Retrograde transport of fluorescent tracers reveals extensive ipsi‐ and contralateral claustrocortical connections in the rat

Abstract

The projections from the claustrum to the cerebral cortex in the rat were examined by means of retrogradely transported fluorescent tracers Fast Blue (FB) and Diamidino Yellow dihydrochloride (DY), injected in the prefrontal, motor, somatosensory, auditory, and visual fields. In all cases, substantial numbers of retrogradely labeled neurons were observed in the ipsilateral and moderate to scant numbers in the contralateral claustrum insulare. Symmetrical bilateral injections of FB and DY as well as simultaneous injections of the tracers in the motor and visual cortex of the same hemisphere revealed no double-labeled neurons in the claustrum. The following conclusions may be drawn: The claustral projections to the motor, somatosensory, and visual cortex are prominent. The projection to the prefrontal cortex is less substantial and that to the auditory cortex is relatively modest. The claustrocortical connections lack the clear-cut topographic pattern of the thalamic nuclei but are, to some degree, preferentially arranged, albeit with considerable overlapping of the subpopulations of corticopetal neurons, a coarse anteroposterior topographic distribution appears to exist also in rodents. Neurons contributing to the claustrocortical connection project either ipsilaterally or contralaterally but not bilaterally. Projections to different cortical fields of one hemisphere also originate from separate claustral neurons.

Susceptibility to Kindling and Neuronal Connections of the Anterior Claustrum

“…These findings are generally consistent with recent studies (Minciacchi et al, 1985;Sloniewski et al, 1986b).…”

“…First, it has long been shown that the claustrum is a cortically related structure originating from the cortex (Meynert, 1868;Brodmann, 1909;de Vries, 1910;Macchi, 1951;Filiminoff, 1966;Bayer and Altman, 1991;Bayer et al, 1993), whereas the dorsal endopiriform nucleus is generated in the palliostriatal ventricular angle (Bayer and Altman, 1991;Bayer et al, 1993). Second, the claustrum is heavily and reciprocally connected with neocortex (Druga, 1972(Druga, , 1982Carey and Neal, 1985;Minciacchi et al, 1985;Morys and Sloniewski, 1986;Sloniewski et al, 1986b;Druga et al, 1990;Clasca et al, 1992;Dinopoulos et al, 1992;Kowianski et al, 1996Kowianski et al, , 1998aSadowski et al, 1997a,b), whereas the dorsal endopiriform nucleus is mainly connected with the piriform, entorhinal, insular, and orbital cortices Price, 1977a,b, 1878a,b;Haberly and Price, 1978;Markowitsch et al, 1984;Wilhite et al, 1986;Witter et al, 1988;Behan and Haberly, 1999).…”

“…Anatomical data indicate that the anterior claustrum has prominent connections with the motor and frontal cortex (Minciacchi et al, 1985;Sloniewski et al, 1986b;Sadowski et al, 1997a,b;Kowianski et al, 1998a,b), which play a pivotal role in kindling (Corcoran et al, 1976;Kelly et al, 1999). We therefore hypothesized that the anterior claustrum is also markedly susceptible to kindling.…”

Hypotheses Relating to the Function of the Claustrum

“…This binding may be effected inside the claustrum in the manner we have suggested. Also, even if the input to claustral cells is unimodal, the output axons from claustral P cells commonly bifurcate and project to more than one modal type of cortex (Divac et al, 1978;Divac, 1979;Sloniewski et al, 1986;Rahman and Baizer, 2007). The experiments reported by Remedios et al (2010) only produce strong evidence that the input to individual claustral P cells in not intermodal.…”

“…It has been claimed that areas of the claustrum in the cat sends "precisely reciprocal" projections back to those area(s) of the cortex whence its inputs derived Sherk and LeVay, 1981;Sherk, 1986). It has also been claimed that the projections to and from the claustrum are diffuse, but quite specific, in both directions (one point to specific points) (Divac et al, 1978;Divac, 1979;Sloniewski et al, 1986). Single cells in the claustrum have been reported to send branched axons to several cortical areas.…”