Involvement of apoptosis in neurological injury after hypothermic circulatory arrest: a new target for therapeutic intervention?

BACKGROUND: This study was undertaken to evaluate the role of apoptosis in neurological injury after hypothermic circulatory arrest (HCA). METHODS: Twenty-one pigs (27 to 31 kg) underwent 90 minutes of HCA at 20 degrees C and were electively sacrificed at 6, 24, 48, and 72 hours, and at 7, 10, and 12 days after HCA, and compared with unoperated controls. In addition, 3 animals that had HCA at 10 degrees C, and 3 treated with cyclosporine A (CsA) in conjunction with HCA at 20 degrees C, were examined 72 hours after HCA. After selective perfusion and cryopreservation, all brains were examined to visualize apoptotic DNA fragmentation and chromatin condensation on the same cryosection of the hippocampus: fluorescent in situ end labeling (ISEL) was combined with staining with a nucleic acid-binding cyanine dye (YOYO). RESULTS: In addition to apoptosis, which was seen at a significantly higher level (p = 0.05) after HCA than in controls, two other characteristic degenerative morphological cell types (not seen in controls) were characterized after HCA. Cell death began 6 hours after HCA and reached its peak at 72 hours, but continued for at least 7 days. Compared with the standard protocol at 20 degrees C, HCA at 10 degrees C and CsA treatment both significantly reduced overall cell death after HCA, but not apoptosis. CONCLUSIONS: The data establish that significant neuronal apoptosis occurs as a consequence of HCA, but at 20 degrees C, other pathways of cell death, probably including necrosis, predominate. Although preliminary results suggest that the neuroprotective effects of lower temperature and of CsA are not a consequence of blockade of apoptotic pathways, inhibition of apoptosis nevertheless seems promising as a strategy to protect the brain from the subtle neurological injury that is associated with prolonged HCA at clinically relevant temperatures.

Cyclosporine A as a potential neuroprotective agent: a study of prolonged hypothermic circulatory arrest in a chronic porcine model.

OBJECTIVE: To assess whether Cyclosporine A (CsA) or cycloheximide (CHX) can reduce ischemia-induced neurological damage by blocking apoptotic pathways, we assessed their effects on cerebral recovery in a chronic animal model of hypothermic circulatory arrest (HCA). METHODS: Twenty-eight pigs (28-33 kg) underwent 90 min of HCA at 20 degrees C. In this blinded study, animals were randomized to placebo (n=12), 5 mg/kg CsA (n=8), given intravenously before and subcutaneously for 7 days after HCA, or a single dose of 1 mg/kg CHX (n=8), given after weaning from cardiopulmonary bypass. Hemodynamics, intracranial pressure (ICP) and neurophysiological data (EEG, SSEP) were assessed for 3 h after HCA; early behavioral recovery was scored, and neurological/behavioral evaluation (9=normal) was carried out daily until elective sacrifice on postoperative day (POD) 7. Brains were selectively perfused and evaluated histopathologically for apoptosis. RESULTS: Basic hemodynamic data revealed no differences between CsA or CHX and control groups. ICP was significantly lower throughout rewarming (P=0.009) and reperfusion (P=0.05) in the CsA group. EEG recovery 3 h after HCA was observed in four of eight CsA animals but in only 1 of 12 controls (P=0.11) and one of eight CHX animals; cortical SSEP recovery also seemed faster in CsA animals, but failed to reach significance. Some early recovery scores were significantly better in the CsA group, and daily behavioral scores were consistently and significantly higher in the CsA-treated animals from POD1 through POD4. CONCLUSIONS: The data indicate that treatment with Cyclosporine A but not cycloheximide has a positive effect on cerebral recovery following HCA. Whether CsA results in inhibition of neuronal apoptosis, and/or inhibits release of cytokines and thereby reduces postischemic cerebral edema remains to be elucidated. The neuroprotective effect of CsA, if confirmed in further studies, would make its clinical application conceivable.

A program for neuropsychological investigation of deep brain stimulation (PNIDBS) in movement disorder patients: development, feasibility, and preliminary data.

OBJECTIVE: This technical report and feasibility study propose a standardized method for collecting neuropsychological data in patients undergoing the deep brain stimulation (DBS) procedure. BACKGROUND: Programs for standardizing motor data collected in studies investigating surgical therapies for Parkinson disease are already widely used (e.g., Core Assessment Program for Intracerebral Transplantations). The development and rationale for the proposed Program for Neuropsychological Investigation of Deep Brain Stimulation (PNIDBS) are outlined, and support for the feasibility of these methodologies is provided via preliminary data. METHOD: The PNIDBS includes a core battery of neuropsychological tests that assesses a wide range of cognitive functions (attention, language, visuospatial, memory, and executive) as well as depression. Using the PNIDBS, three Parkinson disease and two dystonia patients were evaluated at baseline and after surgery, once with stimulation off and once with stimulation on. RESULTS: Patients with severe motor disabilities were able to complete the PNIDBS. These preliminary data suggest that the DBS procedure as a whole had a minimal impact on cognitive functioning in most patients studied. There was also some evidence that the one patient who showed cognitive decline after the DBS procedure had demographic and clinical characteristics that may have put him at risk for this decline. CONCLUSIONS: The procedures in the PNIDBS were systematically developed and are feasible to execute. The relatively brief core battery has multiple versions and can be supplemented to meet individual investigator needs. By evaluating the components of the DBS procedure (electrode placement and stimulation), the PNIDBS can address clinical questions regarding the cognitive effects of the DBS procedure as well as investigate basic scientific issues regarding how different cognitive functions are affected when subcortical-prefrontal circuits are manipulated by the DBS procedure.

Somatosensory evoked potential monitoring in anterior thoracic vertebrectomy.

OBJECT: Spine surgeons have used intraoperative cortical and subcortical somatosensory evoked potential (SSEP) monitoring to detect changes in spinal cord function when intraoperative procedures can be performed to prevent neurological deterioration. However, the reliability of SSEP monitoring as applied to anterior thoracic vertebral body resections has not been rigorously assessed. METHODS: The authors retrospectively reviewed hospital charts and operating room records obtained between August 1993 and December 1998 and found that SSEP monitoring was used in 44 surgical procedures involving an anterior approach for thoracic vertebral body resections. There were no patients in whom SSEP changes did not return to baseline during the surgical procedure. Patients in four cases, despite their stable SSEP recordings throughout the procedure, were noted immediately postoperatively to have experienced significant neurological deterioration. The false-negative rate in SSEP monitoring was 9%. Sensitivity was determined to be 0%. CONCLUSIONS: It is important to recognize high false-negative rates and low sensitivity of SSEP monitoring when it is used to record spinal cord function during anterior approaches for thoracic vertebrectomies. The insensitivity of SSEPs for motor deterioration during anterior thoracic vertebrectomies is likely due to the limitation of SSEPs, which monitor only posterior column function whereas motor paths are conveyed in the anterior and anterolateral spinal cord. The authors believe that SSEPs can not be relied on to detect reversible spinal damage during anterior thoracic vertebrectomies.

Retrograde cerebral perfusion enhances cerebral protection during prolonged hypothermic circulatory arrest: a study in a chronic porcine model.

BACKGROUND: This study was undertaken to confirm earlier findings that retrograde cerebral perfusion (RCP) can improve cerebral outcome after prolonged hypothermic circulatory arrest (HCA), and to determine whether RCP with inferior vena caval occlusion, which is more effective in removing particulate emboli, is superior to conventional RCP in enhancing cerebral protection. METHODS: Sixty-two pigs (27 to 30 kg) were randomly assigned to undergo one of the following for 90 minutes at 20 degrees C: antegrade cerebral perfusion (ACP); conventional RCP (RCP); RCP with occlusion of the inferior vena cava (RCP-O), or HCA with the head packed in ice. RCP flow was regulated to a sagittal sinus pressure of 20 mm Hg. Hemodynamic, electrophysiologic, and metabolic monitoring were carried out until 4 hours after rewarming, daily behavioral and neurologic assessments until elective sacrifice on day 7, and histologic analysis of the brain after death. RESULTS: Complete behavioral recovery was seen in all surviving animals by day 5 after ACP or RCP, but in only 83% after RCP-O and 50% after HCA (p = 0.001). A histopathologic score of 2 or more, indicating more than mild injury, was not found in any animal after ACP, in 27% after RCP, in 47% after HCA, and in 68% after RCP-O (p = 0.002). The median oxygen consumption was 6.66 mL/min after ACP, 1.37 mL/min with RCP, and 1.02 mL/min with RCP-O (p < 0.0001). The median amount of fluid sequestered was 2,450 mL after RCP-O, 760 mL after RCP, and -200 mL after ACP (p < 0.0001). CONCLUSIONS: Conventional RCP without inferior vena caval occlusion results in a significantly better outcome than RCP-O after prolonged HCA, despite more efficient cerebral perfusion during RCP-O, and also provides cerebral protection superior to prolonged HCA alone, but care must be taken during its implementation to minimize cerebral edema and other possible causes of retroperfusion-related cerebral injury.

Can retrograde perfusion mitigate cerebral injury after particulate embolization? A study in a chronic porcine model.

OBJECTIVE: We assessed the impact on histologic and behavioral outcome of an interval of retrograde cerebral perfusion after arterial embolization, comparing retrograde cerebral perfusion with and without inferior vena caval occlusion with continued antegrade perfusion. METHODS: Sixty Yorkshire pigs (27 to 30 kg) were randomly assigned to the following groups: antegrade cerebral perfusion control; antegrade cerebral perfusion after embolization; retrograde cerebral perfusion control; retrograde cerebral perfusion after embolization; retrograde cerebral perfusion with inferior vena cava occlusion, retrograde cerebral perfusion with inferior vena cava occlusion control, and retrograde cerebral perfusion with inferior vena cava occlusion after embolization. After cooling to 20 degrees C, a bolus of 200 mg of polystyrene microspheres 250 to 750 (microm diameter (or saline solution) was injected into the isolated aortic arch. After 5 minutes of antegrade cerebral perfusion, 25 minutes of antegrade cerebral perfusion, retrograde cerebral perfusion, or retrograde cerebral perfusion with inferior vena cava occlusion was instituted. After the operation, all animals underwent daily assessment of neurologic status until the time of death on day 7. RESULTS: Aortic arch return, cerebral vascular resistance, and oxygen extraction data during retrograde cerebral perfusion showed differences, suggesting that more effective flow occurs during retrograde cerebral perfusion with inferior vena cava occlusion, which also resulted in more pronounced fluid sequestration. Microsphere recovery from the brain revealed significantly fewer emboli after retrograde cerebral perfusion with inferior vena cava occlusion. Behavioral scores showed full recovery in all but one control animal (after retrograde cerebral perfusion with inferior vena cava occlusion) by day 7 but were considerably lower after embolization, with no significant differences between groups. The extent of histopathologic injury was not significantly different among embolized groups. Although no histopathologic lesions were present in either the antegrade cerebral perfusion control group or the retrograde cerebral perfusion control group, mild significant ischemic damage occurred after retrograde cerebral perfusion with inferior vena cava occlusion even in control animals. CONCLUSIONS: Although effective washout of particulate emboli from the brain can be achieved with retrograde cerebral perfusion with inferior vena cava occlusion, no advantage of retrograde cerebral perfusion with inferior vena cava occlusion after embolization is seen from behavioral scores, electroencephalographic recovery, or histopathologic examination; retrograde cerebral perfusion with inferior vena cava occlusion results in greater fluid sequestration and mild histopathologic injury even in control animals. Retrograde cerebral perfusion with inferior vena cava occlusion shows clear promise in the management of embolization, but further refinements must be sought to address its still worrisome potential for harm.

Intraoperative mapping of sensate flaps. Electrophysiologic techniques and neurosomal boundaries.

BACKGROUND: The desirability of restoring sensation to the upper aerodigestive tract has led to an expanded use of sensate flaps for reconstruction of mucosal defects. Sensation can be restored via preformed neural pathways through the anastomosis of recipient and donor nerves, provided that the sensate flap falls within the boundaries of the neurosome for the identified sensory nerve. OBJECTIVES: To perform detailed electrophysiologic mappings of neurosomes of potential sensate flap donor sites, to describe their variability, and to investigate the usefulness of intraoperative mapping in terms of flap design and harvesting. DESIGN: A case series of 27 patients who were undergoing free flap reconstruction of various postablative head and neck defects were examined. Two silver-silver chloride recording electrodes were placed in direct contact with the dissected sensory nerve, and the overlying skin was either mechanically or electrically stimulated. Auditory feedback, as well as visualization of the responses on an oscilloscope, determined whether the stimulated area fell within the neurosome. This technique was applied to the lateral antebrachial cutaneous nerve of the radial forearm flap (n = 15), the lateral sural cutaneous nerve of the fibula flap (n = 5), the subcostal nerve of the iliac crest flap (n = 6), and the dorsal cutaneous rami of spinal nerve T-1 or T-2 of the scapula flap (n = 1). RESULTS: The neurosome of the lateral antebrachial cutaneous nerve was relatively consistent with the variability only at the distal boundary (ie, the dorsum of the hand). The neurosome of the lateral sural cutaneous nerve was more variable, falling into 2 distinct innervation patterns: one showing innervation that was limited to the upper lateral and posterior portions of the calf and the other demonstrating significant extension into the lower half of the calf. The neurosome of the subcostal nerve showed little variability and consistently overlapped the proposed skin paddle. The neurosome of the T-1 or T-2 spinal nerve was mapped in 1 patient and is described. CONCLUSIONS: The consistency of neurosomal boundaries is dependent on the donor site. Intraoperative mapping of flap donor sites may not only assure the harvesting of a true sensate flap, but may also allow for intraoperative decision making with regard to possible modifications of flap design and harvesting techniques. Two new sensate flaps from the iliac crest and scapula are accurately described.

Reappraisal of the inferior epigastric flap: a new neurovascular flap model in the rat.

An anatomic, histologic, and electrophysiologic study was carried out in order to determine the distribution and cutaneous sensory territory of the epigastric nerve in the rat. Results for nerve staining (Sihler's method) and electrophysiologic nerve mapping indicate that the neurosome of the epigastric nerve has a different autonomy than the vascular territory of the inferior epigastric artery. Based on these findings, an experimental model for neurovascular free-tissue transfer is proposed.

The effect of retrograde cerebral perfusion after particulate embolization to the brain.

Neurologic injury as a consequence of cerebral embolism of either air or atherosclerotic debris during cardiac or aortic surgery is still a major cause of postoperative morbidity and mortality. While exploring various means of improving cerebral protection during complex cardiothoracic procedures, we have developed a chronic porcine model to study retrograde cerebral perfusion. We have previously demonstrated that retrograde perfusion results in a small amount of nutritive flow and provides cerebral protection that appears to be superior to simple prolonged hypothermic circulatory arrest. The current study was designed to evaluate the efficacy of retrograde cerebral perfusion in mitigating the effects of particulate cerebral embolism occurring during cardiac surgery. Four groups of pigs (19 to 28 kg) underwent cardiopulmonary bypass with deep hypothermia at an esophageal temperature of 20 degrees C: an antegrade control group (AC, n = 5), an antegrade embolism group (AE, n = 10), a retrograde control group (RC, n = 5), and a retrograde embolism group (RE, n = 10). In addition, because of extreme heterogeneity in outcome in the initial RE group, an additional group of 10 animals underwent embolism and retrograde perfusion at a later time. Embolization was accomplished by injection of 200 mg of polystyrene microspheres (250 to 750 micrograms in diameter) via the aortic cannula into an isolated aortic arch preparation in the AE and RE groups; the control groups received injections of 10 ml of saline solution. After infusion of the microspheres or saline solution, conventional perfusion, with the aortic arch pressure maintained at 50 mm Hg, was continued for a total of 30 minutes in the antegrade groups; in the retrograde groups, retrograde flow was initiated via a cannula positioned in the superior vena cava, and was continued for 25 minutes. Superior vena caval flow was regulated to maintain a sagittal sinus pressure of approximately 30 mm Hg in the retrograde groups, and blood returning to the isolated aortic arch was collected and measured. All animals were allowed to recover and were evaluated daily according to a quantitative behavioral score in which 9 indicates apparently complete normalcy, with lower numbers indicating various degrees of cerebral injury. At the time of planned death on day 6, half of the brain was used for recovery of embolized microspheres after digestion with 10N sodium hydroxide. The other half was submitted for histologic study. Neurologic recovery in both the antegrade and retrograde control groups appeared to be complete, although mild evidence of histologic damage was present in some animals in the retrograde control group.(ABSTRACT TRUNCATED AT 400 WORDS)

An auditory conditioned stimulus modulates unconditioned stimulus-elicited neuronal activity in the cerebellar anterior interpositus and dentate nuclei during nictitating membrane response conditioning in rabbits.

The effects of the presentation of an auditory conditioned stimulus (CS) on unconditioned stimulus (US)-elicited neuronal activity in the anterior interpositus (AIPN) and dentate (DN) nuclei of the cerebellum were investigated during the initial stages of classical conditioning of the nictitating membrane (NM) response in rabbits. In Experiment 1, a 500-ms CS (but not a 30-ms CS) facilitated US-elicited single-unit activity in the AIPN and depressed US-elicited activity in the DN during training. In Experiment 2, lesions of the AIPN but not of the DN prevented acquisition of conditioned NM responses. The results are interpreted within the framework of a model of classical conditioning that proposes that conditioned neuronal activity that underlies behavioral plasticity develops from the modulation of US-elicited neuronal activity by the CS.

Effects of amygdala lesions on reflex facilitation and conditioned response acquisition during nictitating membrane response conditioning in rabbit.

The present study demonstrated that large lesions of the amygdala disrupt the maintenance of reflex facilitation of the unconditioned nictitating membrane (NM) response and slow the acquisition of conditioned NM responses in rabbit. Before behavioral training, the central nucleus of the amygdala and adjacent areas were lesioned electrolytically. In the 1st experiment, the lesioned animals exhibited no reflex facilitation of the unconditioned NM response at conditioned stimulus (CS)-unconditioned stimulus (US) intervals of 125-8,000 ms. In the 2nd and 3rd experiments in which one CS-US interval (500 ms) was used, the lesions disrupted the maintenance of reflex facilitation but did not alter the facilitation exhibited in the 1st block of training. The lesions retarded the acquisition of conditioned NM responses when the 1000-Hz tone CS intensity was 65 dB but not when the intensity was 85 dB.

In vivo modulation of N-methyl-D-aspartate receptor-dependent long-term potentiation by the glycine modulatory site.

The role of the glycine modulatory site in N-methyl-D-aspartate receptor function was examined by determining the effect of the glycine site antagonist, 7-chlorokynurenic acid, on the induction of long-term potentiation at the commissural-CA1 synapse in anesthetized rats. Robust long-term potentiation of population excitatory postsynaptic potentials and population spike responses recorded extracellularly in the stratum pyramidale and in stratum radiatum of CA1 developed after high frequency stimulation (100 Hz for 1 s) of commissural fibers during continuous intrahippocampal administration of vehicle solution (0.15 M NaCl). In contrast, infusion of either 7-chlorokynurenic acid (400 microM) or of the N-methyl-D-aspartate receptor antagonist, D-2-amino-5-phosphonovaleric acid (100 microM), significantly attenuated or completely blocked the development of long-term potentiation. When 7-chlorokynurenic acid was infused together with the glycine analog, D-serine (1 mM), long-term potentiation developed that was comparable to that observed in control animals. Intrahippocampal administration of D-serine alone was associated with slightly greater magnitude of long-term potentiation than observed in control animals. Collectively, these findings establish that in intact hippocampus, activity at the glycine modulatory site is necessary for activation of the N-methyl-D-aspartate receptor complex. Furthermore, these results suggest that the glycine modulatory site may not be fully saturated in vivo, and thus can serve to regulate N-methyl-D-aspartate receptor function.

Reflex facilitation of the rabbit nictitating membrane response by an auditory stimulus as a function of interstimulus interval.

The ability of an auditory stimulus to facilitate the amplitude and latency of the unconditioned nictitating membrane (NM) response in rabbits was investigated over a wide range of interstimulus intervals (ISIs) for both delay (Experiments 1-4) and trace (Experiments 3 and 4) procedures. The auditory stimulus was a 1000-Hz tone (T) at either 85 or 95 dB, and the reflex-eliciting stimulus was a 2.0 psi (pounds per square inch) corneal air puff (AP). The results indicate that (a) robust facilitation of the NM response, as measured by an increased amplitude and a reduced latency, can be obtained at long ISIs (2,000-32,000 ms); (b) increasing the tone intensity can increase reflex facilitation of the peak amplitude; (c) at comparable ISIs, delay procedures produce more facilitation of both amplitude and latency than do trace procedures; and (d) when trace procedures are used, amplitude and latency facilitation by a 125-ms tone follows an inverted U-shaped ISI function in which facilitation peaks between 125 and 500 ms, rapidly decreases between 1,000 and 2,000 ms, and disappears by 4,000 ms.

An associative process maintains reflex facilitation of the unconditioned nictitating membrane response during the early stages of training.

The presentation of a neutral or conditioned stimulus (CS) at an appropriate interval prior to the presentation of a corneal airpuff, or a paraorbital shock (unconditioned stimulus, US) can facilitate the amplitude of the unconditioned nictitating membrane (NM) response in rabbit. In two experiments, it was demonstrated that an associative process mediates the maintenance of that facilitation during repeated CS-US pairings. Although CS-alone presentations produced a substantial decrease in the amount of reflex facilitation in animals not pretrained with the CS, pretraining that consisted of paired CS-US presentations prevented that decrease when CS-alone presentations were subsequently given. Conditioned facilitation of the unconditioned response occurred very rapidly (within 5-12 trials in these experiments) and long before the appearance of overt conditioned responses to the CS. In addition, it was demonstrated that conditioned facilitation can be relatively specific to the tonal frequency of the CS. These results indicate the first sign of conditioning of the NM response is exhibited in the amplitude of the unconditioned response.

Reflex facilitation of the nictitating membrane response remains after cerebellar lesions.

Reflex facilitation and associated properties were investigated during classical conditioning of the nictitating membrane (NM) response in rabbit. In the first experiment, the role of the cerebellum was examined by comparing the unconditioned responses of animals with bilateral lesions of the deep cerebellar nuclei with those of operated controls during counterbalanced tone/light (T/L) discrimination training. Both T and L facilitated unconditioned NM responses when used as the CS+ (conditioned stimulus), but neither facilitated when used as the CS-. There were no significant differences in the amount of reflex facilitation exhibited by animals with lesions compared with control animals. Animals with lesions, however, failed to acquire conditioned responses after 10 days of training, whereas all control animals met acquisition criterion within 4 days. In the second experiment, reflex facilitation was shown to decrement in a stimulus-specific manner when nonreinforced presentations of an auditory stimulus were given. The discussion of results focuses on the relation between reflex facilitation and classical conditioning in terms of behavioral properties and underlying neural systems.

Parallel pathways can conduct visual CS information during classical conditioning of the NM response.

Single and combined lesions were made to the lateral geniculate nucleus (LGN), the superficial layers of the superior colliculus (SC), and the pretectal nuclei (Ptc) prior to conditioning of the nictitating membrane (NM) response in rabbit with a visual conditioned stimulus (CS). Due to technical considerations, lesions of the dorsal LGN were accompanied by lesions of the visual cortex, the only output of the dorsal LGN, in order to render the dorsal LGN nonfunctional. Single lesions to any one of the 3 target systems (LGN, SC, Ptc) did not alter the rate of conditioning. Furthermore, double lesions to any 2 of the systems did not prevent conditioning, although LGN + SC lesions significantly retarded acquisition. When all 3 systems were lesioned, however, animals never acquired to the visual CS, although they successfully conditioned to an auditory CS. The results indicate that in rabbit there are parallel visual pathways individually capable of supporting the acquisition of conditioned NM responses.

Hippocampectomy and feature-positive discrimination.

The effects of hippocampal lesions on feature-positive discrimination were investigated using the nictitating membrane response preparation. During training, animals received a simultaneous reinforced compound as the conditioned stimulus (CS+) and a non-reinforced element as the CS-. The compound consisted of a tone and a light, with the tone being more salient than the light. The light and tone served as the CS- in Expts. 1 and 2, respectively. There were no significant differences between hippocampectomized animals and the controls (cortical and sham) when the CS- was the light; however, when the more salient tone stimulus was the CS-, hippocampectomized animals exhibited high levels of responding to both the CS+ and CS- and failed to acquire the discrimination. The results are discussed in terms of attentional and response inhibition theories of hippocampal function.

Hippocampus and trace conditioning of the rabbit's classically conditioned nictitating membrane response.

Rabbits received classical conditioning of the nictitating membrane response (NMR) in a trace conditioning paradigm. In this paradigm, a 250-ms tone conditioned stimulus (CS) occurs, after which there is a 500-ms period of time in which no stimuli occur (the trace interval), followed by a 100-ms air puff unconditioned stimulus (UCS). In Experiment 1, lesions of the hippocampus or cingulate/retrosplenial cortex disrupted acquisition of the long-latency or adaptive conditioned response relative to unoperated controls and animals that received neocortical lesions that spared the cingulate/retrosplenial areas. When animals with hippocampal or cingulate/retrosplenial lesions were switched to a standard delay paradigm in which the CS and UCS were contiguous in time, they acquired in about the same number of trials as naive rabbits. In a second experiment multiple-unit activity in area CA1 of the hippocampus was examined during acquisition of the trace conditioned response (CR). Three groups of animals were tested: animals that had a 500-ms trace interval (Group T-500), animals that received explicitly unpaired presentations of the CS and UCS (Group UP), and animals that underwent conditioning with a 2,000-ms trace interval (Group T-2000). Animals in Group T-500 acquired the CR in about 500 trials. Early in training, and well before any CRs occurred, there was a substantial increase in neuronal activity in the hippocampus that began during the CS and persisted through the trace interval. There was also an increase in the UCS period that modeled the amplitude-time course of the behavioral unconditioned response. Later in conditioning as CRs emerged, there was no longer neuronal bursting throughout the CS + trace period. Rather, the activity shifted to later in the trace interval and formed a model of the amplitude-time course of the behavioral CR. Activity during the UCS period was similar to that seen earlier in conditioning. Animals in Group UP showed no behavioral conditioning and no increase in neuronal activity. Animals in Group T-2000 showed no long-latency behavioral conditioning and no increase in neuronal activity. The data are discussed in terms of the role of the hippocampus in conditioning during situations in which the CS and UCS are not contiguous in time.

Behavioral and neural gustatory responses in rabbit.

To provide more information on a potentially valuable preparation for studies in taste and appetite, we have examined the taste preferences (and aversions) and chorda tympani sensitivity of the rabbit. Adult male New Zealand rabbits were given a two-bottle preference test between water and various molar concentrations of NaCl, KCl, sucrose, sodium saccharin, quinine hydrochloride and HCl. The rabbits exhibited the expected preferences for sucrose and aversions for quinine and HCl. Unexpectedly, however, the rabbits exhibited only a mild preference for NaCl, a stronger preference for KCl, and an aversion to sodium saccharin. Multiunit discharges of the chorda tympani nerve to the same taste stimuli indicated that the anterior tongue receptors are acutely sensitive to KCl, NaCl and quinine, but not to sucrose, HCl and saccharin. The chorda tympani was more responsive to KCl than to NaCl. Dilute concentrations of both NaCl and sodium saccharin elicited a two-component response consisting of an immediate excitatory phase followed by a tonic inhibitory phase. This complex response pattern of the whole nerve to NaCl and sodium saccharin is discussed in relation to the impulse frequencies in hypothesized water-sensitive and salt-sensitive fibers. Both the behavioral and neural data are discussed in relation to similar data obtained in rat and hamster.