Hypertension and components of vascular resistance

1. In renal wrap hypertension in the rabbit and in essential hypertension in humans, non-autonomic components of resistance are the major factors contributing to elevated blood pressure. 2. The central nervous system plays an important role in moment to moment blood pressure control but is not responsible for maintenance of elevated pressure in essential hypertension. 3. Specific regions of the brain-stem maintain vascular tone through the effects of bulbospinal neurones which are organized both topographically and by chemical content. 4. Structural wall thickening in resistance vessels in hypertension is a manifestation of an abnormality of a growth controlling process. 5. Although several structural muscle growth factors have been identified, it is likely that only a few regulatory processes are critical. 6. Future studies in hypertension should examine associations between genetic markers of medial thickening and environmental influences.

Diltiazem and atenolol in essential hypertension: additivity of effects on blood pressure and cardiac conduction with combination therapy

In 15 patients with mild to moderate essential hypertension, the effects of diltiazem (120 mg twice daily) were compared with those of atenolol (50 mg once daily), the two drugs in combination, and placebo in a randomized double-blind cross-over study with treatment phases of 4 weeks duration. Blood pressure was reduced in the active treatment phases (supine blood pressure: diltiazem, 172/92 mmHg; atenolol, 172/92 mmHg; diltiazem plus atenolol, 164/88 mmHg; pooled estimate of s.e.m. by analysis of variance = 3/1) compared with placebo (180/101 mmHg). Factorial analysis confirmed fully additive antihypertensive effects of the drugs in combination. The time interval from the beginning of the P wave to the beginning of the QRS complex (P-R interval) was longer during combination therapy (0.184s) compared with either diltiazem (0.175s) or atenolol (0.174s) alone, or placebo (0.164s); s.e.m. by analysis of variance = 0.003. No clinically significant conduction disturbances occurred. Plasma atrial natriuretic peptide was elevated by atenolol but not diltiazem. Thus, in subjects with uncomplicated essential hypertension, diltiazem and atenolol had equal antihypertensive efficacy when used alone, and fully additive effects in combination, on both blood pressure and cardiac conduction.

Cost-effective treatment of constipation in the elderly: a randomized double-blind comparison of sorbitol and lactulose

PURPOSE

The purpose of this study was to evaluate the use of sorbitol as an inexpensive alternative to lactulose for treating constipation in the elderly.

PATIENTS AND METHODS

Thirty men aged 65 to 86 with chronic constipation were studied in a randomized, double-blind, cross-over trial in which lactulose and 70% sorbitol (0 to 60 mL daily) were each given for 4 weeks preceded by a 2-week washout period.

RESULTS

The average number of bowel movements per week was 6.71 with sorbitol and 7.02 with lactulose (95% confidence interval of the difference: -0.43 to 1.06), and the average number of days per week with bowel movements was 5.23 with sorbitol and 5.31 with lactulose (95% confidence interval of the difference: -0.32 to 0.48). Eleven patients stated a preference for sorbitol, 12 for lactulose, and seven had no preference. On a visual analogue scale measuring severity of constipation (0 to 100 mm), the average score for sorbitol was 35.6 mm versus 37.1 mm for lactulose (95% confidence interval of the difference: -6.4 to 9.3). The sorbitol and lactulose treatment periods were also similar in percent of bowel movements recorded as "normal," frequency and severity of symptoms such as bloating, cramping, and excessive flatulence, and overall health status as assessed by a previously validated five-category questionnaire. There were no significant differences between sorbitol and lactulose in any outcome measured except nausea, which was increased with lactulose (p less than 0.05).

CONCLUSION

These results support the hypothesis that sorbitol and lactulose have no clinically significant differences in laxative effect. Sorbitol can be recommended as a cost-effective alternative to lactulose for the treatment of constipation in the elderly.

Communicating about communicating: when innate is not enough

The cowbird is a brood parasite, providing no parental care to its offspring. The species has often been cited as a model of the usefullness of the construct of innate behavior, as an explanation of how young cowbirds develop species-typical behavior. Here we evaluate the adequacy of this perspective. We show that although it is difficult to explain ontogenetic beginnings without recourse to the concept of innate behaviors, ontogenetic outcomes are less easily accommodated. Constraints on the explanatory power of innateness as an ontogenetic concept are demonstrated with data from the development of singing in cowbirds and the development of babbling in human infants.

Unbiased stereological estimation of the number of neurons in the human hippocampus

The total numbers of neurons in five subdivisions of human hippocampi were estimated using unbiased stereological principles and systematic sampling techniques. The method addresses the problems associated with the results and conclusions of previous quantitative studies, virtually all of which have been based on biased estimates of neuron densities. For each subdivision, the total number of neurons was calculated as the product of the estimate of the volume of the neuron-containing layers and the estimate of the numerical density of neurons in the layers. Each hippocampus was cut into 3-mm-thick slabs, transverse to the rostrocaudal axis. One 70-micron-thick section from each slab was used in the analysis. The volumes of the layers containing neurons in five major subdivisions of the hippocampus (granule cell layer, hilus, CA3-2, CA1, and subiculum) were estimated with point-counting techniques after delineation of the layers on each section. The numerical densities of neurons in each subdivision were estimated on the same sections with optical disectors. The sampling used in both estimates was performed systematically in all three dimensions. In an example of five hippocampi, the mean numbers of neurons (CV = SD/mean) in the different subdivisions were as follows: granule cells 15 X 10(6) (0.28), hilus 2.0 X 10(6) (0.16), CA3-2 2.7 X 10(6) (0.22), CA1 16 X 10(6) (0.32), subiculum 4.5 X 10(6) (0.19). The stereological measurements contributed approximately 25% of the observed variance. Among the five subjects there was a significant inverse relationship between age (which ranged from 47 to 85 years) and the total number of neurons in CA1 (which ranged from 24 to 11 X 10(6)). An optimized sampling scheme for studies of the number of neurons in the human hippocampus has been designed on the basis of an analysis of variance of the estimates at different levels of the sampling scheme. Counting neurons in the five subdivisions of the human hippocampus with the optimized sampling scheme takes less than 4 hours.

The effect of low-level toluene exposure on the developing hippocampal region of the rat: histological evidence and volumetric findings

With the intention of investigating possible morphological alterations effected by toluene in the developing CNS, rat pups were exposed to 100 ppm and 500 ppm of atmospheric toluene from postnatal day 1 until sacrifice at postnatal day 28, when the hippocampal region (area dentata, Ammon's horn, subiculum) was examined light microscopically and alterations in the volumes of the layers of the subdivisions were determined. The layers of Ammon's horn and the subiculum were not affected qualitatively or quantitatively by the 500 ppm exposure. Within the area dentata, the volume of the granule cell layer was 6% smaller in animals exposed to 100 ppm and 13% smaller in animals exposed to 500 ppm than they were in controls. The volumes of the hilus, which is a terminal field of granule cell axons, and the commissural-associational zone of the dentate molecular layer, which is the terminal field of the hilar projection to the granule cells, were smaller (12% and 19%) in animals exposed to 500 ppm than they were in controls. Argyrophilic cells were found in the granule cell layer of all animals exposed to 500 ppm. Pronounced granule cell degeneration was found in one animal exposed to 500 ppm. The granule cell layer of animals exposed to 100 ppm appeared qualitatively normal. The alterations reported here support the few earlier reports of morphological alterations in the CNS of adult laboratory animals. Effects of toluene similar to those described, that is alterations in specific neuron populations and their afferent and efferent terminal fields may complement changes in neurophysiology and behavior that have been observed in prenatally and perinatally exposed rodent pups. Causal relationships, however, remain to be elucidated.

Lack of effect of fish oil supplementation on blood pressure in treated hypertensives

Fish and fish oils have been reported to reduce blood pressure in normotensives and untreated hypertensives. The present study examined the effect of dietary supplementation with fish oil on blood pressure in 20 treated hypertensives with controlled blood pressures who continued their usual antihypertensive drug treatment throughout. A double-blind, randomized crossover design was used, with two phases, each of 8 weeks' duration. In one phase, subjects took fifteen 1 g fish oil capsules (Lipitac; Reckitt and Colman Pharmaceuticals, Sydney, Australia) daily, and in the other, 15 capsules of identical appearance containing 1 g olive oil daily. There was no difference between the treatment phases for any blood pressure parameter, heart rate or body weight, but blood pressure was lower in both phases compared with pretreatment values. The fasting plasma triglyceride concentration was 30% lower in the fish oil phase (P less than 0.001), but there was no difference between the phases for plasma concentrations of total or high-density lipoprotein (HDL) cholesterol. We conclude that, in treated hypertensives with controlled blood pressures, any additional fall in blood pressure produced by dietary supplementation with fish oil is so small that the requirement for antihypertensive drug therapy is unlikely to be reduced.

Quantification of oral epithelial hyperplasia in rats after topical application of the carcinogen 4-nitroquinoline 1-oxide

Hyperplasia of the palatal epithelium was quantified in two groups of rats exposed thrice weekly to the carcinogen 4NQO for 2 weeks and 2 months, respectively. The lengths and areas of the epithelial layers were measured with a computerized line-following device. In the group treated for 2 weeks the maximum area of the nuclear layer was nearly three times and the maximum length of the epithelial/connective tissue interface almost twice the normal at the end of the carcinogen application period. The maximum area of the cornified layer was three times and the maximum lengths of the epithelial surface and the keratin/nuclear layer interface almost one and a half times the normal 1 week after painting with 4NQO. Thereafter the lengths and areas decreased gradually in both experimental groups. The area of the cornified layer and the length of the epithelial/connective tissue interface in the group treated for 2 months were significantly larger than those in animals treated for 2 weeks. These variables may be two of several indicators of prognostic significance in the assessment of dose-related premalignant epithelial hyperplasia.

Automated non-invasive measurement of cardiac output by the carbon dioxide rebreathing method: comparisons with dye dilution and thermodilution

The accuracy and reproducibility of indirect measurement of cardiac output at rest by the carbon dioxide rebreathing (indirect Fick) method with an automated respiratory analysis system (Gould 9000IV) were compared with simultaneous measurements made in duplicate by dye dilution and thermodilution in 25 patients having cardiac catheterisation studies. Measurements of cardiac output by the carbon dioxide rebreathing method were not significantly different from those obtained with dye dilution (mean difference -0.3 l/min, SD 0.76, 95% confidence interval -0.7 to 0.1). Thermodilution significantly over-estimated cardiac output by a mean of 2.2 l/min or 39% (SD 1.5, 95% confidence interval 1.6 to 2.8) compared with the carbon dioxide rebreathing method and significantly overestimated cardiac output by 1.9 l/min or 31% (SD 1.2, 95% confidence interval 1.2 to 2.5) compared with dye dilution. The reproducibility of measurements of cardiac output in individual patients was satisfactory with the dye dilution method but was poor with carbon dioxide rebreathing and thermodilution. Indirect measurement of resting cardiac output by the Gould 9000IV automated carbon dioxide rebreathing method is more accurate but the variability inherent with this method requires that multiple measurements be taken for each determination. Measurement of cardiac output by the thermodilution method by a commercially available cardiac output computer was not satisfactory because not only was there considerable variability between repeat measurements but the method also consistently overestimated cardiac output compared with the dye dilution method.

Stereological studies of the hippocampus: a comparison of the hippocampal subdivisions of diverse species including hedgehogs, laboratory rodents, wild mice and men

The volumes of the fascia dentata, hilus, regio inferior, regio superior and subiculum of 9 species that differ significantly in size and degree of forebrain evolution have been compared with the intent of identifying phylogenetic trends in the internal organization of the mammalian hippocampus. The study includes data from the hippocampi of a basal insectivore, 2 species of wild mice, 3 commonly used laboratory rodents and 3 species (including man) that resemble an ascending primate series. In addition to comparisons of the absolute and relative volumes, an allometric approach is used to identify "progressive" size differences not related to body size. Both regio superior and hilus become larger during evolution, while fascia dentata and regio inferior maintain a relationship to body size that is similar to that for the hippocampus in basal insectivores. The inter-species differences are discussed in terms of neuron number and size, for which data are presented from two species, and with reference to a neural model of the cognitive map theory for hippocampal function. Special emphasis is placed on the unique aspects of the human hippocampus. The data represents a quantitative morphological framework within which the observations from physiological, biochemical and behavioral studies in laboratory animals can be related to studies of the human hippocampus.

Optimal size of cuff bladder for indirect measurement of arterial pressure in adults

This study tested the hypothesis that a sphygmomanometer cuff bladder long enough to encircle the arm in most adults ('obese cuff') would provide a more accurate and precise estimate of intra-arterial pressure than the usual 'standard' cuff bladder. In 53 patients undergoing diagnostic coronary angiography (35 males, 18 females, aged 36-79 years), indirect blood pressure, measured in the left arm with a random-zero sphygmomanometer, was compared with simultaneously measured femoral intra-arterial pressure. Duplicate indirect measurements were made with each of two cuffs containing bladders measuring 39 x 15 cm ('obese') and 23 x 12 cm ('standard'). The obese cuff bladder encircled 80% or more of the arm circumference in all subjects, whereas the standard cuff bladder met this requirement in only 19% of the subjects. For both systolic and diastolic pressure there was marked interindividual variability in the differences between indirect and direct measurements with both cuffs. With the obese cuff there was no systematic error in the diastolic blood pressure measurement. The standard cuff consistently overestimated diastolic pressure by 7.7 +/- 8.3 mmHg (mean +/- s.d.). For both cuffs, the difference between indirect and direct diastolic pressure increased with arm size (P less than 0.05). Both cuffs underestimated systolic blood pressure, the obese cuff by 15.5 +/- 11.7 mmHg and the standard cuff by 7.6 +/- 12.1 mmHg. These systolic blood pressure underestimates were greater at higher blood pressures (P less than 0.01) and with smaller arms (P less than 0.05). Age was not related to measurement error with either cuff.(ABSTRACT TRUNCATED AT 250 WORDS)

Accuracy of the Takeda TM-2420 ambulatory blood pressure monitor

1. The accuracy of blood pressure measurement with the Takeda TM-2420 ambulatory blood pressure monitor and the TM-2020 data recorder have been assessed by comparison with simultaneous measurements taken using auscultation and direct femoral artery measurements. 2. Systolic blood pressure was underestimated by the TM-2420 by a mean of 10 mmHg (s.d. = 6, 95% confidence interval (CI) = -13 to -7) over the range of pressures measured by auscultation. It was underestimated by 23 mmHg (s.d. = 12, 95% CI = -28 to -18) compared with direct femoral artery measurements. 3. Diastolic pressure measurements were similar to those obtained by auscultation. When compared with direct femoral artery recordings, diastolic pressure was overestimated by about 5 mmHg (s.d. = 4, 95% CI = 3.4-6.6), which is consistent with indirect readings, taken with a 'standard' cuff (inflatable bladder 23 cm X 12 cm). 4. The TM-2420/2020 is thus suitable for ambulatory measurements of blood pressure when diastolic pressure is the criterion of interest.

Comparative quantitative study of the hippocampal region of two closely related species of wild mice: interspecific and intraspecific variations in volumes of hippocampal components

To investigate the structural changes in the hippocampal region (subiculum, Ammon's horn, and area dentata) associated with speciation, the volumes of homologous components of this region of the forebrain were compared in the two closely related murine rodent species, Apodemus flavicollis (yellow-necked wood mice) and A. sylvaticus (long-tailed field mice), and in two geographically separated groups of A. sylvaticus. With the exception of the mossy fiber zone, no significant differences were found in the relative sizes of the components of Ammon's horn. Significant interspecific differences were found in the deep subiculum, in the intermediate (medial perforant path) and deep (commissural-associational) zones of the molecular layer of the area dentata, and in the hilus. A significant intraspecific difference was found in the combined intermediate and superficial (medial and lateral perforant path) zone of the dentate molecular layer. Differences found in the relative size of the hilus and the mossy fiber zone of Ammon's horn were complementary in that the combined volumes of these zones, which are both terminal fields of dentate granule cells, did not differ in the species. This finding provides evidence that the distribution of the terminal field of a projection system can be altered while the size of the terminal field is maintained. Within the hippocampal region, components of Ammon's horn appear well suited for quantitative comparative studies that span taxonomic units beyond the species level. In agreement with previous quantitative studies, differences in the volumes of components of Ammon's horn found in species of different orders are more likely to reflect phylogenetic trends rather than changes resulting from specializations of the particular species used. This is not true for the subiculum and the components of the area dentata. Experimentally induced changes in the connectivity of the hippocampal region are discussed in terms of the structural changes which may be responsible for the quantitative differences observed between the two species studied here.

Proximate regulation by mothers: a demonstration of how differing styles affect young children's behavior

An earlier observational study of mothers and toddlers in the supermarket revealed differential success of 2 styles of maternal behavior. A proactive style of preempting opportunities for misbehavior, in contrast to a reactive style of responding only after misbehavior occurred, was correlated with a lower incidence of undesirable child acts. Here, the 2 styles were studied in the laboratory to explore their function further. In an analog of the supermarket situation, mothers behaved proactively and reactively in trials in which the task was to prevent their 2- or 3-year-old children from playing with desirable toys. Children responded to proactive behavior by engaging in acceptable behaviors longer and by violating fewer rules. The 2-year-old children were less able to comply with the rules. The data illustrate the role parents play in promoting and supporting the development of compliance and self-regulation in children.

Limitations of the technique of pressure microinjection of excitatory amino acids for evoking responses from localized regions of the CNS

The aim of this study, performed on anaesthetized cats and rabbits, was to test the assumption that pressure microinjections of excitatory amino acids cause long-lasting excitation of neurones located close to the injection site. Unitary action potentials or antidromic field potentials were recorded from respiratory or 'reticular' neurones in the medulla oblongata and from phrenic motoneurones at different distances from the injection site. Injection of 10-150 nl (5-150 nmol) of L-glutamate or DL-homocysteic acid into these areas resulted in complex and widespread neuronal events. Generally, more distant neurones (500-1300 microns) were excited for variable periods of time (3-15 min), while neurones in the vicinity of the injection site (0-500 microns) showed, after a brief period of excitation time, a long-lasting (up to 30 min) decrease in excitability or silencing of discharge, probably due to a depolarizing block and disturbances in the ionic composition of the extracellular space. These findings show that interpretation of physiological responses following such injections should not be based on an assumption of local neuronal excitation. Some recommendations regarding the use of this technique are made.

Vocalizations of juvenile cowbirds (Molothrus ater ater) evoke copulatory responses from females

The functional attributes of the vocalizations produced by young male cowbirds during their first fall and winter, termed "vocal precursors," were tested by playing the sounds back to female cowbirds. Five classes of vocalizations were tested: subsong, plastic, formatted, and stereotyped song, and songs of nonconspecifics. Females responded selectively to the four classes of cowbird vocalizations. Stereotyped songs evoked the most responding but the key eliciting element was the inclusion of note clusters, which first occurred in plastic song. The data suggest that juvenile cowbirds possess vocalizations capable of evoking biologically relevant responses from companions early in development.

Female visual displays affect the development of male song in the cowbird

The role of social stimulation in avian vocal learning is well documented. The separate contribution of social, as opposed to vocal, stimulation has been difficult to address, however, because in almost all cases both tutor and pupil sing. The opportunity to isolate such effects arose in cowbirds (Molothrus ater ater) after discovering that males housed with non-singing female cowbirds made vocal changes which related directly to the female preferences for native song. Here we report how females communicate with males about songs. We describe a visual display by females, a wing stroke, that is elicited by specific vocalizations. The songs that trigger wing strokes are in turn highly effective releasers of copulatory postures, and thus this previously unnoticed female display has biological significance. The data not only provide the first evidence of the tutorial role of male-female interactions during song ontogeny, they also clearly implicate visual stimulation in song learning, a process that has until now been assumed to be affected only by auditory information.

Estimating the number of granule cells in the dentate gyrus with the disector

A practical example is given of how a newly developed stereological estimator of particle number, the disector, can be used to make estimates of neuron number in the dentate gyrus of rats. The estimates are free of biases related to lost caps, overprojection and assumptions about size, shape and orientation of the objects that are counted. The disector principle and the practical considerations relating to histological preparations and sampling are presented.

Automated non-invasive measurement of cardiac output: comparison of electrical bioimpedance and carbon dioxide rebreathing techniques

Two commercial automated, non-invasive systems for estimation of cardiac output were evaluated. Values of cardiac output obtained by electrical bioimpedance cardiography (BoMed NCCOM3 machine) were compared with values derived from an indirect Fick technique that uses carbon dioxide rebreathing (Gould 9000 IV system) during 103 simultaneous measurements made at rest in 19 randomly selected subjects and on exercise in 11 subjects. Cardiac output values obtained with impedance cardiography were significantly correlated with those measured by the indirect Fick method, although there was a wide scatter with over 73% of the readings lying outside the limits defined by the line of identity +/- 20%. This correlation was greatly reduced when stroke volume index was used instead of cardiac output. Indirect Fick results were linearly related to oxygen uptake both at rest and on exercise, while impedance cardiography results did not correlate with oxygen uptake. Impedance cardiography gave consistently lower results for cardiac output than indirect Fick at all levels of exercise. Both machines were easy to use and produced acceptable mean (SE) coefficients of variation (BoMed NCCOM3 7.7 (1.0)%, Gould 9000 IV 10.6 (1.4)%). Further validation is required before either of these machines can be recommended as an alternative to invasive monitoring in clinical practice.

Enalapril and atenolol in essential hypertension: attenuation of hypotensive effects in combination

In 16 patients with essential hypertension the effects of enalapril 20 mg once daily were compared with those of atenolol 50 mg once daily, with the two drugs in combination and with placebo using a double-blind cross-over design with allocation of treatment order by randomised Latin squares. For each patient there were four treatment phases, each of four weeks duration, which together comprised a 2 x 2 factorial experiment. All blood pressure parameters were reduced in the three active treatment phases compared to placebo (p less than 0.001). Supine blood pressures (group means) were 171/97 (placebo), 147/85 (enalapril), 154/84 (atenolol) and 144/78 (enalapril plus atenolol) (S.E.M. +/- 2/+/- 1-ANOVA), and standing blood pressures were 170/105 (placebo), 146/92 (enalapril), 154/92 (atenolol) and 147/86 (enalapril plus atenolol) (S.E.M. +/- 3/+/- 1). In the combination phase there was an additional hypotensive response but the potential fully additive effects of the two agents were attenuated by 30-50%. The mechanism of the attenuated hypotensive effect of the combined agents has not been determined. Plasma atrial natriuretic peptide (ANP) concentration was doubled in the presence of atenolol (P less than 0.01) suggesting that ANP may contribute to the hypotensive effect of the beta-blocker.

Central serotonergic mechanisms in hypertension

Serotonin-containing neurons in the central nervous system are grouped into a number of discrete and distinctive collections with cell bodies in the brainstem and projections passing to many regions of the brain and spinal cord. Evidence is presented that activation of one projection of serotonin-containing neurons from the midbrain to the hypothalamus elevates arterial pressure. Evidence is also presented that activation of a projection descending from the lateral B3 serotonin cell group to the spinal cord elicits a pressor response that is accompanied by increased release of serotonin in the spinal cord and is independent of the C1 adrenaline-containing neurons that lie close by. In contradistinction, experiments are described demonstrating that activation of the midline group of B3 serotonin cells in the raphe nucleus causes a fall in arterial pressure, consistent with the view that different groups of serotonin neurons in the brain and spinal cord participate in the control of blood pressure in diverse ways and can have different effects on blood pressure. Finally, experiments are described showing that the hypotensive action of methyldopa is mediated in part through central serotonin nerves.

Asymmetry in the hippocampal region specific for one of two closely related species of wild mice

The volumes of the components of the left and right hippocampal regions were compared in male, adult specimens of the two closely related species of wild mice, Apodemus flavicollis (yellow-necked wood mice) and Apodemus sylvaticus (long-tailed wood mice). In one of the species, Apodemus flavicollis, the component containing the deep layers of the subiculum was found to be significantly larger in the hippocampal region of the left side than it was in that of the right side. No other significant asymmetries were found in the hippocampal components of the two species. These findings indicate that significant asymmetries in localized brain regions can arise during a single speciation event.

Volumes of the components of the hippocampus in the aging F344 rat

Much of the recent data on cells, synapses, and other structures in the dentate gyrus and hippocampus as a function of age are packing density or volume fraction data. In order to estimate total numbers, volumes, or surface areas of cells, synapses, vessels, etc., as a function of age, the total volumes of the subregions of the dentate gyrus and hippocampus must be known. The volumes of these subregions, visualized with the Timm stain, have been determined in 24 F344 rats from 4 to 37 months of age. Volumes of the various structures showed age-related increases which were statistically significant for the perforant path zone of the dentate gyrus molecular layer, as well as the total molecular layer, the hilus, and regio inferior and total mossy fiber systems. If the 4-month age group is eliminated from consideration, only the ratio of the volume of the mossy fiber zones to the volume of the perforant path zones of the dentate molecular layer increases significantly with age. Our general finding of lack of volumetric reorganization of the subdivisions of the hippocampal region between 12 and 37 months suggests that studies of the packing densities of structures in most of these zones may be considered comparable across ages, assuming comparability of sampling regions.

Treatment of hypertension with enalapril and hydrochlorothiazide or enalapril and atenolol: contrasts in hypotensive interactions

To determine the nature of the resultant effect on blood pressure when angiotensin converting enzyme (ACE) inhibitors are combined with other hypotensive agents in the treatment of uncomplicated essential hypertension, two randomized, double-blind, crossover trials were conducted. In each trial there were four treatment phases, each 4 weeks in duration, comprising a 2 X 2 factorial experiment. Twenty-one patients completed the first study in which the effects of enalapril (10 mg twice daily) were compared with hydrochlorothiazide (25 mg twice daily), with the two drugs in combination and with placebo. All blood pressure parameters were reduced in the three active treatment phases compared with placebo (P less than 0.001). Enalapril and hydrochlorothiazide were equally effective and in combination their hypotensive effects were fully additive. Sixteen patients completed the second study which compared the effects of enalapril (20 mg daily), atenolol (50 mg daily), the two drugs in combination and placebo. All blood pressure parameters were again reduced in all phases compared with placebo (P less than 0.001). Enalapril and atenolol were also equally effective, but in combination their hypotensive effects were less than fully additive, with attenuation of the potential additive response by 30-50%. These results indicate that a diuretic-ACE inhibitor combination can be expected to have a greater hypotensive effect than a beta-blocker-ACE inhibitor combination. Both hydrochlorothiazide and atenolol increased plasma atrial natriuretic peptide (ANP) concentrations (P less than 0.01), suggesting that ANP could contribute to the hypotensive effects of these two drug classes.

Inhibition of vasodepressor neurons in the caudal ventrolateral medulla of the rabbit increases both arterial pressure and the release of neuropeptide Y-like immunoreactivity from the spinal cord

The role of bulbospinal neuropeptide Y (NPY)-containing neurons of the rostral ventrolateral medulla in the rabbit in mediating the increase in blood pressure that occurs during inhibition of cells in the caudal ventrolateral medulla was investigated in urethane-anaesthetized rabbits. In the present experiments bilateral injections of the GABA agonist, muscimol, into the caudal ventrolateral medulla elicited a slowly-developing rise in arterial pressure that was maximal 15 min after the injection. Accompanying this increase in arterial pressure was an increase in the release of NPY-like immunoreactivity (NPY-LI) into the spinal subarachnoid space. This pattern of response is similar to that seen after direct chemical stimulation of the NPY-containing cells of the rostral ventrolateral medulla. Taken together, these findings suggest that tonically active neurons in the caudal ventrolateral medulla exert their effects by inhibiting sympathoexcitatory NPY-containing neurons whose cell bodies are situated in the rostral ventrolateral medulla.