Changes in plasma corticosterone and cerebral biogenic amines and their catabolites during training and testing of mice in passive avoidance behavior

Dopamine modulates individual differences in avoidance behavior: A pharmacological, immunohistochemical, neurochemical and volumetric investigation

Avoidance behavior is a hallmark in pathological anxiety disorders and results in impairment of daily activities. Individual differences in avoidance responses are critical in determining vulnerability or resistance to anxiety disorders. Dopaminergic activation is implicated in the processing of avoidance responses; however, the mechanisms underlying these responses are unknown. In this sense, we used a preclinical model of avoidance behavior to investigate the possibility of an intrinsic differential dopaminergic pattern between good and poor performers. The specific goal was to assess the participation of dopamine (DA) through pharmacological manipulation, and we further evaluated the effects of systemic injections of the dopaminergic receptor type 1 (D1 antagonist - SCH23390) and dopaminergic receptor type 2 (D2 antagonist - sulpiride) antagonists in the good performers. Additionally, we evaluated the effects of intra-amygdala microinjection of a D1 antagonist (SCH23390) and a D2 antagonist (sulpiride) in good performers as well as intra-amygdala microinjection of a D1 agonist (SKF38393) and D2 agonist (quinpirole) in poor performers. Furthermore, we quantified the contents of dopamine and metabolites (3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA)) in the amygdala, evaluated the basal levels of tyrosine hydroxylase expression (catecholamine synthesis enzyme) and measured the volume of the substantia nigra, ventral tegmental area and locus coeruleus. Our results showed that it could be possible to convert animals from good to poor performers, and vice versa, by intra-amygdala (basolateral and central nucleus) injections of D1 receptor antagonists in good performers or D2 receptor agonists in poor performers. Additionally, the good performers had lower levels of DOPAC and HVA in the amygdala, an increase in the total volume of the amygdala (AMG), substantia nigra (SN), ventral tegmental area (VTA) and locus coeruleus (LC), and an increase in the number of tyrosine hydroxylase-positive cells in SN, VTA and LC, which positively correlates with the avoidance behavior. Taken together, our data show evidence for a dopaminergic signature of avoidance performers, emphasizing the role of distinct dopaminergic receptors in individual differences in avoidance behavior based on pharmacological, immunohistochemical, neurochemical and volumetric analyses. Our findings provide a better understanding of the role of the dopaminergic system in the execution of avoidance behavior.

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The role of dopamine in individual differences in avoidance behavior.

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Dopamine modulates avoidance behavior.

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Dopaminergic evidence of individual difference in avoidance behavior.

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Good and poor avoiders distinction based on dopaminergic signature.

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Dopaminergic signature of avoidance performers: poor versus good avoiders.

Experimental manipulations blunt time-induced changes in brain monoamine levels and completely reverse stress, but not Pb+/-stress-related modifications to these trajectories

This study sought to further understand how environmental conditions influence the outcomes of early developmental insults. It compared changes in monoamine levels in frontal cortex, nucleus accumbens and striatum of male and female Long-Evans rat offspring subjected to maternal Pb exposure (0, 50 or 150ppm in drinking water from 2 months pre-breeding until pup weaning)+/-prenatal (PS) (restraint on GD16-17) or PS+offspring stress (OS; three variable stress challenges to young adults) determined at 2 months of age and at 6 months of age in littermates subsequently exposed either to experimental manipulations (EM: daily handling and performance on an operant fixed interval (FI) schedule of food reward), or to no experience (NEM; time alone). Time alone (NEM conditions), even in normal (control) animals, modified the trajectory of neurochemical changes between 2 and 6 months across brain regions and monoamines. EM significantly modified the NEM trajectories, and except NE and striatal DA, which increased, blunted the changes in monoamine levels that occurred over time alone. Pb+/-stress modified the trajectory of monoamine changes in both EM and NEM conditions, but these predominated under NEM conditions. Stress-associated modifications, occurring mainly with NEM OS groups, were fully reversed by EM procedures, while reversals of Pb+/-stress-associated modifications occurred primarily in nucleus accumbens, a region critical to mediation of FI response rates. These results extend the known environmental conditions that modify developmental Pb+/-stress insults, which is critical to ultimately understanding whether early insults lead to adaptive or maladaptive behavior and to devising behavioral therapeutic strategies. That time alone and a set of EM conditions typically used as outcome measures in intervention studies can themselves invoke neurochemical changes, moreover, has significant implications for experimental design of such studies.

Cortisol and DHEA-S are associated with startle potentiation during aversive conditioning in humans

RATIONALE

Fear conditioning reliably increases the startle reflex and stress hormones, yet very little is known about the effect of stress hormones on fear-potentiated startle. Cortisol and the sulfate ester of dehydroepiandrosterone (DHEA-S) are involved in stress and anxiety. Evidence suggests that low cortisol/DHEA-S ratio has a buffering effect on stress and anxiety in preclinical and clinical studies, suggesting that there may be a relationship between fear-potentiated startle and cortisol and DHEA-S activity.

OBJECTIVE

The aim of the study was to examine whether there is a relationship between cortisol/DHEA-S ratio and fear-potentiated startle.

METHODS

Thirty healthy subjects participated in a differential aversive conditioning experiment during which one of two stimuli (CS+) was paired with a shock, and the other was not (CS-). Conditioned responses were assessed with the startle reflex, defined as startle potentiation during CS+ compared to CS-. DHEA-S and cortisol levels were assayed from blood samples collected in both a baseline and an aversive conditioning session. Subjective state anxiety, arousal, and valence were assessed at various times during testing.

RESULTS

Fear-potentiated startle was larger in individuals with high compared to low cortisol/DHEA-S ratio. Multiple regression analyses revealed that fear-potentiated startle was positively associated with cortisol and negatively associated with DHEA-S. There was no significant correlation between DHEA-S and cortisol levels.

CONCLUSION

These data suggest that cortisol and DHEA-S are involved in fear conditioning.

Dopamine and noradrenaline efflux in the rat prefrontal cortex after classical aversive conditioning to an auditory cue

We used bilateral microdialysis in the medial prefrontal cortex (PFC) of awake, freely moving rats to study aversive conditioning to an auditory cue in the controlled environment of the Skinner box. The presentation of the explicit conditioned stimuli (CS), previously associated with foot shocks, caused increased dopamine (DA) and noradrenaline (NA) efflux. This conditioned response was dependent on the immediate pairing of the two stimuli; in the pseudoconditioned group that received an equal number of both stimuli, but in an unpaired fashion, no conditioned increases in efflux were observed.

Engagement in a non-escape (displacement) behavior elicits a selective and lateralized suppression of frontal cortical dopaminergic utilization in stress

Although the preferential activation of the prefrontal cortical (PFC) dopaminergic system is generally observed in stress, limited exceptions to this have been observed. Certain non-escape behaviors have been demonstrated to attenuate physiological indices of stress (e.g., coping or displacement responses). One well-characterized non-escape behavior observed in stress is chewing, or gnawing, of inedible objects. Engagement in this behavior attenuates stress-related activation of the hypothalamopituitary-adrenal axis, in a variety of species. We examined the degree to which engagement in this non-escape behavior modulates stressor-induced activation of the PFC dopamine (DA) system. Rats and mice were exposed to a brightly lit novel environment (novelty stress) in the presence or absence of inedible objects. Following novelty exposure, various dopaminergic terminal fields were collected and dopamine and its major catabolite, DOPAC, were measured using HPLC with electrochemical detection. DOPAC/DA ratios were calculated as an index of DA utilization. In some cases serotonin (5-HT) and its major catabolite, 5-HIAA, were also measured. In animals that did not chew, novelty exposure elicited significant increases in DOPAC/DA levels within PFC, nucleus accumbens (shell and core subdivisions), and striatum (relative to quiet-controls). DOPAC/DA responses were greater in the right PFC than in the left PFC. Animals that chewed displayed significantly lower DOPAC/DA responses in PFC, but not other dopaminergic terminal fields. This effect of chewing was always observed in the right PFC and less consistently in the left PFC. Chewing did not alter novelty-induced increases in PFC 5-HIAA/5-HT responses. Thus, engagement in this non-escape behavior elicits a neuroanatomically and neurochemically specific attenuation of the PFC DA response in stress. Given the pivotal role of the PFC in certain cognitive and affective processes, behavioral regulation of PFC DA utilization may modulate cognitive and/or affective function in stress.

Serotonin as a regulator of hypothalamic-pituitary-interrenal activity in teleost fish

Evidence for the presence of a serotonin1A (5-HT1A) receptor subtype in the salmonid fish brain has recently been presented. In the present study the potent 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) was tested for its effect on plasma cortisol concentrations in rainbow trout (Oncorhynchus mykiss). Blood was sampled and 8-OH-DPAT administered through a catheter in the dorsal aorta. Thirty minutes after the injection of 40 microg of 8-OH-DPAT/kg, plasma cortisol levels had increased from 12 to 149 ng/ml, whereupon they fell, reaching baseline levels after 4 h. The effect of 1-40 microg 8-OH-DPAT/kg on plasma cortisol concentrations was dose-dependent. The results lends further support to the hypothesis that the brain serotonergic system plays a key role in integrating autonomic, behavioral and neuroendocrine stress-responses in fish as well as mammals, suggesting that not only the structural and biochemical organization, but also the function of the serotonergic system has been conserved during vertebrate evolution.

Elicitation and reduction of fear: behavioural and neuroendocrine indices and brain induction of the immediate-early gene c-fos

The elicitation and reduction of fear were indexed with fear-potentiated startle and corticosterone release and induction of the immediate-early gene c-fos as a marker of neural activity in male Sprague-Dawley rats. Conditioning consisted of pairing one stimulus with footshock, which was withheld when the conditioned stimulus was preceded by a different modality stimulus, the conditioned inhibitor. On the test day, approximately 60% of the rats were used for c-fos in situ hybridization, and were presented with either the conditioned stimulus alone, the conditioned inhibitor alone, a compound of the two stimuli, or no stimuli, and killed 30 min following the presentation of 10 such stimuli. The remaining rats were tested with the fear-potentiated startle paradigm. Rats displayed reliable fear-potentiated startle and corticosterone release to the conditioned stimulus, and both measures were reduced when the conditioned stimulus was preceded by the conditioned inhibitor. The ventral bed nucleus of the stria terminalis, septohypothalamic nucleus, some tegmental nuclei, and the locus coeruleus had particularly high c-fos induction in rats that received the conditioned inhibitor, providing one of the first functional indication that these nuclei might be important in behavioural or endocrine inhibition. Conditioning specific c-fos induction in the three groups that received a stimulus on the test day was observed in many hypothalamic areas, the medial geniculate body and the central gray, structures previously involved in fear and anxiety. The cingulate, infralimbic and perirhinal cortex, nucleus accumbens, lateral septum, dorsal endopiriform nucleus, and ventral tegmental area had higher c-fos induction in rats presented with the fearful conditioned stimulus, confirming previous studies. The amygdala and hippocampus of conditioned rats did not show higher c-fos induction than in rats repeatedly exposed to the context. Many regions displayed c-fos messenger RNA induction in the control condition, suggesting that processes other than fear and anxiety participate in c-fos induction.

Monoamines and their metabolites in the amphibian (Ambystoma tigrinum) brain: Quantitative changes during metamorphosis and captivity

1. Monoamine neurotransmitters (epinephrine, norepinephrine, dopamine, serotonin and some of their metabolites (DOPEG, MHPG, DOPAC, 5-HIAA) were measured by HPLC in extracts from telencephalon (TEL) and diencephalon-midbrain (DM) before, during at the end of metamorphosis. 2. During metamorphosis MHPG increased and 5-HIAA decreased in TEL and DM while DOPEG decreased only in DM. 3. Monoamine levels were greater in the TEL and a larger increase in MHPG occurred there. 4. Captivity without metamorphosis also caused a significant depression of 5-HIAA in TEL and depression of DOPEG, MHPG and DOPAC in DM.

Benzodiazepine receptor ligand influences on acquisition: suggestion of an endogenous modulatory mechanism mediated by benzodiazepine receptors

In rats, pretraining ip administration of the central benzodiazepine receptor antagonist, flumazenil (5.0 mg/kg), or of the inverse agonist, n-butyl-beta-carboline-3-carboxylate (BCCB) (0.2 or 0.5 mg/kg), facilitated retention of a step-down inhibitory avoidance task; the central agonists, clonazepam and diazepam (0.4 or 1.0 mg/kg), had an opposite effect, and the peripheral agonist, 4'-chlordiazepam (1.25 or 6.25 mg/kg), was without effect. Pre- but not post-training flumazenil (2.0 mg/kg) blocked the effect of BCCB (0.5 mg/kg), clonazepam (1.0 mg/kg), or diazepam (1.0 mg/kg) given also pretraining. The post-training administration of all of these drugs had no effect on retention of the avoidance task. Flumazenil (5.0 mg/kg) and BCCB (0.5 mg/kg), given before training, enhanced retention test performance of habituation to a buzzer but not of habituation to an open field. In the three tasks studied, none of the drugs used had any appreciable effect on training session parameters. These results suggest that there is an endogenous mechanism mediated by benzodiazepine agonists, sensitive to inverse agonists, that normally down-regulates acquisition of certain behaviors; this mechanism becomes activated only when the tasks involve or occur with a certain degree of stress or anxiety (i.e., inhibitory avoidance or habituation to the buzzer) and not in less stressful or anxiogenic tasks (i.e., habituation to an open field).

Behavioral and biochemical changes monitored in two inbred strains of mice during exploration of an unfamiliar environment

Mice of the C57BL/6 (C57) and DBA/2 (DBA) strains were introduced individually in an unfamiliar environment (a large cage where food, water and sawdust had been removed). Over a 90-min period of observation, both strains presented a time-dependent decrease of locomotion and leaning and an increase of grooming. C57 mice were characterized by more cage cover climbing than DBA mice during the first 15-min stay in the new cage and by a significant decrease of this behavior after 90 min. During the first 60 min in the new environment, the DBA mice were less active than C57 mice, and both strains presented a significant increase of immobility after 90 min of test. After 30 min in the test situation, C57 presented a larger increase of plasma corticosterone levels than DBA mice. The plasma corticosterone levels were back to control values after 60 min of test in mice of the C57 strain and after 90 min in the DBA strain. Finally, both C57 and DBA mice presented a significant increase of homovanillic acid concentrations in the nucleus accumbens, but not in the striatum at 30, 60 and 90 min of testing. These results are discussed in terms of the possible involvement of mesolimbic dopaminergic system in mouse behavioral responses to an unfamiliar environment and of possible habituation to the stressful properties of this experience.

Virus infection as a stressor: influenza virus elevates plasma concentrations of corticosterone, and brain concentrations of MHPG and tryptophan

Balb/c mice were infected with influenza virus PR8 (H1N1) by the intranasal route. At various subsequent times, brain samples were examined for their content of catecholamine and indoleamine metabolites, and plasma corticosterone was measured. Virus infection was associated with a progressive loss of body and thymus weights, and an increase in plasma corticosterone. Spleen weight initially increased then decreased. There were also increases in the cerebral content of free tryptophan throughout the brain, and of MHPG, a major catabolite of norepinephrine, especially prominent in the hypothalamus. Thus influenza virus can be regarded as a stressor because, like behavioral stressors, it activates the hypothalamic-pituitary-adrenal axis, and increases cerebral concentrations of tryptophan and norepinephrine catabolites. These changes resemble those observed following administration of sheep red blood cells and Newcastle disease virus, noninfectious activators of the immune system, suggesting that noradrenergic and HPA activation are common concomitants of antigenic stimulation. The mediator of these effects may be interleukin-1 released by activated macrophages. It should be noted that animals infected with viruses can be expected to exhibit stress-like endocrine and neurochemical changes.

Stress-related activation of cerebral dopaminergic systems

The changes in dopamine catabolites in various regions of mouse brain have been studied following a variety of behavioral treatments. In confirmation of the results of many others, we find that treatments such as footshock or restraint result in a pronounced activation of dopaminergic systems in the prefrontal cortex, as determined by increases in the content of DOPAC (3,4-dihydroxyphenylacetic acid). However, we also find small but statistically significant increases of DOPAC in the hypothalamus and brain stem even with mild treatments. With restraint and more intense footshock we observe increases of DOPAC in all regions studied, including nucleus accumbens, olfactory tubercle, amygdala, and the striatum. Thus in contrast to previous reports, we find that the DA response in stress is global like that of norepinephrine [as determined by increases of 3-methoxy,4-hydroxyphenylethyleneglycol, (MHPG)], and not specific to the prefrontal cortex. The activation of prefrontal cortex DA metabolism is associated with an activation of the synthetic enzyme tyrosine hydroxylase. The response pattern of catecholamine metabolites is similar following a variety of stressors, including conditioned footshock, training with one footshock in passive avoidance behavior, performance of passive avoidance behavior, and even following exposure to an apparatus in which mice have been shocked previously. Injection of mice with Newcastle disease virus increases plasma corticosterone, and DOPAC and MHPG in the hypothalamus and brain stem, but not the prefrontal cortex. Thus a virus infection can be considered a stressor. Furthermore, intracerebroventricular (ICV) injection of corticotropin-releasing factor (CRF) produces stresslike increases in DOPAC and MHPG concentrations, suggesting that the release of CRF in the brain during stress may mediate the changes in catecholamine metabolism.

Brain regional and adrenal monoamine concentrations and behavioral responses to stress in alcohol-preferring AA and alcohol-avoiding ANA rats

The concentrations of monoamines, precursors and metabolites in various brain regions and the levels of catecholamines in the adrenal glands were determined from naive rats of the AA and ANA lines, and from ones immediately after an escapable shock test. The brain determinations were made with a new step-gradient ion-pair elution method on a reversed phase column and coulometric detection. Several significant differences were observed in the amine concentrations, largely confirming and extending the findings made before the genetic revitalization of the lines: in particular, the AAs, unlike other alcohol-preferring rodents, had higher 5-hydroxytryptamine concentrations. The AA rats tended to have smaller changes than the ANAs in brain aminergic systems and had significantly less change in adrenal epinephrine and dopamine levels after the shock test. The AAs were consistently found to be less active than ANAs in this shock test and in a warm-water swim test, but whether this was a cause or an effect of their brain and adrenal changes could not be determined. Our behavioral results might suggest a reduced reaction of the alcohol-preferring rats to aversive stimulation.

Stress-related changes in cerebral catecholamine and indoleamine metabolism: lack of effect of adrenalectomy and corticosterone

The concentrations of catecholamine and indoleamine metabolites were measured in intact and adrenalectomized mice to determine whether adrenal hormones mediate or modulate the stress-induced responses. Thirty minutes of footshock resulted in significant increases of the ratios of the dopamine (DA) catabolite, dihydroxyphenylacetic acid (DOPAC), to DA in prefrontal cortex, nucleus accumbens, striatum, hypothalamus, and brainstem, and of homovanillic (HVA)/DA ratios in nucleus accumbens, striatum, amygdala, and hypothalamus. Ratios of 3-methoxy-4-hydroxyphenylethyleneglycol to norepinephrine (NE) were also increased in prefrontal cortex, nucleus accumbens, septum, amygdala, hypothalamus, hippocampus, and brainstem. The concentration of NE was decreased in amygdala. 5-Hydroxyindoleacetic acid (5-HIAA)/5-hydroxytryptamine (5-HT, serotonin) ratios and free tryptophan were also increased in every brain region. Very similar data were obtained from mice restrained for 30 min. Adrenalectomy resulted in increased HVA/DA ratios in prefrontal cortex and striatum, and 5-HIAA/5-HT in septum. The stress-related changes were largely similar in adrenalectomized mice. Significant interactions between adrenalectomy and footshock treatment occurred in prefrontal cortical DOPAC/DA and hypothalamic NE which was depleted only in adrenalectomized mice, suggesting tendencies for these measures to be more responsive in adrenalectomized mice. Corticosterone administration (0.5-2.0 mg/kg s.c.) which resulted in plasma concentrations in the physiological range did not alter the concentrations of the cerebral metabolites measured in any region. We conclude that adrenal hormones do not mediate cerebral catecholamine or indoleamine metabolism in stress, although adrenalectomy may affect HVA and 5-HIAA metabolism, and there was a tendency for catecholamines to be more sensitive to stress in adrenalectomized animals.

Induction of cortical cholinergic hypofunction and memory retention deficits through intracortical AF64A infusions

Ethylcholine mustard aziridinium ion (AF64A), an irreversible inhibitor of high-affinity choline uptake on cholinergic nerve terminals, appears to selectively decrease presynaptic cholinergic markers after intracerebral injection. To restrict AF64A's action to cholinergic terminals within the frontoparietal (FP) cortex, the present study utilized multiple-site cortical infusions of the agent. Following an extensive histological analysis, a dose of 1 nmol AF64A/1 microliter was selected for determining AF64A's effects on acetylcholinesterase (AChE) staining, cortical cholinergic/non-cholinergic markers, and passive avoidance behavior. Adult rats given two infusions of AF64A into the right FP cortex had reduced AChE staining throughout 75% of the ipsilateral FP cortex at 10 days following infusion, thus suggesting an extensive cortical diffusion of the agent; minimal non-specific damage was seen (totalling only 4% of the ipsilateral FP cortex for both infusion sites) and no effects on AChE staining were observed in the striatum or hippocampus. Three weeks after bilateral AF64A infusions into the FP cortex (two injections on each side), significant frontal cortex deficits were observed in high-affinity choline uptake, acetylcholine synthesis, acetylcholine release, and hemicholinium-3 binding compared to vehicle-infused controls. However, choline acetyltransferase activity within the anterior cortex did not appear to be consistently affected by AF64A infusion. Cortical glutamic acid decarboxylase activity, as well as cortical monoaminergic markers, and neuropeptide levels were also unaffected. Moreover, animals that received bilateral AF64A infusions and were tested two weeks afterwards showed marked memory retention deficits during both the 24-h and 48-h postshock trials of passive avoidance testing. These results indicate that cortical AF64A infusion induces a specific, long-term cholinergic hypofunction of presynaptic markers within the cortex, resulting in a significant long-term memory impairment. Since the primary cholinergic innervation to the FP cortex, originating in the nucleus basalis of Meynert, appears to become dysfunctional (but not totally degenerative) in Alzheimer's disease, cortical AF64A infusions may closely reflect this cholinergic dysfunction by 'functionally' eliminating cortical cholinergic terminals.

Changes in plasma and brain tryptophan and brain serotonin and 5-hydroxyindoleacetic acid after footshock stress

Brain concentrations of tryptophan, serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) and plasma amino acids were measured after 15 or 30 minutes of intermittent footshock. Footshock treatment significantly decreased the content of 5-HT in prefrontal cortex and hypothalamus, but not brainstem at 15 min, but the decreases were reversed by 30 min. 5-HIAA, the major catabolite of 5-HT, increased in prefrontal cortex after 15 min, and in prefrontal cortex and hypothalamus after 30 min footshock. 5-HIAA:5-HT ratios were increased at both timepoints in all three brain regions. Concomitant changes in the ratios of 3,4-dihydroxyphenylacetic acid (DOPAC) to dopamine and 3-methoxy,-4-hydroxyphenylethyleneglycol (MHPG) to norepinephrine were also observed. Brain concentrations of tryptophan increased progressively during the footshock in all three brain regions. Plasma concentrations of both tryptophan and tyrosine were also significantly increased, while those of histidine and lysine were decreased. It is possible that the stress-related changes in 5-HT metabolism are due to increased plasma tryptophan, in turn causing increased brain tryptophan and 5-HT synthesis. However, the transient decreases in 5-HT suggest a footshock-induced increase of 5-HT release, depleting existing stores of 5-HT, that are replenished by the increased systemic availability of tryptophan.

Long-term neuropathological and neurochemical effects of nucleus basalis lesions in the rat

The long-term effects of excitotoxic lesions in the nucleus basalis magnocellularis of the rat were found to mimic several neuropathological and chemical changes associated with Alzheimer's disease. Neuritic plaque-like structures, neurofibrillary changes, and neuronal atrophy or loss were observed in the frontoparietal cortex, hippocampus, amygdala, and entorhinal cortex 14 months after the lesions were made. Cholinergic markers in neocortex were reduced, while catecholamine and indoleamine metabolism was largely unaffected at this time. Bilateral lesions of the nucleus basalis magnocellularis increased somatostatin and neuropeptide Y in the cortex of the rat by at least 138 and 284 percent, respectively, suggesting a functional interaction between cholinergic and peptidergic neurons that may differ from that in Alzheimer's disease.

Thymic extracts and lymphokine-containing supernatant fluids stimulate the pituitary-adrenal axis, but not cerebral catecholamine or indoleamine metabolism

Injection of thymosin fraction 5 (TF5) or the supernatant fluid from concanavalin A-stimulated rat spleen cells into mice significantly increased plasma concentrations of corticosterone at 1 or 3 h. However, measurement of the concentrations of the catecholamines, norepinephrine and dopamine, the indoleamine, serotonin, and their major metabolites, in prefrontal cortex, parietal cortex, nucleus accumbens, septum, caudate-putamen, hypothalamus, and brain stem did not indicate any statistically significant changes. Nor was there any alteration in splenic norepinephrine content. These data suggest that TF5 and lymphokines do not cause a generalized stress response, but rather a selective activation of the pituitary-adrenal axis, probably by causing release of adrenocorticophic hormone from the pituitary. There was no evidence that the corticotropin-releasing activity of TF5 was related to an effect on hypothalamic biogenic amines. These data are discussed in the light of previous results obtained with lymphokine-containing supernatant fluids.