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Electrophysiological responses of the retina and visual cortex to a series of grating stimuli (6-768 minutes of arc) were recorded in seven sessions using normal beagles, 21 sessions using beagles afflicted with inherited ocular hypertension, and 12 sessions using rhesus monkeys. A 150 field centred around the animal's area centralis or fovea was used to stimulate the central retina. A 30°field, centred on the same spot, was then used to stimulate the larger area. Two recording series were completed on each animal, with both field sizes presented in each recording session. The first recording took place 30 minutes after and the second 2 hours after the injection of thiamylal sodium. Only the signals from the toroidal 150 of the retina of the hypertensive dogs were remarkably larger during the second recording (p=0001). No significant differences were found between the two recordings from the retinas of normal dogs or monkeys, nor were there any significant differences between the two recordings from above the cortex in any group. Several hypotheses are proposed to explain the basis for the interaction of thiamylal with the more peripheral retinal function in clinically glaucomatous dogs. (BrJ Ophthalmol 1993; 77: 502-508) Thiamylal sodium is the thiobarbiturate analogue of secobarbitone. It is an ultra short acting drug, commonly used for induction of general anaesthesia for several short term veterinary surgical procedures. In the dog the drug is metabolised rapidly by the liver,' and has no apparent cumulative effect.23 The duration of anaesthesia in the dog is 10-45 minutes,2 with complete recovery after 113 minutes.3 In mixed breed dogs, disposition of thiamylal is characterised by a rapid distribution phase (half life 38-9 minutes) and an elimination phase with a half life of 666 minutes.4 The total plasma clearance of the drug in dogs is 3-21 ml/min/kg. 18 Despite this wealth of information on the multifactorial effect of anaesthetic drugs and increased IOP on visual electrophysiology, we find no information on the interactions between anaesthesia and OHT in the glaucomatous retina. This is surprising, considering the fact that ERG recordings are used in many institutions to diagnose and monitor the progress of glaucoma in non-verbal patients such as children, mentally handicapped people, and animals.'9-22 They may be used to diagnose glaucoma at early stages, before the appearance of funduscopic changes and visual field losses.'ll22 Frequently at this stage the visual deficits are not entirely diffuse, with the greatest losses in the more peripheral, paracentral regions of the visual field. 19 21 23 We report on interactions between thiamylal and different retinal regions of normal and ocular hypertensive dogs. Materials and methods EXPERIMENTAL ANIMALSSeventeen beagle dogs and seven rhesus monkeys (Macaca mulatta) were used in the study. Of the 17 dogs, 13 were hypertensive and four were normal. Some ofthe animals were used for more than one recording session. In such cases, the minimum inter...

We have investigated the projection patterns of peptidergic small-diameter primary afferent fibers to the cat sacrocaudal spinal cord, a region associated with midline structures of the lower urogenital system and of the tail. Calcitonin gene-related peptide (CGRP)-immunoreactive (CGRP-IR) primary afferent fibers were observed within the superficial laminae, rostrally as the typical inverted U-shaped band that capped the separate dorsal horns (S1 to rostral S2) and caudally as a broad band that spanned the entire mediolateral extent of the fused dorsal horns (caudal S2 and caudal). Within the dorsal gray commissure, labeling was seen as a periodic vertical, midline band. CGRP-IR labeling was prevalent in an extensive mediolateral distribution at the base of the dorsal horn, originating from both lateral and medial collateral bundles that extend from the superficial dorsal horn. Some bundles, in part traveling within the dorsal commissure, conspicuously crossed the midline. In addition to the robust projection to the superficial dorsal horn, there was a more extensive distribution of CGRP-IR fibers within the deeper portions of the cat sacrocaudal dorsal horn than has been reported for other regions of the cat spinal cord. Presumably, these deep projections convey visceral information to projection or segmental neurons at the neck of the dorsal horn and in the region of the central canal. This deep distribution overlaps the reported projections of the pelvic and pudendal nerves. In addition, the contralateral projections of CGRP-IR fibers may form an anatomical substrate of the bilateral receptive fields for selective dorsal horn neurons. The density and variety of CGRP-IR projection patterns is a reflection of the functional attributes of the innervated structures.