Long-lasting effects of early-life intervention in mice on adulthood behaviour, GABAA receptor subunit expression and synaptic clustering.

Variations in the early postnatal environment of rodents produce long-term changes in responses to stress that may underlie neuropsychiatric diseases such as anxiety, depression and schizophrenia. GABAA receptors undergo marked changes in their subunit composition during this period, involving a regionally-dependent replacement of α2 with α1 subunits, the so-called α-subunit switch. In this study we examined the effects of early-life environment on adulthood GABAA receptor α1 and α2 subunit expression and the synaptic clustering of GABAA receptors. Male and female mice were exposed to either 15min daily handling sessions (EH) or no intervention (NH) over postnatal day (PND) 1-14. Adulthood behavioural differences in anxiety were assessed on the elevated plus-maze. Immunoperoxidase histochemistry was used to examine the density of the α1 and α2 subunit proteins. Double-labelling immunofluorescence and confocal microscopy were used to study GABAA receptor synaptic clustering. NH animals showed increased anxiety-type behaviours in the elevated plus maze relative to EH mice. NH males showed a loss of α2 subunits from the thalamus and lower layers of the somatosensory cortex, whilst NH females showed a reduction of α2 but increase in α1 protein in lower layers of the primary somatosensory cortex only. The NH condition also reduced α1 subunit expression in dentate gyrus (DG) in both males and females. Regardless of sex, NH mice showed reduced colocalisation of GABAA receptor α2 subunits with the synaptic marker gephyrin relative to the control condition. These findings suggest that early-life environment has long-lasting effects on GABAA receptors, leading to long-term changes in adulthood behaviour, and are of relevance to neurodevelopmental explanations of stress-augmented neuropsychiatric disorders.

Detection of viral and bacterial respiratory pathogens in patients with cystic fibrosis.

The presence of viral respiratory infections is associated closely with exacerbations in patients with cystic fibrosis. Viral and bacterial multiplex PCRs were developed and applied to nasal swab samples from children with cystic fibrosis. This showed a large number of individuals with cystic fibrosis were infected with rhinoviruses, and more were infected with viral than bacterial pathogens. All individuals with parainfluenza 3 virus had clinical exacerbations of their cystic fibrosis, and although 3/4 of these children were co-infected with HRV. The findings do not suggest a significant association for any other virus or bacteria with exacerbation. There is clear evidence some viral infections are associated with cystic fibrosis that dual infection is more likely to produce symptoms, and mechanisms of viral-induced exacerbation should be elucidated.

Stress and GABA receptors.

GABA(A) receptors are sensitive to subtle changes in the environment in both early-life and adulthood. These neurochemical responses to stress in adulthood are sex-dependent. Acute stress induces rapid changes in GABA(A) receptors in experimental animals, with the direction of the changes varying according to the sex of the animals and the stress-paradigm studied. These rapid alterations are of particular interest as they provide an example of fast neurotransmitter system plasticity that may be mediated by stress-induced increases in neurosteroids, perhaps via effects on phosphorylation and/or receptor trafficking. Interestingly, some studies have also provided evidence for long-lasting changes in GABA(A) receptors as a result of exposure to stressors in early-life. The short- and long-term stress sensitivity of the GABAergic system implicates GABA(A) receptors in the non-genetic etiology of psychiatric illnesses such as depression and schizophrenia in which stress may be an important factor.

Antipsychotic drug administration differentially affects [3H]muscimol and [3H]flunitrazepam GABA(A) receptor binding sites.

Post-mortem studies of the human brain indicate that certain GABA(A) receptor subtypes may be differentially altered in schizophrenia. Increased binding to the total population of GABA(A) receptors using [3H]muscimol is observed in the post-mortem schizophrenic brain, yet a proportion of these receptors which bind benzodiazepines and are labelled with [3H]flunitrazepam, show decreased or unaltered expression. Data from animal studies suggest that antipsychotic drugs alter GABA(A) receptor expression in a subtype selective manner, but in the opposite direction to that observed in schizophrenia. To broaden our understanding of the effects of antipsychotic drugs on GABA(A) receptors, we examined the saturation binding maximum (B(max)) and binding affinity (K(D)) of [3H]muscimol and [3H]flunitrazepam in the prefrontal cortex (PFC), hippocampus and thalamus of male SD rats that received a sucrose solution containing either haloperidol (1.5 mg/kg), olanzapine (6.5 mg/kg) or no drug daily for up to 28 days using quantitative receptor autoradiography. [3H]Muscimol binding density was increased most prominently in the PFC after 7 days, with larger and more prolonged effects being induced by the atypical antipsychotic drug olanzapine in subcortical regions. While no changes were observed in [3H]muscimol binding in any region after 28 days of drug administration, [3H]flunitrazepam binding density (B(max)) was increased for both antipsychotic treatments in the PFC only. These findings confirm that the subset of GABA(A) receptors sensitive to benzodiazepines are regulated differently from other GABA(A) receptor subtypes following antipsychotic drug administration, in a time- and region-dependent manner.

The effects of antipsychotic drugs on GABAA receptor binding depend on period of drug treatment and binding site examined.

Changes in GABA(A) receptors are observed in schizophrenia, with benzodiazepine-sensitive GABA(A) receptor subtypes being affected differently to other subtypes. However, long-term antipsychotic drug use in schizophrenia may underlie these changes. To test this, we examined the effects of administering a typical (haloperidol) and an atypical (olanzapine) antipsychotic drug on the GABA(A) receptor agonist (orthosteric) and benzodiazepine (allosteric) binding sites in rat prefrontal cortex. As antipsychotic drugs have delayed maximal therapeutic effects we also examined different drug treatment periods. Male SD rats received a sucrose solution containing either haloperidol (1.5 mg/kg), olanzapine (6.5 mg/kg) or no drug daily for either 7, 14 or 28 days. Sections of rat brain were then labelled with [(3)H]muscimol, which labels the total population of GABA(A) receptors, or the benzodiazepine site ligand [(3)H]flunitrazepam in separate saturation binding experiments using quantitative receptor autoradiography. [(3)H]Muscimol binding was enhanced in the prefrontal cortex after 7 days but no differences were observed after longer periods of drug administration. In contrast there was a delayed increase in density of benzodiazepine-sensitive GABA(A) receptors in the PFC, suggesting that antipsychotic drugs have different effects on different GABA(A) receptor subtypes. These changes in the properties of GABA(A) receptor binding following antipsychotic drug administration are not consistent with those observed in schizophrenia and suggest a 'reshuffling' in GABA(A) receptor subtypes over time.