No abstract

SummaryInformation on antibiotic therapeutics in laboratory species, especially in rodents and rabbits, is reviewed. A number of areas are considered: interference by antibiotics with an experiment, antibiotic toxicity, routes of administration, effects of formulation on bioavailability, antibiotic prophylaxis, use of combinations of antibiotics, misuse of antibiotics, regulatory approval for antibiotic use in animals, sources of information on antibiotic indications and dose, and extrapolation of dose information from other species.

The welfare of laboratory rats housed on either solid or grid floors was investigated in several ways. No differences were found in body weight gain, food consumption or water consumption amongst rats housed in either condition. When handling was standardized between the 2 groups, there was no correlation between flooring and docility. Preference testing revealed that rats chose to dwell on solid floors rather than grids, regardless of previous housing experience. This preference for solid floors was particularly marked (88%) when the animals were resting and much less marked during activity (55.4%). Since the rats were observed to spend 70 to 75% of their time resting, it was concluded that their welfare was likely to be improved by housing them on solid floors.

Anatomic evidence suggests that direct corticomotoneuronal (CM) projections to hand motoneurons in the New World squirrel monkey (Saimiri sciureus) are weak or absent, but electrophysiological evidence is lacking. The nature of the corticospinal linkage to these motoneurons was therefore investigated first with the use of transcranial magnetic stimulation (TMS) of the motor cortex under ketamine sedation in five monkeys. TMS produced early responses in hand muscle electromyogram, but thresholds were high (compared with macaque monkey) and the onset latency was variable. Second, stimulation of the pyramidal tract (PT) was carried out with the use of chronically implanted electrodes in ketamine-sedated monkeys; this produced more robust responses that were markedly facilitated by repetitive stimulation, with little decrease in latency on the third compared with the first shock. Finally, postsynaptic potentials were recorded intracellularly from 93 arm and hand motoneurons in five monkeys under general chloralose anesthesia. After a single PT stimulus, the most common response was a small, slowly rising excitatory postsynaptic potential (EPSP), either alone (35 of 93 motoneurons) or followed by an inhibitory postsynaptic potential (39 of 93). The segmental delay of the early EPSPs was within the monosynaptic range (mean 0.85 ms); however, the rise time of these EPSPs was slow (mean 1.3 ms) and their amplitude was small (mean 0.74 mV). These values are significantly slower and smaller than EPSPs in a comparable sample of Old World macaque monkey motoneurons. The results show that CM connections do exist in the squirrel monkey but that they are weak and possibly located on the remote dendrites of the motoneurons. The findings are consistent with earlier anatomic studies. Repetitive PT stimulation produced large, late EPSPs in some motoneurons, suggesting that, in this species, there are relatively strong nonmonosynaptic pathways linking the corticospinal tract to hand motoneurons.

Nest-boxes and nesting materials were considered potentially useful items with which to enhance the environment of rats housed in standard laboratory cages. This study was carried out to determine whether such items are actually used by rats, and if so, what features are important in their design. Laboratory rats were allowed to choose between four commercially available nest-boxes. Nest-boxes were preferred to other parts of the cage but the nest-box most frequently selected was not suitable for routine laboratory use. Accordingly a new nest-box was designed, incorporating features apparently attractive to the animals. This was a simple structure of opaque perspex, consisting of a roof and three walls. Similarly, rats were exposed to six commercially available nesting materials and those consisting of long paper strips were most preferred.