An excitatory action of iontophoretically administered lithium on mammalian central neurones

The evolution of the pilocarpine animal model of status epilepticus

The pilocarpine animal model of status epilepticus is a well-established, clinically translatable model that satisfies all of the criteria essential for an animal model of status epilepticus: a latency period followed by spontaneous recurrent seizures, replication of behavioural, electrographic, metabolic, and neuropathological changes, as well as, pharmacoresistance to anti-epileptic drugs similar to that observed in human status epilepticus. However, this model is also characterized by high mortality rates and studies in recent years have also seen difficulties in seizure induction due to pilocarpine resistant animals. This can be attributed to differences in rodent strains, species, gender, and the presence of the multi-transporter, P-glycoprotein at the blood brain barrier. The current paper highlights the various alterations made to the original pilocarpine model over the years to combat both the high mortality and low induction rates. These range from the initial lithium-pilocarpine model to the more recent Reduced Intensity Status Epilepticus (RISE) model, which finally brought the mortality rates down to 1%. These modifications are essential to improve animal welfare and future experimental outcomes.

Dose-Dependent Effects of Lithium Treatment on the Aggravation of Antipsychotic-Induced Pisa Syndrome

Pisa syndrome (PS) is a rare lateral truncal dystonia that is related to dopamine-acetylcholine imbalances, and most cases develop during antipsychotic treatment. Here, we report a case of PS that developed during switching to new antipsychotics and titrating lithium, and PS was aggravated when the lithium dose was increased. Truncal deviation was not relieved with switching back to prior antipsychotics or by discontinuation of all antipsychotics. Pisa syndrome resolved only after discontinuing the lithium treatment. This is the first report of dose-dependent effects of lithium treatment on the aggravation of PS, which may be related to dose-related effects on dopaminergic and cholinergic transmission.

The NMDA receptor/nitric oxide pathway: a target for the therapeutic and toxic effects of lithium

Although lithium has largely met its initial promise as the first drug discovered in the modern era of psychopharmacology, to date no definitive mechanism for its effects has been established. It has been proposed that lithium exerts its therapeutic effects by interfering with signal transduction through G-protein-coupled receptor (GPCR) pathways or direct inhibition of specific targets in signaling systems, including inositol monophosphatase and glycogen synthase kinase-3 (GSK-3). Recently, increasing evidence has suggested that N-methyl-D-aspartate receptor (NMDAR)/nitric oxide (NO) signaling could mediate some lithium-induced responses in the brain and peripheral tissues. However, the probable role of the NMDAR/NO system in the action of lithium has not been fully elucidated. In this review, we discuss biochemical, preclinical/behavioral and physiological evidence that implicates NMDAR/NO signaling in the therapeutic effect of lithium. NMDAR/NO signaling could also explain some of side effects of lithium.

Acute effects of lithium on dopaminergic responses: iontophoretic studies in the rat visual cortex

The interactions between lithium and cortical dopaminergic receptors were investigated using the iontophoretic technique to record and apply dopaminergic compounds, GABA, acetylcholine and LiCl on neurons in the primary visual cortex of the rat. The main responses to dopamine (DA) or to the D1 agonist (+/- )SKF38393 on spontaneously-active (SA) or visually-driven (VD) units was a prolonged decrease in firing and a reduction in the responsiveness to pulses of acetylcholine. The D1 antagonist SCH23390, applied iontophoretically or intravenously, blocked or attenuated the inhibitory responses to both DA and (+/- )SKF38393. The D2 agonist quinpirole (LY171555) either produced only slight excitations or had no effects on both VD and SA units. The concomitant application of lithium blocked the inhibitory responses to DA and to (+/- )SKF38393 but did not modify the responsiveness to LY171555. In addition, the DA- and (+/- )SKF38393-induced decreases in responsiveness to acetylcholine were also suppressed by lithium. These effects were on dopaminergic mechanisms, since the excitatory responses to acetylcholine alone as well as the inhibitions caused by GABA were unchanged by the application of lithium. These results imply that the modifications in sensitivity to dopaminergic agents induced by lithium are mediated by dopamine D1 receptors and are discussed in relation to adenylate-cyclase.

The functional anatomy and pathology of lithium-pilocarpine and high-dose pilocarpine seizures

Subcutaneous treatment of rats with low doses of lithium and pilocarpine or a high dose of pilocarpine results in a severe seizure--brain damage syndrome. Rats thus treated were studied with multiple-depth electrodes, quantitative [14C]2-deoxyglucose autoradiography, and light and electron microscopy. Rats receiving lithium-pilocarpine did not differ from high-dose pilocarpine rats in behavioral, electrographic, metabolic or histopathological findings, but lithium-pilocarpine reproduced the syndrome more reliably and with a lower acute mortality rate. Organized electrographic seizure activity developed just prior to the onset of behavioral forelimb clonus and appeared to originate from ventral forebrain in the vicinity of the ventral pallidum and/or nucleus accumbens. From these sites activity spread rapidly to involve other regions. Once initiated, electrographic seizures persisted for hours. Increased glucose utilization was found in most brain regions during the period of continuous seizure activity. The greatest increases were found in the ventral pallidum, globus pallidus, hippocampus, entorhinal cortex, amygdala, lateral septum, substantia nigra, ventrobasal and mediodorsal thalamus and frontal motor cortex. Animals sustaining seizures displayed a disseminated pattern of neural degeneration not involving globus pallidus or ventral pallidum but otherwise coinciding with the above pattern of enhanced glucose utilization. No consistent correlation was observed between the pattern of brain damage and known regions of high muscarinic cholinergic receptor density. Ultrastructurally, the cytopathological changes, like those associated with various other sustained seizure syndromes, resemble the excitotoxic type of damage glutamate is known to cause. This seizure-brain damage syndrome and that induced by systemic kainic acid appear to be similar in behavioral but not in electrophysiological or metabolic manifestations. During kainic acid seizures, electrographic changes are first recorded in the hippocampus while they are first detected in the ventral forebrain region in pilocarpine seizures. Pilocarpine also induced metabolic activation of ventral forebrain sites not activated by kainic acid. The cytopathology associated with the two syndromes is identical in type but not in pattern, the cholinergic model being characterized by much greater neocortical and slightly less hippocampal damage. Further study of these cholinergic models may provide new insights into the roles of the major excitatory neurotransmitter systems (cholinergic and glutamergic) in limbic epilepsy.

Perfusion with lithium modifies neurophysiological responses in the CA1 region of the hippocampal slice preparation

The effects of acute lithium exposure on extracellular electrophysiological responses in the CA1 region of the in vitro hippocampus were investigated. Field potentials were assessed while perfusing slices with normal media or media in which LiCl was substituted for NaCl in 30, 20, 10 and 2 mM amounts. Lithium concentration in the slice following 20 min perfusion with 20 mM lithium was determined to be about 14 mM. At the higher concentrations, lithium exposure depressed the presynaptic fiber volley and antidromic population spike. On the other hand, the population EPSP and orthodromic population spike were enhanced. No significant changes were found at 2 mM. The findings are compatible with one action of lithium being on the excitability of axons and synaptic terminals. Comparisons were drawn between previous studies involving chronic lithium exposure and the present results. In this acute preparation lithium effects, as reflected in the population EPSP, were in opposition to those found with chronic lithium exposure. Changes demonstrated in this preparation in fiber volley and antidromic population spike paralleled those found with chronic lithium exposure.

Characterization of lithium potentiation of pilocarpine-induced status epilepticus in rats

Subcutaneous administration of pilocarpine to rats that were pretreated with a small dose of lithium chloride results in the evolution of generalized convulsive status epilepticus. The production of status epilepticus is absolutely reproducible, has a very consistent time to onset (22 min), has a duration of several hours, and is extremely severe with a high mortality rate. Experimental results show that this animal model of status epilepticus: (i) requires activation of muscarinic receptors because the initiation of seizures is blocked by atropine; (ii) requires presynaptic cholinergic activity because it is attenuated by hemicholinium-3; (iii) recruits noncholinergic cells because when status epilepticus is established it is not altered by atropine administration; and (iv) is blocked by pretreatment with diazepam and ongoing seizures are terminated by administration of diazepam, similar to certain forms of status epilepticus in humans. The reproducibility, prolonged nature, and involvement of a clearly defined neurochemical system as the triggering mechanism, i.e., cholinergic activation, makes this a potentially valuable animal model of generalized convulsive status epilepticus.

Effects of lithium on [3H](-)quinuclidinyl benzilate [( 3H](-)QNB) binding to rat brain muscarinic cholinergic receptors

Addition of lithium in vitro inhibited the binding of [3H](-)QNB to muscarinic cholinergic receptors of homogenates of tissue prepared from the striatum, cortex, and hippocampus of rat brain. Chronic in vivo exposure of rats to lithium in their food produced serum levels of lithium comparable to therapeutic levels. After in vivo exposure, the tissue homogenates prepared from these rats had an apparent decrease in receptor density in the three brain areas. However, if the tissue homogenates were washed twice, before addition to the assays, no differences in binding were detectable. Similar effects on unwashed and washed tissue homogenates can be demonstrated after in vivo exposure to lithium. Therefore, the apparent decrease in binding after in vivo lithium treatment is probably due to lithium retained in the tissue. No permanent alterations in the muscarinic receptor characteristics were measurable after the removal of the lithium. Nevertheless, in vivo interactions at muscarinic receptors may be important under conditions when therapeutic levels of lithium are present.

Systemic cholinergic agents induce seizures and brain damage in lithium-treated rats

Administration of pilocarpine or physostigmine to rats treated with lithium chloride produced sustained limbic seizures, widespread brain damage, and increased concentrations of D-myo-inositol-1-phosphate (a metabolite of the phosphoinositides, lipids involved in membrane receptor function) in the brain. The syndrome was preventable with atropine. The physostigmine doses and concentrations of blood lithium that caused the syndrome are similar to those considered appropriate for psychiatric chemotherapy.