$162

25. Neurotransmitters II. Monoamines

PROTECTION BY (-)PHYSOSTIGMINE AND ITS ENANTIOMER (!)PHYSOSTIGMINE AGAINST LETHALITY AND MYOPATHY INDUCED BY AN IRREVERSIBLE ORGANOPHOSPHOROUS AGENT

MASARU KAWABUCHI , KAZUHO HIRATA AND EDSON X. ALBUQUERQUE DPT. ANATOMY, FAC. MED., KYUSHU UNIVERSITY, MAIDASHI 3- l - l , FUKUOKA 812, JAPAN; DPT. PHARMAC. & EXP. THERAP., UNIV. MARYLAND, SC. MED., BALTIMORE, MD 21201, USA

The natural alkaloid (-)physostigmine [(-)PHY ]is a reversible anticholinesterase carbamate. In contrast, i ts optical isomer, (+)physostigmine[(+)PHY],is a very weak esterase inactivator. At the concentration used (0.3 mg/kg) there was no detectable inhibition of esterase activity. We examined the protection afforded by (+)PHY or (-)PHY against lethal i ty and myopathy due to organophosphate agents such as sarin. Treatment of rats with atropine (0.5 mg/kg) and (-)PHY (O.l mg/kg) prior to injection of a lethal dose of the irreversible organophosphate sarin (0.]3 mg/kg) not only protected I00% of the animals from lethal i ty but also, l ight micro- scopically, reduced the size of the subjunctional lesions of the nicotinic synapses of skeletal muscle. Similar protection was provided by pretreatment with (+)PHY (O.l, 0.3, 0.5 mg/kg). The major l ight and ultrastructural alterations in the soleus motor endplates I hr after drug treatment were as follows: l) A single sublethal dose of sarin (0.08 mg/kg) produced enlarged, blistered and severely disrupted subjunctional regions, with muscle damage extending beyond the endplate to include myofiber necrosis and subsequent phagocytosis. 2) (+)PHY (0.3 mg/kg) produced no obvious damage in the postjunctional region. 3) (-)PHY (O.l mg/kg) had a selective effect in inducing irregularit ies of the subjunctional sarcomere band patterns without any gross vacuolization. 4) The "protection myopathy" was detectable in most endplates but recognizable changes were markedly less severe than those seen in sarin myopathy. Few instances of extensive muscle damage and myofiber necrosis were visible. The subjunctional myopathy was reversible with substantial recovery being observed on days 5 ("protection myopathy") and IO (sarin myopathy) after drug treatment. The prophylactic effectiveness of (+)PHY against toxic effects of sarin suggests that mechanisms other than AChE blockade may underlie the protection afforded by carbamates in organophosphorous poisoning. This protection is most l ikely due to the ab i l i ty of (+)PHY as well as (-)PHY to block the postsynaptic acetylcholine receptor/ion channel complex.

IDENTIFICATION OF SEROTONIN NEURONS PROJECTING TO THE SUBSTANTIA NIGRA IN THE RAT

USING A COMBINED TECHNIQUE OF IMMUNOHISTOCHEMISTRY AND FLUORESCENT RETROGRADE

TRACING METHOD

SATORU MORI AND YUTAKA SANO, Department of Anatomy, Kyoto Prefectural University of

Medicine, Kawaramachi-Hirokoji, Kamikyo-ku, Kyoto 602, Japan

The origin of serotonin nerve fibers distributed in the rat substantia nigra was

studied by a combined technique of immunohistochemistry using the serotonin antibo-

dy and a retrograde fluorescence True-Blue labeling method on the same tissue sec-

tions. After the unilateral injection of the True-Blue into the substantia nigra,

the confined appearance of True-Blue-labeled neurons in the raphe nuclei was demon-

strated in the dorsal raphe nucleus. A majority of these labeled neurons (62%)

were serotonin-immunoreactive, but the rest (38%) were nonimmunoreactive. True-

Blue-labeled as we]] as serotonin-positive neurons were localized mainly in the

ipsi]atera] lateral (46%) and dorsomedia] aspects (32%), and some were observed in

the ventromedia] (19%) and contra]ateral lateral aspects (3%). These findings

indicate that a majority of these serotonergic fibers projecting to the substantia

nigra originate mainly in the ipsi]atera] lateral and dorsomedia] aspects of the

dorsal raphe nucleus, and that these raphe nigra] pathways contain both seroto-

nergic and nonserotonergic fibers. Similarly, after the unilateral injections of

the True-Blue into the substantia nigra and the propidium iodide into the striatum,

True-Blue-labeled as well as propidium-iodide-]abe]ed neurons were observed in the

dorsomedia] aspect of the dorsal raphe nucleus; these were also serotonin-immuno-

reactive. Therefore, some serotonin neurons projecting to the substantia nigra

were considered to project also to the striatum.