GABA and dopamine interaction in the basal ganglia: dopaminergic supersensitivity following chronic elevation of brain gamma-aminobutyric acid levels

Lamotrigine-Associated Movement Disorder: A Literature Review

BACKGROUND

Lamotrigine (LMT) is a phenyltriazine derivative that was originally described as an antiepileptic drug.

OBJECTIVE

This literature review aims to evaluate the clinical epidemiological profile, pathological mechanisms, and management of lamotrigine-associated movement disorders.

METHODS

Relevant reports in six databases were identified and assessed by two reviewers without language restriction. Reports that the individuals only developed tremor or ataxia after LMT use were not included.

RESULTS

In total 48 reports of 108 cases from 19 countries were assessed. The movement disorders associated with LMT found were 29 tics, 21 dyskinesias, 14 myoclonus, 13 parkinsonism, 10 dystonia, and 1 stuttering. The not clearly defined cases included 10 akathisia, 4 myoclonus, 4 cerebellar syndromes, 1 hypertonia, 1 dyskinesia, and an unknown number of dystonia cases. The mean reported age was 33.34 years (range: 1.574 years). The male was the predominant sex and the most common LMT indication was epilepsy. The mean LMT-dose at the movement disorder onset was 228 mg. The time from LMT start to the onset of movement disorder was within 6 months in 81%. The time from LMT withdrawal to complete recovery was within 1 month in 83%. The most common management was LMT withdrawal.

CONCLUSIONS

In the literature, the majority of the cases did not give a clear picture of the individual, and the times of movement disorder onset and recovery are not described. We believe that before withdrawal LMT, a dose adjustment based on the benefits and adverse events with careful evaluation case-by-case can be done.

Ultrastructure of spared dopamine terminals in caudate-putamen nuclei of adult rats neonatally treated with intranigral 6-hydroxydopamine

Residual dopamine terminals in the dorsal striatum, caudate-putamen nuclei (CPN), of adult rats neonatally lesioned with 6-hydroxydopamine (6-OHDA) sustain a relatively high level of dopamine release. We examined whether there were morphological differences in the spared dopamine terminals that might correlate with this increased efficacy. Postnatal male rat pups from 50 litters were pretreated with desmethylimipramine (DMI) to protect from non-specific monoamine damage, then given unilateral intranigral injections of 6-OHDA or vehicle. Coronal sections through the CPN and substantia nigra of the surviving adult animals from each litter were co-processed for immunoautoradiographic or immunoperoxidase localization of the catecholamine synthesizing enzyme, tyrosine hydroxylase (TH). Quantitative ultrastructural analysis established that in animals showing maximal (greater than 90%) depletions in immunoautoradiographic labeling for TH, the number of TH-labeled axons in the CPN ipsilateral to the 6-OHDA injections was reduced to one third of the number seen in the contralateral, unlesioned hemisphere, or the CPN from vehicle-injected animals. The ultrastructural features of residual terminals ipsilateral to 6-OHDA lesions were morphologically similar to those of the contralateral side or in vehicle-injected animals. However, in comparison with controls, these TH-labeled terminals had significantly larger mean cross-sectional diameters. When subdivided into groups according to size, there were significantly fewer small (0.0-0.1 micron 2) and more large (0.41-0.50 micron 2) TH-immunoreactive profiles in lesioned versus unlesioned CPN. The remaining TH-labeled terminals ipsilateral to the 6-OHDA lesions also appeared to be more often in direct contact with unlabeled soma and proximal dendrites as opposed to dendritic spines in the unlesioned CPN. These results suggest that the enhanced activity of dopamine neurons innervating the CPN after nigral 6-OHDA lesions may contribute to changes in size and target of their terminals. Alternatively, the observed large size of remaining dopamine terminals may reflect selective vulnerability of smaller axons to 6-OHDA toxicity.

GABAA receptors containing alpha 1 and beta 2 subunits are mainly localized on neurons in the ventral pallidum

The gamma-aminobutyric acid (GABA) projection from the nucleus accumbens to the ventral pallidum (VP) is important in the regulation of locomotion. Thus, stimulation and inhibition of GABAA receptors in the VP can alter locomotor activity. To determine whether the GABAA receptors are located presynaptically on accumbens efferents to the VP or postsynaptically on neurons intrinsic to the VP two experiments were performed. In the first, quinolinic acid lesions of the nucleus accumbens did not alter [3H]muscimol binding in the VP, while lesions in the VP significantly reduced (60-80%) binding as measured by light microscopic receptor autoradiography. In the second experiment, in situ hybridization with oligonucleotide probes for mRNAs of the alpha 1 and beta 2 subunits of the GABAA receptor was examined in the nucleus accumbens and VP. No mRNA for either subunit was observed in the nucleus accumbens, although many positively labeled neurons were present within the VP. By contrast, a moderate to high density of cells in both the nucleus accumbens and VP contained mRNA for glutamic acid decarboxylase. These data argue that the majority of GABAA receptors in the VP are not located presynaptically on axonal terminals originating from neurons in the nucleus accumbens.

Effects of inhibition of GABA catabolism by aminooxyacetic acid on enkephalinergic neurons--immunocytochemical and ultrastructural study in the enkephalinergic hypothalamoseptal tract of the guinea-pig

The immunocytochemical and ultrastructural features within [Met]enkephalin neurons of the guinea-pig hypothalamoseptal tract were investigated under chronic inhibition of GABAergic catabolism. This was achieved by raising the brain GABA concentration with aminooxyacetic acid which inhibits GABA-transaminase, the enzyme responsible for the catabolism of GABA. Guinea-pigs were injected intraperitoneally with 10 or 20 mg/kg per day aminooxyacetic acid for two, four or eight days and killed 16 h post-dose. Repeated injections of aminooxyacetic acid produced a great increase in immunoreactivity for GABA in nerve endings surrounding enkephalinergic perikarya in the magnocellular dorsal nucleus of the guinea-pig. Extensive immunocytochemical studies stressed the increase and redistribution of the immunoreaction for [Met]enkephalin in the perikarya of the magnocellular dorsal nucleus under such GABAergic activation. Quantitative and statistical analyses showed that administration of aminooxyacetic acid for eight days significantly increased the intensity of labelling within stimulated perikarya (P less than 0.001). A concomitant accumulation of immunopositive large granules in the enkephalinergic boutons of the lateral septum was observed. In the same way, ultrastructural changes in enkephalinergic cell bodies were analysed and reflected disturbances in the biosynthetic and digestive activities of enkephalinergic perikarya. We postulate that chronic inhibition of the GABAergic catabolism leads to modification in the metabolism of enkephalinergic neurons and to an inhibitory action of GABA on the [Met]enkephalin release from nerve endings. This study give morphological support to the complex functional interactions between GABA and opioid peptide transmitter system.

Methylphenidate in amytal-resistant mutism

Methylphenidate eliminated mutism in a catatonic schizophrenic after Amytal had failed. Response permitted an adequate clinical evaluation and temporary resumption of eating, self-care and sociability. This suggests that methylphenidate has a useful role in the clinical evaluation of the mute patient who fails to respond to Amytal and that 2 psychopharmacological varieties of catatonic mutism may exist.

Can the supersensitivity of rodents to dopamine be regarded as a model of tardive dyskinesia?

1. The paper presents arguments derived from both, clinical work and animal experiments, for or against the traditional hypothesis suggesting that tardive dyskinesia (TD) is caused by supersensitivity to dopamine. The main aim of this study was to answer the question posed in the title - whether the supersensitivity to dopamine evoked in rodents by neuroleptics can be regarded as an adequate pharmacological model of TD. 2. The data presented here prove that chronic administration of neuroleptics to schizophrenic patients cannot be the only factor inducing TD; furthermore, symptoms similar or identical to those of TD are also observed in the course of other disorders, not connected with neuroleptics, e.g. aging or schizophrenia itself. 3. Clinical data offer no clear evidence for the existence of a direct cause-effect relationship between super-sensitivity to dopamine and occurrence of TD. 4. The role of brain degeneration, caused by different factors but in particular by the process of aging, in the pathogenesis of dyskinetic disorders, including TD, has been stressed. 5. Pharmacological and biochemical data show that chronic administration of classic neuroleptics to animals induces an increase in the density of dopamine D-2 receptors (Bmax). It seems that this receptor-mediated supersensitivity may concern both the postsynaptic and the presynaptic D-2 dopamine receptors. On the other hand, it is not clear enough whether a dopamine D-1 receptor-mediated supersensitivity might also be a causal factor of TD. 6. The analysis in animals, of biochemical and pharmacological effects of neuroleptics which do not induce TD showed that in some situations these drugs may also evoke the receptor-mediated supersensitivity concerning dopamine D-2 receptors. 7. The method of a prolonged (approx. 1 year) oral administration of neuroleptics seems to differentiate those which induce TD from those which do not, at least regarding the induction of an increase of Bmax for butyrophenone neuroleptics and an increase of apomorphine-induced stereotypy, however, some exceptions are noted. 8. The above analysis of clinical and experimental data suggests that the supersensitivity to dopamine in rats treated chronically with neuroleptics cannot be accepted as a model which reflects the etiopathogenesis of TD. Neither a positive nor a negative result obtained in this test is reliable enough, and either depends on the tested parameters (apomorphine stereotypy and [3H]spiperon binding seem to be the most reliable), route of neuroleptic administration, duration of treatment and, probably, a number of other, still unknown factors.(ABSTRACT TRUNCATED AT 400 WORDS)

Determination of homovanillic acid, 5-hydroxyindoleacetic acid and pressure in the cerebrospinal fluid of collie dogs following administration of ivermectin

Twelve adult Collie dogs were studied to determine the effects of ivermectin on neurotransmitter metabolites released from the brain into the cerebrospinal fluid (CSF) and on CSF pressure. Ten of the 12 Collies were given ivermectin orally at a concentration of 200 micrograms/kg body weight. Three of these 10 Collies showed clinical signs of ivermectin-induced toxicosis which progressed into a state of unresponsive recumbency in 2 dogs. Cerebrospinal fluid pressures and neurotransmitter metabolite concentrations in cisterna magna CSF were analysed 49 to 50 hours after administration of ivermectin in 6 of the 10 treated dogs, and in the 2 untreated control Collies. Cerebrospinal fluid pressures were within normal limits in all dogs. However, compared to the CSF concentrations in the 2 untreated and 3 non-reactive Collies, the 2 ivermectin-reactive Collies still in recumbency had elevated CSF concentrations of homovanillic acid (HVA), a metabolite of dopamine, and 5-hydroxyindoleacetic acid (5-HIAA), a metabolite of serotonin. These findings suggest an association between altered neurotransmission and severe ivermectin-induced neurological abnormalities. No evidence of elevated intracranial pressure was found.