Dose-response characteristics of methylphenidate on locomotor behavior and on sensory evoked potentials recorded from the VTA, NAc, and PFC in freely behaving rats.

BACKGROUND: Methylphenidate (MPD) is a psychostimulant commonly prescribed for attention deficit/hyperactivity disorder. The mode of action of the brain circuitry responsible for initiating the animals' behavior in response to psychostimulants is not well understood. There is some evidence that psychostimulants activate the ventral tegmental area (VTA), nucleus accumbens (NAc), and prefrontal cortex (PFC). METHODS: The present study was designed to investigate the acute dose-response of MPD (0.6, 2.5, and 10.0 mg/kg) on locomotor behavior and sensory evoked potentials recorded from the VTA, NAc, and PFC in freely behaving rats previously implanted with permanent electrodes. For locomotor behavior, adult male Wistar-Kyoto (WKY; n = 39) rats were given saline on experimental day 1 and either saline or an acute injection of MPD (0.6, 2.5, or 10.0 mg/kg, i.p.) on experimental day 2. Locomotor activity was recorded for 2-h post injection on both days using an automated, computerized activity monitoring system. Electrophysiological recordings were also performed in the adult male WKY rats (n = 10). Five to seven days after the rats had recovered from the implantation of electrodes, each rat was placed in a sound-insulated, electrophysiological test chamber where its sensory evoked field potentials were recorded before and after saline and 0.6, 2.5, and 10.0 mg/kg MPD injection. Time interval between injections was 90 min. RESULTS: Results showed an increase in locomotion with dose-response characteristics, while a dose-response decrease in amplitude of the components of sensory evoked field responses of the VTA, NAc, and PFC neurons. For example, the P3 component of the sensory evoked field response of the VTA decreased by 19.8% +/- 7.4% from baseline after treatment of 0.6 mg/kg MPD, 37.8% +/- 5.9% after 2.5 mg/kg MPD, and 56.5% +/- 3.9% after 10 mg/kg MPD. Greater attenuation from baseline was observed in the NAc and PFC. Differences in the intensity of MPD-induced attenuation were also found among these brain areas. CONCLUSION: These results suggest that an acute treatment of MPD produces electrophysiologically detectable alterations at the neuronal level, as well as observable, behavioral responses. The present study is the first to investigate the acute dose-response effects of MPD on behavior in terms of locomotor activity and in the brain involving the sensory inputs of VTA, NAc, and PFC neurons in intact, non-anesthetized, freely behaving rats previously implanted with permanent electrodes.

Chronic administration of methylphenidate produces neurophysiological and behavioral sensitization.

The electrophysiological properties of acute and chronic methylphenidate (MPD) on neurons of the prefrontal cortex (PFC) and caudate nucleus (CN) have not been studied in awake, freely behaving animals. The present study was designed to investigate the dose-response effects of MPD on sensory evoked potentials recorded from the PFC and CN in freely behaving rats previously implanted with permanent electrodes, as well as their behavioral (locomotor) activities. On experimental day 1, locomotor behavior of rats was recorded for 2 h post-saline injection, and sensory evoked field potentials were recorded before and after saline and 0.6, 2.5, and 10 mg/kg, i.p., MPD administration. Animals were injected for the next five days with daily 2.5 mg/kg MPD to elicit behavioral sensitization. Locomotor recording was resumed on experimental days 2 and 6 after the MPD maintenance dose followed by 3 days of washout. On experimental day 10, rats were connected again to the electrophysiological recording system and rechallenged with saline and the identical MPD doses as on experimental day 1. On experimental day 11, rat's locomotor recording was resumed before and after 2.5 mg/kg MPD administration. Behavioral results showed that repeated administration of MPD induced behavioral sensitization. Challenge doses (0.6, 2.5, and 10.0 mg/kg) of MPD on experimental day 1 elicited dose-response attenuation in the response amplitude of the average sensory evoked field potential components recorded from the PFC and CN. Chronic MPD administration resulted in attenuation of the PFC's baseline recorded on experimental day 10, while the same treatment did not modulate the baseline recorded from the CN. Treatment of MPD on experimental day 10 resulted in further decrease of the average sensory evoked response compared to that obtained on experimental day 1. This observation of further decrease in the electrophysiological responses after chronic administration of MPD suggests that the sensory evoked responses on experimental day 10 represent neurophysiological sensitization. Moreover, two different response patterns were obtained from PFC and CN following chronic methylphenidate administration. In PFC, the baseline and effect of methylphenidate expressed electrophysiological sensitization on experimental day 10, while recording from CN did not exhibit any electrophysiological sensitization.

The identification of child abuse in Harris County in 1998

Characteristics of child abuse cases are not well known. In this study I collected data on 70 child abuse cases that were reported to Children's Protective Services in Harris County in 1998. The purpose of this study was to determine the factors in Harris County that lead to the identification of physical and sexual abuse. In order to answer the questions of who, what, where and when relative to the discovery of abuse I applied the same questionnaire (see Appendix) to each of 35 Sexual Abuse case reports and to each of 35 Physical Abuse/Neglect case reports. Answers to the first four questions were arranged by frequency distribution to show the predominant reporter, the 10 most common indicators, the most common locale, and the most frequent timing. Tables of the age, sex, and ethnicity of the children indicate the identity of those whose victimization was most reported. In addition the relationship between the form questions and the characteristics of the children was explored. A comparison of Sexual Abuse cases with Physical Abuse/Neglect cases was conducted and the results were analyzed and recorded in the Tables. ^ Child maltreatment often has negative short and long term effects on children's mental health and development. Suicide, violence, delinquency, drug and alcohol abuse and other forms of criminality are frequently child abuse related. Early detection and treatment helps to alleviate the myriad mental and physical ailments that untreated victims present as adults. This translates into medical dollar savings. ^ The long term objectives of my research were to reduce the number of undetected and unreported child abuse cases in Harris County by formulating better educational programs and literature for medical professionals and other personnel who are in contact with children. ^

Identification of maltreatment type in children with disabilities using the National Child Abuse and Neglect Data System (NCANDS)

This study was a retrospective design and used secondary data from the National Child Abuse and Neglect Data System (NCANDS), provided by the National Data Archive on Child Abuse and Neglect Family Life Development Center administered by Cornell University. The dataset contained information for the year 2005 on children from birth to 18 years of age. Child abuse and neglect for disabled children, was evaluated in-depth in the present study. Descriptive and statistical analysis was performed using the children with and without disabilities. It was found that children with disabilities have a lower rate of substantiation that likely indicates the interference of reporting due to their handicap. The results of this research demonstrate the important need to teach professionals and laypersons alike on how to recognize and substantiate abuse among disabled children.^