Robert L. Hakan

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Repeated exposure to nicotine increases both the number of central nicotinic receptors and the behavioral stimulant effect of nicotine. In the present experiments, the behavioral response to nicotine was examined in photocell activity cages. Groups of rats were tested using doses from 0.1 to 1.6 mg/kg both before and after all rats were exposed for 5 days(More)
Rats were given daily injections of nicotine sulfate in doses ranging from 0.1 to 0.4 mg/kg. The behavioral effect of these injections was measured as locomotor activity in photocell cages. Repeated administration of the same dose to each rat resulted in an enhancement of the stimulant effect of nicotine. This enhanced behavioral effect was quite pronounced(More)
Single-unit recordings of nucleus accumbens septi (NAS) neurons in halothane-anesthetized rats revealed that microinfusions of morphine into the ventral tegmental area (VTA) primarily inhibited spontaneously active NAS units. These inhibitory effects were reversed by alpha-flupenthixol (s.c.), suggesting a role for dopamine (DA) in the observed(More)
Responses of nucleus accumbens (NAS) neurons to ventral pallidum (VP) stimulation were examined in anesthetized rats. Results demonstrated: (1) NAS to VP projection neurons reside primarily in the relatively lateral aspects of the NAS, and (2) substantial VP to NAS feedback also exists. These feedback projections are widely distributed throughout the NAS.(More)
The nucleus accumbens septi (NAS) receives afferent input from the amygdala via the stria terminalis and from the hippocampus via the fimbria. Extracellular recordings from 196 NAS neurons in halothane-anesthetized rats revealed heterogeneous response patterns following stimulation of the amygdala. The observation that 30% of anterior NAS units but only 16%(More)
Rats repeatedly exposed to small doses of nicotine will demonstrate a significant augmentation of locomotor activity in response to a subsequent test dose of nicotine. A sensitization of brain tissue is hypothesized to account for this effect but Pavlovian conditioning might also be a major factor. Therefore the present study assessed the possible role of(More)
Electrophysiological parameters of spontaneous cellular activity in the nucleus accumbens septi (NAS) and responses evoked by afferent (fimbria) stimulation were characterized in halothane-anesthetized rats. A heterogeneous pattern of cell activity and single cell responses to stimulation were observed throughout the NAS. Stimulation-evoked discharges from(More)
Extracellular recordings of neurons in the nucleus accumbens septi of anesthetized rats have previously shown systemic opiates to have mixed effects on rates of unit activity. However, these effects become more predictable as nucleus accumbens septi neurons are functionally categorized by their responses to afferent stimulation. In the present study, the(More)
Studies of peripheral nicotinic receptors have revealed that, after an initial agonist action, the receptors remain inhibited either through continued depolarization blockade due to continued presence of the agonist or through a brief inactivation of the receptor following its activation. If a similar phenomenon occurs at central nervous system nicotinic(More)
Extracellular recordings within the nucleus accumbens (NAS) of halothane anesthetized rats have revealed that iontophoretically applied morphine and nicotine have contrasting effects on neuronal responses evoked by fimbria or VP stimulation. Iontophoretically applied morphine inhibited NAS single-unit responses evoked by VP stimulation but did not affect(More)