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R P Freeman

Publications and source records attributed to R P Freeman.

4 recordsLinked to original sources
PubMed1995

Melatonin agonists modulate 5-HT2A receptor-mediated neurotransmission: behavioral and biochemical studies in the rat.

Interactions between melatonin and serotonin type 2A (5-HT2A) receptors in the regulation of the sleep-wakefulness cycle in the rat have been reported. We studied the acute effects of melatonin and related agonists on 5-HT2A neurotransmission as reflected in behavioral (head shake) and biochemical [phosphoinositide (PI) hydrolysis] responses to 5-HT2A receptor stimulation. Like 5-HT1A agonists and antidepressants, acute administration of melatonin and related agonists inhibited the 5-HT2A-mediated (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane-induced head shake in a dose-dependent manner. Consistent with these behavioral findings, in vitro incubation of cortical slices with melatonin agonists robustly inhibited 5-HT2A receptor-mediated PI hydrolysis in a noncompetitive manner. 2-Iodomelatonin-induced reductions in 5-HT2A-stimulated PI hydrolysis were blocked by preincubation with the melatonin antagonist N-acetyltryptamine. Further, pretreatment of rats in vivo with melatonin and related agonists reduced the cortical PI hydrolysis response to the 5-HT2A agonist alpha methyl-5-HT but did not alter cortical 5-HT2A receptor density. The present data support an interaction between melatonin and 5-HT2A receptors in the central nervous system.

Amphetamines↗
PubMed1993

Discriminative feature integration by individuals.

A tactile pattern on the skin generally comes to be recognised from its function within action. What is perceived tactually and may generate a textural or geometrical sensation is therefore a set of dynamic characteristics that can be extracted by mechanoreceptors and central neural processing from the physics of the interactions of hands, mouth or other parts of the body with common objects and materials. The recognised dynamic (as is true of any sensory modality) may be diagnosable as distinct features that are integrated by the whole system's operation. If so, this transmission of feature information over a channel or in a dimension can be measured as the strength of the influence of that aspect of the stimulating pattern on the observed output, in units of the acuity of response differences for deviations of the pattern from its familiar configuration of features. When applied at the individual level, such multidimensional discrimination analysis provides powerful diagnoses of pattern-recognition processes.

Attention↗
PubMed1993

5-HT-dependent myoclonus in guinea pigs: mediation through 5-HT1A-5-HT2 receptor interaction.

Investigations utilizing agonists for 5-HT receptor subtypes have been conducted to determine which 5-HT receptor subtype(s) subserve myoclonus in the guinea pig. Administration of a nonselective 5-HT agonist such as 5-MeODMT (5-HT1A/5-HT2 agonist) induces a dose-dependent behavior characterized by head jerking at low doses (1-2 mg/kg, SC) and full-blown myoclonus (continuous rhythmic whole-body jerking) at higher doses (2.5-5 mg/kg, SC). In contrast, the selective 5-HT1A receptor agonist 8-OH-DPAT and the selective 5-HT2 receptor agonist DOI do not induce myoclonus, and elicit only limited head jerking across an otherwise behaviorally active range of doses (1-5 mg/kg, SC). Importantly, the coadministration of both 8-OH-DPAT and DOI results in the emergence of dose-dependent myoclonic behavior. These data suggest that coactivation of 5-HT1A and 5-HT2 receptors may be required for the induction of myoclonus in the guinea pig.

8-Hydroxy-2-(di-n-propylamino)tetralin↗