Evaluation of an osmotic pump for microdialysis sampling in an awake and untethered rat

Abstract

The feasibility of using an osmotic pump in place of a syringe pump for microdialysis sampling in rat brain was investigated. The use of an osmotic pump permits the rat to be free from the constraints of the standard tethered system. The in vitro flow rates of a microdialysis syringe pump (set at 10.80 microl/h) and the osmotic pump (pump specifications were 11.35 microl/h) with no probe attached were compared, yielding results of 10.87 microl/h+/-1.7% and 10.95 microl/h+/-8.0%, respectively. The average of four flow rate experiments in vivo yielded R.S.D.s less than 10% and an average flow rate of 11.1 microl/h. Following the flow rate studies, in vivo sampling of neurotransmitters was accomplished with the osmotic pump coupled to a microdialysis probe implanted in the brain. Finally, after determination of basal levels of 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindole-3-acetic acid (5-HIAA) in the rats, the rats were dosed with benserazide followed by l-3,4-dihydroxyphenylalanine (l-DOPA). The results from the dosing study showed at least a 10-fold increase in compounds in the l-DOPA metabolic pathway (DOPAC and HVA) and a slight or no increase in 5-HIAA (serotonin metabolic pathway.) These results indicate that the osmotic pump is a viable alternative to the syringe pump for use in microdialysis sampling.

Figure 1

Schematic of the on-animal collection system with the microdialysis probe and osmotic pump

Figure 2

Flow rate profiles for the 2ML1 osmotic pump with and without brain probe attached (in vitro and in vivo). Collection intervals were 90 minutes.

Figure 3

Recovery and delivery data obtained for caffeine and theophylline using a using the 2ML1 osmotic pump. Flow rate was 10.8 μL/hr. Collection intervals were 60 minutes.

Figure 4

Monitoring in vivo release of neurotransmitters using the 2ML1 osmotic pump and the on-rat collection device. Rats (n = 3) were dosed with 50 mg/kg of benserazide and L-DOPA. Samples were collected every 60 minutes. The pump flow rate was approximately 11 μL/hr. Analytes in Figure 4 are: (a) HVA, (b) DOPAC and (c) 5-HIAA.

Figure 4

Monitoring in vivo release of neurotransmitters using the 2ML1 osmotic pump and the on-rat collection device. Rats (n = 3) were dosed with 50 mg/kg of benserazide and L-DOPA. Samples were collected every 60 minutes. The pump flow rate was approximately 11 μL/hr. Analytes in Figure 4 are: (a) HVA, (b) DOPAC and (c) 5-HIAA.

Figure 4

Monitoring in vivo release of neurotransmitters using the 2ML1 osmotic pump and the on-rat collection device. Rats (n = 3) were dosed with 50 mg/kg of benserazide and L-DOPA. Samples were collected every 60 minutes. The pump flow rate was approximately 11 μL/hr. Analytes in Figure 4 are: (a) HVA, (b) DOPAC and (c) 5-HIAA.