The influence of dsRNA viruses on the biology of plant pathogenic fungi.

Double-stranded RNA viruses are ubiquitous in fungi. They are non-infective and, like most prokaryotic plasmids, are only transmitted to compatible strains via cell fusion. Most are cryptic, but some with an established phenotype, such as the hypoviruses of the chestnut-blight fungus, have been studied for their potential as biological control agents of fungi.

Circulating levels of glucocorticoid hormones in WHHL and NZW rabbits: circadian cycle and response to repeated social encounter.

Social environment influences the progression of atherosclerosis in an important experimental model of disease, the Watanabe Heritable Hyperlipidemic rabbit (WHHL). Although the hypothalamic-pituitary-adrenocortical (HPA) system is likely to play an important role in the behavioral modulation of disease, relatively little is known about the glucocorticoid responses in these animals, or in other strains of rabbits. The purpose of the present study was to: (1) evaluate the rabbit glucocorticoid circadian rhythm, (2) compare plasma cortisol and corticosterone responses to social stress, and (3) examine strain differences (i.e., WHHL vs. New Zealand White (NZW)) in rabbit glucocorticoid responses to assess whether WHHLs have an aberrant HPA system. It was found that male rabbits secrete both corticosterone and cortisol in a circadian rhythm that peaks in the afternoon and reaches a nadir at 0600 h, i.e., approximately 12 h out-of-phase with the human glucocorticoid rhythm. Both glucocorticoids responded similarly to social stress induced by repeated daily 4 h pairings with another male rabbit; after 10 days of pairings, glucorticoid values were significantly correlated with the amount of defensive agonistic behavior exhibited. Finally, there were no significant strain differences in glucocorticoid circadian rhythms, baselines, or responses to social stress. These data suggest that glucocorticoid responses (i.e., circadian rhythms, responses to social stress) in the WHHL are similar to glucocorticoid responses in standard laboratory white rabbits.

Lateral subthalamic area as mediator of classically conditioned bradycardia in rabbits.

This study was conducted to examine whether a central efferent pathway passing through the lateral zona incerta (LZI) of the subthalamus selectively mediates the bradycardia conditioned response (CR) in rabbits. Electrodes were implanted bilaterally in LZI or in control sites just dorsal or ventral to LZI. Two days following surgery, animals were subjected to Pavlovian conditioning or to pseudoconditioning. Subsequent bilateral electrolytic lesions did not influence the heart rate (HR) orienting response, unconditioned response, baseline, or lack of response to pseudoconditioning. Bilateral LZI lesions alone abolished the HR CR. In a follow-up experiment, the corneoretinal potential (CRP) CR and HR were recorded. Bilateral LZI lesions following conditioning to a criterion of 65% CRP CRs abolished the HR CR without affecting CRP CRs. The present findings indicate that LZI is part of an efferent pathway that selectively mediates the HR CR in rabbits.

A computerized grid walking system for evaluating the accuracy of locomotion in rats.

A microcomputer-based system employing photoelectric devices to record rat movements and footfalls in the grid walking test paradigm was developed and evaluated. Behavioral data obtained from the system were: distance traversed on the grid, time taken to traverse the distance, number of footfalls, times of footfalls, positions of footfalls, durations of footfalls, and whether the footfall was due to a hind or a fore limb. Validation of the system was performed by comparing the data obtained from the videotape analysis with that obtained from the computerized system. Correlation coefficients between the data obtained from the two methods were found to be 0.92 for one observer, 0.84 for a second observer, and 0.88 with the mean of the two observers. An experimental study in which a group of rats was administered dorsal hemisection lesions of the spinal cord was also conducted. Animals in the lesion group took the same amount of time to cross the runway as the control animals, but made more footfalls per crossing and had longer durations per footfall. The studies validate the capacity of the computerized system to efficiently detect fine locomotory deficits, suggesting that it is a viable tool for the evaluation of neurological dysfunctions in experimental rats.

Behavioral characteristics of defense and vigilance reactions elicited by electrical stimulation of the hypothalamus in rabbits.

An automated tracking system was used to assess the behavioral changes elicited by electrical stimulation of the hypothalamic sites that yield the cardiorespiratory components of defense reaction and vigilance reaction in rabbits. Electrical stimulation of the hypothalamic defense area (HDA) at intensities near threshold led to cessation of body movements coupled with head movements suggesting increased attention to the environment. HDA stimulation at higher intensities evoked agitated running and hindlimb thumping; the amount of running was proportional to stimulus intensity. Electrical stimulation of the hypothalamic vigilance area (HVA) at intensities near threshold elicited orienting behaviors that were similar to those elicited by stimulating the HDA at low suprathreshold current intensities. Stimulation of the hypothalamic vigilance area (HVA) at higher intensities elicited phasic immobility, increased extensor muscle tension, and head tremor. The behavioral changes elicited by HDA and HVA stimulation were accompanied by pupil dilation and exophthalmos.

The role of amygdaloid central nucleus in the retention of differential pavlovian conditioning of bradycardia in rabbits.

The present study examined the role of the amygdaloid central nucleus (ACE) in the retention of differential pavlovian conditioning of bradycardia in rabbits. Electrodes were implanted bilaterally in ACE or in control sites just dorsal and rostral to ACE. 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. Subsequent electrolytic lesions abolished the heart rate (HR) conditioned response (CR), yet had no effect on HR orienting response, unconditioned response, or baseline. In a follow-up experiment, corneoretinal potential (CRP) and HR were recorded. Bilateral ACE lesions profoundly attenuated or abolished the HR CR without abolishing CRP CRs. The major finding of this study is that bilateral lesions of ACE selectively attenuate the HR CR while not necessarily abolishing other CRs.

Sinoaortic denervation does not prevent differential Pavlovian conditioning of bradycardia in rabbits.

Recent findings suggest that descending projections from the amygdaloid central nucleus (ACE) to the nucleus of the solitary tract (NTS) may modulate the baroreceptor reflex and thereby facilitate the expression of the bradycardiac conditioned response (CR) in rabbits. The purpose of the present study was to examine the role of the afferent limb of the baroreceptor reflex in differential Pavlovian conditioning of bradycardia in rabbits. Animals received either aortic denervation, sinoaortic denervation or sham denervation. After recovery from surgery, animals received one differential Pavlovian conditioning session per day over the next 6 days. Sinoaortic denervation abolished the baroreceptor reflex as assessed by intravenous injections of phenylephrine. In addition, sinoaortic denervation increased baseline heart rate (HR), altered the topography of the HR unconditioned response, but did not abolish the HR orienting response or prevent the acquisition of bradycardiac CRs. The findings of the present study suggest that afferent barosensory input is necessary for the expression of the HR CR in rabbits. However, descending ACE projections may still play a role in the HR CR by directly affecting NTS neurons.

Afferents to the central nucleus of the amygdala and functional subdivisions of the periaqueductal gray: neuroanatomical substrates for affective behavior.

Evidence suggests the periaqueductal gray (PAG) is involved in the integration of behavioral and autonomic components of affective behavior. Our laboratory has shown that electrical stimulation of the ventrolateral periaqueductal gray (vl PAG) versus the dorsolateral periaqueductal gray (dl PAG), in the rabbit, elicits two distinct behavioral/cardiorespiratory response patterns. Furthermore, evidence suggests that the amygdaloid central nucleus (ACe) may influence cardiovascular activity during emotional states. The purpose of this study was to delineate the topography and determine the origin of forebrain projections to the PAG and the ACe, as well as commonalties and differences in the pattern of afferents. Examination of common afferents may lend insights into their function as components of a forebrain system regulating autonomic activity during emotional states. Separate retrograde tracers were injected into functional subdivisions of the PAG and the ACe in rabbits. PAG injections led to neuronal labeling in numerous cortical regions including the ipsilateral medial prefrontal and insular cortices. Additionally, bilateral labeling was observed in several hypothalamic nuclei including the paraventricular nucleus, the dorsomedial nucleus and the ventromedial nucleus as well as the region lateral to the descending column of the fornix. Sparse labeling was also seen in various basal forebrain regions, thalamic nuclei and amygdaloid nuclei. Many of these regions were also labeled following injections in the ACe. Although double-labeled cells were never observed, afferents to the ACe were often proximal to PAG afferents. Implications of these findings are discussed in terms of two functionally distinct behavioral/cardiovascular response patterns.

Electrolytic and ibotenic acid lesions of the medial subnucleus of the medial geniculate prevent the acquisition of classically conditioned heart rate to a single acoustic stimulus in rabbits.

The present study examined the role of the medial subnucleus of the medial geniculate (mMG) in classical heart rate (HR) conditioning to a single acoustic conditioned stimulus (CS) in rabbits. Previous electrophysiological and neuroanatomical studies have implicated the mMG as a potential site of plasticity in forming the HR conditioned response (CR) to acoustic stimuli. In addition, several studies have found that bilateral lesions of the rabbit mMG prevent differential conditioning to acoustic stimuli, however animals still exhibit a significant bradycardiac response to the tones. In order to determine if the residual bradycardia seen in differential conditioning studies was due to learned responses or non-associative effects, rabbits with either bilateral electrolytic or ibotenic acid lesions of mMG, and animals with lesions outside of mMG (lesion control), were subjected to one session of single tone Pavlovian conditioning. In this paradigm, an acoustic CS was paired with an aversive unconditioned stimulus (US) in the conditioning groups, and in a pseudoconditioning group the CS and US were unpaired. The results suggest that bilateral lesions of mMG prevent the acquisition of the HR CR relative to control lesioned animals. The results also suggest that cells intrinsic to mMG are involved in conditioned bradycardia to a single tone, as well as in the discrimination between two tones, as reported previously. The lesion effects upon CRs are discussed with respect to other areas in the acoustic thalamus.

The role of the medial geniculate region in differential Pavlovian conditioning of bradycardia in rabbits.

The present study examined the role of the medial geniculate region (MGN) in differential Pavlovian conditioning of bradycardia and corneo-retinal potential (CRP) to acoustic stimuli in rabbits. Injections of horseradish peroxidase into the amygdala central nucleus, an area that mediates the bradycardia-conditioned response (CR), produced cell body and fiber labeling at the ventral and medial borders of the MGN. Then, bilateral electrolytic lesions were made at the medial border of the MGN or in control sites dorsal and/or rostral to the MGN. Ten days after surgery, lesioned and unoperated control animals were subjected to 7 days of differential Pavlovian conditioning. In the control lesion and unoperated groups, the CS+ consistently elicited larger bradycardia responses than the CS-. However, animals with bilateral lesions in the medial MGN did not demonstrate differential bradycardia CRs. Bradycardia response magnitude in MGN lesion animals was not affected. Evidence of CRP differential conditioning was present in each group. The present findings suggest that a region just medial to the MGN is involved in bradycardia differential conditioning in rabbits. The fact that bradycardia responses were still present after medial MGN lesions suggests that other auditory regions may also be involved in the mediation of the bradycardia CR.

Involvement of cortical and thalamic auditory regions in retention of differential bradycardiac conditioning to acoustic conditioned stimuli in rabbits.

Our previous findings indicate that lesions in the medial division of the medial geniculate nucleus (mMGN) prevent the acquisition of differential conditioning of bradycardia to acoustic stimuli in rabbits. In the present experiment, the effect of lesions in mMGN on retention of differential bradycardiac conditioning was examined. In addition, the possible involvement of auditory cortex in differential conditioning was investigated. Electrodes were chronically implanted in mMGN, the ventral division of the medial geniculate nucleus (vMGN), or auditory cortex. After 7 days of recovery, animals received one differential Pavlovian conditioning session. At the end of the session, lesions were produced through the implanted electrodes. All animals demonstrated differential bradycardiac conditioning during the prelesion session. Animals with vMGN lesions also demonstrated differential conditioning during the postlesion session. However, mMGN and auditory cortex lesion animals failed to demonstrate differential conditioning during the postlesion session due to an increased response magnitude to the unpaired tone (CS-). These data support the hypothesis that mMGN plays a role in differential conditioning of bradycardia to tonal stimuli. In addition, these findings suggest that a possible corticothalamic pathway may be involved in the inhibition of the response to the CS-.

Ibotenic acid lesions in the medial geniculate region prevent the acquisition of differential Pavlovian conditioning of bradycardia to acoustic stimuli in rabbits.

The present study examined the effect of ibotenic acid lesions in the medial portion of the medial geniculate nucleus (mMGN) on differential heart rate (HR) conditioning to acoustic stimuli in rabbits. Lesions in mMGN prevented the acquisition of differential HR conditioned responses but not bradycardiac responses to the conditioned stimuli. The data suggest that cells in this region play an important role in the discriminative component of HR conditioning.

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.

Electrophysiological evidence for hypothalamic defense area input to cells in the lateral tegmental field of the medulla of rabbits.

Single cell recordings were made from neurons in the lateral tegmental field of the medulla (LTFM) during electrical stimulation of the hypothalamic defense area (HDA) of the rabbit. Fifty-four cells were inhibited by HDA stimulation; 23 of these cells received barosensory input. Twenty-two LTFM cells showed an increase in firing rate during HDA stimulation; 10 of these cells received barosensory input. The results of this study provide evidence that the hypothalamic defense area makes functional connections with cardiovascular-influenced neurons in the LTFM.

Immunohistochemical expression of the c-Fos protein in the spinal trigeminal nucleus following presentation of a corneal airpuff stimulus.

This study examined the expression of the c-Fos protein in the rabbit's central nervous system to determine which areas are activated by the presentation of a corneal airpuff. Previous work has shown that pairing a corneal airpuff unconditioned stimulus (US) with a tone conditioned stimulus (CS) produces reliable heart rate (HR) conditioning. In this study restrained awake rabbits received 100 corneal airpuffs. Brains were then processed immunohistochemically for the c-Fos protein. In animals that received the airpuff the ventral portion of the ipsilateral spinal trigeminal subnucleus caudalis (SVc) and interpolaris (SVi), and the dorsal raphe nucleus exhibited a greater number of c-Fos labeled cells compared to control animals. Another group of animals was given microinjections of WGA-HRP in the medial nucleus of the medial geniculate (mMG) to determine if this critical auditory area of the HR conditioning circuitry receives projections from SVc and SVi. These injections produced retrograde labeling in the same areas of SVc and SVi activated by the airpuff. Thus, a corneal airpuff activates neurons in SVc and SVi which could then activate neurons in mMG. This provides additional evidence that CS and US information converge in mMG.

Simultaneous single unit recording in the medial nucleus of the medial geniculate nucleus and amygdaloid central nucleus throughout habituation, acquisition, and extinction of the rabbit's classically conditioned heart rate.

The present study examined single neuron activity in the medial nucleus of the medial geniculate (mMG) and amygdaloid central nucleus (ACe) simultaneously across several phases of differential heart rate conditioning (habituation, acquisition, and extinction). Within the same animals, the magnitude of mMG and ACe unit responses to two tone conditioned stimuli (CS) exhibited habituation, differential acquisition, and extinction. Neurons in each area developed a differential response latency to the CSs during acquisition, suggesting that mMG and ACe may be involved in changes of synaptic efficacy. Units in both areas rapidly developed a differential response magnitude to the CSs (< 6 acquisition trials), however, mMG units responded to the CSs with a shorter latency than ACe units across all phases of training. This suggests that unlearned and learned CS information may access mMG before ACe. These results are consistent with the notion that conditioning-induced plasticity which occurs in mMG may influence the conditioning-induced plasticity that occurs further downstream in the amygdala.

Recovery of vibrissae-dependent behavioral responses following barrelfield damage is not dependent upon the remaining somatosensory cortical tissue.

Previous work has demonstrated that damage to the primary somatosensory cortex produces substantial deficits in a vibrissal cue-dependent discrimination task which recover gradually over the course of post-injury testing. The present study was designed to evaluate the possible site(s) and mechanisms underlying behavioral recovery in this task. Wistar rats were trained under red light in a T-maze to produce ipsilateral turns depending upon the presence of a vibrissal cue. Animals were then subjected to photothrombotic infarctions of either the ipsilateral medial parietal cortex, the ipsilateral primary and secondary somatosensory cortex (SI/SII), the primary and secondary somatosensory cortices of both hemispheres (bilateral SI/SII) or sham surgical procedures. Behavioral testing resumed 24 hours following surgery, and continued for a total of 60 days. The performance of animals with infarcts restricted to the medial parietal cortex did not differ from that of sham-operated controls. Animals with either unilateral or bilateral SI/SII infarcts exhibited a significant decrease in percent correct responding as compared to shams and rats in the medial parietal group. These deficits recovered to pre-infarct levels over approximately 35-40 days. This rate of recovery was slower than the recovery exhibited by animals given medial parietal infarcts which spared the primary barrelfield cortex. The results of this study suggest that neither the contralateral somatosensory cortex nor the vibrissal representation within ipsilateral SII cortex play a critical role in the recovery process. The possibility that subcortical structures underlie the deficits observed following barrelfield cortical damage is discussed.

Modulation of neuronal firing in the medullary solitary complex by electrical stimulation of the hypothalamic defense and vigilance areas in rabbits.

The present study sought to establish functional connections between two regions in the hypothalamus associated with the cardiorespiratory concomitants of affective behavior, and neurons in the dorsal medulla thought to be involved in the mediation of the baroreceptor reflex. Single cell recordings were made in the solitary complex of the medulla (nucleus of the tractus solitarius and dorsal vagus nucleus) of anesthetized rabbits. An attempt was made to modulate the activity of these neurons by electrically stimulating two hypothalamic sites: the hypothalamic defense area (HDA) and the hypothalamic vigilance area (HVA). Responses of solitary complex neurons to a bolus injection of phenylephrine and an injection of physiological saline in a blind sac preparation were assessed in order to test for baroreceptor input. Electrical stimulation of the HDA or the HVA was found to decrease the firing rate of most solitary complex neurons that responded to hypothalamic stimulation. The cells that did show an increase in firing rate were responding to HVA stimulation. Ninety-two percent of the neurons in the solitary complex that responded to HDA or HVA stimulation were also affected by baroreceptor activation. The connections between the HDA, HVA and the solitary complex may account, in part, for the distinctive patterns of cardiorespiratory responses observed when stimulating these two hypothalamic regions.

Auditory cortex lesions prevent the extinction of Pavlovian differential heart rate conditioning to tonal stimuli in rabbits.

The present study examined the role of the auditory cortex in the extinction of differentially conditioned heart rate (HR) responses in rabbits. Lesions were placed bilaterally in either the auditory cortex or the visual cortex. Three days after recovery from surgery, the auditory cortex lesion group and the visual cortex lesion control group were habituated to the tonal conditioned stimuli (CSs), and then given 2 days of Pavlovian differential conditioning (60 trials per day) in which one tone (CS+) was always paired with the unconditioned stimulus and another tone (CS-) was never paired with the unconditioned stimulus. Animals that had demonstrated reliable differential conditioning (CS+ response at least 5 beats greater than the CS- response) were placed on an extinction schedule for 7 days. The extinction schedule was identical to the differential conditioning schedule with the exception that shock never followed the CS+. The results of the study indicate that auditory cortex lesions prevent the extinction of differential bradycardia conditioned responses (CRs) to tonal CSs. Whereas the bradycardia responses to the CS+ quickly extinguished in the group that had control lesions in the visual cortex, the auditory cortex lesion group continued to exhibit significantly larger bradycardiac HR CRs to the CS+ relative to the CS- during all 7 days of extinction. These results suggest that the animals in the auditory cortex lesioned group did not inhibit responses to a previously reinforced stimulus (i.e., CS+) as well as animals with control lesions in the visual cortex.

Anatomical and functional connections of neurons of the rostral medullary raphe of the rabbit.

Single cell recordings were made from neurons in the rostral medullary raphe (RMR) of the rabbit. The recording sites were ones that had been shown to yield pressor responses from electrical stimulation and by pressure injections of glutamate. Electrical stimulation of the intermediolateral (IML) region of the spinal cord led to antidromic activation of 12 of the 100 cells studied. Eleven of these cells were located in raphe pallidus or raphe magnus, and one cell was located in raphe obscurus. These findings were consistent with the results of horseradish peroxidase (HRP) histochemistry experiments. Injections of HRP into the IML led to heavy cell body labeling in raphe pallidus and raphe magnus, but sparse labeling in raphe obscurus. Cells in the RMR could be orthodromically activated by electrical stimulation of the putative defense area of the periaqueductal (PAG) but not by stimulation of putative defense areas in the hypothalamus. Most of these cells were located in raphe pallidus or raphe magnus. Similarly, HRP injections into raphe pallidus and raphe magnus led to heavy cell body labeling in the PAG but not the hypothalamus; no cell body labeling was found in the PAG when injections were made into raphe obscurus.