Early abrupt recovery from ataxia during vestibular compensation in goldfish.

1. Vestibular compensation was studied in goldfish that had had the utriculus and semicircular canal organs unilaterally removed. Characteristic postoperative behavioural deficits of postural asymmetry were quantitatively scored. Operated animals were compared with those subject to the same duration of anaesthesia and restraint during a sham operation. 2. The period of several minutes following the operation was characterized by severe postural asymmetry and locomotor ataxia. In the operated fish, but not the sham-operated ones, the eyes rolled tonically towards the operated side without nystagmus, the body was flexed towards the operated side, and any swimming was disoriented with rolling motion towards the operated side. These deficits lasted less than 30 min after revival from the anaesthesia. All three behavioral deficits ended abruptly within 1 min of each other for individual fish, and normal, nearly upright swimming was then maintained, even in the dark. 3. We interpret this recovery as one of the first stages in the central process of vestibular compensation. The unusually abrupt end of these deficits in adult goldfish compared with that in other vertebrates suggests a remarkable capacity for the central nervous system to adapt. The speed of recovery of three distinct motor outputs supports models of early compensation that utilize central modulation or gain control of existing pathways, rather than anatomical reorganization.

Postural changes occurring during one month of vestibular compensation in goldfish.

1. Postural behavioural changes during vestibular compensation were studied in goldfish. The tilting posture induced by directional light in the dorsal light reflex (DLR) was monitored by an automated camera system. Responses were measured over a 1-month period following a partial unilateral labyrinthectomy. 2. After the fish had recovered from the ataxic stage, the first observable DLR had shifted strongly towards the operated side. This early bias decreased rapidly, then more gradually. Mean values for the DLR reached a steady state within 2 weeks. 3. Recovery rates were slowest for DLR tilts elicited by light presented from the operated side. 4. The DLR did not recover to preoperative control values for light from either the intact or operated side. Shortly after the operation, light from the operated side produced DLR values nearly double the normal; light from the intact side had an effect very little different from normal. At steady state, the light effect from the operated side had decreased from the high immediately post-ataxic levels to a level roughly 1.5 times normal, but the light effect from the intact side had increased, also reaching a level roughly 1.5 times normal. Thus the final values again show symmetry. 5. Variability appears to be an important feature of the response.

The effect of age on ethanol metabolism and on the hypothermic and hypnotic responses to ethanol in the Fischer 344 rat.

The hypothesis that the central nervous system (CNS) of aged rats is more sensitive to acute ethanol effects was examined by measuring ethanol elimination rates, and the hypothermic and hypnotic responses to ethanol in four age groups (3, 12, 21, and 30 months) of Fischer 344 rats. Following a 2.5 g/kg intraperitoneal dose of ethanol, rectal temperature and blood ethanol concentration (BEC) were measured at regular intervals for 8 hr. The 30-month group's hypothermic response to ethanol was equivalent to the 3-month group's despite lower peak BEC. Response to a hypnotic dose (3.0 g/kg) of ethanol was evaluated by measuring the time for regain of righting reflex (RORR) and the BEC at RORR. The 3-month group slept for a shorter time, and awoke at a higher BEC, than the 12- or 21-month groups. The response of the 30-month group was more complex. Although this group had the lowest BEC at RORR, their sleep time was equivalent to the 3-month group. The shortened sleep time of the 30-month group is consistent with the observation of significantly lower peak BEC and higher metabolic rate (calculated from Widmark r values) in this group. Thus, aged rats of the Fischer 344 strain may be more sensitive to acute ethanol, but these CNS effects may be partially offset by enhanced ethanol disposition at older ages.