The Claustrum in the Squirrel Monkey

Abstract

The claustrum (CLA) is a subcortical structure that is reciprocally and topographically connected with the cerebral cortex. The complexity of the cerebral cortex varies dramatically across mammals, raising the question of whether there might also be differences in CLA organization, circuitry, and function. Species variations in the shape of the CLA are well documented. Studies in multiple species have identified subsets of neurochemically distinct interneurons; some data suggest species variations in the nature, distribution, and numbers of different neurochemically identified neuronal types. We have studied the CLA in a smooth-brained primate, the squirrel monkey, using Nissl-stained sections and immunohistochemistry. We found that the shape of the CLA is different from that in other primates. We found several different neurochemically defined populations of neurons equally distributed throughout the CLA. Immunoreactivity to GAD 65/67 and GABA A receptors suggest that GABAergic interneurons provide widespread inhibitory input to CLA neurons. Immunoreactivity to glutamate transporters suggests widespread and overlapping excitatory input from cortical and possibly subcortical sources. Comparison of CLA organization in different species suggests that there may be major species differences both in the organization and in the functions of the CLA.

Anatomical and Physiological Characteristics of Claustrum Neurons in Primates and Rodents

“…Macaques show a single class of large cells, some of which resemble cortical pyramidal neurons, others inhibitory interneurons (Reynhout & Baizer 1999). PV-positive neurons have also been reported in squirrel monkeys (Baizer et al 2020) and in marmosets (Pham et al 2019), the latter finding variable densities along the insular claustrum and the Endopiriform nucleus.…”

“…In the marmoset, the distribution of CB-positive neurons is heterogenous, with a high density of CBpositive neurons reported in the caudal sections of the Endopiriform nucleus (Pham et al 2019). In the squirrel monkey, CB immunoreactivity was only apparent in the somas and extreme proximal processes of positive neurons (Baizer et al 2020).…”

“…They are mostly bipolar with round or elongated soma (up to 20 µm diameter), with a few larger cells having a triangular soma (Pirone et al 2014, Prensa et al 2003. In macaques, they are bipolar cells with oval somas (Reynhout & Baizer 1999), and in squirrel monkeys they have round, oval, or elongated somas (Baizer et al 2020).…”

The claustrum of the sheep and its connections to the visual cortex

“…CBPs immunoreactivity was seen throughout the Cl of other mammal species (rat: Druga et al ., 1993; monkey: Reynhout and Baizer, 1999; cat: Hinova‐Palova et al ., 2007; Rahman and Baizer, 2007; human: Hinova‐Palova et al ., 2014; human, chimpanzee, macaque: Pirone et al ., 2014; dog: Pirone et al ., 2015; squirrel monkey: Baizer et al ., 2020), suggesting that similar subclasses of Cl neurons exist in multiple species and share a homogeneous spatial distribution pattern throughout the anterior–posterior extent of the Cl.…”

Origin and Development of the Claustrum in Rhesus Macaque

“…More than a decade ago, Crick and Koch (1) suggested that the claustrum plays a role in consciousness. Their integrated conscious percept model was based on the claustrum's widespread connectivity profile, with identified projections to and from the sensory, motor, and associative cortical areas (2)(3)(4)(5)(6)(7). Knowledge of the physiological functions of the claustrum evolved in the past few decades as advanced anatomic and electrophysiological approaches were applied to claustrum studies in various species (7)(8)(9)(10)(11)(12)(13)(14)(15).…”