Effects of morphine on sensory‐evoked responses recorded from central gray, reticular formation, thalamus, hypothalamus, limbic system, basal ganglia, dorsal raphe, locus ceruleus, and pineal body

Abstract

Field potential recordings of acoustic and photic-evoked responses were obtained from 15 brain sites of freely behaving unanesthetized rats previously implanted stereotaxically with permanent electrodes. Several dosages of morphine (1, 5, 10, 30, and 50 mg/kg) were examined. The activities recorded from all the structures in this study, except the cochlear nucleus (CoN), were affected by morphine. Different sensitivities to morphine threshold were observed between structures, and several structures exhibited dose-related patterns (ventromedial hypothalamus (VMH), caudate nuucleus (CN), central gray (CG), hippocampus (Hipp), and lateral septum (Spt)). Several brain sites, after the initial dose of morphine, did not recruit more responses to subsequent doses of the drug, ie, exhibited all-or-none responses (pineal body (PB), medial thalamus (MTh), anterior hypothalamus (AH), mesencephalic reticular formation (MRF), and the dorsal raphe (DR)). In some structures, morphine induced increases in the response amplitudes, while in other sites decreases in response amplitudes were elicited. Biphasic responses, ie, increases in response amplitude after low doses of the drug and decreases in response amplitude after higher dosages, were also observed (VMH, CN, DR, CG, and MRF). The acoustic-evoked responses were affected by morphine more than the photic responses. The present observations indicated that 1) morphine exerts effects in many parts of the central nervous system (CNS); 2) some structures are more sensitive to morphine than others; 3) only a few structures exhibit dose-related patterns and, thus, may represent sites of direct morphine action; 4) some structures exhibit all-or-none responses; and 5) morphine depressed activity in some structures and increased activity in others, ie, morphine elicited different effects in different structures.

Functional magnetic resonance imaging studies of opioid receptor-mediated modulation of noxious-evoked BOLD contrast in rats

“…The effects of morphine on BOLD signal intensity correspond well with the described localisation of μ-opioid receptors in the CNS (Mansour et al 1987) and their functional effect on behavioural and neuronal responses (Dafny et al 1980;Presley et al 1990;Hill et al 1982;Lewis and Gebhart 1977;Manning and Mayer 1995;Yeung et al 1977) and on cerebral glucose metabolism (Cohen et al 1991). Our rat data are in keeping with human fMRI imaging studies demonstrating opioid receptor-mediated modulation of activity in cortical brain areas (Borras et al 2004;Petrovic et al 2002) and the nucleus accumbens (Borras et al 2004).…”

Acute and chronic methylphenidate alters prefrontal cortex neuronal activity recorded from freely behaving rats

“…If at this location there was no spike activity with signal to noise ratio of at least 3:1, the electrodes were moved down in steps of about 5μm until they showed spike activity with good signal to noise ratio. Once good signal was obtained, the electrode was permanently fixed to the skull with dental acrylic cement and the second electrode in the other hemisphere was implanted in a similar way (Dafny et al, 1973, 1979, 1980, 1981, 1983; Dafny and Terkel, 1990; Yang et al, 2006b, c). The electrode leads were attached to an amphenol plug and the latter was cemented to the skull.…”

Dose effects of morphine on the spontaneous unit activity recorded from the thalamus, hypothalamus, septum, hippocampus, reticular formation, central gray, and caudate nucleus

“…The different response patterns observed within each region after morphine administration were expected by the investigators; it has been previously reported [Dafny and Burks, 1976a;Dafny et al, 1979Dafny et al, , 1980Gebhart, 19821 that within a particular structure different response patterns to morphine treatment were obtained. Since "simple" agents such as acetylcholine or dopamine, as well as somatosensory stimulation, induced different response patterns within specific CNS nuclei [Bloom et al, 1965;Dafny and Feldman, 1970;Kitai et al, 19761, it was expected that a "complex" drug such as morphine would induce an even larger variety of response patterns.…”