Invest. Ophthalmol. Vis. Sci. 620 Reports October 1981 to the ones described in Jagadeesh et al.,5 with Effects of apomorphine on the rabbit elec- variations in the way the drug was injected and in data processing. A brief summary indicating the troretinogram. J. M. JAGADEESH AND R. appropriate variations is given below. SANCHEZ. The ERG recording system consisted of an Experiments were conducted in both albino and pig- LSI-11/03 computer (Digital Equipment Corp.) mented rabbits to determine the effects of apomorphine with 32K words of memory, a HAWK disk drive on the electroretinogram (ERG). Injection of apomor- (Control Data Corp.) and an AD AC Model 600- phine (0.1 to 1.5 mg/kg) into the left carotid artery pro- LSI-11, 12-bit data-acquisition module. The light duced dose-related decreases in the b-wave, predomi- stimulus was from a Grass Model PS22 pho- nantly in the b-wave amplitude, and also increases in tostimulator. A Grass Model PS16 preamplifier the c-wave amplitude. No significant changes were ob- and a Tektronix Model AM502 amplifier were served in the a-wave amplitude or in the attendant used to amplify the ERG signal. The overall gain latencies. The ERG changes apparently were not related to systemic drug effects. The effects of the drug were was set to 5000, and AC coupling was used with a similar for both albino and pigmented rabbits. Apomor- bandwidth of 0.2 to 2.0 kHz. A Burian-Allen elec- phine, a dopamine agonist, has the opposite effect on the trode was used to record ERG. The data were b-wave of the ERG when compared with the effect of processed on a PDP-11/34 computer (Digital chlorpromazine, a dopamine antagonist. Involvement of Equipment Corp.) equipped with VT-11 refresh dopamine receptors is not unexpected, since the retina is graphics scope and Tektronix Model 4662 plotter. rich in dopamine, especially the inner plexifonn layer. The general anesthetics used were 100 mg/ml (INVEST OPHTHALMOL VIS SCI 21:620-625, 1981.) ketamine (Ketalar; Parke, Davis & Co.) and 20 Extensive research has been conducted on the mg/ml xylazine (Rompun; Haver-Lockhart Labora- synthesis, storage, release, uptake, and metabo- tories). Proparacaine (Alcaine) and tropicamide lism of dopamine (DA) during the past two de- (both manufactured by Alcon Laboratories) were cades. Since the discovery of its presence in the used as local anesthetic and to dilate the pupil, brain in the 1950s, DA has been identified in vari- respectively. ous organs, including the retina, and this catechol- The rabbit was dark-adapted for about 20 min amine has now been accepted as a neurotransmit- and then anesthetized by an intramuscular injec- ter in its own right. It has been demonstrated1"3 tion of 50 mg/kg ketamine and 10 mg/kg xylazine. that the retinas of several species contain large With the rabbit's eyes completely covered with concentrations of DA. Among these, the rabbit black tape, an incision was made into the rabbit's retina has one of the largest concentrations of DA4 neck to expose the arteries. A canula with a T was and is thus a good model to study receptor effects. inserted into the left carotid artery. The animal Understanding of the DA receptors is perhaps a was then placed in a metal box with its head inside precursor to the understanding of dopaminergic a globe, set up with flash for a ganzfeld system. systems, and hence the study of DA receptors has The animal was kept anesthetized by a multidose received the greatest attention in recent years. administration of a mixture of 4 ml of keta- Such studies invariably include experiments utiliz- mine + 4 ml of xylazine + 12 ml of 0.5% saline ing specific-acting agonists and antagonists. In our solution. No data were collected for the first 30 to previous study5 intravenous injection of chlor- 45 min after the rabbit was placed in the metal promazine markedly increased the b-wave of the box. Three intensity levels corresponding to 1-1, electroretinogram (ERG). If, indeed, chlorpro- 4, and 16 of the PS22 photostimulator were used at mazine was acting on the DA receptors in the ret- random. One ERG was recorded every minute. ina, we expected that such a DA antagonist would Normal ERGs were recorded for about 20 min, have an effect opposite to that of an agonist. Apo- and then apomorphine was injected through the morphine has been extensively studied as a spe- left carotid artery via the canula. Drug doses rang- cific-acting DA agonist in the central nervous sys- ing from 0.1 through 2 mg/kg were used. The ex- tem. In order to establish DA agonist/antagonist periments were conducted on both albino and pig- drug effects on the ERG, we conducted detailed mented rabbits. In a few experiments, the animals experiments concerning the effect of apormor- were light-adapted with high illumination (100 w phine on rabbit ERG, and the results are reported incandescent light in addition to normal fluores- here. cent room light) for about 10 min, and then the Methods. The methods used were very similar ERGs were recorded through the dark-adaptation 0146-0404/81/100620+05$00.50/0 © 1981 Assoc. for Res. in Vis. and Ophthal., Inc. Downloaded from iovs.arvojournals.org on 09/26/2021 Volume 21 Number 4 Reports 621 180 PIGMENTED RABBIT APOMORPHINE 1 mg/kg 19 min. BEFORE DRUG FLASH INTENSITY = 16 16 min. AFTER DRUG 3- 15 min. AFTER DRUG UJ Q • 51 min. AFTER DRUG 60 _l Q_ 0 -60 - 0 0.115 0.230 0.345 0.460 0.575 0.690 0.805 TIME (S) Fig. 1. ERG waveforms before and after intra-arterial injection of apomorphine. The ERGs were digitized with a 12-bit analog to digital converter and the sampling period was 0.5 msec. process. A few experiments were also conducted ished. There was a slight reduction in the bj-wave with chlorpromazine by injecting the drug intra- amplitude. The reduction in b2-wave amplitude arterially to compare with our previous results was significantly greater than the reduction in using an intravenous injection. The blood pressure bj-wave amplitude in both types of animals and at was recorded on a Physiograph (Narco Bio-Sys- all dose levels. There was no measurable change in tems, Inc.) using the femoral artery. Experiments the a-wave amplitude. The c-wave amplitude in- were conducted on five albino and six pigmented creased after the injection of the drug. A very clear rabbits with drug and four albino and three pig- dose-amplitude relationship could not be estab- mented rabbits without drug. lished for the c-wave amplitude or latency. The An interactive program was used to calculate latencies of a-, br, b2-, and c-waves were the same the a-, b-, and c-wave amplitudes and latencies. before and after the drug injection. The results Each ERG was displayed on the VT-11 graphics were similar at all flash intensities except that the scope, and a flashing cursor was moved across the c-wave was absent at the lowest intensity. A series screen. When the operator judged that the cursor of ERGs taken before and after apomorphine was was located at the peak of interest, he typed an injected is shown in Fig. 1. The amplitudes of the "o"; the amplitude and the latency values at the br and b2-waves as a function of time before and cursor were stored on the disk. These disk files after the drug injection are shown in Fig. 2, A. were used to plot various graphs. The recovery of the ERG waveform was gradual Results. The nomenclature used in this report and dose-dependent. The reduction in the bj- and for different wavelets of the electroretinogram is b2-wave amplitudes was also dose-dependent. The given in the inset of Fig. 3. This nomenclature is maximum reduction for each dose was calculated very similar to the one given by Armington6 ex- and these values for different doses are given in cept that photopic (bp) and scotopic (bs) b-wave Table I. are labeled as bx- and b2-waves, respectively. Four Soon after the drug had been injected, there discrete doses (0.1, 0.6, 1.0, and 1.5 mg/kg) were was a small dip in the arterial blood pressure, and tested on both pigmented and albino rabbits. At it returned to predrug level in about 1 to 3 min, as doses higher than 2 mg/kg the recording was un- shown in Fig. 2, A. This transient change in blood stable. In all cases the b2-wave amplitude was re- pressure was observed in all experiments. There duced dramatically, irrespective of the type of ani- was also a gradual fall in blood pressure progress- mal. For large doses the b-2-wave almost van- ing toward the end of the experiment. We also Downloaded from iovs.arvojournals.org on 09/26/2021 Invest. Ophthalmol. Vis. Sci. 622 Reports October 1981 en 500 A UJ 400 cr Z) O) t C/) O O LJJ LU 300 -O O O O OOOOOO O O TO '1 Z) Q ^ 200 O CL 50 AP0M0RPHINE O.lmg/kg ALBINO RABBIT - 30 < 100 FLASH INTENSITY=I6 1 i il i i i i i i i i UJ 00 10 20 30 40 50 60 70 80 TIME(min) B 240 V V X Y Y v xx xxxx i c 'E 180 \ o_ en LU c Q APOMOF PHINE lmg/kg 120 LU FLASH INTENSITY = I6 Q_ or 60 ^ 60 - _ / V y—"\ - 40 g 20 g n i i i i i 1 Q_ 0 25 150 00 50 75 100 125 LU TIME (min) cr Fig.