Differential effects of paclitaxel treatment on cognitive functioning and mechanical sensitivity

Neurobehavioral manifestations in female rats after intermittent exposure to an anticancer agent, paclitaxel

Paclitaxel (PTX), a widely used chemotherapeutic agent, causes both peripheral and central neurotoxicity, leading to significant behavioral impairments. However, inadequate literature is available on PTX-induced neurobehavioral sequelae associated with anxiety, depression, and cognition in adults during and after chemotherapy. Therefore, the present study aimed to investigate neurobehavioral impairments in adult female rats following PTX exposure, with a specific focus on anxiety-like behaviors and cognitive functions such as learning and memory. In this study, we used adult female Wistar rats aged 10-12 weeks (average weight: 180 ± 5 g) and administered clinically relevant therapeutic doses of PTX (1.6 and 3.2 mg/kg body weight) intravenously once weekly for 6 weeks, simulating the clinical chemotherapy regimen. Neurobehavioral assessments were conducted after the first and sixth doses of PTX using validated mazes, including the photoactometer, open-field maze, elevated plus-maze (EPM; for anxiety-like behaviors), and the step-down latency test (SDL; for cognitive performance). Neurobehavioral patterns were recorded using autotracking software (ANY-maze, Stoelting Co., Wood Dale, Illinois, USA). Our findings revealed substantially reduced locomotor activity in the photoactometer, increased anxiety-like behaviors with amplified fear emotionality in the open-field and EPM tests, and memory impairment in the SDL test. These results suggest that the manifestation of anxiogenic and cognitive behavioral changes is associated with the administration of a higher dose (3.2 mg/kg) of PTX. In conclusion, our study indicates that PTX causes significant neurobehavioral impairments in rats after exposure to equivalent therapeutic doses of PTX.

Functional ultrasound imaging reveals microvascular rarefaction, decreased cerebral blood flow, and impaired neurovascular coupling in a mouse model of paclitaxel-induced chemobrain

Chemotherapy-induced cognitive impairment (CICI), often referred to as "chemobrain," significantly affects the quality of life in cancer survivors. Although traditionally attributed to neuronal toxicity, emerging evidence suggests a key role of cerebrovascular dysfunction in its pathogenesis. We hypothesized that paclitaxel (PTX, Taxol) treatment induces long-term cerebrovascular dysfunction, including microvascular rarefaction, impaired neurovascular coupling (NVC), and altered cerebral blood flow (CBF), which contribute to CICI. Using a clinically relevant PTX treatment regimen in non-tumor-bearing mice, we evaluated the long-term effects of PTX on cerebrovascular health. Ultrasound localization microscopy (ULM) and functional ultrasound imaging (fUS) were employed to assess microvascular density, CBF, and NVC. PTX treatment resulted in a significant reduction in microvascular density in the cerebral cortex and hippocampus, key regions involved in cognitive function. PTX significantly reduced blood velocity in the middle cerebral artery. Moreover, PTX impaired NVC responses, as evidenced by a diminished CBF increase in response to whisker stimulation, indicative of impaired reactive hyperemia. In conclusion, these findings demonstrate that PTX induces long-lasting cerebrovascular dysfunction, including microvascular rarefaction, impaired NVC, and altered CBF dynamics, which likely contribute to CICI. This study underscores the critical role of cerebrovascular health in cognitive function and highlights the potential of targeting cerebrovascular pathways as a therapeutic approach for mitigating chemotherapy-induced cognitive deficits.

Changes in cognition and astrocytic reactivity in a female rodent model of chemotherapy-induced cognitive impairment are variable both acutely and chronically

Chemotherapy-induced cognitive impairment (CICI) affects female cancer survivors, with impairment recognised in populations such as breast cancer survivors, where 1 in 3 are affected. Impairments include issues with memory, learning, concentration, and processing speed, negatively impacting quality of life. Several mechanisms are proposed to drive these, with evidence implicating neuroinflammation as a key contributor. However, the time course over which impairments occur is less well-established, with fewer longer-term time-points investigated. This study aimed to understand the evolution of cognitive changes following methotrexate (MTX) or 5- fluorouracil (5-FU) chemotherapy, assessing three time-points: acute (96-hour), sub-acute (31-days) and chronic (93-days). Further, we investigated whether alterations in cognition were associated with concomitant changes in astrocytic reactivity. Female Sprague Dawley rats received two intraperitoneal injections of MTX, 5-FU or saline and were assessed on the novel object recognition, 5-choice serial reaction time task and Barnes maze. Hippocampal and prefrontal cortex tissue was examined for GFAP expression. Both MTX and 5-FU exposure were associated with spatial memory, task acquisition, and processing speed impairments at 31-days, with impairment ameliorated by 93-days. While both MTX and 5-FU induced changes in GFAP expression across various time-points and regions, with most notable changes at 96-hours, 5-FU exhibited expression changes in the hippocampus consistently across all time-points. These results provide valuable insight into the complexity of a mediator of neuroinflammation in CICI. While neuroinflammation may be a promising therapeutic target, further markers should be assessed to elucidate the full neuroimmune response, and thus which aspects to target and when, to ensure optimal outcomes for cancer patients treated with chemotherapy.

Effect of vitamin E on doxorubicin and paclitaxel-induced memory impairments in male rats

PURPOSE

In addition to peripheral neuronal dysfunction, conventional chemotherapy can be associated with other neurological treatment-limiting adverse effects, including cognitive dysfunction, memory impairment, and anxiety, which are referred to as "chemobrain". This study aimed to investigate the effects of doxorubicin (DOX) and paclitaxel (PAC) on learning and memory in rats using radial arm water maze (RAWM) and investigated a potential beneficial effect of vitamin E (Vit. E).

METHODS

Adult male rats were injected with four doses of 2 mg/kg/week DOX, or 2 mg/kg PAC every other day intraperitoneally. Vit. E was co-administered with these drugs in other groups to study its antioxidative effects. Using the RAWM, each rat was assessed for learning and memory performance through two sets of six trials separated by a 5-min rest period evaluating both short- and long-term effects on memory.

RESULTS

There was no deficit in learning or long-term memory in both drug groups compared to control. However, rats in both drug groups made significantly more errors in all short-term memory trials. This effect was mitigated when Vit. E was co-administered with either drug. Moreover, PAC (but not DOX) induced hippocampal lipid peroxidation by increasing the levels of standard biomarker thiobarbituric acid reactive substances (TBARS). Interestingly, Vit. E prevented PAC-induced hippocampal oxidative stress. Furthermore, both DOX and PAC were correlated with reduction in Brain-Derived Neurotrophic Factor (BDNF) expression levels in the hippocampus, which was overcome by the co-administration of Vit. E.

CONCLUSION

There is a potential role of Vit. E in alleviating short-term memory impairment in rats exposed to chemotherapy, possibly by reducing hippocampal oxidative stress and neurodegeneration.

Paclitaxel induces cognitive impairment via necroptosis, decreased synaptic plasticity and M1 polarisation of microglia

CONTEXT

Paclitaxel (PTX) leads to chemotherapy brain (chemo-brain) which is characterised by cognitive impairment. It has been reported that necroptosis is associated with cognitive impairment in some neurodegenerative diseases, but it is not clear whether it is related to the development of chemo-brain.

OBJECTIVE

To investigate the role of necroptosis and related changes in PTX-induced cognitive impairment.

MATERIALS AND METHODS

C57bl/6n mice were randomly divided into five groups: control, vehicle, and different concentrations of PTX (6, 8, 10 mg/kg). Two additional groups received pre-treatment with Gdcl3 or PBS through Intracerebroventricular (ICV) injection before PTX-treatment. Cognitive function, necroptosis, synaptic plasticity and microglia polarisation were analysed.

RESULTS

PTX (10 mg/kg) induced significant cognitive impairment, accompanied by changes in synaptic plasticity, including decreased density of PSD95 (0.65-fold), BDNF (0.44-fold) and dendritic spines (0.57-fold). PTX induced necroptosis of 53.41% (RIP3) and 61.91% (MLKL) in hippocampal neurons, with high expression of RIP3 (1.58-fold) compared with the control group. MLKL (1.87-fold) exhibited the same trend, reaching a peak on the 14th day. The increased expression of iNOS (1.63-fold) and inflammatory factors such as TNF-α (1.85-fold) and IL-β (1.89-fold) compared to the control group suggests that M1 polarisation of microglia is involved in the process of cognitive impairment. Pre-treatment with Gdcl3 effectively reduced the number of microglia (0.50-fold), inhibited the release of TNF-α (0.73-fold) and IL-β (0.56-fold), and improved cognitive impairment.

CONCLUSION

We established a stable animal model of PTX-induced cognitive impairment and explored the underlying pathophysiological mechanism. These findings can guide the future treatment of chemo-brain.

Chemobrain in Breast Cancer: Mechanisms, Clinical Manifestations, and Potential Interventions

Among the potential adverse effects of breast cancer treatment, chemotherapy-related cognitive impairment (CRCI) has gained increased attention in the past years. In this review, we provide an overview of the literature regarding CRCI in breast cancer, focusing on three main aspects. The first aspect relates to the molecular mechanisms linking individual drugs commonly used to treat breast cancer and CRCI, which include oxidative stress and inflammation, reduced neurogenesis, reduced levels of specific neurotransmitters, alterations in neuronal dendrites and spines, and impairment in myelin production. The second aspect is related to the clinical characteristics of CRCI in patients with breast cancer treated with different drug combinations. Data suggest the incidence rates of CRCI in breast cancer vary considerably, and may affect more than 50% of treated patients. Both chemotherapy regimens with or without anthracyclines have been associated with CRCI manifestations. While cross-sectional studies suggest the presence of symptoms up to 20 years after treatment, longitudinal studies confirm cognitive impairments lasting for at most 4 years after the end of chemotherapy. The third and final aspect is related to possible therapeutic interventions. Although there is still no standard of care to treat CRCI, several pharmacological and non-pharmacological approaches have shown interesting results. In summary, even if cognitive impairments derived from chemotherapy resolve with time, awareness of CRCI is crucial to provide patients with a better understanding of the syndrome and to offer them the best care directed at improving quality of life.

Effects of taxol on neuronal differentiation of postnatal neural stem cells cultured from mouse subventricular zone

Taxol (paclitaxel), a chemotherapeutic agent for several cancers, can adversely affect the peripheral nervous system. Recently, its negative impact on cognitive function in cancer patients has become evident. In rodents, taxol impaired learning and memory, with other possible negative effects on the brain. In this study, we investigated the effects of taxol on cultured neural stem cells (NSCs) from the mouse neurogenic region, the subventricular zone (SVZ). Taxol significantly decreased both proliferation and neuronal differentiation of NSCs. Transient treatment with taxol for one day during a 4-day differentiation greatly decreased neurogenesis along with an abnormal cell cycle progression. Yet, taxol did not kill differentiated Tuj1+ neurons and those neurons had longer neurites than neurons under control conditions. For glial differentiation, taxol significantly reduced oligodendrogenesis as observed by immunostaining for Olig2 and O4. However, differentiation of astrocytes was not affected by taxol. In contrast, differentiated oligodendrocytes were extremely sensitive to taxol. Almost no Olig2-positive cells were observed after three days of treatment with taxol. Taxol has distinct effects on neurons and glial cells during their production through differentiation from NSCs as well as post-differentiation. Thus, we suggest that taxol might interfere with neurogenesis of NSCs possibly through a disturbance in the cell cycle and may eliminate differentiated oligodendrocytes.

Nicotinamide riboside relieves paclitaxel-induced peripheral neuropathy and enhances suppression of tumor growth in tumor-bearing rats

Nicotinamide riboside (NR) is a vitamin B3 precursor of NAD that blunts diabetic and chemotherapy-induced peripheral neuropathy in preclinical models. This study examined whether NR also blunts the loss of intraepidermal nerve fibers induced by paclitaxel, which is associated with peripheral neuropathy. The work was conducted in female rats with N-methyl-nitrosourea (MNU)-induced tumors of the mammary gland to increase its translational relevance, and to assess the interaction of NR with paclitaxel and NR's effect on tumor growth. Once daily oral administration of 200 mg/kg NR p.o. beginning with the first of 3 i.v. injections of 6.6 mg/kg paclitaxel to tumor-bearing rats significantly decreased paclitaxel-induced hypersensitivity to tactile and cool stimuli, as well as place-escape avoidance behaviors. It also blunted the loss of intraepidermal nerve fibers in tumor-bearing rats, as well as a separate cohort of tumor-naive rats. Unexpectedly, concomitant administration of NR during paclitaxel treatment further decreased tumor growth; thereafter, tumor growth resumed at the same rate as vehicle-treated controls. Administration of NR also decreased the percentage of Ki67-positive tumor cells in these rats. Once daily administration of NR did not seem to alter tumor growth or the percentage of Ki67-positive tumor cells in rats that were not treated with paclitaxel and followed for 3 months. These results further support the ability of NR to play a protective role after nerve injury. They also suggest that NR may not only alleviate peripheral neuropathy in patients receiving taxane chemotherapy, but also offer an added benefit by possibly enhancing its tumor-suppressing effects.

Chemotherapy-induced cognitive impairment (CICI): An overview of etiology and pathogenesis

Many cancer patients treated with chemotherapy develop chemotherapy-induced cognitive impairment (CICI), often referred to as chemo-brain, which manifest during or post-treatment with variable degrees, onset and duration thereby affecting the patients' quality of life. Several chemotherapeutic agents have been studied to determine its possible association with cognitive impairment and to fully comprehend their contribution to CICI. A vast number of studies have emerged proposing several candidate underlying mechanisms and etiologies contributing to CICI such as direct neurotoxicity, BBB disruption, decreased hippocampal neurogenesis, white matter abnormalities, secondary neuro-inflammatory response and increased oxidative stress; however, the exact underlying mechanisms are still not well defined. This review summarizes CICI associated with most commonly used chemotherapeutic agents with emphasizes the possible underlying pathogenesis in both animal and clinical studies.

A novel preventive therapy for paclitaxel-induced cognitive deficits: preclinical evidence from C57BL/6 mice

Chemotherapy-induced central nervous system (CNS) neurotoxicity presents an unmet medical need. Patients often report a cognitive decline in temporal correlation to chemotherapy, particularly for hippocampus-dependent verbal and visuo-spatial abilities. We treated adult C57Bl/6 mice with 12 × 20 mg kg^-1 paclitaxel (PTX), mimicking clinical conditions of dose-dense chemotherapy, followed by a pulse of bromodesoxyuridine (BrdU) to label dividing cells. In this model, mice developed visuo-spatial memory impairments, and we measured peak PTX concentrations in the hippocampus of 230 nm l^-1, which was sevenfold higher compared with the neocortex. Histologic analysis revealed a reduced hippocampal cell proliferation. In vitro, we observed severe toxicity in slowly proliferating neural stem cells (NSC) as well as human neuronal progenitor cells after 2 h exposure to low nanomolar concentrations of PTX. In comparison, mature post-mitotic hippocampal neurons and cell lines of malignant cells were less vulnerable. In PTX-treated NSC, we observed an increase of intracellular calcium levels, as well as an increased activity of calpain- and caspase 3/7, suggesting a calcium-dependent mechanism. This cell death pathway could be specifically inhibited with lithium, but not glycogen synthase kinase 3 inhibitors, which protected NSC in vitro. In vivo, preemptive treatment of mice with lithium prevented PTX-induced memory deficits and abnormal adult hippocampal neurogenesis. In summary, we identified a molecular pathomechanism, which invokes PTX-induced cytotoxicity in NSC independent of cell cycle status. This pathway could be pharmacologically inhibited with lithium without impairing paclitaxel's tubulin-dependent cytostatic mode of action, enabling a potential translational clinical approach.

The chemotherapeutic agent paclitaxel selectively impairs learning while sparing source memory and spatial memory

Chemotherapeutic agents are widely used to treat patients with systemic cancer. The efficacy of these therapies is undermined by their adverse side-effect profiles such as cognitive deficits that have a negative impact on the quality of life of cancer survivors. Cognitive side effects occur across a variety of domains, including memory, executive function, and processing speed. Such impairments are exacerbated under cognitive challenges and a subgroup of patients experience long-term impairments. Episodic memory in rats can be examined using a source memory task. In the current study, rats received paclitaxel, a taxane-derived chemotherapeutic agent, and learning and memory functioning was examined using the source memory task. Treatment with paclitaxel did not impair spatial and episodic memory, and paclitaxel treated rats were not more susceptible to cognitive challenges. Under conditions in which memory was not impaired, paclitaxel treatment impaired learning of new rules, documenting a decreased sensitivity to changes in experimental contingencies. These findings provide new information on the nature of cancer chemotherapy-induced cognitive impairments, particularly regarding the incongruent vulnerability of episodic memory and new learning following treatment with paclitaxel.

Long-lasting impairments in adult neurogenesis, spatial learning and memory from a standard chemotherapy regimen used to treat breast cancer

The negative impact of chemotherapy on cognitive function in cancer patients has gained increasing attention in the last decade. Whilst the short-term acute effects on cognition are expected following chemotherapy, the persistence of such impairments in the long-term is still in question. This is despite clinical evidence indicating cognitive difficulties may persist well beyond treatment and affect quality of life. In the present study, we assessed the long-term (3 months) cognitive impact of chemotherapy in a mouse model intended to mimic the human female post-menopausal population receiving chemotherapy for breast cancer. Ovariectomized, female, C57BL/6J mice received two doses of Doxorubicin, Cyclophosphamide, and 5-Fluorouracil or saline vehicle (control), separated by one week. During this interval, mice received BrdU injections to label dividing cells. Results indicate a persistent impairment in learning and recall (1h, 24h and 48h) on the Morris water maze, reduced survival and differentiation of new neurons (BrdU+/NeuN+), and a persistent decline in proliferation of new cells (Ki67(+)) in the dentate gyrus. Locomotor activity, motor performance, and anxiety-like behavior were unaffected. We further evaluated the efficacy of a diet enriched in omega-3-fatty acids (DHA+EPA+DPA), in reversing long-term chemotherapy deficits but no rescue was observed. The model described produces long-term cognitive and cellular impairments from chemotherapy that mimic those observed in humans. It could be useful for identifying mechanisms of action and to test further the ability of lifestyle interventions (e.g., diet) for ameliorating chemotherapy-induced cognitive impairments.

The impact of sustained and intermittent docetaxel chemotherapy regimens on cognition and neural morphology in healthy mice

RATIONALE

A subset of cancer survivors demonstrates impairments in cognition long after chemotherapy completion. At present, it is unclear whether these changes are due to direct neurotoxic effects of chemotherapy.

OBJECTIVES

This study examined the impact of variable docetaxel (DTX) chemotherapy dosing on brain DTX exposure via analyses of neural morphology and changes in cognition.

METHODS

Male CD-1 mice were treated with DTX either intermittently (8 mg/kg i.p. weekly) or via a sustained delivery system (DTX-PoLigel), which continuously releases DTX. Both groups received total DTX doses of 32 mg/kg. Mice were assessed on the novel object recognition (NOR) task and the Morris water maze (MWM) shortly after treatment.

RESULTS

Post-treatment behavioral testing demonstrated impaired NOR in mice treated with either dosing schedule relative to controls. No differences were observed between groups in MWM training and initial testing, though control mice performed better than chance while DTX-treated mice did not. Appreciable amounts of DTX were found in the brain after both treatment regimens. DTX treatment did not significantly increase levels of apoptosis within the CNS. However, some elevation in neural autophagy was observed following DTX treatment. Analysis of astrocytic activation demonstrated that intermittent DTX treatment resulted in an elevation of GFAP-positive astrocytes for 48 h after administration. Sustained chemotherapy demonstrated prolonged but lower levels of astrocyte activation over 9 days following implantation.

CONCLUSIONS

DTX treatment induced cognitive impairment shortly after treatment. Further, these findings suggest an association between DTX dosing, neurotoxicity, and cognitive effects.

The short and long term effects of docetaxel chemotherapy on rodent object recognition and spatial reference memory

AIMS

Previous animal studies have examined the potential for cytostatic drugs to induce learning and memory deficits in laboratory animals but, to date, there is no pre-clinical evidence that taxanes have the potential to cause cognitive impairment. Therefore our aim was to explore the short- and long-term cognitive effects of different dosing schedules of the taxane docetaxel (DTX) on laboratory rodents.

MAIN METHODS

Healthy male hooded Wistar rats were treated with DTX (6 mg/kg, 10mg/kg) or physiological saline (control), once a week for 3 weeks (Experiment 1) or once only (10mg/kg; Experiment 2). Cognitive function was assessed using the novel object recognition (NOR) task and spatial water maze (WM) task 1 to 3 weeks after treatment and again 4 months after treatment.

KEY FINDINGS

Shortly after DTX treatment, rats perform poorly on NOR regardless of treatment regimen. Treatment with a single injection of 10mg/kg DTX does not appear to induce sustained deficits in object recognition or peripheral neuropathy.

SIGNIFICANCE

Overall these findings show that treatment with the taxane DTX in the absence of cancer and other anti-cancer treatments causes cognitive impairment in healthy rodents.

Effects of early chemotherapeutic treatment on learning in adolescent mice: implications for cognitive impairment and remediation in childhood cancer survivors

PURPOSE

Among children diagnosed with acute lymphoblastic leukemia (ALL) and given chemotherapy-only treatment, 40% to 70% of survivors experience neurocognitive impairment. The present study used a preclinical mouse model to investigate the effects of early exposure to common ALL chemotherapeutics methotrexate (MTX) and cytarabine (Ara-C) on learning and memory.

EXPERIMENTAL DESIGN

Preweanling mouse pups were treated on postnatal day (PND) 14, 15, and 16 with saline, MTX, Ara-C, or a combination of MTX and Ara-C. Nineteen days after treatment (PND 35), behavioral tasks measuring different aspects of learning and memory were administered.

RESULTS

Significant impairment in acquisition and retention over both short (1 hour) and long (24 hours) intervals, as measured by autoshaping and novel object recognition tasks, was found following treatment with MTX and Ara-C. Similarly, a novel conditional discrimination task revealed impairment in acquisition for chemotherapy-treated mice. No significant group differences were found following the extensive training component of this task, with impairment following the rapid training component occurring only for the highest MTX and Ara-C combination group.

CONCLUSIONS

Findings are consistent with those from clinical studies suggesting that childhood cancer survivors are slower at learning new information and primarily exhibit deficits in memory years after successful completion of chemotherapy. The occurrence of mild deficits on a novel conditional discrimination task suggests that chemotherapy-induced cognitive impairment may be ameliorated through extensive training or practice.

Cognitive impairments caused by oxaliplatin and 5-fluorouracil chemotherapy are ameliorated by physical activity

RATIONALE

Studies in women with breast cancer, and in animal models, have demonstrated that chemotherapy can have a negative impact on cognitive function. Which chemotherapy agents cause problems with cognition and the aetiology of the impairment is unknown. Furthermore, there is no proven treatment.

OBJECTIVES

This study aimed to evaluate the effects of 5-fluorouracil (5FU) and oxaliplatin (OX) chemotherapy agents commonly used to treat colorectal cancer on cognition in laboratory rodents. Furthermore, we assessed physical activity as a potential remedy for the observed chemotherapy-induced cognitive deficits.

RESULTS

In rodents, treatment with 5FU and OX alone impairs memory as measured by novel object recognition. But combined treatment appears to have greater detrimental effects on hippocampal-dependent tasks, contextual fear recall and spatial reference memory (water maze), yet had no effect on cued fear recall, a non-hippocampal task. These impairments were prevented by 4 weeks of wheel running overnight after 5FU/OX treatment. We found a significant interaction between chemotherapy and exercise: rats receiving both 5FU/OX and exercise had improved cognition relative to non-exercising 5FU/OX rats on novel object recognition and spatial reference memory.

CONCLUSIONS

The combination 5FU/OX had a significant impact on cognition. However, rats treated with 5FU/OX that exercised post chemotherapy had improved cognition relative to non-exercising rats. This suggests that physical activity may prove useful in ameliorating the cognitive impairments induced by 5FU/OX.

Disruption of learning processes by chemotherapeutic agents in childhood survivors of acute lymphoblastic leukemia and preclinical models

OBJECTIVE

With the survival rate of acute lymphoblastic leukemia (ALL) surpassing 90 percent within this decade, new research is emerging in the field of late effects. A review of the research investigating the relationship of treatment regimens for ALL to specific late effect deficits, underlying mechanisms, and possible remediation is warranted to support continued studies.

METHODS

The clinical literature was briefly surveyed to describe the occurrence and topography of late effects, specifically neurocognitive deficits. Additionally, the preclinical literature was reviewed to uncover potential underlying mechanisms of these deficits. The advantages of using rodent models to answer these questions are outlined, as is an assessment of the limited number of rodent models of childhood cancer treatment.

RESULTS

The literature supports that childhood survivors of ALL exhibit academic difficulties and are more likely to be placed in a special education program. Behavioral evidence has highlighted impairments in the areas of attention, working memory, and processing speed, leading to a decrease in full scale IQ. Neurophysiological and preclinical evidence for these deficits has implicated white matter abnormalities and acquired brain damage resulting from specific chemotherapeutic agents commonly used during treatment.

CONCLUSIONS

The exact role of chemotherapeutic agents in learning deficits remains mostly unknown. Recommendations for an improved rodent model of learning deficits in childhood cancer survivors are proposed, along with suggestions for future directions in this area of research, in hopes that forthcoming treatment regimens will reduce or eliminate these types of impairments.

Intraepidermal nerve fiber loss corresponds to the development of taxol-induced hyperalgesia and can be prevented by treatment with minocycline

Loss of intraepidermal nerve fibers (IENFs) has been speculated to play a critical role in the development of various neuropathies. In this study, the density of IENFs were studied over time during the induction of Taxol (Bristol-Myers Squibb, NY, USA)-induced chemoneuropathy and compared with the changes in IENFs in animals co-treated with Taxol plus the protective agent minocycline. Rats were injected (intraperitoneally) with 2mg/kg of Taxol every other day for four injections (day 1, 3, 5, and 7). Minocycline (25mg/kg) was given in a separate group of rats 24h prior to the first dose of Taxol and every day for the next 9days (day 0 through 9). Animals were tested for mechanical paw withdrawal thresholds prior to any drug administrations and again on day 7, 14, and 30. Immunohistochemistry using the pan-neuronal marker protein gene product 9.5 was performed on glabrous skin of the hind-paw foot pad to stain for IENFs also on day 7, 14, and 30. The results show that Taxol-treated animals developed mechanical sensitivity and corresponding IENF loss. Animals receiving minocycline plus Taxol showed no hyperalgesia or loss of IENFs. This study confirms, for the first time, that a loss of IENFs occurs as a neuropathy develops, and further shows a protection against both IENF loss and hyperalgesia with minocycline treatment. The progression of Taxol-induced mechanical hypersensitivity coincides with loss of intraepidermal nerve fibers, and the hyperalgesia and nerve fiber loss were prevented with minocycline treatment.