An overview of the safety pharmacology society strategic plan.

Safety Pharmacology studies are conducted to characterize the confidence by which biologically active new chemical entities (NCE) may be anticipated as safe. Non-clinical safety pharmacology studies aim to detect and characterize potentially undesirable pharmacodynamic activities using an array of in silico, in vitro and in vivo animal models. While a broad spectrum of methodological innovation and advancement of the science occurs within the Safety Pharmacology Society, the society also focuses on partnerships with health authorities and technology providers and facilitates interaction with organizations of common interest such as pharmacology, physiology, neuroscience, cardiology and toxicology. Education remains a primary emphasis for the society through content derived from regional and annual meetings, webinars and publication of its works it seeks to inform the general scientific and regulatory community. In considering the future of safety pharmacology the society has developed a strategy to successfully navigate forward and not be mired in stagnation of the discipline. Strategy can be defined in numerous ways but generally involves establishing and setting goals, determining what actions are needed to achieve those goals, and mobilizing resources within the society to accomplish the actions. The discipline remains in rapid evolution and its coverage is certain to expand to provide better guidance for more systems in the next few years. This overview from the Safety Pharmacology Society will outline the strategic plan from 2016 to 2018 and beyond and provide insight into the future of the discipline which builds upon a previous strategic plan established in 2009.

Magnetic resonance imaging assessment of the ventricular system in the brains of adult and juvenile beagle dogs treated with posaconazole IV Solution.

INTRODUCTION: Noxafil® (posaconazole; POS) is a potent, selective triazole antifungal approved for use in adults as an oral suspension, oral tablet and intravenous (IV) Solution. In support of pediatric administration of POS IV Solution to childrentwo years of age, two studies were undertaken using magnetic resonance imaging (MRI) to monitor brain ventricle size longitudinally during three months administration of POS IV in adult and juvenile dogs. Necropsy was performed on all animals at the end of the studies. From the baseline MRI images, great variability in ventricle size was noted in both the adult and juvenile dogs; these images were used to distribute differently sized ventricles between treatment and vehicle groups as to not skew group means during the course of the study. RESULTS: POS IV Solution had no effect on ventricle volume at any timepoint during dosing in either the adult or the juvenile dogs. Further, no gross or histomorphologic differences between groups were observed in either study. Compared to juvenile dogs, MRI analysis showed that adult dogs had larger ventricles, lower variability in all ventricle volumes, and a greater rate of increase in total ventricle volume. DISCUSSION: Information on growth and development of brains is one of the few areas in which more detailed information is available about humans than about the standard laboratory animals used to model disease and predict toxicities. The use of MRI helped elucidate large natural variabilities in the dog brain, which could have altered the interpretation of this de-risking study, and provided a valuable noninvasive means to monitor the brain ventricles longitudinally.

Injury severity and sensitivity to treatment after controlled cortical impact in rats.

We sought to determine sensitivity of the cortical impact injury model of traumatic brain injury (TBI) to severity of injury and to treatment. We examined the pattern of motor and cognitive deficits and recovery following TBI over a range of injury severities, and examined the efficacy of surface-induced moderate hypothermia at three disparate injury levels. In experiment I, Sprague-Dawley rats were injured at one of eight injury severity levels from 0 mm (sham) to 2.5 mm depth of penetration. On postinjury day 1, balance beam, rotorod performance, and posture reflexes were evaluated. Motor outcome was increasingly impaired with increasing injury levels, with the pattern of deficits showing a step-like function. Cognitive deficits, assessed using water maze on day 7, were more severe for the 2.5-mm group than for the 1.6-mm injury group, while the 1.0-mm group did not differ from the sham controls. In experiments II-IV, hypothermia, 30 degrees C for 3-h duration or normothermia was applied to three injury levels: 1.0 mm, the least cortical deformation; 2.5 mm, the most deformation; and 1.6 mm, representing a level in-between. Neurologic outcome was assessed relative to shams on postinjury days 1, 3, and 5. The 1.0-mm group exhibited small deficits that recovered completely by day 3; the 1.6-mm group recovered to the level of shams by day 5, and the 2.5-mm group did not show significant recovery during the testing period. Hypothermia effectively attenuated behavioral deficits for the 1.6-mm group, but had no effect on the other two groups. These three observations--that increasing injury severity is associated with increasing motor and cognitive deficits, that injury severity is related to recovery time, and that hypothermia treatment is selectively effective--have each been reported in the human TBI population; thus, moderate cortical impact injury in rats may be a model with clinical predictability for evaluating neuroprotective therapies.

Treatment window for hypothermia in brain injury.

OBJECT: The goal of this study was to evaluate the therapeutic window for hypothermia treatment following experimental brain injury by measuring edema formation and functional outcome. METHODS: Traumatic brain injury (TBI) was produced in anesthetized rats by using cortical impact injury. Edema was measured in the ipsilateral and contralateral hemispheres by subtracting dry weight from wet weight, and neurological function was assessed using a battery of behavioral tests 24 hours after TBI. In injured rats, it was found that brain water levels were elevated at I hour postinjury, compared with those in sham-injured control animals, and that edema peaked at 24 hours and remained elevated for 4 days. Hypothermia (3 hours at 30 degrees C) induced either immediately after TBI or 60 minutes after TBI significantly reduced early neurological deficits. Delay of treatment by 90 or 120 minutes postinjury did not result in this neurological protection. Immediate administration of hypothermia also significantly decreased the peak magnitude of edema at 24 hours and 48 hours postinjury, compared with that in normothermic injured control animals. When delayed by 90 minutes, hypothermia did not affect the pattern of edema formation. CONCLUSIONS: When hypothermia was administered immediately or 60 minutes after TBI, injured rats showed an improvement in functional outcome and a decrease in edema. Delayed hypothermia treatment had no effect on functional outcome or on edema.

MDL 101,002, a free radical spin trap, is efficacious in permanent and transient focal ischemia models.

The present work describes the neuroprotective effects of the free radical spin trap, MDL 101,002, in models of permanent and transient focal ischemia. Permanent focal ischemia was carried out by occlusion of the distal segment of the middle cerebral artery (MCA) and CCA's in Spontaneously Hypertensive (SH) and Wistar rats. Transient focal ischemia was undertaken by occluding the origin of the MCA for 180 min by the intraluminar monofilament method in Wistar rats. With permanent distal MCA occlusion in SH rats, 100 mg/kg i.v. at 30 min post-ischemia resulted in a significant 40% reduction in infarct volume. Similarly, a 75 mg/kg bolus + 45 mg/kg-h dose of MDL 101,002 given i.v. at 5 min post-ischemia resulted in a 90% or 60% decrease in infarct volume in the mixed permanent/transient distal MCA model with Wistar rats using 120 or 180 min of CCA occlusion, respectively. When full reperfusion was established, after 180 min of occlusion in the proximal MCA model, a dose of 40 mg/kg + infusion and 75 mg/kg + infusion resulted in a significant 50% and 70% decrease in ischemic damage, respectively. MDL 101,002 is clearly an effective neuroprotective agent in all models examined. This work would suggest that this novel cyclic nitrone spin trap affords effective neuroprotection and is useful for the treatment of ischemic stroke.

Protective effects of moderate hypothermia on behavioral deficits but not necrotic cavitation following cortical impact injury in the rat.

A number of experimental studies have reported that moderate hypothermia can produce significant protection against behavioral deficits and/or morphopathological alterations following traumatic brain injury; a Phase 3 clinical trial is currently examining the therapeutic potential for moderate hypothermia (32 degrees C) to improve outcome following severe traumatic brain injury in humans. The current study examined whether hypothermia (32 degrees C) provided behavioral protection following experimental cortical impact injury. The extent of focal cortical contusion was also examined in the same rats. A total of 30 male Sprague-Dawley rats were trained on beam balance and beam walking tasks prior to injury. Under isoflurane anesthesia, cortical impact was produced on the right parietal cortex of 20 rats. Ten rats underwent all surgical procedures but were not impacted (sham-injured rats). Ten of the injured rats were cooled to 32 degrees C (measured in temporalis muscle) beginning 5 min postinjury, maintained for 2 h and rewarmed slowly for 1 h. In the other 10 injured rats, normothermic temperatures (37.5 degrees C) were maintained for the same duration. Beam balance and beam walking performance was assessed daily for 5 days following injury. At 11 days postinjury, rats were assessed for 5 days on acquisition of the Morris water maze task. Following behavioral assessments, rats were perfused and the brain removed. Coronal sections were cut through the site of cortical impact injury and stained with hematoxylin and eosin. Hypothermic treatment resulted in significantly less beam balance and beam walking deficits than observed in normothermic rats. Hypothermia also significantly attenuated spatial memory performance deficits. Quantitative morphometric analyses failed to detect any significant differences in volumes of necrotic tissue cavitation in cortices of hypothermic and normothermic rats. Hypothermic treatment also had no effect on volumes of dorsal hippocampal tissue or numbers of cells in CA1 or CA3 regions of the hippocampus. These data suggest that hypothermia, consistent with the reports of others, can produce significant behavioral protection following cortical impact injury that is not necessarily correlated with changes in focal cortical necrosis within the first 15 days following injury.

Six-hour window of opportunity for calpain inhibition in focal cerebral ischemia in rats.

BACKGROUND AND PURPOSE: Stroke patients often experience a significant temporal delay between the onset of ischemia and the time to initiation of therapy. Thus, there is a need for neuroprotectants with a long therapeutic window of opportunity. The efficacy of a potent, central nervous system-penetrating calpain inhibitor (MDL 28,170) was evaluated in a temporary model of focal cerebral ischemia to determine the window of opportunity for intracellular protease inhibition. METHODS: An ex vivo brain protease inhibition assay established pharmacodynamic dosing parameters for MDL 28,170. Middle cerebral artery (MCA) occlusion was accomplished by advancing a monofilament through the internal carotid artery to the origin of the MCA. Postmortem infarct volumes were determined by quantitative image analysis of triphenyltetrazolium-stained brain sections. RESULTS: Maximal inhibition of brain protease activity was observed 30 minutes after injection of MDL 28,170 with an estimated pharmacodynamic half-life of 2 hours. MDL 28,170 caused a dose-dependent reduction in infarct volume when administered 30 minutes after MCA occlusion. A window of opportunity study was conducted to determine the maximal delay between the onset of ischemia and the initiation of efficacious therapy. MDL 28,170 reduced infarct volume when therapy was delayed for 0.5, 3, 4, and 6 hours after the initiation of ischemia. The protective effect of MDL 28,170 was lost after an 8-hour delay. CONCLUSIONS: These data indicate that the therapeutic window of opportunity for calpain inhibition is at least 6 hours in a reversible focal cerebral ischemia model. This protection is observed despite the lethal hypoxic and excitotoxic challenge, suggesting that calpain activation may be an obligatory, downstream event in the ischemic cell death cascade.

Behavioral recovery patterns in rats receiving the NMDA receptor antagonist MDL 100,453 immediately post-stroke.

Rats were given MDL 100,453 ((R)-4-Oxo-5-phosphononorvaline) in a pre-determined neuroprotective dose consisting of a bolus of 24.8 mg/kg followed by an infusion of 1.05 mg/kg*h for 24 h (MDL group; n = 8) or saline of the same volume (SALINE group; n = 8) 30 min. after the onset of a 90 min. period of middle cerebral artery occlusion. Eight animals underwent SHAM surgery. Rats were evaluated post-operatively for 14 days using seven neurological tests, including water maze. SALINE animals exhibited a pattern of neurological impairment compared to SHAMs (poor performance in five of the six motor/reflex tests) peaking five days post-injury. Relative to the SALINE group, the MDL group exhibited significantly improved outcome on two of the tests and a pattern of improved behavior on the remainder of the battery. By day 14 post-ischemia, all groups exhibited recovery on the motor/reflex tests. Learning ability was disrupted in the SALINE group on days 17 and 18, whereas the MDL group's performance was not distinguishable from the SHAM group in the water maze. Thus, a neuroprotective dose of MDL 100,453 produced a pattern of behavioral sparing in the immediate post-ischemic days that was uniquely different than saline. The addition of behavioral outcome measures to histological neuroprotection data adds significantly to the ability to better evaluate a putative neuroprotective compound.

Glutamate antagonist MK-801 attenuates incomplete but not complete infarction in thrombotic distal middle cerebral artery occlusion in Wistar rats.

The purpose of this study was to investigate the effects of a non-competitive N-methyl-D-aspartate antagonist, MK-801, on incomplete infarction (selective neuronal necrosis), a zone of which had been found previously in a thrombotic distal middle cerebral artery (MCA) occlusion model in Wistar rats. Male Wistar rats were treated with 1 mg/kg of MK-801 or saline 30 min before MCA occlusion. Laser irradiation with intravenous administration of Rose Bengal dye was used to cause thrombotic distal MCA occlusion. The ipsilateral common carotid artery was occluded permanently and the contralateral carotid artery for 60 min. Head temperature was controlled at 36 degrees C. Cerebral blood flow (CBF) was determined with laser-Doppler flowmetry. Three days after the ischemic insult, brains were perfusion-fixed and volumes of cortical (complete and incomplete) infarction were determined. There were no significant differences in physiological variables or CBF between the two groups. Volumes of complete infarction were equivalent between the two groups (94.9 +/- 15.6 mm3 and 91.6 +/- 14.0 mm3 in the control and MK-801 treated groups, respectively). In MK-801 treated group, the volume of incomplete infarction was reduced by 44% (6.4 +/- 1.7 mm3 vs. 3.6 +/- 2.1 mm3 in control and MK-801 treated groups, respectively, P < 0.05). Although the zone responsive to MK-801 was small in this thrombotic MCA occlusion model, our present study revealed that MK-801 has a beneficial effect on the tissue zone containing selective neuronal alterations (incomplete infarction). Our results support the concept that this drug is effective in the area of less severe ischemia.

Recovery of sensorimotor function after distal middle cerebral artery photothrombotic occlusion in rats.

BACKGROUND AND PURPOSE: The purpose of the present study was to delineate the behavioral correlates of focal thrombotic occlusion of the distal middle cerebral artery in rats and to compare the pattern of deficits and subsequent recovery to that following proximal middle cerebral artery occlusion. METHODS: Ten Sprague-Dawley rats underwent photothrombotic occlusion of the distal middle cerebral artery with tandem occlusion of the common carotid arteries (dMCAO group); 10 animals served as operated controls. Beginning on postischemia day 2, animals were given a battery of five tests that assessed sensorimotor integration, attentional mechanisms, and muscle strength; testing continued twice weekly until day 30. Nine days of cognitive testing on the learning set of the water maze task were then given. Infarct volume and hemispheric atrophy were determined for each dMCAO animal. RESULTS: After ischemia, the dMCAO group exhibited significant behavioral deficits in posture reflex, ability to place a forelimb to various stimuli, limb adduction during rearing, and neglect of contralateral space. These deficits showed variable recovery rates. No deficits were observed in muscle strength or cognitive performance. The deficits and patterns of recovery were related to infarct location and to degree of hemisphere atrophy. CONCLUSIONS: The present study suggests that a battery of tests is necessary to fully characterize the pattern of behavioral deficits after focal cerebral ischemia. Location of infarct damage and associated degree of hemispheric atrophy were important variables in determining behavioral outcome. The present results are compared with those of the more traditional model of electrocoagulation of the proximal middle cerebral artery.

Comparative histopathologic consequences of photothrombotic occlusion of the distal middle cerebral artery in Sprague-Dawley and Wistar rats.

BACKGROUND AND PURPOSE: We have developed a minimally invasive model of photothrombotic occlusion of the distal middle cerebral artery in rats and have evaluated the patterns and features of the resulting histopathologic injury in two normotensive strains. METHODS: Food-deprived male Sprague-Dawley (n = 14) and Wistar (n = 10) rats anesthetized with halothane/nitrous oxide underwent a small craniotomy to expose the right distal middle cerebral artery just above the rhinal fissure. The animals were injected intravenously with the photosensitizing dye rose bengal, and the distal middle cerebral artery was irradiated with light from an argon laser-activated dye laser at three separate points to induce thrombotic occlusion. The ipsilateral common carotid artery was then permanently occluded, and the contralateral common carotid artery was occluded for 60 minutes. Three days later, the brains were perfusion-fixed and prepared for histopathologic examination, and infarct volume was determined by quantitative planimetry. RESULTS: In Sprague-Dawley rats, a large consistent temporoparietal cortical infarct was observed; mean +/- SD infarct volume was 130.5 +/- 40.0 mm3 (coefficient of variation, 30.7%) and a relatively small adjacent zone of selective neuronal necrosis ("incomplete infarction"), amounting to only 9.1% of the total injury volume, was also seen. By contrast, Wistar rats had smaller and more variable cortical infarcts (volume, 48.4 +/- 26.9 mm3; coefficient of variation, 55.6%) but displayed a much more substantial zone of incomplete cortical infarction (volume, 20.8 +/- 10.1 mm3; 30.1% of the total injury volume). In neither strain was infarct size related to alterations of blood pressure. In both strains, infarcts were limited to the cortex, typically involving the parietal cortex, somatosensory cortex, and forelimb region. Three rats exhibited infarcts in the contralateral hemisphere. CONCLUSIONS: This model has the advantages of necessitating only minimal surgery, allowing the dura to remain intact, and avoiding mechanical trauma to the brain surface. In Sprague-Dawley rats, the resulting large cortical infarct exhibited relatively small interanimal variation, making the model suitable, for example, for replicate studies of pharmacotherapy. In Wistar rats, the large zone of incomplete infarction, a unique feature heretofore undescribed in rodent models of permanent focal ischemia, lends the model to the study of the pathomechanisms underlying graded cortical ischemic injury.

Ibotenic acid lesions in the amygdaloid central nucleus but not in the lateral subthalamic area prevent the acquisition of differential Pavlovian conditioning of bradycardia in rabbits.

The present study examined the effect of ibotenic acid lesions in the amygdaloid central nucleus (ACe) or in the lateral zona incerta of the subthalamus (LZI) on the acquisition of differential Pavlovian conditioning of bradycardia in rabbits. Previous work has shown that bilateral electrolytic lesions in either ACe or LZI abolished the retention of conditioned heart rate (HR) responses. In order to determine whether these findings were due to destruction of cells intrinsic to ACe or LZI, ibotenic acid lesions were placed bilaterally in either structure or in control sites. Following recovery, animals were subjected to differential Pavlovian conditioning in which one tone (CS+) was paired with periorbital shock and a second tone (CS-) was presented alone. It was found that destruction of cell bodies in ACe, but not LZI, prevented the acquisition of the differential bradycardiac conditioned response. In addition, ACe lesions did not interfere with baseline HR, the HR orienting response, the HR unconditioned response to shock, or the concomitantly conditioned corneoretinal potential. The results of this study suggest that destruction of cells intrinsic to ACe selectively prevents the acquisition of differentially conditioned HR, and perhaps other conditioned responses related to conditioned arousal, but does not affect unlearned HR responses or specific somatomotor conditioned responses.

Protective effects of brain hypothermia on behavior and histopathology following global cerebral ischemia in rats.

The present experiments were designed to assess whether brain hypothermia can reduce the behavioral and histopathological deficits associated with global forebrain ischemia. Animals were subjected to 12.5 min of four vessel occlusion (4VO) with moderate hypotension, and brain temperature maintained at either 37 degrees C (4VO-37) or 30 degrees C (4VO-30). Behavioral tests designed to assess forelimb reflexes and sensorimotor function were given on post-operative weeks 2 and 4. Beginning in week 5, the rats were trained on a variety of navigation problems in the Morris water maze. Histopathological examination of the tissue 2 months following reperfusion revealed that 4VO-37 animals sustained substantial cell death in hippocampal region CA1 and moderate damage to the dorsolateral neostriatum. 4VO-30 animals showed minimal cell death in CA1 and neostriatum. There were no group differences for any of the sensorimotor measures, or for acquisition performance on either the simple place task or visible platform version of the water maze. In contrast, during acquisition of the learning set task, the performance of 4VO-37 animals was impaired relative to either of the other groups, whereas the performance of 4VO-30 animals was not significantly different from the sham controls. These data suggest that moderate intra-ischemic brain hypothermia provides long-lasting protection from behavioral deficits as well as neuronal injury following transient global ischemia.

Sensorimotor and cognitive consequences of middle cerebral artery occlusion in rats.

Rats were subjected to either right proximal middle cerebral artery (MCA) occlusion or sham operation, and examined for an extended period on a battery of tests designed to measure simple motor function, sensorimotor integration and cognitive function. Rats with MCA occlusion showed extensive neuronal loss in the dorsolateral striatum and variable neuron loss in the parietal, temporal and frontolateral neocortex. MCA occluded animals exhibited significant impairments in tests of postural reflex, visual and tactile forelimb placing, locomotor coordination, and a test of simultaneous bilateral tactile extinction. The reflex and sensorimotor function deficits recovered to pre-operative levels by Day 30 post-ischemia. Five weeks following surgery, rats were tested in 2 versions of the Morris water task. Rats with MCA occlusion demonstrated significant impairments in their ability to navigate to a hidden platform, but were not significantly impaired on the visible (cued) version of the task. This general pattern of transient sensorimotor and reflex deficits, but with more persistent cognitive impairments, is similar to that seen in humans following MCA infarcts.

Lesions of the amygdaloid central nucleus block conditioned cardiac arrhythmias in the rabbit receiving digitalis.

We have previously reported [15] that malignant cardiac arrhythmias can be evoked in the rabbit receiving digitalis by cardiovascular changes in response to (a) a Pavlovian aversively conditioned stimulus (CS) or (b) electrical stimulation of the amygdaloid central nucleus (ACE), a structure which contributes to Pavlovian-conditioned cardiovascular responses in the rabbit. The present study was designed to examine further the role of the ACE in arrhythmogenesis by determining the effect of lesions of the ACE on the occurrence of CS-evoked arrhythmias during digitalis administration in the rabbit. Two groups of rabbits (ACE lesion and SHAM) received electrodes implanted bilaterally in the ACE, while a third group (UNOP) served as an unoperated control. All rabbits were given Pavlovian conditioning trials in which a tone conditioned stimulus (CS) was paired with an eyelid shock as an unconditioned stimulus (US). Twenty-four h later, rabbits in the lesion group received bilateral lesions of the ACE. Twenty-four h after the lesion, rabbits in all three groups were given a retention test in which an i.v. infusion of ouabain was delivered, followed by 20 CS alone trials. Presence or absence of arrhythmias was scored during the pre-CS baseline and CS periods for each trial. All three groups exhibited few instances of pre-CS baseline arrhythmias, the frequency of which did not differ between groups. The SHAM and UNOP control groups exhibited a significant increase in the occurrence of CS-arrhythmias compared to pre-CS levels. This increase was blocked in the group receiving lesions of the ACE, as was CS-induced bradycardia which typically occurs in response to the CS in the rabbit.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypothalamic, midbrain and bulbar areas involved in the defense reaction in rabbits.

The present study mapped neuroanatomical sites in the hypothalamus and periaqueductal gray (PAG) of the rabbit which, when stimulated electrically, evoked the cardiorespiratory components of the defense reaction (CRDR). This included increases in heart rate, blood pressure, hindlimb blood flow and respiration rate. All of the components of the CRDR were elicited by electrical stimulation of the posterior hypothalamus, at sites dorsal and medial to the fornix. Although there were regions throughout the PAG in which electrical stimulation elicited concomitant increases in blood pressure, hindlimb blood flow and respiration rate, only stimulation of the dorsal PAG evoked tachycardia. Injection of horseradish peroxidase into the rostral ventrolateral medulla (RVLM) led to heavy retrograde and anterograde labeling in the region of the hypothalamus that yielded the CRDR when stimulated electrically. Heavy labeling was also observed in the dorsal and ventral PAG. The results of this study provide evidence that the posterior hypothalamus and the dorsal PAG are nodal structures in the mediation of the CRDR and that cells in posterior hypothalamus, dorsal PAG and ventral PAG make monosynaptic connections with the RVLM.

The organization of dorsal medullary projections to the central amygdaloid nucleus and parabrachial nuclei in the rabbit.

The amygdaloid central nucleus and the pontine parabrachial nucleus receive direct, ascending projections from autonomic regulatory nuclei of the dorsal medulla and are recognized as important components of a forebrain system which contributes to autonomic regulation. The present study was designed to provide more detailed information on the anatomical organization of this ascending system in the rabbit by determining (a) the extent to which separate populations of neurons within the solitary complex project to the central nucleus and parabrachial nucleus, (b) the topographical distribution of the projections of the solitary complex within the amygdaloid central nucleus and parabrachial nucleus and (c) the extent to which projections from the solitary complex to the parabrachial nucleus terminate in the region of origin of projections from the parabrachial nucleus to the amygdaloid central nucleus. A fluorescent dye, double retrograde-labeling technique demonstrated that separate populations of neurons in the solitary complex projected to the amygdaloid central nucleus and parabrachial nucleus. Neurons of both populations were more heavily concentrated within the caudal two thirds of nucleus of the solitary tract and were most numerous within the commissural, medial and dorsomedial subnuclei. Labeled neurons were also located within the dorsal motor nucleus of the vagus nerve. Autoradiographic experiments demonstrated that injections of amino acids into the solitary complex resulted in terminal labeling in the central nucleus. This labeling extended rostrally into the adjacent sublenticular substantia innominata and lateral component of the bed nucleus of the stria terminalis. Label was also observed within the lateral, medial, and Kolliker-Fuse regions of the parabrachial nucleus. A particularly dense field was observed overlying cells located within the ventrolateral region of the lateral parabrachial nucleus. This region contained the majority of labeled neurons within the parabrachial nucleus following fluorescent dye injections into the central nucleus. Furthermore, injections of amino acids into this region resulted in terminal labeling within the central nucleus, with a particularly dense area observed within the medial aspect of the nucleus. The results demonstrate that separate populations of neurons within the solitary complex of the rabbit project to the central amygdaloid and parabrachial nuclei and that the majority of these are located within the caudal two-thirds of the complex.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurobehavioral contributions to cardiac arrhythmias during aversive pavlovian conditioning in the rabbit receiving digitalis.

Clinical observations suggest that a prevalent condition for the occurrence of cardiac arrhythmias is the synergistic interaction of several risk factors including digitalis glycosides, myocardial ischemia and psychological stress. However, little research has been directed toward controlled, systematic investigations of such synergistic interaction, particularly with respect to psychological stress and digitalis glycosides. The present research was undertaken to develop an animal model with which to study the behavioral and neurobiological contributions to arrhythmias during psychological stress in the presence of digitalis. The model used the rabbit as the experimental animal, a pavlovian aversive conditioning procedure and ouabain, a digitalis glycoside. Rabbits received pavlovian conditioning trials in which a tone as a conditioned stimulus (CS) was paired with an eyelid shock as an unconditioned stimulus (US). Twenty-four hours later, a retention test was given in which either of two doses of ouabain or saline was given, followed by 20 CS presentations alone. The CS presentations were given every 120 s (+/- 10 s). During ouabain infusion, the CS significantly increased the frequency of arrhythmic episodes compared to pre-CS baseline frequencies. These arrhythmic episodes were invariably preceded by CS-induced bradycardia. Both parasympathetic and sympathetic involvement were suggested in arrhythmogenesis, since the CS-induced increase in arrhythmic episodes was blocked by pretreatment with either atropine methylnitrate or atenolol. Furthermore, electrical stimulation of the amygdaloid central nucleus, an area implicated in the expression of bradycardia to a pavlovian CS in the rabbit produced arrhythmic episodes in the presence of ouabain. These arrhythmic episodes were similar in topography to CS-induced arrhythmias within any one animal and were decreased by atropine methylnitrate pretreatment. Insights into central and peripheral nervous system mechanisms by which psychological stress is capable of evoking cardiac arrhythmias in the presence of ouabain should ultimately lead to more effective treatment strategies for the prevention of these arrhythmias.