Sensitivity to the effects of sedative-hypnotics on motor performance: influence of task difficulty and chronic phenobarbital administration

The motor-impairing effects of GABA(A) and GABA(B) agonists in gamma-hydroxybutyrate (GHB)-treated rats: cross-tolerance to baclofen but not flunitrazepam

gamma-Hydroxybutyrate (GHB) is believed to function as a neurotransmitter in the mammalian brain by binding to a GHB-specific binding site. In addition, GHB may also indirectly enhance the neuroinhibitory actions of gamma-aminobutyric acid (GABA) by converting to GABA at neuronal synapses. The purpose of the present study was to examine the effects of representative GABA(A) and GABA(B) receptor agonists in rats treated chronically with GHB. Using a rotorod apparatus, the motor-impairing effects of GHB, the indirect GABA(A) receptor agonist, flunitrazepam, and the direct GABA(B) receptor agonist, baclofen, were examined before, during and after chronic treatment with 1000 mg/kg GHB, b.i.d. Prior to chronic treatment, all three drugs produced dose-dependent decreases in motor performance at low (8 rpm) and high (32 rpm) rotational speeds. Chronic treatment with GHB significantly decreased the potency of baclofen at both speeds, but did not alter the potency of either GHB or flunitrazepam. Following termination of chronic treatment, the potency of baclofen increased significantly at both speeds and returned to that observed prior to chronic treatment. These data indicate that chronic treatment with GHB confers tolerance to a GABA(B) receptor agonist under conditions in which tolerance is not conferred to a GABA(A) receptor agonist. These findings are consistent with the in vivo behavioral profile of GHB, which reveals a greater role for GABA(B) receptors than for GABA(A) receptors in its behavioral effects.

The effect of repeated isoflurane anesthesia on spatial and psychomotor performance in young and aged mice

Exposure to general anesthesia may contribute to postoperative cognitive impairment in elderly patients, but the relationship remains poorly understood. We investigated whether aged mice, 18-19 mo, are more susceptible to postanesthetic cognitive impairment than young mice, 3-4 mo, using spatial memory (Barnes maze) and psychomotor (rotarod) tasks. Initially we studied the effect of a single anesthetic episode on asymptotic maze performance. We then tested whether repeated anesthesia would impair spatial memory and psychomotor performance to a greater extent in aged mice. Mice were anesthetized with isoflurane (1.4% atm) for 30 min; controls received 90% oxygen. Anesthesia, administered during the asymptotic period of maze learning, did not impair performance tested the following day (P > 0.05). Repeated anesthesia, 2-3 h after each session, did not impair overall maze or rotarod performance in young or aged mice (P > 0.05). Spatial learning appeared to be facilitated by anesthesia, F(1,204) = 7.97, P < 0.01 for pooled results. Asymptotic performance-when learning had stabilized-remained unimpaired in both the maze and rotarod tasks. These results suggest that an age-related risk of anesthetic-induced impairment appears to be limited to acquisition of a novel motor skill and that anesthesia alone does not lead to prolonged cognitive impairments in aged mice.

IMPLICATIONS

This study demonstrates that repeated isoflurane general anesthesia impaired psychomotor performance in aged mice during the initial learning period; however, spatial learning improved and, overall, spatial memory and psychomotor performance were unimpaired. Thus, general anesthesia alone does not appear to result in prolonged cognitive deficits in aged mice.

Distinct forelimb and hind limb stepping impairments in unilateral dopamine-depleted rats: use of the rotorod as a method for the qualitative analysis of skilled walking

The rotorod test, in which animals walk on a rotating drum, is widely used to assess motor status in laboratory rodents. Performance is measured by the duration that an animal stays up on the drum as a function of drum speed. Here we report that the task provides a rich source of information about qualitative aspects of walking movements. Because movements are performed in a fixed location, they can readily be examined using high-speed video recording methods. The present study was undertaken to examine the potential of the rotorod to reveal qualitative changes in the walking movements of hemi-Parkinson analogue rats, produced by injection of 6-hydroxydopamine (6-OHDA) into the nigrostriatal bundle to deplete nigrostriatal dopamine (DA). Beginning on the day following surgery and then periodically over the next two months, the rats were filmed from frontal, lateral, and posterior views as they walked on the rotorod. Behavior was analyzed by frame-by-frame replay of the video records. Rating scales of stepping behavior indicated that the hemi-Parkinson rats were chronically impaired in their posture and in the use of the limbs contralateral to the DA-depletion. The contralateral limbs not only displayed postural and movement abnormalities, they participated less in initiating and sustaining propulsion than did the ipsilateral limbs. These findings not only reveal new deficits secondary to unilateral DA-depletion, but also show that the rotorod can provide a robust tool for the qualitative analysis of movement.