Stereological methods for estimating the total number of neurons and synapses: issues of precision and bias

The emergence of a new generation of stereological techniques for counting objects in histological sections has prompted a debate about whether or not these methods are better than previously available techniques when they are used to make estimates of the total numbers of neurons and synapses in a neural structure. During this debate, the concepts of an unbiased estimate and that of a precise estimate have often been confused. A full understanding of the distinction between these two separate aspects of an estimate is required in order to be able to appreciate the virtues of these new counting methods and to apply them correctly. This review intends to make the fundamental issues of this debate more clear, and describes (1) the fundamental differences between the newer design-based counting techniques and previously available assumption-based techniques, and (2) the distinction between an unbiased estimate and a precise estimate.

The relationship between oral dyskinesias produced by long-term haloperidol treatment, the density of striatal preproenkephalin messenger RNA and enkephalin peptide, and the number of striatal neurons expressing preproenkephalin messenger RNA in rats

Neuroleptic-induced oral dyskinesias in rats, a putative analogue to human tardive dyskinesia, may be due to excitotoxic degeneration within the striatum. Haloperidol treatment for 34 weeks increased the optical density of preproenkephalin messenger RNA in individual striatal neurons and enkephalin peptide in the neuropil, regardless of the level of oral dyskinesia produced. However, using unbiased stereological methods, an increased number of striatal neurons expressing preproenkephalin messenger RNA was observed only in rats that did not develop pronounced oral dyskinesias during haloperidol treatment. Said in another manner, the haloperidol-treated animals that developed pronounced oral dyskinesias, failed to produce an increase in the number of neurons expressing preproenkephalin messenger RNA. These results indicate that the mechanism by which neuroleptics induce oral dyskinesias in rats, and perhaps tardive dyskinesia in humans, involves a functional disturbance or even damage to a subpopulation of enkephalinergic neurons in the striatum.

Initiation and evaluation of a research-based fall prevention program

This study evaluated the effectiveness of research-based interventions in preventing falls. The interventions were based on research studies, experts' opinions, and a pilot study. Thirteen units (72%) had reduced fall rates. The fall rate two years before (O = 7.07; SD = 1.7) and two years after (O = 6.33; SD = 1.731) the intervention was significantly different at p < 0.003. Sixteen patients who fell were at risk (fall assessment score = 17.4 +/- 5.3) and had a history of falls. The most common site for falls was at the bedside. Most falls occurred during walking, climbing over the siderails, and accidentally rolling out of bed. Thus, a research-based fall prevention is effective in reducing falls.

Visual and song nuclei correlate with courtship skills in brown-headed cowbirds

We assessed courtship success in 14 adult male brown-headed cowbirds, Molothrus ater. Volumes of song control nuclei and visual nuclei were measured in Nissl stained tissue. Variation in courtship success was found to be related to variation in two areas of the avian brain: the song control nucleus, area X, and the thalamic visual area, nucleus rotundus. Volume of area X was negatively correlated with song potency, as assessed by female playback, and with rate of vocalizing. Volume of nucleus rotundus was positively correlated with song potency, vocalizing to females and courtship persistence. These data are the first to implicate a visual nucleus in the use of song. The data also complement previous findings with cowbirds suggesting that song learning involves visual attention to females. Taken as a whole, these results suggest that use of song depends on integration of auditory, vocal and visual information. In that female songbirds in many species assess multimodal performance of song, these findings with cowbirds suggest that future studies of brain and behaviour include a broader view of possible behavioural and neural correlates. Copyright 1998 The Association for the Study of Animal Behaviour.

Translational induction of the c-myc oncogene via activation of the FRAP/TOR signalling pathway

Previous studies on the regulation of c-myc have focused on the transcriptional control of this proto-oncogene. We have investigated the signalling pathways involved under circumstances in which there is a translational upregulation in the levels of c-myc protein. We have demonstrated an up to tenfold serum-dependent increase of c-myc protein levels in Epstein-Barr virus immortalized B-cell lines 2-4 h after disruption of cellular aggregates, which is not accompanied by an equivalent increase in mRNA. Overall protein synthesis rates only increased threefold suggesting that the c-myc message was being selectively translated. We observed increases in the phosphorylation of p70 and p85 S6 kinases and of initiation factor eIF-4E binding protein 1 (4E-BP1) 1-2 h after stimulation, suggesting activation of the FRAP/TOR signalling pathway. The increased phosphorylation of 4E-BP1 led to a decrease in its association with eIF-4E and an increase in its association with the eIF-4G component of the eIF-4F initiation complex. The signalling inhibitors rapamycin and wortmannin blocked the phosphorylation of 4E-BP1 and abolished the translational component of the c-myc response. Our data suggest that dissociation of eIF-4E from 4E-BP1, leading to an increase in the formation of the eIF-4F initiation complex, relieves the translation repression imposed on the c-myc mRNA by its structured 5'UTR.

Failure of central nervous system myelination in MBP/c-myc transgenic mice: evidence for c-myc cytotoxicity

c-myc is a member of the helix-loop-helix/leucine zipper family of proteins that modulate the transcriptional activity of specific target genes. Although aberrant c-myc expression has been reported to play a role in multistage carcinogenesis in astrocytic gliomas, little is known about the effects of the expression of c-myc on oligodendrocytes. Using transgenic animals expressing a human c-myc oncogene under transcriptional control of the myelin basic protein gene, we investigated the effect of overexpression of this oncogene in oligodendrocytes. The MBP/c-myc transgenic mice developed severe neurological disturbances characterized by action tremors and recurrent seizures, and premature death during postnatal weeks three to five. Affected transgenic mice of various strains had severely hypomyelinated central nervous systems and expressed low levels of c-myc, myelin basic protein (MBP) and proteolipid protein (PLP) mRNAs in the brain. These c-myc transgenic mice also exhibited an increased number of TUNEL positive nuclei, which in most cases were located in cells that expressed c-myc, as judged by double immunohistochemistry. There was no evidence of brain tumors in the c-myc transgenic mice, including heterozygous mice from two strains that had normal lifespans. These observations indicate that the myelin deficiency observed in the MBP/c-myc transgenic animals results from a cytotoxic effect of the c-myc transgene.

Total number of neurons in the layers of the human entorhinal cortex

The total number of neurons in the major laminae of the human entorhinal cortex were estimated with a design-based stereological technique, the optical fractionator. Detailed descriptions of the laminar organization and the cortical limits of the region required for the analysis are provided, along with detailed descriptions of the sampling scheme employed. The individual, mean values, and variances for estimates made in layers II, III, V, and VI are presented and discussed in terms of the precision of the estimation procedure and the results of other studies. Neuron numbers were estimated to be about 1 million layer II cells, 5 million layer III cells, 2 million layer V cells, and 4 million layer VI cells, for a total of slightly more that 13 million neurons in the entorhinal cortex. Combined with data from a similar study carried out in the human hippocampus, the data presented represent the first rigorous stereological evidence of the divergence of entorhinal projections to the hippocampus. The data presented also indicate that projections from layer II of the entorhinal cortex to the dentate gyrus and CA2/3 and projections from layer III of the entorhinal cortex to CA1 differ in the degrees of their divergence.

Neurological disturbances, premature lethality, and central myelination deficiency in transgenic mice overexpressing the homeo domain transcription factor Oct-6

Pit, Oct, Unc (POU) homeo domain transcription factors have been implicated in various developmental processes, including cell division, differentiation, specification, and survival of specific cell types. Although expression of the transcription factor Oct-6 in oligodendroglia is confined to the promyelin stage and is downregulated at the myelin stage of development, the effect of Oct-6 overexpression on oligodendrocyte development has not been established. Here we show that transgenic animals overexpressing Oct-6 at late oligodendrocyte development develop a severe neurologic syndrome characterized by action tremors, recurrent seizures, and premature death. Axons in the central nervous system of Oct-6 transgenics were hypomyelinated, hypermyelinated, or dysmyelinated, and ultrastructural analyses suggested that myelin formation was premature. The vulnerability of developing oligodendroglia to Oct-6 deregulation provides evidence that the POU factor may play a direct role in myelin disease pathogenesis in the mammalian CNS.

Combining propofol with morphine in patient-controlled analgesia to prevent postoperative nausea and vomiting

We have studied the antiemetic effects of propofol when mixed with morphine in a patient-controlled analgesia (PCA) pump after major gynaecological surgery. In a double-blind, randomized, controlled study, 50 women, ASA I or II, received a standardized anaesthetic comprising thiopental, morphine, atracurium, nitrous oxide and oxygen with enflurane, and received postoperative PCA with morphine mixed with either 1% propofol or lvelip. The PCA bolus was morphine 1 mg with propofol 5 mg or lvelip 0.5 ml, with a lockout time of 5 min. Postoperative nausea and vomiting (PONV) were assessed by the nursing staff using a four-point ordinal scale and by the patient using a visual analogue scale for 48 h after surgery. The two groups were similar in the potential factors influencing the incidence of PONV. There were no significant differences between the two groups in any of the study measurements of PONV. There were, no side effects after propofol. Propofol, when mixed with morphine in this dose combination for PCA, did not decrease the incidence of nausea and vomiting in women undergoing major gynaecological surgery.

Renin-angiotensin system gene polymorphisms and left ventricular hypertrophy. The case against an association

There is accumulating evidence for association between genetic polymorphisms of components of the renin angiotensin system (RAS), especially angiotensin-converting enzyme (ACE), and cardiovascular disease. However, there is lack of agreement that the ACE polymorphism is associated with left ventricular hypertrophy (LVH) in hypertension. A possible paradigm for the development of LVH involves the ACE gene polymorphism influencing cardiac mass by an action on plasma and/or tissue levels of angiotensin II. Such a model has experimental support and provides the basis for examining the lack of agreement between studies. The finding of lack of association between RAS gene polymorphism and LVH may be due to methodological problems, differences in genetic background between populations, interactions between genetic variants of RAS components or to the model being inappropriate. Low predictability of ACE genotype markers for LVH together with conflicting reports on the influence of RAS genetic variants on angiotensin II production suggests that the simple RAS paradigm may not apply for hypertension. Further information on the nature of the link between the ACE polymorphism and ACE regulation as well as the relation between the RAS and pathophysiology of LVH is needed. At present there is insufficient evidence to accept ACE gene polymorphism as a susceptibility marker for LVH.

A brain of her own: a neural correlate of song assessment in a female songbird

The song control region in the avian forebrain is a series of discrete, interconnected nuclei mediating song learning and production. It has been studied in males or in species where both sexes sing. Little is known about the neural correlates of song perception in nonsinging females, often the intended recipients of song. We studied cowbirds (Molothrus ater), a species in which only males sing but in which females discriminate between males on the basis of song. We focused on nucleus lMAN because it has been implicated in early song acquisition, a stage relevant to both sexes to choose among competing acoustic models. We found that volume of lMAN was monomorphic in cowbirds. Moreover, the volume and neuronal number of female lMAN were positively correlated with selectivity of copulatory responding. The results provide strong evidence of nonsinging female's use of "song" control nuclei for song perception without the possibility of song production.

Investigation of aberrant translational control of c-myc in cell lines derived from patients with multiple myeloma

In cell lines derived from patients with multiple myeloma (MM) we have found an elevation in the amount of the c-myc protein which is not accompanied by an increase in the level of mRNA or a change in the half-life of the protein. There is a 3.4 fold enhancement in the degree of association of the c-myc message with polysomes. This is not accompanied by an alteration in polysome size or a change in the transit time of the c-myc mRNA on the polysomes thus suggesting that there is in increase in the degree of mobilisation of the c-myc message. Sequencing of the c-myc 5'UTR has revealed the presence of a mutation in all the MM cell lines studied and we demonstrate that this mutation causes altered binding of cellular proteins to this RNA species.

Neuron numbers in the presubiculum, parasubiculum, and entorhinal area of the rat

Estimates of neuron numbers have been useful in studies of neurodegenerative disorders, and in their animal models, and in the computational modeling of hippocampal function. Although the retrohippocampal region (presubiculum, parasubiculum, and entorhinal area) is an integral part of the hippocampal circuitry and is affected selectively in a number of disorders, estimates of neuron numbers in the rat retrohippocampal region have yet to be published. Such data are necessary ingredients for computational models of the function of this region and will also facilitate a comparison of this region in rats and primates, which will help to determine how well we may expect rat models to predict function and dysfunction in primate brains. In the present study, we used the optical fractionator to estimate the number of neurons in the rat retrohippocampal region. The following estimates were obtained: 3.3 x 10(5) in presubicular layers II and III, 1.5 x 10(5) in parasubicular layers II and III, 2.2 x 10(5) in the combined pre- and parasubicular layers V and VI, 6.6 x 10(4) in medial entorhinal area (MEA) layer II, 1.3 x 10(5) in MEA layer III, 1.9 x 10(5) in MEA layers V and VI, 4.6 x 10(4) in lateral entorhinal area (LEA) layer II, 1.2 x 10(5) in LEA layer III, and 1.4 x 10(5) in LEA layers V and VI. A surprising finding was the large numbers of neurons in the pre- and parasubiculum, which indicate an important role of these areas in the control of the entorhino-hippocampal projection. A comparison of the numbers of neurons in the hippocampus and entorhinal areas in rats with similar estimates in humans revealed that gross input-output relations are largely conserved. Differences between rats and humans may be accounted for by more prominent entorhino-neocortical projections in primates and consequent increases in the number of neurons in the hippocampus and retrohippocampal region, which are dedicated to these projections.

Spinal cord excitatory amino acid receptors and plasma catecholamine autonomic responses in the conscious rabbit

Intrathecal administration of the specific glutamate subtype receptor agonist NMDA (N-methyl-D-aspartate), or the non-NMDA receptor agonist AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid), at the level of the lower thoracic spinal cord in the conscious rabbit, produces increased levels of plasma norepinephrine and a rise in blood pressure. These responses are specifically inhibited with prior intrathecal administration of the NMDA receptor antagonist AP-5 (2-amino-5-phosphonovaleric acid) or non-NMDA receptor antagonist DNQX (6, 7-dinitroquinoxaline-2, 3-dione), respectively. In contrast, arterial baroreflex activation induced by transient hypotension following intravenous sodium nitroprusside increases levels of plasma norepinephrine which are inhibited with intrathecal AP-5, but not DNQX. The experiments are consistent with glutamate acting as a neurotransmitter in the spinal cord influencing control of sympathetic nerve function via activation of spinal cord NMDA and non-NMDA subtype receptors. The results support previous work suggesting that baroreflex function is predominantly mediated by spinal NMDA receptors and that spinal glutamate receptors are important in baroreflex control of the circulation.

Second Australian National Blood Pressure Study (ANBP2). Australian Comparative Outcome Trial of ACE inhibitor- and diuretic-based treatment of hypertension in the elderly. Management Committee on behalf of the High Blood Pressure Research Council of Australia

The Second Australian National Blood Pressure Study (ANBP2) is a comparative outcome trial being conducted in general practices throughout Australia of ACE inhibitor- and diuretic-based treatment in 6000 hypertensive patients aged 65-84 years. The study is using a prospective randomised open-label design with blinding of endpoint assessments. The primary objective is to determine whether there is any difference in total cardiovascular events (fatal and non-fatal) over a five year treatment period between the two treatment regimens. Eligible hypertensive patients (average sitting blood pressure at the 2nd and 3rd screening visits > 160 mm Hg systolic and/or > 90 mm Hg diastolic) may be either untreated or previously treated and should have no history of recent cardiovascular morbidity or serious intercurrent illness. Patients are randomised to one of the treatment arms with randomisation stratified for practice and for age. Following randomisation each patient's blood pressure is managed by his/her general practitioner according to guidelines relevant to each treatment arm. Over 700 patients have now been randomised with recruitment intended to be complete by the end of 1997.

Association of the brain natriuretic peptide gene with blood pressure and heart weight in the rat

1. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are important in the control of body fluid homeostasis, blood pressure (BP) regulation and vascular remodelling. The genes for these peptides may, therefore, be involved in the pathogenesis of genetic hypertension. We have previously described a quantitative trait locus (QTL) for BP in the ANP gene region on rat chromosome 5. We have now assessed the possibility that this QTL lies at the closely linked BNP locus. 2. Intra-arterial BP and heart weight were measured in 12-week-old (n = 207) and 24-week-old (n = 88) F2 rats derived from crosses between Wistar-Kyoto normotensive rats and spontaneously hypertensive rats. We designed polymerase chain reaction primers to amplify a microsatellite in the BNP gene from genomic DNA. Analysis of variance was used for cosegregation analysis. Linkage mapping and localization of QTL was performed using the Mapmaker computer package. 3. A significant correlation was found between genotype for the BNP gene and systolic BP (P < 0.001) in 12-week-old rats. The ANP gene, but not the BNP gene, was associated with systolic BP in 24 week rats. There was no segregation of heart weight with BNP genotype at 12 or 24 weeks of age. The BNP gene mapped approximately 20 cM from the ANP gene in our rat hybrids, away from the previously described QTL. There was evidence for a second BP locus near to but distinct from the BNP gene. 4. These results suggest that BP QTL are present in the natriuretic peptide gene region but that the ANP and BNP genes themselves have no major effect on BP in this cross.

Association analysis of six candidate genes in a sample of Australian hypertensive patients

1. Essential hypertension is characterized by increased vascular resistance due to narrowing of the small arterioles. This may be influenced by vasoactive substances, cell growth and vascular remodelling. 2. A sample of Australian hypertensive and normotensive subjects was investigated for association with genetic markers which are candidates for a role in blood pressure (BP) regulation due to potential effects on vascular diameter. 3. The six markers used were for genes encoding vasoconstrictors, growth factors and a structural protein of the extracellular matrix. 4. No significant association of any of the markers used was found with BP status in this sample of patients.

Growth factors released into the coronary circulation after vascular injury promote proliferation of human vascular smooth muscle cells in culture

OBJECTIVES

This study sought to 1) assess in vivo release of platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF) into the coronary circulation after vascular injury in human subjects; and 2) evaluate mitogenic effects of PDGF and bFGF on the patient's own vascular smooth muscle cells (VSMCs).

BACKGROUND

Circumstantial evidence suggests involvement of PDGF and bFGF peptides in the neointimal response to vascular injury. To date, no study has shown biologically active growth factors within the coronary circulation after vascular injury in human subjects.

METHODS

In 18 patients, plasma PDGF AB, platelet factor 4 (PF4) and beta-thromboglobulin (beta-TG) levels were measured in coronary sinus blood obtained before and up to 30 min after angioplasty. In five patients undergoing atherectomy, coronary sinus serum was added to cultured VSMCs derived from atherectomy tissue to assess the mitogenic potential of the serum. Mitogenicity attributable to PDGF and bFGF was determined using neutralizing antibodies to these factors. PDGF A, PDGF B and bFGF were localized within the atherectomy tissue using immunocytochemical analysis.

RESULTS

Before angioplasty, PDGF AB, PF4 and beta-TG levels were elevated threefold in patients scheduled for angioplasty compared with those in control patients (p < 0.01). Within 5 min of angioplasty, PDGF AB levels increased twofold and returned toward preangioplasty levels at 30 min; PF4 and beta-TG levels remained elevated. Serum obtained at 30 min after atherectomy showed a sixfold increase in mitogenicity compared with preatherectomy serum (p = 0.01). This increase in mitogenicity was reduced by 20%, 40% and 65% in the presence of neutralizing antibodies to PDGF, bFGF and PDGF + bFGF, respectively. PDGF A, PDGF B and bFGF were visualized within the intima of the atherectomy tissue.

CONCLUSIONS

The change in plasma PDGF level is consistent with first-phase release of PDGF after vascular injury. The increase in mitogenicity of serum suggests that PDGF and bFGF are biologically active.

Feasibility of conducting cardiovascular outcome research in Australian general practice: results from the ANBP2 pilot study. Australian National Blood Pressure Study

1. The present study aimed to determine the feasibility of conducting a 5 year cardiovascular outcome trial of the treatment of 6000 elderly hypertensive patients in Australian general practices. 2. General practitioners (GPs) were invited to participate by mail and personal follow-up. Patient records were reviewed to identify subjects for a blood pressure (BP) screening programme. Blood pressure was measured on three occasions and eligible subjects were included if the average BP was > or = 160 mmHg systolic or > or = 90 mmHg diastolic if systolic BP was > or = 140 mmHg. 3. Seven hundred and forty-one GPs were approached and 89 were enrolled in the study (12% of mail invites and 75% of those receiving a personal contact). In 16 practices where screening was completed, 82,000 records were reviewed to identify 4% patients eligible for screening. Twenty-two per cent of eligible subjects attended screening. Of 1938 subjects screened, 180 (9%) had BP > or = 160/90 mmHg. Forty-seven per cent of subjects (n = 916) were receiving antihypertensive therapy and 184 (20%) were withdrawn from therapy. One hundred and sixteen (63%) of these subjects had BP return to study entry levels within 6 weeks. Fifty-seven newly diagnosed and 81 previously treated subjects were randomized (7% of the screened population). 4. Based on the high participation rate of GPs, the response rate of patients to attend a BP screening programme and the 7% randomization to screening ratio for entry into the study, the ANBP2 pilot study has demonstrated that it is feasible to recruit subjects from Australian general practices to a cardiovascular outcome trial.

Unbiased stereological estimation of the total number of synapses in a brain region

Modern stereological methods have been used to make unbiased estimates of the total number of synapses in the striatum radiatum of the hippocampal CA1 region of five rabbits. The approach used involved a two stage analysis and is generally applicable to all parts of the nervous system. During the first stage of the analysis, the reference volume was estimated by point counting, at the light microscope level, according to the Cavalieri principle. During the second stage, the numerical density of synapses was estimated with dissectors at the electron microscopic level. The total number of synapses was calculated as the product of the numerical density and the volume of the region. The sampling with points and dissectors was carried out in all three dimensions of the entire CA1 region in a manner that ensured that all parts of the region and all synapses within it had equal probabilities of being sampled. An analysis of the precision of the estimate of total synapse number has been performed in terms of the variances of volume and synaptic numerical density at different levels of sampling, i.e. at the level of points, sections, individual animals and group of animals. Detailed descriptions of the procedures used to estimate the total number of synapses, evaluate the precision of the estimates, and optimize the sampling scheme are provided.

Cosegregation of genes on chromosome 5 with heart weight and blood pressure in genetic hypertension

Genetic factors may be involved in both essential hypertension and cardiac hypertrophy. To identify genes contributing to elevated for blood pressure and cardiac hypertrophy in the spontaneously hypertensive rat (SHR), we performed a cosegregation analysis between blood pressure and heart weight and microsatellite markers for the candidate gene ANF on chromosome 5 in F2 animals obtained by mating SHR with Wistar-Kyoto (WKY) rats. We found evidence for a quantitative trait locus (QTL) determining mean blood pressure on chromosome 5 between atrial natriuretic factor (ANF) and MITR-3893 loci. No evidence for a QTL influencing heart weight was found. We propose that in SHR, blood pressure and heart weight may be independently controlled by different genetic mechanisms and that a gene close to ANF locus on chromosome 5 contributes towards hypertension in these animals.

Aberrant translational control of the c-myc gene in multiple myeloma

We demonstrate a 10- to 25-fold increase in the amount of c-myc protein in several independent cell lines derived from patients with multiple myeloma (MM). This is not accompanied by a corresponding increase in the overall level of the c-myc mRNA. There is, however, a 3.4-fold increase in the amount of c-myc mRNA associated with the polysomes in these cell lines without any detectable change in either the polysome size or the rate of translation elongation, thus suggesting that there is an increase in the extent of mobilisation of c-myc mRNA to the polysomes in MM. Analysis of the 5' untranslated region of c-myc has revealed the presence of a mutation, in all of the MM cell lines examined, in a region which has been implicated previously in the translational control of this mRNA species. These data suggest aberrant translational control of the c-myc gene in cell lines derived from patients with MM, which may contribute towards pathogenesis of the disease.