John M. Littleton

Background: The ethanol withdrawal (EWD) syndrome is typically treated using benzodiazepines such as diazepam. However there is concern that benzodiazepines may not prevent neurotoxicity associated with EWD. Antagonists of glutamate/N‐Methyl‐D‐Aspartate receptors (NMDARs) such as MK801 have been shown to be effective against both EWD‐induced neurotoxicity in vitro and seizures in vivo. However, most of these agents have adverse side effects. An exception is the moderate affinity NMDAR channel blocker memantine, used in Alzheimer’s dementia. The present studies examined the ability of memantine to protect against EWD‐related toxicity in vitro and seizures in vivo.Methods: Organotypic hippocampal slice cultures from neonatal rat pups were treated starting at 15 days in vitro with 100 mM ethanol for 10 days followed by a 24‐hour EWD period. During the 24‐hour EWD period cultures were treated with memantine (15 or 30 μM). MK801 (10 μM) was utilized as a positive control. For the in vivo studies, the ability of memantine (2, 5, 10, and 15 mg/kg) to reduce convulsions was analyzed in Swiss‐Webster mice using the handling induced convulsion test paradigm.Results: In vitro studies demonstrated that memantine is effective at blocking EWD‐induced neurotoxicity. In vivo experiments showed that memantine also significantly reduced convulsions induced by EWD in mice.Conclusions: Memantine may be of therapeutic value during alcohol detoxification by virtue of its having neuroprotective effects in addition to anti‐seizure activity. The potential role of memantine in treatment of alcoholism is deserving of further study.

In general, 'drinkers smoke', and a high proportion of the alcohol-dependent population is also nicotine-dependent. Statistically, the majority of alcoholics will die of smoking-related, rather than alcohol-related, disease. This co-dependent sub-population may have higher levels of nicotine dependence, and find smoking cessation more difficult. Major reasons are that concurrent alcohol use, and/or prior alcohol exposure, may change the reinforcing effects of nicotine, and that each drug becomes a pharmacological cue for the expectation of the other. If so, then smokers whose nicotine dependence is impacted by alcohol, represent a large and distinct sub-population in which both the therapeutic and molecular targets for smoking cessation are altered. This, in turn, has implications for the validity of animal models of nicotine reinforcement, and for the development of novel smoking cessation medications. It is no longer possible to ignore the fact that the two most prevalent and damaging addictive drugs in our society are very commonly used by the same individuals. Without a better understanding of the psychological and pharmacological interactions between alcohol and nicotine that impact dependence, we cannot hope to provide appropriate medications for this large and problematic patient group. Our intention in this opinion overview is to use the current literature to provide a framework for future studies into the impact of alcohol use on the reinforcing effects of nicotine.

To have a future in the pharmaceutical industry, plant drug discovery must compete with combinatorial chemistry and high-throughput pharmacologic screening (HTPS). Plant functional genomics coupled with HTPS may achieve this; thus, functional biology can identify ‘libraries’ of candidate plant species from which individuals can be prioritized by ‘differential HTPS’. The full genomic potential of a species for bioactivity can be accessed by cellular mutagenesis and elicitation, with HTPS identifying clones with novel activity. The comparison of ‘positive’ clonal phenotypes with their almost identical ‘negatives’ facilitates the identification of active compounds and ‘genomic’ products. The logical conclusion is to use combinatorial genomics together with HTPS to direct plant cellular ‘evolution’ continuously towards metabolites with specific pharmacologic activity. Mankind would then become the orchestrator of plant secondary metabolism, rather than its passive beneficiary.

Background: Previous studies have shown that withdrawal from ethanol (EtOH) exposure induces neuronal damage, as indicated by propidium iodide (PI) uptake, in organotypic hippocampal slice cultures. This is prevented by MK801, suggesting that damage is “excitotoxic,” resulting from activation of N‐methyl‐d‐aspartate (NMDA) receptors by endogenous glutamate. To avoid reliance on a single indicator, and to enable assessment of recovery from the EtOH withdrawal (EWD) insult, we assessed changes in cell markers for neurons and glia, as well as cell division, following either EWD or NMDA challenge (as a positive control).Methods: Organotypic cultures from postnatal day (PND) 8 rats were cultured for 5 days before exposure to EtOH (mean concentration ∼65 mM) for 10 days before EWD. Cultures of the same “days in vitro” age (DIV16) were exposed to NMDA (200 μM) for 1 hour. Neuronal injury was visualized using PI and indices of neurons, glia, or cell division were measured at intervals up to 10 days following the neurotoxic insults. Each time point and measurement used separate slice cultures, and these were treated as separate experiments with paired controls. Regional neuronal content was assessed by neuronal nuclear protein (NeuN) and calbindin D28k (Calb), glial content by glial fibrillary acidic protein (GFAP), and cell division by bromodeoxyuridine (BrdU) incorporation, all measured immunohistochemically.Results: Chronic exposure to EtOH was associated with a dramatic reduction in BrdU incorporation in all regions of cultures. Propidium iodide fluorescence in the CA1 region was elevated significantly after EWD and more so after NMDA challenge. Reduced immunoreactivity (IR) of NeuN and Calb suggested that loss of neurons resulted from the EWD insult. Bromodeoxyuridine incorporation was initially depressed even further by EWD, but had returned to control levels after 3 days. In contrast, following NMDA insult, BrdU incorporation was significantly and persistently elevated above control levels after 3 days. Glial fibrillary acidic protein was reduced immediately after both EWD and NMDA challenge. Several days after EWD, expression of neuronal and glial markers, although variable, had generally returned to control levels. In contrast, NeuN IR remained significantly reduced after NMDA challenge.Conclusions: In general, the use of additional markers supports data obtained with PI uptake alone and suggests that neurons (and glia) are lost from the culture following EWD or NMDA challenge. These cell markers recover several days after EWD, but it is unclear whether functional recovery accompanies these changes. If the dramatic effect of EtOH exposure and EWD on BrdU incorporation reflects reduced neuro‐ and gliogenesis, it is likely that this adversely affects long‐term recovery from EWD. Finally, some markers showed significant and consistent changes after EWD, whereas others did not. This information may facilitate the use of this model in evaluation of potential medications that protect against and/or promote recovery from neurotoxicity.

Few medications for treating alcohol dependence exist. Greater partnership is needed between academia and the pharmaceutical industry to develop, licence and market efficacious medications for treating alcohol dependence. Methodologies that span the divide between preclinical and large-scale clinical studies need to be developed in order to provide sufficient information on safety, toleration, drug-interaction profile and efficacy, with which to guide development decisions. Due to the heterogeneous nature of alcohol dependence, the effort of developing an efficacious medication is likely to be enhanced by clearer choices about the characteristics of the population. Careful consideration of potential mechanism of action of the putative therapeutic medication should enable the appropriate choice of drinking endpoint. The pharmaceutical industry in collaboration with academia might need to develop new approaches to determining appropriate treatment endpoints with regulatory bodies. The investment risk to industry should be appraised not only in terms of the rather poor results of previous marketing efforts but with a view to the opportunity to penetrate a potentially enormous and largely untapped market.

Naltrexone and acamprosate may ultimately prove to be useful additions to pharmacotherapy for alcoholism by reducing relapse. Naltrexone is a relatively selective competitive antagonist at mu‐opioid receptors, and this activity may explain its anti‐relapse action either because endogenous opioids are involved in the positively reinforcing effects of alcohol and/or because these same transmitters are involved in the conditioned anticipation of these effects. In contrast, the pharmacology of acamprosate is still poorly understood. This is not surprising because it is a small flexible molecule with similarities to several neuro‐active amino acids and is used in high doses. All these factors suggest that it may have multiple actions. Currently, the best explanation for the effects of acamprosate seems to be that it inhibits the glutamatergic transmitter system involved in both the negative reinforcing effects of alcohol and the conditioned “pseudo‐withdrawal” that may be important in cue‐induced relapse.