What Can Cause Peripheral Neuropathy?
The causes of peripheral neuropathy are in many cases unfortunately unknown. In fact, the most common cause of neuropathy in this day and age may actually be what’s called idiopathic, meaning of unknown certainty. It’s no longer just diabetes.
In our modern world, we are subjected and exposed to many environmental toxins, including heavy metals. We also are seeing patients surviving cancer and living much longer. Unfortunately, one of the undesired complications of chemotherapy is the development of peripheral neuropathy. We are also seeing patients developing compression neuropathy, such as carpal tunnel, chronic sciatica and back pain and nerve damage associated with conditions like degenerative spinal disc disease and spinal stenosis. Part of this, of course, is because we are living longer and being more active than ever before.
Another common but often overlooked cause of peripheral neuropathy is the use of statin medication, which has expanded exponentially. It’s not too long ago that the statins were heralded to be the cure-all for many of mankind’s greatest diseases and illnesses. This is not the forum to debate the appropriate use of statins but if you or a family member are taking them, you do need to be aware that peripheral neuropathy is a potential complication.
There are other causes of peripheral neuropathy, like kidney disease and hormonal diseases that occur in patients with hyperthyroidism, as well as Cushing’s disease, which affects the adrenal glands and the output of cortisol. Alcoholism can cause peripheral neuropathy, as can vitamin deficiencies, especially deficiencies of thiamin, or vitamin B1. There are still more causes: chronic hypertension, cigarette-smoking, immune-complex diseases, generalized degenerative lifestyles that include obesity, poor diet combined with cigarette smoking, abuse of over-the-counter medications, etc.
The hormones produced by your adrenal glands, particularly the stress hormone cortisol, play an important role in regulating your immune system.
If your cortisol levels go too low or too high, this can lead to regular infections, chronic inflammation, autoimmune diseases or allergies.
In type 2 diabetic subjects, hypothalmic-pituitary-adrenal activity is enhanced in patients with diabetes complications and the degree of cortisol secretion is related to the presence and number of diabetes complications.
Diabetic neuropathy is associated with increased activity of the hypothalamic-pituitary-adrenal axis.
Overall, these results suggest that diabetic neuropathy is associated with a specific and persistent increase in the activity of the hypothalamic-pituitary-adrenal axis.
Med Hypotheses. 1991 Mar;34(3):198-208.
Cortisol and immunity
The relationship between adrenocortical function and immunity is a complex one. In addition to the well-known detrimental effects of large, pharmacologic dosages of glucocorticoids upon the immune process, there is impressive evidence that physiologic amounts of cortisol, the chief glucocorticoid normally produced by the human adrenal cortex, is necessary for the development and maintenance of normal immunity. This evidence is reviewed, and the importance of differentiating between physiologic and pharmacologic dosages and effects is discussed.
The popular use of synthetic derivatives of cortisol, which differ greatly from the natural hormone in strength, and the dynamic nature of the normal adrenocortical response, which varies with the degree of stress being experienced, have contributed to the confusion. Further studies of the nature of the beneficial effect of cortisol, and possibly of other normal adrenocortical hormones, upon immunity in humans are needed, especially in view of recent evidence of a feedback relationship between the immune system and the hypothalamic-pituitary-adrenal axis, and with the increasing awareness not only that the immune process provides protection against infection, but also that its impairment seems to be involved in the development of autoimmune disorders, malignancies and the acquired immunodeficiency syndrome (AIDS).
Ageing Res Rev. 2005 May;4(2):141-94.
The stress system in the human brain in depression and neurodegeneration
Swaab DF1, Bao AM, Lucassen PJ.
Cortisol and CRH may well be causally involved in the signs and symptoms of depression
Corticotropin-releasing hormone (CRH) plays a central role in the regulation of the hypothalamic-pituitary-adrenal (HPA)-axis, i.e., the final common pathway in the stress response. The action of CRH on ACTH release is strongly potentiated by vasopressin, that is co-produced in increasing amounts when the hypothalamic paraventricular neurons are chronically activated. Whereas vasopressin stimulates ACTH release in humans, oxytocin inhibits it.
ACTH release results in the release of corticosteroids from the adrenal that, subsequently, through mineralocorticoid and glucocorticoid receptors, exert negative feedback on, among other things, the hippocampus, the pituitary and the hypothalamus. The most important glucocorticoid in humans is cortisol, present in higher levels in women than in men. During aging, the activation of the CRH neurons is modest compared to the extra activation observed in Alzheimer’s disease (AD) and the even stronger increase in major depression. The HPA-axis is hyperactive in depression, due to genetic factors or due to aversive stimuli that may occur during early development or adult life.
At least five interacting hypothalamic peptidergic systems are involved in the symptoms of major depression. Increased production of vasopressin in depression does not only occur in neurons that colocalize CRH, but also in neurons of the supraoptic nucleus (SON), which may lead to increased plasma levels of vasopressin, that have been related to an enhanced suicide risk. The increased activity of oxytocin neurons in the paraventricular nucleus (PVN) may be related to the eating disorders in depression. The suprachiasmatic nucleus (SCN), i.e., the biological clock of the brain, shows lower vasopressin production and a smaller circadian amplitude in depression, which may explain the sleeping problems in this disorder and may contribute to the strong CRH activation.
The hypothalamo-pituitary thyroid (HPT)-axis is inhibited in depression. These hypothalamic peptidergic systems, i.e., the HPA-axis, the SCN, the SON and the HPT-axis, have many interactions with aminergic systems that are also implicated in depression. CRH neurons are strongly activated in depressed patients, and so is their HPA-axis, at all levels, but the individual variability is large.
It is hypothesized that particularly a subgroup of CRH neurons that projects into the brain is activated in depression and induces the symptoms of this disorder. On the other hand, there is also a lot of evidence for a direct involvement of glucocorticoids in the etiology and symptoms of depression. Although there is a close association between cerebrospinal fluid (CSF) levels of CRH and alterations in the HPA-axis in depression, much of the CRH in CSF is likely to be derived from sources other than the PVN.
Furthermore, a close interaction between the HPA-axis and the hypothalamic-pituitary-gonadal (HPG)-axis exists. Organizing effects during fetal life as well as activating effects of sex hormones on the HPA-axis have been reported. Such mechanisms may be a basis for the higher prevalence of mood disorders in women as compared to men. In addition, the stress system is affected by changing levels of sex hormones, as found, e.g., in the premenstrual period, ante- and postpartum, during the transition phase to the menopause and during the use of oral contraceptives. In depressed women, plasma levels of estrogen are usually lower and plasma levels of androgens are increased, while testosterone levels are decreased in depressed men.
This is explained by the fact that both in depressed males and females the HPA-axis is increased in activity, parallel to a diminished HPG-axis, while the major source of androgens in women is the adrenal, whereas in men it is the testes. It is speculated, however, that in the etiology of depression the relative levels of sex hormones play a more important role than their absolute levels. Sex hormone replacement therapy indeed seems to improve mood in elderly people and AD patients. Studies of rats have shown that high levels of cumulative corticosteroid exposure and rather extreme chronic stress induce neuronal damage that selectively affects hippocampal structure.
Studies performed under less extreme circumstances have so far provided conflicting data. The corticosteroid neurotoxicity hypothesis that evolved as a result of these initial observations is, however, not supported by clinical and experimental observations. In a few recent postmortem studies in patients treated with corticosteroids and patients who had been seriously and chronically depressed no indications for AD neuropathology, massive cell loss, or loss of plasticity could be found, while the incidence of apoptosis was extremely rare and only seen outside regions expected to be at risk for steroid overexposure.
In addition, various recent experimental studies using good stereological methods failed to find massive cell loss in the hippocampus following exposure to stress or steroids, but rather showed adaptive and reversible changes in structural parameters after stress. Thus, the HPA-axis in AD is only moderately activated, possibly due to the initial (primary) hippocampal degeneration in this condition. There are no convincing arguments to presume a causal, primary role for cortisol in the pathogenesis of AD. Although cortisol and CRH may well be causally involved in the signs and symptoms of depression, there is so far no evidence for any major irreversible damage in the human hippocampus in this disorder.
Encephale. 2001 May-Jun;27(3):245-59.
[Role of the neurohypophysis in psychological stress].
Scantamburlo G1, Ansseau M, Legros JJ.
In schizophrenic patients, studies using the apomorphine stimulation suggest increased oxytoninergic and decreased vasopressinergic functions.
Effects of different psychological stimuli on oxytocin (OT) and vasopressin (AVP) secretion are reviewed in animals and in humans. The secretion of neuropituitary hormones is also discussed in various psychiatric diseases such an anorexia nervosa, bipolar disorder, schizophrenia and obsessive-compulsive disorder.
AVP and OT are secreted into the hypophyseal portal circulation by neurons which project from the paraventricular nucleus to the external zone of the median eminence. AVP and OT-containing neurons in the suprachiasmatic and paraventricular nuclei project to limbic areas, including the hippocampus, the subiculum, the ventral nucleus of the amygdala and the nucleus of the diagonal band. Specific AVP receptors which are pharmacologically different from the pressor and antidiuretic AVP receptors have been found in the anterior pituitary. OT receptors have been identified in a variety of forebrain sites.
The neurohypophyseal secretion is regulated by the cholinergic muscarinic, histaminergic and beta-adrenergic systems. Stress alters the secretion of one or more of the hypothalamic factors which interact at the pituitary to increase the secretion of ACTH. AVP and OT have been shown to modulate the effect of Corticotropin-Releasing Factor (CRF) on ACTH secretion and appear to play a key role in mediating the ACTH response to stress. Although AVP is a relatively weak secretagogue for ACTH, it markedly potentiates the activity of CRF both in vitro and in vivo. The role of OT is more complex. In vitro, OT stimulates ACTH release at high doses whereas in human it inhibits ACTH secretion at low doses. The type of stressor appear to determine the relative importance of these secretatogues in ACTH response.
Several recent studies indicate that psychological stressors display a similar degree of variety of secretagogue release patterns as was found earlier for physical stressors. A bewildering array of technique produces a bewildering array of conclusions. In rats, OT may be an important secretagogue during a novel stimulus, whereas the role for AVP is less clear. Indeed two studies out of ten suggest a stimulating role for AVP.
In response to frustration and submission, OT and AVP are secreted. Regarding social isolation, results are difficult to interpret and the role of AVP could be species-dependent. In contrast plasma OT levels do not change. After restraint, ACTH release is primarily mediated by the active increase of OT and AVP does not appear to play a role. When restraint is associated with moderate levels of physical components and during immobilisation, all two secretagogs are involved in the ACTH response.
With fear, ACTH response appears to be driven by OT. In humans, one study indicates that high emotionality women increase plasma OT in response to uncontrollable noise. Various neuroendocrine dysregulations have been observed in psychiatric disease. Either an increase or a decrease of the hypothalamic-pituitary-adrenal (HPA) function have been described in several illnesses. Effects of OT appear to be reciprocal to the effects of AVP. OT has been called the “amnestic” neuropeptide due to its capacity to attenuate memory consolidation and retrieval. AVP exhibits a central activating action on mood, memory and selective attention. Underweight patients with anorexia nervosa have abnormally high levels of centrally directed AVP and reduced OT levels.
These modifications could enhance the retention of cognitive distortions of aversive consequences of eating. Patients with bipolar disorder show a biphasic secretion of AVP. Depressive episodes are associated with decreased vasopressinergic activity whereas manic episodes involve an increased release. AVP might be responsible for an increased catecholamine activity. In addition, lithium could act as an antagonist to AVP.
In schizophrenic patients, studies using the apomorphine stimulation suggest increased oxytoninergic and decreased vasopressinergic functions. These findings are consistent with the beneficial role of AVP on schizophrenic symptoms noted in several trials.
The increased OT could be responsible for “positive” symptomatology such as delusions and hallucinations. Obsessive compulsive disorder (OCD) includes a range of cognitive and behavioral disturbances that could be influenced by OT. In animals, several studies have emphasized the role of AVP in promoting repetitive grooming behaviors and maintaining conditioned response to aversive stimuli.
In OCD patients, one study have reported that AVP/OT ratio was negatively correlated with symptom severity. However, an independent report found similar AVP concentrations in OC patients without a personal or family history of tic disorder and in normal subjects. Whether these modifications are only a consequence of the central disturbances or whether those peptides could participate in the pathogenesis of these affections remains to be elucidated.
Dan Med Bull. 2007 Nov;54(4):266-88.
Studies on the neuroendocrine role of serotonin.
Serotonin affect the secretion of CRH and ACTH both at the hypothalamic, pituitary portal and pituitary gland level, and possibly also at the adrenal level.
The aim of the thesis was to investigate in male Wistar rats, the involvement of serotonin (5-HT) and 5-HT receptors in the regulation of the gene expression of hypothalamic hormones and in the secretion of the pituitary gland hormones prolactin (PRL), adrenocorticotropic hormone (ACTH), vasopressin (AVP) and oxytocin in basal and stress conditions. Furthermore, to study the significance of some distinctive central nuclei in these processes, and the metabolism of 5-HT in the hypothalamus and the dorsal raphe nucleus (DRN). The experiments were focused on (1) determination of involved neurons and nuclei (2) the hypothalamic level and (3) the pituitary gland level of regulation.
The studies were typically performed in vivo but some studies were performed in vitro. Stereotactically neurotoxic lesion with 5,7-dihydroxy-5-HT in the dorsal raphe nucleus (DRN) or the hypothalamic paraventricular nucleus (PVN) reduced the ACTH and AVP response to stress, indicating an importance of these structures for this response. In situ hybridization on rat brain slices with oligopeptides showed an increase of corticotropin releasing hormone (CRH) mRNA in the PVN and proopiomelanocortin in the anterior pituitary lobe upon stimulation of the 5-HT1A, 5-HT1B, 5-HT2A and 5-HT2C receptors.
Stimulation of 5-HT2A+2C receptors increased AVP mRNA in the PVN but not in the supraoptic nucleus (SON), whereas the level of oxytocin (OT) mRNA was increased both in the SON and the PVN and this effect was in addition mediated via 5-HT1A+1B receptors. Serotonin infused directly into the PVN by microdialysis stimulated local release of AVP. CRH was found to have a major role but not a complete responsibility in the 5-HT-induced release of ACTH, since immunoneutralisation of CRH inhibited the POMC gene expression and the ACTH response and since 5-HT and 5-HT antagonists were able to modulate the ACTH release from anterior pituitary gland cells in vitro.
Through the years of investigation, the classification of the 7 main groups of 5-HT receptors (5-HT1 – 5-HT7) has changed due to molecular biological characterisation of the receptors and new receptors have been identified. With a battery of 5-HT agonists and antagonists several pharmacological experiments were performed with systemically or central administration of compounds and radioimmuno assay of plasma for pituitary gland hormone levels.
Specific substances were not available for all 5-HT receptors and subreceptors thus some conclusions are a based on combination of experiments. The 5-HT induced PRL response is mediated via 5-HT1A, 5-HT2A, 5-HT2C and 5-HT3 receptors. In addition an involvement of 5-HT1B, 5-HT5 or 5-HT7 receptors seem possible. The ACTH response to 5-HT is mediated via 5-HT1A, 5-HT1B, 5-HT2A and 5-HT2C receptors and an involvement of the 5-HT4, 5-HT5 and 5-HT7 receptors is proposed. Peripheral secretion of AVP upon stimulation with 5-HT is mediated via 5-HT2C, 5-HT4 and 5-HT7 receptors but not 5-HT1A receptors.
The secretion of OT is primarily mediated via 5-HT1A, 5-HT2C and 5-HT4 receptors and probably also 5-HT1B, 5-HT2A, 5-HT5A and 5-HT7 receptors. Physical and psychological stress activates hippocampal and hypothalamic 5-HT neurons. In contrast to other stress factors, restraint stress increases the content of 5-HT in the DRN but do not increase the metabolism of 5-HT and does not induce changes in hypothalamic levels of 5-HT.
Large variations are found in the literature with different kinds of stress, different measurements and different time schedules. Restraint or ether stress induced secretion of PRL involves 5-HT2 and 5-HT3 receptors, whereas the ACTH secretion is mediated via 5-HT1A, 5-HT2A and 5-HT2C receptors. In the present study restraint stress increased AVP secretion, but opposite findings has reported possibly due to differences in the stress procedure. The 5-HT2, 5-HT3 and 5-HT4 receptor is involved in the AVP response to restraint whereas the OT response involves the 5-HT1A and the 5-HT2 receptor. The 5-HT2 receptor is involved in the OT response to dehydration or haemorrhage, whereas the AVP responses to these stressors probably do not involve 5-HT.
It can be concluded that 5-HT is involved in basal and stress-induced regulation of PRL, ACTH, AVP and oxytocin mainly via the 5-HT2A+2C receptors but other receptors are also important but differs from hormone to hormone. Serotonin affect the secretion of CRH and ACTH both at the hypothalamic, pituitary portal and pituitary gland level, and possibly also at the adrenal level.