The neuroprotective and therapeutic effects of nicotine on forepaw stepping in the 6- OHDA animal model of Parkinson’s disease

Andrew J. Caraganis  (Neuroscience)

Advisor: John E. Kelsey

Based upon observations that people who smoke have a significantly lower risk of developing Parkinson’s disease, I examined the effects of nicotine’s neuroprotective and therapeutic effect on the unilateral injection of the selective dopamine neurotoxin 6- hydroxydopamine (6-OHDA) into the medial forebrain bundle on forelimb stepping. My experiment showed that the unilateral 6-OHDA lesions decreased stepping with the right paw and that this deficit was not affected by pretreatment with 1.0 mg/kg nicotine given 30 min prior to and 4 hrs after surgery followed by 0.5 mg/kg nicotine given once a day for five days. On the other hand, acute injections of 0.4 mg/kg nicotine after the lesion did transiently improve stepping with the right paw, but not as much as did injections of 8 mg/kg L-DOPA. Moreover, 0.4 mg/kg nicotine failed to potentiate the therapeutic effects of 8 mg/kg L-DOPA. This study suggest that deficits in stepping are a very reliable means for determining akinesia in lesioned rats, and that nicotine indeed has a small therapeutic effect which warrants continued research.

Bidirectional locomotor cross-sensitization between sucrose and amphetamine

Sarah Martin Gray (Neuroscience- Honors)

Advisor: John E. Kelsey

The dopamine (DA) hypothesis of reward suggests that all substances that produce reward do so because they increase DA transmission. Consistent with this hypothesis, repeated administration of rewarding drugs, like amphetamine, progressively increases DA release and locomotion, and this effect cross sensitizes to related drugs such as cocaine. If the DA hypothesis is correct, we might expect that sensitization to such drugs could cross sensitize to real reward such as sucrose, and vice versa. Experiment 1 showed that daily injections of 3 mg/kg amphetamine subsequently increased the locomotor response to a small taste of 10% sucrose, and Experiment 2 showed that 12 daily 12-hr exposures to 10% sucrose enhanced the subsequent locomotor response to 0.5 mg/kg amphetamine. In Experiment 3, I found that lesions of the basolateral amygdala (BLA), a structure implicated in both drug and food reward, enhanced the locomotor cross-sensitization from sucrose to amphetamine. These studies suggest possible mechanisms for the co-morbidity between eating disorders, especially binge eating, and drug abuse and also suggest that the BLA may have differential roles in mediating sensitization to drugs and food.

Medial septal lesions enhance cocaine-induced suppression of saccharin intake in rats

Lindsey R. Hamilton (Neuroscience)

Advisor: John E. Kelsey

Pairings of saccharin solution with injections of an addictive drug can induce rats to suppress their subsequent intake of saccharin. It has been hypothesized that this effect is mediated by presumed aversive properties of the addictive drug, similar to traditional conditioned taste aversions produced by pairing a novel taste with an illness-inducing substance. However, it has also been suggested that addictive drug-induced suppression of saccharin intake is mediated by the rewarding effects of the drugs since pairing saccharin with sucrose, a substance presumably without aversive properties, is also able to induce suppression of saccharin intake. In order to determine which of these competing theories is correct, the effect of medial septal lesions on 15 mg/kg cocaine-induced suppression of .15% saccharin intake was investigated. Animals received daily pairings of saccharin and cocaine during six 5-min 1-bottle conditioning trials alternating with six presentations of water. On the day following the final conditioning trial, animals were presented with both saccharin and water solutions in a 10-min 2-bottle test. Animals that.had cocaine paired with saccharin drank less saccharin than the controls which had saline paired with saccharin. The medial septal lesions had no effect on saccharin or water intake during the 1-bottle conditioning trials. However, in the 2-bottle test, medial septal lesions decreased the percentage of saccharin consumed in rats in which saccharin had been paired with cocaine. Since medial septal lesions appear to enhance the rewarding effects of drugs of abuse, this finding suggests that cocaine-induced suppression of saccharin intake may be mediated by the rewarding properties of cocaine, i.e., the more rewarding the drug, the greater the suppression.

Spinal cord injury: neuroprotection, regeneration, rehabilitation

Amy Hempstead (Neuroscience)

Advisor: Nancy Kleckner

Metabotropic glutamate 2/3 receptor agonist, LY379268, reverses PCP-induced behaviors in a model of schizophrenia

Caitlin H. Hornberger (Neuroscience)

Advisor: John E. Kelsey

Recent findings that the positive, negative, and cognitive symptoms of schizophrenia can be induced by injections of the glutamate NMDA receptor antagonist seemed to implicate reduced glutamate in schizophrenia. However, recent evidence suggests that PCP may enhance glutamate transmission at non-NMDA receptors. In this study, PCP (4.0 mg/kg) was shown to induce hyperlocomotion and decrease head dipping in rats, two behaviors presumed to reflect the positive and negative symptoms, respectively. These PCP-induced behaviors were found to be reversed when the subjects were pretreated with 1.5 and 3.0 mg/kg of LY379268, a metabotropic glutamate receptor 2/3 agonist. Since LY379268 is assumed to act on autoreceptors to reduce glutamate release, these findings are consistent with the suggestion that schizophrenia may be due to enhanced glutamate transmission at non-NMDA receptors. Finally, given the high correlation between smoking and schizophrenia, rats were also administered nicotine at various doses (0.1, 0.2, 0.4, and 0.8 mg/kg). This treatment was not consistently effective but tended to increase the PCP-induced locomotion, while reducing the PCP-induced decrease in dips. Future studies should investigate the effects of metabotropic glutamate receptor 2/3 agonists and nicotine on cognitive deficits associated with schizophrenia.

The effects of cocaine preexposure and medial septal lesions on cocaine mediated taste avoidance

Lauren Jacobs (Psychology)

Advisor: John E. Kelsey

If a novel taste, such as .15% saccharin, is followed by an injection of an otherwise rewarding drug such as cocaine, rats reliably develop an avoidance of this taste. Two competing hypotheses have been developed to explain this paradoxical finding. One suggests that the centrally rewarding drugs also have initially aversive peripheral effects that account for the avoidance. The second suggests that the powerful rewarding effects of cocaine overshadows and thereby diminishes the rewarding effects of saccharin. This thesis was undertaken with the goal of providing clear evidence for one of these theories. In Experiment 1, rats received 10 days of 10 mg/kg cocaine preexposure determine how sensitization to cocaine would affect the strength of taste aversions. Pairings of 10 mg/kg of cocaine with .15% saccharin did not produce taste avoidance but 15 mg/kg of cocaine did produce a taste avoidance. However, there was no effect of preexposure. In Experiment 2, lesions of the medial septum were created in an effort to determine whether the presumed facilitation of reward produced by the lesion would affect the strength of taste aversions. Medial septal lesions have been shown to increase reward values and therefore lesioned animals should show an increased taste aversion if the reward-comparison hypothesis is correct. Pairings of .15% saccharin with 15 mg/kg of cocaine produced taste avoidance but there was no effect of lesion on the strength of taste avoidance. Thus, these two experiments failed to provide differential support for either theory.

Effects of Tetrandrine (TET), isolated from the Chinese herb, Stephania tetrandra, on NMDA receptors expressed in Xenopus laevis oocytes

Kate Kolstad (Biochemistry & Neuroscience)

Advisor: Nancy Kleckner

The purpose of the present study was to extract the compound, Tetrandrine (TET), from the root of Stephania tetrandra S. Moore and explore TET’s effect on NMDA receptor subunits (NR1/NR2A) expressed in Xenopus laevis oocytes. Based upon TET’s well characterized calcium channel antagonizing character, it was expected that TET would inhibit NMDA-induced currents. Methylene chloride extraction and column chromatography was used to isolate TET. Cells pre-perfused with TET inhibited NMDA/Glycine currents with a greater magnitude than cells that were not pre-perfused. The sample size in this experiment was too small to determine any significant difference. Dose-response data indicate that there was a significant effect of treatment when TET was applied at varying concentrations (100μM and 300μM). However, pairwise comparisons indicate that only recovery currents were significantly different from initial NMDA/Glycine and TET/NMDA/Glycine currents. Furthermore, the calcium chelator, 2 -bis-2aminophenoxy ethane -N,N,N’ ,N’ -tetraacetic acid (BAPTA), reduced any effects TET had on NMDA-induced currents. Further research investigating TET’s ability to cross the cell membrane and bind calcium is necessary to determine whether TET functions similarly to that of intracellular calcium chelators. It would also be beneficial to study TET’s dose-response effects (with a greater range of concentrations), voltage -dependence, and use-dependence to better characterize the means by which TET effects NRI/NR2A mediated cellular activity in Xenopus laevis ooctyes.

Correlation of salivary cortisol levels with performance on fontal lobe versus non-fontal lobe task

Elizabeth Lewis (Neuroscience- Honors)

Advisor: Cheryl McCormick

Research investigating the impact of stress has focused on cognitive functions associated with the hippocampus, a brain structure sensitive to stress hormones.  However, new findings implicate other brain regions in the effects of stress.  Recently, in the rhesus monkey brain, unlike in the rat brain, stress hormone receptors have been shown to be relatively absent in the hippocampus, yet present in the prefrontal cortex.  Therefore, early extrapolation from rat studies may have been misleading.  I attempted to elucidate the effect of the stress hormone cortisol on the prefrontal cortex by testing performance on a cognitive task associated with the prefrontal cortex.  Participants were also tested on a cognitive task associated with the parietal cortex, a region without stress hormone receptors.  Half of the eighty subjects were stressed prior to testing; the other half were not.  The stressor consisted of performing rapid addition of numbers while being videotaped.  This task is known to elevate cortisol levels.  Salivary cortisol levels were obtained several times throughout the session, measured using radioimmunoassay, and correlated with performance on each task to determine the relationship between stress, cortisol, and the frontal lobe.  It was hypothesized that cortisol levels would correlate with performance on the frontal lobe task, but not on the non-frontal lobe task.

Effects of Aβ25-35 and Aβ42 on α7 and α4β2 nicotinic acetylcholine receptors expressed in Xenopus laevis oocytes

Elise Abigail McVarish (Neuroscience)

Advisor: Nancy Kleckner

Recent studies have demonstrated a potential role for nicotinic acetylcholine receptors (nAChR) in the pathology of Alzheimer’s Disease (AD). Alzheimer’s disease results from the degradation of the cholinergic system in the brain leading to cognitive dysfunction phenotypically represented by severe memory disruption. The AD brain produces the protein beta amyloid1-42 (Aβ42) at a higher rate than healthy brains ultimately causing the formation of amyloid plaques; a fragment of the protein, Aβ25-35 has been shown to be neurotoxic in culture. Neurotoxicity can be attenuated with application of an α4β2 nAChR agonist. Furthermore, α7 coimmunoprecipitates with Aβ plaques; it has been demonstrated that Aβ42 binds to α7 nAChR with differing effects depending on concentration and application. The present study endeavored to investigate how these proteins might directly affect the aforementioned receptors. nAChR subtypes α7 and α4β2 were expressed inXenopus laevis oocytes and tested for activation in response to Aβ42 and Aβ25-35. Neither protein independently activated either receptor but when perfused in conjunction with ACh there was a marked diminution in response as compared to the ACh control response.

The incubation of cocaine-induced locomotor sensitization in rats is eliminated by the administration of saline during the initial abstinence period: implications for the cue-dependency of incubation

Randi Rawson (Neuroscience)

Aram Parsegian (Psychology)

Advisor: John E. Kelsey

Previous studies in both reinstatement and behavioral sensitization models have shown that the expression of cocaine- and amphetamine-induced addictive behaviors increase or incubate across abstinence periods as great as 3 months or more. Experiments 1 and 2 were attempts to replicate this incubation phenomenon using locomotor sensitization in response to repeated injections of cocaine. Rats were pretreated daily with either 0.9% saline or 10 mg/kg of cocaine for 8 consecutive days and then abstained for 3, 8, or 15 days before receiving a cocaine challenge, to which their locomotor response was measured using a video tracking system. While a small challenge dose of 5 mg/kg in Experiment 1 failed to induce incubation of locomotor sensitization, a 10 mg/kg challenge dose in Experiment 2 induced the predicted incubation i.e., the previously sensitized animals were more active in response to the cocaine challenge after 15 days of abstinence than after 3 or 8 days. Experiment 2 also indicated that twice daily injections of the glutamate NMDA antagonist, MK-801, during the first 5 days of abstinence eliminated the incubation. However, saline injections during abstinence were at least as effective. This latter finding suggests that these injections may have eliminated incubation by extinguishing the cues, e.g., handling and injections, that had previously predicted cocaine. This interpretation would suggest that incubation is cue-dependent; although, subsequent studies will be necessary to determine the direct cause of this elimination.

Acute daytime administration of melatonin does not impair rat spatial memory

Sarah Persing  (Psychology)

Advisor: Roxanne Prichard

Melatonin, a hormone that modulates circadian rhythm, is being sold over the counter for treatment of insomnia as an alternative to benzodiazepines (BZs), which produce decrements in various facets of cognitive performance. Recent research suggests that melatonin may also produce decrements in neurobehavioral performance. To date, very little research has been conducted investigating melatonin’s acute effects on memory in healthy, non-impaired individuals. In the present experiment, rats (n=12) were first tested on their spatial memory performance using the Morris water maze with respect to the time of day for which rats are inactive (08:00h) or active (18:00h) in Experiment 1. Distance traveled (%) in the SE quadrant and time (in sec) to reach the platform was recorded. For Experiment 2, a 10mg/kg injection of melatonin or control was administered during the rats’ inactive phase (08:00h). Rats performed the water maze task 20min following the injection in order to see if melatonin produced any decrements in spatial memory. The results indicated that there was no significant difference in rat spatial memory performance between inactive and active phases in Experiment 1. For Experiment 2, injections with melatonin did not impair spatial memory performance and a minor enhancement was found for distance traveled in the Southeast (SE) quadrant of the water maze in the first trial of Day 1, suggesting that rats were remembering the original position of the platform. Based on the present study, exogenous treatment with melatonin during the daytime does not seem to produce any decrements in spatial memory performance, and may even enhance memory.

Effects of exposure to nicotinic receptor agonist and secreted form of α-cleaved amyloid precursor protein following β-amyloid-induced toxicity in hippocampal culture

Timothy D. Talbot (Neuroscience)

Advisor: Nancy Kleckner

Alzheimer’s Disease (AD) is a neurodegenerative disorder that is characterized by memory loss and dementia as a result of the formation of β-amyloid (Aβ)plaques within the hippocampus. It is the direct exposure of this toxic APP-cleaved peptide to neuronal cultures that causes cell death through a believed interaction with specific nicotinic acetylcholine receptors (nAChR). This study looked at similar ways in which Aβ-induced toxicity could be attenuated using nicotine or sAPPα on hippocampal neurons cultured from embryonic day 18 rats. The toxicity of Aβ was consistently observed in a dose-dependent manner with concentrations ranging from 0.5-30 μM, and respective decreases in viable cell populations by 20-65%. Evidence of neuroprotection was not displayed in any experiments utilizing nicotine or the alternatively cleaved APP product, both of which had previously been shown to attenuate some of the Aβ-related cell death by other researchers. Pre-incubations for 24 hours with the two substances showed little to no difference in comparison to same timed combinations with Aβ. It is proposed that the cultures used in this study may have lacked the necessary nAChR expression levels for either the nicotine or the sAPPα  product to take on any significant protective effect.