Mutations in the parkin gene cause autosomal recessive juvenile parkinsonism

Parkinson's disease is a common neurodegenerative disease with complex clinical features. Autosomal recessive juvenile parkinsonism (AR-JP) maps to the long arm of chromosome 6 (6q25.2-q27) and is linked strongly to the markers D6S305 and D6S253; the former is deleted in one Japanese AR-JP patient. By positional cloning within this microdeletion, we have now isolated a complementary DNA done of 2,960 base pairs with a 1,395-base-pair open reading frame, encoding a protein of 465 amino acids with moderate similarity to ubiquitin at the amino terminus and a RING-finger motif at the carboxy terminus. The gene spans more than 500 kilobases and has 12 exons, five of which (exons 3-7) are deleted in the patient. Four other AR-JP patients from three unrelated families have a deletion affecting exon 4 alone. A 4.5-kilobase transcript that is expressed in many human tissues but is abundant in the brain, including the substantia nigra, is shorter in brain tissue from one of the groups of exon-4-deleted patients. Mutations in the newly identified gene appear to be responsible for the pathogenesis of AR-JP, and we have therefore named the protein product 'Parkin'.

Diagnosis and management of dementia with Lewy bodies: third report of the DLB Consortium

The dementia with Lewy bodies (DLB) Consortium has revised criteria for the clinical and pathologic diagnosis of DLB incorporating new information about the core clinical features and suggesting improved methods to assess them. REM sleep behavior disorder, severe neuroleptic sensitivity, and reduced striatal dopamine transporter activity on functional neuroimaging are given greater diagnostic weighting as features suggestive of a DLB diagnosis. The 1-year rule distinguishing between DLB and Parkinson disease with dementia may be difficult to apply in clinical settings and in such cases the term most appropriate to each individual patient should be used. Generic terms such as Lewy body (LB) disease are often helpful. The authors propose a new scheme for the pathologic assessment of LBs and Lewy neurites (LN) using alpha-synuclein immunohistochemistry and semiquantitative grading of lesion density, with the pattern of regional involvement being more important than total LB count. The new criteria take into account both Lewy-related and Alzheimer disease (AD)-type pathology to allocate a probability that these are associated with the clinical DLB syndrome. Finally, the authors suggest patient management guidelines including the need for accurate diagnosis, a target symptom approach, and use of appropriate outcome measures. There is limited evidence about specific interventions but available data suggest only a partial response of motor symptoms to levodopa: severe sensitivity to typical and atypical antipsychotics in approximately 50%, and improvements in attention, visual hallucinations, and sleep disorders with cholinesterase inhibitors.

Familial Parkinson disease gene product, parkin, is a ubiquitin-protein ligase

Autosomal recessive juvenile parkinsonism (AR-JP), one of the most common familial forms of Parkinson disease, is characterized by selective dopaminergic neural cell death and the absence of the Lewy body, a cytoplasmic inclusion body consisting of aggregates of abnormally accumulated proteins. We previously cloned PARK2, mutations of which cause AR-JP (ref. 2), but the function of the gene product, parkin, remains unknown. We report here that parkin is involved in protein degradation as a ubiquitin-protein ligase collaborating with the ubiquitin-conjugating enzyme UbcH7, and that mutant parkins from AR-JP patients show loss of the ubiquitin-protein ligase activity. Our findings indicate that accumulation of proteins that have yet to be identified causes a selective neural cell death without formation of Lewy bodies. Our findings should enhance the exploration of the molecular mechanisms of neurodegeneration in Parkinson disease as well as in other neurodegenerative diseases that are characterized by involvement of abnormal protein ubiquitination, including Alzheimer disease, other tauopathies, CAG triplet repeat disorders and amyotrophic lateral sclerosis.

Antisense transcription in the mammalian transcriptome

Antisense transcription (transcription from the opposite strand to a protein-coding or sense strand) has been ascribed roles in gene regulation involving degradation of the corresponding sense transcripts (RNA interference), as well as gene silencing at the chromatin level. Global transcriptome analysis provides evidence that a large proportion of the genome can produce transcripts from both strands, and that antisense transcripts commonly link neighboring "genes" in complex loci into chains of linked transcriptional units. Expression profiling reveals frequent concordant regulation of sense/antisense pairs. We present experimental evidence that perturbation of an antisense RNA can alter the expression of sense messenger RNAs, suggesting that antisense transcription contributes to control of transcriptional outputs in mammals.

Immunohistochemical detection of 4-hydroxynonenal protein adducts in Parkinson disease

There is growing evidence that oxidative stress and mitochondrial respiratory failure with attendant decrease in energy output are implicated in nigral neuronal death in Parkinson disease (PD). It is not known, however, which cellular elements (neurons or glial cells) are major targets of oxygen-mediated damage. 4-Hydroxy-2-nonenal (HNE) was shown earlier to react with proteins to form stable adducts that can be used as markers of oxidative stress-induced cellular damage. We report here results of immunochemical studies using polyclonal antibodies directed against HNE-protein conjugates to label the site of oxidative damage in control subjects (ages 18-99 years) and seven patients that died of PD (ages 57-78 years). All the nigral melanized neurons in one of the midbrain sections were counted and classified into three groups according to the intensity of immunostaining for HNE-modified proteins--i.e., no staining, weak staining, and intensely positive staining. On average, 58% of nigral neurons were positively stained for HNE-modified proteins in PD; in contrast only 9% of nigral neurons were positive in the control subjects; the difference was statistically significant (Mann-Whitney U test; P < 0.01). In contrast to the substantia nigra, the oculomotor neurons in the same midbrain sections showed no or only weak staining for HNE-modified proteins in both PD and control subjects; young control subjects did not show any immunostaining; however, aged control subjects showed weak staining in the oculomotor nucleus, suggesting age-related accumulation of HNE-modified proteins in the neuron. Our results indicate the presence of oxidative stress within nigral neurons in PD, and this oxidative stress may contribute to nigral cell death.

An unfolded putative transmembrane polypeptide, which can lead to endoplasmic reticulum stress, is a substrate of Parkin

A putative G protein-coupled transmembrane polypeptide, named Pael receptor, was identified as an interacting protein with Parkin, a gene product responsible for autosomal recessive juvenile Parkinsonism (AR-JP). When overexpressed in cells, this receptor tends to become unfolded, insoluble, and ubiquitinated in vivo. The insoluble Pael receptor leads to unfolded protein-induced cell death. Parkin specifically ubiquitinates this receptor in the presence of ubiquitin-conjugating enzymes resident in the endoplasmic reticulum and promotes the degradation of insoluble Pael receptor, resulting in suppression of the cell death induced by Pael receptor overexpression. Moreover, the insoluble form of Pael receptor accumulates in the brains of AR-JP patients. Here, we show that the unfolded Pael receptor is a substrate of Parkin, the accumulation of which may cause selective neuronal death in AR-JP.

Ubiquitination of a new form of alpha-synuclein by parkin from human brain: implications for Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the progressive accumulation in selected neurons of protein inclusions containing alpha-synuclein and ubiquitin. Rare inherited forms of PD are caused by autosomal dominant mutations in alpha-synuclein or by autosomal recessive mutations in parkin, an E3 ubiquitin ligase. We hypothesized that these two gene products interact functionally, namely, that parkin ubiquitinates alpha-synuclein normally and that this process is altered in autosomal recessive PD. We have now identified a protein complex in normal human brain that includes parkin as the E3 ubiquitin ligase, UbcH7 as its associated E2 ubiquitin conjugating enzyme, and a new 22-kilodalton glycosylated form of alpha-synuclein (alphaSp22) as its substrate. In contrast to normal parkin, mutant parkin associated with autosomal recessive PD failed to bind alphaSp22. In an in vitro ubiquitination assay, alphaSp22 was modified by normal but not mutant parkin into polyubiquitinated, high molecular weight species. Accordingly, alphaSp22 accumulated in a non-ubiquitinated form in parkin-deficient PD brains. We conclude that alphaSp22 is a substrate for parkin's ubiquitin ligase activity in normal human brain and that loss of parkin function causes pathological alphaSp22 accumulation. These findings demonstrate a critical biochemical reaction between the two PD-linked gene products and suggest that this reaction underlies the accumulation of ubiquitinated alpha-synuclein in conventional PD.

Deficiencies in complex I subunits of the respiratory chain in Parkinson's disease

Immunoblotting studies on mitochondria prepared from the striata of patients who died of Parkinson's disease were performed using specific antisera against Complexes I, III and IV. In 4 out of 5 patients with Parkinson's disease, the 30-, 25- and 24-kDa subunits of Complex I were moderately to markedly decreased. No clear difference was noted in immunoblotting studies on subunits of Complexes III and IV between the control and Parkinson's disease. Deficiencies in Complex I subunits seem to be one of the most important clues to elucidate pathogenesis of Parkinson's disease.

Protein-bound acrolein: potential markers for oxidative stress

Acrolein (CH2==CH---CHO) is known as a ubiquitous pollutant in the environment. Here we show that this notorious aldehyde is not just a pollutant, but also a lipid peroxidation product that could be ubiquitously generated in biological systems. Upon incubation with BSA, acrolein was rapidly incorporated into the protein and generated the protein-linked carbonyl derivative, a putative marker of oxidatively modified proteins under oxidative stress. To verify the presence of protein-bound acrolein in vivo, the mAb (mAb5F6) against the acrolein-modified keyhole limpet hemocyanin was raised. It was found that the acrolein-lysine adduct, Nepsilon-(3-formyl-3, 4-dehydropiperidino)lysine, constitutes an epitope of the antibody. Immunohistochemical analysis of atherosclerotic lesions from a human aorta demonstrated that antigenic materials recognized by mAb5F6 indeed constituted the lesions, in which intense positivity was associated primarily with macrophage-derived foam cells and the thickening neointima of arterial walls. The observations that (i) oxidative modification of low-density lipoprotein with Cu2+ generated the acrolein-low-density lipoprotein adducts and (ii) the iron-catalyzed oxidation of arachidonate in the presence of protein resulted in the formation of antigenic materials suggested that polyunsaturated fatty acids are sources of acrolein that cause the production of protein-bound acrolein. These data suggest that the protein-bound acrolein represents potential markers of oxidative stress and long-term damage to protein in aging, atherosclerosis, and diabetes.

Mutations in the dystrophin-associated protein gamma-sarcoglycan in chromosome 13 muscular dystrophy

Severe childhood autosomal recessive muscular dystrophy (SCARMD) is a progressive muscle-wasting disorder common in North Africa that segregates with microsatellite markers at chromosome 13q12. Here, it is shown that a mutation in the gene encoding the 35-kilodalton dystrophin-associated glycoprotein, gamma-sarcoglycan, is likely to be the primary genetic defect in this disorder. The human gamma-sarcoglycan gene was mapped to chromosome 13q12, and deletions that alter its reading frame were identified in three families and one of four sporadic cases of SCARMD. These mutations not only affect gamma-sarcoglycan but also disrupt the integrity of the entire sarcoglycan complex.

Structural dimorphism in the mitochondrial targeting sequence in the human manganese superoxide dismutase gene. A predictive evidence for conformational change to influence mitochondrial transport and a study of allelic association in Parkinson's disease

Mitochondrial targeting sequence (MTS) has a common property to form an amphiphilic helical structure which is essential for its effective transport of mitochondrial protein. Natural polymorphism in human MTS which affects its mitochondrial transport ability has not been reported. Furthermore, no structural polymorphism for manganese superoxide dismutase (MnSOD) gene has been studied in human population. We here identify diallelic polymorphism (Ala-9Val) in the MTS of human MnSOD in a Japanese population. Calculation of a helix forming potential predicted the typical amphiphilic helical structure in -9Ala allele and its disruption in -9Val allele. We here suggest that this mutation may reflect functional polymorphism of mitochondrial transport of human MnSOD. An association study using this polymorphism showed significant allelic deviation for -9Ala allele (12.1% vs. 19.3%) in Parkinson's disease.

Histochemical detection of apoptosis in Parkinson's disease

Apoptosis may be an important mechanism of cell death in some experimental disease models as well as in human neurodegenerative disorders. We report evidence to indicate apoptosis in the substantia nigra of Parkinson's disease patients. We studied the midbrains of 7 patients with late onset PD, 4 patients with young onset PD and 6 control subjects using the nick-end labeling method. Intense nuclear staining indicating apoptotic process was observed in 8 out of 11 parkinsonian patients studied. Apoptosis may be a contributor to the nigral neuronal death in Parkinson's disease (PD).

Beta-sarcoglycan (A3b) mutations cause autosomal recessive muscular dystrophy with loss of the sarcoglycan complex

The dystrophin associated proteins (DAPs) are good candidates for harboring primary mutations in the genetically heterogeneous autosomal recessive muscular dystrophies (ARMD). The transmembrane components of the DAPs can be separated into the dystroglycan and the sarcoglycan complexes. Here we report the isolation of cDNAs encoding the 43 kD sarcoglycan protein beta-sarcoglycan (A3b) and the localization of the human gene to chromosome 4q12. We describe a young girl with ARMD with truncating mutations on both alleles. Immunostaining of her muscle biopsy shows specific loss of the components of the sarcoglycan complex (beta-sarcoglycan, alpha-sarcoglycan (adhalin), and 35 kD sarcoglycan). Thus secondary destabilization of the sarcoglycan complex may be an important pathophysiological event in ARMD.

Brain-derived growth factor and nerve growth factor concentrations are decreased in the substantia nigra in Parkinson's disease

Using highly sensitive sandwich enzyme-linked immunosorbent assays (ELISA), we measured for the first time the concentrations of brain-derived growth factor (BDNF) in the brain (substantia nigra, caudate nucleus, putamen, cerebellum, and frontal cortex) from control and parkinsonian patients. BDNF in the human brain (the order of ng/mg protein) was significantly lower specifically in the nigrostriatal dopamine (DA) regions from parkinsonian patients than in those from control patients. The concentration of nerve growth factor (NGF) was also significantly decreased in the substantia nigra of parkinsonian patients in comparison with that in the controls. Since BDNF and NGF may play important roles in survival and differentiation of neuronal cells, the present data indicate that the lack of neurotrophins, especially BDNF, may be involved in the pathogenesis of PD during progress of neurodegeneration of the nigrostriatal DA neurons.

Increase of deleted mitochondrial DNA in the striatum in Parkinson's disease and senescence

A mutant mitochondrial DNA (mtDNA) with a 4,977-bp deletion was detected in the parkinsonian brain by using the polymerase chain reaction. Although the deleted mtDNA was detectable even in the brain of aged controls, the proportion of deleted mtDNA to normal mtDNA in the striatum was higher in the parkinsonian patients than in the controls. In both the parkinsonian patients and the aged controls, the proportion was higher in the striatum than in the cerebral cortex. These results indicate that age-related accumulation of deleted mtDNA is accelerated in the parkinsonian striatum and suggest that the deletion contributes to pathophysiological processes underlying Parkinson's disease.

Methylglyoxal modification of protein. Chemical and immunochemical characterization of methylglyoxal-arginine adducts

Methylglyoxal (MG), an endogenous metabolite that increases in diabetes and is a common intermediate in the Maillard reaction (glycation), reacts with proteins and forms advanced glycation end products. In the present study, we identify a novel MG-arginine adduct and also characterize the structure of a major fluorescent adduct. In addition, we describe the immunochemical study on the MG-arginine adducts using monoclonal antibody directed to MG-modified protein. Upon incubation of Nalpha-acetyl-L-arginine with MG at 37 degrees C, two nonfluorescent products and one fluorescent product were detected as the major products. The nonfluorescent products were identified as the Ndelta-(5-hydro-5-methyl-4-imidazolon-2-yl)-L-ornithine derivatives (5-hydro-5-methylimidazolone) and a novel MG-arginine adduct having a tetrahydropyrimidine moiety (Ndelta-(4-carboxy-4,6-dimethyl-5, 6-dihydroxy-1,4,5,6-tetrahydropyrimidine-2-yl)-L-ornithine). On the basis of the following chemical and spectroscopic evidence, the major fluorescent product, putatively identified as Ndelta-(5-methylimidazolon-2-yl)-L-ornithine (5-methylimidazolone), was found to be identical to Ndelta-(5-hydroxy-4, 6-dimethylpyrimidine-2-yl)-L-ornithine (argpyrimidine): (i) the low and high resolution fast atom bombardment-mass spectrometry gave a molecular ion peak at m/z of 297 (M+H) and a molecular formula of C10H25O6N4, respectively, which coincided with argpyrimidine; (ii) the 1H NMR spectrum of this product in d6-Me2SO showed a singlet at 2.10 ppm corresponding to six protons; (iii) the peak corresponding to the 5-methylimidazolone derivative was not detected by the liquid chromatography-mass spectrometry with the mode of selected ion monitoring; (iv) incubation of 5-hydro-5-methylimidazolone, a putative precursor of 5-methylimidazolone, at 37 degrees C for 14 days scarcely generated 5-methylimidazolone. On the other hand, as an immunochemical approach to the detection of these MG adducts, we raised the monoclonal antibodies (mAb3C and mAb6B) directed to the MG-modified protein and found that they specifically recognized the major fluorescent product, argpyrimidine, as the dominant epitope. The immunohistochemical analysis of the kidneys from diabetic patients revealed the localization of argpyrimidine in intima and media of small artery walls. Furthermore, the accumulation of argpyrimidine was also observed in some arterial walls of the rat brain after middle cerebral artery occlusion followed by reperfusion. These results suggest that argpyrimidine may contribute to the progression of not only long term diabetic complications, such as nephropathy and atherosclerosis, but also the tissue injury caused by ischemia/reperfusion.

Aldosterone production is activated in failing ventricle in humans

BACKGROUND

Recent reports have indicated that aldosterone is produced in extra-adrenal tissues in animals. The present study was designed to examine whether aldosterone is produced in human heart.

METHODS AND RESULTS

Plasma levels of aldosterone, BNP, and angiotensin-converting enzyme were measured in anterior interventricular vein (AIV), coronary sinus (CS), and aortic root (Ao), respectively, in 20 patients with left ventricular systolic dysfunction (LVSD), 25 patients with LV diastolic dysfunction (LVDD), and 23 control subjects. Aldosterone levels were significantly higher in AIV and CS than Ao in LVSD (98+/-10 versus 72+/-9 pg/mL, P:<0.001, and 97+/-11 versus 72+/-9 pg/mL, P:<0.001, respectively) and LVDD (87+/-10 versus 71+/-9 pg/mL, P:<0.01, and 84+/-10 versus 71+/-9 pg/mL, P:<0.01, respectively) groups, but no differences were observed in levels for these sites in the control group. Levels of ACE activity and BNP also were higher in AIV than Ao in both LV dysfunction groups. The difference in aldosterone levels between AIV and Ao and those in BNP and angiotensin-converting enzyme had a significant positive correlation with LVEDP and a significant negative correlation with LV ejection fraction in the LVSD group.

CONCLUSIONS

Production of aldosterone, angiotensin-converting enzyme, and BNP are activated in failing human ventricle in proportion to severity.

Pathologic and biochemical studies of juvenile parkinsonism linked to chromosome 6q

We report the results of pathologic and biochemical studies in a patient with 6q-linked autosomal recessive juvenile parkinsonism (AR-JP). Neuronal loss and gliosis were restricted to the substantia nigra and the locus ceruleus. No Lewy bodies were found, but neurofibrillary tangles and argyrophilic astrocytes were seen in the cerebral cortex and brainstem nuclei. The later findings, which have not been reported previously in AR-JP, suggest the pathologic heterogeneity of 6q-linked AR-JP.

Cretinism with combined hormone deficiency caused by a mutation in the PIT1 gene

Cretinism is marked by irreversible mental and growth retardation. We describe here an entirely new case of cretinism showing combined pituitary hormone deficiencies of thyrotropin, growth hormone and prolactin that appears to be caused by homozygosity for a nonsense mutation in the gene for the pituitary specific transcription activator, Pit-1/GHF-1 (designated PIT1 in humans for pituitary specific factor 1). This is the first report in humans of a defect in a transcription activator causing deficiency of multiple target genes.

Remnant lipoprotein levels in fasting serum predict coronary events in patients with coronary artery disease

BACKGROUND

Remnant lipoproteins are atherogenic, but assays of remnants have not been available in routine clinical laboratories because of the lack of practical and validated methods. A simple and reliable method for such an assay, using an immunochemical approach, has recently been developed. This study prospectively examined whether remnant lipoprotein levels in fasting serum, measured by our method, may have prognostic value in patients with coronary artery disease (CAD).

METHODS AND RESULTS

Remnant lipoprotein levels in fasting serum were measured in 135 patients with CAD by an immunoaffinity mixed gel containing anti-apolipoprotein (apo) A-1 and anti-apoB-100 monoclonal antibodies. Patients were followed up for </=36 months until occurrence of 1 of the following clinical coronary events: recurrent or refractory angina pectoris requiring coronary revascularization, nonfatal myocardial infarction, or cardiac death. Kaplan-Meier analysis demonstrated a significantly higher probability of developing coronary events in patients with the highest tertile of remnant levels (>5.1 mg cholesterol/dL; 75th percentile of distribution of remnant levels) than in those with the lowest tertile of remnant levels (</=3.3 mg cholesterol/dL; 50th percentile of the distribution). Higher levels of remnants were a significant and independent predictor of developing coronary events in multivariate Cox hazard analysis including the following covariates: extent of coronary artery stenosis, age, sex, smoking, hypertension, diabetes mellitus, hypercholesterolemia, low HDL cholesterol, and hypertriglyceridemia.

CONCLUSIONS

Higher levels of remnant lipoproteins in fasting serum predict future coronary events in patients with CAD independently of other risk factors. Thus, measurement of fasting remnant levels, assessed by the current immunoseparation method, may be helpful in assessment of CAD risk.

Molecular genetic analysis of a novel Parkin gene in Japanese families with autosomal recessive juvenile parkinsonism: evidence for variable homozygous deletions in the Parkin gene in affected individuals

Autosomal recessive juvenile parkinsonism (AR-JP) is a distinct clinical and genetic entity characterized by selective degeneration of nigral dopaminergic neurons and young-onset parkinsonism with remarkable response to levodopa. Recently, we mapped the gene locus for AR-JP to chromosome 6q25.2-q27 by linkage analysis and we identified a novel large gene, Parkin, consisting of 12 exons from this region; mutations of this gene were found to be the cause of AR-JP in two families. Now we report results of extensive molecular analysis on 34 affected individuals from 18 unrelated families with AR-JP. We found four different homozygous intragenic deletional mutations, involving exons 3 to 4, exon 3, exon 4, and exon 5 in 10 families (17 affected individuals). In addition to the exonic deletions, we identified a novel one-base deletion involving exon 5 in two families (2 affected individuals). All mutations so far found were deletional types in which large exonic deletion accounted for 50% (17 of 34) and the one-base deletion accounted for 6% (2/34); in the remaining, no homozygous mutations were found in the coding regions. Our findings indicate that loss of function of the Parkin protein results in the clinical phenotype of AR-JP and that subregions between introns 2 and 5 of the Parkin gene are mutational hot spots.

Immunohistochemical and subcellular localization of Parkin protein: absence of protein in autosomal recessive juvenile parkinsonism patients

Autosomal recessive juvenile parkinsonism (AR-JP) is a distinct clinical entity characterized by a selective degeneration of nigral neurons. Recently, the parkin gene responsible for AR-JP has been identified. Now, we report the subcellular localization of Parkin protein in patients with AR-JP or Parkinson's disease (PD) and in controls by immunoblotting and immunohistochemistry using antibodies raised against the Parkin molecule. Parkin protein was absent in all regions of the brains of patients with AR-JP. Parkin protein was not decreased in the brains of sporadic PD patients. Immunoreactivity was detected in a few Lewy bodies. Parkin protein was located in both the Golgi complex and cytosol.

Caspase activities and tumor necrosis factor receptor R1 (p55) level are elevated in the substantia nigra from parkinsonian brain

The activities of caspase-1 and caspase-3 were measured by use of fluoropeptides as substrates for the first time in the brain (substantia nigra, caudate nucleus, putamen, cerebellum, and frontal cortex) from control and parkinsonian patients. The activities of caspases in the brain were significantly higher in the substantia nigra from parkinsonian patients than those in the brain from control patients (p < 0.01). However, the activities of caspases in the caudate nucleus, putamen, cerebellum, and frontal cortex showed no significant difference between parkinsonian and control patients. The tumor necrosis factor (TNF) receptor R1 (TNF-R1, p55) level was also elevated in the substantia nigra of the parkinsonian brain in comparison with that of controls (p < 0.05). Since both caspases and TNF-R1 may play important roles in apoptotic cell death through TNF-alpha-induced signaling pathway, our present data suggest the presence of a proapoptotic environment in the substantia nigra of parkinsonian brain, probably inducing vulnerability of neurons and glias towards a variety of noxious factors.

Mechanism of the rapid effect of 17 beta-estradiol on medial amygdala neurons

The mechanism by which sex steroids rapidly modulate the excitability of neurons was investigated by intracellular recording of neurons in rat medial amygdala brain slices. Brief hyperpolarization and increased potassium conductance were produced by 17 beta-estradiol. This effect persisted after elimination of synaptic input and after suppression of protein synthesis. Thus, 17 beta-estradiol directly changes the ionic conductance of the postsynaptic membrane of medial amygdala neurons. In addition, a greater proportion of the neurons from females than from males responded to 17 beta-estradiol.

Glucose responding neurons in the nucleus tractus solitarius of the rat: in vitro study

Glucose response of 162 neurons in the nucleus tractus solitarius (NTS) was examined in brainstem slices. When glucose was applied by addition to the bath medium or by electrophoresis, approximately 27% of the neurons responded; 20% were glucose-sensitive neurons which decreased in activity and 7% glucoreceptor neurons which increased in activity. Significantly more glucose-sensitive neurons were found in the caudal part than in the rostral part, while non-glucose responding neurons were distributed widely within the NTS. The populations of glucose-sensitive and glucoreceptor neurons were 11% and 5% in the rostral part, and 28% and 8% in the caudal part of the NTS. Intracellular horseradish peroxidase staining of NTS neurons revealed that glucose-sensitive neurons were medium-sized, fusiform or pyramidal cells with many more dendrites than non-responding small oval cells. Specific functional and morphological characteristics of these glucose responding neurons were clarified by this study.