Socio-economic differences in body mass index: the contribution of genetic factors

BACKGROUND

Higher mean body mass index (BMI) among lower socioeconomic position (SEP) groups is well established in Western societies, but the influence of genetic factors on these differences is not well characterized.

METHODS

We analyzed these associations using Finnish health surveys conducted between 1992 and 2017 (N = 33 523; 53% women) with information on measured weight and height, polygenic risk scores of BMI (PGS-BMI) and linked data from administrative registers to measure educational attainment, occupation-based social class and personal income.

RESULTS

In linear regressions, largest adjusted BMI differences were found between basic and tertiary educated men (1.4 kg/m2, 95% confidence interval [CI] 1.2; 1.6) and women (2.5 kg/m2, 95% CI 2.3; 2.8), and inverse BMI gradients were also found for social class and income. These SEP differences arose partly because mean PGS-BMI was higher and partly because PGS-BMI predicted BMI more strongly in lower SEP groups. The inverse SEP gradients of BMI were steeper in women than in men, but sex differences were not found in the genetic contributions to these differences.

CONCLUSIONS

Better understanding of the interplay between genes and environment provides insight into the mechanisms explaining SEP differences in BMI.

Marital status and genetic liability independently predict coronary heart disease incidence

AIMS

Married individuals have a lower coronary heart disease (CHD) risk than non-married, but the mechanisms behind this are not fully understood. We analyzed whether genetic liability to CHD may affect these associations.

METHODS

Marital status, a polygenic score of CHD (PGS-CHD), and other risk factors for CHD were measured from 35,444 participants (53% female) in Finnish population-based surveys conducted between 1992 and 2012. During the register-based follow-up until 2020, there were 2439 fatal and non-fatal incident CHD cases. The data were analyzed using linear and Cox regression models.

RESULTS

Divorced and cohabiting men and women had a higher genetic risk of CHD than married individuals, but the difference was very small (0.023-0.058 standard deviation of PGS-CHD, p-values 0.011-0.429). Both marital status and PGS-CHD were associated with CHD incidence, but the associations were largely independent. Adjusting for behavioral and metabolic risk factors for CHD explained part of these associations (11-20%). No interaction was found between marital status and PGS-CHD for CHD incidence.

CONCLUSIONS

We showed minor differences between the marital status categories in PGS-CHD and demonstrated that marital status and genetic liability predicted CHD incidence largely independently. This emphasizes the need to measure multiple risk factors when predicting CHD risk.

Educational attainment, health outcomes and mortality: a within-sibship Mendelian randomization study

BACKGROUND

Previous Mendelian randomization (MR) studies using population samples (population MR) have provided evidence for beneficial effects of educational attainment on health outcomes in adulthood. However, estimates from these studies may have been susceptible to bias from population stratification, assortative mating and indirect genetic effects due to unadjusted parental genotypes. MR using genetic association estimates derived from within-sibship models (within-sibship MR) can avoid these potential biases because genetic differences between siblings are due to random segregation at meiosis.

METHODS

Applying both population and within-sibship MR, we estimated the effects of genetic liability to educational attainment on body mass index (BMI), cigarette smoking, systolic blood pressure (SBP) and all-cause mortality. MR analyses used individual-level data on 72 932 siblings from UK Biobank and the Norwegian HUNT study, and summary-level data from a within-sibship Genome-wide Association Study including >140 000 individuals.

RESULTS

Both population and within-sibship MR estimates provided evidence that educational attainment decreased BMI, cigarette smoking and SBP. Genetic variant-outcome associations attenuated in the within-sibship model, but genetic variant-educational attainment associations also attenuated to a similar extent. Thus, within-sibship and population MR estimates were largely consistent. The within-sibship MR estimate of education on mortality was imprecise but consistent with a putative effect.

CONCLUSIONS

These results provide evidence of beneficial individual-level effects of education (or liability to education) on adulthood health, independently of potential demographic and family-level confounders.

Polygenic Prediction of Education and Its Role in the Intergenerational Transmission of Education: Cohort Changes Among Finnish Men and Women Born in 1925-1989

Major changes in the educational distribution of the population and in institutions over the past century have affected the societal barriers to educational attainment. These changes can possibly result in stronger genetic associations. Using genetically informed, population-representative Finnish surveys linked to administrative registers, we investigated the polygenic associations and intergenerational transmission of education for those born between 1925 and 1989. First, we found that a polygenic index (PGI) designed to capture genetic predisposition to education strongly increased the predictiveness of educational attainment in pre-1950s cohorts, particularly among women. When decomposing the total contribution of PGI across different educational transitions, the transition between the basic and academic secondary tracks was the most important. This transition accounted for 60-80% of the total PGI-education association among most cohorts. The transition between academic secondary and higher tertiary levels increased its contribution across cohorts. Second, for cohorts born between 1955 and 1984, we observed that one eighth of the association between parental and one's own education is explained by the PGI. There was also an increase in the intergenerational correlation of education among these cohorts, which was partly explained by an increasing association between family education of origin and the PGI.

Height, social position and coronary heart disease incidence: the contribution of genetic and environmental factors

BACKGROUND

The associations between height, socioeconomic position (SEP) and coronary heart disease (CHD) incidence are well established, but the contribution of genetic factors to these associations is still poorly understood. We used a polygenic score (PGS) for height to shed light on these associations.

METHODS

Finnish population-based health surveys in 1992-2011 (response rates 65-93%) were linked to population registers providing information on SEP and CHD incidence up to 2019. The participants (N=29 996; 54% women) were aged 25-75 at baseline, and there were 1767 CHD incident cases (32% in women) during 472 973 person years of follow-up. PGS-height was calculated based on 33 938 single-nucleotide polymorphisms, and residual height was defined as the residual of height after adjusting for PGS-height in a linear regression model. HRs of CHD incidence were calculated using Cox regression.

RESULTS

PGS-height and residual height showed clear gradients for education, social class and income, with a larger association for residual height. Residual height also showed larger associations with CHD incidence (HRs per 1 SD 0.94 in men and 0.87 in women) than PGS-height (HRs per 1 SD 0.99 and 0.97, respectively). Only a small proportion of the associations between SEP and CHD incidence was statistically explained by the height indicators (6% or less).

CONCLUSIONS

Residual height associations with SEP and CHD incidence were larger than for PGS-height. This supports the role of material and social living conditions in childhood as contributing factors to the association of height with both SEP and CHD risk.

Association between genetic risk of alcohol consumption and alcohol-related morbidity and mortality under different alcohol policy conditions: Evidence from the Finnish alcohol price reduction of 2004

AIMS

Harmful alcohol consumption is influenced by both genetic susceptibility and the price of alcohol. Many previous studies have observed that genetic susceptibility to consumption of alcohol is more predictive in less restrictive drinking conditions. We assess whether such a pattern applies when the prices of alcoholic beverages are decreased.

DESIGN

Data consist of genetically informed population-representative surveys (FINRISK 1992, 1997, 2002 and Health 2000) linked to administrative registers. We analysed the interaction between a polygenic score (PGS) for alcoholic drinks per week consumed and price reduction in predicting the incidence of alcohol-related hospitalizations and deaths in difference-in-difference and interrupted time-series frameworks.

SETTING

Individuals in Finland were followed quarter-yearly from 1 March 2000 to 31 May 2008.

PARTICIPANTS

A total of 22 152 individuals (607 132-person quarter-years, 1399 outcome events) aged 30-79 years.

INTERVENTION

A natural experiment stemming from the alcohol tax reduction in March 2004 and import deregulation in May 2004.

MEASUREMENTS

Outcome was quarter-yearly-measured alcohol-related death or hospitalization. The independent variables of main interest were PGS and a price reform indicator. We adjusted for gender, age, age squared, season, 10 first principal components of the genome, data collection round and genotyping batch.

FINDINGS

Both alcohol price reduction and one standard deviation change in PGS were associated with alcohol-related health outcomes; odds ratios (ORs) were 1.32, 95% confidence interval (CI) = 1.13, 1.53 and 1.26, 95% CI = 1.12, 1.42 in the 8-year follow-up, respectively. The association between PGS and alcohol-related morbidity was similar before and after the alcohol price reform (PGS × price reform interaction OR = 0.96, 95% CI = 0.81, 1.14). These results were robust across different follow-up periods and measurement and analysis strategies.

CONCLUSIONS

Although the decrease of alcohol price in Finland in 2004 substantially increased overall alcohol-related morbidity and mortality, the genetic susceptibility to alcohol consumption did not become more manifest in predicting them.

Changes in sibling similarity in education among Finnish cohorts born in 1950-89: the contribution of paternal and maternal education

Among the many social characteristics that run in the family, education is one of the most strongly persistent. The long-term changes in educational reproduction within families and across generations and the gender-specific drivers of these changes remain partially unclear. Using population data for all Finnish siblings and their parents, we assessed the level of and trends in the intergenerational persistence of education among cohorts born between 1950 and 1989. The variance in education shared among siblings was 37% and remained stable over time. Parental education steadily increased its explanatory power in the shared variance, from 30% among cohorts born in the 1950s to 40% among cohorts born in the 1970s and 1980s. The direct contribution of maternal education net of paternal education for sibling similarity more than doubled across cohorts (from 5% in 1950 to 13% in 1989). The direct contribution of paternal education (10-12%) remained stable. Same-gender siblings resembled each other in education more closely than their opposite-gender counterparts. The growing importance of maternal education over time, which surpasses the predictive power of paternal education, demonstrates an important qualitative change in the determinants of educational stratification. The growing importance of mothers' education can plausibly result from the strengthening meritocratic achievement of women in education and the associated increase of women in defining the social position of the family. Incorporating the education of both parents in future analyses of intergenerational reproduction of education will probably be increasingly salient.

Joint associations of depression, genetic susceptibility and the area of residence for coronary heart disease incidence

BACKGROUND

Depression is a risk factor for coronary heart disease (CHD), but less is known whether genetic susceptibility to CHD or regional-level social indicators modify this association.

METHODS

Risk factors of CHD including a Polygenic Risk Score (PRS) were measured for 19 999 individuals residing in Finland in 1997, 2002, 2007 and 2012 (response rates 60%-75%). During the register-based follow-up until 2015, there were 1381 fatal and non-fatal incident CHD events. Unemployment rate, degree of urbanisation and crime rate of the municipality of residence were used as regional level social indicators. HRs were calculated using register-based antidepressant purchases as a non-reversible time-dependent covariate.

RESULTS

Those having depression and in the highest quartile of PRS had somewhat higher CHD risk than predicted only by the main effects of depression and PRS (HR for interaction 1.53, 95% CI 0.95 to 2.45). Depression was moderately associated with CHD in high crime (HR 1.51, 95% CI 1.20 to 1.90) and weakly in low crime regions (HR 1.07, 95% CI 0.86 to 1.33; p value of interaction=0.087). Otherwise, we did not found evidence for interactions.

CONCLUSIONS

Those having both depression and high genetic susceptibility need a special attention in healthcare for CHD.

Joint association between education and polygenic risk score for incident coronary heart disease events: a longitudinal population-based study of 26 203 men and women

BACKGROUND

Genetic vulnerability to coronary heart disease (CHD) is well established, but little is known whether these effects are mediated or modified by equally well-established social determinants of CHD. We estimate the joint associations of the polygenetic risk score (PRS) for CHD and education on CHD events.

METHODS

The data are from the 1992, 1997, 2002, 2007 and 2012 surveys of the population-based FINRISK Study including measures of social, behavioural and metabolic factors and genome-wide genotypes (N=26 203). Follow-up of fatal and non-fatal incident CHD events (N=2063) was based on nationwide registers.

RESULTS

Allowing for age, sex, study year, region of residence, study batch and principal components, those in the highest quartile of PRS for CHD had strongly increased risk of CHD events compared with the lowest quartile (HR=2.26; 95% CI: 1.97 to 2.59); associations were also observed for low education (HR=1.58; 95% CI: 1.32 to 1.89). These effects were largely independent of each other. Adjustment for baseline smoking, alcohol use, body mass index, igh-density lipoprotein (HDL) and total cholesterol, blood pressure and diabetes attenuated the PRS associations by 10% and the education associations by 50%. We do not find strong evidence of interactions between PRS and education.

CONCLUSIONS

PRS and education predict CHD events, and these associations are independent of each other. Both can improve CHD prediction beyond behavioural risks. The results imply that observational studies that do not have information on genetic risk factors for CHD do not provide confounded estimates for the association between education and CHD.

How voter turnout varies between different chronic conditions? A population-based register study

BACKGROUND

While poor self-rated health is known to decrease an individual's propensity to vote, disaggregation of the components of health on turnout has thus far received only little attention. This study deepens on the understanding of such relationships by examining the association between chronic diseases and voting.

METHODS

The study uses an individual-level register-based data set that contains an 11% random sample of the entire electorate in the 1999 Finnish parliamentary elections. With information on hospital discharge diagnoses and reimbursements for drugs prescribed, we identify persons with chronic hospital-treated diseases (coronary heart disease, chronic obstructive pulmonary disease (COPD) and asthma, depression, cancer, psychotic mental disease, diabetes, cerebrovascular disease, rheumatic disease, epilepsy, arthrosis, alcoholism, dementia, atherosclerosis, Parkinson's disease, other degenerative brain diseases, multiple sclerosis and kidney disease).

RESULTS

After adjusting for gender, age, education, occupational class, income, partnership status, cohabitation with underaged children and hospitalisation during Election Day, neurodegenerative brain diseases had the strongest negative relationship with voting (dementia OR=0.20, 95% CI 0.18 to 0.22; others up to OR=0.70). Alcoholism (OR=0.66) and mental disorders also had a negative association (depression OR=0.91; psychotic mental disease OR=0.79), whereas cancer and COPD/asthma had a positive association (both OR=1.05). Having more than one condition at a time further decreased voting probability.

CONCLUSIONS

By showing how different health conditions are related to voter turnout, this study provides essential information for identifying gaps in the potential for political participation and for further inquiries aiming to develop models that explain the link between health and voting probability.

Status Epilepticus Induces Changes in the Expression and Localization of Endogenous Palmitoyl-Protein Thioesterase 1

Kainic acid (KA)-induced experimental epilepsy, a model of excitotoxicity, leads to selective neuronal death and synaptic restructuring. We used this model to investigate the effects of neuronal hyperactivation on palmitoyl-protein thioesterase 1 (PPT1), the deficiency of which causes drastic neurodegeneration. Immunological stainings showed that epileptic seizures in adult rats led to a progressive and remarkable increase of PPT1 in limbic areas of the brain. Within 1 week, the maximal expression was observed in CA3 and CA1 pyramidal neurons of the hippocampus. In the surviving pyramidal neurons, PPT1 localized in vesicular structures in cell soma and neuritic extensions. After seizures, colocalization of PPT1 with synaptic membrane marker (NMDAR2B) was enhanced. Further, synaptic fractionation revealed that after seizures PPT1 was readily observed on the presynaptic side of synaptic junction. These data suggest that PPT1 may protect neurons from excitotoxicity and have a role in synaptic plasticity.

Post-insult activity is a major cause of delayed neuronal death in organotypic hippocampal slices exposed to glutamate

We investigated the pathophysiological mechanisms of glutamate-induced delayed neuronal damage in rat hippocampal slice cultures [Stoppini et al. (1991) J. Neurosci. Methods 37, 173-182], with propidium iodide as a marker of cell death. Exposure of the cultures to growth medium containing 10 mM glutamate for 30 min resulted in a slowly developing degeneration of hippocampal principal cells, starting from the medial end of the CA1 region and reaching the dentate gyrus by 48 h. By 24 h, most pyramidal cells in CA1 were damaged. An acute phase of degeneration preceded the delayed damage at 2-6 h, affecting cells in a spatially diffuse manner. When tetrodotoxin (0.5 microM) was present during the glutamate insult, a marked protection (mean 57%, P<0.001) of the CA1 damage was observed. Rather strikingly, when tetrodotoxin was applied immediately following or even with a delay of 30 min after the insult, a similar amount of protection was achieved. In field recordings carried out after the insult, the glutamate-treated slices exhibited spontaneously occurring negative shifts with a duration of 1-10 s and an amplitude of up to 400 microV in the CA3 region, whereas the control slices were always quiescent. Taken together, the results suggest that post-insult neuronal network activity, rather than the direct action of exogenous glutamate, is a major cause of delayed CA1 pyramidal cell death in the organotypic slices. These observations may have implications in the design of neuroprotective strategies for the treatment of brain traumas which are accompanied by delayed and/or distal neuronal damage.

The K+/Cl- co-transporter KCC2 renders GABA hyperpolarizing during neuronal maturation

GABA (gamma-aminobutyric acid) is the main inhibitory transmitter in the adult brain, and it exerts its fast hyperpolarizing effect through activation of anion (predominantly Cl-)-permeant GABA(A) receptors. However, during early neuronal development, GABA(A)-receptor-mediated responses are often depolarizing, which may be a key factor in the control of several Ca2+-dependent developmental phenomena, including neuronal proliferation, migration and targeting. To date, however, the molecular mechanism underlying this shift in neuronal electrophysiological phenotype is unknown. Here we show that, in pyramidal neurons of the rat hippocampus, the ontogenetic change in GABA(A)-mediated responses from depolarizing to hyperpolarizing is coupled to a developmental induction of the expression of the neuronal (Cl-)-extruding K+/Cl- co-transporter, KCC2. Antisense oligonucleotide inhibition of KCC2 expression produces a marked positive shift in the reversal potential of GABAA responses in functionally mature hippocampal pyramidal neurons. These data support the conclusion that KCC2 is the main Cl- extruder to promote fast hyperpolarizing postsynaptic inhibition in the brain.

Selegiline treatment after transient global ischemia in gerbils enhances the survival of CA1 pyramidal cells in the hippocampus

Selegiline (L-deprenyl) has shown neuroprotective effects in a variety of degenerative processes. The present experiments were designed to test whether post-ischemia administered selegiline would alleviate delayed neuronal death of the gerbil hippocampal pyramidal cells following transient global ischemia. Common carotid arteries were occluded for 5 min. Saline or selegiline, 0.25 mg/kg s.c., was administered 2 h after the ischemia followed by a daily injection for either 3 or 7 days. After decapitation, the delayed death of the hippocampal CA1 pyramidal cells was assessed using Nissl-stained sections. In situ hybridization was used to reveal the expression of hsp70 mRNA 1, 3 or 7 days after the ischemia. Animals treated with selegiline for 7 days showed significantly lower damage score (scale 0-3: 0, normal; 1, < 10% of the neurons damaged; 2, 10-50% damaged; 3, > 50% damaged) compared to the saline-treated animals 1.73 +/- 0.18 and 2.41 +/- 0.16 (mean +/- S.E.M., P = 0.0133), respectively. A similar trend was found in animals after the 3-day treatment: 1.68 +/- 0.32 vs. 2.06 +/- 0.25 (P > 0.5). The expression of hsp70 mRNA in the CA1 pyramidal cell layer was strong still 3 days after the ischemic insult but vanished by 7 days. Densitometric measurements using 14C-plastic standards showed that the intensity of the CA1a hsp70 signal on the 3rd day correlated negatively to the cell-damage score (r = -0.72, P < 0.001), suggesting that hsp70 does not serve as a quantitative marker for CA1 neuronal injury in this model. Instead, the hsp70 expression was associated with improved neuronal survival lasting often longer in selegiline-treated animals (P > 0.5). The results show that a low dose of selegiline can alleviate the delayed hippocampal neuronal death in gerbils when administered 2 h after an ischemic insult.

Failure of carbamazepine to prevent behavioural and histopathological sequels of experimentally induced status epilepticus

Sustained electrical stimulation of the perforant pathway was used to induce long-lasting hippocampal seizures in conscious rats. One hour prior to stimulation, rats were given i.p. injections of either saline or a commonly used antiepileptic drug, carbamazepine (5H-dibenz[b, f]azepine-5-carboxamide; CBZ; 20 mg/kg). When tested 2 weeks later in a water maze, both the saline- and the carbamazepine-pretreated rats showed similarly a severe impairment in spatial learning compared to non-stimulated controls. Histological evaluation revealed that the pyramidal cell damage was (P < 0.05) milder in the carbamazepine-pretreated group in the CA1, but not the CA3c subfield. However, the number of somatostatin-immunoreactive neurons in both stimulated groups was reduced equally. Thus, at the dose of 20 mg/kg, which is a usual anticonvulsive dose in humans, carbamazepine seems to offer only partial protection against pyramidal cell damage, but no protection against the hilar somatostatin-immunoreactive neuron loss or the spatial learning deficit after perforant pathway stimulation in rats. The result clearly differs from that obtained either with a GABA (gamma-aminobutyric acid)-enhancing drug and a novel antiepileptic, vigabatrin (4-amino-hex-5-enoic acid) or with a competitive NMDA (N-methyl-D-aspartate) receptor antagonist, CGP 39551 (DL-[E]-2-amino-4-methyl-5-phosphono-3-pentenoic acid carboxyethylester) in the same test situation.

d-Cycloserine, a partial agonist at the glycine site, enhances the excitability of dentate granule cells in vivo in rats

The present study investigated the dose-dependent effects of d-cycloserine, a partial agonist at the glycine modulatory site associated with the NMDA receptor complex, on the hippocampal field potentials of dentate granule cells in awake, freely moving rats. Five sequential field potentials were recorded from the dentate gyrus of the dorsal hippocampus, by stimulating the perforant path in the entorhinal cortex at 30-s intervals. The slope of the population excitatory postsynaptic potential (e.p.s.p.) and the amplitude of the population spike of these field potentials were analysed and averaged with a computer. The effects of d-cycloserine (1.0, 3.0, 9.0 mg/kg) were recorded 40 min and 24 h after the i.p. injection. Although the slope of the population e.p.s.p. showed no significant change after the administration of d-cycloserine, the high doses produced a substantial increase in the amplitude of the population spike. This increase was observed 40 min but not 24 h after the injection. These findings indicate that d-cycloserine does not change the synaptic input from the perforant path to the granule cells but dose dependently enhances the excitability of the hippocampal dentate granule cells. In addition, the data give further support to the suggestion that in the brain area where NMDA receptor density is relatively high, the glycine site of the NMDA receptor may not be fully saturated by endogenous glycine in normal in vivo conditions. This suggests that there is a possibility for pharmacological modulation of NMDA receptor-mediated synaptic events by exogenous glycine or glycine analogues.

Spatial learning and noradrenaline content in the brain and periphery of young and aged rats

The present experiment studied whether a dysfunction of the noradrenergic neurons is related to spatial learning impairment by investigating the levels of noradrenaline in the brain and periphery as well as the acquisition of water maze task in saline-pretreated young rats, in noradrenergic neurotoxin (DSP-4)-pretreated young rats and in saline-pretreated aged rats. Aged rats, which had an increased escape latency onto the hidden platform, revealed a decreased noradrenaline content in the heart, but not in the hippocampus, striatum, or hypothalamus, whereas DSP-4-pretreated rats had decreased noradrenaline content in the brain; the acquisition of water maze task was not impaired. These results suggest that the peripheral noradrenergic system can show age-related changes different from those in the central noradrenergic system, and they failed to provide support for the hypothesis that decreased activity of the central noradrenergic nerves is related to impairment in the acquisition of the water maze task.

The effects of selective alpha-2 adrenergic agents on the performance of rats in a 5-choice serial reaction time task

The present study investigated how the systemic administration of alpha-2 adrenergic agents that modulate the function of the noradrenergic system in brain, affect rousal and sustained attention. Food-deprivated rats were trained to detect and respond to brief flashes of light presented randomly in one of five spatially diverse locations. The effects of single-dose administrations of dexmedetomidine, an alpha-2 agonist, and atipamezole, an alpha-2 antagonists, on the choice accuracy, errors of omissions, speed of responding, and collection of the reward could be assessed in this task. Dexmedetomidine increased the amount of omissions, speed of response, and decreased the number of premature responses, although it did not markedly lengthen response latencies and food collection latency. Atipamezole increased the number of premature responses. Neither dexmedetomidine nor atipamezole had any effect on choice accuracy of rats in this task. The results suggest that dexmedetomidine decreased behavioral activity and arousal of rats, whereas atipamezole had mild stimulant effect on behavior.

Preservation of hippocampal NMDA receptors may be crucial for spatial learning after epileptic seizures in rats

Sustained electrical stimulation of the perforant pathway (PP) was used to induce hippocampal seizures in conscious rats. About 4.5 h prior to stimulation, animals were given i.p. injections of either saline or CGP 39551 (10 mg/kg), a competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor. When tested 2 weeks later in water maze, the saline pretreated rats showed a severe impairment in spatial learning whereas the animals treated with CGP 39551 had the same escape latencies as the non-stimulated controls. Histological evaluation of cellular degeneration revealed that the number of somatostatin-immunoreactive (SOM-IR) neurons in both stimulated groups was reduced almost equally, but in the CGP 39551 treated animals pyramidal cell damage was partly protected. However, in contrast to the placebo group, NMDA-sensitive [3H]glutamate binding in strata radiatum and oriens of the CA1 area was not significantly reduced in the CGP 39551 group. Thus, the present results suggest that the CGP 39551 treatment was able to protect against the delayed phase of the excitotoxic cell damage, and that the preservation of NMDA receptors partly accounts for the good learning ability of the CGP 39551 pretreated, PP-stimulated rats.

Epileptogenic spikes and seizures but not high voltage spindles are induced by local frontal cortical application of gamma-hydroxybutyrate

Combining the methods of microdialysis and EEG recording, we have examined the effect of unilaterally, intracortically applied gamma-hydroxybutyrate (GHB) on frontal cortical EEG activity in freely moving rats. GHB, a natural endogenous GABA metabolite, is known to induce rhythmic spike and wave activity, resembling generalized petit mal epilepsy. Without GHB, spontaneous high voltage spindles (HVS, 6-9 Hz) were observed during awake and immobile behavior in most of the animals (HVS rats), while others never had any HVS. In those both groups of animals intracortical application of GHB induced epileptogenic spikes (< 0.5 Hz) behaviorally accompanied by occasional myoclonic jerks and epileptic discharges (< 2 Hz) with behavioral convulsions and contraversive movements towards the left hindlimb (seizures) but did not induce HVS or spike and waves, as reported after systemic application. In the group of rats with spontaneous occurring HVS the amplitude of the HVS on the side of the microdialysis probe was suppressed by GHB and GHB-induced spikes invading the contralateral cortex frequently triggered and terminated local HVS. The results point to different neural mechanisms for the generation of HVS and spikes and epileptic discharges (seizures) induced after local intracortical application of GHB.

Long-term alterations in NMDA-sensitive L-[3H]glutamate binding in the rat hippocampus following fimbria-fornix lesioning

Subcortical deafferentation of the rat hippocampus has been suggested to offer a model for developing limbic epilepsy. In the present study, the long-term effect of fimbria-fornix lesioning on the density and distribution of hippocampal N-methyl-D-aspartate (NMDA)-sensitive L-[3H]glutamate binding was studied using quantitative autoradiography. Compared to controls of the same age, the fimbria-fornix-lesioned (FFL) rats showed 1 year after lesioning a uniform, 20-33% increase in NMDA receptor density throughout the hippocampus, which was statistically significant in the stratum radiatum of the CA1 area (P = 0.001 and P < 0.05) and in the inner and outer halves of the dentate molecular layer (P < 0.05 for both). The increased receptor density in the FFL rats may reflect a long-term process of regeneration within the hippocampal formation, which could partly account for the maintenance or development of epileptogenity. The control animals, which were over 1 year old, showed lower binding density than young animals in all areas measured, thus suggesting a decrease in NMDA receptor binding during normal aging.

NMDA-sensitive [3H]glutamate binding in the epileptic rat hippocampus: an autoradiographic study

Sustained stimulation of the perforant pathway (PP) offers a model for studying seizure-induced pathology of the hippocampal formation. Using quantitative autoradiography, NMDA-sensitive glutamate binding was evaluated in the rat hippocampus three weeks after PP-stimulation. Decreased receptor binding (38-44%) was found together with pyramidal cell damage and gliosis in the CA1 area, ipsilateral to the stimulation (p < or = 0.001). In the dentate gyrus, however, a 20% increase in receptor density was observed bilaterally within the molecular layer (significant within the outer molecular layer of the contralateral side, on the suprapyramidal location; p < or = 0.05). These results are similar to those found in epileptic patients and suggest a prominent role for NMDA receptors in epilepsy.

Biochemical and morphological changes in the rat hippocampus following transection of the fimbria-fornix

According to electrophysiological studies, the subcortically denervated hippocampus has been suggested as a model for limbic epilepsy. We investigated a) whether fimbrial lesioning leads to any biochemical or morphological changes in the rat hippocampus, b) if these changes give any explanation to the previously indicated hyperexcitability, and c) if the changes are in line with the findings in other experimental models and human epilepsy. The fimbria-fornix transection was done by aspiration. Four months later, spontaneous EEG activities were recorded, and the hippocampal formation was processed for histology. In addition, a separate group of lesioned rats was used for hippocampal amino acid analysis. Hyperexcitable functioning of the hippocampus was seen as frequent and rhythmic spiking activity in 25% of the fimbria-fornix-lesioned rats, although the rest of them had spikes occasionally. The amino acids analysis revealed a notable decrease in the concentration of GABA but no significant changes in the amount of excitatory amino acids. This suggests impaired GABAergic functioning but does not exclude possible abnormalities in the release of both excitatory and inhibitory amino acids. The number of somatostatin-immunoreactive (SOM-IR) neurons, a subpopulation of GABAergic neurons, was decreased in all the areas of the hippocampus (CA3 > CA1 > hilus), but this was statistically significant only in the CA3 area. Interestingly, it is the region from which interictal spiking activity in the subcortically denervated rat presumable originates. Immunostaining for synaptophysin showed a dense band of granules in the inner molecular layer of the dentate gyrus, indicating probable synaptic reorganization of associational afferents.

Acute effects of gamma-vinyl GABA on the GABAergic system in rats as studied by microdialysis

The acute effects of the irreversible gamma-aminobutyric acid (GABA) transaminase inhibitor, gamma-vinyl GABA (Vigabatrin), were studied in the central nervous system of the rat. GABA concentrations were monitored in the hippocampus by implantation of microdialysis probes. Two doses of gamma-vinyl GABA (1.6 and 8.0 mM) were administered via the probes and were found to cause a transient increase in the basal GABA outflow (10-fold) during the period of drug administration. In addition, gamma-vinyl GABA pretreatment (1.6 mM) seemed to decrease K(+)-evoked GABA release (P < 0.05). The immediate increase of GABA outflow after gamma-vinyl GABA administration may be the result of direct blockade of GABA uptake sites, a finding which further indicates that the action of GABA transaminase inhibitors may be mediated partly through GABA uptake inhibition.

Somatostatin release in rat neocortex during gamma-hydroxybutyrate-provoked seizures: Microdialysis combined with EEG recording

Gamma-hydroxybutyrate (GHB) was intracortically applied in two doses (first 10 and then 20 mg/ml) to awake Wistar rats using microdialysis. Simultaneously, EEG and the release of somatostatin-like immunoreactivity (SLI) were measured from the frontal cortex. Intracerebrally administered GHB induced cortical epileptogenic spikes, but not high voltage spindles (HVS) as reported after systemic administration, and seizures with myoclonic jerks and contraversive head movements. Compared to the basal level, GHB (10 mg/ml) initially increased the release of SLI (p < 0.05). However, when the frequency of spikes and seizures rose rapidly (p < 0.001), SLI release decreased significantly (p < 0.001). Minimum release of SLI occurred when seizures were most frequent (during perfusion with 20 mg/ml GHB), while after removal of the drug it rose above the basal level (p < 0.05). According to these results, intracortically applied GHB increases the release of SLI in the surrounding tissue. However, further exposure of GHB leads to a manifestation of epileptic spikes and seizures, during which the release of SLI is significantly attenuated. This suggests that release of somatostatin is affected during epileptic phenomena induced also by intracortical GHB application.

D-cycloserine, a modulator of the N-methyl-D-aspartate receptor, improves spatial learning in rats treated with muscarinic antagonist

The results of the present study indicate that D-cycloserine, a partial agonist at the glycine binding site, which is a positive modulation site of the N-methyl-D-aspartate receptor, could improve dose dependently the acquisition of a water maze task in rats treated with scopolamine, a muscarinic antagonist. The low to moderate doses of D-cycloserine which improved learning did not affect swimming speed in scopolamine-treated rats. The higher dose did not improve learning, but it increased swimming speed in scopolamine-treated rats. These results show a dissociation between impaired acquisition and abnormal behavioral activity in scopolamine-treated rats in the water maze task. Furthermore, the present results suggest that D-cycloserine can act as a cognitive enhancer at the appropriate doses.

Pattern of neuronal death in the rat hippocampus after status epilepticus. Relationship to calcium binding protein content and ischemic vulnerability

The pattern of hippocampal cell death has been studied following hippocampal seizure activity and status epilepticus induced by 110-min stimulation of the perforant pathway in awake rats. The order of vulnerability of principal cells in the different hippocampal subfields--as determined by silver impregnation--was found to be very similar to the pattern found in ischemia; i.e., dentate hilus greater than CA1, subiculum greater than CA3c greater than CA3a,b greater than dentate granule cells. The hilar somatostatin-containing cells were the most vulnerable cell type, whereas all other subpopulations of nonprincipal neurons--visualized by immunocytochemistry for the calcium binding proteins parvalbumin and calbindin--were remarkably resistant. Pyramidal cells in the CA3 region containing neither of the examined calcium binding proteins were more resistant to overexcitation than CA1 pyramidal cells, most of which do contain calbindin. This indicates that no simple relationship exists between vulnerability in status epilepticus and neuronal calcium binding protein content, and that local and/or systemic hypoxia during status epilepticus may be responsible for the ischemic pattern of cell death.

Tetrahydroaminoacridine improves passive avoidance retention defects induced by aging and medial septal lesion but not by fimbria-fornix lesion

The present study examines whether tetrahydroaminoacridine (THA) can improve the deterioration in passive avoidance (PA) retention performance induced by medial septal (MS) and fimbria-fornix (FF) lesions in young rats or by aging. Retention of young MS-lesioned rats was improved by pretraining injection of THA at 3 mg/kg, but not by THA at 1 mg/kg or by either of the posttraining doses of THA (1 and 3 mg/kg). Pretraining injections of THA at 1 or 3 mg/kg had no effect on the PA retention performance of FF-lesioned rats. Age-induced PA failure was alleviated by pretraining administration of THA at 1 and 3 mg/kg. Posttraining injections of THA (1 or 3 mg/kg) had no effect on PA retention performance of aged rats. These results demonstrate that 1) THA may improve hippocampal cholinergic denervation-induced functional deficits and 2) some of the age-related PA deficits may be due to a cholinergic deficit and can be reversed with THA.

Behavioural, electrophysiological and histopathological changes following sustained stimulation of the perforant pathway input to the hippocampus: effect of the NMDA receptor antagonist, CGP 39551

Sustained stimulation of the perforant path has been shown to damage the CA1 area and impair spatial memory in rats. The pattern of cell death is similar in human epileptics, who also exhibit memory deficits. In this study we demonstrate that the learning/memory impairment in water maze test and the development of interictal spikes that also followed stimulation-induced damage were antagonized by CGP 39551. Pretreatment with this NMDA receptor antagonist also slightly diminished somatostatin cell loss in the hilus but not CA1 pyramidal cell damage. These results indicate that the impairment of spatial learning/memory seems to be dependent not only on the degree of cell degeneration in the CA1 subfield of the hippocampus but also on the frequency of interictal spikes, at least in this model of epilepsy.

Vigabatrin pre-treatment prevents hilar somatostatin cell loss and the development of interictal spiking activity following sustained simulation of the perforant path

Somatostatin-containing neurons in the hilus of the dentate gyrus are known to be exceptionally vulnerable in experimental models of epilepsy, as well as in human temporal lobe epilepsy. The position of these cells in the circuitry of the dentate gyrus is ideal for gating the activation evoked by afferents from the entorhinal cortex. In the present study we have shown that the loss of hilar somatostatin-containing neurons, and the development of interictal spiking activity induced by sustained perforant pathway stimulation can be prevented by high doses (500 mg/kg), but not by low doses (100 mg/kg) of vigabatrin, an irreversible inhibitor of GABA-transaminase.

The effect of subchronic administration of vigabatrin on learning and memory in nonepileptic rats

The present experiments investigated whether subchronic administration of vigabatrin, a GABA-mimetic drug, affects the performance of normal rats in the behavioural tasks assessing learning and memory. The effects of vigabatrin [50-200 mg/kg (IP)/day] administration on the acquisition and retention of water maze and passive avoidance task were studied. According to the results of three experiments, vigabatrin treatment did not markedly impair the acquisition or retention of water maze task. Furthermore, vigabatrin-treated rats were not inferior to saline-treated rats in reversal learning of water maze task. On the other hand, vigabatrin treatment slightly increased the speed of swimming in rats. The administration of vigabatrin did not affect the performance (training latency, number of training trials, testing latency) of rats in the passive avoidance task. According to these results, the effects of vigabatrin, a new antiepileptic drug, on the performance of nonepileptic rats were modest in behavioural tasks used to assess learning and memory.

Effect of antiepileptic drugs on somatostatin release in vitro

In the present study we investigated the effect of antiepileptic drugs on high potassium (50 mM) stimulated somatostatin release in rat cortical slices in a superfusion system. The somatostatin-like immunoreactivity (SLI) in superfusate was determined by radioimmunoassay. The antiepileptic drugs studied, vigabatrin, valproate, carbamazepine, phenobarbital, primidone, clonazepam and phenytoin were tested at a concentration range of 1-1000 microM). Of the drugs used vigabatrin had the most significant inhibitory effect on SLI release (IC50 = 240 microM). Vigabatrin also caused a concomitant, dose-dependent increase in superfusate gamma-amino butyric acid (GABA) level. A 30% decrease in the release of SLI followed incubation with valproate and carbamazepine, but only at high drug concentrations (1000 microM). Phenobarbital, primidone, clonazepam and phenytoin did not affect SLI release. Addition of GABA to superfusate caused a dose-dependent decrease in the amount of SLI release (IC50 = 56 microM). In conclusion, at low concentrations the antiepileptic drugs had only minor effects on SLI release. At higher concentrations, however, vigabatrin and valproate decreased the release of SLI, which may relate to their ability to elevate tissue levels of GABA.