Nansie S. Sharpless

The effects of Δ9-tetrahydrocannabinol on potassium-evoked release of dopamine in the rat caudate nucleus: an in vivo electrochemical and in vivo microdialysis study

The effect of systemically administered delta 9-tetrahydrocannabinol (THC), the psychoactive ingredient in marijuana, on the potassium-evoked release of dopamine (DA) was examined in the neostriatum of the chloral hydrate anesthetized rat. Both in vivo electrochemical and in vivo microdialysis techniques were employed. A low dose of THC (0.5 mg/kg, i.p.) increased the time course of potassium-evoked in vivo electrochemical signals corresponding to released extracellular DA. In vivo microdialysis showed an increase in potassium-evoked DA release following 0.5 and 2.0 mg/kg doses of THC. Potassium-evoked electrochemical signals corresponding to released extracellular DA were augmented in time course following i.p. administration (5.0 mg/kg) of nomifensine, a recognized and potent catecholaminergic reuptake blocker. In addition, in vivo brain microdialysis studies of nomifensine (5.0 mg/kg i.p.) on neostriatal potassium-evoked DA release showed that DA levels were augmented in magnitude over the time course of the microdialysis. Taken together, these studies indicate that THC has a potent presynaptic augmenting effect on at least the neostriatal portions of the mesotelencephalic DA system in the rat, although the possibility that this effect could be mediated transsynaptically cannot be ruled out. Given the previous extensive evidence for an involvement of portions of the mesotelencephalic DA system in mediating the reinforcing and euphorigenic properties of many classes of abused drugs, and in mediating direct electrical brain stimulation reward, we suggest that the presently demonstrated effects of THC on forebrain dopamine function may be related to marijuanas euphorigenic properties and, thus, to its abuse potential.

Long-lasting depletion of dopamine in the rat amygdala induced by kindling stimulation

Kindling, first described by Goddard et al. in 1969 (ref. 13), has become an important experimental model for the study of epileptogenesis 31. The mechanisms by which daily application of a brief subconvulsive electrical stimulus to certain brain structures results in the gradual appearance and intensification of enduring behavioral responses are still unknown. We have found that unilateral lesions of the stria terminalis facilitate the development of the earliest behavioral changes produced by ipsilateral amygdaloid kindling and have suggested that this could be due to the destruction of catecholamine-mediated inhibitory amygdaloid afferents 9. This conclusion is consistent with other studies that indicate catecholamines to be inhibitory in the amygdala 2, to seizures in general la,21 and to kindling in particularX, 6. The following study was performed to examine the hypothesis that kindling itself might produce a decrease in catecholamine-mediated inhibitory influences at the stimulation site, since this could be one mechanism of kindled alterations in excitability. Under light pentobarbital anesthesia, the basolateral amygdalae of 22 male Sprague-Dawley rats, weighing approximately 300 g, were stereotaxically implanted with bipolar electrodes of 0.009 inch enamel-coated N ichrome wire (2.5 mm posterior, 3.5 mm lateral, and 8.8 mm deep to the bregma). These electrodes were soldered to microminiature Amphenol connectors, along with a ground wire placed under the temporalis muscle, and fixed to the skull with stainless steel hooks and acrylic cement. Rats were then handled daily for two weeks and placed in the test box once a day on the last two days before stimulation. Daily stimulation trials began on the fifteenth day when rats were divided into two groups; 16 rats were stimulated and 6 were treated as non-stimulated controls. For stimulated rats, 300 #A, 60 cps sinusoidal current was delivered via the bipolar electrodes for one second each day with a specially constructed constant current stimulator. Electrical activity was recorded from the amygdala on a Grass EEG machine before and after stimulus delivery, and the length of afterdischarge was noted. Rats were stimulated until a stage 5 (ref. 26) convulsion

Striatal met-enkephalin concentration increases following nigrostriatal denervation

Following specific lesion of the nigrostriatal dopaminergic pathways in rat brain, striatal met-enkephalin on the lesioned side increased to 245% of that on the non-lesioned side. This increase was evident only after a lag period of 7 days and the increase was maintained for at least 2 months after lesion. By contrast, there was no change in striatal somatostatin or vasoactive intestinal polypeptide concentration, indicating that the effect was not a generalised one. Levels of all three of these neuropeptides were unchanged in frontal cortex. These findings support the concept of a dopaminergic-enkephalinergic functional interrelationship in the striatum. In addition, the findings provide evidence that, following destruction of nigrostriatal dopaminergic neurons, not only is there a gradually developing postsynaptic dopamine receptor supersensitivity but also a compensatory alteration in the enkephalinergic system.

Kindling in developing rats: variability of afterdischarge thresholds with age

In the kindling model, the occurrence of afterdischarges is necessary for the development of seizures. In this study, the afterdischarge thresholds of the amygdala were determined in rats of 4 different age groups, beginning with 15-day-old suckling rats. Afterdischarges were triggered in 75% of the suckling rats and in all of the rats in the older age groups. The afterdischarge thresholds varied with age, being highest in the suckling group, lowest in the 35-day-old group and intermediate in the older groups. This variability of the thresholds did not correlate with the alterations in the catecholamine levels in the amygdala that occur during maturation. The failure of 25% of suckling rats to develop afterdischarges may explain why some suckling rats do not kindle.

Acute and chronic effects of oral physostigmine and lecithin in Alzheimer's disease

Alzheimer patients were treated with lecithin and gradually increasing doses of oral physostigmine during a drug trial to determine if these compounds would improve memory. Memory was measured using a selective reminding task. Of 16 patients, 10 showed improvement in total recall, retrieval from long-term storage and a decrease in intrusions. The optimal dose was 2.0 mg or 2.5 mg of physostigmine per dose for most patients. During a replication study, all 10 patients again responded. During long-term (4 to 20 months) treatment of five patients, most demonstrated continued drug response initially but then lost responsiveness to physostigmine and their dementia progressed. Physostigmine treatment appeared to improve memory with or without concomitant lecithin therapy. However, progressive dementia ensued despite physostigmine therapy. The degree of memory improvement correlated with increasing cerebrospinal fluid cholinesterase inhibition suggesting that memory improvement is associated with entry of physostigmine into the brain.

Choline chloride fails to improve cognition in Alzheimer's disease

Seven mildly to moderately demented patients with Alzheimers disease were treated with either placebo or choline chloride (50, 100 and 200 mg/kg/24 hrs) in a double blind, crossover study. Detailed psychometric analysis was carried out at the end of each two-week period of drug or placebo administration. No subjects showed significant overall improvement at any dose level despite more than a doubling of the baseline plasma choline level.

Ventricular fluid homovanillic acid and 5-hydroxyindoleacetic acid concentrations in patients with movement disorders.

Ventricular fluid concentrations of homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), the respective metabolites of dopamine and serotonin, were measured in 57 patients undergoing thalamotomy for relief of movement disorders. The diseases included were Parkinson disease, dystonia, cerebral palsy, multiple sclerosis, and posttraumatic or posthypoxic encephalopathy. Untreated parkinsonian patients had the lowest mean HVA level (119 ng per milliliter). Patients with multiple sclerosis or with posttraumatic or posthypoxic encephalopathy with both intellectual impairment and bilateral motor involvement had lower mean HVA levels (197 and 177 ng per milliliter, respectively) than cerebral palsy patients with bilateral motor disease (233 ng per milliliter), dystonia patients (246 ng per milliliter), or multiple sclerosis patients with normal intellect (376 ng per milliliter). The data suggest that diffuse cerebral disease may lead to diminished dopaminergic activity. Ventricular fluid 5-HIAA levels were similar in all groups of patients. Chronic cerebellar stimulation markedly increased ventricular fluid HVA and 5-HIAA levels, indicating that cerebellar stimulation affected cerebral dopaminergic and serotonergic systems.

Dopamine receptor sensitivity following nigrostriatal lesion in the aged rat.

This investigation sought to determine whether the ability to regulate dopamine receptor sensitivity following removal of dopaminergic innervation is altered during aging. Aged (24-26 months old) Fisher 344 rats compared with young (6 months old) rats had lower levels of dopamine and dopamine receptor binding ([3H]ADTN), but no change of dopamine-stimulated adenylate cyclase activity. Unilateral lesion of the nigrostriatal pathway produced equivalent dopaminergic denervation in rats of both age groups. The denervated striata of young rats had greatly enhanced dopaminergic sensitivity as evidenced by apomorphine induced rotational behavior and increased dopamine stimulated adenylate cyclase activity and [3H]ADTN binding. Old rats responded similarly with a very high degree of increased dopaminergic sensitivity in both the behavioral and biochemical parameters, demonstrating that the ability to regulate dopamine receptors remains basically intact. However, deficits of supersensitivity occurred in apomorphine induced rotational behavior and [3H]ADTN binding and there was a large deficit in the guanine nucleotide sensitive subcomponent of [3H]-ADTN binding. Supersensitivity of dopamine stimulated adenylate cyclase was not altered. The diminished ability to develop supersensitivity to [3H]ADTN binding could contribute to decreased [3H]ADTN binding in unlesioned rats.

Free and conjugated dopamine in human ventricular fluid

Free dopamine and an acid hydrolyzable conjugate of dopamine were measured in human ventricular fluid specimens with a radioenzymatic assay and by high performance liquid chromatography (HPLC) with electrochemical detection. Only trace amounts of free norepinephrine and dopamine were detected in ventricular fluid from patients with movement disorders. When the ventricular fluid was hydrolyzed by heating in HClO4 by lyophilization in dilute HClO4, however, a substantial amount of free dopamine was released. Values for free plus conjugated dopamine in ventricular fluid from patients who had never taken L-DOPA ranged from 139 to 340 pg/ml when determined by HPLC and from 223 to 428 pg/ml when measured radioenzymatically. The correlation coefficient for values obtained by the two methods in the same sample of CSF was 0.94 (P less than 0.001). Patients who had been treated with L-DOPA had higher levels of conjugated dopamine in their ventricular CSF which correlated inversely with the time between the last dose of L-DOPA and withdrawal of the ventricular fluid. Additionally, one patient with acute cerebral trauma had elevated levels of free norepinephrine and both free and conjugated dopamine in his ventricular fluid. Conjugation may be an important inactivation pathway for released dopamine in man.

Vasoactive intestinal peptide in cerebrospinal fluid

Immunoreactive vasoactive intestinal peptide (VIP) was measured in lumbar and ventricular cerebrospinal fluid (CSF) from patients with various neurological disorders and in 2 hour aliquots of cisternal fluid removed continuously from rhesus monkeys. Although most of the VIP in concentrated pools of human ventricular fluid and of monkey cisternal fluid co-eluted with synthetic porcine VIP28 on a column of Sephadex G-25 superfine, there was evidence that smaller immunoreactive fragments were also present. A circadian pattern of CSF VIP concentration was observed in 2 of the 3 monkeys studied, with highest levels occurring at night and lowest during the day. Ventricular fluid VIP levels were highest in hydrocephalic children and lowest in patients with multiple sclerosis or epilepsy, while VIP was not detectable in ventricular fluid from patients in coma following a severe head injury. There were no significant differences in VIP concentrations in CSF from patients with dystonia. Parkinsons disease, or Alzheimers disease, suggesting that VIP containing neurons are not affected in these disorders. Lumbar fluid VIP levels were low in patients undergoing aneurysm surgery. Since VIP is a potent vasodilator, these findings may have important implications in relation to the development of vasospasm following subarachnoid hemorrhage.