Behind the Mask: An Exploratory Assessment of Female Surgeons' Experiences of Gender Bias

Though overt sexism is decreasing, women now experience subtle, often unconscious, gender bias as microaggressions. The authors sought to explore the prevalence and impact of the sexist microaggressions female surgeons experience, using a sequential exploratory mixed methods approach (January 2018-April 2018), to identify opportunities for education and prevention. First, all resident, fellow, and attending female surgeons at the University of New Mexico Health Sciences Center (UNM HSC) were invited to participate in focus groups conducted by experienced moderators using a semistructured interview guide based on the 7 Sexist Microaggressions Experiences and Stress Scale (Sexist MESS) domains. Qualitative analysis was performed using line-by-line manual coding to identify themes aligned with the Sexist MESS domains as well as other gender bias experiences of female surgeons. Next, a survey was sent to all resident, fellow, and attending female surgeons at the UNM HSC, which included the Sexist MESS questionnaire and questions related to surgeon-specific experiences of gender bias that the authors developed based on major thematic categories from the focus groups.Four focus groups of 23 female surgeons were conducted, revealing 4 themes: exclusion, increased effort, adaptation, and resilience to workplace slights. The survey response rate was 64% (65/101 surgeons). Across Sexist MESS domains, the frequency and severity of microaggressions was higher for trainees than attendings. The variables of non-White race/ethnicity, having children under 18, and fellowship training generally did not demonstrate statistical significance. This exploratory study adds to the growing body of evidence that gender bias in surgery continues and frequently manifests as microaggressions. Trainees reported the highest rates and severity of microaggressions and bias experiences. Further research should investigate how to address microaggressions, the experiences of male surgeons, the perspectives of medical students and groups who were reported as often perpetuating gender bias, and the efficacy of possible interventions.

Gender Bias Experiences of Female Surgical Trainees

OBJECTIVE

Medical schools now average approximately 50% female students, yet a disproportionate number of women continue to choose nonsurgical over surgical specialties. Once in training, studies indicate that pervasive gender stereotypes, sexism and harassment negatively affect female surgeons. The aim of this study is to describe female surgeons' experiences with gender bias and microaggressions in the workplace during residency and fellowship training, and understand if differences exist in the experiences of trainees in male-dominant vs female-dominant surgical specialties.

DESIGN

A mixed methods approach was used to explore the experiences of female surgical trainees. Participants were recruited from all surgical disciplines at an academic center. Initially, focus groups were used to explore themes that trainees face related to gender bias. A trained moderator conducted all focus groups, which were audio recorded and transcribed. Qualitative analysis of de-identified transcripts was performed to identify emerging themes. We then created an online survey using the validated 44-question Sexist Microaggression Experiences and Stress Scale to assess frequency and psychologic impact of these events with additional questions developed from the focus groups. The survey was sent to all female residents and fellows at one academic institution.

SETTING

University of New Mexico Hospital, a tertiary care academic medical center.

PARTICIPANTS

Fifteen female surgical trainees participated in focus groups. Thirty-three female surgical trainees participated in the online survey.

RESULTS

Two focus groups including 15 female trainees were conducted, revealing 4 themes: Exclusion, Adaptation, Increased effort, and Development of Resilience Strategies. All participants had experienced gender bias or discrimination during medical school or surgical training. The quantitative survey had a 66% response rate (33/50 female trainees). Significant differences were found in the experience of female trainees in male-dominant vs female-dominant specialties, with those in male-dominant fields often reporting more frequent, severe, and stressful microaggression experiences. When describing how gender bias would affect their future in medicine, trainees in male-dominant specialties were more likely to report that due to gender bias, they "may leave medicine/retire early" (33% vs 6%, p = 0.040) and that they "would not recommend my profession to trainees or family members" (40% vs 6%, p = 0.015)."

CONCLUSIONS

Female surgical trainees continue to experience gender bias. A culture of sexism leads to physical and social adaptations to fit into the role of surgeon. Participants expressed significant effort to sustain this level of adaptation, leading to fatigue and creation of resilience mechanisms. The environment in which a trainee operates (male-dominant vs female-dominant) significantly impacts their experience. Those experiencing more bias were less likely to recommend their specialty and reported plans to leave medicine earlier. Culture change across institutions and system-level interventions are necessary to create meaningful and sustainable change that improves the experience of female surgical trainees.

Resident and Program Director's Perceptions of Milestone-Based Feedback in Obstetrics and Gynecology

INTRODUCTION

In July 2014, US residency programs fully implemented the Next Accreditation System including the use of milestone evaluation and reporting. Currently, there has been little investigation into the result of implementation of this new system. Therefore, this study sought to evaluate perceptions of Obstetrics and Gynecology residents and program directors regarding the use of milestone-based feedback and identify areas of deficiency.

METHODS

A Web-based survey was sent to US-based Obstetrics and Gynecology residents and program directors regarding milestone-based assessment implementation.

RESULTS

Out of 245 program directors, 84 responded to our survey (34.3% response rate). Of responding program directors, most reported that milestone-based feedback was useful (74.7%), fair (83.0%), and accurate (76.5%); however, they found it administratively burdensome (78.1%). Residents felt that milestone-based feedback was useful (62.7%) and fair (70.0%). About 64.3% of residents and 74.7% of program directors stated that milestone-based feedback is an effective tool to track resident progression; however, a sizable minority of both groups believe that it does not capture surgical aptitude. Qualitative analysis of free response comments was largely negative and highlighted the administrative burden and lack of accuracy of milestone-based feedback.

CONCLUTION

Overall, both Obstetrics and Gynecology program directors and residents report that milestone-based feedback is useful and fair. Issues of administrative burden, timeliness, evaluation of surgical aptitude, and ability to act on assigned milestone levels were identified. Although this study is limited to one specialty, such issues are likely important to all residents, faculty, and program directors who have implemented the Next Accreditation System requirements.

Methods of changing patterns of substance use among individuals with co-occurring schizophrenia and substance use disorder

Individuals with a severe mental illness and substance use disorder tend to have medical and social problems and to make slower progress in treatment than those who have either disorder alone. Nevertheless, little attention has been paid to the discovery of effective methods of modifying substance use in the severely mentally ill (SMI). The purpose of this study was to collect qualitative data as a way to help identify techniques that might help to change patterns of substance use in the SMI. The participants were 21 men and women who were psychiatric clinic outpatients and who had a current schizophrenia spectrum diagnosis. A total of 18 participants had a lifetime diagnosis of alcohol abuse or dependence, and 21 lifetime other drug diagnoses were recorded for the sample. These individuals participated in focus group discussions about topics related to substance use and people's experiences with trying to quit. The results showed that participants identified several therapeutic and extratherapeutic factors that helped them to initiate and maintain changes in their substance use, as well as factors that hindered change. The findings are related to knowledge about the effectiveness of substance use disorder treatment techniques in general, and implications of the data are discussed for the conduct of integrated treatment of individuals with severe mental illness and a substance use disorder.

Decisional balance regarding substance use among persons with schizophrenia

State-of-the-science treatment of substance abuse relies on decisional balance activities (weighing pros and cons of continued substance use) to enhance motivation for change. Few data are available regarding the feasibility of these activities among persons dually diagnosed with schizophrenia and substance use disorder. To address this lacuna in the literature, we completed focus groups with 21 participants, all of whom had a schizophrenia-spectrum diagnosis and lifetime substance abuse or dependence. These key informants discussed the pros and cons of substance use as well as the pros and cons of quitting in response to a structured group interview. Our qualitative data indicate that persons living with schizophrenia can generate rich and diverse decisional balance information. We describe salient themes, contrast complementary perspectives (i.e., the pros of using and cons of quitting), and suggest treatment implications based on these findings.

Presynaptic or postsynaptic location of receptors for angiotensin II and substance P in the medial solitary tract nucleus

1. Microinjection of angiotensin (Ang) II or substance P (SP) into the medial nucleus tractus solitarii (nTS) produces similar decreases in arterial pressure and heart rate. We previously reported that some medial nTS neurons responsive to SP were also excited by Ang II, and that Ang II increased the release of SP from medulla slices. Both electrophysiological and anatomic data suggest that the cardiovascular effects of these peptides may be mediated by a common neuronal pathway consisting of SP-containing vagal afferent fibers with presynaptic Ang II receptors that innervate medial nTS neurons with SP receptors. To evaluate the validity of this model, we established the presynaptic or postsynaptic location of the receptors for Ang II and SP that mediate excitation of medial nTS neurons by determining the capacity of each peptide to activate the cell before and after blocking synaptic transmission in rat dorsal medulla slices. 2. Extracellular recordings were obtained from 55 medial nTS neurons responsive to Ang II or SP in 400-microns horizontal slices of the dorsal medulla. Neuronal excitation by Ang II and SP was tested before, during, and after reversal of synaptic blockade with low-Ca2+ (0.2 mM), high Mg2+ (5 mM) artificial cerebrospinal fluid (aCSF). Elimination of synaptically evoked short latency responses of the neuron to current pulses applied to afferent fibers in the solitary tract (TS) documented blockade of synaptic transmission by low-Ca2+ aCSF. In most cases, the basal firing rate of the cell increased slowly during perfusion with low-Ca2+ aCSF and stabilized after approximately 30 min at a higher level of spontaneous activity. Responses to the peptides and TS stimulation were also documented after synaptic blockade had been reversed by adding aCSF containing 2-mM Ca2+. 3. Of the 55 medial nTS neurons, 41 were responsive to Ang II; whereas, 50 of the 55 cells were responsive to SP. The neurons were divided into three subgroups on the basis of their responsiveness to Ang II and SP. Although most neurons were responsive to both Ang II and SP (n = 36), five other cells were excited only by Ang II, and 14 neurons were activated only by SP. Of the 55 neurons, 26 were also responsive to L-glutamate: 14 of 17 cells responsive to both Ang II and SP, all 5 neurons excited by Ang II but not by SP, and 7 of 10 neurons responsive only to SP were also excited by L-glutamate. The latency of the action potentials evoked by TS stimulation was much shorter in those neurons responsive only to Ang II (3.6 ms) than in cells excited by both Ang II and SP (6.8 ms) or responsive only to SP (7.4 ms). 4. In 21 of the 36 medial nTS neurons responsive to both Ang II and SP, Ang II continued to excite the cell when synaptic responses to TS stimulation were prevented by low-Ca2+ aCSF, but had no effect on the firing rate of the other 15 neurons during synaptic blockade. Excitation induced by Ang II was also prevented in two of the five medial nTS neurons responsive only to Ang II when synaptic transmission in the slice was blocked. Low-Ca2+ aCSF failed to prevent excitation by SP or L-glutamate in all medial nTS cells responsive to these agonists (n = 50 and n = 26, respectively). In contrast to these observations in medial nTS neurons, Ang II-induced excitation was not altered during synaptic blockade in any of the six dmnX cells studied. No responses to SP or L-glutamate were blocked in dmnX neurons, as also seen in the medial nTS. 5. When all medial nTS neurons responsive to Ang II were examined, the latencies of the response to TS stimulation were significantly shorter in those neurons with presynaptic Ang II receptors than in the group of cells with postsynaptic receptors. In addition, neurons with presynaptic Ang II receptors were distributed differently within the medial nTS than cells with postsynaptic Ang II receptors.(ABSTRACT TRUNCATED)

Mechanisms of angiotensin-induced hypotension and bradycardia in the medial solitary tract nucleus

The selective angiotensin (ANG) II antagonists losartan (AT1) and CGP-42112A (AT2) were used to determine the receptor subtype and neuronal pathways that mediate the hypotension and bradycardia produced by 200 fmol of ANG II microinjected into the dorsal medial nucleus tractus solitarii (NTS) or dorsal motor nucleus of the vagus (dmnX) in anesthetized rats. At dorsal medial NTS sites (0.3 mm below the surface) where L-glutamate microinjections produced maximal decreases in mean arterial pressure (MAP) and heart rate (HR), ANG II (200 fmol, 50 nl, n = 16) elicited hypotension (-22 +/- 1 mmHg) and bradycardia (-26 +/- 2 beats/min). Although L-glutamate also suppressed respiration, ANG II injections in the medial NTS did not alter respiration. Losartan injected at the medial NTS site caused a dose-dependent reduction of ANG II-induced decreases in MAP and HR. At 2 pmol, the AT1 antagonist attenuated the response to ANG II, whereas 100 pmol abolished the effects of ANG II microinjections. In contrast, the AT2 antagonist CGP-42112A (100 pmol) had no effect on the responses to ANG II. Neither ANG II antagonist altered the cardiovascular effects of L-glutamate injections. Losartan injected into the dmnX blocked hypotension and bradycardia produced by ANG II at that site but did not prevent responses to subsequent ANG II injections in the medial NTS.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphology and projections of neurobiotin-labeled nucleus tractus solitarii neurons recorded in vitro

The suitability of the anterograde tracer neurobiotin to provide information about the morphology and projections of extracellularly or intracellularly recorded medial nucleus tractus solitarii (nTS) neurons was evaluated in horizontally oriented rat dorsal medulla in vitro slices. After responsiveness to angiotensin (Ang) II, substance P (SP), and L-glutamate was evaluated, neurons were labeled by electrophoresis of neurobiotin at the recording site. Extracellular application (2 microA for 2 min) produced discrete injection sites (40-70 microns) with a small group of labeled neurons. Ejections into the solitary tract documented that the tracer was not taken up by axons traversing the injection site. Neuronal perikarya, primary and secondary dendrites, and axons exhibited a dense Golgi-like appearance, with well-defined dendritic spines and axonal varicosities. Dendritic or axonal processes could be followed for more than 1 mm from the cell soma in a 50 microns thick section, documenting the horizontal architecture of the medial nTS. Intracellular electrophoresis filled the soma, primary and secondary dendrites, and axons of neurons characterized for responsiveness to peptides, L-glutamate and solitary tract stimulation. The location within the nTS and axonal projections of neurons responsive to Ang II and SP appeared to differ from those of cells responsive to Ang II and L-glutamate. Thus, either extracellular or intracellular application of neurobiotin in the in vitro slice can reveal differences in axonal or dendritic targets of neuronal subgroups responsive to different neurotransmitters or peptides and provide evidence for the likely autonomic significance of the neurons.

The reliability of ERP components in the auditory oddball paradigm

Nineteen adolescents (average age 15 years, 3 months) were tested and retested using a standard 40 target, auditory oddball ERP paradigm across an interval of 1 year, 10 months to determine reliability of the ERP components, both in terms of intersubject stability and score agreement and in terms of trait (between-session reliability) versus state (within-session reliability). Significant trait stability was found for the N100, P200, and P300 latencies (r = .48, .51, and .74, respectively), and for P300 amplitude (r = .62), supporting the P300 as a reliable measure, with the stability required for group research but not necessarily for clinical applications. Discussion and examples illustrate the application of reliability information to the planning and evaluation of ERP paradigms.

Receptor subtype that mediates the neuronal effects of angiotensin II in the rat dorsal medulla

We have shown previously that many neurons in the caudal medial nucleus tractus solitarii (nTS) are excited by angiotensin (Ang) II. The selective Ang II receptor antagonists losartan (AT1; DuP 753) and CGP 42112A or PD 123177 (AT2) were used to evaluate the receptor subtype that mediates excitation of medial nTS neurons by Ang II (1 microM) in rat medulla in vitro slices. Neither losartan nor the AT2 antagonists altered the baseline firing of either Ang II-sensitive or Ang II-unresponsive neurons. However, in six cells with low-frequency spontaneous activity that remained above baseline after excitation by Ang II, subsequent administration of losartan reversed the firing pattern to the initial low-frequency activity. Losartan (10 microM) blocked the excitation by Ang II in 29 medial nTS neurons. The Ang II-induced excitation recovered from Type I blockade in 1 h. In contrast, both CGP 42112A (10 and 100 microM, n = 12) and PD 123177 (100 microM, n = 7) failed to block excitation by Ang II in all neurons tested. Furthermore, the AT2 antagonists were ineffective in preventing Ang II-induced neuronal excitation both when they were the first antagonist tested and when they were evaluated after the neuron had recovered from AT1 receptor blockade. These studies suggest that the Ang II-induced excitation of caudal medial nTS neurons is mediated by AT1 Ang II receptors.

Light microscopic localization of angiotensin II binding sites in canine medulla using high resolution autoradiography

Angiotensin II (Ang II) produces dose-related, site-specific cardiovascular effects in the canine and rat dorsal medulla. Our previous studies suggested that Ang II binding sites are associated with presynaptic vagal afferent fibers in the nucleus tractus solitarii (nTS) and vagal efferent neurons in the dorsal motor nucleus of the vagus (dmnX). High resolution autoradiography now establishes the relationship of putative Ang II receptors to the cytoarchitecture of these nuclei. Sections of the canine medulla oblongata were processed for film or emulsion autoradiography with 0.3-1 nM 125I-Ang II. Quantitative densitometry of films before and after processing sections for emulsion coating confirmed no selective alteration in labeling. In emulsion coated sections, dense labeling was seen over the majority of the large perikarya and surrounding neuropil in the ventral dmnX. Bands of label overlaid vagal efferent fibers coursing ventrolaterally to exit the medulla. In the nTS, Ang II binding was restricted to regions with heavy vagal afferent innervation. In the dorsal nTS, label was distributed over both cell bodies and neuropil, with highest density capping the solitary tract. In the medial nTS, label was concentrated over perikarya, with scattered grains over the intervening neuropil. The discrete subnuclear association of Ang II binding sites in the dorsal medulla with vagal cells and fibers documents that Ang II receptors are present on both afferent vagal fibers and intrinsic medullary neurons, and reveals an anatomical substrate for the autonomic effects of Ang II in this region.

Area Postrema: A Unique Regulator of Cardiovascular Function

The area postrema, which does not have a blood-brain barrier, can sense changes in levels of blood-borne hormones. This circumventricular organ plays an important role in animal models of hypertension, recovery from hemorrhage, control of baroreflexes, and homeostasis of water and ions.

Pressor effect of centrally administered sodium chloride: role of the ventral third ventricle region and the area postrema

To determine the site(s) responsible for the central cardiovascular effect of hypertonic saline, 0.2 ml of 1.5 M NaCl was administered to anesthetized dogs via three routes, a lateral ventricle, the third ventricle and the cisterna magna. Intracisternal administration of hypertonic NaCl produced much prompter pressor and tachycardic responses than did administration via the other two routes. Covering the ventral third ventricle region with a petroleum jelly plug had the effect of abolishing the pressor response to lateral ventricular hypertonic NaCl but did not modify the response to intracisternal hypertonic NaCl. By contrast, electrolytic lesion of the area postrema attenuated the rise in blood pressure produced by the intracisternal NaCl without affecting the response to lateral ventricular NaCl. These results indicate that at least two sites, the ventral third ventricle region in the hypothalamus and the area postrema in the lower brainstem, are responsible for the acute hypertension induced by an increase in NaCl concentration in the cerebrospinal fluid of the dog.

Functional interactions between angiotensin II and substance P in the dorsal medulla

Low doses of either angiotensin (Ang) II or substance P (SP) microinjected into the medial nucleus tractus solitarii (NTS) produce hypotension and bradycardia, mimicking activation of the baroreceptor reflex. Anatomical evidence suggests that Ang II binding sites in the medial NTS are located presynaptically on vagal afferent fibers that may contain SP and are codistributed with SP binding sites located postsynaptically on intrinsic medial NTS neurons. To evaluate whether the similar cardiovascular effects of Ang II and SP in the medial NTS could involve Ang II-evoked release of SP, we compared the effects of these peptides on the spontaneous activity of medial NTS neurons recorded in vitro and determined whether Ang II evoked release of SP from rat medulla slices. Both Ang II and SP (1 microM in artificial cerebrospinal fluid) excited 11 of 40 medial NTS neurons. In these cells, the peak response latency was significantly longer to Ang II than to SP (59.5 +/- 4.7 versus 26.5 +/- 2.4 seconds, p less than 0.0001). When rat medulla slices were perfused with Ang II (2 microM in Krebs' bicarbonate), release of SP immunoreactivity was increased by 400% over control perfusion with Krebs' solution alone (p less than 0.05). We have provided the first evidence for an excitatory action of Ang II on neurons in the NTS of the rat and for excitation by both Ang II and SP of a subset of neurons in the medial NTS. Moreover, we have shown for the first time that Ang II can stimulate the release of SP immunoreactivity from the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurophysiological responses to angiotensin-(1-7)

The aim of this study was to investigate the action of the heptapeptide angiotensin-(1-7) on the spontaneous activity of paraventricular neurons using microiontophoresis. Recent immunocytochemical investigations have shown that this product of angiotensin I is predominantly located in cells and fibers of the forebrain and brain stem. Our results show that most neurons in the paraventricular nucleus are excited by angiotensin-(1-7) at a dose of 50-80 nA. In comparison with angiotensin II or angiotensin III, the onset of response and the occurrence of the maximal effect were significantly delayed. With higher doses of angiotensin-(1-7), there was a decrease in latency and a dose-dependent increase in firing frequency. Of all the angiotensin compounds tested, angiotensin III was the most potent. Preliminary results obtained with an angiotensin antagonist show that the action of angiotensin II, angiotensin III, and angiotensin-(1-7) is blocked by the angiotensin receptor subtype 2 antagonist CGP 42112A. Because the angiotensin-(1-7) system in the brain is associated with central vasopressinergic pathways, vasopressin was tested in a similar way. Neurons in the paraventricular nucleus that were excited by iontophoretically applied angiotensins showed a weak response to vasopressin. Occasionally, a small excitatory action was observed. Our results support the hypothesis that the heptapeptide angiotensin-(1-7) is a biologically active neuropeptide. The data also suggest that amino terminal fragments of angiotensin II are not inactive degradation products.

Angiotensin II and angiotensin (1-7) excite neurons in the canine medulla in vitro

Our group showed previously that the heptapeptide angiotensin (1-7) [Ang-(1-7)] is a bioactive product of the renin-angiotensin system, and produces dose-dependent cardiovascular effects similar to those evoked by Ang II when microinjected into the nucleus tractus solitarii (nTS) of the rat. The effects of Ang II were compared with those of Ang-(1-7) on single neuron activity recorded from the medial nTS or dorsal motor nucleus of the vagus (dmnX) in perifused horizontal slices of the canine dorsomedial medulla. Ang II excited 48% of 31 medial nTS neurons, but only activated 14% of 22 dmnX cells. Ang-(1-7) also excited half of the medial nTS cells and 14% of the dmnXl neurons. Although most medial nTS neurons excited by Ang II were also activated by Ang-(1-7), two cells were excited by Ang II but not by Ang-(1-7), and one cell was excited by Ang-(1-7) but not by Ang II. Because Ang-(1-7) lacks direct vasoconstrictor effects, neurons in the dorsomedial medulla may have different receptor characteristics than peripheral tissues. The observation of a few medial nTS neurons excited by only one Ang peptide suggests that there may be a separate Ang-(1-7) receptor that participates in the physiological effects of Ang peptides mediated by the brain.

Pathways of angiotensin formation and function in the brain

New findings from this laboratory suggest that fragments of angiotensin derived from the amino (N-)terminus are biologically active end products of the renin-angiotensin system. In vitro and in vivo experiments revealed that the heptapeptide angiotensin-(1-7) [Ang-(1-7)] is a major endogenous product of the renin-angiotensin system cascade in the brains of rats and dogs. Additional studies with enzyme inhibitors showed that Ang-(1-7) is produced directly from angiotensin I by an enzyme other than the angiotensin converting enzyme. Immunocytochemical fibers within the hypothalamo-neurohypophyseal vasopressinergic system of the rat. Although Ang-(1-7) is as potent as angiotensin II (Ang II) in stimulating release of vasopressin from superperfused hypothalamo-neurohypophyseal explants, the heptapeptide has no dipsogenic or vasoconstrictor activity. In contrast, Ang-(1-7) mimics the effects of Ang II in augmenting the intrinsic discharge rate of neurons within the vagal-solitary complex and in causing monophasic depressor responses after microinjection into the medial region of the nucleus tractus solitarii. The evidence obtained in these experiments suggests novel mechanisms for the generation of angiotensin peptides in the brain. Additionally, the findings suggest that some of the biological actions ascribed to Ang II might be conveyed by the endogenous production of other angiotensin peptides that are generated by enzymatic pathways alternate to those described in the peripheral circulation.

The canine nucleus tractus solitarii: light microscopic analysis of subnuclear divisions

The nucleus tractus solitarii (nTS) is a complex structure situated in the dorsal medulla oblongata. This region receives primary visceral and gustatory sensory afferent fibers and has widespread interconnections with brainstem structures, hypothalamus, and limbic forebrain. In both rat and cat distinct subnuclei correlate with specific functions of the nTS. Since the canine model is used extensively for physiological study and evidence from this laboratory supports a critical role for the canine nTS in cardiovascular function, we examined its morphological organization. Light microscopic analysis of cellular and fiber patterns of the nTS revealed nine discrete regions based on cytoarchitecture: the commissural, lateral, ventral, dorsal, intermediate, interstitial and medial subnuclei, the subnucleus gelatinosa, and the dorsal parasolitary region. Analysis of each subnucleus revealed that both the lateral and ventral subnuclei contained two distinct neuronal groups based on cell size. Neurochemical and functional correlates are being provided by ongoing analyses of each subnucleus of the nTS.

Distribution of catecholaminergic neuronal systems in the canine medulla oblongata and pons

The distribution of catecholamine-containing neurons, fibers, and varicosities in the brainstem of both adult and juvenile dogs was mapped in detail with glyoxylic acid histofluorescence. Four separate groups of catecholamine-fluorescent neurons were identified within the canine medulla and pons in locations comparable to the A1, A2, A5, and A6 regions reported in other species. However, aspects of the pattern and density of the catecholaminergic neuronal systems appeared to be unique to the dog. The A1 neurons of the caudal ventrolateral medulla were much more scattered than in rats or rabbits, but relatively similar to cats. In the A2 region of the dorsomedial medulla, catecholaminergic cells and fibers were uniquely distributed compared to other species: fluorescent neurons were scattered only within the dorsal motor nucleus of the vagus, and a distinctive pattern of fibers and varicosities outlined the nucleus of the solitary tract and dorsal motor nucleus of the vagus. The A5 neurons of the rostral ventrolateral medulla appeared at the rostral limit of the A1 region. Fluorescent A5 cells were more sparse than in rats or primates, and were patterned similarly to cats and rabbits. The canine A6 region contained the most extensive and dense grouping of catecholamine neurons and was similar in pattern to the rabbits but less extensive than that seen in cats or primates. An ascending catecholaminergic fiber pathway was traced through the central tegmental field of the canine medulla and pons, with features similar to the primate. The present study provides the first description of the catecholaminergic neuronal systems of the canine medulla.

Neuronal responses to angiotensin II in the in vitro slice from the canine medulla

The present studies utilized the in vitro slice preparation of the canine dorsomedial medulla, which we have recently developed, to obtain direct evidence for the effects of angiotensin II (Ang II) on the activity of single neurons in this region. Horizontally oriented slices (300 micron) containing the area postrema, nucleus tractus solitarii (NTS), and dorsal motor nucleus of the vagus were perifused with oxygenated artificial cerebrospinal fluid. The effects of microdrop application of Ang II and its antagonist [Sar1,Thr8]Ang II on spontaneous firing rate were determined in 27 extracellularly recorded neurons. Ang II substantially increased the firing rate of 13 neurons located in the medial NTS, but it did not alter the spontaneous activity of the remaining 14 neurons. In most cases Ang II elicited a slowly developing, prolonged excitatory response. The effects of both Ang II and [Sar1,Thr8]Ang II were tested in 13 neurons. [Sar1,Thr8]Ang II produced a short latency, brief excitation in three neurons, marked inhibition of spontaneous firing in two cells, and no effect on the other eight neurons. Administration of [Sar1,Thr8]Ang II blocked the excitatory effects of subsequent administration of Ang II in three neurons. To our knowledge, these observations provide the first evidence for direct actions of both Ang II and [Sar1,Thr8]Ang II on neurons in the canine NTS and for the specificity of the neuronal effects of Ang II as documented by blockade of the excitatory response to Ang II by [Sar1,Thr8]Ang II.

Effect of area postrema lesion on low-frequency arterial pressure oscillations in dogs

To explore the possibility that chronic inactivation of the area postrema (AP) may alter the frequency distribution of oscillations in blood pressure, the power spectra for mean arterial pressure (MAP) were evaluated in conscious dogs before and after heat coagulation (n = 4) or sham lesions (n = 6) of the AP. No significant changes in MAP were observed in either group of dogs after surgery. Tachycardia was seen in AP-lesioned animals after surgery; no consistent changes in heart rate were found in sham-lesioned dogs. Spectra were averaged to provide a group spectral estimate for the AP-lesioned and sham-lesioned groups, respectively, for each experimental period. In the sham-lesioned group a variance peak was observed at approximately 0.03 Hz both before and after surgery. The same peak was seen in the AP-lesioned group during the control period but disappeared following AP lesion, apparently because a greater proportion of the variance was shifted toward frequencies below 0.03 Hz. In addition, a peak related to respiratory rate was present in both groups before surgery but was selectively abolished by AP lesion. AP lesion also substantially reduced the power associated with frequencies between 0.1 and 0.4 Hz. The use of spectral analysis has allowed us to demonstrate that a low-frequency oscillation of MAP in conscious, resting dogs requires the integrity of the AP and that the 0.1- to 0.4-Hz components of the variability of MAP are attenuated after removal of the AP.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of area postrema pressor mechanisms in the regulation of arterial pressure

This article discusses the data which established that angiotensin II modulates the tonic and reflex control of cardiovascular function by actions on the nuclear regions of the dorsal medulla oblongata. Although physiological evidence for the modulatory actions of angiotensin II in structures of the lower brainstem has been gathered over the past 16 years, only the recent application of new neurobiological techniques has allowed a more definitive understanding of its role. The identification of high affinity angiotensin II binding sites within the parenchyma of the area postrema with the technique of in vitro receptor autoradiography has provided anatomical validity for a role of angiotensin II in the central nervous system. The added discovery of angiotensin II binding sites in subnuclear components of the nucleus tractus solitarii and the motor nucleus of the tenth cranial nerve provides additional information on the various mechanisms through which angiotensin II may affect the intrinsic activity of the brainstem neuronal circuits involved in the integration of baroreceptor and sensory visceromotor function.

Pressor responses of angiotensin II microinjected into the dorsomedial medulla of the dog

Angiotensin II (Ang II) was injected into regions of the dorsomedial medulla of dogs where both specific Ang II binding and neural elements containing this peptide are found. Picomole amounts of the peptide were delivered simultaneously from a linear array of 3 micropipettes with tips positioned concurrently in either the area postrema (ap), nucleus tractus solitarii (nTS), dorsal motor nucleus of the vagus (dmnX), or hypoglossal nucleus (nXII). Significant increases in blood pressure occurred with Ang II injections into the medial nTS (+12 +/- 2 mm Hg), the ap(+9 +/- 3 mm Hg), and the nXII (+6 +/- 2 mm Hg). In both the medial nTS and the nXII, the pressor responses were accompanied by significant increases in heart rate (+13 +/- 3 beats/min and +8 +/- 3 beats/min, respectively). Ang II injected into the dmnX did not produce consistent effects on blood pressure or heart rate. These data demonstrate that unilateral injections of picomole amounts of Ang II produce changes in blood pressure and heart rate which involve neural elements in the ap and medial nTS.

Projections of the carotid sinus nerve to the medulla in the dog

The afferent and efferent projections of the carotid sinus nerve were examined within the medulla of the dog with axonal transport of horseradish peroxidase (HRP), and compared with the projections of the glossopharyngeal nerve. The carotid sinus nerve was identified electrophysiologically prior to injection of tracer. Carotid sinus nerve afferent fibers entered the medulla as part of the glossopharyngeal nerve root near the caudal limits of the cochlear nuclei. Labeled axons entered the solitary tract and ran caudally to about 3 mm anterior to the obex, where they began to enter the nucleus tractus solitarii (nTS). Carotid sinus afferent fibers and presumptive terminals were discretely localized within limited portions of the ipsilateral dorsal, medial, and lateral nTS as far as 3 mm caudal to the obex. A few fibers entered the dorsolateral area postrema ipsilateral to HRP injection. Labeled fibers in the commissural nTS crossed the midline and entered the contralateral medial nTS. Efferent neurons were observed only in half of the cases, and were limited to one to three labeled perikarya in the periphery of the retrofacial nucleus. Comparison of the carotid sinus distribution with the previously described vagal afferent projections to the canine nTS revealed partially overlapping, but clearly distinctive patterns, which support a viscerotopic organization of the nTS.

Functional characteristics of neuropeptides in the dorsal medulla oblongata and vagus nerve

The dorsomedial medulla plays an integral role in the processing of primary sensory afferent information from the respiratory, cardiovascular, and gastrointestinal systems. A correlation has also been made between the topographical organization of these vagal afferent fibers in the dorsal medulla and the distribution of a variety of neuropeptides and their receptors in this brain region. In this paper, the evidence for the presence of several neuropeptides and their receptors in the dorsomedial medulla and intra- and/or extracranial segments of the vagus nerve is presented. The possible physiological significance of these peptides and their putative receptors in the vagus nerve is also addressed, with emphasis on angiotensin II and its cardiovascular actions in this region.

Correlation between angiotensin II binding sites and substance P in the canine brain stem

Specific angiotensin II (ANG II) binding sites in the dorsal aspects of the medulla oblongata of dogs and rats were shown previously to be dependent upon intact sensory and motor components of the vagus nerve. The present studies compared the distribution of ANG II binding sites in the canine medulla with the visualization of substance P immunoreactive fibres, since this peptide is known to be present in vagal afferent fibres. Dense bands of substance P-containing fibres were found to cap the tractus solitarius (TS) in the dorsal subdivision of the nucleus tractus solitarii (nTS) at a level corresponding to the region of highest ANG II binding. In addition, moderate densities of both substance P immunoreactivity and ANG II binding sites were dually localized in the medial nTS and the ventral portion of the dorsal motor nucleus of the vagus (dmnX). Since previous studies indicated that ANG II binding sites are associated with vagal afferent fibres in the nTS and efferent motor neurons in the dmnX, their apparent association with substance P immunoreactive fibres suggests that a functional interaction may occur between these two peptides in the central integration of cardiovascular function.

Contribution of the vagus nerve to angiotensin II binding sites in the canine medulla

Specific angiotensin II (Ang II) binding sites are present in the dorsal medulla of several species, and dose-related cardiovascular effects are produced by microinjection of the peptide into this region. Because the anatomical location of Ang II binding sites in the area postrema (ap), nucleus tractus solitarii (nTS), and dorsal motor nucleus of the vagus (dmnX) coincides with the topography of vagal afferent fibers and efferent motor neurons, the effect of either nodose ganglionectomy or cervical vagotomy on Ang II binding sites in the dorsomedial medulla was investigated in dogs by in vitro receptor autoradiography. Two weeks after unilateral ganglionectomy, there was a marked reduction in the density of specific Ang II binding sites in the ipsilateral ap, nTS, and dmnX, and an absence of binding sites in the region where vagal afferent fibers course through the rostral medulla. Unilateral cervical vagotomy, which has been shown to spare central processes of afferent fibers, resulted in a loss of binding only in the ipsilateral dmnX. We also show that Ang II binding sites are present in the nodose ganglion and central and peripheral processes of the vagus nerve. The data indicate that medullary Ang II binding sites are associated with both vagal afferent fibers and efferent motor neurons.

Contribution of area postrema to pressor actions of angiotensin II in dog

To generate quantitative data on the contribution of the area postrema (AP) to the pressor activity of angiotensin II (ANG II), the peptide (7 ng X kg-1 X min-1) was infused intravenously in 10 conscious dogs for 6 h before, and several weeks after, AP lesion. Mean arterial pressure (MAP) and heart rate (HR) were recorded continuously, and plasma renin activity (PRA), ANG II immunoreactivity (ANG II-IR), aldosterone (ALDO), arginine vasopressin (AVP), norepinephrine (NE), epinephrine (EPI), and serum Na+ and K+ were measured at 3 and 6 h. Three hours into the infusion, MAP averaged 123 +/- 2 compared with 96 +/- 2 mmHg for controls (P less than 0.01). The increases in pressure were associated with unchanged HR, but increased lability of MAP and HR. PRA fell, whereas plasma levels of ANG II-IR and ALDO rose. Plasma levels of AVP, NE, serum Na+ and K+ did not change, but plasma EPI was significantly elevated at 6 h. Removal of the AP produced mild hypotension and decreased lability. Within 8 to 21 days after AP ablation, a significant decrease in the plateau phase (3-6 h) of the ANG II pressor response was recorded in all dogs. The attenuation of the pressor effects was not sustained, since 4-7 wk after AP lesion, the increases in pressure were equivalent to those obtained during the control period. These data indicate that the AP participates in the production of the pressor response to intravenous infusion of ANG II in conscious dogs. However, in the absence of this structure, alternative mechanisms are brought into play to restore the loss of its function.(ABSTRACT TRUNCATED AT 250 WORDS)

Area postrema lesions augment the pressor activity of centrally administered vasopressin

The effects of arginine vasopressin given into either the vertebral arteries, a peripheral vein (IV), or the cisterna magna of 15 morphine-chloralose anesthetized dogs were measured before and after pharmacological blockade with the antagonist [d(CH2)5 Tyr(Me) AVP]. The contribution of the area postrema to the pressor activity of vasopressin was assessed in nine other dogs by comparing the responses to vasopressin before and after surgical ablation of this structure. Administration of vasopressin either via the vertebral arteries or intravenously produced comparable gradual rises in blood pressure, accompanied by bradycardia and decreases in the plasma levels of norepinephrine. Administration of intracisternal vasopressin elicited a smaller rise in arterial pressure, tachycardia, and increases in plasma norepinephrine levels. The pressor and bradycardic effects of IV vasopressin were abolished when the antagonist was given via the same route. In contrast, intravertebral infusion of the vasopressin antagonist caused tachycardia and modest hypotension in response to intravenous or intravertebral infusions of vasopressin. Pressor effects of vasopressin given into the cisterna magna were not altered by systemic delivery of the vasopressin blocker. Removal of the area postrema selectively augmented the pressor effects of intravertebral vasopressin, whereas the pressor activity of IV vasopressin remained unchanged. These findings provide new evidence for an action of circulating vasopressin in cardiovascular regulation, mediated in part by the area postrema.

The anteroventral third ventricle region. Participation in the regulation of blood pressure in conscious dogs

The anteroventral third ventricle (AV3V) region plays an important role in fluid and electrolyte balance and cardiovascular control in the rat; however, experiments in other species have raised questions about the universality of findings in the rat. The effects of discrete lesions placed within the AV3V area on hydromineral balance, the pressor response to angiotensin II given intravenously, and the initiation of a renin-dependent model of hypertension were examined in the dog. A transpharyngeal approach to the optic chiasm enabled us to destroy only the anterior aspects of the AV3V region (aAV3V group) or to include the entire nucleus medianus (NM) as well (aAV3V + NM group). Lesions of the aAV3V caused polydipsia and transient hypernatremia and hyperosmolality. In contrast, adipsia and a sustained increase in plasma sodium levels and osmolality were observed in dogs with lesions of the aAV3V plus the entire NM. Neither lesion altered baseline arterial pressure, heart rate, plasma levels of catecholamines and vasopressin, or total plasma protein levels. Only in aAV3V + NM lesioned dogs was there a tendency for plasma angiotensin II immunoreactivity to be elevated above control values at 2 and 4 days after operation. Neither lesion attenuated the pressor response to intravenous angiotension II or the initiation of renal hypertension induced by aortic coarctation. As observed in other species, structures within the AV3V region participate in hydromineral balance in the dog; however, in the dog portions of the NM dorsal to the AV3V region are essential for the mediation of drinking behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II receptor localization in the canine CNS

Specific binding of [125I]angiotensin II [(125I]Ang II) to sections of dog brain was determined by in vitro receptor autoradiography. Highly discrete, dark images representing specific binding of [125I]Ang II were observed in areas corresponding to the nucleus of the solitary tract, dorsal motor nucleus of the vagus, area postrema, ventrolateral medulla, pineal, subfornical organ, nucleus medianus, septum, organum vasculosum of the lamina terminalis and the anterior pituitary. The specific binding was frequently present either as a narrow band or tiny spot within a small portion of the nuclei to which the binding corresponded. The location of these Ang II recognition sites in regions associated with regulation of autonomic and neuroendocrine function provides further evidence for a role of this peptide within the central nervous system.

Hypotensive actions of microinjections of angiotensin II into the dorsal motor nucleus of the vagus

Angiotensin II (ANG II) was injected via double-barrelled micropipettes into brain stem nuclei of 83 chloralose anaesthetized rats at doses between 8 fmol and 250 pmol. Femtomole injections of ANG II confined to the dorsal motor nucleus of the vagus (dmnX) and the ventral portion of the medial nucleus tractus solitarius (NTS) produced falls in blood pressure (BP) and heart rate (HR) of 28 and 12%, respectively, which were significantly greater than those produced by vehicle injections at these same sites (9 and 6% for BP and HR, respectively). ANG II injections into either the medial NTS or the hypoglossal nucleus were not different from vehicle. Prior administration of methylatropine (intraperitoneally) or bilateral cervical vagotomy significantly attenuated the bradycardia without affecting the fall in blood pressure. These data provide the first evidence for a direct action of low doses of ANG II within discrete nuclei of the dorsal medulla. The findings suggest that activation of the parasympathetic nervous system primarily accounts for the bradycardia. However, inhibition of sympathetic nervous system activity may contribute to the hypotension. Additionally, these data are consistent with a neurotransmitter or neuromodulator role for ANG II in the brain stem of rats.

Contribution of vasopressin to hypertension after solitary tract lesioning in the dog

The relative contributions of vasopressin and sympathetic outflow to the acute hypertension that followed central baroreceptor deafferentation at the level of the rostral solitary tract (TS) were examined. In nine dogs (TS lesion group) baroreflex control of heart rate was abolished, confirmed histologically with bilateral interruption of the solitary tracts. Baroreflex tests were positive and one solitary tract was spared in three dogs (incomplete lesion group). Blood pressure rose rapidly after discontinuation of anaesthesia in the animals of the TS lesion group. Administration of an antagonist of the vascular effects of vasopressin 2 1/2 h after lesioning produced a significant decrease in mean arterial pressure and tachycardia in the TS lesion animals, but did not alter blood pressure in the incomplete lesion group. Subsequent ganglionic blockade with hexamethonium produced comparable falls in mean arterial pressure in both groups of dogs. We conclude that vasopressin contributes significantly to the elevated blood pressure only in animals with complete interruption of the baroreceptor afferents in the rostral TS.

Participation of the area postrema in cardiovascular control in the dog

Investigations have demonstrated that the pressor effects of low-dose intravertebral angiotensin II (Ang II) in the dog are mediated by the area postrema (AP). Chronic ablation of the AP has been shown to produce both mild hypotension and blunting of the pressor effects of peripherally administered Ang II, which suggests a tonic influence by this structure on the regulation of blood pressure. These findings motivated a correlated series of neurophysiological and anatomical studies to characterize further the AP pressor pathway. The pressor response to electrical stimulation of the AP was shown to be mediated by increased central sympathetic outflow, as shown previously for the response to intravertebral Ang II, and unopposed by the central nervous system baroreflex pathways. Neuroanatomical investigations demonstrated a three-layer structure in the dog's AP, with efferent projections into the medial nucleus tractus solitarii bilaterally. These studies have provided new evidence about the functional and structural mechanisms by which the AP participates in cardiovascular regulation.

Afferent projections of the cervical vagus and nodose ganglion in the dog

The distribution within the brain stem of the afferent projections of the cervical vagus and the nodose ganglion was studied with horseradish peroxidase (HRP) and HRP-wheat germ agglutinin conjugate. Two to eight days after application of tracer into the cervical vagosympathetic trunk or the nodose ganglion the brain stems and ganglia were perfused and processed by the tetramethyl benzidine method. Vagal afferent fibers entered the lateral medulla as a distinct bundle spatially separate from the vagal efferent rootlets which were caudal and ventral to the afferents. Labeled axons in the solitary tract began to enter the nucleus tractus solitarii (nTS) 4.5 mm anterior to obex and were seen throughout the ipsilateral nTS as far as 3.5 mm caudal to obex. Label density varied within the nTS, with heaviest labeling in the dorsal and dorsolateral portions. Label was also seen in the ipsilateral area postrema (ap) and dorsal motor nucleus of the vagus. Labeled fibers crossed in the commissural portions of ap and nTS to enter the contralateral ap and nTS.

Location of the area postrema pressor pathway in the dog brain stem

Electrical stimulation of the dog's area postrema (AP) induces a response that mimics the pressor response produced by intravertebral infusion of low-dose angiotensin II, which causes an increase in mean arterial pressure associated with transient tachycardia and increased peripheral resistance. The present study investigated in morphine-chloralose anesthetized dogs whether: 1) the characteristics of the AP pressor response are influenced by the presence of carotid sinus afferents; 2) structures rostral to the medulla influence the AP pressor response; and 3) the pressor pathway is initiated by neurons within the AP. Since bilateral cervical sinovagal denervation, which potentiated the phenylephrine pressor response, did not affect the pressor response to AP stimulation, the data provide evidence for an inhibitory influence exerted upon the central baroreflex mechanism by the AP pressor mechanism. The unaltered AP pressor response after midcollicular transection suggests that the efferent pathway is contained within the brain stem caudal to the pons. Finally, the elimination of the pressor response following kainic acid microinjection into the AP provides evidence that the AP pressor mechanism is initiated by neurons within the AP, rather than by fibers of passage from other pressor centers. These results suggest that the AP produces its facilitation of central sympathetic vasomotor outflow via a pathway contained within the medulla.

A technique for difficult arthrodesis of the knee

Twenty knees, in which a total of 32 previous operations had been performed, were arthrodesed by the Charnley compression technique combined with intramedullary nailing. Patients with previous infection were excluded from the series, but three neuropathic knees were included. Bony union was evident after an average of six months in all but one patient who died three months after operation. One patient developed deep infection that resolved after removing the nail. The combined technique is simple and only limited bone resection is needed; it gives immediate stability and relief of pain with minimal morbidity.

Arginine vasopressin modulates the central action of angiotensin II in the dog

Endogenous vasopressin may interact with central autonomic nervous system factors in the regulation of cardiovascular function. In 25 morphine/chloralose-anesthetized dogs, we studied the magnitude of the pressor response produced by an infusion of angiotensin II (AII) into the vertebral arteries (VA), before and after intracisternal (n = 10), intravertebral (n = 9), or intravenous (n = 6) administration of a competitive antagonist of arginine vasopressin (AVP) [d(CH2)5Tyr(Me) AVP]. The dose response curve to vertebral artery infusion of AII (range 2-20 ng/kg/min) was significantly (p less than 0.05) shifted to the right of control after injection of the AVP antagonist (10 micrograms/kg) into the cisterna magna; the ED at 20 mm Hg being almost double after central AVP blockade. This effect of AVP blockade was confined only to the cardiovascular response mediated by AII via the vertebral arteries. When pressor doses of AII were injected into either a vein (i.v.) or the cisterna magna of these same dogs, the increases in mean blood pressure were the same before and after AVP antagonist treatment. In another group of anesthetized dogs, we investigated whether the reduced reactivity to intravertebral AII could be duplicated by giving the AVP antagonist either via the vertebral artery or i.v. Only the cisterna magna route was effective in causing a blunting of the pressor response to vertebral artery AII. These data demonstrate a previously unknown interaction between vasopressin and the centrally mediated pressor response to intravertebral AII.

Brainstem distribution of neurons with efferent projections in the cervical vagus of the dog

The distribution within the brainstem of cell bodies and efferent fibers projecting in the cervical vagus was studied with retrograde transport of horseradish peroxidase (HRP). Five to eight days after multiple microinjections of HRP into either the cervical vagosympathetic trunk or the nodose ganglion the brainstems and nodose ganglia were perfused and processed by the tetramethyl benzidine method. HRP-positive neurons were found in three brainstem regions: a dorsal cell column comprising the dorsal motor nucleus of the vagus (dmnX), a ventrolateral group in the region of nucleus ambiguus (nA), and scattered cells along a line between these columns. The density of labeled neurons was greatest within dmnX. Axons from cells of the ventrolateral column projected dorsomedially; just ventral to dmnX they turned laterally to exit the medulla in multiple rootlets. Within nA labelled neurons were distributed according to size, with larger cells more medial and smaller ones more lateral. Caudal to nA in nucleus retroambigualis and nucleus dorsalis medialis cell bodies appeared segregated into clusters.

Chromatin from the unicellular red alga Porphyridium has a nucleosome structure

We have isolated a crude nuclear preparation from the unicellular red alga Porphyridium aerugineum and investigated the structure of Porphyridium chromatin. Electrophoresis of deproteinized DNA fragments produced by micrococcal nuclease digestion of Porphyridium nuclei gives a typical ladder pattern, indicative of a repeating structure. The DNA repeat-length, calculated from plots of multimer length against multimer number, varies somewhat between different digestions, ranging from 160 to 180 base-pairs (average 173). We interpret this as evidence of heterogeneity in repeat-length; the calculated repeat-length depends on the extent of digestion because chromatin sub-populations with longer repeat-lengths are on average digested earlier. Polyacrylamide/sodium dodecyl sulphate gel electrophoresis of basic proteins purified from Porphyridium nuclear preparations gives a pattern characteristic of core histones. Although our interpretation is complicated by some degradation, the result strongly suggests that Porphyridium chromatin contains each of the four core histones and that they are similar to those of higher eukaryotes. This, together with the micrococcal nuclease digestion results, demonstrates that Porphyridium chromatin is not fundamentally different from that of higher eukaryotes.

Bone and Joint tuberculosis in Greater Manchester 1969-79

The records of 74 patients diagnosed as suffering from tuberculous (TB) bone or joint disease between 1969 and 1979 were analysed retrospectively. Most were resident in the Greater Manchester County. Thirty-eight patients were first-generation immigrants, and teenage males were particularly prominent in this group. In the indigenous patients the diagnosis was often delayed several months or years, and in a number of subjects there was a history of previous bone and joint tuberculosis. There was a wide range of affected sites, especially in the immigrant group, and evidence of nonarticular TB was found in only a minority of patients. Diagnosis is most satisfactorily based on open biopsy and submission of pathological material to culture and histology. British subjects were more likely to have to undergo remedial surgery for the disease, especially when weight bearing joints were involved. Antituberculous chemotherapy should be given for at least 1 year to prevent recurrence of the disease.

Neurogenic hypertension produced by lesions of the nucleus tractus solitarii alone or with sinoaortic denervation in the dog

The cardiovascular effects of bilateral lesions of the nucleus tractus solitarii (NTS) were compared with those of subsequent sinoaortic denervation in the same dogs. Destruction of the lateral but not the medial component of the NTS between + 0.5 and 3 mm anterior to the obex produces mild hypertension and tachycardia, not always sustained for more than 2 weeks. Rises in pressure were accompanied by increased lability which was not present regularly in all dogs but correlated with the baseline level of arterial pressure. On the other hand, sinoaortic denervation following lateral NTS lesions produced the first demonstration of fulminant hypertension in the dog, which led to death within hours. These data suggest that, while NTS lesions in the dog probably only partially interrupt central baroreceptor pathways, the addition of sinoaortic denervation completely disrupts baroreceptor inputs to the central nervous system, thus releasing central sympathetic outflow completely from baroreceptor inhibition.

Characterization of the sympatho-facilitative area postrema pathway

1. The mechanism by which the area postrema augments central sympathetic drive during electrical stimulation is presently unknown. This pathway may involve either direct facilitation of brain-stem vasomotor neurons or inhibition of the sympatho-inhibitory baroreceptor relay in the nucleus tractus solitarii. 2. The present study employed selective lesions within the solitary tract nucleus to assess the participation of the primary baroreceptor relay in the pressor response during electrical stimulation of the area postrema. 3. The magnitude of the pressor response was unchanged after destruction of the solitary tract and lateral solitary nucleus which centrally interrupted the baroreceptor reflex. However, microknife cuts through the medial solitary nucleus, which spared the carotid sinus reflex, significantly reduced the magnitude of the area postrema pressor response. 4. Previous anatomical studies support these results and confirm that, although the area postrema pressor pathway traverses the most medial portion of the solitary complex, it does not produce augmented sympathetic outflow by inhibition of the primary baroreflex relay.

A morphological characterization of the canine area postrema

The cellular morphology of the dog's area postrema (AP) was demonstrated with the Golgi-Cox technique. Golgi preparations suggested division of the canine AP into three regions: a periventricular mantle zone, a central region, and a junctional zone adjacent to the nucleus tractus solitarii. The distinctive feature of the dog's AP was arrays of periventricular neurons intermixed with glialoid cells. Additional Bodian sections revealed a commissural fiber network connecting the halves of the AP at the obex. The interconnected three-layer structure implies a polysynaptic pathway by which AP stimulation activates central sympathetic outflow.

Effect of hyaluronidase on acute spinal cord injury

Three control and five experimental dogs were subjected to 500 gm-cm injury of the midthoracic spinal cord by the weight dropping technique. Five hundred units per kilogram of hyaluronidase injected intravenously 20 minutes after injury in the experimental animals did not alter the loss of dorsal column evoked potentials (nonaveraged) or improve the pathological results up to three hours. These results imply that hyaluronidase will not significantly alter the functional outcome of trauma of the spinal cord in dogs.

Angiotensin and CNS regulation of blood pressure

It appears that angiotensin II (AII) has access to the CNS by three routes: endogenous formation within the brain, passage into CSF, or transfer across "gaps" in the blood-brain barrier. The mode of access influences both the characteristics and the magnitude of the cardiovascular effects exerted by AII within the CNS. In the dog the effects of blood-borne AII on the area postrema (AP) in the IV ventricle seem to have the most physiological significance. In recent experiments we have characterized both the histological composition of this structure and its physiological effects. While electrical stimulation of the AP, in similarity to the pressor effects of intravertebral AII, produces a hypertensive response dependent on sympathetic vasomotor outflow, ablation of this structure results in mild hypotension associated with decreased hemodynamic variability and altered vascular responsiveness to intravenous AII and norepinephrine. Recent data suggest that the sympatho-facilitative action of AII on the AP may involve endogenous opiates in the brainstem.

Cutaneous sensory function in diabetes mellitus

That disorders of cutaneous sensation are common in diabetes mellitus can be substantiated by quantitative cutaneous sensory testing. Cutaneous sensory disturbances are not clearly related to clinical factors such as the type, treatment, or duration of diabetes, or ocular complications. Diabetics can be distinguished from nondiabetics on quantitative examination of skin sensation. Juvenile diabetics appear to have fewer cutaneous abnormalities than adults who develop the disease, but the juvenile diabetic is not spared. Disorders of cutaneous sensation may represent a fundamental abnormality of the nervous system in diabetes mellitus. While altered peripheral sensory mechanisms are likely, abnormality of central sensory processing is not excluded by the results of this study.