In vivo intracranial microdialysis is a valuable technique yielding novel and useful insight into normal or pathological neurochemical processes in the brain by means of sampling of interstitial fluid of cells in a living animal. It's most important advantage is that it can continuously monitor time-related changes in the concentration of neurotransmitters and their metabolites, other neuromodulators, energy substrates, as well as exogenous drugs in the extracellular fluid of specific brain areas of interest. While the development and standardization of the intracranial microdialysis technique in our laboratory was the main aim of the current study, a pilot application study was also performed during which the effect of several locally administered pharmacological agents on brain glutamate levels in a genetic rat model of depression was investigated. Abnormal neuronal glutamate levels have been implicated in various psychiatric conditions including major depressive disorder. The Flinders Sensitive Line (FSL) is a genetic line of Sprague-Dawley rat that displays various behavioral and neurochemical traits akin to that observed in depression. The Flinders Resistant Line (FRL) rat is used as the normal control. The prefrontal cortex is an important brain area involved in the neuropathology of depression. Prefrontal cortical glutamate levels in a small number of FSL and FRL rats were therefore compared at baseline and following local administration of potassium chloride (100 mM), the latter in order to study changes in evoked glutamate release. Ketamine hydrochloride (9 mM) and fluoxetine (30 μM) respectively were also administered via reverse dialysis. Prior to initiating the microdialysis studies, an HPLC-fluorescence method was developed to analyze the levels of glutamate in the microdialysate. As part of the development and standardization of the microdialysis technique, a number of validation studies were performed. This included refining the stereotaxic surgery procedure, determining the most appropriate anesthesia protocol, and standardizing the microdialysis procedure with regard to perfusion fluid, flow rate, sample volume, duration of dialysis, and anatomical verification of probe location. The HPLC-fluorescence method for the analysis of glutamate was also developed and validated. This technique proved to be sensitive and specific for the determination of glutamate with a linearity of 0.991 in the concentration range of standards tested (0.1 – 10 μM) and an intra-assay repeatability (precision value) yielding relative standard deviations of less than 10.5%, Mean elution time was between 24 and 26 minutes for glutamate in the microdialysis sample and the limit of detection and quantification was both 0.1 μM. Results from the application study indicated that baseline values of glutamate in the prefrontal cortex did not differ between FRL and FSL rats during the 1 hour period of dialysis. However, potassium chloride-evoked glutamate release was greater in FSL vs. FRL rats, although this difference was not statistically significant. Local perfusion by reverse dialysis of ketamine hydrochloride produced statistically significant increases in glutamate concentrations at certain time points in FSL rats. Although glutamate levels were also increased in FRL rats in response to ketamine, it was not statistically different compared to baseline levels. Fluoxetine perfusion did not affect glutamate release in either of the two rat groups. In conclusion, we have successfully developed and established an intracranial in vivo microdialysis procedure in our laboratory, as well as standardized and validated a sensitive method to analyze glutamate in microdialysate samples. These techniques were then applied in a small number of FSL vs. FRL rats in order to confirm their application in a typical research scenario. Although the data were too limited to make any valid conclusions about glutamate concentrations in an animal model of depression or the effect of drugs on the release thereof, these novel techniques and analyses will be valuable in future studies. / Thesis (MSc (Pharmacology))--North-West University, Potchefstroom Campus, 2013.

In vivo intracranial microdialysis is a valuable technique yielding novel and useful insight into normal or pathological neurochemical processes in the brain by means of sampling of interstitial fluid of cells in a living animal. It's most important advantage is that it can continuously monitor time-related changes in the concentration of neurotransmitters and their metabolites, other neuromodulators, energy substrates, as well as exogenous drugs in the extracellular fluid of specific brain areas of interest. While the development and standardization of the intracranial microdialysis technique in our laboratory was the main aim of the current study, a pilot application study was also performed during which the effect of several locally administered pharmacological agents on brain glutamate levels in a genetic rat model of depression was investigated. Abnormal neuronal glutamate levels have been implicated in various psychiatric conditions including major depressive disorder. The Flinders Sensitive Line (FSL) is a genetic line of Sprague-Dawley rat that displays various behavioral and neurochemical traits akin to that observed in depression. The Flinders Resistant Line (FRL) rat is used as the normal control. The prefrontal cortex is an important brain area involved in the neuropathology of depression. Prefrontal cortical glutamate levels in a small number of FSL and FRL rats were therefore compared at baseline and following local administration of potassium chloride (100 mM), the latter in order to study changes in evoked glutamate release. Ketamine hydrochloride (9 mM) and fluoxetine (30 μM) respectively were also administered via reverse dialysis. Prior to initiating the microdialysis studies, an HPLC-fluorescence method was developed to analyze the levels of glutamate in the microdialysate. As part of the development and standardization of the microdialysis technique, a number of validation studies were performed. This included refining the stereotaxic surgery procedure, determining the most appropriate anesthesia protocol, and standardizing the microdialysis procedure with regard to perfusion fluid, flow rate, sample volume, duration of dialysis, and anatomical verification of probe location. The HPLC-fluorescence method for the analysis of glutamate was also developed and validated. This technique proved to be sensitive and specific for the determination of glutamate with a linearity of 0.991 in the concentration range of standards tested (0.1 – 10 μM) and an intra-assay repeatability (precision value) yielding relative standard deviations of less than 10.5%, Mean elution time was between 24 and 26 minutes for glutamate in the microdialysis sample and the limit of detection and quantification was both 0.1 μM. Results from the application study indicated that baseline values of glutamate in the prefrontal cortex did not differ between FRL and FSL rats during the 1 hour period of dialysis. However, potassium chloride-evoked glutamate release was greater in FSL vs. FRL rats, although this difference was not statistically significant. Local perfusion by reverse dialysis of ketamine hydrochloride produced statistically significant increases in glutamate concentrations at certain time points in FSL rats. Although glutamate levels were also increased in FRL rats in response to ketamine, it was not statistically different compared to baseline levels. Fluoxetine perfusion did not affect glutamate release in either of the two rat groups. In conclusion, we have successfully developed and established an intracranial in vivo microdialysis procedure in our laboratory, as well as standardized and validated a sensitive method to analyze glutamate in microdialysate samples. These techniques were then applied in a small number of FSL vs. FRL rats in order to confirm their application in a typical research scenario. Although the data were too limited to make any valid conclusions about glutamate concentrations in an animal model of depression or the effect of drugs on the release thereof, these novel techniques and analyses will be valuable in future studies. / Thesis (MSc (Pharmacology))--North-West University, Potchefstroom Campus, 2013.

The rising number of the population that present with major depressive disorder has intensified the need to identify and elucidate new biological markers for the diagnosis and treatment of depression. Depression presents with evidence of changes in the nitric oxide (NO) pathway. In this study, levels of various endogenous markers of the NO cascade, viz. nitrite (NO2–), asymmetrical dimethylarginine (ADMA) and arginase II activity, were investigated in the Flinders Sensitive Line (FSL) rat, a genetic animal model of depression. The aim of the current study was to determine if there are differences between these markers in the plasma of the FSL rat compared to its healthy control, the (Flinders Resistant Line) FRL rat, with the possibility of considering their use as biomarkers of depression. Nitrite was chosen as metabolite over nitrate (NO3–) because the dietary intake of nitrite and/or nitrate does not significantly affect nitrite (NO2–) levels in plasma. Although this is of no significance if applied to rats, it is an important factor to be considered when doing clinical studies. For neurochemical determination of nitrite a sensitive fluorometric reversed phase high–performance liquid chromatographic (HPLC) assay was developed to analyze nitrite in human and rat plasma. Derivatization of sample nitrite was performed with 2,3–diaminonaphthalene (DAN) followed by the quantification of the stable and highly fluorescent product, 2,3–naphthotriazole (NAT). Determination of arginase II activity was performed by measuring L–arginine and L–ornithine concentrations in the plasma, while ADMA was measured simultaneously with L–arginine and L–ornithine using liquid chromatography/tandem mass spectrometry, or LC/MS/MS. Plasma nitrite levels of FSL rats were significantly decreased compared to plasma nitrite levels in the FRL rat, but neither the levels of ADMA nor arginase II activity showed a significant difference between the FSL and FRL rat groups. From these results it is concluded that in accordance with previous studies, the NO pathway plays an important role in the pathophysiology of depression, as depicted in the differences found between plasma nitrite levels in the FSL rat compared to its healthy control. / Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2011.

Major depression is a highly prevalent mood disorder with chronic debilitating effects. Additional to a rising rate in incidence, depression is highly co–morbid with other psychiatric disorders, but also chronic cardiometabolic illnesses that present with an inflammatory component. The exact aetiology of depression is still unknown, being multifactorial in its possible aetiology. Various hypotheses have attempted to shed light on both endogenous and exogenous risk factors as well as the underlying pathology that may lead to the development of the disease. This has led to a wide range of mediators being implicated, including biogenic amines, the HPA–axis, neurotrophic factors, inflammatory agents, the cholinergic system and circadian rhythm, to name a few. The mechanisms of action of current treatment strategies, except for a few atypical and novel treatment approaches, are limited to interactions with monoamines and are at best only 65% effective. Many of these are also plagued by troubling side–effects, relapse and recurrence. It has therefore become imperative to explore novel targets for the treatment of depression that may produce more rapid, robust and lasting antidepressant effects with a less daunting side–effect profile. The strong co–morbidity between depression and various cardiometabolic disorders, including cardiovascular disease, atherosclerosis, type 2 diabetes mellitus (T2DM) and metabolic syndrome (MetS) has led to the proposal that a metabolic disturbance may be a vital component that drives inflammatory and immunological dysfunction in depression. Supporting of this is evidence for a role of inflammatory cytokines and neurotrophic factors in the pathogenesis of depression. It has also been demonstrated that a link exists between insulin– and nitric oxide (NO)– mediated pathways in the brain, which further highlights the role of oxidative stress and cell damage. Furthermore, evidence supports a role for oxidative stress and NO in T2DM and/or insulin resistance. Insulin has also been implicated in various physiological processes in the central nervous system (CNS) and may also influence the release and reuptake of neurotransmitters. Preclinical and clinical evidence has provided support for the antidepressant–like effects of insulin–sensitizing peroxisome proliferator activated receptor (PPAR)– agonists, such as rosiglitazone and pioglitazone. In preclinical studies, however, these effects are limited to acute treatment with pioglitazone or sub–chronic (5 days) treatment with rosiglitazone. It is well–recognized that such findings need to be confirmed by chronic treatment paradigms. The aim of the current study was therefore to further investigate the proposed antidepressant–like effects of pioglitazone in a genetic animal model of depression, the Flinders sensitive line (FSL) rat, using a chronic treatment protocol. The FSL rat model was reaffirmed as presenting with inherent depressive–like behaviour compared to its more resilient counterpart, the Flinders resistant line (FRL) rat. Moreover, imipramine demonstrated a robust and reliable antidepressant–like effect in these animals using the forced swim test (FST), thus confirming the face and predictive validity of the FSL rat model for depression. In contrast to previous preclinical studies, acute dose–ranging studies with pioglitazone in Sprague Dawley rats delivered no significant anti–immobility effects in the FST, whereas results similar to that seen in the dose–ranging studies were observed following chronic treatment using FSL rats. Since altered pharmacokinetics could possibly influence the drug’s performance, another route of administration, viz. the subcutaneous route, was utilized as an additional measure to exclude this possibility. The results of the subcutaneous study, however, were congruent with that observed after oral treatment. In order to confirm an association between altered insulin sensitivity and antidepressant action and demonstration by recent studies that thiazolidinediones may augment the efficacy of existing antidepressants, we therefore investigated whether concomitant treatment with gliclazide (an insulin releaser and insulin desensitizer) or pioglitazone (an insulin sensitizer) may alter the antidepressant–like effects evoked by chronic treatment with imipramine. Pioglitazone did not positively or negatively affect the antidepressant effect of imipramine, although gliclazide tended to decrease the anti–immobility effects induced by this antidepressant. Taken together and considering the current available literature, this finding supports evidence linking the insulin–PPAR pathway to depression. However, further explorative studies are required to delineate the role of insulin sensitivity and glucose homeostasis in depression and antidepressant response. / Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2012.

The rising number of the population that present with major depressive disorder has intensified the need to identify and elucidate new biological markers for the diagnosis and treatment of depression. Depression presents with evidence of changes in the nitric oxide (NO) pathway. In this study, levels of various endogenous markers of the NO cascade, viz. nitrite (NO2–), asymmetrical dimethylarginine (ADMA) and arginase II activity, were investigated in the Flinders Sensitive Line (FSL) rat, a genetic animal model of depression. The aim of the current study was to determine if there are differences between these markers in the plasma of the FSL rat compared to its healthy control, the (Flinders Resistant Line) FRL rat, with the possibility of considering their use as biomarkers of depression. Nitrite was chosen as metabolite over nitrate (NO3–) because the dietary intake of nitrite and/or nitrate does not significantly affect nitrite (NO2–) levels in plasma. Although this is of no significance if applied to rats, it is an important factor to be considered when doing clinical studies. For neurochemical determination of nitrite a sensitive fluorometric reversed phase high–performance liquid chromatographic (HPLC) assay was developed to analyze nitrite in human and rat plasma. Derivatization of sample nitrite was performed with 2,3–diaminonaphthalene (DAN) followed by the quantification of the stable and highly fluorescent product, 2,3–naphthotriazole (NAT). Determination of arginase II activity was performed by measuring L–arginine and L–ornithine concentrations in the plasma, while ADMA was measured simultaneously with L–arginine and L–ornithine using liquid chromatography/tandem mass spectrometry, or LC/MS/MS. Plasma nitrite levels of FSL rats were significantly decreased compared to plasma nitrite levels in the FRL rat, but neither the levels of ADMA nor arginase II activity showed a significant difference between the FSL and FRL rat groups. From these results it is concluded that in accordance with previous studies, the NO pathway plays an important role in the pathophysiology of depression, as depicted in the differences found between plasma nitrite levels in the FSL rat compared to its healthy control. / Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2011.

Major depression is a highly prevalent mood disorder with chronic debilitating effects. Additional to a rising rate in incidence, depression is highly co–morbid with other psychiatric disorders, but also chronic cardiometabolic illnesses that present with an inflammatory component. The exact aetiology of depression is still unknown, being multifactorial in its possible aetiology. Various hypotheses have attempted to shed light on both endogenous and exogenous risk factors as well as the underlying pathology that may lead to the development of the disease. This has led to a wide range of mediators being implicated, including biogenic amines, the HPA–axis, neurotrophic factors, inflammatory agents, the cholinergic system and circadian rhythm, to name a few. The mechanisms of action of current treatment strategies, except for a few atypical and novel treatment approaches, are limited to interactions with monoamines and are at best only 65% effective. Many of these are also plagued by troubling side–effects, relapse and recurrence. It has therefore become imperative to explore novel targets for the treatment of depression that may produce more rapid, robust and lasting antidepressant effects with a less daunting side–effect profile. The strong co–morbidity between depression and various cardiometabolic disorders, including cardiovascular disease, atherosclerosis, type 2 diabetes mellitus (T2DM) and metabolic syndrome (MetS) has led to the proposal that a metabolic disturbance may be a vital component that drives inflammatory and immunological dysfunction in depression. Supporting of this is evidence for a role of inflammatory cytokines and neurotrophic factors in the pathogenesis of depression. It has also been demonstrated that a link exists between insulin– and nitric oxide (NO)– mediated pathways in the brain, which further highlights the role of oxidative stress and cell damage. Furthermore, evidence supports a role for oxidative stress and NO in T2DM and/or insulin resistance. Insulin has also been implicated in various physiological processes in the central nervous system (CNS) and may also influence the release and reuptake of neurotransmitters. Preclinical and clinical evidence has provided support for the antidepressant–like effects of insulin–sensitizing peroxisome proliferator activated receptor (PPAR)– agonists, such as rosiglitazone and pioglitazone. In preclinical studies, however, these effects are limited to acute treatment with pioglitazone or sub–chronic (5 days) treatment with rosiglitazone. It is well–recognized that such findings need to be confirmed by chronic treatment paradigms. The aim of the current study was therefore to further investigate the proposed antidepressant–like effects of pioglitazone in a genetic animal model of depression, the Flinders sensitive line (FSL) rat, using a chronic treatment protocol. The FSL rat model was reaffirmed as presenting with inherent depressive–like behaviour compared to its more resilient counterpart, the Flinders resistant line (FRL) rat. Moreover, imipramine demonstrated a robust and reliable antidepressant–like effect in these animals using the forced swim test (FST), thus confirming the face and predictive validity of the FSL rat model for depression. In contrast to previous preclinical studies, acute dose–ranging studies with pioglitazone in Sprague Dawley rats delivered no significant anti–immobility effects in the FST, whereas results similar to that seen in the dose–ranging studies were observed following chronic treatment using FSL rats. Since altered pharmacokinetics could possibly influence the drug’s performance, another route of administration, viz. the subcutaneous route, was utilized as an additional measure to exclude this possibility. The results of the subcutaneous study, however, were congruent with that observed after oral treatment. In order to confirm an association between altered insulin sensitivity and antidepressant action and demonstration by recent studies that thiazolidinediones may augment the efficacy of existing antidepressants, we therefore investigated whether concomitant treatment with gliclazide (an insulin releaser and insulin desensitizer) or pioglitazone (an insulin sensitizer) may alter the antidepressant–like effects evoked by chronic treatment with imipramine. Pioglitazone did not positively or negatively affect the antidepressant effect of imipramine, although gliclazide tended to decrease the anti–immobility effects induced by this antidepressant. Taken together and considering the current available literature, this finding supports evidence linking the insulin–PPAR pathway to depression. However, further explorative studies are required to delineate the role of insulin sensitivity and glucose homeostasis in depression and antidepressant response. / Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2012.