Cells of origin of spinothalamic tract projections to the medial and lateral thalamus in the cat

Abstract

The double fluorescent retrograde labeling method was used to examine the distribution of spinothalamic tract (STT) cells that project to the medial and lateral thalamus in the cat. Injections of one fluorescent tracer (Fast Blue or Diamidino Yellow) were made throughout the lateral thalamus and injections of the other tracer were made in the medial thalamus at sites extrapolated from recording track coordinates. Survival times were successively extended (up to 5 weeks) in order to maximize labeling in both the cervical and lumbosacral spinal cord. On average, over 2,000 labeled contralateral STT cells were counted in serial sections from segments C5-7 and L5-S2. Numerical variability of the order of a factor of two was attributable to inherent differences between individual animals. The total number of cells labeled with fluorescent tracers was comparable to the number labeled with horseradish peroxidase in control cases, although there were significant differences between the laminar distributions of labeling produced by the two methods. Injections made anterior to the thalamus to control for labeling due to leakage or passing fibers did not produce substantial spinal labeling. The laminar distribution of fluorescent dye-labeled STT cells was consistent; about half (47%) were located in lamina I, 8% were in lamina V, 5% in lamina VI, 20% in lamina VII, and 20% in lamina VIII. The proportions of STT cells in laminae I and V were higher in cervical segments (57% and 12%, respectively) than in lumbosacral segments (38% and 6%). The dominant contribution of lamina I cells to the STT thus revealed by the fluorescent tracers is striking. The proportions of STT cells labeled from the medial and the lateral thalamus varied with segmental and laminar location and with injection placement. The majority (62%) of STT cells in most cases projected only to the medial thalamus, 25% projected only to the lateral thalamus, and 13% projected to both. The STT cell populations in laminae I, VII, and VIII each displayed this common projection pattern. In contrast, cells in laminae V and VI projected predominantly to the lateral thalamus. Twice as many STT cells in lamina I (19%) projected to both the medial and the lateral thalamus as from other laminae. A greater proportion of laminae V-VIII STT cells in segments L5-6 projected to the lateral thalamus, and in S1-2, more projected to the medial thalamus.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphology and Distribution of Spinothalamic Lamina I Neurons in the Monkey

“…In more ventral sections, labeled cells were limited to the most lateral and medial aspects of the substantia gelatinosa (lamina II), which was quite recognizable with brightfield or darkfield microscopy. Labeled cells in lamina II were very rare, consistent with prior studies (Carstens and Trevino, 1978;Willis et al, 1979;Craig et al, 1989). The portion of lamina I that extends ventrally along the extreme lateral aspect of the dorsal horn was not cut tangentially in horizontal sections, so that cell shape was more difficult to determine, but nearly all of the relatively few labeled cells in this portion were recognizable as bipolar fusiform cells.…”

“…A few labeled cells were present within the white matter overlying lamina I, near the entering dorsal root fibers. The majority of labeled lamina I cells were found in the region of the dorsal cap (Snyder, 1982), overlying the lateral third of the dorsal horn, where lamina I is ϳ300 m thick and where lamina I STT cells are concentrated (Apkarian and Hodge, 1989;Craig et al, 1989). Labeled lamina I STT cells were present throughout the entire mediolateral extent of the superficial aspect of the dorsal horn, which particularly in the cervical and lumbosacral enlargements spanned only a few sections.…”

“…It contains a unique concentration of nociceptive and thermoreceptive neurons (Christenson and Perl, 1970), and it is the source of about one-half of the spinothalamic tract (STT; Carstens and Trevino, 1978;Willis et al, 1979;Apkarian and Hodge, 1989;Craig et al, 1989). Lamina I STT axons ascend in the lateral STT, which is critical for pain and temperature sensation (Nathan and Smith, 1979;Norrsell, 1979;Craig, 1991;Ralston and Ralston, 1992).…”

Termination Zones of Functionally Characterized Spinothalamic Tract Neurons Within the Primate Posterior Thalamus

“…Collateral branches might target posterior thalamic nuclei even though the parent axon continues rostrally to VPL. Consistent with this idea, double-labeling experiments have shown that as many as 10 -20% of STT axons branch and terminate in both medial and lateral thalamic nuclei (Applebaum et al 1979;Craig et al 1989;Giesler et al 1981;Kevetter and Willis 1983). A subpopulation of STT neurons that project to both the posterior thalamus as well as to VPL could contribute to nociceptive processing at both sites.…”

Response characteristics of ventral posteromedial thalamic nociceptive neurons in the anesthetized rat

“…이외에도 시상의 복후 핵은 유해자극과 온도자극에 관한 정보를 전달하는 주요한 상행경로인 척수시상로와 삼차신경시상로로부터 감각정보 를 받는데, 척수후각에서 시작된 척수시상로는 복후외측핵 으로 투사하고, 척수감각핵에서 시작된 삼차신경 시상로는 복후내측핵으로 투사한다 1,2) . 척수시상로로부터 정보를 받 는 복후외측핵 뉴론은 대뇌피질 체성감각영역으로 투사되 며, 통각의 식별에 관여할 것으로 사료되어 왔다 [4][5][6] . 원숭이 [7][8][9] , 고양이10-12), 너구리 13) , 쥐 [14][15][16][17] 를 사용한 전기생리학적 연 구에서 수용야에 가해진 유해한 기계적 자극 혹은 열자극에 반응하는 뉴론이 시상의 복후외측핵에 존재함이 관찰되었 다.…”