Effects of restraint stress on alpha(1) adrenoceptor mRNA expression in the hypothalamus and midbrain of the rat

Nerve injury alters restraint-induced activation of the basolateral amygdala in male rats

The amygdala is critical for the production of appropriate responses towards emotional or stressful stimuli. It has a characteristic neuronal activation pattern to acute stressors. Chronic pain and acute stress have each been shown to independently modulate the activity of the amygdala. Few studies have investigated the effect of pain or injury, on amygdala activation to acute stress. This study investigated the effects of a neuropathic injury on the activation response of the amygdala to an acute restraint stress. Chronic constriction injury of the right sciatic nerve (CCI) was used to create neuropathic injury and a single brief 15-min acute restraint was used as an emotional/psychological stressor. All rats received cholera toxin B (CTB) retrograde tracer injections into the medial prefrontal cortex (mPFC) to assess if the amygdala to mPFC pathway was specifically regulated by the combination of neuropathic injury and acute stress. To assess differential patterns of activity in amygdala subregions, cFos expression was used as a marker for "acute", restraint triggered neuronal activation, and FosB/ΔFosB expression was used to reveal prolonged neuronal activation/sensitisation triggered by CCI. Restraint resulted in a characteristic increase in cFos expression in the medial amygdala, which was not altered by CCI. Rats with a CCI showed increased cFos expression in the basolateral amygdala (BLA), in response to an acute restraint stress, but not in neurons projecting to the prefrontal cortex. Further, CCI rats showed an increase in FosB/ΔFosB expression which was exclusive to the BLA. This increase likely reflects sensitisation of the BLA as a consequence of nerve injury which may contribute to heightened sensitivity of BLA neurons to acute emotional/ psychological stressors.

Increased beta(2)-adrenergic receptor activity by thyroid hormone possibly leads to differentiation and maturation of astrocytes in culture

(1) Our earlier studies indicate a downsteam regulatory role of the beta-adrenergic receptor (beta-AR) system in thyroid hormone induced differentiation and maturation of astrocytes. In the present study we have investigated the contributions of the subtypes of beta-AR in the above phenomenon. (2) Primary astrocyte cultures were grown under thyroid hormone deficient as well as under euthyroid conditions. [(125)I]Pindolol ([(125)I]PIN) binding studies showed a gradual increase in the specific binding to beta(2)-AR when observed at 5, 10, 15, and 20 days under both cultural conditions. Thyroid hormone caused an increase in binding of [(125)I]PIN to beta(2)-AR compared to thyroid hormone deficient controls at all ages of astrocyte culture. (3) Saturation studies using [(125)I]PIN in astrocyte membranes prepared from 20-day-old cultures showed a significant increase in the affinity of the receptors (K (D)) in the thyroid hormone treated cells without any change in receptor number (B (max)). (4) beta(2)-AR mRNA levels were measured by real-time PCR during ontogenic development as well as during exposure of 10-day-old hypothyroid cultures to normal levels of thyroid hormone for 2, 6, 12, and 24 h. None of the conditions caused any significant change in the beta(2)-adrenergic receptor mRNA levels when compared with corresponding hypothyroid controls. (5) Over expression of beta(2)-AR cDNA in hypothyroid astrocytes caused morphological transformation in spite of the absence of thyroid hormone in the medium. (6) Taken together, results suggest thyroid hormone causes a selective increase in [(125)I]PIN binding to beta(2)-AR due to increase in receptor affinity, which may lead to maturation of astrocytes.

Prazosin administered prior to inescapable stressor blocks subsequent exaggeration of acoustic startle response in rats

Exposure to traumatic stress can result in a number of pathophysiological conditions, including post-traumatic stress disorder (PTSD). PTSD is characterized by a number of persistently heightened physiological and behavioral indicators, including increased sensory arousal and increased startle response. Similar effects can be seen in an animal model of PTSD in which stress results from restraint and inescapable tailshocks to rats. The present study used this animal model to investigate the effects of prazosin, an alpha(1) adrenoceptor antagonist, on stress-induced elevation of acoustic startle response (ASR). To investigate this, male Sprague-Dawley rats were injected with 0.5 mg/kg of prazosin 30 min before restraint and inescapable tail shock on three consecutive days. ASR testing was performed 1, 4, 7 and 10 days post-stress and compared to baseline and control values. Results show a significant reduction of ASR hyperarousal in the group treated with prazosin prior to stress compared to vehicle treated stressed animals and controls. Pre-stress treatment with lower levels of prazosin (0.25, 0.1 and 0.05 mg/kg) showed similar results. These findings further implicate an alpha(1) adrenoceptor role in the pathophysiological response to traumatic stress and suggest a potential preventative role for prazosin.

Alpha(1)-adrenergic and alpha(2)-adrenergic balance in the dorsal pons and gross behavioral activity of mice in a novel environment

RATIONALE

Central alpha(1)- and alpha(2)-adrenoceptors in a number of different brain regions are known to have opposing actions on gross behavioral activity, with the former stimulating and the latter inhibiting activity. Therefore, blockade of alpha(1)-receptors may induce inactivity by leading to unopposed alpha(2) activity.

OBJECTIVE

The aim of this study was to test if central blockade of alpha(2)-receptor function restores behavioral activity in alpha(1)-receptor-blocked mice.

METHODS

Dose-response studies were undertaken on the effects of alpha(1)- and alpha(2)-agonists and antagonists microinjected into the dorsal pons on gross behavioral activity in a novel cage test.

RESULTS

The behavioral inactivity resulting from blockade of alpha(1)-receptors in the pons with the antagonist, terazosin, was reversed by either a low dose of an alpha(2)-antagonist, atipamezole, or a low dose of an alpha(2)-agonist, dexmedetomidine, but was exacerbated by a high dose of the alpha(2)-agonist.

CONCLUSION

The results support the hypothesis that blockade of alpha(1)-receptors in the dorsal pons of mice produces inactivity by causing unopposed activity of alpha(2)-receptors. This condition may be relevant to inactive states seen after stress or during depressive illness.

Effects of single and repeated prolonged stress on mu-opioid receptor mRNA expression in rat gross hypothalamic and midbrain homogenates

This study tested the hypothesis that stress-induced opioid peptides may have stimulative and inhibitive influence on mu opioid receptor (MOR) mRNA expression and hypothalamus. Several studies have investigated the effects of stress on MOR mRNA expression in rat brain, but almost none compared the response to single versus repeated stresses. Here, we examined the effects of single and repeated stress on MOR mRNA expression in different rat brain regions using reverse transcriptase-polymerase chain reaction (RT-PCR). Following a single episode of restraint stress for 4 h (1R) or 4 h per day on 2 (2R) or 3 (3R) consecutive days, the hypothalamus and midbrain were removed immediately and MOR mRNA levels in both regions were determined by RT-PCR. Blood samples were also collected for simultaneous measurement of serum adrenocorticotropic hormone (ACTH) and corticosterone (CS). MOR mRNA expression was significantly higher in both regions in the 2R group, whereas expression levels in the 3R group did not differ from controls. In the 1R group, hypothalamic MOR expression was equivalent to that in controls, but expression was significantly higher in the midbrain. Serum ACTH levels were significantly higher only in the 1R group, whereas serum CS was significantly higher in both the 1R and 3R groups. Our findings indicate that the influence of restraint stress on MOR mRNA expression in the hypothalamus is different than in the midbrain region in rats. Endogenous opioid peptides released in response to stress may paradoxically have an effect on the HPA axis.

Effect of immobilization and concurrent exposure to a pulse-modulated microwave field on core body temperature, plasma ACTH and corticosteroid, and brain ornithine decarboxylase, Fos and Jun mRNA

Exposure of humans and rodents to radiofrequency (RF) cell phone fields has been reported to alter a number of stress- related parameters. To study this potential relationship in more detail, tube-restrained immobilized Fischer 344 rats were exposed in the near field in a dose-dependent manner to pulse-modulated (11 packets/s) digital cell phone microwave fields at 1.6 GHz in accordance with the Iridium protocol. Core body temperatures, plasma levels of the stress-induced hormones adrenocorticotrophic hormone (ACTH) and corticosterone, and brain levels of ornithine decarboxylase (Odc), Fos and Jun mRNAs were measured as potential markers of stress responses mediated by RF radiation. We tested the effects of the loose-tube immobilization with and without prior conditioning throughout a 2-h period (required for near-field head exposure to RF fields), on core body temperature, plasma ACTH and corticosteroids. Core body temperature increased transiently (+/-0.3 degrees C) during the initial 30 min of loose-tube restraint in conditioned animals. When conditioned/tube-trained animals were followed as a function of time after immobilization, both the ACTH and corticosterone levels were increased by nearly 10-fold. For example, within 2-3 min, ACTH increased to 83.2 +/- 31.0 pg/dl, compared to 28.1 +/- 7.7 pg/dl for cage controls, reaching a maximum at 15-30 min (254.6 +/- 46.8 pg/dl) before returning to near resting levels by 120 min (31.2 +/- 10.2 pg/dl). However, when non-tube-trained animals were submitted to loose-tube immobilization, these animals demonstrated significantly higher (3-10-fold greater) hormone levels at 120 min than their tube-trained counterparts (313.5 +/- 54.8 compared to 31.2 +/- 10.2 pg/dl; corticosterone, 12.2 +/- 6.2 microg/dl compared to 37.1 +/- 6.4 microg/dl). Hormone levels in exposed animals were also compared to those in swim-stressed animals. Swimming stress also resulted in marked elevation in both ACTH and corticosterone levels, which were 10-20 fold higher (541.8 compared to 27.2-59.1 pg/dl for ACTH) and 2-5 fold higher (45.7 compared to 8.4- 20.0 microg/dl for corticosteroids) than the cage control animals. Three time-averaged brain SAR levels of 0.16, 1.6 and 5 W/ kg were tested in a single 2-h RF-field exposure to the Iridium cell phone field. When RF-exposed and sham-exposed (immobilized) animals were compared, no differences were seen in core body temperature, corticosterone or ACTH that could be attributed to near-field RF radiation. Levels of Odc, Fos and Jun mRNA were also monitored in brains of animals exposed to the RF field for 2 h, and they showed no differences from sham-exposed (loose-tube immobilized) animals that were due to RF-field exposure. These data suggest that a significant stress response, indicated by a transient increase in core body temperature, ACTH and corticosterone, occurred in animals placed in even the mild loose-tube immobilization required for near-field RF exposure employed here and in our other studies. Failure to adequately characterize and control this immobilization response with appropriate cage control animals, as described previously, could significantly mask any potential effects mediated by the RF field on these and other stress-related parameters. We conclude that the pulse-modulated digital Iridium RF field at SARs up to 5 W/kg is incapable of altering these stress-related responses. This conclusion is further supported by our use of an RF-field exposure apparatus that minimized immobilization stress; the use of conditioned/tube-trained animals and the measurement of hormonal and molecular markers after 2 h RF-field exposure when the stress-mediated effects were complete further support our conclusion.