Serotonin 5-HT1A and 5-HT2/1C receptors in the midbrain periaqueductal gray differentially modulate defensive rage behavior elicited from the medial hypothalamus of the cat

Recent studies have established that the expression of defensive rage behavior in the cat is mediated over a descending pathway from the medial hypothalamus to the dorsolateral quadrant of the midbrain periaqueductal gray matter (PAG). The present study was designed to determine the roles played by 5-HT1A and 5-HT2/1C receptors in this region of PAG in modulating defensive rage behavior elicited from the cat's medial hypothalamus. Monopolar stimulating electrodes were implanted into the medial hypothalamus from which defensive rage behavior could be elicited by electrical stimulation. During the course of the study, the 'hissing' component of the defensive rage response was used as a measure of defensive rage behavior. Cannula-electrodes were implanted into sites within the PAG from which defensive rage could also be elicited by electrical stimulation in order that 5-HT compounds could be microinjected into behaviorally identifiable regions of the PAG at a later time. Microinjections of the selective 5-HT1A agonist, (+)-8-hydroxy-dipropylaminotetralin hydrobromide (8-OHDPAT) (50 pmol, 2.0 and 3.0 nmol), into the PAG suppressed the hissing response in a dose-dependent manner. Administration of the selective 5-HT1A antagonist, 4-iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl] ethyl]-N-2-pyridinyl-benzamide hydrochloride (p-MPPI) (1.5 and 3.0 nmol), blocked the suppressive effects of 8-OHDPAT upon hissing. In contrast, microinjections of the 5-HT2/1C receptor agonist (+)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane hydrochloride ((+)-DOI hydrochloride) (0.01, 1.0 and 1.5 nmol) facilitated the occurrence of hissing elicited from the medial hypothalamus in a dose-dependent manner. Immunohistochemical analysis revealed the presence of 5-HT axons and preterminals throughout the PAG, and in particular, in its dorsolateral aspect which receives major inputs from the medial hypothalamus in association with defensive rage behavior. The overall findings of the study provide evidence that activation of 5-HT1A and 5-HT2/1C receptors within the midbrain PAG differentially modulate the expression of defensive rage behavior elicited from the medial hypothalamus of the cat.

Suicidality among HIV-positive psychiatric in-patients

Rates of suicidality with HIV-infected, seriously mentally ill individuals were investigated. Fifty asymptomatic HIV-positive psychiatric in-patients were compared to a demographically-matched HIV-negative cohort. The groups were similar, except that seropositive subjects were less likely to be diagnosed with schizophrenia. Both groups had high rates of suicidality, with higher rates associated with non-schizophrenic diagnoses. HIV-positive subjects had higher rates of suicidality, with those diagnosed with schizophrenia showing the greatest difference from their HIV-negative counterparts. HIV-positive patients required less in-patient treatment. These data expand previous reports showing an association between HIV and increased suicidality, even among individuals with already elevated suicidal rates.

Prostaglandin E1 infusion compared with prostacyclin infusion in patients with refractory heart failure: effects on hemodynamics and neurohumoral variables

Prostaglandin E1 or prostacyclin were randomly infused in 18 patients with severe chronic heart failure who did not respond to oral treatment. Maximally tolerated dosages of both agents increased cardiac index; however, only prostacyclin decreased mean arterial pressure and increased plasma norepinephrine significantly. Twelve hours after 50% peak dose reduction, atrial natriuretic peptide levels, right atrial pressure, mean pulmonary artery pressure, and mean arterial pressure continued to decrease with prostaglandin E1, whereas the increase in cardiac index was sustained; in contrast, at 50% prostacyclin dose reduction, cardiac index decreased toward baseline, suggesting that, with reduced dosages for chronic infusions, desired hemodynamic changes seem to be sustained with prostaglandin E1 only.

Hemodynamic and neurohumoral effects of long-term prostaglandin E1 infusions in outpatients with severe congestive heart failure

BACKGROUND

Prostaglandins of the E type are potent endogenous vasodilators that also interfere with the activity of the sympathetic nervous system. Thus treating patients with end-stage heart failure with prostaglandin E1 (PGE1) infusions seems to accord well with the hypothesis that neurohumoral imbalance rather than hemodynamic derangements should be the priority in the treatment of heart failure.

METHODS

We sought to investigate neurohumoral in addition to hemodynamic changes during long-term PGE1 infusion and determined plasma renin activity, atrial natriuretic peptide, norepinephrine, and big endothelin plasma levels in 13 male patients with heart failure whose symptoms remained severe in spite of optimized oral therapy with digitalis, nitrates, furosemide (185 +/- 72 mg/d) and enalapril (33 +/- 3 mg/d). PGE1 infusion rate was started with 2.5 ng/kg/min and stepwise increased to the maximum tolerated dose (26 +/- 4 ng/kg/min), which was halved for continuous infusion through the following 12 hours and further stepwise reduced to an average dose of 8 +/- 1 ng/kg/min. Right heart catheterization was performed for acute hemodynamic studies and after 4 weeks. All patients were discharged with a catheter that was connected to a portable pump for home therapy.

RESULTS

Acute effects of PGE1 were reductions in systemic blood pressure, (p < 0.05), right atrial pressure (p < 0.001), pulmonary artery pressure (p < 0.05), pulmonary capillary wedge pressure (p < 0.01), systemic and pulmonary vascular resistance index (both p < 0.01) and an increase in cardiac and stroke volume index (both p < 0.001) without a change in heart rate. After 4 weeks a persistent increase from baseline in cardiac index (from 1.9 +/- 0.1 to 2.5 +/- 0.2 L/min/m2; p < 0.01) and in pulmonary vascular resistance index (from 479 +/- 50 to 331 +/- 29 dynes x sec/cm5 x m2; p < 0.05) was observed. Atrial natriuretic peptide (p < 0.05) decreased, and norepinephrine and big endothelin showed a tendency to a lower level. Concomitantly, New York Heart Association functional class changed (p = 0.0001), with one patient's condition remaining class IV, the conditions of seven patients decreasing to class II, and the conditions of five patients decreasing to class III.

CONCLUSION

Thus long-term parenteral home therapy with PGE1 infusions in patients with severe end-stage heart failure elicited beneficial clinical and hemodynamic effects without activating neurohumoral counterregulatory systems.

Prostaglandin E1--bridge to cardiac transplantation. Technique, dosage, results

BACKGROUND

Heart transplantation candidates who remain severely symptomatic despite therapy are normally hospitalized. Continuous infusion of intravenous drugs from a portable pump may allow such patients to live a fairly active life until a donor heart is found.

AIM

To investigate in an open pilot study if heart transplantation can be safely accomplished if these patients are continuously bridged with various regimens including inotropic support with low-dose dobutamine in conjunction with dopamine and prostaglandin E1.

METHODS

We report on 5 years' experience with prostaglandin E1, a potent vasodilator with proven efficacy in severe heart failure when coupled with catecholamines. From 1990 to 1995 54 heart transplantation candidates were bridged with prostaglandin E1 in addition to dobutamine 5 micrograms.kg-1. min-1 and dopamine 3 micrograms.kg-1 min-1 (group A; n = 32) or in addition to 3 micrograms.kg-1 min-1 dopamine alone (group B; n = 22), and 11 heart transplantation candidates were bridged with dobutamine 5 micrograms.kg-1. min-1 and dopamine 3 micrograms.kg-1 min-1 only (group C; n = 11). In an initial dose-ranging test, prostaglandin E1 was uptitrated to side effect limit (29 +/- 1 ng.kg-1.min-1). Haemodynamics, except for stroke volume index, were similar in all patients at baseline and a sufficient haemodynamic response (20% increase in stroke volume) was observed during the acute study. Fifty percent of the peak dose was used for initiating chronic therapy; the dose of prostaglandin E1 was further reduced if side effects recurred.

RESULTS

Twenty-nine (54%) patients in groups A and B and six in group C could be discharged home with chronic therapy via a Hickman catheter connected to a portable pump. After 4 weeks in six patients in group A and in 13 patients in group B, when prostaglandin E1 had been reduced from 15 +/- 2 ng.kg-1.min-1 to 8 +/- 1 ng.kg-1 min-1 increases in cardiac index and decreases in systemic vascular resistance were sustained, and a permanent decrease in pulmonary vascular resistance index was observed in group B. Intravenous therapy was changed in nine patients (3/1/5) because of side effects and worsening heart failure. Prostaglandin E1 was withdrawn in three of these patients because of an increase in serum creatinine (3 mg.100 ml-1), and in one because of noncompliance. In total, there were 17 cardiac deaths (9/6/2), 42 heart transplants (22/14/6) and six (1/2/3) weaned survivors (including one non-cardiac death) in this study. Overall outcome was similar in groups A and B, but distribution after 2 months appeared to be different (P < 0.05) based on more transplantations in group A.

CONCLUSION

We concluded that chronic infusions with prostaglandin E1 at reduced dosages is a feasible and safe therapeutic adjunct to bridge end-stage heart failure patients and may yield desirable effects in a subset of patients in the absence of inotropic support by dobutamine.

Differential effects of ethanol on feline rage and predatory attack behavior: an underlying neural mechanism

Previous studies have shown that, at certain dose levels, ethanol can exert a powerful, facilitatory effect on aggressive behavior in both animals and humans. In the cat, however, it was discovered that ethanol differentially alters two forms of aggression that are common to this species. Defensive rage behavior is significantly enhanced, whereas predatory attack behavior is suppressed by ethanol administration. One possible mechanism governing alcohol's potentiation of defensive rage behavior is that it acts on the descending pathway from the medial hypothalamus to the midbrain periaqueductal gray (PAG)-an essential pathway for the expression of defensive rage behavior that uses excitatory amino acids as a neurotransmitter. This hypothesis is supported by the finding that the excitatory effects of alcohol on defensive rage behavior are blocked by administration of the N-methyl-D-aspartate antagonist alpha-2-amino-7-phosphoheptanoic acid (AP-7) when microinjected into the periaqueductal gray, a primary neuronal target of descending fibers from the medial hypothalamus that mediate the expression of defensive rage behavior. Thus, the present study establishes for the first time a specific component of the neural circuit for defensive rage behavior over which the potentiating effects of ethanol are mediated.

NMDA receptors in the midbrain periaqueductal gray mediate hypothalamically evoked hissing behavior in the cat

The present study was designed to test the hypothesis that the descending pathway from the medial hypothalamus to the dorsal periaqueductal gray (PAG) is critical for the expression of defensive rage behavior in the cat and utilizes excitatory amino acids as a neurotransmitter. In the first phase of the study, monopolar stimulating electrodes were implanted into the medial hypothalamus from which defensive rage behavior could be elicited by electrical stimulation. For the entire study, the hissing response was used as a measure of defensive rage behavior. Cannula electrodes were implanted into the PAG from which defensive rage sites could be identified and were later used for microinfusion of the NMDA receptor antagonist, DL-2-amino-7-phosphoheptanoic acid (AP-7), into behaviorally identified sites within the PAG. Initially, intracerbral microinjections of the NMDA receptor antagonist, AP-7 (0.2, 2.0 nmol), which were placed directly into sites within the PAG from which defensive rage had been elicited, blocked the occurrence of hypothalamic hissing. Microinjections of similar doses of AP-7 into the PAG also blocked the facilitatory effects of medial hypothalamic stimulation upon hissing behavior elicited from the PAG. However, microinjections of 2 nmol into the PAG had no effect upon hissing that was also elicited from the region of the injection site. This finding indicates that AP-7 selectively blocks hissing elicited from the medial hypothalamus and that the suppressive effects of AP-7 cannot be the result of anesthetic or other nonselective properties of the drug. The next phase of the study, which employed immunohistochemical, receptor autoradiographic techniques, identified NMDA receptors to be present in highest concentrations in the dorsolateral aspect of the PAG where defensive rage is typically elicited. The final phase of the study, which employed a combination of retrograde labeling procedures following microinjections of Fluoro-Gold into defensive rage sites in the dorsal PAG and the immunocytochemical labeling of glutamatergic neurons, identified large numbers of neurons in the medial hypothalamus that were labeled positively for both Fluoro-Gold and glutamate. The overall findings of this study support the hypothesis that descending fibers of the medial hypothalamus that supply the dorsal aspect of the PAG mediate defensive rage behavior and utilize excitatory amino acids that act upon NMDA receptors within the dorsal PAG.

Activities of enzymes in platelet activating factor biosynthetic pathways in the gerbil model of cerebral ischemia

The activities of enzymes in platelet activating factor (PAF) biosynthetic pathways were analyzed in hippocampal and cerebral cortical regions of normal and ischemic gerbil brain to assess changes in enzyme activities and potential modulators that could explain the accentuated production of PAF seen in ischemia. Global forebrain ischemia was produced by bilateral carotid artery ligation, and the effectiveness of the ligation was shown by free fatty acid release and ATP depletion. Specific activities of 1-alkyl-2-acetyl-sn-glycerol (AAG) choline phosphotransferase, 1-alkyl-sn-glycero-3-phosphate (AGP) acetyl transferase, and 1-alkyl-sn-glycero-3-phosphocholine (lyso PAF) acetyl transferase in tissue homogenates were in the ratio 4:1:0.1, respectively. Sham-operated and ischemic or ischemic-reperfused tissues showed similar activities for individual enzymes, indicating that enzyme levels or activation states did not change in ischemic or reperfused tissues. However, small metabolites (relevant to ischemia) added to the in vitro assays did modify enzyme activities. Physiological concentrations of MgATP severely inhibited AGP acetyl transferase activity, and this resulted in the ratio of AGP acyl transferase to AGP acetyl transferase activities changing from 48:1 in the presence of 2.5 mM MgATP to 6:1 in the absence of MgATP. This suggests that falling ATP levels in cerebral ischemia may promote the de novo pathway of PAF biosynthesis by releasing inhibition of AGP acetyl transferase. Lyso PAF acetyl transferase was much less active than AGP acetyl transferase and was also inhibited by MgATP. AAG choline phosphotransferase was not inhibited by MgATP but was inhibited by calcium. However the superior specific activity of the choline phosphotransferase in comparison with the AGP acetyl transferase suggested that the lowered choline phosphotransferase activity in the presence of rising intracellular calcium would not seriously compromise the synthesis of PAF by the de novo route. Both acetyl transferase enzymes were also inhibited by oleoyl CoA.

Medial amygdaloid suppression of predatory attack behavior in the cat: I Role of a substance P pathway from the medial amygdala to the medial hypothalamus

The medial amygdala is known to powerfully suppress predatory attack behavior in the cat, but the mechanisms underlying such modulation remain unknown. The present study tested the hypothesis that medial amygdaloid suppression of predatory attack is mediated, in part, by a pathway from the medial amygdala to the medial hypothalamus which utilizes substance P as a neurotransmitter. Stimulating electrodes were implanted into the medial amygdala and cannula electrodes were implanted into both the medial and lateral hypothalamus. Predatory attack behavior was elicited by electrical stimulation of the lateral hypothalamus. In the first phase of the study, paired trials compared attack latencies of single stimulation of the lateral hypothalamus with those following dual stimulation of the lateral hypothalamus and medial amygdala. Attack latencies were significantly elevated following dual stimulation of the medial amygdala and lateral hypothalamus. In the second phase of the study, dose and time dependent decreases in response suppression were noted following the infusion of the substance P (NK1) receptor antagonist, CP96.345 (in doses of 0.05, 0.5 and 2.5 nmol) into the medial hypothalamus. In third phase of the study, the effects of microinjections of the substance P receptor agonist, [Sar9.Met(O2)11]-substance P (in doses of 0.5, 1.0 and 2.0 nmol), directly into the medial hypothalamus upon lateral hypothalamically elicited predatory attack behavior were determined. Microinfusion of this drug elevated attack response latencies in a dose- and time-dependent manner. In addition, pretreatment with CP96,345 into the medial hypothalamus blocked the suppressive effects of subsequent delivery of [Sar9,Met(O2)11]-substance P into the same medial hypothalamic site. Other parts of the study demonstrated the presence of: (1) high densities of substance P receptors in the ventromedial hypothalamus, and (2) neurons that are positively labeled for substance P that project from the medial amygdala to the ventromedial hypothalamus as demonstrated by retrograde labeling with Fluoro-Gold. These findings provide support for the hypothesis that medial amygdaloid suppression of lateral hypothalamically elicited predatory attack behavior includes a substance P pathway from the medial amygdala to the medial hypothalamus. The findings further suggest that stimulation of the medial amygdala activates substance P receptors in the medial hypothalamus, thus triggering an inhibitory mechanism from the medial to the lateral hypothalamus, resulting in suppression of predatory attack behavior.

Medial amygdaloid suppression of predatory attack behavior in the cat: II. Role of a GABAergic pathway from the medial to the lateral hypothalamus

The medial amygdala is known to powerfully suppress predatory attack behavior elicited by electrical stimulation of the lateral hypothalamus of the cat. In the preceding paper, it was shown that the initial limb of a pathway subserving suppression of predatory attack from the medial amygdala to the lateral hypothalamus projects to the ventromedial hypothalamus and its functions are mediated by substance P. The present study tested the hypothesis that the second limb of the pathway subserving medial amygdaloid suppression of predatory attack behavior projects from the medial to lateral hypothalamus and its functions are mediated by GABA. Cannula electrodes were implanted into the lateral hypothalamus for elicitation of predatory attack behavior as well as for the microinfusion of GABA compounds. Monopolar stimulating electrodes were implanted into sites within the medial amygdala from which subseizure levels of stimulation could suppress predatory attack behavior. Initially, the effects of dual stimulation of the medial amygdala and lateral hypothalamus upon response latencies for predatory attack were compared with single stimulation of the lateral hypothalamus alone. Dual stimulation was shown to significantly suppress predatory attack elicited from the lateral hypothalamus. Then, the GABAA receptor antagonist, bicuculline, was microinjected into sites within the lateral hypothalamus from which predatory attack was elicited in doses of 0.015, 0.075 and 0.15 nmol and paired trials of single and dual stimulation were again repeated in a manner identical to that applied prior to drug administration. Drug infusion produced a blockade of medial amygdaloid suppression of predatory attack in a time- and dose-dependent manner. Conversely, microinfusions of the GABAA receptor agonist, muscimol (10, 25 and 50 pmol), into the same lateral hypothalamic 'attack' site in the absence of medial amygdaloid stimulation suppressed predatory attack, thus simulating the effects of medial amygdaloid stimulation. Furthermore, pretreatment with bicuculline microinjected into the lateral hypothalamus blocked the suppressive effects of substance P, that was infused into the ventromedial hypothalamus, upon predatory attack. Receptor autoradiography demonstrated the presence of high affinity binding for GABAA receptors in the lateral hypothalamus. A combination of immunocytochemical and retrograde axonal tract tracing procedures, in which Fluoro-Gold was microinjected into the lateral hypothalamic attack sites, revealed the presence of populations of neurons labeled for both Fluoro-Gold and GABA in the ventromedial hypothalamus. These findings provide new evidence for the existence of a pathway from the medial to lateral hypothalamus whose functions are mediated by GABA. Thus, the overall findings provide support for the view that the pathway from the medial amygdala to the lateral hypothalamus underlying suppression of predatory attack behavior involves a two-neuronal arc: the first neuron projects from the medial amygdala to the medial hypothalamus and its functions are mediated by substance P: the second neuron involves a GABAergic pathway originating in the ventromedial hypothalamus and which projects to the lateral hypothalamus.

Clinical efficacy of SPECT bone imaging for low back pain

METHODS

We conducted a comprehensive structured review of the literature, analyzing 940 citations from 1966 through September 1993 and completed a narrative review. We also attempted quantitative synthesis of the accuracy of SPECT evaluation of low back pain.

RESULTS

We found thirteen reports on accuracy. Only three provided a reasonable gold standard reference test and allowed the calculation of sensitivity and specificity. There is weak evidence that SPECT is useful in: (a) detecting pseudarthroses after failed spinal fusion, (b) evaluating young patients with back pain and (c) distinguishing benign from malignant lesions in cancer patients. SPECT has not been sufficiently studied in any other setting. We found no reports on the clinical outcome of SPECT or its cost-effectiveness.

CONCLUSION

The decision to use SPECT in most patients with low back pain cannot be supported by clinical trials. Its effect on clinical management and cost-effectiveness are unknown. The medical community should mount a large-scale, prospective evaluation of SPECT in low back pain.

[The "Freiburg Spinal Study"--epidemiology of occupationally-induced spinal diseases of health care employees in Germany]

Musculoskeletal diseases are very common in modern societies. As several international investigations have shown that the etiology of these diseases is correlated with working conditions in some professions. With financial subsidy by the German insurance company for the regulation and compensation of occupational diseases in the health care sector (BGW), we investigated in 6 different projects the possible relation of working conditions and musculoskeletal diseases among health care professionals, esp. nurses. Our contribution describes the design of the different sub-projects and presents some results. The summarising discussion points out that there was a strong tendency in all sub-projects to confirm the hypothesis that nurses run a significantly higher risk to suffer from work-related musculoskeletal diseases and disorders. The results of the sub-project "cohort study in nursing pupils" support this hypothesis. The results do not only supply important background information for the process of compensating occupational diseases in this field but also indicate a tremendous personal and structural need for more and better prevention.

[Total hip endoprosthesis following resection arthroplasty]

From 1976 to December 1994, a total of 347 patients underwent implantation of a hip prosthesis at the ENDO-Klinik for treatment of an unsatisfactory condition following resection arthroplasty. From 1976 to 1987, 143 patients were treated and in 1989 the results obtained in these patients were analysed: 99 of them were available for a follow-up examination in 1989, and 64 for a further examination in 1995. In 130 cases infection had been the reason for joint resection. At the time of the prosthesis operation (1-20 years later) intraoperative biopsy revealed that infection was still present in 41 cases (31.5%). Only 15 of these infections had been detected preoperatively by joint aspiration. This shows that the value of resection arthroplasty as a method of treating periprosthetic infection is limited and lends support to the one-stage exchange operation, which is the method we prefer in cases of infected hip prostheses. The operative technique and preparation for implantation of the prosthesis are described, as are septic and aseptic complications and the measures that can be taken to treat them. In spite of the patients' generally poor initial condition and with due consideration for the further revision operations, the medium-term results finally obtained are poor in only 9%.

[Epidemiology of spinal diseases in nurses]

Epidemiology of spinal pathology among nurses. A cross-sectional study of 3300 German nurses was carried out in the course of an investigation of the prevention of occupation--related back problems. A much higher incidence of lumbar-spinal problems was observed than in a control group of office staff, not required to lift or carry. Evidence of much greater risk, especially of severe sciatic symptoms, was supported by a case-controlled study of patients with the diagnosis of disc-prolapse or disc-protrusion, carried out in two neuroradiology units. Nurses were significantly over represented. A lack of preventive measures for carrying and lifting patients was clearly demonstrated (availability and use of mechanical aids). To what extent the perception of spinal problems is influenced by psychological factors and not only by physical factors will be demonstrated by the recording of stress factors.

Distribution of Bergmann glial somata and processes: implications for function

We have used immunocytochemistry for glial fibrillary adidic protein and glutamine synthetase to selectively label Bergmann glia in the adult rat cerebellum. From measurements of radial, tangential and en face sections we provide new data on the distribution and disposition of these glial cells. Specifically, Bergmann glia were found to have a mean areal packing density of 8,269 somata/mm2, their radial processes are packed at a mean density of 39,000/mm2, and their endfeet at the pial surface have a mean density of 19,973/mm2. Each Bergmann glial cell ist "responsible" for the equivalent of a column of cerebellar cortex having a base of 11 microns x 11 microns, a height of 170 microns, and a volume of 20,559 microns3. There are 8.1 Bergmann glia for each Purkinje cell, and each glial cell ensheaths between 2,142 and 6,358 Purkinje cell synapses. We use these data to offer insights on the roles of Bergmann glia during development and in the adult brain.

Neurotransmitters regulating feline aggressive behavior

The experiments described in this review reveal that the expression and modulation of aggressive responses in the cat are organized by two distinct sets of pathways. One set of pathways is associated with the elicitation of a specific form of attack behavior. It includes the medial hypothalamus and its projections to the PAG for the expression of defensive rage behavior and the lateral hypothalamus and its descending projections for the expression of predatory attack behavior. The primary focus of the present review is upon the analysis of defensive rage behavior. It was demonstrated that the pathway from the medial hypothalamus to the PAG, which appears to be essential for elicitation of defensive rage, is powerfully excitatory and utilizes excitatory amino acids that act upon NMDA receptors within the PAG. The other pathways examined in this review arise from different nuclei of the amygdala and are modulatory in nature. Here, two facilitatory systems have been identified. The first involves a projection system from the basal complex of amygdala that projects directly to the PAG. Its excitatory effects are manifest through excitatory amino acids that act upon NMDA receptors within the PAG. The second facilitatory pathway arises from the medial nucleus of the amygdala. However, its projection system is directed to the medial hypothalamus rather than the PAG. Its neurotransmitter appears to be substance P that acts upon NK1 receptors within the medial hypothalamus (see Figure 10). It has yet to be determined whether substance P acts upon any of the other neurokinin receptor subtypes. It should also be pointed out that the substance P pathway from the medial amygdala to the medial hypothalamus functions to suppress predatory attack behavior elicited from the lateral hypothalamus. In this network, it is likely that the modulatory effects of the medial amygdala require the presence of a second, inhibitory pathway from the medial hypothalamus that innervates the lateral hypothalamus. At the present time, the neurochemical nature of this second pathway remains unknown, although it is suggested that such neurons may be GABAergic. One major inhibitory pathway was also identified. It arises principally from the central nucleus of the amygdala and projects to the PAG. Its powerful suppressive effects upon PAG elicited defensive rage behavior are mediated through opioid peptides that act upon mu receptors within the PAG. While the present series of studies have begun to define the structural and functional nature of the neural systems that regulate aggressive behavior, our understanding of the overall mechanisms regulating different forms of aggressive behavior remains incomplete.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuroanatomical and neurochemical mechanisms underlying amygdaloid control of defensive rage behavior in the cat

1. It is well established that the hypothalamus and midbrain periaqueductal gray (PAG) play important roles in the expression of defensive rage behavior. While defensive rage is not elicited from the amygdala, this region of the limbic system nevertheless serves an important role in the modulation of defensive rage behavior. The present paper attempts to address the question of how the amygdala modulates defensive rage behavior in the cat. The studies were conducted using brain stimulation, pharmacological, neuroanatomical and immunocytochemical methods to identify the likely neural pathways and their associated neurotransmitters by which different regions of the amygdala modulate defensive rage behavior in the cat. 2. The experimental evidence provided thus far establishes that three regions of the amygdala have been identified as powerful modulators of defensive rage behavior. These include the medial nucleus, basal complex and central nucleus of the amygdala. Experiments involving dual stimulation of an amygdaloid nucleus and sites within the medial hypothalamus or PAG from which defensive rage behavior was elicited demonstrated that two of the regions facilitated defensive rage --the medial nucleus and basal complex--and a third region--the central nucleus--suppressed defensive rage. The mechanisms and substrates underlying modulation for each of these regions are different. Medial amygdaloid facilitation of defensive rage involves a pathway (i.e., the stria terminalis) that projects directly to the medial hypothalamus and utilizes substance P as a neurotransmitter. Basal amygdaloid facilitation of defensive rage behavior makes use of a pathway to the PAG in which excitatory amino acids acting on NMDA receptors are utilized as a neurotransmitter. The central nucleus also projects to the PAG. However, it is strongly inhibitory and utilizes enkephalins that act upon mu receptors within the PAG.

Electrical stimulation of the dorsal midbrain periaqueductal gray suppresses peripheral blood natural killer cell activity

This study examined the effects of dorsal midbrain periaqueductal gray (PAG) stimulation on both splenic and peripheral blood natural killer (NK) cell function as well as the proliferative response of lymphocytes to phytohemagglutinin mitogen. Male Sprague-Dawley rats were implanted with bipolar electrodes in the dorsal PAG. Following recovery, bipolar electrical stimulation eliciting a flight response was delivered at the rate of one/min for 30 min to freely moving rats. While dorsal PAG stimulation did not alter mitogen response or splenic NK activity, stimulation of this region of the PAG produced a marked decrease in peripheral blood NK response. In order to begin to explore a possible mechanism regulating suppression of peripheral blood NK activity, naltrexone (10 mg/kg) was administered prior to dorsal PAG stimulation. The results of this experiment replicated the findings that demonstrated suppression of peripheral blood NK following dorsal PAG stimulation. Naltrexone did not effect PAG induced suppression of peripheral blood NK. These findings point to the importance of the dorsal aspect of the PAG in the regulation of peripheral blood NK activity and further suggest that this phenomenon may not be opioid mediated.

Basal amygdaloid facilitation of midbrain periaqueductal gray elicited defensive rage behavior in the cat is mediated through NMDA receptors

The present study tested the hypotheses that: (1) defensive rage behavior elicited from the midbrain periaqueductal gray (PAG) in the cat is facilitated from the basal complex of amygdala; and (2) such facilitation from this region of amygdala is mediated via a pathway in which excitatory amino acids acting upon NMDA receptors within the PAG are utilized as a neurotransmitter. In the first phase of this study, cannula electrodes were implanted into PAG sites for the elicitation of defensive rage behavior as well as for drug delivery. Then, a second monopolar electrode was implanted into the basal nucleus of amygdala from which facilitation of defensive rage could be obtained. As a result of dual stimulation of the basal amygdala and PAG, response latencies for defensive rage were significantly lowered relative to PAG stimulation alone (P < 0.01). In the second phase of this experiment, 3 doses of a selective NMDA receptor antagonist, AP-7 (0.1, 0.5, 1.0 mg/kg), were peripherally (i.p.) administered in 5 animals. The results indicated a significant decrease in the facilitatory effects of amygdaloid stimulation in a dose and time dependent manner (P < 0.001). In the third phase, AP-7 was administered intracerebrally into PAG defensive rage sites in doses of 0.2 and 2.0 nmol. It was noted that intracerebral microinjections of AP-7 at the higher dose (2.0 nmol) also significantly suppressed the facilitatory effects of amygdaloid stimulation (P < 0.01); however, these effects were somewhat less potent then those observed following peripheral drug administration. A fourth phase of the study was conducted at the completion of the pharmacological experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

The transcription of a mammalian voltage-gated potassium channel is regulated by cAMP in a cell-specific manner

The transcript of Kv1.5, a Shaker-like delayed rectifier K+ channel cloned in our laboratory, is regulated in both tissue and developmentally specific manners. In this study we characterized the 5'-flanking region of the Kv1.5 gene. The gene lacks a canonical TATA box, has several transcription start sites, and the 5'-noncoding sequence is intronless. A cAMP response element (CRE) consensus signal was identified in the 5'-noncoding region. cAMP regulates the expression of Kv1.5 gene in a cell-specific manner. In primary cardiac cells, cAMP induces a 6-fold increase in the steady state levels of Kv1.5 transcript. However, in GH3 cells cAMP induces a 5-6-fold decrease in steady state levels of Kv1.5 transcript. The half-life of Kv1.5 transcript is 37 min and is not affected by cAMP. Nuclear run-on experiments show that in GH3 cells, cAMP reduces the transcription rate of Kv1.5 gene. Transient transfection assays using 5'-deletion mutations of Kv1.5 5'-flanking sequences revealed that the CRE located at +636 can confer the cAMP inducibility to Kv1.5 reporter gene constructs and binds to CRE-binding protein (CREB) and CRE modulator protein (CREM) in electromobility gel shift assays. Furthermore, KCl-induced depolarization can increase the steady state levels of Kv1.5 transcript in primary atrial cells and decrease it in GH3 cells. We conclude that cAMP and depolarization play an important role in regulating K+ channel expression and thus may induce long term effects on the pattern of electrical activity of excitable cells.