John M. Dose

Time Course of Changes in Lactate and Free Fatty Acids after Experimental Brain Injury and Relationship to Morphologic Damage

Regional levels of lactate and free fatty acids (FFA) were measured after lateral fluid percussion (FP) brain injury in rats. At 5 min after injury, tissue concentrations of lactate were elevated in the cortices and hippocampi of both ipsilateral and contralateral hemispheres. Whereas lactate levels had returned to normal by about 20 min after injury in the penumbra and contralateral cortices, their elevation persisted in the ipsilateral injured cortex and hippocampus for 24 h after injury. Increases in the levels of FFA (particularly stearic and arachidonic acids) were observed in the cortices and hippocampi of both ipsilateral and contralateral hemispheres at 5 min after injury; these levels returned to normal in only the penumbra and contralateral cortices by 20 min after injury. Increased amounts of palmitic and oleic acids were also found only in the injured left cortex and ipsilateral hippocampus at 20 min or later after injury. In general, these elevations persisted for as long as 6 to 24 h in the injured cortex and for 2.5 to 24 h after injury in the ipsilateral hippocampus. Histologic studies revealed a similar extent of damage in the cortex between 5 min and 24 h after injury, whereas damage in the CA3 region of the ipsilateral hippocampus increased during that period. These findings suggest a role for lactic acid and FFA, two secondary injury factors, in neuronal cell loss after brain injury.

Activation of phosphatidylinositol bisphosphate signal transduction pathway after experimental brain injury: a lipid study

Regional levels of phosphatidylinositol 4,5-bisphosphate (PIP2), diacylglycerol (DG) and free fatty acids (FFA), involved in the signal transduction pathway of the excitatory neurotransmitter system, were measured after lateral fluid percussion (FP) brain injury in rats. At 5 min postinjury, tissue PIP2 concentrations were significantly reduced in the cortices and hippocampi of both ipsilateral and contralateral hemispheres. Only levels of stearic and arachidonic acids were substantially decreased in PIP2 in these regions of the brain. At the same time after injury, both DG and FFA were significantly increased in the cortices and hippocampi of both hemispheres. As was true for PIP2, only levels of stearic and arachidonic acids markedly changed in both DG and FFA in these regions of the brain. At 20 min postinjury, a significant decrease in PIP2 concentration and significant increases in levels of DG and FFA were observed only in the injured left cortex. In addition to the increases in stearic and arachidonic acids in FFA, increased amounts of palmitic and oleic acids were also found in the injured left cortex at 20 min after injury. These results suggest that the PIP2 signal transduction pathway is activated in the cortex and hippocampus at the onset of lateral FP brain injury and that the enhanced phospholipase C-catalyzed phosphodiestric breakdown of PIP2 is a major mechanism of liberation of FFA in these sites immediately after such injury.

Impact of d-Amphetamine on Temporal Estimation in Pigeons Tested with a Production Procedure

The influence of d-amphetamine on timing in pigeons was examined with a production procedure. Birds were trained with a fixed time schedule in which food reinforcement was contingent on the first response made after a duration signal had appeared for 30 s. Probe tests involved trials in which the duration signal was extended to 90 s and reinforcement was omitted. In Experiment 1, 2.0 mg/kg d-amphetamine shifted peak responding to a duration shorter than that found with saline. In Experiment 2, the dose-response function for this drug effect was examined. A 0.3-mg/kg dose of d-amphetamine had no impact on performance, but a 1.0-mg/kg dose shifted the peak duration significantly relative to saline; a 2.0-mg/kg dose shifted the function even more. These results complement previous findings with rats tested with the peak procedure and pigeons tested with a discrimination procedure.

Amphetamine affects the behavioral outcome of lateral fluid percussion brain injury in the rat

This study examined the effects of (D)-amphetamine, methoxamine (an al-adrenergic receptor agonist), and prazosin (an al-adrenergic receptor antagonist) on the behavioral outcome of lateral fluid percussion brain injury. Rats trained to perform a beam walking task were subjected to brain injury of moderate severity (2.1-2.2 atm). At 10 min after injury, rats were treated with amphetamine, methoxamine or prazosin at two different dose levels. Amphetamine-treated animals displayed significantly lower impairment in beam walking ability from days 1 to 5 after brain injury. Neither methoxamine nor prazosin significantly affected the impairment in beam walking ability from day 1 to day 7 after injury. However, prazosin treatment at both dose levels increased the post-injury mortality and the incidences of failure to recovery from hemiplegia. Amphetamine-treatment at 4 mg/kg, but not at 2 mg/kg, improved the spatial learning abilities of the injured animals. Neither methoxamine nor prazosin affected the spatial learning abilities. These results indicate that amphetamine facilitated beam walking recovery and improved cognitive function after concussive fluid percussion injury. Although the methoxamine experiments suggest that the norepinephrine-α1-adrenergic receptor system may not be involved in the pathophysiology of fluid percussion brain injury, our results with amphetamine (beneficial effects) and prazosin (deleterious effects) and the results observed in other models of brain injury point out that further investigations are necessary to understand the role of a1-adrenergic receptors in brain injury.

Amphetamine administration improves neurochemical outcome of lateral fluid percussion brain injury in the rat

This study examined the effects of the administration of D-amphetamine on the regional accumulation of lactate and free fatty acids (FFAs) after lateral fluid percussion (FP) brain injury in the rat. Rats were subjected to either FP brain injury of moderate severity (1.9 to 2.0 atm) or sham operation. At 5 min after injury, rats were treated with either d-amphetamine (4 mg/kg, i.p.) or saline. At 30 min and 60 min after brain injury, brains were frozen in situ, and cortices and hippocampi were excised at 0 degrees C. In the saline-treated brain injured rats, levels of lactate were increased in the ipsilateral left cortex and hippocampus at 30 min and 60 min after injury. These increases were attenuated by the administration of D-amphetamine at 5 min after lateral FP brain injury. At 30 and 60 min after FP brain injury, increases in the levels of all individual FFAs (palmitic, stearic, oleic and arachidonic acids) and of total FFAs were also observed in the ipsilateral cortex of the saline-treated injured rats. These increases in the ipsilateral cortex and hippocampus were also attenuated by the administration of d-amphetamine. Neither levels of lactate nor levels of FFAs were increased in the contralateral cortex in the saline-treated injured rats at 30 min or 60 min after FP brain injury. The levels of lactate and FFAs in the contralateral cortex were also unaffected by the administration of D-amphetamine. These results suggest that the attenuation of increases in the levels of lactate and FFAs in the ipsilateral cortex and hippocampus may be involved in the amphetamine-induced improvement in behavioral outcome after lateral FP brain injury.

Physiological and behavioral effects of early embryonic exposure to ethanol and cocaine in the young chick

The physiological and behavioral effects of embryonic exposure to ethanol and cocaine, given during active neurogenesis (embryonic days E3 and E4), were studied in 1- and 2-day-old chicks. Broiler chicks (n = 131) from five embryonic treatment conditions were tested: incubative controls (n = 28), vehicle (saline plus 50 micrograms/ml bacitracin; n = 27), 10 mg ethanol (n = 20), 150 micrograms cocaine (n = 25), or co-drug (10 mg ethanol and 150 micrograms cocaine; n = 31). Compared with controls, embryo mortality for the cocaine alone embryos was significantly increased. No significant embryonic treatment effects among chicks were found for hatching times, body weights at hatch and testing, and temperature regulation when cold stressed. Behaviorally, chicks were first trained to key-peck for heat/light reward (autoshaping). Chicks in all groups increased responding from autoshape session 1 to session 2 (24 trials/session). In an acquisition-extinction session (12 trials/phase), chicks in all groups except those in the co-drug group decreased responding from acquisition to extinction. In a second acquisition-extinction session following a drug challenge of 0.5 mg/kg apomorphine, chicks in all embryonic treatment groups showed enhanced responding. Hence, in those chicks that survived, the selected doses of ethanol and cocaine produced minimal physiological and behavioral effects individually, but when given together did produce a significant deficit in extinction responding.

Separate and combined effects of dopamine D1 and D2 receptor agonists on key pecking in the developing chick

The separate and combined effects of dopamine D1 and D2 agonists on key-peck responding of young chicks for heat reinforcement were determined. In the first experiment, 1- and 4-day-old chicks (n = 96) were injected SC with either distilled water or 5 mg/kg reserpine 18 h before testing. Twenty minutes before a 24-trial autoshaping session, chicks were injected IP with either distilled water or 10 mg/kg SKF 38393 and 2 mg/kg quinpirole. Chicks receiving both dopamine agonists had enhanced key-peck responding in both pretreatment conditions. In Experiment 2, 1- and 4-day-old chicks (n = 192) of two strains received 5 mg/kg reserpine SC 18 h before testing. Twenty minutes before their autoshaping session these chicks were injected IP with either distilled water, 10 mg/kg SKF 38393, 2 mg/kg quinpirole, or 10 mg/kg SKF 38393 and 2 mg/kg quinpirole. After reserpine pretreatment, chicks of both strains responded on more trials when given both dopamine agonists compared with controls given either distilled water or single agonist treatment. No age or strain differences in key pecking were produced by the combined administration of these dopamine agonists. Therefore, functional coupling of the dopamine D1 and D2 receptors is found within 1 day after hatching in the domestic chick.

An analysis of the rewarding and aversive associative properties of nicotine in the neonatal quinpirole model: Effects on glial cell line-derived neurotrophic factor (GDNF)

This study analyzed the associative properties of nicotine in a conditioned place preference (CPP) paradigm in adolescent rats neonatally treated with quinpirole (NQ) or saline (NS). NQ produces dopamine D2 receptor supersensitivity that persists throughout the animals lifetime, and therefore has relevance towards schizophrenia. In two experiments, rats were ip administered quinpirole (1mg/kg) or saline from postnatal day (P)1-21. After an initial preference test at P42-43, animals were conditioned for eight consecutive days with saline or nicotine (0.6mg/kg free base) in Experiment 1 or saline or nicotine (1.8mg/kg free base) in Experiment 2. In addition, there were NQ and NS groups in each experiment given the antipsychotic haloperidol (0.05mg/kg) or clozapine (2.5mg/kg) before nicotine conditioning. A drug free post-conditioning test was administered at P52. At P53, the nucleus accumbens (NAc) was analyzed for glial cell-line derived neurotrophic factor (GDNF). Results revealed that NQ enhanced nicotine CPP, but blunted the aversive properties of nicotine. Haloperidol was more effective than clozapine at blocking nicotine CPP in Experiment 1, but neither antipsychotic affected nicotine conditioned place aversion in Experiment 2. NQ increased accumbal GDNF which was sensitized in NQ rats conditioned to nicotine in Experiment 1, but the aversive dose of nicotine reduced GDNF in NQ animals in Experiment 2. Both antipsychotics in combination with the aversive dose of nicotine decreased accumbal GDNF. In sum, increased D2 receptor sensitivity influenced the associative properties and GDNF response to nicotine which has implications towards pharmacological targets for smoking cessation in schizophrenia.

The effects of nicotine in the neonatal quinpirole rodent model of psychosis: Neural plasticity mechanisms and nicotinic receptor changes

Abstract Neonatal quinpirole (NQ) treatment to rats increases dopamine D2 receptor sensitivity persistent throughout the animal’s lifetime. In Experiment 1, we analyzed the role of &agr;7 and &agr;4&bgr;2 nicotinic receptors (nAChRs) in nicotine behavioral sensitization and on the brain‐derived neurotrophic factor (BDNF) response to nicotine in NQ‐ and neonatally saline (NS)‐treated rats. In Experiment 2, we analyzed changes in &agr;7 and &agr;4&bgr;2 nAChR density in the nucleus accumbens (NAcc) and dorsal striatum in NQ and NS animals sensitized to nicotine. Male and female Sprague‐Dawley rats were neonatally treated with quinpirole (1 mg/kg) or saline from postnatal days (P)1‐21. Animals were given ip injections of either saline or nicotine (0.5 mg/kg free base) every second day from P33 to P49 and tested on behavioral sensitization. Before each injection, animals were ip administered the &agr;7 nAChR antagonist methyllycaconitine (MLA; 2 or 4 mg/kg) or the &agr;4&bgr;2 nAChR antagonist dihydro beta erythroidine (Dh&bgr;E; 1 or 3 mg/kg). Results revealed NQ enhanced nicotine sensitization that was blocked by Dh&bgr;E. MLA blocked the enhanced nicotine sensitization in NQ animals, but did not block nicotine sensitization. NQ enhanced the NAcc BDNF response to nicotine which was blocked by both antagonists. In Experiment 2, NQ enhanced nicotine sensitization and enhanced &agr;4&bgr;2, but not &agr;7, nAChR upregulation in the NAcc. These results suggest a relationship between accumbal BDNF and &agr;4&bgr;2 nAChRs and their role in the behavioral response to nicotine in the NQ model which has relevance to schizophrenia, a behavioral disorder with high rates of tobacco smoking.

The effects of adolescent methylphenidate exposure on the behavioral and brain-derived neurotrophic factor response to nicotine

This study analyzed the interaction of adolescent methylphenidate on the behavioral response to nicotine and the effects of these drug treatments on brain-derived neurotrophic factor in the nucleus accumbens and hippocampus in male and female Sprague-Dawley rats. Animals were intraperitoneal administered 1 mg/kg methylphenidate or saline using a “school day” regimen (five days on, two days off) beginning on postnatal day (P)28 and throughout behavioral testing. In Experiment 1, animals were intraperitoneal administered 0.5 mg/kg (free base) nicotine or saline every second day for 10 days from P45–P63 and tested after a three-day drug washout on the forced swim stress task on P67–P68. Results revealed that adolescent methylphenidate blunted nicotine behavioral sensitization. However, methylphenidate-treated rats given saline during sensitization demonstrated decreased latency to immobility and increased immobility time on the forced swim stress task in males that was reduced by nicotine. In Experiment 2, a different set of animals were conditioned to nicotine (0.6 mg/kg free base) or saline using the conditioned place preference behavioral paradigm from P44–P51, and given a preference test on P52. On P53, the nucleus accumbens and hippocampus were analyzed for brain-derived neurotrophic factor. Methylphenidate enhanced nicotine-conditioned place preference in females and nicotine produced conditioned place preference in males and females pre-exposed to saline in adolescence. In addition, methylphenidate and nicotine increased nucleus accumbens brain-derived neurotrophic factor in females and methylphenidate enhanced hippocampus brain-derived neurotrophic factor in males and females. Methylphenidate adolescent exposure using a clinically relevant dose and regimen results in changes in the behavioral and brain-derived neurotrophic factor responses to nicotine in adolescence that are sex-dependent.