Investigation of the Effects of a Depressant and a Stimulant on Brain Stimulation Reinforcement. Rebecca Foster, Sacha Shellenbarger, John Renfrew, and Cynthia Prosen, Northern Michigan University, Psychology Department, Marquette, MI 49855
The medial forebrain bundle (MFB) has been identified as a pleasure center in the brain. Research has demonstrated that subjects of various species would respond to produce electrical stimulation of this structure. The present study examined the effects of two commonly ingested chemical substances on the pleasure mechanism. It was hypothesized that the stimulant drug would suppress the threshold, therefore increasing the frequency of bar presses. Additionally, it was hypothesized that the depressant would increase the threshold, thus decreasing the frequency of bar presses. A stimulant, caffeine, and a depressant, alcohol, were given to rats to assess the effects these drugs would have on self-stimulatory pleasure-seeking behavior. Subjects underwent a surgical implantation of an electrode into the MFB. Each subject received 35mL of water per day. During the treatment period, the chemical variable was delivered to the subject through the water supply. A baseline period was established for each subject for com parison during the treatment period. During treatment, each subject was randomly selected to receive one of the variables. Treatment lasted a period of four weeks with the subject tested biweekly. Histologies were performed on each subject to determine the exact location of the implanted electrode.
Continuing Exploration of Functional Deficits in Mice Lacking Auditory Efferent System Receptors. Sacha Shellenbarger, Crystal Ebert, Joe Greising, Alyssia Rogers, and Cynthia Prosen, Northern Michigan University, Psychology Department, Marquette, MI 49855
The auditory olivocochlear (OC) efferent nerve pathway begins in the brainstem and projects to the inner ear. Research has demonstrated that animals with lesions in this pathway have hearing deficits in noisy environments, while preliminary human data suggest that OC-damaged humans cannot focus auditory attention. Since the lesioning procedure did not ensure a precise and complete removal of the efferent system, a genetically altered mouse ([euro]9 Ach receptor subunit knockout) was developed in which the peripheral cochlear Ach receptor sites were deleted. A previous study from our laboratory that compared knockout and normal hearing mice found that both groups had comparable intensity difference thresholds when tested in noise. In the current study, six female CBA/J mice were tested with different frequency bands of background noise to increase the auditory attention demands of the task. Preliminary data suggest that the normal mice could focus on the differing frequencies of the noise bands. A planned expe riment will compare these control data with those from [euro]9 knockout mice.
The Functional Age of Hearing Loss in a Mouse Model of Premature Hearing Loss. Neil Pascoe, Kathleen Curran, Lisa Gardner, Casey Vogelheim, Cynthia Prosen, Northern Michigan University, Psychology Department, Marquette, MI 49855
Presbycusis is a human hearing disorder that progresses with age. The decay advances from higher to lower frequencies, causing particular deficits of hearing in noisy backgrounds. The mutant strain of C57BL/6J mice has a progressive hearing disorder that parallels the human condition of presbycusis. The purpose of this research was to determine how similar the progressive hearing loss in C57BL/6J mice was to mice of CBA/CaJ strain, which have normal hearing abilities throughout their lifespan. Both strains of mice were tested in a tone detection task with and without background noise. The hearing loss in C57BL/6J mice generally occurred in two phases, one gradual and the other abrupt. Further, C57BL/6J mice had a hearing loss that was first detectable with background noise and advanced from higher to lower frequencies. …