Department of Medicine

Permanent URI for this community

https://scholar.sun.ac.za/handle/10019.1/159

Browse

Browsing Department of Medicine by Subject "ACTH"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    An investigation of two animal models of anxiety : central administration of corticotropin-releasing factor on the behaviour and neurochemistry of rats, and the effect of pharmacotherapy on spontaneous stereotypical behaviour and NMDA receptor function in mice
    (Stellenbosch : Stellenbosch University, 2004-12) Richter, Lelanie; Daniels, W. M. U.; Stein, D. J.; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Medicine.
    ENGLISH ABSTRACT: Corticotropin-releasing factor (CRF) study Background: Hypothalamic pituitary adrenal (HPA)-axis dysfunction is a common symptom of patients with anxiety disorders like posttraumatic stress disorder (PTSO), panic disorder and obsessive-compulsive disorder (OCD). Depressive patients also have HPA-axis dysfunction similar to patients with anxiety disorders. PTSD patients usually show decreased basal plasma cortisol levels whereas OCD and depressive patients show an increase in plasma cortisol. A blunted adrenocorticotropin hormone (ACTH) response to CRF is seen in these patients and mostly an increased level of CRF in their cerebrospinal fluid (CSF). It has been proposed that the CSF level of CRF is a reflection of activity of both hypothalamic and extra-hypothalamic CRF systems. Since the amygdala has been shown to be involved in the endocrine and behavioural response to stress, and CRF is involved in the mediation of this response, we investigated whether chronic elevation of CRF in the amygdala is involved in development of the symptoms of psychiatric disorders. We chronically injected rats with CRF in this area to see what the effect is on their behaviour and HPA-axis response. It has been shown that the hippocampal serotonergic (5-HT) system is involved in both anxiety and depression and that the 5-HT system is regulated by CRF. We therefore measured hippocampal 5- HT1A receptor density and affinity in CRF-injected and control rats. Materials and methods: Male Sprague-Dawley and Wistar rats were stereotaxically implanted with unilateral and bilateral chronic cannulae in the basolateral amygdala (BLA). After recovery unilaterally implanted rats were injected with 10ng (n=7) or 1DOng(n=6) of CRF or saline (n=6) daily for 5 days. Behaviour was tested on day 5 in the elevated plus-maze and open field. Rats with bilateral implants were injected with 100ng CRF (n=19) or saline (n=17) on either side for 5 days. On day 5, behaviour was tested on the elevated plusmaze and open field. Group 1 was tested at baseline levels (n=6 for saline and n=7 for CRF) and group 2 after 5 min. of restraint (n=11 for saline and n=12 for CRF). The stress response of all rats was tested 2 days later. The rats were divided into 3 groups: The first group was decapitated at baseline level (n=6 for each group), the second and third groups restrained for 10 min. and decapitated 15 min. (n=6 for saline and n=7 for CRF) and 60 min. (n=5 for saline and n=6 for CRF) after restraint stress. Blood was collected for plasma ACTH and corticosterone determinations. A group of naïve rats was also included in this experiment to control for the possible effect of the operation (n=6 for each time point). Hippocampi were dissected out and used for 5-HT1A radioligand binding studies. Results: Rats that were unilaterally injected with 1DOngCRF, showed significant increase in the amount of entries into the open arms as well as the amount of time spent in the open arms of the elevated plus-maze compared to controls and rats injected with 10ng CRF. There were no differences between the groups in other parameters of the elevated plus-maze or open field behaviour. There were no significant differences in behaviour of bilateral injected rats compared to controls, but an increase of grooming in the open field was observed in CRFinjected rats that were stressed before behavioural tests. The ACTH and corticosterone response of rats were normal as seen by a significant increase in both concentrations 15 min. after stress and a return to near basal values 60 min. post stress. There were no differences in plasma ACTH concentrations between the groups at any time point. The basal corticosterone level of CRF-injected rats was however significantly lower than controls, but no difference were found 15 or 60 min. post stress. There were no significant differences in hippocampal 5-HT1A receptor densities or affinities of CRF-injected and control rats. Conclusions: We did not observe increased anxiety levels or decreased activity in CRF injected rats. Instead, we observed increased activity in unilateral injected rats. We suspect that the lower dosage of CRF may have this effect on the behaviour of rats, since other authors have also found this result. The lack of differences in the 5-HT1A receptor populations of CRF-injected rats and control rats also confirms this result, since there was no increase in anxiety levels of CRF-injected rats. The chronic elevation of CRF in the SLA caused decreased basal levels of corticosterone in the rats and we speculate that CRF caused adrenal insufficiency although the mechanism is unknown. Stereotypical behaviour study Background: OCD affects 1-2% of the adult human population and is amongst the most common psychiatric disorders. This disorder is characterized by obsessions and compulsions. These compulsions or repetitive behaviours are suggested to be the cause of a hyperactive cortical-striatal-thalamic-cortical (CSTC) circuit in the brain, because of imbalance of the direct and indirect pathways. CSTC pathways are modulated by both 5-HT and dopaminergic (DA) neurons and it has been suggested that a hyperglutamatergic state exists in the frontal cortex of OCD patients. Two types of animal models of stereotypical behaviour are used to investigate neurotransmitter abnormalities related to OCD. These are drug induced stereotypies and environmentally induced (spontaneous) stereotypies. It has been shown that in deermice (Peromyscus manicula tis), drug induced stereotypies are topographically different from spontaneous stereotypies, and our aims were to characterize a deermice model of spontaneous stereotypy for OCD in terms of face, predictive and construct validity. We injected adult deermice, showing spontaneous stereotypies, for a time period of 8 weeks with risperidone (D2/5-HT2 antagonist), citalopram (selective serotonin reuptake inhibitor) and inositol (a metabolic precursor to the phosphatidylinositol second messenger cycle). All these drugs have been shown to improve symptoms of OCD in humans, and we investigated whether the drugs can reduce stereotypies in deermice. Materials and methods: 40 Adult deermice were raised and housed in standard laboratory cages and randomly divided into four groups (6 females and 4 males per group). After baseline recordings of behaviour (3 times per week for a total of 15 min.) the mice were injected daily for 8 weeks with risperidone, citalopram, inositol or saline. Video recordings were made for the 8 week trial and rated afterwards by raters that were blind to the medication status of the animals. A 5 sec. interval scoring system was used for ratings in which the absence or presence of a stereotypy (backward somersault) was noted. After 8 weeks of treatment, the mice were decapitated, brains were dissected and the frontal cortices were stored in liquid nitrogen until radioligand binding studies were performed on NMDA receptors. Results: There were no significant differences in the amount of somersaults between saline injected and drug treated groups when the data was analysed using an ANOVA with repeated measures. There was a significant difference between the control group and drug treated groups at week 8 in male mice when the data was analysed using a Mann-Whitney test. The amount of somersaults shown by saline injected mice increased over the 8 week trial while it stayed more constant in all three drug treated groups. There were no significant differences between the control group and treatment groups in Bmax and Kd values of NMDA receptors in the frontal cortex. There was a trend towards increased receptor densities in all treatment groups compared to the control group and a decrease in affinity in the risperidone group. Conclusions: We found limited evidence for the involvement of both 5-HT and DA systems in the development of spontaneous stereotypical behaviour of deermice. Risperidone, citalopram and inositol were useful in suppressing the increase in somersaults observed in the control group towards week 8 of the trial. This increase was presumably due to stress from handling and injections. The fact that there was a trend towards increased receptor densities in all treatment groups and decreased affinity in the risperidone group also point to the involvement of 5-HT and DA in spontaneous stereotypies. The limitation of this study was small group numbers and excessive stress experienced by the animals.