinguish between arrays that differed in every position from those that matched in one or more positions. Reaction times were shorter to identical arrays in both conditions, indicating that identity effects observed in this and previous studies must be attributed to identity per se and not to decision or response factors. Mathematical analysis of the data revealed that, although a serial self-terminating model could be modified to give a good description of processing in this task, a model based on parallel processing was able to provide a better account both quantitatively and qualitatively. The analysis also indicated that subjects reduced their average reaction times by terminating the comparison process prematurely on some trials, and this guessing strategy was shown to have important implications for the shapes of the reaction time functions observed in this task.

Effect of identity in the multiletter matching task

This study was concerned with the nature of the character-comparison process involved in same-different judgments of arrays of letters. One condition replicated the standard matching task, with subjects pressing one key to indicate that the two arrays of letters were identical in all positions, and another key to indicate difference in one or more positions. A second condition reversed the standard decision rule and required the subjects to distinguish between arrays that differed in every position from those that matched in one or more positions. Reaction times were shorter to identical arrays in both conditions, indicating that identity effects observed in this and previous studies must be attributed to identity per se and not to decision or response factors. Mathematical analysis of the data revealed that, although a serial self-terminating model could be modified to give a good description of processing in this task, a model based on parallel processing was able to provide a better account both quantitatively and qualitatively. The analysis also indicated that subjects reduced their average reaction times by terminating the comparison process prematurely on some trials, and this guessing strategy was shown to have important implications for the shapes of the reaction time functions observed in this task.

The effect of pretreatment with reserpine on the diastolic potential of guinea-pig atrial cells

It has previously been suggested that the reserpine-induced nonspecific increase in sensitivity of the guinea-pig heart to the chronotropic effect od drugs occurs as a result of an alteration in the electrophysiological properties of the cell membrane. The results obtained in the present study provide support for this suggestion. The diastolic potential of atrial cells of perfused hearts obtained from guinea pigs treated with rerpine (0.1 mg/kg/day) for 7 days was significantly less than control. This treatment schedule of reserpine results in a significant increase in the sensitivity of perfoused hearts to the chronotropic effects of drugs...

Electrophysiological correlations with postjunctional supersensitivity

Several lines of evidence have been found which suggest that a partial depolarization is an important event in the development of postjunctional (nondeviation) supersensitivity in the vas deferens and atrium. In the vas deferens of the guinea pig, experiments with microelectrodes indicate that a depolarization of approximately 10 mV occurs after denervation or decentralization. The time course of the depolarization is the same as the time course of the development of supersensitivity found 7 days after denervation in the rat vas deferens. An analysis of the magnitude of junction potentials in the vas deferens supports the conclusion that changes in adrenergic receptors are not a significant factor in postjunctional supersensitivity. An analysis of membrane potential in guinea pig atria demonstrates a high correlation between the appearance of supersensitivity and a partial depolarization in that tissue alsomit is suggested that chronic interruption of the innervation to smooth or cardiac muscle leads to an alteration in the binding of calcium to the cell membrane and a consequent depolarization. The result is a resting membrane potential closer to the threshold for excitation.

Cyclic AMP and cyclic GMP may mediate opposite neuronal responses in the rat cerebral cortex

Electrophysiologically identified pyramidal tract neurons in the rat cerebral cortex were tested with norepinephrine, acetylcholine, adenosine 3',5'-monophosphate (cyclic AMP), and guanosine 3',5'-monophosphate (cyclic GMP) applied by microiontophoresis. The neurons were usually inhibited by norepinephrine and cyclic AMP, but excited by acetylcholine and cyclic GMP. These opposing responses of pyramidal tract neurons to cyclic AMP and cyclic GMP suggests that these two nucleotides could function as reciprocal intracellular second messengers for norepinephrine and acetylcholine, respectively.

Effects of viewed violence and aggression: stimulation and catharsis

Tests of the catharsis hypothesis involving viewed violence have led to conflicting results. It was suggested that the inconsistencies were due in part to the use of two different types of response measures, aggressive responses and hostile responses. This study involved a direct comparison of the two types of responses under conditions of instigation versus no instigation and aggressive versus neutral film. It was hypothesized that viewing an aggressive film would lead to a decrease in hostile responses (catharsis) and an increase in aggressive responses (stimulation) when compared with a neutral film condition. It was also hypothesized that both stimulation and catharsis effects would be enhanced under instigation conditions. A main effect of instigation was found with subjects in the instigation condition having higher scores than those in the noninstigated condition. A main effect of film was found with subjects having lower scores in the aggressive film condition than in the neutral film condition. A significant Film times Response Outlet interaction was found which offered support for the predicted catharsis effect on the hostility measure. There was no support for the predicted stimulation effect on the aggression measure. The results of the study offer support for the main thesis that in examining the effects of viewed violence, separation of hostile responses and aggressive responses is necessary for full understanding.