The effects, in rats, of peripherally administered capsaicin were evaluated on body temperature and on brain neurophysiological activity. Capsaicin (5 mg/kg, SC) produced a rapid, long-lasting fall in body temperature. A second dose given 4.5 hr after the first showed a moderate decrement in hypothermic effect. The same dose of capsaicin caused discernible changes in deep EEG activity in the anterior hypothalamus (AH), medial habenula (HB), substantia nigra (SN), and dorsal raphe (DR). The EEG changes were more pronounced at doses of 10 and 20 mg/kg. Capsaicin in all doses modified sensory evoked responses recorded from all four brain areas. Response amplitudes after acoustic stimulation were increased at all doses of capsaicin in a dose related pattern. Photic evoked responses, like body temperature effects, showed diminished effects with second and third doses. Peripherally administered capsaicin, therefore, can affect body temperature and brain electrical activity.

Animals↗

PubMedDate not supplied

NMDA receptor antagonist disrupts acute and chronic effects of methylphenidate.

Methylphenidate (MPD) is a drug widely used for treating attention-deficit/hyperactivity disorder in children. Because of its extensive consumption and because it has pharmacological stimulant properties similar to amphetamine and cocaine, MPD has the potential of abuse. N-methyl-D-aspartate (NMDA) receptors are suggested to be involved in CNS effects of stimulants, and antagonists of the NMDA receptor can potentially alter the stimulants' effects. Dizocilpine (MK-801), a non-competitive antagonist of the NMDA receptor, has been reported to prevent sensitization elicited by repeated administration of amphetamine and cocaine. The objective of the present study was to use the tail-flick latency assay, rectal temperature, and body weight gain to assess effects of repetitive treatment of MPD and whether MK-801 treatment would alter these effects in Sprague-Dawley rats. It was found that: (Ia) Acute administration of MPD or MK-801 did not alter the tail-flick latency, (Ib) Repeated administration of MPD decreased tail-flick latency, while repeated administration of MK-801 had no significant effect on tail-flick latency, (Ic) MK-801 given prior to or with MPD reversed the chronic effect on tail-flick latency produced by MPD; (IIa) When both drugs were independently given, MPD elicited a decrease in rectal temperature, while MK-801 alone produced an increase in temperature, (IIb) When given together, MK-801 had a transient effect in blocking the sensitization to MPD but failed to reverse the sensitization of MPD once it had developed; and (III) Both MK-801 and MPD caused an unstable pattern of body weight gain. Hence, the results of this study in rats suggest that MK-801 can modulate non-motor effects of MPD.

Analgesics, Opioid↗

PubMedDate not supplied

Urethane modification of EEG-like activity and acoustically evoked field potentials recorded from deep nuclei.

Average acoustic-evoked responses (AAER) and EEGs were recorded from the lateral hypothalamus (LH), ventromedial hypothalamus (VMH), medial forebrain bundle (MFB) and reticular formation (RF) of freely behaving rats before and after various doses (0.2, 0.4, 0.8, 1.2 g/5g) of the anesthetic drug, urethane. The effect of a surgical level of urethane (1.2 g/5g) over time (8--14 h) was also studied. Urethane produced a dose-dependent slowing in the EEG frequency. The effect of 1.2 g/kg over time was a bimodal depression of the EEG frequency. Three components of the AAER were recorded consistently and evaluated in terms of amplitude. With increasing doses, the early component (P2) was depressed in the LH2, VMH and MFB, but not in the RF which remained at control values or higher. The later components (N2 and P2) were depressed in all four structures. This suggests that urethane may be blocking the integrative function of the RF, as well as in the thalamus, resulting in lower sensory input to higher CNS structures.

Acoustic Stimulation↗

PubMedDate not supplied

Effect of hydrocortisone on single cell activity in the anterior hypothalamus.

Explore the source record for details and available documents.

Animals↗