Somatotopic distribution of trigeminal nociceptive neurons in ventrobasal complex of cat thalamus

Abstract

Recordings were made from single thalamic units in the urethan-chloralose anesthetized cat. Altogether 2,905 trigeminal single units having a receptive field in the contralateral trigeminal integument were isolated from the somatosensory part of nucleus ventralis posteromedialis, or VPM proper. Each isolated unit was tested for responses to a series of mechanical stimuli. The stimuli included brushing the skin, touch, pressure, noxious pinch, and pinpricks. The majority of VPM proper units responded with the greatest discharge frequency to gentle mechanical stimulation: either hair movement or light pressure to the trigeminal integument, but 341 units were identified as trigeminal nociceptive units. They were partitioned into two functionally defined subclasses, nociceptive specific (NS) and wide dynamic range (WDR) units, but not intermingled with low-threshold mechanoreceptive (LTM) units. Both NS and WDR units were found at or near the margin of the VPM proper but not outside this nucleus. This marginal area was referred to as the shell region of the VPM proper. A total of 248 NS units was found within the shell region of the caudal third of the VPM proper. This part was called the NS zone. These units were somatotopically organized. In the rostral part of the NS zone, ophthalmic NS units having a receptive field in the contralateral ophthalmic division were located dorsolaterally, maxillary NS units occurred dorsomedially, and mandibular NS units were found ventromedially. In the caudal part of the NS zone, maxillary NS units were encountered in the dorsal shell region, whereas mandibular NS units were found in the ventromedial shell region. Ophthalmic NS units were not found in this part of the NS zone. Altogether 93 WDR units were encountered in the shell region of the VPM proper. They were confined to a narrow band approximately 300 micron wide just rostral to the NS zone. These units were somatotopically organized. Ophthalmic WDR units having a low-threshold center of the receptive field in the contralateral ophthalmic division were located dorsolaterally, maxillary WDR units were located dorsomedially, and mandibular WDR units were located ventromedially. The majority of maxillary as well as mandibular WDR units were activated by electrical stimulation of the contralateral maxillary and/or mandibular canine tooth pulp afferents. Both NS and WDR zones of the VPM proper extended into the shell region of the nucleus ventralis posterolateralis (VPL).(ABSTRACT TRUNCATED AT 400 WORDS)

Thalamic mechanism of pain: Shell theory of thalamic nociception.

“…Taking these results together, it may be assumed that nociceptive neurons are located in a shell-like fashion around the whole VB complex. We have confirmed that trigeminal as well as spinal nociceptive neurons were in fact located in a shell-like fashion around the ventrobasal complex consisting of the VPM proper and VPL [27,28]. We have called this marginal area the shell region of the VB complex.…”

“…Maxillary NS and WDR neurons occurred in the dorsomedial shell region, and mandibular NS and WDR neurons were found in the ventromedial shell region along the border between the VPM proper and VPMpc. In the caudal part of the NS zone only maxillary NS neurons were found in the dorsal shell region, whereas mandibular NS neurons were located in the caudal ventromedial shell region [28,30,31]. The distribution of trigeminal nociceptive neurons within the shell region of the VPM proper followed a pattern generally consistent with the somatotopic arrangement established for other somatosensory input to the VPM proper.…”

“…We have found two additional classes of nociceptive neurons in the YPM proper of the cat thalamus [28,30,31]. One class consisted of nociceptive specific (NS) neurons.…”

“…from the shell region of the VPM proper, but they were confined to a narrow band approximately 300 µm wide just rostral to the NS zone. This narrow band is called the trigeminal WDR zone [28].…”

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

“…Guilbaud 등 15) 은 유해 자극에 반응하는 뉴론이 쥐의 복 후 외 측 핵 을 통 해 산 재 한 다 고 보 고 한 바 있 으 며 , Peschanski 등 17) 은 쥐 시상의 복후외측핵내 유해성 뉴론이 유해 자극의 위치, 강도, 지속기간에 대한 정확한 정보를 전 달할 수 있다고 하였다. 고양이 [18][19][20] 나 원숭이 21) 의 복후내측 핵에서도 역시 구강안면부에 가해진 유해한 자극에 반응하 는 다수의 유해성 뉴론이 존재한다고 보고되었다. 해부학적 연구에 따르면 쥐에서 시상의 복후내측핵은 반 대측 뇌간에 위치한 삼차신경 주감각핵, 극간소핵 뿐만 아 니라 미측소핵으로부터 투사를 받는다 22,23) .…”