Spontaneous and cortically-evoked unit activity in the caudate nucleus after systemic morphine

85 .td.

Center, Lub8th, 1982)

The ability, o f administered morphip,e to alter spontaneous and cortical!yoevoked single unit activity in rat caudmenueleus was assessed in this study, The animals were prepared with permanently imp tamed mieroeteetrode guide eannulas and cortical stimulating electrodes. For recording sessions, e stereotaxic device. Morphine was ad/kg. Neither spontaneous activity nor aneous activity was depressed m 12 of uced in 7 of 36 units and enhar~ce0 in 9 o f 36 ~ l w A large :I~r.o~rtion of the responses to morphine were not reversed by ! mg/kg halo×one, estmem~l!~,' ~.hec ~ e s in cortically-evoked firing. These r~ults demonstrate a multiplicity of change~ in ~ne0u~s orfically-evoked activity of caudate nucleus neurons following systemically administered morpMne~

The eaudate nucleus ( C N ) i s known to receive e×c~tatory inputs from the neoeortex [t|, and these inputs ~eem to dominate over other CN afferent influences [7, 16]. tt h ~ been demonstrated that t h e CN contains a po~ulatior~ of neurons w h o ~ spontaneous firing rates are affected by systemically admi ai~tered morphine

~'3~,'82

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enough to perform such surgery as would be n ~ s a r y f o r a n acute p r ~ a t i o n . Conseq! . . . . . tion we1 mg/~:g. vided a design [122. . . . . A tungsten microelectrode was lowered through t h e guide ~to : I ~ a t e : a spontaneously active caudate neuron. Only one celt was eva|tinted ~ : t ~ i n a : ~ sion. The number of sessions conducted with a single: an;raal v -:~ ~oneto three. If r~ultip|e recording.q were obtained ~rom a~ animal, at least 4 ~ays e l a p ~ between recordings. Monophasic square wave pu 1~ses (0.25 ,-~5 mA,• 0~3,:~ , • 1 HZ) were ~sed for conical stimulation. The optimal cortk:al ~ke aru~ threshold ~,~arreat neces:~ary for driving the unit were determined. Before admirii~ering drug, fi~e ,

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doses of morphine. # . Morphine af Electe~1 cort1~y,evokeA f~rflug in even fewer c.elts (Table I). Evoked activity was unchanged in more than half of the units (20/36~. Evoked firing of 7 rleurorls

the drug to antagon~¢ ~his etfcct in 8 of the 9 urfits). Under the . . . . . of caudate taneous fid~ et al. [t l] and Finnerty and Chan [5]~ recording caudate u~fit~ in ~cutely-prepar,.~i, pentobarbital-anesthetfized rats, found that the spontan~:as activity of nearly at~ cells was markedly reduced following intracarotid or intravenou,~ injection of morphine; ~ mg/kg aa]oxonc antagonized the morph~ne-induc¢~i depression iv ~ll eei|~ tested. Conversely, other ~nvesfiga~or~ who studied caudat¢ mukiple-unit actw~ty i:~ awake, freely moving rats observed var:ied resg~oa~'s to morphine adm~ntstered ~n~ traperitoneally [3, 4]. In the later studies, some l ~ p u ~ f i o a s were d~press~di some TABLE ! MORPHINE-INDUCED CHANGES IN SPONTANEOUS AND EVOKED FIRING OF CAUDATE NEURONS Morphine effect

N~loxon¢ effect

Spontaneous activity (n= 33)

De, teased

Antagonism NO anu~gonism

8a 4

3 4

~acr~sed

Ant~onism No an~affonism

2 3

~. 8

aNomb~z of cells wi~ ~ i g a a ~ e d I~t~¢ra o f response to m ~ r ~

Evoked activity (n = 36)

~ad ~ d o x o ~ :

-~

receptor mediated ~

O~S

S activity ~n 1100f33 eaudate neurons and

f ~ , whether produced within the CN or indirr:etly by an action ouk, iSe ~he .~rNt~rn (e,g. the ~ub~tantia ~ig~a [5, 8, 9, 1tL shoutd be ~aken into account when considering the rote of the striatum ~n the pharmacological ef%cts of morphine. F~rthermore, since morphine did not produce a consistent effec~ on all c a r d , re tN~ ity o f ~esponse t o the drug mu~ also be co~:~;idered. We are grateful to Endo Laboratories for the gift of nalono~e. This work was supported b_VUSPHS)BRSG ~R05773 and MH29653 and by Tarbox Parkinson's Disease Institute at Te~,as TeCh University Health Sciences Center~ I Buehwald, N.A., Price, D . D . Vernon, L, and Hull, C.D,, Caudate in~raceltuhr resp6nses ~o thalami¢ arid cortical ~nput~, E×p. NeuroL, 38 {t973) 311~323. 2 C~art8~ K.-J~ and Cuta~recazaa, P., Heter~genehy and properfie~ of oNate receptors, ~ed. Prec., 3 Dafny, N., ~¢~wa,~-,M,, B'~rk~,¢ TAr. a~d Rigor, B.i**io, Fatter~ of u~it resp~ase~ to ~ncremer~al ~ o ~ of morphine ir~ central gray, reticular formatkm, medial ~ha~amu~, cauda~e nucleus, hypohiNmca~pu~ ~a u~ane~;thefized ra~, Neurophar~acok~gy, ]~ (~9~9~ ~.

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aW~ ~ o r , B~o~ Cham~te~i~fio~ of unh ~c~,~6~:yrecc~de~ from sep~:um,~thalamus, fo~lo~'ir~g opiate ~reat~c~L L Ne~r~io Res., 5(~9~9) H7-~27~

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