Isolation and mapping of identified buccal ganglia neurons in Helisoma trivolvis.
Abdul Bachani (Neuroscience, ’03)
Advisor: Nancy Kleckner
Complex motor activity is controlled by activity of underlying neuronal networks called the central pattern generator (CPG). The feeding CPG in the pond snail Helisoma trivolvis is a highly plastic system and is comprised of three subunits – S1, S2, and S3. Glutamate has been identified as the key neurotransmitter in this system. Glutamate from B2, an S2 interneuron thought to modulate the feeding pattern, has been shown to inhibit the activity of two key motor neurons – B5 and B19, of S1 and S3, respectively. This is unlike the actions of glutamate in the vertebrate systems, whereby its effects are almost excitatory. Not much is known about the inhibitory effects of glutamate and the pharmacology and mechanisms underlying it. Various studies using the intact nervous system have been aimed at studying the same, however, studying neurons in isolation would give us a better idea of whether the effects of glutamate are direct, and also study its effects in isolation from the natural environment, without the interference of the normal signals that theses neurons received. Also important was mapping the interneuron B2 so as to enable us characterize and understand the diverse functions and effects that glutamate has in the Helisoma nervous system, and hence enhance our understanding of the same. Isolation of neurons B5 and B19 was done in an attempt to study the neurons in isolation from their normal environment, and intracellular staining techniques – using Lucifer yellow and Cobalt Chloride, were employed to map out the interneuron B2. The cells did not survive in culture past a couple of days and the staining techniques were not as successful. Though preliminary results are promising, these techniques need to be perfected and ironed out in order to further this study.
An animal model of schizophrenia: electrolytic medial septal lesion produces behavioral symptoms of schizophrenia in a hole board apparatus (HBA).
Lesley Boakye-Danquah (Neuroscience, ’03)
Advisor: John Kelsey
Schizophrenia is a complex, dishabilitating, psychiatric disorder that currently affects at least 2 million Americans (Ellenbrook & Cools, 2000). One of the more recently recognized characteristics of schizophrenia is the common incidence of substance abuse (Selzer & Lieberman,1993). The “self-medication hypothesis” has previously suggested that schizophrenics turn toward addictive drugs to alleviate aspects of their psychosis, negative symptoms, cognitive impairment or medication side effects (Buckley, 1998; Chambers et al., 2001; Zisook et al., 1992). In challenge of this hypothesis Chambers and colleagues (2001) offer that schizophrenic individuals may be vulnerable to drug-addiction, based on neurochemistry, physiology and behaviors that are consistent in both schizophrenia and the pathology of addiction. Seeing that the medial septal area has been implicated as a mediator of processes that underlie locomotor sensitization to addictive drugs (Kelsey & Graberek), it was examined in this thesis as a potential neurosubstrate mediating the symptomology of schizophrenia. The findings showed that lesion to the medial septal area seem to be able to produce both increased activity and reduced exploratory behavior (measured by head dips) in the hole board apparatus, potentially indicative of positive and negative symptoms of schizophrenia, respectively, however on further drug studies with raclopride, ketanserin and clozapine this conclusion is less clear. Implications for the medial septal area as a potential model of the disease are discussed.
Spatial memory in feminized male rats: The effects of altered spatial cues.
Peter Currie (Psychology, ’03)
Advisor: Cheryl McCormick
The spatial memory of adult male rats was examined following administration of pre- and postnatal flutamide to block the effects of androgens on early development. While androgens are necessary for male development their absence is a crucial component of female development. Thus, early flutamide treatment results in the physical and cognitive feminization of males. It was hypothesized that treatment with flutamide would lead to impaired performance on a Morris water maze test, as females demonstrate poorer spatial abilities than males. The results of Experiment I did not support this hypothesis, however, as no difference in performance was found between flutamide treated and control males. Several factors may account for this, as the animals used were older (4 months of age) than those in most studies, and it is possible that both androgens in later life, as well as estrogens during early development, may have affected spatial ability. Previous studies have found that males and females depend on different visual aspects of the environment to guide their performance on spatial tasks. In Experiment 2 the visual cues of the testing room were rearranged and the effect of this change on performance was examined. The results indicated that controls were more impaired on the first trial in this rearranged environment than were flutamide treated males, although this difference was not significant. Future studies will do much to clarify the cumulative contributions of sex hormones, at all stages of development, to spatial ability.
Electrolytic Lesions of the Core, but not the Shell of the Nucleus Accumbens Enhance Context-Specific Locomotor Sensitization to Nicotine
Lyle P. Gerety (Neuroscience, ’03)
Advisor: John Kelsey
The mesolimbic dopamine (DA) system, extending from the ventral tegmental area to the n. accumbens (NAS), is commonly considered the primary neural substrate of reward and addiction. Recent studies have shown that two anatomically distinct sub regions of the NAS, the “shell” and “core”, may be functionally dissociable. To further our understanding of the function of these two sub-regions, we examined the effects of separate core and shell lesions on context-specific locomotor sensitization to repeated injections of 0.4 mg/kg nicotine. Bilateral electrolytic lesions of the n. accumbens core increased locomotion, tended to increase the initial locomotor response to nicotine, and increased context-specific sensitization by enhancing sensitization in animals that had previously received nicotine in the testing environment (paired), and abolishing sensitization in animals that had received nicotine in an environment distinct from the locomotor testing environment (unpaired). Bilateral electrolytic lesions of the NAS shell tended to increase locomotion, decreased the acute locomotor response to nicotine, and did not alter locomotor sensitization to repeated injections of nicotine. Given the presumed role of the n. accumbens core in reward and in learning about reward, this finding of enhanced context-specific sensitization following core lesions was surprising. The enhanced sensitization in the core-lesioned, paired animals may be related to the increased activity and acute response to drugs. The decreased sensitization in the core-lesioned, unpaired animals may reflect a decreased ability to generalize. These results suggest that the n. accumbens core and shell are differentially involved in mediating reward.
Gender-Specific Effects of Meditation on Cognitive Performance in Novice Meditators
JooRi Jun (Neuroscience, ’03)
Advisor: Cheryl McCormick
The hypothesis that meditation facilitates cognitive processing of the right hemisphere was tested in novice-meditators and non-meditators. Male and female novice meditators were trained in Brain Respiration, an energy-based meditation technique. Performance data of novice and non-meditators on a left-hemisphere mediated verbal test and a right-hemisphere mediated spatial test were compared. Verbal scores between the groups were not significantly different. Spatial scores of males between the groups were not significantly different, but spatial scores of female novice meditators were lower than that of female non-meditators. The results suggest a gender-specific effect of meditation on hemispheric laterality in novice meditators. It is possible that some other factor, correlated with subjects’ sex may be responsible for this gendered difference.
The Neuroprotective and Therapeutic Effects of Caffeine on Forepaw Stepping in an Animal Model of Parkinson’s Disease
Kimberly H. Martell (Neuroscience, ’03)
Advisor: John Kelsey
Based on observations that coffee drinkers are less likely to develop Parkinson’s disease (PD), the purpose of this study was to detennine if caffeine would exert neuroprotective or therapeutic effects in an animal model of PD. This was done by measuring the effects of both pre- and post-surgical caffeine treatments on the forelimb stepping deficits produced by injections of the selective dopamine neurotoxin 6-hydroxydopamine (6 -OHDA) into the nigrostriatal pathway at either the medial forebrain bundle (MFB) or the corpus striatum. Experiments 1 and 2 showed a slight neuroprotective effect of caffeine on forward, but not lateral stepping, and also a therapeutic effect of acute caffeine administration that peaked at 20 mg/kg. Experiment 3 showed that acute treatment’s of a combination of L- Dopa (8 mg/kg) and caffeine (20 mg/kg) act synergistically to not just improve, but to eliminate the stepping deficits entirely. This study demonstrates the potential neuroprotective abilities of caffeine and highlights its use acutely, both alone and especially in combination with L-Dopa, for treating PD. Future studies should examine the effects of more specific adenosine A2A antagonists both as neuroprotective and therapeutic agents.
Identification of the inhibitory glutamate receptor pathway in motor neurons involved in the feeding mechanism of the pond snail, Helisoma trivolis.
Kate Percarpio (Biology, ’03)
Advisor: Nancy Kleckner
A primary neurotransmitter in the vertebrates and invertebrate glutamate and its receptors are an essential focus of study in the scientific community. The much examined vertebrate glutamate receptor primarily activates excitation of the cell whereas invertebrate glutamate receptors mostly cause cellular inhibition. The purpose of this study was to identify the mechanism through which the binding of glutamate to invertebrate glutamate receptors causes the opening of ion channels and subsequent inhibition of the cell. In the pond snail, Helisoma trivolvis, glutamatergic neurons, B5 and B19, are integral to the central pattern generator of the feeding behavior. Intracellular recording technique was used to monitor activity of B5 and B19. A bath perfusion system was used to apply glutamate and possible antagonists to the cells. While glutamate inhibited the cells, known blockersof several inhibitory intracellular pathways, picrotoxin, pertussis toxin, NDGA, and BPB, were tested for their effects on cellular activity. A known blocker of ligand-gated chloride channels, picrotoxin toxin, did not block the inhibitory effects of glutamate in B5 and B19. Pertussis toxin and NDGA, both blockers of the lipoxygenase pathway, did not fully permeate the membrane of the cells and did not block the inhibitory pathway. BPB, a blocker of the lipoxygenase pathway, when applied to B5 was shown to have permeated the membrane but did not lock the inhibition by glutamate. This study concludes that inhibition by glutamate in the neurons B5 and B19 does not act through a Cl-gated ion channel, but instead through a G protein-linked intracellular pathway. The intracellular pathway is not, however, the lipoxygenase pathway of the arachidonic acid metabolism.
The Failure of Mecamylamine, a Nicotinic Receptor Antagonist, to Block Cocain-Induced Place Preference and Cocaine-Induced Behavioral Sensitization
Kristin A. Pick (Psychology, ’03)
Advisor: John Kelsey
The dopamine hypothesis of reward assumes that the rewarding/addicting/sensitizing effects of all addictive drugs are due to their ability to activate the meso limbic dopamine (DA) system. However, contrary to this hypothesis, locomotor sensitization to cocaine can be blocked by co -administration of the nicotinic receptor blocker, mecamylamine (Schoffelmeer et al., 2002). Because sensitization and reward are closely related, the first experiment investigated mecamylamine’s ability to block a more traditional measure of reward, conditioned place preference (CPP) in Long-Evans rats. Rats that were co-administered 3 mg/kg mecamylamine with 15 mg/kg cocaine developed a CPP that was comparable to rats that were administered saline with 15 mg/kg cocaine, indicating that mecamylamine does not have the ability to block the rewarding value of cocaine as measured in this task. The second experiment was done to see if mecamylamine could block cocaine-induced sensitization in our hands. These data showed that although co-administration of 3.0 mg/kg mecamylamine tended to decrease the development of locomotor sensitization to 7.5 mg/kg cocaine in paired animals, which received cocaine in the activity boxes (and saline in an alternative room), it did not affect the expression of sensitization to a challenge injection of 0.5 mg/kg amphetamine. Expression of sensitization to this challenge injection of amphetamine was reduced in unpaired animals, which received cocaine in the alternative environment (and saline in the activity boxes), indicating context-specific cross sensitization. As in the paired animals, expression of the cross-sensitization in the unpaired animals was not affected by prior treatment with mecamylamine. Thus, we were unable to find a role for nicotinic acetylcholine (ACh) receptor in either the CPP or locomotor sensitization produced by cocaine, indicating that the role of these receptors in mediating reward may not be extensive.
The effects of prenatal and neonatal treatment with flutamide on sexual behavior in the female rat.
Lynn Shaughnessey (Neuroscience, ’03)
Advisor: Cheryl McCormick
Previous research has shown that androgen exposure, early in development, is essential for the masculinization of the male reproductive phenotype (Hotchkiss, Ostby, Vandenburgh & Gray, 2002). Additionally, masculinization of behavior occurs when female rats are exposed to androgens prior to 10 days of age (Nelson, 2000). It has therefore been assumed that male behavior requires the effects of androgens whereas female behavior occurs in the absence of androgenic effects. The sexual behavior of females prenatally exposed to the anti-androgen flutamide has been examined and some studies have found an increase in female sexual behavior while others have found no significant results (Brand & Slob, 1991; Gladue & Clemens, 1981). The present thesis expanded on these conflicting studies and examined the effects of prenatal and neonatal flutamide on sexual behavior in the female rat. Long-Evans females were given injections of the anti-androgen flutamide or the control vehicle, oil, late in gestation (either from day 14 or day 19) and then from days 0-5 postnatally. Females were then ovariectomized in adulthood and sexual behavior was tested using paced mating. Flutamide was found to have no significant effect on lordosis behavior in the flutamide treated females. The proceptive behavior of ear wiggling was also not altered by prenatal and neonatal flutamide treatment. Although these aspects of sexual behavior remained normal, the attractivity of the flutamide treated females was significantly reduced. Males were not as interested in those females who had received flutamide; this was seen in decreased mounting of flutamide treated females when compared to mounts received by control females. The results of the present study suggest that flutamide altered some aspect of female attractivity. The flutamide females were exhibiting normal proceptive behaviors yet receiving fewer mounts by the male indicating flutamide may have altered some sort of androgen dependent olfactory source in the female rat. Future research into this possibility is needed.
The effects of chronic stress and testosterone on spatial memory in male rats.
Jennifer Tjepkema (Neuroscience ’03)
Advisor: Cheryl McCormick
Chronic stress on male rats’ spatial performance has previously been observed to be impaired, whereas chronically stressed female rats have enhanced performance in the radial arm maze. It was hypothesized that male rats impairments in spatial learning tasks might be due to testosterone because in females estrogen played a significant role in mediating the effects of chronic stress on the hippocampus. McCormick et al., (2002) observed that stressed GDX male rats spatial performance in the Morris water was enhanced compared to non-stressed GDX male rats. Based upon these findings I hypothesized that testosterone would impair chronically stressed male rats performance in the Morris water maze. For twenty-one days, thirty GDX, T-GDX or intact males were stressed six hours a day in Plexiglas restrainers. After the twenty-first day of restraint, rats were tested in the Morris water maze. The first day of testing was designed to habituate the animals to the Morris water maze, a curtain was draped around the perimeter of the tank to prevent spatial mapping. On the second day of testing the curtain was removed and the platform was submerged. The first day of testing there was a significant decrease of both latency and distance for stressed and non-stressed male rats to the visible platform. There was a significant effect of hormone on latency; intact rats had the shorter latency. On day two the first trial was not included in statistical analysis because during this trial subjects were “forming” a spatial map. There was no significant effect of hormone on latency or distance to the submerged platform for stressed or non stressed male rats. Stressed rats latency and distance did significantly decrease across trials compared to non-stressed male rats latencies and distances. These results indicate that testosterone neither has detrimental or beneficial effects on spatial performance, but chronic stress does have beneficial affects on spatial performance for male rats in the Morris water maze. One of the main reasons why this study might not have observed impairment in spatial memory as other studies have, could possibly be due to the fact that past studies tested male rats in the RAM not the MWM. The MWM, unlike the RAM, almost exclusively tests spatial memory whereas the RAM also tests associative and working memory. Furthermore, MWM is stressful, whereas the radial arm maze requires food deprivation. Other factors such as different restraining techniques, types of stressors, length of stressing, or the influence of other brain structures instead of the hippocampus (i.e. amygdala) on spatial performance could contribute to reasons why spatial memory has been observed to be enhanced or impaired in chronically stressed rats depending on the testing apparatus.
The effects of chronic restraint stress on male and female rat hippocampi.
Patti Waters (Biochemistry ’03)
Advisors: Glen Lawson & Cheryl McCormick
The hippocampus has been implicated in a variety of memory tasks, and damage to the hippocampus causes a decrease in performance for these tasks (He et al., 2002; Holland et al., 1999; Sziklas and Petrides, 2002; Deacon et al., 2002; Gilbert and Kesner, 2002). Stress has been shown to cause damage to the hippocampus and to cause deficits on hippocampal-dependent tasks (Conrad et al., 1996; Conrad et al., 1999; Diamond et al., 1999; Beck and Luine, 1999; Blank et al., 2002; Kim et al., 2001; Pavlides et al., 2002; Shors et al., 2001). Apoptosis is one of the forms of damage that occurs in the hippocampus as a result of stress (Conrad et al., 1996; Conrad et al., 1999). Bax and Bc1- 2 are apoptosis regulating proteins and can be used as a measure of apoptosis. This study looks at Bax and Bcl-2 levels in the hippocampi of male and female rats with and with out chronic stress. Previous studies have demonstrated significant sex differences on the effects of stress in the hippocampus (Moser et al., 2002; Holmes et al., 2002; Stein, 2001; Schors et al., 2001; Kavaliers et al., 1998), so here we will compare the damage occurring in males and females as well as the behavioral differences observed by Moser et al. (2002) with the same subjects. My results show that there is a non-significant trend for stress to lower Bcl-2 levels in both males and females, but no significant relationship was found to exist between stress and Bax levels. The Bcl-2 data contradicts the behavioral data; while both groups sustained damage at approximately equal levels, neither group showed a deficit in the Morris water maze. In fact, the males actually increased performance in the water maze (Moser et al., 2002). Therefore, the males’ performance on a hippocampal-dependent maze, the Morris water maze, must be due to activity outside the hippocampus and the increase in performance after stress must be due to an increase in function outside the hippocampus. Bartolomucci et al. (2002) also found that stress caused both damage to the hippocampus and an improvement on hippocampal dependent tasks in one group of animals. These results indicate that more investigation is necessary to understand the mechanisms and structures involved in these hippocampal dependent tasks.