Roberta L. Moldow

Cocaine induced secretion of ACTH, beta-endorphin, and corticosterone

The effect of intraperitoneal administration of cocaine on the concentrations of hypothalamic corticotropin releasing factor like-immunoreactivity (CRF-LI), plasma ACTH, beta-endorphin, and corticosterone was investigated. Groups of rats were injected with 20 mg/kg cocaine HCI or 0.9% NaCl and then killed 0, 10, 20, 30 or 60 minutes later. Hypothalamic CRF-LI, plasma ACTH, beta-endorphin, and corticosterone concentrations were determined by radioimmunoassay. A significant increase in plasma ACTH, beta-endorphin, and corticosterone concentrations was observed after cocaine administration. In contrast, cocaine had no significant effect on hypothalamic CRF-LI concentrations. Intravenous administration of 0.5 and 2.0 mg/kg cocaine to rats in which the endogenous release of CRF was blocked by chlorpromazine, morphine, and pentobarbital elicited a significant increase in plasma corticosterone concentrations. These results demonstrate that cocaine induces the release of ACTH, beta-endorphin, and corticosterone and suggest that this response is mediated at the pituitary level.

A stress-induced anxious state in male rats: Corticotropin-releasing hormone induces persistent changes in associative learning and startle reactivity

BACKGROUND Exposure to intense inescapable stressors induces a persistent anxious state in rats. The anxious state is evident as increased sensory reactivity and enhanced associative learning. METHODS We examine whether similar neurobehavioral changes are observed after intracerebroventricular (ICV) administration of corticotropin releasing hormone (CRH). Two behaviors were observed: acoustic startle responses (ASRs) and acquisition of the classically conditioned eyeblink response. Male Sprague-Dawley rats were administered ICV CRH either in a single dose (1.0 microg/rat) or in three doses each separated by 30 min. RESULTS Exaggerated ASRs were evident 2 hours after either CRH treatment; however, only the rats given three injections exhibited a persistently exaggerated ASR apparent 24 hours after CRH treatment. Rats administered three injections of CRH also exhibited faster acquisition of the eyeblink conditioned response beginning 24 hours after treatment. Yet, we did not find evidence for a persistent activation of the HPA-axis response; three CRH injections did not lead to elevated basal plasma corticosterone levels the following morning. CONCLUSIONS Repeated treatment with CRH over a 1.5-hour period models some of the behavioral changes observed after exposure to intense inescapable stressors.

Arachidonylethanolamide (AEA) activation of FOS proto-oncogene protein immunoreactivity in the rat brain.

It is thought that the physiological actions of endogenous cannabinoid arachidonylethanolamide (AEA), as well as exogenous cannabinoids such as Delta9-tetrahydrocannabinol (THC), are mediated by two subtypes of cannabinoid receptors, CB1 and CB2, which have recently been characterized. Injection of AEA leads to alterations in motor behavior and endocrine function. While these phenomena have been well characterized, the neuronal substrate of AEAs actions remains undetermined. In this study, FOS immunoreactivity (FOSir) was used to map rat brain nuclei that are responsive to a single intracerebroventricular injection of AEA. The results showed that FOSir was induced in several nuclei including the bed nucleus of the stria terminalis (BNST), paraventricular nucleus of the hypothalamus (PVN), central nucleus of the amygdala (Ce), periaqueductal gray area (PAG), dentate gyrus in the hippocampus (Dg), paraventricular nucleus of the thalamus (PVA), median preoptic nucleus (MnPO), periventricular nucleus (Pe), caudate putamen (CPU) and the ependymal lining of the ventricles. The pattern of activation identified correlates, in part, with the distribution of CB receptors. At the same time, a new subset of nuclei, without demonstrable CB receptors, have been shown to respond to an AEA challenge. Activation of these nuclei is consistent with the physiological effects of AEA. These findings provide valuable information on the response to AEA at the level of neuronal activation and provide the basis for a broader understanding of the possible role of CB receptors in the modulation of motor and endocrine function associated with the use of exogenous cannabinoids, such as marijuana.

Persistent Neuroendocrine Changes in Multiple Hormonal Axes after a Single or Repeated Stressor Exposures

Many researchers have studied acute responses to stress in animals and how they are modified by prior stressor exposure, but relatively few have examined whether responses to stressors might last for prolonged periods of time. We have previously demonstrated that trough plasma corticosterone levels in rats are elevated for three to five days after single or repeated exposures to mild restraint and inescapable tailshock. The current study measured other aspects of me adrenal axis, and activity in other neuroendocrine systems, 24 hours after one or three consecutive exposures to the same stress paradigm. The data indicated persistent activation of the adrenal axis and prolactin levels, whereas the thyroid and reproductive hormone axes were inhibited after either one or three stress sessions. These changes are remarkable in that one would have expected acute responses to even intense stressors to have ended within hours after the end of the stressor. It will be important to understand the interactions among these responding neuroendocrine systems and to know how long such persistent changes last. Finally, it will be critical to understand the relative contributions of neuroendocrine and psychological factors in maintaining these persistent neuroendocrine changes after exposure to intense stressors.

Facilitated acquisition of the classically conditioned eyeblink response in women taking oral contraceptives.

Although anecdotal reports suggest that associative learning processes are affected by menstrual phase, empirical evidence has been equivocal. Moreover, there is a dearth of research concerning fluctuations of artificial or exogenous female hormones on learning and memory. Therefore, in this preliminary study we assessed learning in women who take oral contraceptives and those who do not during the three phases of the menstrual cycle: early, middle, and later cycle. The behavioral assessment included short-trace eyeblink conditioning, acoustic startle reactivity, and a fine motor coordination task (grooved pegboard). Oral contraceptive users generally acquired the conditioned eyeblink response better than non-users. Similar enhancements were observed for fine motor coordination and startle responsiveness. Further research will need to distinguish whether the hormone influence is upon the associative processes or the sensory-motor pathways involved in nonassociative learning.

Circadian rhythm of corticotropin releasing factor-like immunoreactivity in rat hypothalamus.

Levels of hypothalamic corticotropin releasing factor-like immunoreactivity (CRF-LI) were measured by radioimmunoassay (RIA) over a 24 hour light-dark cycle and found to exhibit two peaks. One peak was detected at 1100 hr and a secondary smaller peak was found at 2000 hr. The trough between the two peaks was detected at 1700 hr which coincided with the peak in plasma corticosterone levels. The results are consistent with a decreased level of hypothalamic CRF-LI at 1700 hr reflecting an increased release of peptide followed successively by the release of ACTH and corticosterone.

Effects of the circadian rhythm of corticosteroids on leukocyte-endothelium interactions in the AM and PM.

Circadian rhythms are responsible for a number of key cycles within the body. In vivo microscopy was used to investigate the hypothesis that the circadian rhythm of corticosterone in rats produces different leukocyte-endothelium interactions throughout the day. The data indicate that corticosterone levels range from 12 ng/ml in the AM to 260 ng/ml in the PM. In contrast, the number of circulating polymorphonuclear leukocytes (PMNs) yields peak values in the AM (630 PMNs/microl) and trough values in the PM (262 PMNs/microl). During surgical stress there is a significant increase in the number of circulating PMNs in the PM but little change in the AM. Furthermore, there is significantly greater leukocyte-endothelium adhesion in the PM (5.2 cells/100 microm) than in the AM (2.9 cells/100 microm). Addition of the chemoattractant FMLP increased adhesion 125% in the AM but only 62% in PM. Both exogenous glucocorticoid supplementation for 2 weeks and bilateral adrenalectomy abolished the circadian rhythms of circulating PMNs, the number of sticking white blood cells and the initial stages of an acute inflammatory response. These findings suggest that the circadian rhythm of corticosterone alters leukocyte-endothelium interactions throughout the day.

Morphine Affects the Brain-Immune Axis by Modulating an Interleukin-1 Beta Dependent Pathway

In response to a pathological condition, cytokines, such as interleukin 1-beta (IL-lβ), are released and induce an immune response, i.e. inflammation. In association with the inflammatory response, however, the host often enters a catabolic state because these cytokines can also cause fever and loss of appetite.1,2 Through its central nervous system (CNS) effects, IL-lβ can also stimulate the hypothalamic-pituitary-adrenal (HPA) axis to produce ACTH and glucocorticoids, which are anti-inflammatory.3 In such a way, both the induction and progression of immune responses are highly regulated through the modulatory actions of cytokines on the CNS4 as well as on the immune system.5 It has, therefore, been suggested that the HPA axis may function as a feedback loop between the CNS and the immune system.6 This intricate interrelationship between the neuroendocrine and immune systems is schematically illustrated in Figure 1.

Stress interacts with peripheral cholinesterase inhibitors to cause central nervous system effects

Pyridostigmine bromide (PB), a peripheral cholinesterase inhibitor, has been shown to have central cholinesterase inhibition properties under certain conditions (such as when ingested with other chemical compounds or following a high level of stress). Here we tested if stressing rats, using an intermittent 1 hr tailshock protocol, affected the degree of brain acetylcholinesterase (AChE) inhibition caused by a subsequent single injection of PB (2.0 mg/kg) or neostigmine bromide (NB, 0.32 mg/kg), another peripheral carbamate cholinesterase inhibitor. Stressed rats treated with PB had lower levels of AChE activity in the basal forebrain/striatum, but not in other brain areas. Stressed rats treated with NB did not show basal forebrain/striatum AChE activity changes but did show minor reductions of AChE activity in the cortex and cerebellum. These results confirm that prior stress can change the characteristic actions of certain peripherally acting drugs, thus possibly leading to unexpected central nervous system effects. Possible causes for these effects are discussed.

Chronic Treatment with Morphine and Ethanol, But Not Cocaine, Attenuates IL-1β Activation of FOS Expression in the Rat Hypothalamic Paraventricular Nucleus

Interleukin-1 beta (IL-1 beta) is a key mediator of immunological and pathological responses to stress, injury and disease and it has been suggested to have profound effects on neuroendocrine-immune functions. We have shown that central treatment with IL-I beta induces the expression of FOS proto-oncogene protein immunoreactivity (FOS-IR) in several hypothalamic nuclei including the paraventricular nucleus (PVN). Since FOS expression has been used as an anatomical marker of neuronal function, these results suggested that the involvement of IL-1 beta in the neuro-endocrine-immune axis may be mediated through the PVN. Treatment with several substances of abuse has been shown to modify immune function in vivo and in vitro. In this study, we compared the effects of morphine, ethanol and cocaine on IL-1 beta induction of FOS-IR in the rat hypothalamus. Acute treatment with morphine or ethanol induced FOS-IR in several nuclei including the PVN. Cocaine, which induced FOS-IR in the Caudate-Putamen (CPU), nucleus Accumbens (nAcc) and Locus Coeruleus (LC), however, did not induce FOS-IR in the PVN. Chronic treatment with morphine desensitized FOS responsiveness to morphine and IL-1 beta in the PVN since FOS-IR was no longer induced by IL-1 beta or morphine in the PVN after this treatment. Similarly, chronic ethanol treatment desensitized FOS responsiveness to ethanol and to IL-1 beta in the PVN. By contrast, chronic cocaine did not affect FOS responsiveness to IL-1 beta in the PVN even though the treatment was able to desensitize the FOS responsiveness to acute cocaine in the CPU, nAcc, and LC. These results suggest that the PVN may be a site where actions of IL-1 beta converge with those of morphine and ethanol, but not cocaine, to modulate neuro-endocrine-immune functions.