Carey D. Balaban

Central neurotoxic effects of intraperitoneally administered 3-acetylpyridine, harmaline and niacinamide in Sprague-Dawley and Long-Evans rats: A critical review of central 3-acetylpyridine neurotoxicity

Previous studies indicate that 3-acetylpyridine (3-AP) intoxication produces discrete lesions of the inferior olive (IO) and other central structures in rats and mice. As a result, it has been widely employed in investigations of the influences of climbing fibers on cerebellar function. This study examines the central toxicity of a protocol reported to produce lesions restricted to the inferior olive in rats. Adult male Long-Evans (n = 12) and Sprague-Dawley (n = 18) were given serial injections of 3-AP (75-80 mg/kg), harmaline (15 mg/kg) or saline, and niacinamide (300 mg/kg). Silver degeneration staining (cupric-silver method) after 6-48 h survival revealed consistent patterns of degenerating neurons in IO, nucleus ambiguus, hypoglossal nucleus, dorsal motor nucleus X, nucleus intercalatus, nucleus dorsalis raphe, medial terminal nucleus, interpeduncular nucleus, substantia nigra, ventral tegmental area, entopeduncular nucleus, hippocampus (dentate gyrus and CA 3-4), horizontal limb of the nucleus of the diagonal band, and lateral entorhinal cortex, which were not produced by control experiments with 3 saline injections or with two saline injections followed by niacinamide. These data apparently resolve conflicts in the literature regarding central 3-AP toxicity and indicate that the 3-AP-harmaline-niacinamide protocol produces degeneration that is similar to 3-AP alone. However, they also document the discrete, reproducible susceptibility of certain neuronal populations to 3-AP intoxication and suggest that the motor symptoms of intoxication are not solely due to IO destruction. Finally, they form a basis for biochemical investigations of 3-AP toxicity in susceptible central structures.

The human pre-saccadic spike potential: Influences of a visual target, saccade direction, electrode laterality and instructions to perform saccades

Three components of pre-saccadic evoked potentials have been identified in humans: a slow negative shift (SNS), a positive antecedent potential (AP) and a spike potential (SP). This study examined the influences of: instructions to the subject to make saccades; the presence of a visual target; and the direction of the saccades on the amplitude of the averaged SP, which was recorded from P3 and P4 (International 10/20 System) in 20 normal, right-handed subjects. Recordings were made for spontaneous saccades prior to receiving instructions in six subjects. Twenty subjects performed self-paced saccades in the presence of a 10 degrees visual target (two red LEDs) and while blindfolded in a dark room. The SP was either absent or grossly altered (broadened) for spontaneous saccades in an illuminated room; it was robust for self-paced saccades in light or darkness. Three-way analysis of variance revealed a highly significant cortical laterality (P3 vs P4) X saccade direction interaction (P less than 0.001), reflecting that for a given saccade direction, the SP was larger over the contralateral recording site for the self-paced light (SPL) paradigm (Newman-Keuls test). In the self-paced dark (SPD) paradigm, though, this was only true for saccades to the right. By contrast, scatter plots of the directional indices (D.I. = [(SP for contralateral) - (SP for ipsilateral)]/[(SP for contralateral) + (SP for ipsilateral saccades)] for left (P3) and right (P4) recording sites from individual subjects revealed a significant negative correlation for both SPL (r = 0.78) and SPD (r = 0.74) paradigms.(ABSTRACT TRUNCATED AT 250 WORDS)

Motor disturbances and neurotoxicity induced by centrally administered somatostatin and vasopressin in conscious rats: interactive effects of two neuropeptides

Barrel rotation (BR) is an abnormal, long-axis rotation induced by intracerebroventricular (i.c.v.) injections of peptides, including somatostatin (SRIF) and arginine-vasopressin (AVP). This study examined the effects of two i.c.v. doses of SRIF and combined injections of SRIF and AVP in conscious, adult Wistar and Sprague-Dawley rats. Mortality after i.c.v. SRIF was dose-dependent; 0/16 rats died after a 20 microgram dose, while 21/43 died after 40 micrograms SRIF. On the other hand, BR incidence was similar after the two doses, but the hazard function of the BR latency data was shifted to the left by the higher dose. Although the incidence data imply that BR and mortality are independent, the hazard function of BR latency data is predictive of mortality. An interaction study employing a combined i.c.v. dose of 20 micrograms SRIF and 0.5 micrograms AVP established that the effects add non-linearly. This is illustrated by a marked increment in mortality (0/16 for 20 micrograms SRIF, 1/25 for 0.5 micrograms AVP and 12/18 for SRIF + AVP). The hazard plot shows a similar, non-linear interaction. In addition, SRIF, but not AVP, produced a characteristic pattern of Purkinje cell death in cerebellar regions projecting to the fastigial and lateral vestibular nuclei. These results imply that SRIF and AVP act at independent sites to produce BR and mortality, and that the effects summate non-linearly at a common central site. This raises the issue of whether these neuropeptides, endogenous in human CSF, interact to produce similar biological effects.

Central effects of aldosterone infused into the rat subcommissural organ region

D-Aldosterone (5 ng/microliter/h) was infused for 6 days into the region of the subcommissural organ (SCO) of conscious, adult male Sprague-Dawley rats. Aldosterone increased urinary sodium loss and the sodium/potassium ratio. Although probably central in origin, these effects still occurred when cannulae were displaced up to 1 mm from the targeted SCO placement. Aldosterone decreased adrenal medullary cross-sectional area without affecting cell density. This effect was highly dependent on proper cannula placement and was not observed when the cannula tip was not in contact with the cerebrospinal fluid of the pineal recess over the rostral two-thirds of the SCO. We conclude that aldosterone increases sodium excretion by an action in the SCO and/or adjacent structures. We also postulate a negative trophic relationship between mineralocorticoids and the adrenal medulla mediated by the SCO.

Site-dependent central effects of aldosterone in rats

A relationship between the subcommissural organ (SCO) and the adrenal glands has long been suspected. This report provides further information about the effects of a continuous D-aldosterone infusion into the SCO area of conscious, adult male Sprague-Dawley rats. A 6-day aldosterone infusion (5 ng/h) increased urinary sodium excretion, decreased adrenal medullary cross-sectional area, elevated adrenal corticosterone content and terminal plasma epinephrine concentration. Mineralocorticoid infusions directly into a lateral cerebral ventricle did not affect these parameters but, unlike SCO area infusions, decreased consummatory behavior. Infusions of tritiated aldosterone into the SCO area revealed that radioactivity was mainly confined to dorsomedial portions of the brain near the SCO, whereas the pineal body contained only background radioactivity. The data support the concept that the SCO area interacts with physiological systems related to both the adrenal cortex and medulla.

The Subcommissural Organ: Immunohistochemistry and Potential Relations to Salt/Water Balance

The subcommissural organ (SCO) seems to be an “orphan” among the circumventricular organs (CVO). It attracts relatively little research activity and there is no clear-cut indication of what normal physiological function(s) it contributes to the day-to-day life of an animal. By contrast, other CVOs with more clearly defined roles attract considerable research effort. For example, the area postrema and the nearby nucleus tractus solitarius are well known for their involvement in cardiovascular reflex mechanisms (Miselis et al. 1987). Similarly, there is considerable information, including anatomical connectivity, about the subfornical organ and its linkage to water ingestion and vasopressin secretion (Lind 1987).

Localization of methadone in the brain of young rats by computer-assisted autoradiography

The distribution of systemically administered [14C]methadone in the brain of 21-day-old rats was examined by computer-assisted autoradiography. Methadone binding differed 2.5-fold across the more than 90 neural structures examined, with the dentate nucleus having the highest levels and lamina I of the anterior parietal cortex the lowest. Since a full normal probability plot demonstrated that the binding was distributed normally across brain structures (r = 0.99), binding classes were defined in terms of 0.5 standard deviation units from the mean. In addition to marked binding differences between neuronal structures, there were prominent laminar differences in the cerebral cortex, hippocampus, superior colliculus and cerebellar cortex. These highly specific patterns of methadone localization were specifically related to the opioid receptor because naloxone blocked the antinociceptive effects of methadone on the hot-plate test and abolished the distribution of methadone binding in the central nervous system. The relatively high levels of methadone binding in layers III and V of neocortex, sensory relay nuclei, inferior olive, pontine nuclei, cerebellar nuclei and cerebellar molecular layer suggest that the constellation of physiological and neurobehavioral sequelae of perinatal opioid exposure result from specific binding at multiple sites involved in sensory, motor and integrative information processing.

Protein-O-car☐ylmethyltransferase in the rat brain: High regional levels in the substantia nigra, locus coeruleus and paraventricular nucleus

Immunocytochemical techniques were used to localize protein-O-carboxylmethyltransferase in the rat brain. Particularly high levels of immunoreactive protein-O-carboxylmethyltransferase were found in the paraventricular and supraoptic nucleus, the substantia nigra and the locus coeruleus. The enhanced expression of the methyltransferase in these brain regions suggests that protein carboxylmethylation is of particular importance in these areas. These findings are consistent with previous biochemical studies which suggest that protein methylation plays a role in presynaptic monoaminergic neurons and in the release and/or processing of neurohypophyseal peptides.

Diazepam attenuation of somatostatin-induced motor disturbances and neurotoxicity

Intracerebroventricular somatostatin administration to conscious rats results in a characteristic motor abnormality (barrel rotation), convulsions that are frequently fatal and destruction of cerebellar Purkinje cells. This study demonstrates that each of these manifestations of this neuropeptide can be attenuated by pretreatment with diazepam (Valium, 5 mg/kg, i.p.) but not in vehicle-pretreated controls. Specifically, the incidence of mortality was reduced from 5/12 controls to 2/20 diazepam-treated rats, the incidence of barrel rotation was reduced from 6/12 controls to 2/20 diazepam-treated rats and the incidence of Purkinje cell death was reduced from 4/4 examined controls to 4/13 diazepam-treated animals. Vehicle pretreated rats did not differ from untreated rats. Thus, in addition to blocking somatostatin-induced motor dysfunction and mortality, diazepam offers significant protection from central neuronal cell death in the cerebellar cortex.

Inferior olivary lesions after local injections of 3-acetylpyridine in rabbits

This report presents evidence that local injections of 3-acetylpyridine (3-AP) produce circumscribed lesions of the inferior olive (IO) in rabbits. These restricted lesions, assessed in both cresyl violet-stained sections after a 14-day survival and cupric-silver-stained sections after a 16-24 h survival period, are similar in appearance to lesions produced by systemic 3-AP administration in rats. Two types of degeneration are observed: destruction of cells at the injection site and more diffuse cell death in the ipsilateral and contralateral inferior olive. The latter type of degeneration appears to result from IO fiber-of-passage uptake of 3-AP. There was no evidence of lesions in surrounding structures or in sources of axons passing through periolivary regions. Thus, this protocol is a promising tool for studies of climbing fiber connectivity and physiology in rabbits.